Heat shrinkable film, heat shrinkable film rolls, heat shrinkable labels

Abstract

To provide a heat-shrinkable film that has excellent resistance to natural shrinkage, can suppress problems caused by reduced film elongation after storage in warehouses where temperature is not controlled, and has good shrinkage finish and shrinkage processability. [Solution] A heat-shrinkable film having a layer made of a polyester resin composition containing a polyester resin, wherein the heat-shrinkable film satisfies the following a) to c). a) The polyester resin contains terephthalic acid and ethylene glycol, and further contains a copolymerized polyester resin containing amorphous components. b) When the total diol component of the polyester resin contained in the polyester resin composition is taken as 100 mol%, the amorphous component is present in an amount of 33 mol% or more. c) The shrinkage rate in the main shrinkage direction is 20-50% when immersed in 80°C hot water for 10 seconds, and 60-85% when immersed in 99°C hot water for 10 seconds.

Description

Technical Field

[0001] The present invention relates to a heat-shrinkable film, a heat-shrinkable film roll, and a heat-shrinkable label that can be suitably used for packaging materials for foods, packaging materials for beverages, packaging materials for pharmaceuticals and medical products, packaging materials for chemicals, packaging materials for cosmetics, packaging materials for toiletries, industrial packaging materials, packaging materials for agricultural materials, and the like.

Background Art

[0002] Heat-shrinkable films are widely used for shrink packaging, shrink bundling, shrink labels for plastic containers (such as PET bottles), anti-scattering packaging for glass containers, cap sealing, and the like. Among them, stretched films made of polyvinyl chloride (PVC), polystyrene-based resins, and polyester-based resins are used as labels for various containers.

[0003] Conventionally, PVC-based heat-shrinkable films have been mainly used. However, since PVC has a problem of generating harmful substances such as chlorine-based gases during incineration, in recent years, replacement with polystyrene-based heat-shrinkable films and polyester-based heat-shrinkable films has been promoted. The polystyrene-based heat-shrinkable film is widely used for beverage PET bottles because it has a good finish when heat-shrunk. However, it has drawbacks such as low solvent resistance compared to other materials, the need to use special inks, and a tendency to shrink naturally. When attempting to perform gravure printing on such a film with a high natural shrinkage rate, dimensional changes may occur during storage, or the film dimensions may become unstable due to the penetration of ink solvents or the heat of the drying oven during printing, and troubles such as incorrect printing pitch are likely to occur. Furthermore, even after forming into a sleeve shape as a label for a PET bottle, the diameter of the label may become smaller during storage, and troubles such as difficulty in attaching to the container may occur when attempting to attach it. Regarding such polystyrene-based heat-shrinkable films, polyester-based heat-shrinkable films do not generate harmful substances during incineration, have high solvent resistance, and have a low natural shrinkage rate, so they are attracting attention as materials that are difficult to shrink during storage and transportation.

[0004] In domestic distribution, heat-shrinkable films or processed products such as labels are mainly transported by truck. However, depending on the season, the ambient temperature in the truck bed can exceed 40°C, which may lead to problems due to natural shrinkage as described above. Similarly, in product storage, if the warehouse is not temperature-controlled, the temperature may rise during the day, potentially causing natural shrinkage. In addition to natural shrinkage, exposure to high temperatures can also degrade the polymer, reducing the film's elasticity and making it more prone to tearing. This can lead to problems such as film breakage during the printing process. Therefore, it is common practice to use refrigerated trucks or warehouses for transporting and storing products during periods of rising ambient temperatures to suppress natural shrinkage and polymer degradation.

[0005] However, in recent years, reforms to the working styles of truck drivers have been implemented, which may lead to a decrease in transport capacity due to restrictions on traditional logistics functions, and an increase in the cost of refrigerated transport. Furthermore, the use of refrigerated trucks and warehouses increases energy consumption, which is also detrimental from an environmental perspective. For this reason, there is a demand for heat-shrinkable films or labels that can be processed in the same way as conventional methods, without the need for refrigerated trucks and warehouses.

[0006] As an example of a heat-shrinkable film with a low natural shrinkage rate, Patent Document 1 discloses a heat-shrinkable polyester film characterized by a natural shrinkage rate of 0.30% or less in the main shrinkage direction after storage at 40°C for 30 days, and a shrinkage rate of 20% or more and less than 80% in the main shrinkage direction when the film is immersed in 80°C hot water for 10 seconds. However, in seasons when the outside temperature rises, or in the cargo bed of a truck in the summer, the film will be exposed to environments exceeding 40°C for long periods of time, and there is a risk that these heat-shrinkable films will undergo natural shrinkage and deterioration. Furthermore, Patent Document 2 proposes a heat-shrinkable film with a high glass transition temperature (Tg) to suppress polymer degradation, making it less likely to tear (break) even when stored or used in high-temperature environments. However, as the glass transition temperature increases, the temperature at which thermal shrinkage in the main shrinkage direction of the film begins tends to become higher. This makes it difficult to shrink the heat-shrinkable film or its labels under the same temperature conditions as before, resulting in insufficient shrinkage. Consequently, it becomes impossible to suitably use the heat-shrinkable film or labels under the same processing conditions as before. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2012-36273 [Patent Document 2] Japanese Patent Publication No. 2022-84685 [Overview of the project] [Problems that the invention aims to solve]

[0008] The object of the present invention is to provide a heat-shrinkable film that has excellent resistance to natural shrinkage, can suppress problems caused by a decrease in film elongation after storage in warehouses or other places where the temperature is not controlled, and has good shrinkage finish and shrinkage processability. [Means for solving the problem]

[0009] The present invention provides the following [1] to [8]. [1] A heat-shrinkable film having a layer made of a polyester resin composition containing a polyester resin, wherein the heat-shrinkable film satisfies the following a) to c). a) A copolymerized polyester resin containing terephthalic acid and ethylene glycol, and further containing at least one amorphous component selected from the group consisting of 1,4-cyclohexanedimethanol, neopentyl glycol, spiroglycol, diethylene glycol, polytetramethylene glycol, isosorbide, and 1,3-propanediol. b) The content of the amorphous component in the diol component of the polyester resin contained in the polyester resin composition is 33 mol% or more, relative to 100 mol% of the total amount of the diol component. c) The shrinkage rate in the main shrinkage direction is 20-50% when immersed in 80°C hot water for 10 seconds, and 60-85% when immersed in 99°C hot water for 10 seconds. [2] The heat-shrinkable film according to [1], wherein the natural shrinkage rate in the main shrinkage direction and the natural shrinkage rate in a direction perpendicular to the main shrinkage direction after treatment for 720 hours in an atmosphere of 55°C and 10% relative humidity are 0.7% or less. [3] The heat-shrinkable film according to [1] or [2], wherein the polyester resin comprises at least two selected from the group consisting of 1,4-cyclohexanedimethanol, neopentyl glycol, spiroglycol, and diethylene glycol as amorphous components. [4] A heat-shrinkable film according to any one of [1] to [3], comprising a copolymer polyester resin having a glass transition temperature of 77°C or higher, as measured by differential scanning calorimetry in accordance with JIS K7122 (2012) for the copolymer polyester resin. [5] A heat-shrinkable film according to any one of [1] to [4], wherein the glass transition temperature of the layer made of the polyester resin composition, as measured by differential scanning calorimetry in accordance with JIS K7122 (2012), is 75 to 90°C. [6] A heat-shrinkable film according to any of [1] to [5], wherein the shrinkage rate (α) in the main shrinkage direction when immersed in 70°C hot water for 10 seconds is 0 to 20%. [7] The heat-shrinkable film according to [6], wherein (α)-(β)=7% or less when (β) is the shrinkage rate in the principal shrinkage direction after being treated for 168 hours in an atmosphere of 40°C and 90% relative humidity and then immersed in 70°C hot water for 10 seconds. [8] A heat-shrinkable film according to any of [1] to [7], wherein the tensile elongation (A) in a direction perpendicular to the principal shrinkage direction at 23°C and 10% relative humidity, measured in accordance with JIS K7127 (1999), and the tensile elongation (B) in a direction perpendicular to the principal shrinkage direction after treatment at 55°C and 10% relative humidity for 168 hours, satisfy the following formula (1). Rate of change (X) = Tensile elongation (A) / Tensile elongation (B) = 0.8~1.6 ... (1) A heat-shrinkable film roll comprising any of the heat-shrinkable films described in [9] [1] to [8].

[10] A heat-shrinkable label using a heat-shrinkable film as described in any of [1] to [8]. [Effects of the Invention]

[0010] The heat-shrinkable film of the present invention exhibits excellent resistance to natural shrinkage, suppresses a decrease in tensile elongation even after long-term storage at high temperatures, and has good shrinkage finish and shrinkage processability. [Modes for carrying out the invention]

[0011] In this specification, "x and / or y (where x,y are any combination)" means at least one of x and y, and can mean x only, y only, or x and y. In this specification, when "X~Y" (where X and Y are any numbers) is used, unless otherwise specified, it means "X or greater and Y or less," and also includes the meanings of "preferably greater than X" or "preferably less than Y." In this specification, when we express "greater than or equal to X" (where X is any number) or "less than or equal to Y" (where Y is any number), we also mean "preferably greater than X" or "preferably less than Y." In the numerical ranges described in stages in this specification, the upper or lower limit of one stage of the numerical range can be arbitrarily combined with the upper or lower limit of another stage of the numerical range. Furthermore, in the numerical ranges described in this specification, the upper or lower limit of that range can be replaced with the values ​​shown in the examples. In this specification, "film" encompasses a range of materials, from thick sheets to thin films. In this specification, "longitudinal direction (MD)" refers to the flow direction from the extruder in the manufacturing process of heat-shrinkable film, and "transverse direction (TD)" refers to the direction perpendicular to the flow direction from the extruder. Furthermore, "main shrinkage direction" refers to the direction of greater heat shrinkage among the longitudinal and transverse directions. In this specification, "main component" means that other components may be included to the extent that they do not interfere with the action and effect of the resin contained as the main component. Furthermore, "main component" does not limit the specific content, but it is preferable that the component accounts for 50% by mass or more of the total constituent components, more preferably 70% by mass or more, even more preferably 80% by mass or more, and also preferable that the component accounts for 100% by mass or less.

[0012] A heat-shrinkable film according to one embodiment of the present invention (hereinafter sometimes referred to as "this heat-shrinkable film") has a layer made of a polyester resin composition containing a polyester resin (hereinafter referred to as "polyester resin layer"). Each layer constituting this heat-shrinkable film will be described in detail below.

[0013] <Polyester resin layer> The polyester resin layer is made of a polyester resin composition containing a polyester resin, and preferably made of a polyester resin composition containing a polyester resin as a main component.

[0014] [Polyester resin] The polyester resin is usually obtained by polymerizing a polymerization component containing a dicarboxylic acid component and a diol component. In the present invention, the polyester resin contains a copolymerized polyester resin described later. The copolymerized polyester resin will be described below.

[0015] [Copolymerized polyester resin] The copolymerized polyester resin contains terephthalic acid as a dicarboxylic acid component, ethylene glycol and an amorphous component as a diol component. Also, the copolymerized polyester resin may contain one or more kinds.

[0016] <00​​​​​​Among these, aromatic dicarboxylic acids are preferred.

[0017] The terephthalic acid content in the dicarboxylic acid component is typically 60 mol% or more, preferably 65 mol% or more, and more preferably 70 mol% or more, based on 100 mol% of the total amount of the dicarboxylic acid component, from the viewpoint of mechanical properties such as rigidity, thermal shrinkage, and fracture resistance. The upper limit is typically 100 mol%.

[0018] Furthermore, if the dicarboxylic acid component includes other dicarboxylic acid components besides terephthalic acid, the content of these components is usually 10 mol% or less, preferably 5 mol% or less, and more preferably 3 mol% or less, based on 100 mol% of the total amount of dicarboxylic acid components.

[0019] (Diol component) The aforementioned diol component includes ethylene glycol and an amorphous component.

[0020] The amorphous components are added to reduce orientation during stretching, suppress excessive increases in mechanical strength and elastic modulus in the stretching direction, and raise the glass transition temperature of the polyester resin to suppress natural shrinkage. Examples include at least one selected from the group consisting of 1,4-cyclohexanedimethanol, neopentyl glycol, spiroglycol, diethylene glycol, polytetramethylene glycol, isosorbide, and 1,3-propanediol.

[0021] The aforementioned diol component may include other diol components besides ethylene glycol and amorphous components. Examples of the other diol components include aliphatic diols such as 1,4-butanediol, diethylene glycol, polytetramethylene glycol, and 1,3-propanediol, and alicyclic diols such as 1,1-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,2-cyclohexanediol, and 1,4-cyclohexanediol. These can be used individually or in combination of two or more. Among these, diethylene glycol and 1,4-butanediol are preferred.

[0022] The ethylene glycol content in the diol component is usually 35 mol% or more, preferably 40 mol% or more, more preferably 50 mol% or more, and particularly preferably 55 mol% or more, based on 100 mol% of the total diol component amount. The upper limit is usually 67 mol%.

[0023] Furthermore, the amorphous component content in the diol component is usually 15 mol% or more, preferably 20 mol%, and particularly preferably 25 mol%, based on 100 mol% of the total amount of diol components. The upper limit is usually 70 mol%, and preferably 60 mol%. When the amorphous component content is within the above range, it tends to be easier to adjust the product to have excellent resistance to natural shrinkage and good shrinkage finish and shrinkage processability.

[0024] If the diol component contains other diol components, their content is usually 30 mol% or less, preferably 25 mol% or less, and more preferably 20 mol% or less, relative to 100 mol% of the total amount of diol components.

[0025] The copolymerized polyester resin can be manufactured using conventional methods for producing polyester resins, such as direct polymerization or transesterification, and in batch or continuous processes.

[0026] The glass transition temperature of the copolymerized polyester resin, as measured by differential scanning calorimetry in accordance with JIS K7122 (2012), is preferably 77°C or higher, more preferably 80°C or higher, and even more preferably 85°C or higher. The upper limit is usually 100°C, and preferably 95°C. If the polyester resin composition contains two or more copolymerized polyester resins, it is sufficient if the glass transition temperature of at least one copolymerized polyester resin is within the above range, but it is preferable that the glass transition temperatures of all contained copolymerized polyester resins are within the above range.

[0027] The intrinsic viscosity (IV value) of the copolymerized polyester resin is typically 0.4 to 1.5 dL / g, preferably 0.5 to 1.2 dL / g. If the intrinsic viscosity of the copolymerized polyester resin is above the lower limit, sufficient mechanical properties tend to be obtained, and if the intrinsic viscosity is below the upper limit, good moldability tends to be obtained. The intrinsic viscosity was measured at 30°C in a mixed solvent of phenol / 1,1,2,2-tetrachloroethane (mass ratio 1:1).

[0028] The copolymerized polyester resin content in the polyester resin is usually 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, and particularly preferably 80% by mass or more. The upper limit is usually 100% by mass, and preferably 90% by mass.

[0029] Furthermore, the polyester resin may also contain other polyester resins besides the copolymerized polyester resin.

[0030] The intrinsic viscosity (IV value) of the aforementioned other polyester resins is typically 0.5 to 1.5 dL / g, preferably 0.6 to 1.2 dL / g. If the intrinsic viscosity of the other polyester resins is above the lower limit, sufficient mechanical properties tend to be obtained, and if the intrinsic viscosity is below the upper limit, good moldability tends to be obtained. The aforementioned intrinsic viscosity was measured at 30°C in a mixed solvent of phenol / 1,1,2,2-tetrachloroethane (mass ratio 1:1).

[0031] If the polyester resin contains other polyester resins, the content is usually 40% by mass or less, preferably 30% by mass or less, and particularly preferably 20% by mass or less.

[0032] (Other ingredients) The polyester resin composition may also contain other resins besides the polyester resin in an amount that does not hinder the effects of the present invention (for example, 10% by mass or less of the polyester resin composition).

[0033] Other resins include polystyrene resins, polyvinyl chloride resins, polyolefin resins, polycarbonate resins, polyamide resins, fluoropolymer resins, polyvinyl alcohol resins, polyacrylonitrile resins, polyether resins, cellulose resins, polyimide resins, polyurethane resins, polyphenylene sulfide resins, polyphenylene ether resins, polyvinyl acetal resins, polyamide-imide resins, polyamide-bismaleimide resins, polyarylate resins, polyetherimide resins, polyetheretherketone resins, polyetherketone resins, polyethersulfone resins, polyketone resins, polyacetal resins, polysulfone resins, and aramid resins. These can be used individually or in combination of two or more.

[0034] Furthermore, additives commonly used in resin compositions may be added to the polyester resin composition as appropriate, provided that they do not significantly impair the effects of the present invention. The aforementioned additives are added for the purpose of improving and adjusting the moldability, productivity, and various physical properties of the heat-shrinkable film.

[0035] Examples of the aforementioned additives include antiblocking agents, pigments such as titanium dioxide and carbon black, flame retardants, weather stabilizers, heat stabilizers, antistatic agents, melt viscosity modifiers, crosslinking agents, lubricants, nucleating agents, plasticizers, anti-aging agents, antioxidants, light stabilizers, ultraviolet absorbers, neutralizing agents, anti-fogging agents, slip agents, and colorants. These can be used individually or in combination of two or more.

[0036] Examples of the antiblocking agent include inorganic oxides such as silica, inorganic particles such as talc and calcium carbonate, and organic particles such as crosslinked acrylic resins, crosslinked polyester resins, crosslinked polystyrene resins, and silicone resins. Furthermore, organic particles forming a multilayer structure through multi-stage polymerization can also be used. Among these, silica and organic particles are preferred.

[0037] The antiblocking agent works by roughening the film surface to provide slipperiness and antiblocking properties. Therefore, if the appropriate amount and type of antiblocking agent are not selected, it will impair the transparency and gloss of the film. For this reason, the antiblocking agent content is usually 0.01 to 2% by mass, preferably 0.015 to 1.5% by mass, and more preferably 0.02 to 1% by mass, based on the total mass of the polyester resin composition (100% by mass). If the antiblocking agent content is too low, it is difficult to form irregularities on the film surface, and sufficient slipperiness and antiblocking properties tend to be difficult to achieve. Conversely, if there is too much, excessive irregularities are likely to occur on the film surface, which tends to impair transparency due to surface roughness and cause misalignment of the film roll due to excessive slipperiness.

[0038] The shape of the antiblocking agent is not particularly limited, but a spherical shape is preferably used from the viewpoint of suppressing aggregation, uniform dispersion, suppressing diffuse reflection of transmitted light, and creating irregularities on the film surface.

[0039] Furthermore, the particle size of the antiblocking agent is usually 0.5 to 10 μm, preferably 1 to 8 μm, and more preferably 1 to 6 μm. If the particle size of the antiblocking agent is too small, it is difficult for it to precipitate on the surface, and even if the antiblocking agent precipitates on the surface, it tends not to provide sufficient surface irregularities to exhibit slipperiness and antiblocking properties. On the other hand, if the particle size of the antiblocking agent is too large, when printing is applied to the heat-shrinkable film to enhance its design, ink bleeding and other issues are likely to occur, which tends to impair the appearance of the printed design. The particle size distribution of the antiblocking agent is not particularly limited, but due to the relationship between the disadvantages caused by the size of the particle size, a narrow particle size distribution is preferable. If the particle size distribution is too wide, it may include particles that deviate from the range of particle sizes that are preferably used as described above.

[0040] The polyester resin composition is obtained by mixing the polyester resin with other components as needed.

[0041] In polyester resin compositions, transesterification reactions generally occur in the molten state during molding. Therefore, when two or more types of polyester resins are used, it can be difficult to identify the content ratio of each resin or to determine whether it is a mixture or a copolymer. For this reason, the properties of the heat-shrinkable film can be carefully examined based on the types of dicarboxylic acid and diol components contained in the polyester resin composition, and their content.

[0042] The terephthalic acid content in the dicarboxylic acid component of the polyester resin contained in the aforementioned polyester resin composition is usually 60 mol% or more, preferably 65 mol% or more, and more preferably 70 mol% or more, based on 100 mol% of the total amount of the dicarboxylic acid component, from the viewpoint of mechanical properties such as rigidity, heat shrinkage, and fracture resistance. The upper limit is usually 100 mol%.

[0043] The ethylene glycol content in the diol component of the polyester resin contained in the polyester resin composition is usually 35 mol% or more, preferably 40 mol% or more, more preferably 50 mol% or more, and particularly preferably 55 mol% or more, based on 100 mol% of the total amount of the diol component. The upper limit is usually 67 mol% or less.

[0044] The polyester resin contained in the aforementioned polyester resin composition preferably contains at least one amorphous component selected from the group consisting of 1,4-cyclohexanedimethanol, neopentyl glycol, spiroglycol, diethylene glycol, polytetramethylene glycol, and 1,3-propanediol as the diol component, in terms of resistance to natural shrinkage, good shrinkage finish, and shrinkage processability, and more preferably contains at least two selected from the group consisting of 1,4-cyclohexanedimethanol, neopentyl glycol, spiroglycol, and diethylene glycol.

[0045] The content of the amorphous component in the diol component of the polyester resin contained in the polyester resin composition is 33 mol% or more, preferably 34 mol% or more, and particularly preferably 35 mol% or more, based on 100 mol% of the total amount of the diol component. The upper limit is usually 45 mol% or less, and preferably 40 mol% or less. When the content of the amorphous component is within the above range, it tends to have excellent resistance to natural shrinkage and good shrinkage finish and shrinkage processability.

[0046] By forming a film from the aforementioned polyester resin composition, a polyester resin layer can be obtained. Furthermore, the layer structure of this heat-shrinkable film only needs to have the aforementioned polyester resin layer, and can be appropriately selected as needed from the viewpoint of required quality and application. For example, this heat-shrinkable film may be a single-layer film consisting only of a polyester resin layer, or it may be a multi-layer laminated film in which other resin layers are laminated to the polyester resin layer. The following describes the manufacturing method of this heat-shrinkable film.

[0047] The method for producing this heat-shrinkable film is not particularly limited and can be carried out by conventionally known methods. For example, the polyester resin composition may be melt-extruded at a temperature of 200 to 300°C using an extruder to obtain an unstretched film. The obtained unstretched film may then be stretched in at least one direction, and subsequently subjected to annealing, cooling, and, if necessary, corona discharge treatment.

[0048] Furthermore, if the heat-shrinkable film is a laminated film, it can be made into a laminated film by known methods, such as co-extruding the resin composition constituting the other resin layers with the polyester resin composition, or by overlapping and heat-sealing the films of each layer after they have been formed, or by joining them with an adhesive or the like.

[0049] The extrusion method is not particularly limited, and methods such as the T-die method and the tubular method can be used. In the case of the T-die method, for example, after extrusion, the film is rapidly cooled on a casting drum with a surface temperature of 15 to 80°C to form an unstretched film.

[0050] Examples of stretching methods include stretching in at least one direction using methods such as roll stretching, tenter stretching, tubular stretching, and long-spacing stretching. Stretching can also be performed by combining these stretching methods. The extension direction may be vertical only, horizontal only, vertically and then horizontally, or horizontally and then vertically. Furthermore, the extension may be performed two or more times in the same direction, or vertically, horizontally, and then vertically. Furthermore, the stretching may be carried out simultaneously in the longitudinal and transverse directions using a simultaneous biaxial stretching machine. Furthermore, when forming an unstretched film by the tubular method, the tubular unstretched film may be stretched radially by internal pressure. In addition, it is preferable that the main shrinkage direction of this heat-shrinkable film is the transverse direction (TD).

[0051] The stretching temperature needs to be adjusted depending on the softening temperature of the resin constituting the heat-shrinkable film and the required shrinkage characteristics, but it is preferably 60 to 130°C, more preferably 70 to 120°C, and even more preferably 80 to 110°C.

[0052] The stretching ratio needs to be varied depending on the components of the heat-shrinkable film, the stretching method, the stretching temperature, the desired heat shrinkage rate, etc., but the stretching ratio in the main shrinkage direction is preferably 2 to 8 times, more preferably 3 to 7 times, and particularly preferably 4 to 6 times.

[0053] When this heat-shrinkable film is used for applications such as overlapping containers or trays, it is preferable that it be stretched in both the longitudinal and transverse directions. In this case, the primary shrinkage direction may be the longitudinal or transverse direction, but the transverse direction is preferable. Furthermore, when used in applications requiring nearly unidirectional shrinkage characteristics, such as labels attached to food containers or beverage containers, it is preferable to stretch the material in the uniaxial direction of the main shrinkage direction. However, stretching the material in a direction perpendicular to the main shrinkage direction (hereinafter also referred to as the "orthogonal direction") at a stretching ratio of 1.03 to 1.5 times is also effective in imparting good shrinkage characteristics.

[0054] After stretching, heat treatment or relaxation treatment can be performed at a temperature of 50 to 120°C as needed to adjust the thermal shrinkage rate and other physical properties of the heat-shrinkable film.

[0055] The aforementioned relaxation treatment, by relaxing the heat-shrinkable film in the longitudinal and / or transverse directions, can remove residual strain during heat shrinkage, which tends to suppress natural shrinkage and improve heat resistance during the drying process after printing and coating.

[0056] The relaxation rate of the heat-shrinkable film in the longitudinal and / or transverse directions is typically 0.1 to 10%, preferably 0.5 to 5%, in each direction.

[0057] Furthermore, shrinkage properties can be imparted to heat-shrinkable films by rapidly cooling them within the time frame in which molecular orientation does not relax after stretching, heat treatment, or relaxation treatment.

[0058] Furthermore, this heat-shrinkable film can be subjected to surface treatments and finishes such as chemical treatment, corona discharge treatment, plasma treatment, ozone treatment, chemical treatment, and printing, as well as bag making and perforation processes using various solvents and heat sealing. In addition, various coating layers such as vapor deposition layers and layers containing antistatic agents can be added as needed.

[0059] Examples of the aforementioned antistatic agents include cationic antistatic agents, anionic antistatic agents, amphoteric antistatic agents, and nonionic antistatic agents. These may be used individually or in combination of two or more types.

[0060] The thickness of the heat-shrinkable film obtained in this way is not particularly limited, but is usually 5 to 200 μm, preferably 7 to 150 μm, more preferably 10 to 70 μm, and most preferably 15 to 50 μm. If the thickness is below the upper limit, the film tends to have excellent transparency, and if the thickness is above the lower limit, the film tends to have excellent handling properties.

[0061] <Physical properties of heat-shrinkable films> This heat-shrinkable film may have the following physical properties.

[0062] The glass transition temperature of the polyester resin layer of this heat-shrinkable film, as measured by differential scanning calorimetry in accordance with JIS K7122 (2012), is preferably 75 to 90°C, and more preferably 78 to 85°C. In other words, the polyester resin layer of this heat-shrinkable film has a relatively higher glass transition temperature than the polyester resin used in ordinary heat-shrinkable films. Therefore, it tends to suppress the deterioration of the polyester resin even when stored at high temperatures.

[0063] When measuring the glass transition temperature of the polyester resin layer by differential scanning calorimetry, it is preferable to measure the value of the 2nd Run. That is, if the polyester resin layer contains crystalline components, the molecular chains of the polyester resin layer become oriented due to processes such as stretching. If the glass transition temperature of this polyester resin layer is measured in the 1st Run, it may not be possible to accurately measure the glass transition temperature of the polyester resin layer due to the influence of molecular chain orientation crystallization, etc. Therefore, when measuring the glass transition temperature of the polyester resin layer, it is preferable to measure the value of the 2nd Run, which is obtained by raising the temperature in the 1st Run to reset the molecular chain orientation, then lowering or rapidly cooling, and then raising the temperature again.

[0064] The thermal shrinkage rate (α) in the main shrinkage direction of this heat-shrinkable film when immersed in 70°C hot water for 10 seconds is preferably 0 to 20%, more preferably 0 to 10%, even more preferably 0 to 7%, and particularly preferably 0 to 6%. By keeping the shrinkage rate within the above numerical range, the natural shrinkage rate tends to be reduced. The thermal shrinkage rate of this heat-shrinkable film in the main shrinkage direction when immersed in 75°C hot water for 10 seconds is typically 2-40%, preferably 4-30%, and particularly preferably 7-25%. This heat-shrinkable film has a heat shrinkage rate in the main shrinkage direction of 20-50% when immersed in 80°C hot water for 10 seconds, preferably 23-47%, and particularly preferably 25-45%. Furthermore, when this heat-shrinkable film is immersed in 90°C hot water for 10 seconds, the heat shrinkage rate in the main shrinkage direction is typically 40-80%, preferably 45-77%, and particularly preferably 55-75%. Furthermore, when this heat-shrinkable film is immersed in 99°C hot water for 10 seconds, its heat shrinkage rate in the main shrinkage direction is 60-85%, preferably 63-82%, and particularly preferably 65-80%.

[0065] When this heat-shrinkable film is treated at 40°C and 90% relative humidity for 168 hours and then immersed in 70°C hot water for 10 seconds, the thermal shrinkage rate (β) in the main shrinkage direction is typically 0-10%, preferably 0-8%, more preferably 0-6%, and particularly preferably 0-4%. When this heat-shrinkable film is treated in an atmosphere of 40°C and 90% relative humidity for 168 hours and then immersed in 75°C hot water for 10 seconds, the heat shrinkage rate in the main shrinkage direction is typically 0 to 35%, preferably 0 to 30%, and particularly preferably 1 to 25%. After treating this heat-shrinkable film in an atmosphere of 40°C and 90% relative humidity for 168 hours, and then immersing it in 80°C hot water for 10 seconds, the heat shrinkage rate in the main shrinkage direction is 20-50%, preferably 23-47%, and particularly preferably 25-45%. After treating this heat-shrinkable film in an atmosphere of 40°C and 90% relative humidity for 168 hours, and then immersing it in 90°C hot water for 10 seconds, the heat shrinkage rate in the main shrinkage direction is typically 40-80%, preferably 45-77%, and particularly preferably 55-75%. After treating this heat-shrinkable film in an atmosphere of 40°C and 90% relative humidity for 168 hours, and then immersing it in 99°C hot water for 10 seconds, the heat shrinkage rate in the main shrinkage direction is 60-85%, preferably 63-82%, and particularly preferably 65-80%.

[0066] Furthermore, when the heat shrinkage rate in the main shrinkage direction of this heat shrinkable film is (α) when immersed in 70°C hot water for 10 seconds, and (β) is the heat shrinkage rate in the main shrinkage direction when the heat shrinkable film is treated in an atmosphere of 40°C and 90% relative humidity for 168 hours and then immersed in 70°C hot water for 10 seconds, it is preferable that (α)-(β) is 7% or less, more preferably 6% or less, and even more preferably 5% or less. By keeping (α)-(β) within the above range, the heat shrinkable film tends to maintain good shrinkage finish even when stored for a long period of time.

[0067] Generally, heat-shrinkable films are attached to an object, such as a container, by covering it with the film and then passing it through a heated atmosphere (heated by a heater, hot air, or steam) for a relatively short time (a few seconds to about 10 seconds) to shrink it and attach it to the object. Therefore, the heat shrinkage rate of a heat-shrinkable film serves as an indicator for judging its adhesion and shape conformability to the object being covered. Accordingly, if the heat shrinkage rate in the main shrinkage direction when immersed in hot water for 10 seconds is greater than or equal to the aforementioned value, the heat-shrinkable film tends to be able to attach sufficiently to the object being covered within the shrinkage processing time. Furthermore, in the shrinking process in which the heat-shrinkable film is shrunk and attached to the object to be covered, the film is slightly shrunk (pre-shrinked) at a low temperature before completely covering the object to be covered, and the position of the film on the object to be covered is fixed in place. At this time, if the heat shrinkage rate at each temperature is within the above-mentioned preferred range, there is a tendency to be able to gradually shrink the film onto the object to be covered starting from a lower temperature.

[0068] Preferably, the heat-shrinkable film has a natural shrinkage rate of 0.7% or less in the direction perpendicular to the main shrinkage direction after 720 hours of treatment at 55°C and 10% relative humidity.

[0069] Furthermore, the heat-shrinkable film preferably has a natural shrinkage rate of 0.7% or less, and more preferably 0.6%, in the direction perpendicular to the main shrinkage direction after 720 hours of treatment at 40°C and 90% relative humidity.

[0070] This heat-shrinkable film exhibits a low rate of natural shrinkage even when exposed to environments exceeding 40°C for extended periods. To achieve the aforementioned range for the natural shrinkage rate of this heat-shrinkable film, examples include methods such as incorporating amorphous components into the polyester resin, adjusting the content of amorphous components in the polyester resin, raising the glass transition temperature of the polyester resin layer to a higher level than usual, or combining these methods.

[0071] The heat shrinkage rate and natural shrinkage rate are specifically measured by the method described in the examples.

[0072] The tensile elongation (A) of this heat-shrinkable film, measured in accordance with JIS K7127 (1999) at 23°C and 10% relative humidity, in the direction perpendicular to the principal shrinkage direction, is usually 350% or more, preferably 400% or more, more preferably 450% or more, and particularly preferably 500% or more. A tensile elongation of this value or higher tends to reduce the likelihood of problems such as the heat-shrinkable film tearing during secondary processing steps such as printing. The upper limit is usually 900%, preferably 800%.

[0073] Furthermore, the tensile elongation (B) of this heat-shrinkable film, measured in accordance with JIS K7127 (1999), in the direction perpendicular to the main shrinkage direction after 168 hours of processing at 55°C and 10% relative humidity, is usually 340% or more, preferably 400% or more, more preferably 450% or more, and particularly preferably 500% or more. A tensile elongation of this value or higher tends to reduce the likelihood of problems such as the heat-shrinkable film tearing during secondary processing steps such as printing. The upper limit is usually 900%, preferably 800%.

[0074] Furthermore, the tensile elongation (C) of this heat-shrinkable film, measured in accordance with JIS K7127 (1999), in the direction perpendicular to the main shrinkage direction after 720 hours of treatment at 55°C and 10% relative humidity, is usually 350% or more, preferably 400% or more, more preferably 450% or more, and particularly preferably 500% or more. A tensile elongation of this value or higher tends to reduce the likelihood of problems such as the heat-shrinkable film tearing during secondary processing steps such as printing. The upper limit is usually 900%, preferably 800%.

[0075] It is preferable that the tensile elongation (A) relative to the tensile elongation (B) of this heat-shrinkable film satisfies the following formula (1). Rate of change (X) = Tensile elongation (A) / Tensile elongation (B) = 0.8 to 1.6 ... (1) It is more preferable that the rate of change (X) is between 0.9 and 1.4.

[0076] Furthermore, it is preferable that the tensile elongation (A) relative to the tensile elongation (C) of this heat-shrinkable film satisfies the following formula (2). Rate of change (Y) = Tensile elongation (A) / Tensile elongation (C) = 0.8 to 1.6 ... (2) It is more preferable that the rate of change (Y) is between 0.9 and 1.4.

[0077] This heat-shrinkable film exhibits minimal degradation of the polyester resin even when exposed to environments exceeding 40°C for extended periods, resulting in a small decrease in the film's elongation. For this heat-shrinkable film to satisfy formulas (1) and (2), examples include methods such as incorporating amorphous components into the polyester resin, adjusting the content of amorphous components in the polyester resin, raising the glass transition temperature of the polyester resin layer to a higher level than usual, or combining these methods.

[0078] <Heat-shrinkable film roll> The manufactured heat-shrinkable film can be trimmed of its edges, etc., and wound onto a core using a winding machine or the like to form a roll of heat-shrinkable film.

[0079] <Heat shrinkable label> This heat-shrinkable film is suitable for use in food packaging, beverage packaging, pharmaceutical and medical packaging, chemical packaging, cosmetic packaging, toiletry packaging, industrial packaging, agricultural packaging, and the like. In particular, it is preferable to form a printed layer on one or both sides of this heat-shrinkable film to create a heat-shrinkable label that can be attached to glass containers or plastic containers such as PET bottles.

[0080] The heat-shrinkable label is typically subjected to a printing layer or overcoat layer formed on at least one of its front and back surfaces, either entirely or partially, by a known method such as gravure printing, flexographic printing, offset printing, or bar coating. The printing ink is not particularly limited and can be appropriately selected according to the printing method. Examples include solvent-based (non-aqueous) or aqueous acrylic resin-based or urethane resin-based inks, foaming inks, and heat-foaming inks.

[0081] Furthermore, the heat-shrinkable label is processed from a flat shape to a cylindrical shape, etc., depending on the object to be packaged, before being used for packaging. For example, for cylindrical containers such as PET bottles that require printing, the necessary image is first printed on one side of a wide flat film wound on a roll, then it is cut to the required width, folded so that the printed side is on the inside, and center-sealed (the shape of the sealed part is what is known as envelope sealing) to form a cylindrical shape. There are several methods for center sealing, including sealing with an organic solvent, heat sealing, adhesive, and impulse sealing, but considering the appearance, it is preferable to use the sealing method with an organic solvent. [Examples]

[0082] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention. In the examples, "parts" and "%" refer to mass. First, prior to the examples, the following components were prepared.

[0083] <Polyester resin> [Copolymerized polyester resin] • PET-1: A polyester resin consisting of 100 mol% terephthalic acid as the dicarboxylic acid component, and 65 mol% ethylene glycol, 32 mol% 1,4-cyclohexanedimethanol, and 3 mol% diethylene glycol as the diol components (intrinsic viscosity (IV): 0.84 dl / g) • PET-2: A polyester resin consisting of 100 mol% terephthalic acid as the dicarboxylic acid component, and 56 mol% ethylene glycol, 30 mol% 1,4-cyclohexanedimethanol, and 14 mol% diethylene glycol as diols (intrinsic viscosity (IV): 0.77 dl / g) • PET-3: A polyester resin consisting of 100 mol% terephthalic acid as the dicarboxylic acid component, and 44 mol% ethylene glycol, 55 mol% 1,4-cyclohexanedimethanol, and 1 mol% diethylene glycol as the diol components (intrinsic viscosity (IV): 0.78 dl / g) • PET-4: A polyester resin consisting of 100 mol% terephthalic acid as the dicarboxylic acid component, and 75 mol% ethylene glycol, 21 mol% spiroglycol, and 4 mol% diethylene glycol as the diol components (intrinsic viscosity (IV): 0.64 dl / g) • PET-5: A polyester resin consisting of 100 mol% terephthalic acid as the dicarboxylic acid component, and 77 mol% ethylene glycol, 15 mol% 2-butyl-2-ethyl-1,3-propanediol, and 8 mol% diethylene glycol as the diol components (intrinsic viscosity (IV): 0.75 dl / g) • PET-6: A polyester resin consisting of 100 mol% terephthalic acid as the dicarboxylic acid component, and 66 mol% ethylene glycol, 31 mol% neopentyl glycol, and 3 mol% diethylene glycol as the diol components (intrinsic viscosity (IV): 0.83 dl / g)

[0084] [Other polyester resins] • PET-1': A polyester resin consisting of 100 mol% terephthalic acid as the dicarboxylic acid component and 100 mol% 1,4-butanediol as the diol component (intrinsic viscosity (IV): 0.86 dl / g) • PET-2': A polyester resin consisting of 90 mol% terephthalic acid and 10 mol% isophthalic acid as dicarboxylic acid components, and 100 mol% 1,4-butanediol as a diol component (intrinsic viscosity (IV): 0.85 dl / g)

[0085] [Glass transition temperature (Tg)] The glass transition temperature of the aforementioned polyester resin was determined from the DSC curve obtained when the temperature was increased from 0°C to 300°C at a heating rate of 10°C / min, in accordance with JIS K7122 (2012) by differential scanning calorimetry. The results are shown in Table 1 below.

[0086] <Antiblocking agent> • Silica-1: Average particle size 3 μm

[0087] <Example 1> A polyester resin composition was prepared by mixing 80 parts of "PET-1," 20 parts of "PET-3," and 0.1 parts of "Silica-1" according to the formulation and composition shown in Table 1 below. The polyester resin composition was then supplied to a twin-screw extruder set to a temperature of 250°C, and melt-kneaded in the extruder to obtain a single-layer unstretched film. Next, the obtained unstretched film was uniaxially stretched 5.2 times in the TD direction in a film tenter facility set to a preheating temperature of 102-107°C, a stretching temperature of 90°C, and a heat treatment temperature of 100°C to obtain a heat-shrinkable film. The main shrinkage direction of the obtained heat-shrinkable film is the TD direction.

[0088] <Example 2> A mixture was prepared using the raw material ratios listed in Table 1 below, and a single-layer unstretched film was obtained in the same manner as in Example 1. The obtained unstretched film was stretched and heat-treated in the same manner as in Example 1, and a relaxation treatment was performed at 85°C for 2 seconds while relaxing by 1.1% in the TD direction to obtain a heat-shrinkable film.

[0089] <Example 3> A mixture was prepared using the raw material ratios listed in Table 1 below, and a single-layer unstretched film was obtained in the same manner as in Example 1. The obtained unstretched film was then subjected to film formation in the same manner as in Example 1, except that the preheating temperature was changed to 107-112°C and the stretching temperature to 97°C, to obtain a heat-shrinkable film.

[0090] <Example 4> A mixture was prepared using the raw material ratios listed in Table 1 below, and a single-layer unstretched film was obtained in the same manner as in Example 1. The obtained unstretched film was stretched and heat-treated in the same manner as in Example 3, and a relaxation treatment was performed at 85°C for 2 seconds while relaxing by 1.1% in the TD direction to obtain a heat-shrinkable film.

[0091] <Example 5> A mixture was prepared using the raw material ratios listed in Table 1 below, and a single-layer unstretched film was obtained in the same manner as in Example 1. The obtained unstretched film was then subjected to film formation in the same manner as in Example 3, except that the stretching temperature was changed to 96°C, to obtain a heat-shrinkable film.

[0092] <Example 6> A mixture was prepared using the raw material ratios listed in Table 1 below, and a single-layer unstretched film was obtained in the same manner as in Example 1. The obtained unstretched film was stretched and heat-treated in the same manner as in Example 1, except that the stretching temperature was changed to 83°C. A relaxation treatment was performed at 90°C for 2 seconds while relaxing in the 1.1% TD direction to obtain a heat-shrinkable film.

[0093] <Example 7> A mixture was prepared using the raw material ratios listed in Table 1 below, and a single-layer unstretched film was obtained in the same manner as in Example 1. The obtained unstretched film was subjected to film formation in the same manner as in Example 1, except that the preheating temperature was changed to 100-95°C, the stretching temperature to 88°C, the heat treatment temperature to 110°C, and the stretching ratio to 5.3 times, to obtain a heat-shrinkable film.

[0094] <Example 8> A mixture was prepared using the raw material ratios listed in Table 1 below, and a single-layer unstretched film was obtained in the same manner as in Example 1. The obtained unstretched film was subjected to film formation in the same manner as in Example 1, except that the heat treatment temperature was changed to 105°C. A relaxation treatment was performed at 80-70°C for 5 seconds while relaxing by 2.6% in the TD direction to obtain a heat-shrinkable film.

[0095] <Comparative Example 1> A mixture was prepared using the raw material ratios listed in Table 1 below, and a single-layer unstretched film was obtained in the same manner as in Example 1. The obtained unstretched film was then subjected to film formation in the same manner as in Example 8 to obtain a heat-shrinkable film.

[0096] <Comparative Example 2> A mixture was prepared using the raw material ratios listed in Table 1 below, and a single-layer unstretched film was obtained in the same manner as in Example 1. The obtained unstretched film was fabricated in the same manner as in Example 8, and a relaxation treatment was performed at 80-70°C for 5 seconds while relaxing by 2.3% in the TD direction to obtain a heat-shrinkable film.

[0097] <Comparative Example 3> A mixture was prepared using the raw material ratios listed in Table 1 below, and a single-layer unstretched film was obtained in the same manner as in Example 1. The obtained unstretched film was fabricated in the same manner as in Example 8, and a relaxation treatment was performed at 80-70°C for 5 seconds while relaxing by 2.6% in the TD direction to obtain a heat-shrinkable film.

[0098] The thermal shrinkage rate, natural shrinkage rate, tensile elongation, and glass transition temperature of the heat-shrinkable films obtained in the examples and comparative examples were measured using the following methods. The results are shown in Table 1 below.

[0099] (1) Thermal shrinkage The obtained heat-shrinkable film was cut into strips with dimensions of MD 10 mm and TD 200 mm. Marks were made at 100 mm intervals so that the center of the TD was in the middle. Then, the strips of film were immersed for 10 seconds in hot water baths set to 70°C, 75°C, 80°C, 90°C, and 99°C, respectively, and the distance between the markings after shrinkage was measured to determine the amount of shrinkage of the TD (= markings before shrinkage - markings after shrinkage). The heat shrinkage rate of the TD was calculated as the ratio of the amount of shrinkage to the markings before shrinkage (= (amount of shrinkage / markings before shrinkage) × 100%). In addition, the films were placed in a constant temperature bath adjusted to an atmosphere of 40°C and 90% relative humidity and treated for 168 hours. After being removed from the constant temperature bath, the heat shrinkage rate of the heat-shrinkable films after 168 hours of treatment was measured in the same manner.

[0100] (2) Natural contraction rate The obtained heat-shrinkable film was cut into strips with dimensions of MD 1,000 mm and TD 50 mm to serve as samples. These samples were then treated for 720 hours in a constant temperature chamber adjusted to either 40°C and 90% relative humidity, or 55°C and 10% relative humidity. After treatment, each sample was removed from the chamber, its MD dimensions were measured, and the natural shrinkage rate was calculated using the following formula: Natural shrinkage rate (%) = (Natural shrinkage amount / Length before treatment (=1,000 mm) × 100) Furthermore, the obtained heat-shrinkable film was cut to sizes of MD 50 mm and TD 1,000 mm and used as samples. Except for this, the same measurement procedure as for measuring the shrinkage rate of MD was performed to measure the natural shrinkage rate of TD.

[0101] (3) Tensile elongation The obtained heat-shrinkable film was cut to a size of MD120mm and TD15mm. Referring to JIS K7127 (1999), the tensile elongation (A) of the MD of the film was measured at an ambient temperature of 23°C with a chuck distance of 150mm and a tensile speed of 200mm / min, and the average of five measured values ​​was calculated. Furthermore, the films were placed in a constant temperature bath adjusted to an atmosphere of 55°C and 10% relative humidity, and after 168 hours and 720 hours of treatment, they were removed from the bath, and the tensile elongation of the film after 168 hours of treatment (B) and the tensile elongation of the film after 720 hours of treatment (C) were measured in the same manner. In addition, the rates of change (X) and (Y) were calculated from the following equations (1) and (2). Rate of change (X) = Tensile elongation (A) / Tensile elongation (B) ... (1) Rate of change (Y) = Tensile elongation (A) / Tensile elongation (C) ... (2)

[0102] (4) Glass transition temperature The obtained heat-shrinkable film was subjected to a differential scanning calorimetry (DSC) measurement in accordance with JIS K7122 (2012). This involved a first differential scanning calorimetry (1st Run) consisting of heating from 0°C to 300°C at a heating rate of 10°C / min, holding at 300°C for 1 minute, and then cooling from 300°C to 0°C at a cooling rate of 10°C / min. A second differential scanning calorimetry (2nd Run) was then performed, consisting of heating from 0°C to 300°C at a heating rate of 10°C / min. The glass transition point was determined from the DSC curve obtained from the second differential scanning calorimetry measurement.

[0103] [Table 1]

[0104] From the results in Table 1 above, the heat-shrinkable films of Examples 1 to 8 exhibited excellent resistance to natural shrinkage, suppressed a decrease in tensile elongation even after long-term storage at high temperatures, and possessed good shrinkage finish and shrinkage processability. On the other hand, the heat-shrinkable films of Comparative Examples 1 to 3, which had a low amorphous content and a low glass transition temperature of the polyester resin layer, exhibited poor resistance to natural shrinkage after long-term storage at high temperatures, and showed a large rate of change in tensile elongation after long-term storage at high temperatures, resulting in a decrease in tensile elongation. [Industrial applicability]

[0105] This heat-shrinkable film can be suitably used for food packaging materials, beverage packaging materials, pharmaceutical and medical packaging materials, chemical packaging materials, cosmetic packaging materials, toiletry packaging materials, industrial packaging materials, agricultural packaging materials, and the like.

Claims

1. A heat-shrinkable film having a layer made of a polyester resin composition containing a polyester resin, wherein the heat-shrinkable film satisfies the following a) to c). a) A copolymerized polyester resin containing terephthalic acid and ethylene glycol, and further containing at least one amorphous component selected from the group consisting of 1,4-cyclohexanedimethanol, neopentyl glycol, spiroglycol, diethylene glycol, polytetramethylene glycol, isosorbide, and 1,3-propanediol. b) The content of the amorphous component in the diol component of the polyester resin contained in the polyester resin composition is 33 mol% or more relative to 100 mol% of the total amount of the diol component. c) The shrinkage rate in the main shrinkage direction is 20-50% when immersed in 80°C hot water for 10 seconds, and 60-85% when immersed in 99°C hot water for 10 seconds.

2. The heat-shrinkable film according to claim 1, wherein the natural shrinkage rate in the main shrinkage direction and the natural shrinkage rate in a direction perpendicular to the main shrinkage direction after 720 hours of treatment in an atmosphere of 55°C and 10% relative humidity are 0.7% or less.

3. The heat-shrinkable film according to claim 1, wherein the polyester resin comprises at least two selected from the group consisting of 1,4-cyclohexanedimethanol, neopentyl glycol, spiroglycol, and diethylene glycol as amorphous components.

4. The heat-shrinkable film according to claim 1, comprising a copolymer polyester resin having a glass transition temperature of 77°C or higher, as measured by differential scanning calorimetry in accordance with JIS K7122 (2012) for the copolymer polyester resin.

5. The heat-shrinkable film according to claim 1, wherein the glass transition temperature of the layer made of the polyester resin composition, as measured by differential scanning calorimetry in accordance with JIS K7122 (2012), is 75 to 90°C.

6. The heat-shrinkable film according to claim 1, wherein the shrinkage rate (α) in the main shrinkage direction when immersed in 70°C hot water for 10 seconds is 0 to 20%.

7. The heat-shrinkable film according to claim 6, wherein when the shrinkage rate in the main shrinkage direction after being treated for 168 hours in an atmosphere of 40°C and 90% relative humidity and then immersed in 70°C hot water for 10 seconds is (β), (α) - (β) = 7% or less.

8. The heat-shrinkable film according to claim 1, wherein the tensile elongation (A) in a direction perpendicular to the main shrinkage direction at 23°C and 10% relative humidity, measured in accordance with JIS K7127 (1999), and the tensile elongation (B) in a direction perpendicular to the main shrinkage direction after treatment at 55°C and 10% relative humidity for 168 hours, satisfy the following formula (1). Rate of change (X) = Tensile elongation (A) / Tensile elongation (B) = 0.8 to 1.6 ... (1)

9. A heat-shrinkable film roll comprising the heat-shrinkable film described in any one of claims 1 to 8.

10. A heat-shrinkable label using a heat-shrinkable film according to any one of claims 1 to 8.

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