Heat-shrinkable polyester films, labels and packaging

Abstract

This invention provides a heat-shrinkable polyester film that exhibits excellent heat-sealing strength at low temperatures, high heat shrinkage rate in the width direction, and is suitable for assembly in automated machinery as well as addressing environmental concerns. The heat-shrinkable polyester film of this invention uses polyethylene terephthalate as the main component and satisfies the following requirements (1) to (4): (1) The ring stiffness in the width direction is 6 mN / 25 mm or more to 200 mN / 25 mm or less; (2) The heat shrinkage rate in the width direction after shrinking in hot water at 80°C for 10 seconds is 20% or more to 70% or less; (3) When one side of the film is heat-sealed with the other side at 140°C and 0.1 MPa for 1 second, the peel strength during a shear test in the width direction is 20 N / 15 mm or more to 80 N / 15 mm or less; (4) The wetting tension of at least one outermost layer is 40 mN / m or more to 55 mN / m or less.

Description

[Technical Field]

[0001] This invention relates to a heat-shrinkable polyester film, label, and packaging with excellent heat-sealability. Specifically, the aforementioned heat-shrinkable polyester film is suitable for ring-shaped labels such as noodle containers in convenience stores, and exhibits excellent environmental adaptability and suitability for automated assembly machines. [Previous Technology]

[0002] In recent years, extended films (so-called heat-shrinkable films) made of polyvinyl chloride (PVC), polystyrene (PS), and polyester resins have been widely used in applications such as protecting glass bottles or PET (polyethylene terephthalate) bottles, labeling products, securing containers and lids of convenience store lunches, and securing labels to containers. Among these heat-shrinkable films, PVC films have the following problems: low heat resistance, production of hydrogen chloride gas during combustion, and potential to become dioxins. Polystyrene films have the following problems: poor solvent resistance, the need for specially formulated inks during printing, the requirement for high-temperature combustion, and the production of unpleasant odors and large amounts of black smoke during combustion. Therefore, polyester heat-shrinkable films, which have high heat resistance, are easy to burn, and have excellent solvent resistance, have been widely used as shrink labels, and their usage is showing an increasing trend.

[0003] In recent years, there has been an increasing trend of pre-cooked udon noodles or ramen noodles being sold in convenience stores and other similar establishments. This involves placing the cooked noodles or similar contents into a deep plastic container, covering it from the top, and then securing the container and lid with a ring-shaped shrink film (so-called strip label packaging). Heat-shrinkable polyester films are widely used, particularly those that shrink significantly in the width direction. In the case of label films for bottles or strip labels for bento boxes, the film is made into a ring shape, attached to the bottle or bento container, and then heat-shrinked. As an example of making a ring label, the shrink film rolled from a film roller is cut along its width, and the two ends of the cut film are joined together. When joining the two ends of the film (making the ring label), it is often simultaneously covered onto the packaged object (noodle container, etc.). The ring film thus made is then heated with hot air or similar means to shrink it, thereby creating a tight seal with the packaged object and becoming a strip label that secures the container and lid.

[0004] As a performance characteristic of heat shrink film used to make strip labels, it goes without saying that the shrinkage and conformability to the container are important properties; however, the adhesion must also be non-peeling. As a bonding method, heat sealing using the film itself is widely employed. Conventional techniques to prevent peeling of the heat seal have involved increasing heat seal strength or reducing shrinkage stress. For example, Patent Document 1 discloses a polyester-based heat shrink film that uses a monomer that is amorphous and shrinks along the long side of the roll. However, the film in Patent Document 1 does not achieve the heat seal strength required by current technology. In recent years, to improve the yield of strip label manufacturing, equipment has been upgraded to higher speeds and heat sealing time has been reduced. Consequently, higher heat seal strength at low temperatures is increasingly required for the film.

[0005] In contrast, Patent Document 2 discloses a film that reduces the planar alignment through uniaxial extension, thereby increasing heat-sealing strength and reducing shrinkage stress, thus suppressing peeling of the heat-sealed portion. However, because the film system in Patent Document 2 is uniaxially extended, the final area elongation ratio (longitudinal × transverse) of the film is lower, leaving room for improvement in productivity. As Patent Document 2 points out, if the intention is to improve productivity through biaxial extension, peeling of the heat-sealed portion due to the decrease in heat-sealing strength and the increase in shrinkage stress cannot be avoided.

[0006] In addition, the heat shrink film used for strip labels requires the opposite characteristics of thinness and stiffness. Regarding the former, in recent years, environmental awareness has increased, demanding that not only all supply chain-related businesses, including retailers and food manufacturers, but also consumers, minimize packaging material consumption. On the other hand, from the perspective of demanding not only efficiency but also addressing labor shortages, the automation of food packaging machinery has advanced further, requiring films to be adaptable to automated machinery. The adaptability of strip labels to machinery refers to the ability to precisely clamp the film onto a robotic arm during the step of cutting the film along its width and heat-sealing it into a ring, and to prevent the film from wobbling on a high-speed strip label production line. These characteristics are related to the stiffness and tightness of the film; the greater the progress in thinness, the lower the stiffness, i.e., the adaptability to machinery, creating a dilemma.

[0007] Furthermore, Patent Document 3 describes performing a predetermined surface treatment as a means to improve the alkali-removable properties when depositing an alkali-removable ink layer onto a film. However, this technique only slightly improves the heat-sealing properties and does not have sufficient effectiveness. [Prior Art Documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent No. 4411556. [Patent Document 2] Japanese Patent No. 6988440. [Patent Document 3] Japanese Unexamined Patent Application Publication No. 2004-139067. [Non-Patent Documents]

[0009] [Non-patent document 1] A. Mahendrasingam et al "Effect of draw ratio and temperature on the strain induced crystallization of poly (ethylene terephthalate) at fast draw rates" Polym. 40 5556 (1999). [Summary of the Invention]

[0010] [Problem to be Solved by the Invention] The present invention was made in view of the foregoing circumstances, and its object is to provide a heat-shrinkable polyester film that exhibits excellent heat-sealing strength at low temperatures, high heat shrinkage rate in the width direction, and also considers suitability for assembly in automated machinery and environmental protection. [Means for Solving the Problem]

[0011] In order to solve the aforementioned problems, the inventors conducted an examination. As a result, the structure of the present invention is as follows. 1. A heat-shrinkable polyester film, which uses polyethylene terephthalate as the main component and satisfies the following requirements (1) to (4): (1) The loop stiffness in the width direction is more than 6 mN / 25 mm to less than 200 mN / 25 mm; (2) The heat shrinkage rate in the width direction when shrinking in hot water at 80°C for 10 seconds is more than 20% to less than 70%; (3) When one side of the film is heat-sealed with the other side at a temperature of 140°C and a pressure of 0.1 MPa for 1 second, the peel strength by shear test in the width direction is more than 20 N / 15 mm to less than 80 N / 15 mm; (4) The wetting tension of at least one outermost layer is more than 40 mN / m to less than 55 mN / m. 2. The heat-shrinkable polyester film as described in item 1, wherein the reversible heat capacity difference from 25°C to 140°C, measured by a temperature-modulated differential scanning calorimeter, is 0.4 J / g·K or more and less than 1.4 J / g·K. 3. The heat-shrinkable polyester film as described in item 1 or 2, wherein the proportion of oxygen atoms present on the film surface obtained from the C1s spectrum obtained by X-ray electron spectrometry (ESCA) at the peak of 285 eV to 290 eV is 27% or more and less than 31% in at least one outermost layer. 4. The heat-shrinkable polyester film as described in any one of items 1 to 3, wherein the thickness is 20 μm or more and less than 50 μm. 5. The heat-shrinkable polyester film as described in any one of items 1 to 4, wherein the polyester component constituting the film contains, from 1 mol% to 30 mol% of phthalic acid, neopentyl glycol, 1,4-cyclohexanediol, butanediol, and diethylene glycol. 6. The heat-shrinkable polyester film as described in any one of items 1 to 5, wherein the raw material constituting the film is a polyester raw material obtained by physically and / or chemically recycling PET bottles. 7. A label, at least a portion of which uses a ring-shaped label with the heat-shrinkable polyester film as described in any one of items 1 to 6, wherein the heat-shrinkable polyester film is bonded to itself or to other films, and the shear strength of the bonded portion is from 20 N / 15 mm to 80 N / 15 mm or more. [Invention Benefits]

[0012] By means of the present invention, a heat-shrinkable polyester film can be provided, which has excellent heat-sealing strength at low temperature, high heat shrinkage rate in the width direction, and takes into account the assembly suitability for automatic machinery and the response to environmental issues.

Implementation Method

[0014] 1. Polyester raw material used in heat-shrinkable polyester film The polyester used in the heat-shrinkable polyester film of the present invention uses polyethylene terephthalate units as the main constituent component. The polyethylene terephthalate units account for at least 50 mol% of 100 mol% of the polyester constituent units, more preferably at least 55 mol% and even more preferably at least 60 mol%.

[0015] Other dicarboxylic acid components constituting the polyester of the present invention may include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid; aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid; and alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid. Among these, isophthalic acid or phthalic acid are preferred.

[0016] When the polyester contains aliphatic dicarboxylic acids (such as adipic acid, sebacic acid, and decanedicarboxylic acid), it is preferable that the content is less than 3 mol% (in 100 mol% of dicarboxylic acid content). Furthermore, it is preferable that the polyester does not contain trivalent or higher polycarboxylic acids (such as trimellitic acid, pyromellitic acid, and their anhydrides). In heat-shrinkable polyester films obtained using polyesters containing these polycarboxylic acids, it is difficult to achieve the necessary high shrinkage rate.

[0017] Other diol components constituting the polyester of the present invention may include alicyclic diols such as neopentyl glycol and 1,4-cyclohexanediethanol, aliphatic diols such as 1,4-butanediol, diethylene glycol, 1,3-propanediol, and hexanediol, and aromatic diols such as bisphenol A. Among the foregoing, neopentyl glycol, 1,4-cyclohexanediethanol, 1,4-butanediol, and diethylene glycol are preferred.

[0018] Preferably, the total amount of the aforementioned polyester composition includes at least one component selected from the group consisting of isophthalic acid, neopentyl glycol, 1,4-cyclohexanediol, butanediol, and diethylene glycol, ranging from 1 mol% to 50 mol%. If the total amount of these components is less than 1 mol%, it is difficult to set the heat shrinkage rate or heat seal strength within a predetermined range, which is undesirable. On the other hand, if the total amount of these components exceeds 50 mol%, while achieving the thinness that is the main objective of the present invention, it is difficult to maintain the ring stiffness, an indicator of stiffness, at 6 mN / 25 mm or more. The total amount of the aforementioned components is more preferably from 5 mol% to 45 mol%, and more preferably from 10 mol% to 40 mol%. The most preferred upper limit is 30 mol% or less.

[0019] In addition to the polyester raw material having the aforementioned constituent components, the membrane of the present invention may also use a polyester elastomer. By using a polyester elastomer, the reversible heat capacity difference (ΔCp) of the membrane described later can be reduced, which is therefore preferable. Examples of polyester elastomers include copolymers of ε-caprolactone and 1,4-butanediol or polybutanediol.

[0020] Furthermore, in addition to using the aforementioned polyester raw materials, from the perspective of the environmental relevance of the present invention, it is also preferable to use polyester raw materials obtained by recycling used waste such as PET bottles. For example, as polyester resin obtained by recycling PET bottles, examples include: polyester resin obtained by screening, crushing and washing used PET bottles collected from the market or society to thoroughly remove surface contaminants and foreign matter, exposing them to high temperature to thoroughly wash away contaminants and other substances remaining in the resin, and then obtaining polyester resin by physical regeneration through regranulation (hereinafter sometimes referred to as physically recycled polyester resin); and polyester resin obtained by decomposing polyester resin contained in used packaging containers down to the monomer level, removing contaminants and other substances, and then repolymerizing (hereinafter sometimes referred to as chemically recycled polyester resin).

[0021] The recycled raw material that can be preferably used in this invention is a recycled product of a container mainly composed of polyethylene terephthalate. For example, a recycled product of a beverage container such as a tea beverage or a soft drink can be preferably used. It can also be appropriately oriented and is preferably colorless, but may also contain some coloring components.

[0022] The polyester, which is made from recycled materials such as PET bottles that can be readily utilized, is manufactured and molded using conventional polymerization and solid-state polymerization methods. It is preferably polyethylene terephthalate (PET) as the main component, although the presence of other polyester components and copolymer components is permissible. It may also contain metal compounds such as antimony, germanium, and titanium as catalysts, and phosphorus compounds as stabilizers. Generally, germanium is frequently used as a catalyst in polyesters used for PET bottles. If recycled PET bottle materials are used for film formation, the film will contain more than 1 ppm of germanium. However, since this is only the content of the catalyst, it is generally higher than 100 ppm and usually lower than 50 ppm.

[0023] Various additives may be added to the polyester raw material used in this invention as needed. The aforementioned additives are not particularly limited, and are, for example, known additives such as waxes, antioxidants, antistatic agents, nucleating agents, viscosity reducers, heat stabilizers, pigments for coloring, color-resistant agents, and ultraviolet absorbers. Furthermore, to ensure good workability (slipability) of the film, the aforementioned polyester raw material preferably contains microparticles used as lubricants. As for the aforementioned microparticles, any type of microparticle, whether inorganic or organic, can be selected. Examples of inorganic microparticles include: silicon dioxide, alumina, titanium dioxide, calcium carbonate, kaolin, barium sulfate, etc. Examples of organic microparticles include: acrylic resin particles, melamine resin particles, polysiloxane resin particles, cross-linked polystyrene particles, etc. When measured using a Coulter counter, the average particle size of the aforementioned microparticles is preferably in the range of approximately 0.05 μm to 3.0 μm. If the particle size is less than 0.05 μm, there is a risk that the necessary slippage may not be achieved during strapping. On the other hand, if the particle size exceeds 3.0 μm, the particles may aggregate and become too coarse, becoming foreign matter and causing a significant deterioration in appearance quality. The particle size is preferably between 0.06 μm and 2.99 μm, and more preferably between 0.07 μm and 2.98 μm. Furthermore, the amount of microparticles added is preferably in the range of 100 ppm to 4000 ppm relative to the membrane system.

[0024] There is no particular limitation on the method of incorporating the aforementioned microparticles into the aforementioned polyester raw material. For example, they can be added at any stage of manufacturing the polyester resin. However, it is preferable to add them as a slurry dispersed in ethylene glycol or the like at the esterification stage or at the stage after the transesterification reaction and before the start of the polycondensation reaction, so as to carry out the polycondensation reaction. Alternatively, the following methods can also be used: using a compounding extruder with venting holes to blend the slurry of microparticles dispersed in ethylene glycol or water with the polyester resin raw material; or using a compounding extruder to blend dried microparticles with the polyester resin raw material, etc.

[0025] 2. Characteristics of the heat-shrinkable polyester film of the present invention (1) Ring stiffness The ring stiffness of the film of the present invention in the width direction must be 6 mN / 25 mm or more and 200 mN / 25 mm or less. Ring stiffness is an indicator of the stiffness of the film; the lower the value, the less stiffness. If the ring stiffness is less than 6 mN / 25 mm, poor assembly is likely to occur when the film is heat-sealed by the assembly machine, which is undesirable. If the ring stiffness exceeds 200 mN / 25 mm, it is easy for consumers to feel that it is difficult to open the tape label, or the film is easy to injure their hands, which is undesirable. The ring stiffness is preferably 8 mN / 25 mm or more and 198 mN / 25 mm or less, and more preferably 10 mN / 25 mm or more and 196 mN / 25 mm or less.

[0026] (2) Heat Shrinkage Rate The heat shrinkage rate of the membrane in the width direction when it shrinks in hot water at 80°C for 10 seconds must be 20% or more and 70% or less. Here, the "width direction" is the direction orthogonal to the length direction (machine direction; MD), also known as the transverse direction (TD). If the heat shrinkage rate in the width direction at 80°C is less than 20%, the membrane will not shrink sufficiently when shrinking to the object and will not be able to fit together aesthetically, resulting in poor appearance, which is undesirable. On the other hand, if the heat shrinkage rate in the width direction at 80°C exceeds 70%, the shrinkage stress during shrinkage tends to increase, which is also undesirable. The heat shrinkage rate in the width direction at 80°C is preferably 25% or more and 65% or less, more preferably 30% or more and 60% or less.

[0027] (3) Heat-sealing strength The film of the present invention is heat-sealed with one side of the film to the other side at a temperature of 140°C and a pressure of 0.1 MPa for 1 second. The strength of the heat-sealing strength when peeled by shear test must be 20 N / 15 mm or more and 80 N / 15 mm or less. The value of the heat-sealing strength when peeled by shear test is different from the value measured by 90-degree peel or 180-degree peel. The inventors have found that the value of the heat-sealing strength measured by this method is an indicator of the openability of the strip label. If the heat-sealing strength is 20 N / 15 mm or less, the strip label can be easily opened, which is undesirable. On the other hand, if the heat-sealing strength is 80 N / 15 mm or more, consumers may find it difficult to open the strip label, which is also undesirable. The heat-sealing strength is preferably 25 N / 15 mm or more and 75 N / 15 mm or less, and more preferably 30 N / 15 mm or more and 70 N / 15 mm or less.

[0028] (4) Wetting Tension The wetting tension of at least one outermost layer of the film of the present invention must be 40 mN / m or more and 55 mN / m or less. By setting the wetting tension of the outermost layer of the film to 40 mN / m, it is easy to achieve the aforementioned heat seal strength of 20 mN / m or more. If the wetting tension is less than 40 mN / m, it is difficult to achieve the aforementioned heat seal strength of 20 mN / m, which is undesirable. On the other hand, if the wetting tension exceeds 55 mN / m, the surfaces of the film are prone to sticking together during the process of rolling the film into a roller and storing it in a warehouse or similar facility. If sticking occurs, the film is prone to breakage when rolled out from the roller, which is undesirable. The wetting tension is preferably 41 mN / m or more and 54 mN / m or less, and more preferably 42 mN / m or more and 53 mN / m or less.

[0029] (5) Reversible heat capacity difference (ΔCp) The membrane of the present invention is measured by a temperature-modulated differential scanning calorimeter (temperature-modulated DSC) from 25°C to 140°C. The reversible heat capacity difference (hereinafter sometimes referred to as ΔCp) is preferably 0.4 J / g K or more to 1.4 J / g K or less. The relationship between ΔCp and heat seal strength is described below.

[0030] The high-dimensional structures of polyesters are broadly classified into two types: crystalline and amorphous. In recent years, amorphous molecules have been further classified into rigid amorphous and mobile amorphous molecules based on their mobility. Mobile amorphous molecules are considered to move at the glass transition temperature (Tg), equivalent to previously understood amorphous molecules. The presence rate of mobile amorphous molecules can be quantified by determining the difference in reversible heat capacity before and after the start of glass transition using a temperature-modulated DSC in heat-only mode. Rigid amorphous systems are generally estimated to exist between mobile and crystalline amorphous systems, and their mobility is also considered to be intermediate between the two. Unlike mobile amorphous molecules, rigid amorphous molecules are believed to not exhibit glass transition. However, since the reversible heat capacity shows a slow increase between the glass transition temperature and the melting point, rigid amorphous systems change to mobile amorphous molecules in the temperature range after the glass transition temperature. Based on the foregoing, it can be assumed that movable and rigid amorphous materials move through heat sealing, resulting in close contact between the heat-sealed surfaces and thus exhibiting heat-sealing strength. Furthermore, in actual measurement data, even at the lower temperature side (glass state) below the glass transition temperature, the reversible heat capacity often increases. The mechanism of this is not yet clear, but it is believed that the change in reversible heat capacity from around room temperature to Tg is also related to the manifestation of heat-sealing strength.

[0031] Therefore, the inventors took the increase in reversible heat capacity difference from room temperature to heat-sealing temperature as the sum of the changes in movable amorphous and rigid amorphous materials, and examined its relationship with heat-sealing temperature. The results showed that by controlling the changes in movable and rigid amorphous materials within predetermined ranges, appropriate heat-sealing strength and heat resistance could be ensured. By setting ΔCp to 0.4 J / g·K or higher, it is easy to set the aforementioned heat-sealing strength to 20 N / 15 mm or higher. On the other hand, although ΔCp exceeding 1.4 J / g·K improves the heat-sealing strength, it is not ideal because the required film strength may be insufficient. ΔCp is more preferably 0.45 J / g·K or higher to 1.35 J / g·K or lower, and more preferably 0.5 J / g·K or higher to 1.3 J / g·K or lower. The film-forming method and conditions for setting ΔCp within the preferred range will be described later.

[0032] (6) Thickness The thickness of the film of the present invention is preferably 20 μm or more to 50 μm or less. By setting the thickness to 20 μm or more, it is easy to set the ring stiffness to 6 mN / 25 mm or more, which is therefore preferred. On the other hand, if the film thickness exceeds 50 μm, not only is the ring stiffness likely to exceed 200 mN / 25 mm, but it is also difficult to contribute to the environmental responsiveness (resource saving based on thinness) that is the main purpose of the present invention, which is therefore undesirable. The thickness is more preferably 22 μm or more to 48 μm or less, and even more preferably 24 μm or more to 46 μm or less.

[0033] (7) Thermal shrinkage rate in the long side direction The thermal shrinkage rate in the long side direction (mechanical direction; MD) of the film of the present invention when immersed in hot water at 80°C for 10 seconds is preferably -5% or more to 8% or less. If the thermal shrinkage rate in the long side direction at 80°C is less than -5%, it is easy to over-stretch and become wrinkled when shrinking to the object, and a good shrinkage appearance cannot be obtained, which is undesirable. On the other hand, if the thermal shrinkage rate in the long side direction at 80°C exceeds 8%, it is easy to deform or shrink mark after shrinkage, which is undesirable. The thermal shrinkage rate in the long side direction at 80°C is preferably -4% or more to 7% or less, and more preferably -3% or more to 6% or less.

[0034] (8) Glass transition temperature (Tg) The Tg of the film of the present invention is preferably 50°C or higher to 100°C or lower. If the Tg is less than 50°C, the film is prone to sticking when stored as a roller, which is undesirable. On the other hand, if the Tg exceeds 100°C, it is difficult to set ΔCp to 0.4 J / g·K or higher, and it is difficult to set the aforementioned heat seal strength to 20 N / 15 mm. As described above, the present invention presumes that ΔCp is related to the heat seal strength and believes that ΔCp is closely related to Tg. In the case of heat sealing by an actual assembly machine, even if the temperature of the heat sealing bar is the same as the set temperature, the temperature applied to the film is lower than the set temperature when heat sealing is performed at high speed (e.g., 1 second). Therefore, if the Tg of the film exceeds 100°C, the film cannot undergo devitrification when heat sealing is performed at low temperature and high speed (e.g., 140°C, 1 second), and it is difficult to set ΔCp to 0.4 J / g·K or higher. The temperature range (Tg) is preferably between 55°C and 95°C, and even more preferably between 60°C and 90°C.

[0035] (9) Inherent viscosity IV The inherent viscosity IV of the membrane of the present invention is preferably 0.6 dL / g or more to 1.2 dL / g or less. If the inherent viscosity IV is less than 0.6 dL / g, not only will the minimum mechanical strength required for the membrane be insufficient, but it will also be prone to breakage during membrane fabrication. On the other hand, if the inherent viscosity IV exceeds 1.2 dL / g, the pressure will increase when the raw material is melted by the extruder, which will easily cause deformation of the membrane, etc., which is undesirable. The inherent viscosity IV is more preferably 0.65 dL / g or more to 1.15 dL / g or less, and more preferably 0.7 dL / g or more to 1.1 dL / g or less.

[0036] (10) Maximum heat shrinkage stress in the width direction When the film of the present invention is shrunk in hot air at 90°C for 30 seconds, the maximum heat shrinkage stress in the width direction is preferably 3 MPa or more to 22 MPa or less. If the maximum heat shrinkage stress in the width direction at 90°C exceeds 22 MPa during heat shrinkage, for example, even if the aforementioned heat seal strength is set to 20 N / 15 mm or more, the possibility of the sealed portion of the label peeling off during shrinkage becomes higher, which is undesirable. On the other hand, if the maximum heat shrinkage stress in the width direction is less than 3 MPa, the object is likely to fall off even after shrinkage to the object, which is also undesirable. The maximum heat shrinkage stress in the width direction is more preferably 4 MPa or more to 21 MPa or less, and more preferably 5 MPa or more to 20 MPa or less.

[0037] (11) Heat-sealing initiation temperature When heat-sealing one side of the film of the present invention to the other side, the heat-sealing initiation temperature is preferably 100°C or higher to 150°C or lower. The heat-sealing initiation temperature is the temperature at which the strength of peeling during shear test begins to reach 2N / 15mm or higher when the heat-sealing temperature is changed in 5°C increments from 90°C to 160°C under a pressure of 0.1MPa for 1 second. A heat-sealing initiation temperature exceeding 150°C indicates poor low-temperature sealing performance, which can be detrimental to high-speed assembly of automated machines (resulting in a lower yield rate for strip label manufacturing). On the other hand, if the heat-sealing initiation temperature is below 100°C, the low-temperature sealing performance is improved, which is better; however, when the film is stored as a roller, adhesion is more likely to occur, which is undesirable. The heat-sealing initiation temperature is more preferably 105°C or higher to 145°C or lower, and more preferably 110°C or higher to 140°C or lower.

[0038] (12) Oxygen Atom Presence Ratio on the Membrane The oxygen atom presence ratio on the membrane surface of the present invention, as obtained from the spectrum obtained by X-ray electron spectroscopy (ESCA) showing the peaks of oxygen atoms and the peaks of carbon atoms, is preferably 27% to 31% or more in at least one outermost layer. Detailed methods for determining the oxygen atom presence ratio are described below. If the oxygen atom presence ratio is 27% or more, it is easy to set the wetting tension to 40 mN / m, and it is easy to achieve the aforementioned heat seal strength of 20 N / 15 mm or more. A higher oxygen atom presence ratio is better because it increases the wetting tension and heat seal strength; however, it is less desirable because it is prone to sticking when wound into rolls for storage.

[0039] It can be considered that if the proportion of oxygen atoms is high, then functional groups such as carboxyl or hydroxyl groups will be more abundant on the membrane surface. These functional groups can be considered to be in a polarized state (e.g., oxygen atoms in the δ+ system, hydrogen atoms in the δ- system), therefore, when the membrane surfaces approach each other, the electrostatic attraction becomes stronger, and the heat-sealing strength is increased. Furthermore, it can be considered that these functional groups protrude three-dimensionally from the membrane surface, thus acting as wedges. As described above, it can be considered that the heat-sealing strength is improved through the electrostatic and physical interactions of functional groups containing oxygen atoms. The proportion of oxygen atoms is preferably 27.5% to 30.5%, and more preferably 28% to 30%.

[0040] (13) Haze The haze of the membrane of the present invention is preferably 2% or more to 20% or less. If the haze value exceeds 20%, the transparency becomes poor, and it is difficult to see the object (contents), which is undesirable. The haze is more preferably 19% or less, and even more preferably 18% or less. In addition, the lower the haze value, the better; however, considering that a predetermined amount of lubricant or the like must be added to the membrane for the purpose of providing the sliding properties required for practical use, about 2% is the lower limit.

[0041] 3. Method for manufacturing the heat-shrinkable polyester film of the present invention The film of the present invention can be manufactured by stretching an unstretched film obtained by melt extrusion of the aforementioned polyester raw material using an extruder, under the following methods and conditions. Furthermore, the polyester can be obtained by polycondensation of the aforementioned suitable dicarboxylic acid component and diol component using a known method. In addition, generally two or more types of fragmented polyester are mixed as the raw material for the film. The following details each step.

[0042] 3.1 Melt Extrusion When melting and extruding the raw material resin, it is preferable to use a hopper dryer, paddle dryer, or vacuum dryer to dry the polyester raw material. After drying the polyester raw material, it is melted and extruded into a film using an extruder at a temperature of 200°C to 330°C. Any existing method, such as the T-die method or the tubular method, can be used for extrusion. Then, an unstretched film can be obtained by rapidly cooling the extruded sheet-like molten resin. Alternatively, the following method can be used to rapidly cool the molten resin: by casting the molten resin from a nozzle onto a rotating drum for rapid cooling and curing, substantially unoriented resin sheets can be obtained.

[0043] The film of the present invention can be obtained by extending the obtained unstretched film along the long side (longitudinal) direction and the width (transverse) direction using the method detailed below. As the extension direction, uniaxial extension in either the longitudinal or transverse direction or biaxial extension in both the longitudinal and transverse directions is possible; however, considering the productivity of the present invention, biaxial extension is preferred. In the case of biaxial extension, it can be a gradual biaxial extension extending in the residual direction after extension in either the longitudinal or transverse direction, or a simultaneous biaxial extension extending in both the longitudinal and transverse directions simultaneously. The method and conditions for a longitudinal-transverse gradual biaxial extension following longitudinal extension are described below.

[0044] 3.2. Longitudinal Stretching In the manufacture of the film of the present invention, it is preferable to feed a substantially unaligned film into a longitudinal stretching machine having multiple rollers arranged in succession, heat it using a preheating roller, and then perform longitudinal stretching at a ratio of 1.0 to 4.5 times. When the longitudinal stretching ratio is 1.0, it is essentially not longitudinally stretched. On the preheating roller, it is preferable to perform preheating until the film temperature reaches 60°C to 110°C. If the film temperature is below 60°C, it is difficult to stretch during longitudinal stretching (i.e., it is easy to break), which is undesirable. In addition, if the temperature is above 110°C, the film is easy to stick to the roller, and the productivity is significantly reduced due to the film being wound on the roller, which is also undesirable.

[0045] After the film temperature reaches the aforementioned range, the film is longitudinally stretched using the speed difference of the rollers. At this time, by increasing the roller distance used for longitudinal stretching, it is possible to increase the longitudinal stretching ratio while simultaneously reducing the film's ΔCp. This is believed to be because a longer roller distance reduces the longitudinal stretching speed, thus better suppressing crystallization or rigid amorphization. However, a longer roller distance also increases the necking (Poisson's ratio) in the direction orthogonal to the stretching direction (here, the width direction), leading to a decrease in productivity. That is, if the film width decreases after longitudinal stretching, the inlet width for transverse stretching in the next step (the tenter frame) becomes narrower, and consequently, the outlet width of the tenter frame also decreases accordingly. The roller distance is preferably 80 mm to 500 mm, and more preferably 90 mm to 490 mm. When the transverse stretching ratio is increased to compensate for this decrease in productivity, ΔCp easily becomes less than 0.4 J / g·K. Therefore, to achieve a ΔCp of 0.4 J / g·K or higher even with high longitudinal extension ratios and to improve productivity, it is preferable in this invention to divide the longitudinal extension into multiple stages. Specifically, it is preferable to increase the configuration (number of extension stages) of the rollers used for longitudinal extension from the usual two stages (1 stage extension) for low speed and high speed to three stages (2 stages extension) for low speed, medium speed, and high speed, and four stages (3 stages extension) for low speed, medium-low speed, medium-high speed, and high speed. The more stages extension there are, the more significant and better this effect becomes; however, the equipment becomes larger, so the preferred number of extension stages is one to three stages. The extension ratio of each stage in the longitudinal extension is preferably 1.0 to 3.2 times, more preferably 1.1 to 3.1 times.

[0046] 3.3 Intermediate Heat Treatment After Longitudinal Stretching After longitudinal stretching, it is preferable to perform intermediate heat treatment with the aim of reducing the thermal shrinkage rate along the long side. The intermediate heat treatment temperature is preferably 100°C to 160°C, more preferably 105°C to 155°C, and even more preferably 110°C to 150°C. In addition, during intermediate heat treatment, by relaxing the film along the long side (relaxation along the long side), the shrinkage rate of the film in the long side direction that occurs during longitudinal stretching can be reduced. Moreover, by relaxing along the long side, the bowing phenomenon (strain) that occurs in the tenter frame can be reduced. The relaxation rate along the long side is preferably 0% to 60% (0% relaxation rate means no relaxation). Since the upper limit of the relaxation rate along the long side is determined by the raw materials used and the longitudinal stretching conditions, relaxation cannot be performed beyond this upper limit. Relaxation along the long side can be achieved by heating the longitudinally stretched film at a temperature between 65°C and 100°C and adjusting the speed difference of the rollers. Heating methods can include rollers, near-infrared radiation, far-ultraviolet radiation, hot air heaters, etc. Furthermore, even if relaxation along the long side is not performed immediately after longitudinal stretching, for example, even during transverse stretching (including a preheating zone) or final heat treatment, relaxation along the long side can be achieved by reducing the clip spacing along the long side (in this case, since both ends of the film width direction are also relaxed along the long side, the buckling strain is reduced), and it can be performed at any time. After relaxation along the long side (which is longitudinal stretching without relaxation), it is preferable to temporarily cool the film, preferably using cooling rollers with a surface temperature of 20°C to 40°C.

[0047] 3.2. The film system, after longitudinal stretching or relaxation along the long side, is continuously guided to the tenter frame for transverse stretching after preheating. The temperature of the preheating zone is preferably 80°C to 150°C. If the preheating temperature is less than 80°C, not only will the molecules easily align and crystallize during transverse stretching, causing ΔCp to easily fall below 0.4 J / g·K, but the film will also easily break, which is undesirable. Conversely, if the preheating temperature exceeds 150°C, the thickness unevenness in the width direction will worsen, and the winding quality when wound onto a roll will decrease, which is also undesirable. The residence time in the preheating zone is preferably 2 seconds to 10 seconds. If the residence time is less than 2 seconds, the film will have difficulty reaching the temperature required for transverse stretching, causing the same concerns as when the preheating zone temperature is less than 80°C. On the other hand, even if the residence time exceeds 10 seconds, transverse stretching itself is unlikely to cause problems, but there is a tendency for the scale of the production equipment to increase accordingly, which is also undesirable.

[0048] After the preheating zone, the lateral extension is continuously performed in the lateral extension zone, which expands the distance between the clips in the width direction of the tenter frame. The inventors have discovered that, similar to longitudinal extension, during lateral extension, even if the extension ratio increases with the number of extension segments, the increase in ΔCp can be suppressed, ensuring the necessary heat seal. Specifically, compared to the conventional method of setting the clip pattern from the start of lateral extension to the end as a straight line (Fig. 1), multi-segment extension (e.g., Fig. 2; three-segment extension) with non-extension sections (returning the clip pattern to parallel with the direction of travel) can balance productivity and the predetermined ΔCp. This is believed to be because the molecular chains extended by the extension are thermally tempered under tension in the non-extension sections. For example, Figure 8 of Non-Patent Document 1 shows X-ray diffraction images of polyethylene terephthalate immediately after stretching (upper section) and approximately 0.2 seconds after stretching (lower section) from stretching ratios of 2.0 (a, b) to 4.0 (i, j). The structural changes over time after stretching can be observed. Here, it can be seen that at a stretching ratio of 4.0, crystallization occurs approximately 0.2 seconds after stretching (j), while at a stretching ratio of approximately 2.2, there is no structural change, and the amorphous state is maintained (b, d). Furthermore, Figure 2 shows X-ray diffraction images of polyethylene terephthalate immediately after stretching (upper section) and approximately 0.2 seconds after stretching (lower section) when the stretching temperature is changed from 85°C to 130°C. Here, it can be seen that at 130°C, no crystallization occurs even after stretching over time (p). Non-Patent Literature 1 points out that the reason why orientation crystallization did not occur after stretching (i, j in Figure 8 and p in Figure 2) is that the rate of molecular relaxation caused by heat is faster than the rate of molecular orientation caused by stretching. In this invention, since a polyester that is more difficult to crystallize (amorphous) than polyethylene terephthalate is used as the raw material, it is conceivable that the stretching ratio at which orientation crystallization occurs is in a larger region compared to polyethylene terephthalate, and thus the stretched orientation molecules are in a state that is easily thermally relaxed. In the past, in order to relax the aligned molecular chains, the clamp spacing in the width direction of the tenter frame could be reduced (relaxation in the width direction). However, since the width of the tenter frame exit is reduced, there is a problem of sacrificing productivity. Therefore, after reviewing various methods for maintaining or improving productivity while retaining the required ΔCp for the film, the inventors discovered that by using an amorphous polyester raw material and, as described above, setting non-stretched sections (multi-segment stretching) along the transverse stretching region, it is possible to efficiently reduce ΔCp by thermally modulating the aligned molecular chains. Based on this technical concept, the more stretching segments, the better it is to maintain ΔCp within a predetermined range while improving productivity; however, there is a concern about the increased length of the tenter frame.The number of horizontal extension segments is preferably between 2 and 4.

[0049] The elongation ratio of each segment in the lateral extension is preferably 1.1 times to less than 3 times, and the final elongation ratio (the value obtained by multiplying the elongation ratios of all extension segments) is preferably 3.5 times to less than 6 times. Furthermore, the lateral extension temperature is preferably 80°C to less than 150°C, regardless of its position in the extension segments. The passage time for each segment in the lateral extension is preferably 1 second to less than 10 seconds; however, this can be appropriately changed as it is affected by the elongation ratio or linear velocity.

[0050] 3.3. Heat Treatment As described above, the film that has undergone lateral stretching can also be heat-treated in the tenter frame while the two ends in the width direction are held by clamps, as needed. Here, heat treatment means heat treatment at a temperature of 80°C to 120°C for 1 to 9 seconds. Such heat treatment improves dimensional stability after storage, thus allowing for better use. If the heat treatment temperature is below 80°C, the aforementioned effects of heat treatment cannot be effectively achieved. On the other hand, if the heat treatment temperature is above 120°C, the thermal shrinkage rate in the width direction is likely to fall below the lower limit of 20%. The longer the heat treatment time, the easier it is to achieve the desired effect; however, if it is too long, the equipment will become bulky, so it is better to control it to 1 to 9 seconds. More preferably, it is 5 to 8 seconds. In addition, during the heat treatment step, by reducing the distance between the clamps in the tenter frame, relaxation in the width direction can also be implemented. However, as mentioned above, due to reduced productivity, a relaxation rate of 0% to 10% is preferable.

[0051] 3.4. Surface Treatment Preferably, at least one outermost layer of the film is treated to increase heat-sealing strength. Examples of surface treatments include corona treatment, plasma treatment, flame treatment, sandblasting, and coating. Among these, corona treatment, plasma treatment, and coating are preferred. In the case of corona treatment or plasma treatment, it is easy to set the wetting tension to 40 mN / m or more. The degree of treatment (wetting tension) of corona treatment and plasma treatment varies depending on the distance between the treatment electrode and the film, the discharge voltage, and the film's moving speed (linear velocity), and is determined according to a combination of these conditions.

[0052] Regarding coating, for example, the low-temperature heat-sealing property of the film is improved by coating a heat-sealing resin onto the film surface. Examples of heat-sealing resins include the polyester resins exemplified in "1. Polyester raw materials used in heat-shrinkable polyester films". These resins can be used alone or in combination with two or more other resins, and the solution after dissolving them in a solvent can be coated onto the film surface. Among the aforementioned polyester components, isophthalic acid, neopentyl glycol, and 1,4-cyclohexanediol are preferred. In the case of coating, sebacic acid and 1,3-propanediol are also preferred. It is preferable that the coating solution contains 40 mol% to 100 mol% of one or more of these components selected from the group. If the total amount of these components is less than 40 mol%, it is difficult to dissolve them in a solvent during the preparation of the coating solution, which is undesirable. The coating solution can be applied at any point in the film-forming process exemplified above. The film obtained after the aforementioned steps is preferably wound into a roller shape on a winding core such as a paper tube, and is thus provided as a film roller.

[0053] 4. Circular Label The circular label of the present invention uses at least a portion of the heat-shrinkable polyester film of the present invention, wherein the heat-shrinkable polyester film of the present invention is bonded to itself or to other films, and the heat seal strength when the bonded portion is peeled off by a shear test is 20 N / 15 mm or more to 80 N / 15 mm or less. Furthermore, the length (circumference) or the number of bonded portions of the circular label of the present invention can be arbitrary. Preferably, it is the aforementioned strip label.

[0054] As other films constituting the ring-shaped label of the present invention, regardless of whether they have the characteristics exemplified in "2. Characteristics of the heat-shrinkable polyester film of the present invention" above, conventionally known films can be used in any length. The material of the film can also be arbitrary, for example, polyester, polyolefin, polyamide, etc.

[0055] Examples of bonding methods necessary for forming the ring-shaped label of the present invention include heat sealing, ultrasonic sealing, hot glue (hot melt glue) or cold glue, and center seal using solvents. Among these, heat sealing or ultrasonic sealing is preferred, and heat sealing is even more preferred. The heat seal strength varies depending on the temperature, pressure, and sealing time of the heat sealing rod (the surface in contact with the film), and is determined according to the combination of these conditions. For example, even if the heat sealing temperature is temporarily increased, as long as the sealing time is shortened, the actual temperature applied to the film will also decrease. As an example, the heat sealing temperature is preferably 100°C to 180°C, more preferably 110°C to 170°C, and even more preferably 120°C to 160°C. If the heat sealing temperature is less than 100°C, the heat seal strength is easily less than 20 N / 15 mm. If the heat sealing temperature is greater than 180°C, the heat seal strength is improved and better; however, the film is prone to thermal shrinkage, which may cause changes in the label size of the heat-sealed portion and deterioration in appearance. The heat-sealing pressure is preferably between 0.05 MPa and 0.6 MPa, more preferably between 0.1 MPa and 0.55 MPa, and even more preferably between 0.15 MPa and 0.5 MPa. If the pressure is less than 0.05 MPa, the heat-sealing rod becomes difficult to transfer sufficient heat to the film, easily resulting in a heat-sealing strength of less than 20 N / 15 mm. According to the inventors' review, as long as the pressure is above 0.05 MPa, the heat-sealing strength does not change significantly; however, if the pressure is above 0.6 MPa, there are concerns about film rupture.

[0056] The heat sealing time is preferably 0.1 seconds to 3 seconds, more preferably 0.2 seconds to 2.9 seconds, and even more preferably 0.3 seconds to 2.8 seconds. If the heat sealing time is less than 0.1 seconds, the heat seal strength is likely to be less than 20 N / 15 mm. If the heat sealing time exceeds 3 seconds, the heat seal strength is improved and thus better; however, this is undesirable because it violates the improvement in productivity that is the main purpose of this invention.

[0057] 5. Packaging Body The packaging system of the present invention is characterized by the use of the circular label of the present invention. Specifically, at least a portion of the packaged object is covered with the circular label of the present invention, and the heat-shrinkable polyester film of the present invention is heat-shrinkable. The heat-shrinkable material may also be a portion of the heat-shrinkable polyester film used for the circular label of the present invention. The packaged object is not limited; examples include, for instance, square or round plastic containers, PET bottles, etc. (Example)

[0058] Next, the present invention will be specifically described using examples and comparative examples. However, the present invention is not limited to the forms described in these examples, and changes may be made without departing from the spirit of the invention. The following characteristics are evaluated for each polyester listed in Table 2 below.

[0059] [Thickness] Measured using a dial gauge in accordance with JIS K7130-1999 A method.

[0060] [Tg (Glass Transfer Point)] Using a temperature-modulated differential scanning calorimeter (DSC250) (manufactured by TA Instruments), the membrane used as the sample was weighed at 5.0 mg ± 0.2 mg into a T-zero pan or aluminum pan (flat pan shape). The reverse heat flow was measured using the heat-only mode of the MDSC (registered trademark) at an average heating rate of 2 °C / min and a modulation period of 40 seconds. Furthermore, when sealing the sample into the pan, the sample was overlapped with the pan bottom surface in a manner that ensured good adhesion, and was then stamped into a circular shape (4.5 mm in diameter) using a stamping machine. "Good adhesion to the pan bottom surface" means that when the sample was sealed into the pan, the membrane sample inside the pan was not folded, and the lid was pressed down sufficiently, leaving no space between the overlapping membranes. Furthermore, it is acceptable if the film has wrinkles before stamping; however, it is preferable to straighten the wrinkles before stamping the sample. Additionally, the shape or size of the stamped sample (stamping machine) is not limited as described above, as long as the sample is neatly stored on the bottom of the pan without bending. The measured reverse heat flow is used to determine Tg, which appears as a signal that changes in stages from the baseline. Specifically, on the lower Tg side and the higher Tg side, the extension lines of the baselines of each heat flow are drawn, and the intersection points with the tangents at the inflection point (Tg) are determined. The value of the horizontal axis at this intersection point is read, and the average value of the lower and higher Tg sides is set as Tg.

[0061] [Inherent Viscosity IV (film, polyester raw material)] The film or polyester raw material (resin) was dissolved in a 6 / 4 (weight ratio) mixed solution of phenol and 1,1,2,2-tetrachloroethane and the result was measured at 30°C.

[0062] [Wetting Tension] The wetting tension of the membrane surface was measured after aging the membrane at 23°C and 50% relative humidity for 24 hours using the method described in JIS K6768:1999.

[0063] [Oxygen Atom Presence Ratio] The film surface was measured using an X-ray electron spectroscopy (ESCA) instrument (K-Alpha, Thermo Fisher Scientific). Excitation X-rays: Monochromatic AlKα rays X-ray output: 12kV, 6mA Photoelectron detachment angle: 90° Spot size: 400μmφ Pass energy: 50eV (narrow scan), 200eV (full element scan) Step size: 0.1eV (narrow scan), 1eV (full element scan) Narrow scans were performed on C, N, O, and Si systems. The peak intensity ratio obtained by dividing the peak intensity of oxygen atoms (530eV to 540eV) by the peak intensity of carbon atoms (280eV to 290eV) was taken as the oxygen atom presence ratio on the film surface. In addition, the measurement was repeated 4 times, and the average value of the peak intensity ratio was calculated.

[0064] [Ring Stiffness] Short strips of film with a width of 25.4 mm and a length of 110 mm were cut from the laminated films prepared in the Examples and Comparative Examples as samples for ring stiffness measurement. The long side of the short strip was aligned with the direction of the test object. The cut strips were placed in a ring stiffness tester manufactured by Toyo Seiki Co., Ltd., and the repulsive force was measured. The measurement frequency was set to 50 Hz. The measured repulsive force value (mN) was defined as the ring stiffness.

[0065] [Heat Shrinkage Rate (Hot Water Heat Shrinkage Rate)] Cut the film into 10cm×10cm squares, immerse them in hot water at 80℃±0.5℃ for 10 seconds under no load to allow for heat shrinkage, then immerse them in water at 25℃±0.5℃ for 10 seconds. Pull the film out of the water and measure its longitudinal and transverse dimensions. Calculate the respective heat shrinkage rates according to Formula 1. The direction with the larger heat shrinkage rate is designated as the main shrinkage direction (width direction). Heat shrinkage rate (%) = {(Length before shrinkage - Length after shrinkage) / Length before shrinkage} × 100 Formula 1

[0066] [Heat Seal Strength] The heat seal strength was determined according to JIS Z1707. The specific sequence is briefly shown below. Using a heat sealer, the outermost layer of one side of the film sample was sealed to the outermost layer of the other side. The heat seal conditions were set as follows: upper rod temperature 140°C, lower rod temperature 30°C, pressure 0.2 MPa, and time 2 seconds. Ten samples were then cut with a seal width of 15 mm. Peel strength was measured using a tensile testing machine (Shimadzu Autograph AG-Xplus) at a tensile speed of 200 mm / min. The peel direction was as shown in Figure 3, in a shear direction. The heat seal strength is set as the average of 10 tests, expressed as strength per 15 mm (N / 15 mm).

[0067] [Heat-sealing initiation temperature] The heat-sealing initiation temperature was evaluated according to JIS Z1707. The specific sequence is simply shown. Using a heat-sealing machine, the outermost layer of one side of the film sample was sealed to the outermost layer of the other side. The heat-sealing conditions were set as follows: lower rod temperature 30°C, pressure 0.2 MPa, time 2 seconds, and upper rod temperature varied in 5°C intervals from 90°C to 160°C, producing samples at each temperature. Ten samples were cut from each upper rod temperature, with a seal width of 15 mm. Peel strength was measured using a tensile testing machine (Shimadzu Autograph AG-Xplus) at a tensile speed of 200 mm / min. The peel direction was as shown in Figure 3, in a shear direction. The heat-sealing strength was set as the average of 10 tests, expressed as strength per 15 mm (N / 15 mm). The heat-sealing initiation temperature was defined as the temperature at which the heat-sealing strength began to reach 2 N / 15 mm or higher.

[0068] [Maximum Heat Shrinkage Stress] A sample with a length of 200 mm in the main shrinkage direction (width direction) and a width of 20 mm (long side direction) was cut from the polyester film and measured using a tensile strength tester (Tensilon, a registered trademark of Orientec) with an auxiliary heating furnace. The heating furnace was preheated to 90°C, and the distance between the clamps was set to 100 mm. The air supply to the heating furnace was temporarily stopped and the door of the heating furnace was opened. After the aforementioned sample was installed in the clamp, the door of the heating furnace was quickly closed and the air supply was resumed. The heat shrinkage stress in the width direction after shrinking for 30 seconds in hot air at 90°C was measured, and the maximum value of the aforementioned heat shrinkage stress was set as the maximum heat shrinkage stress (MPa).

[0069] [Reversible Heat Capacity Difference] Using a temperature-modulated differential scanning calorimeter (DSC) "DSC250" (manufactured by TA Instruments), the membrane sample was weighed at 5.0 mg ± 0.2 mg into a T-zero pan or aluminum pan (flat pan shape). The reverse heat flow was measured using the pure heating mode of the MDSC (registered trademark) at an average heating rate of 2°C / min and a modulation period of 40 seconds. When sealing the sample into the pan, good adhesion to the bottom surface of the pan was ensured. The membranes were overlapped and stamped into a circular shape (4.5 mm in diameter) using a stamping machine. "Good adhesion to the bottom surface of the pan" means that when the sample was sealed into the pan, the membrane sample inside the pan was not folded, and the lid was pressed down sufficiently without any space between the overlapping membranes. Furthermore, wrinkles in the membrane before stamping are acceptable; however, it is preferable to straighten the wrinkles before stamping the sample. Furthermore, the shape or size of the stamped sample (stamping machine) is not limited as mentioned above, as long as the sample is neatly housed on the bottom of the pan without bending. In the resulting reverse heat flow, the reversible heat capacity difference from 30°C to 140°C is calculated using the accompanying analytical software (Trios, manufactured by TA Instruments), as shown in Equation 2. Reversible heat capacity difference ΔCp = Cp1 - Cp2 Equation 2 Cp1: Heat capacity at 140°C Cp2: Heat capacity at 30°C

[0070] [Haze] The haze was measured using a haze meter "500A" (manufactured by Nippon Denshoku Kogyo Co., Ltd.) according to JIS K7136. The measurement was performed twice, and the average value of the two measurements was calculated.

[0071] [Anti-adhesion] Adhesion value was determined according to ASTM D1893-67. Two film samples were cut out with a length of 150mm and a width of 200mm, and overlapped with different sides. The overlapped samples were held in place with a smooth glass plate (250mm square), and 20kg (5kg x 4 weights) of weights were placed on top. The samples were then placed in a hot air furnace set at 60℃±2℃ for 24 hours. The film samples were then removed and subjected to a 1-hour conditioning treatment at 23℃ and 65% humidity. The adjusted sample was peeled approximately 3 cm from its end. The sample was then mounted on the upper clamp of an Autograph (Shimadzu AG-Xplus). A 6 mm diameter rod was mounted on the lower clamp. The force required to peel the adhered portion using the rod at a speed of 100 m / min was measured. Furthermore, with the rod horizontal to the peeling surface, the measurement direction (the direction of clamp movement) was along the long side of the membrane. Two measurements were performed, and the average value was calculated as the adhesion value (unit: mN / 200 mm). The calculated adhesion value was evaluated according to the following criteria: Before measurement, the sample was peeled and evaluated as ○; when mounted on the clamp, the sample could not be peeled by hand and evaluated as ×. Evaluation ○: Adhesion value 0 mN / 200 mm or more to less than 1000 mN / 200 mm. Evaluation ×: Adhesion value 1000 mN / 200 mm or more.

[0072] [Assembly Suitability] A 90mm section was cut along the long side and a 250mm section along the width. The film was placed on a plastic noodle container (220mm long side × 150mm short side × 50mm height) sold in convenience stores and transported on a belt conveyor set at a speed of 20cm / s. The film's positional deviation was evaluated. Furthermore, as preparation for transport on the belt conveyor, the film was placed along the short side of the container along its long side, and the end position of the film was marked on the container, with the initial position recorded. The distance by which the film position deviated from the initial position after transport on the belt conveyor was measured. Evaluation was performed according to the following criteria: Evaluation ○: Deviation distance less than 1cm; Evaluation ×: Deviation distance greater than 1cm.

[0073] [Shrink Finish Property] A film is cut from a plastic noodle container (220mm long side × 150mm short side × 50mm height) sold in convenience stores, with the film's long side direction (width of the strip label) being 90mm. The container body and lid are fixed together with the film, and two films are placed on top and bottom of the container. The ends of the films are then heat-sealed together (at 140°C). That is, the heat-sealed, ring-shaped film covers the noodle container. The shrinkage direction (width direction) of the film is aligned with the circumference of the ring-shaped film. The long sides of the noodle container are fixed together with the ring-shaped film, and the midpoint of the width direction of the ring-shaped film coincides with the midpoint of the long side of the container. Furthermore, the slack of the ring-shaped film relative to the container is set to 25%. The packaging consisting of this noodle container and the ring label was subjected to a hot air shrink tunnel (Nippon Technology Solution TORNADO 2500) at a set temperature of 110°C to heat and shrink the ring label, and the shrinkage completion was evaluated. The evaluation of shrinkage completion included assessing the seal to the container and the rupture of the heat seal.

[0074] (Seamless Contact with Container) The seal of the container is evaluated based on whether the container detaches from the ring label when the package is picked up by hand while holding the retracted ring label, as follows: Evaluation ○: The container does not detach from the ring label and remains in place. Evaluation ×: The container detaches from the ring label.

[0075] (Delamination of the heat-sealed portion) Delamination of the heat-sealed portion is determined by observing the heat-sealed portion at two locations after shrinkage is completed, and is judged based on the following criteria. Evaluation ○: No delamination Evaluation ×: At least one part or all of the heat-sealed portion has delamination

[0076] <Synthesis of Polyester Raw Materials> [Synthesis of Polyester Raw Material A] In a polymerization apparatus equipped with a stirrer, distillation column, and pressure regulator, terephthalic acid and glycols (ethylene glycol, neopentyl glycol, diethylene glycol) are added in a certain ratio (G / T: molar ratio of glycol to terephthalic acid). The esterification reaction is carried out at a reaction temperature of 240°C and a reaction pressure of 0.35 MPa, while sequentially removing the water generated during esterification. Next, a certain amount of an ethylene glycol solution of an aluminum compound (basic aluminum acetate) and an ethylene glycol solution of a phosphorus compound (Irganox 1222) are added. The system temperature is raised to 280°C over 1 hour, while the system pressure is slowly reduced to 0.15 kPa. While maintaining the aforementioned system conditions, the glycols generated during the polycondensation reaction are sequentially removed, while the polycondensation reaction is carried out. At the predetermined stirring torque point, the reaction vessel is purged with nitrogen to restore atmospheric pressure. The polyester resin is then removed from the polymerization equipment, water-cooled and cured, and granulated using a strand cutter to obtain polyester raw material A. Table 1 shows the monomer composition of polyester raw material A. In Table 1, the "Acid Components" column indicates the content of each monomer component per 100 mol% of all acid components, and the "Polyol Components" column indicates the content of each monomer component per 100 mol% of all polyol components. In Table 1, TPA is terephthalic acid, IPA is isophthalic acid, EG is ethylene glycol, BD is butanediol, NPG is neopentyl glycol, CHDM is cyclohexanediol, DEG is diethylene glycol, and SA is sebacic acid.

[0077] [Synthesis of Polyester Raw Material B to Polyester Raw Material E] Polyester raw materials B to E with different monomer compositions were obtained by the same method as described above for polyester raw material A, as shown in Table 1. Furthermore, polyester raw material D was manufactured by adding SiO2 (Sylysia 266 manufactured by Fuji-Sylysia Co., Ltd.; average particle size 1.5 μm) as a lubricant at a ratio of 7,000 ppm relative to the polyester. Each polyester raw material was appropriately shaped into fragments.

[0078] [Synthesis of Polyester Raw Material F] As polyester raw material F, a physically recycled polyester raw material was prepared using the following sequence. After washing and draining residual beverage and other foreign matter from a beverage PET bottle, the material was pulverized to obtain flakes. The obtained flakes were washed with a 3.5% by weight sodium hydroxide solution at a flake concentration of 10% by weight, at 85°C, for 30 minutes, under stirring. After alkali washing, the flakes were removed and washed with distilled water at a flake concentration of 10% by weight, at 25°C, for 20 minutes, under stirring. The aforementioned water washing was repeated twice, replacing the distilled water. After water washing, the flakes were dried and melted in an extruder. The material was then filtered a second time using a filter with a finer mesh size to remove finer foreign matter, and a third time using a filter with a minimum sieve size of 50 μm to obtain polyester raw material F with an intrinsic viscosity of 0.69 dl / g and an isophthalic acid content of 3.0 mol%.

[0079] [Synthesis of Polyester Raw Material G] As polyester raw material G, a chemically recycled polyester raw material is prepared in the following order: Collected and recycled PET bottle bundles are fed into a wet grinder, and a mixture containing 500g of liquid kitchen detergent in 1000L of water is added. The mixture is ground while circulating in the wet grinder. A gravity separator connected to the grinder is used to precipitate heavier materials such as metal, sand, and glass, and flakes are taken out from the upper layer. The aforementioned flakes are washed with pure water and centrifuged to obtain recycled flakes. In an autoclave equipped with a stirrer, 30 kg of the recovered flakes, melted in a undried state, were added to a mixture of 150 kg of preheated ethylene glycol and 150 g of zinc acetate dihydrate. After removing fractions with boiling points lower than ethylene glycol, such as water and acetic acid, the reaction was carried out at 195°C to 200°C for 4 hours using a reflux condenser. After the reaction, the temperature of the reactor contents was lowered to 97°C to 98°C, and the mixture was hot-filtered to remove suspended solids and precipitates. The filtrate was then cooled until the crude BHET (bis-2-hydroxylethyl terephthalate) was completely dissolved. The solution was then passed through an activated carbon bed at 50°C to 51°C for 30 minutes, followed by a pre-purification process through an anion / cation exchange mixed bed.

[0080] The aforementioned pre-refined liquid is placed back into a stirred autoclave and heated to distill off the remaining ethylene glycol at atmospheric pressure, obtaining a concentrated BHET melt. The obtained concentrated BHET melt is stirred under a nitrogen atmosphere and allowed to cool naturally before being removed from the autoclave, yielding concentrated BHET fragments. These fragments are reheated to 130°C and melted, then fed to a thin-film vacuum evaporator via a metered pump for evaporation, cooling, and condensation to obtain refined BHET. This refined BHET is used as a raw material for melt polymerization to obtain chemically recycled polyester raw material G.

[0081] [Synthesis of Coating Polyester Raw Material H and Polyester Raw Material I] Using the same method as described above for polyester raw material A, as shown in Table 1, coating polyester raw materials H and I with different monomer compositions were obtained. Each polyester raw material was appropriately shaped into fragments.

[0082] [Table 1] Polyester raw material Polyester raw material composition (mol%) lubricant Dosage (ppm) acid components polyol components TPA IPA EG BD NPG CHDM DEG SA A 100 - 62 - 26 - 12 - - B 100 - 68 - 30 - 2 - - C 100 - 68 - - 30 1 - - D 100 - 99 - - - 1 - 7000 E 100 - - 100 - - - - - F 90 10 99 - - - 1 - - G 100 - 99 - - - 1 - - H 54 46 80 - 15 - - 5 - I 50 50 63 - 37 - - - -

[0083] [Example 1] Polyester raw materials A, D, and F were mixed in a mass ratio of 80:8:12 and fed into an extruder. This mixed resin was melted at 280°C and extruded from a T-die. Rapid cooling was performed on rotating metal rollers cooled to a surface temperature of 30°C to obtain an unstretched film with a thickness of approximately 250 μm. The unstretched film was guided to a longitudinal stretching machine with multiple roller groups arranged continuously, and longitudinal stretching was performed using the speed difference between the rollers. The rollers were set to low speed, medium-low speed, medium-high speed, and high speed, dividing the longitudinal stretching interval into three zones for longitudinal stretching. In the low-to-medium-low speed zone (first stretching zone) and the medium-to-medium-high speed zone (second stretching zone), the film pass line did not wrap around the rollers but traveled in a straight line, with the film held by nip rolls on each roller. In the medium-high speed zone (third stretching zone), the roller pass line wrapped around the rollers and traveled in a cross-shaped pattern. The distance between the extension zones is adjusted by setting the rollers to 200 mm between the first and second extension zones, and to 120 mm between the rollers in the third extension zone. Regarding the temperature and magnification of each extension zone, longitudinal extension is performed at 85°C and 1.6 times magnification in the first extension zone, at 85°C and 1.7 times magnification in the second extension zone, and at 90°C and 1.5 times magnification in the third extension zone, for a total longitudinal extension magnification of 4.1.

[0084] Subsequently, the longitudinally stretched film is guided to a heating furnace heated by far-infrared rays for intermediate heat treatment. The temperature of the heating furnace is 130°C, and a 40% relaxation treatment is performed in the long side direction using the speed difference between the rollers at the inlet and outlet of the heating furnace. The relaxed film is then guided to a transverse stretching machine (tenator), preheated to 130°C, and as shown in Figure 2, the clamping mode is returned to a non-stretching zone (relief zone) parallel to the direction of travel, and transverse stretching is performed in three stages. Specifically, in the first stretching zone, the film is stretched to 1.5 times its original size at a temperature of 100°C and a stretching speed of 30% / second; in the second stretching zone, the film is stretched to 1.6 times its original size (the ratio from the outlet of the first stretching zone to the outlet of the second stretching zone) at a temperature of 95°C and a stretching speed of 30% / second; and in the third stretching zone, the film is stretched to 1.7 times its original size at a temperature of 93°C and a stretching speed of 15% / second. The total transverse stretching ratio is 4.1 times. Then, heat treatment is carried out at 90°C in the final heat treatment zone.

[0085] Next, the membrane was guided to a corona treatment machine, and the treatment temperature was set to 40°C and the output to 0.3kW to perform corona treatment on the upper surface (F side) of the membrane. Afterwards, the membrane was rolled into a roll with a width of 500mm by cutting off the two edges, and a membrane with a thickness of 25μm was continuously manufactured to a predetermined length, thus obtaining the membrane of Example 1. Table 2 shows the manufacturing conditions of the membrane of Example 1. The membrane of Example 1 was evaluated using the aforementioned method. Table 3 shows the evaluation results.

[0086] [Example 2] In Example 1 above, various manufacturing conditions were changed as shown in Table 2. Except for changing the corona treatment to coating, the film was obtained in the same manner as in Example 1. The film was coated by the method shown below. Polyester raw material H and polyester raw material I were mixed at a ratio of 80:20 and heated to dissolve in ethyl acetate to prepare a coating solution. This coating solution was coated on the lower surface (B side) of the film with a thickness of 2 μm to manufacture the film of Example 2. Table 2 shows the manufacturing conditions of the film of Example 2. Table 3 shows the evaluation results.

[0087] [Examples 3 to 7, Comparative Examples 1 to 4] The membranes of Examples 3 to 7 and Comparative Examples 1 to 4 were manufactured as shown in Table 2. Table 3 shows the evaluation results of the membranes of Examples 3 to 7 and Comparative Examples 1 to 4.

[0088] [Table 2A] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 membrane Raw material composition (quality%) Polyester raw material A 80 80 80 0 0 0 Polyester raw material B 0 0 0 0 75 0 Polyester raw material C 0 0 0 82 0 60 Polyester raw material D 8 8 8 8 5 5 Polyester raw material E 0 0 0 0 10 15 Polyester raw material F 12 12 12 10 0 0 Polyester raw material G 0 0 0 0 10 20 Monomer components Quantity (mol%) isophthalic acid 1.2 1.2 1.2 1.0 0 0 Neopentyl glycol 20.8 20.8 20.8 0 22.5 0.0 1,4-Cyclohexanediethanol 0 0 0 24.6 0 18.0 Butylene glycol 0 0 0 0 10.0 15.0 diethylene glycol 9.8 9.8 9.8 1.0 1.7 0.9 Raw material extrusion Extrusion temperature (°C) 280 300 265 280 270 280 Vertical extension First Extension Zone path straight line straight line straight line - straight line straight line Extension distance (mm) 200 250 300 - 200 200 Extended temperature (°C) 85 90 90 - 85 83 Extension ratio 1.6 1.6 2.2 - 1.6 2.2 Second Extension Area path straight line Hook Cross - straight line Cross Extension distance (mm) 200 120 120 - 250 120 Extended temperature (°C) 85 90 92 - 85 87 Extension ratio 1.7 1.4 1.8 - 1.6 1.8 Third Extension Zone path Cross straight line - - Cross - Extension distance (mm) 120 200 - - 120 - Extended temperature (°C) 90 90 - - 90 - Extension ratio 1.5 1.7 - - 1.5 - Total extension ratio (first × second × third) 4.1 3.8 4.0 1.0 3.8 4.0 Intermediate heat treatment Furnace temperature (°C) 130 125 130 - 130 125 Relaxation rate (%) 40 38 35 - 38 35 Horizontal extension preheating Temperature (°C) 130 130 128 110 128 130 First Extension Zone Temperature (°C) 100 95 103 95 95 92 Extension speed (% / second) 30 30 30 30 25 33 magnification 1.5 4.0 1.4 1.6 1.7 1.8 easing zone Temperature (°C) 95 - 98 88 92 92 Dwell time (seconds) 2 - 2 3 2 2 Second Extension Area Temperature (°C) 95 - 98 88 90 92 Extension speed (% / second) 30 - 30 30 30 33 magnification 1.6 - 1.6 1.8 1.4 1.5 easing zone Temperature (°C) 93 - 95 86 90 90 Dwell time (seconds) 2 - 2 3 2 2 Third Extension Zone Temperature (°C) 93 - 95 86 90 90 Extension speed (% / second) 15 - 15 15 18 14 magnification 1.7 - 1.7 1.8 1.7 1.3 Total extension ratio (first × second × third) 4.1 4.0 3.8 5.2 4.0 3.5 Final heat treatment Temperature (°C) 90 90 110 95 95 88 Extension area ratio Total multiplier (vertical x horizontal) 10.0 9.4 9.8 5.2 9.6 9.0 Corona treatment Processing temperature (°C) 40 40 40 40 40 40 Output (kW) 0.3 0.1 0.2 0.2 0.2 0.2 Processing surface F F F F F F Coating Resin composition (quality%) Polyester raw material H - 80 - - - - Polyester raw material I - 20 - - - - Thickness (μm) - 2 - - - - Coated surface - B - - - - Membrane thickness (μm) 25 twenty two 40 25 25 30

[0089] [Table 2B] Example 7 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 membrane Raw material composition (quality%) Polyester raw material A 0 80 80 0 0 Polyester raw material B 0 0 0 0 75 Polyester raw material C 60 0 0 82 0 Polyester raw material D 5 8 8 8 5 Polyester raw material E 15 0 0 0 10 Polyester raw material F 0 12 12 10 0 Polyester raw material G 20 0 0 0 10 Monomer components Quantity (mol%) isophthalic acid 0 1.2 1.2 1.0 0 Neopentyl glycol 0.0 20.8 20.8 0 22.5 1,4-Cyclohexanediethanol 18.0 0 0 24.6 0 Butylene glycol 15.0 0 0 0 10.0 diethylene glycol 0.9 9.8 9.8 1.0 1.7 Raw material extrusion Extrusion temperature (°C) 280 280 280 280 270 Vertical extension First Extension Zone path straight line straight line straight line - straight line Extension distance (mm) 200 200 200 - 200 Extended temperature (°C) 81 85 85 - 85 Extension ratio 1.1 1.6 1.6 - 1.6 Second Extension Area path Cross straight line straight line - straight line Extension distance (mm) 150 200 200 - 250 Extended temperature (°C) 85 85 85 - 85 Extension ratio 1.1 1.7 1.7 - 1.6 Third Extension Zone path - Cross Cross - Cross Extension distance (mm) - 120 120 - 120 Extended temperature (°C) - 90 90 - 90 Extension ratio - 1.5 1.5 - 1.5 Total extension ratio (first × second × third) 1.2 4.1 4.1 1.0 3.8 Intermediate heat treatment Furnace temperature (°C) - 130 130 - 130 Relaxation rate (%) - 40 40 - 38 Horizontal extension preheating Temperature (°C) 130 130 130 105 128 First Extension Zone Temperature (°C) 92 100 100 100 95 Extension speed (% / second) 33 30 30 30 25 magnification 1.8 1.5 1.5 1.5 1.7 easing zone Temperature (°C) 92 95 95 100 92 Dwell time (seconds) 2 2 2 3 2 Second Extension Area Temperature (°C) 92 95 95 100 90 Extension speed (% / second) 33 30 30 30 30 magnification 1.6 1.6 1.6 1.5 1.4 easing zone Temperature (°C) 90 93 93 100 90 Dwell time (seconds) 2 2 2 3 2 Third Extension Zone Temperature (°C) 90 93 93 100 90 Extension speed (% / second) 14 15 15 15 18 magnification 1.5 1.7 1.7 1.8 1.7 Total extension ratio (first × second × third) 4.3 4.1 4.1 4.1 4.0 Final heat treatment Temperature (°C) 88 90 90 130 95 Extension area ratio Total multiplier (vertical x horizontal) 5.2 10.0 10.0 4.1 9.6 Corona treatment Processing temperature (°C) 40 - 40 40 45 Output (kW) 0.2 - 0.3 0.3 0.4 Processing surface F - F F F Coating Resin composition (quality%) Polyester raw material H - - - - 80 Polyester raw material I - - - - 20 Thickness (μm) - - - - 2 Coated surface - - - - B Membrane thickness (μm) 30 25 12 25 25

[0090] [Table 3] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Membrane thickness (μm) 25 twenty two 40 25 25 30 30 25 12 25 25 Glass transition temperature Tg (°C) of the membrane 65 65 65 73 68 63 63 65 65 72 68 Intrinsic viscosity of the membrane IV (dL / g) 0.62 0.59 0.70 0.68 0.65 0.64 0.64 0.62 0.62 0.68 0.65 Wetting tension (mN / m) F side 52 42 47 49 51 50 49 36 53 49 57 Side B 36 36 36 36 36 36 36 36 36 36 36 Oxygen atom content (%) F side 28.8 27.1 28.0 28.3 28.7 28.5 28.1 26.5 29.4 28.3 31.3 Side B 26.5 26.5 26.4 26.5 26.4 26.6 26.5 26.5 26.4 26.5 26.7 Ring stiffness (mN / 25mm) width direction 14 8 187 17 15 42 44 14 2 15 19 80℃ Hot water thermal shrinkage rate (%) Long side direction 5.4 4.1 7.7 0.2 5.1 4.6 5.2 4.0 6.2 1.2 0.4 width direction 42.1 37.1 22.0 56.3 46.3 51.7 63.3 40.4 45.6 13.5 55.0 Heat seal strength at 140℃ (N / 15mm) width direction 54 77 26 57 48 61 51 1 32 18 65 Heat sealing start temperature (°C) width direction 120 130 125 125 120 120 125 160 115 125 95 Maximum thermal shrinkage stress (MPa) width direction 12.2 15.1 8.9 16.3 13.1 14.4 15.5 12.9 12.2 6.3 5.5 Reversible heat capacity difference (J / g·K) 0.61 1.27 0.48 0.51 0.58 0.55 0.52 0.62 0.61 0.36 0.73 Haze (%) 4.6 3.8 6.8 6.2 4.4 5.4 5.6 4.3 4.6 5.9 5.3 Anti-adhesion ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ × Assembly suitability evaluation results ○ ○ ○ ○ ○ ○ ○ ○ × ○ ○ Shrinkage completion evaluation result Tightness ○ ○ ○ ○ ○ ○ ○ - ○ × ○ peeling ○ ○ ○ ○ ○ ○ ○ × ○ ○ ○

[0091] The films of Examples 1 to 7 satisfy the requirements of the present invention, and any one of them is a heat-shrinkable polyester film suitable for strip labels. In contrast, in Comparative Example 1, since the heat seal strength is as low as 1, the heat seal peeled off during the evaluation of shrinkage completion. Therefore, since the shrinkage completion cannot be evaluated, the column for the tightness of shrinkage completion recorded in Table 3 is marked with "-". In Comparative Example 2, since the ring stiffness is as low as 2mN / 25mm, the film moves during transport on a belt conveyor, resulting in poor assembly suitability.

[0092] Comparative Example 3 is a heat-shrinkable polyester film with poor shrinkage completion due to its low heat shrinkage rate in the width direction. Comparative Example 4 is a film with poor anti-blocking properties due to its excessively high wetting tension of 57 mN / m. [Industrial Applicability]

[0093] The heat-shrinkable polyester film of the present invention has the aforementioned characteristics and can therefore be appropriately used for labeling applications, etc. [Simplified Explanation of the Diagram]

[0013] [Figure 1] is a schematic diagram showing the lateral extension of the tenter frame as a single extension. [Figure 2] is a schematic diagram showing the lateral extension of the tenter frame as a triple extension. [Figure 3] is a schematic diagram showing the peeling direction as the shearing direction when measuring heat seal strength.

Claims

1. A heat-shrinkable polyester film, comprising polyethylene terephthalate as the main component, having an outermost layer on one side and an outermost layer on the other side, and satisfying the following requirements (1) to (4): (1) the ring stiffness in the width direction is 6 mN / 25 mm or more to 200 mN / 25 mm or less; (2) the heat shrinkage rate in the width direction when shrinking in hot water at 80°C for 10 seconds is 20% or more to 70% or less; (3) when one side of the film is heat-sealed with the other side at 140°C and 0.1 MPa for 1 second, the peel strength by shear test in the width direction is 20 N / 15 mm or more to 80 N / 15 mm or less; (4) the wetting tension of at least one outermost layer is 40 mN / m or more to 55 mN / m or less.

2. The heat-shrinkable polyester film described in claim 1, wherein the reversible heat capacity difference from 25°C to 140°C is greater than 0.4 J / g K and less than 1.4 J / g K, as measured by a temperature-modulated differential scanning calorimeter.

3. The heat-shrinkable polyester film as described in claim 1 or 2, wherein the proportion of oxygen atoms present on the film surface obtained from the C1s spectrum of X-ray electron spectroscopy (ESCA) at the peak of 285 eV to 290 eV is more than 27% and less than 31% in at least one outermost layer.

4. The heat-shrinkable polyester film described in claim 1 or 2 has a thickness of 20 μm or more but less than 50 μm.

5. The heat-shrinkable polyester film as described in claim 1 or 2, wherein the polyester component constituting the film contains any one of phthalic acid, neopentyl glycol, 1,4-cyclohexanediol, butanediol and diethylene glycol, ranging from more than 1 mol% to less than 30 mol%.

6. The heat-shrinkable polyester film as described in claim 1 or 2, wherein the raw material constituting the film is a polyester raw material obtained by recycling PET bottles and subjecting them to physical and / or chemical recycling.

7. A label, at least a portion of which is an annular label using a heat-shrinkable polyester film as described in any one of claims 1 to 6, wherein the heat-shrinkable polyester film is bonded to each other or to other films, and the strength of the bonded portion when peeled off by a shear test is 20 N / 15 mm or more and 80 N / 15 mm or less.

8. The label as described in claim 7, wherein the aforementioned adhesive portion is heat-sealed.

9. A packaging body that uses a label as described in claim 7 or 8.

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