Heat-shrinkable polyester film, heat-shrinkable label, and package

Abstract

Provided is a heat-shrinkable polyester film having a high thermal shrinkage in the main shrinkage direction, a high film puncture strength, a high density, and thus an excellent elastic feeling, and a high bag breaking resistance when a bottle falls. A heat-shrinkable polyester film containing 60 mol% or more and 95 mol% or less of terephthalic acid ethylene glycol units in 100 mol% of all ester units, 5 mol% or more and 40 mol% or less of diethylene glycol in 100 mol% of polyol components, and 0 mol% or more and 5 mol% or less of constituent units derived from a monomer component capable of becoming an amorphous component in all polyester resin components, the film having a hot water heat shrinkage rate when immersed in hot water at 90°C for 10 seconds, a film puncture strength, a film density, and a refractive index in the film length direction within a prescribed range.

Description

TECHNICAL FIELD

[0001] The present application relates to a heat-shrinkable polyester film, and particularly to a heat-shrinkable polyester film having high puncture strength, excellent bag drop property, and high puncture strength when forming a label for a PET bottle beverage, a heat-shrinkable label, and a package. BACKGROUND

[0002] In recent years, in the fields of label packaging, cap sealing, assembly packaging, and the like, which take into account the protection of glass bottles, PET bottles, and the like, and the labeling of products, a stretched film (so-called heat-shrinkable film) formed of a polyvinyl chloride-based resin, a polystyrene-based resin, a polyester-based resin, or the like is widely used. Among such heat-shrinkable films, a polyvinyl chloride-based film has problems in that not only is the heat resistance low, but also hydrogen chloride gas is generated upon incineration, which is a cause of dioxin. In addition, a polystyrene-based film has problems in that not only is the solvent resistance poor, but also a special composition of ink must be used upon printing, and incineration at a high temperature is required, which generates a large amount of black smoke accompanied by an offensive odor upon incineration. Therefore, a polyester-based heat-shrinkable film, which has high heat resistance, is easy to incinerate, and has excellent solvent resistance, is widely used as a shrink label, and there is a tendency for the amount to increase as the circulation of PET containers increases.

[0003] A general heat-shrinkable polyester film widely uses a heat-shrinkable polyester film that is greatly shrunk in the width direction. The film is stretched by a tenter stretching method or the like, a wide-width parent roll is produced, and then the parent roll is slit at an arbitrary width while being wound into a roll of an arbitrary length, to form a film roll product. In order to give the film designability and product labeling, the film is submitted to a printing process in the form of a roll. After printing, the film is again slit to a necessary width, wound into a roll, and then subjected to a center sealing process using solvent adhesion to produce a tube, and wound into a roll (a label roll is formed).

[0004] The label produced in the tube, which is wound into a roll, is unrolled from the roll, and cut to a necessary length to form a label in a ring shape. The ring-shaped label is attached to a package by a method such as hand covering, and shrunk by a steam passage or a hot air passage, or the like, to form a label.

[0005] In recent years, in order to reduce the amount of garbage, the weight of PET bottle containers has been reduced, and the thickness of PET bottle containers has also been made thinner. If the thickness of a PET bottle container is made thinner, problems such as deformation of the PET bottle container and breakage of the label upon falling occur. In addition, labels using a heat-shrinkable film have also been reduced in size, and labels having a thin thickness are sought. The thickness of the film has also increased from 45 to 60 μm to 20 to 40 μm in recent years. However, the bag drop property of the label deteriorates as the thickness of the film decreases. Therefore, it is important to improve the bag drop property of the film. In addition, if the thickness is made thinner, the elastic feeling decreases, and after a label is formed by printing a film, in the process of attaching the label to a PET bottle, the label is bent, and there is a possibility that the attachment will be poor.

[0006] A method for improving bag breakage resistance at the time of film falling is described in Patent Literature 1. If based on this, as a film property, for bag breakage resistance, puncture strength becomes an important main reason. However, in Patent Literature 1, it is described that evaluation of bag breakage resistance at the time of bag formation of a non-heat shrinkable film using a composition in which polyester and polybutylene terephthalate are mixed is performed, and for a heat shrinkable film, a label using a heat shrinkable film is not described.

[0007] In addition, a method for improving label bending to form installation failure in the process of installation to a PET bottle is described in Patent Literature 2. If based on this, it is described that by biaxially stretching a film in a non-shrinking direction and a shrinking direction, the film strength in the height direction (non-shrinking direction) at the time of label installation is improved. However, when using this method, there is a biaxial stretching process of stretching not only in the film width direction but also in the length direction, and therefore the equipment is necessarily large, and therefore is not preferable.

[0008] Prior Art Documents

[0009] Patent Literature

[0010] Patent Literature 1: Japanese Patent Application Laid-Open No. 2020-12086

[0011] Patent Literature 2: Japanese Patent Application Laid-Open No. 2014-24253 SUMMARY

[0012] Problems to be Solved by the Invention

[0013] An object of the present application is to provide a heat shrinkable polyester film having a high heat shrinkage rate in the main shrinking direction, a high film puncture strength, bag breakage resistance at the time of bottle falling, and a high film density, and therefore an excellent elastic feeling.

[0014] Solution to Problem

[0015] The present application for solving the above problem contains the following technical features.

[0016] 1. A heat shrinkable polyester film, characterized by containing, in 100 mol% of all ester units, ethylene terephthalate units of 60 mol% or more and 95 mol% or less, containing, in 100 mol% of polyol components, diethylene glycol of 5 mol% or more and 40 mol% or less, and containing, in all polyester resin components, a constitutional unit derived from a monomer component capable of becoming an amorphous component of 0 mol% or more and 5 mol% or less, which satisfies the following conditions (1) to (5),

[0017] (1) a hot water heat shrinkage rate at the time of immersion of the film in hot water at 90°C for 10 seconds is 40% or more and 80% or less in the film width direction

[0018] (2) the hot water heat shrinkage ratio of the film when immersed in hot water at 90°C for 10 seconds is -5% or more and 15% or less in the film length direction

[0019] (3) the puncture strength of the film is 0.2 N / μm or more and 0.6 N / μm or less

[0020] (4) the density of the film is 1.330 g / cm 3 or more and 1.385 g / cm 3 or less

[0021] (5) the refractive index in the film length direction is 1.575 or less.

[0022] 2. The heat-shrinkable polyester film according to 1, characterized in that the thickness of the film is 15 μm or more.

[0023] 3. The heat-shrinkable polyester film according to 1 or 2, characterized in that the haze of the film is 2% or more and 10% or less when the thickness of the film is 20 μm.

[0024] 4. The heat-shrinkable polyester film according to any one of 1 to 3, characterized in that the puncture strength after the film is shrunk by 10% in the width direction is 0.1 N / μm or more and 0.5 N / μm or less.

[0025] 5. A heat-shrinkable label using the heat-shrinkable polyester film according to any one of 1 to 4.

[0026] 6. A package characterized by being formed by covering at least a part of the outer periphery of a package object with the heat-shrinkable label according to 5 and heat-shrinking it.

[0027] Effects of the Invention

[0028] The heat-shrinkable polyester film of the present application has not only a high shrinkage ratio but also a high puncture strength after 10% shrinkage, so that the label after being installed on a PET bottle is not easily broken even if it falls. In addition, since the density is high, the problem of poor installation on a PET bottle can be reduced. DETAILED DESCRIPTION

[0029] The heat-shrinkable polyester film of the present application will be described in detail below. Note that the method for producing the heat-shrinkable polyester film will be described in detail later, but the heat-shrinkable film is generally obtained by conveying and stretching using a roll or the like. At this time, the conveying direction of the film (the film production direction) is referred to as the length direction, and the direction orthogonal to the aforementioned length direction is referred to as the film width direction. Therefore, the width direction of the heat-shrinkable polyester film shown below refers to the direction perpendicular to the winding and unwinding direction, and the film length direction refers to the direction parallel to the winding and unwinding direction.

[0030] The heat-shrinkable polyester film of the present application is characterized in that it contains ethylene terephthalate units in 60 mol% or more and 95 mol% or less of 100 mol% of all ester units, contains diethylene glycol in 5 mol% or more and 40 mol% or less of 100 mol% of the polyol component, and contains a constitutional unit derived from a monomer component capable of becoming an amorphous component in 0 mol% or more and 5 mol% or less of all polyester resin components, and satisfies the following conditions (1) to (5),

[0031] (1) The hot water shrinkage rate when the film is immersed in hot water at 90°C for 10 seconds is 40% or more and 80% or less in the film width direction

[0032] (2) The hot water shrinkage rate when the film is immersed in hot water at 90°C for 10 seconds is -5% or more and 15% or less in the film length direction

[0033] (3) The puncture strength of the film is 0.2 N / μm or more and 0.6 N / μm or less

[0034] (4) The density of the film is 1.33 g / cm 3 or more and 1.385 g / cm 3 or less

[0035] (5) The refractive index in the film length direction is 1.575 or less.

[0036] In the heat-shrinkable polyester film, in order to obtain high shrinkability, for example, a homopolymer (PET) composed of ethylene terephthalate is widely used in copolymerization with other polycarboxylic acid components and other polyol components. As the polyol component used as the component for the copolymerization, for example, neopentyl glycol and 1,4-cyclohexanedimethanol are widely used. In the case of a film copolymerized with these components, the chemical cost is high compared to a diethylene glycol film. In addition, in the case of obtaining a raw material resin copolymerized with diethylene glycol, diethylene glycol is a liquid at normal temperature, and therefore a melting process necessary for a powder raw material such as neopentyl glycol is not necessary. Furthermore, it also has the advantages that the polymerization activity is high compared to neopentyl glycol, and that the foaming during polymerization, which leads to a decrease in productivity, is less.

[0037] In addition, compared with diethylene glycol, polyester raw materials copolymerized with neopentyl glycol and 1,4-cyclohexanediethanol have lower density, so the films made from them have lower density and poorer elasticity.

[0038] The film of the present invention uses polyethylene terephthalate as the main component. Here, "main component" refers to polyethylene terephthalate comprising 60 mol% or more of the total polymer components constituting the film. More preferably, it contains 65 mol% or more of polyethylene terephthalate. By using polyethylene terephthalate as the main component, high density, excellent mechanical strength, and transparency can be achieved.

[0039] As for the polymerization method of polyethylene terephthalate (hereinafter sometimes simply referred to as PET), any manufacturing method can be used, such as direct polymerization, which involves the direct reaction of terephthalic acid and ethylene glycol, as well as other dicarboxylic acid components and glycol components as needed; and transesterification, which involves the transesterification reaction of dimethyl terephthalate (which may contain methyl esters of other dicarboxylic acids as needed) and ethylene glycol (which may contain other glycol components as needed).

[0040] Other dicarboxylic acid components besides terephthalic acid in the polyester used to form the film of the present invention can be listed as aromatic dicarboxylic acids such as isophthalic acid, naphthalenedicarboxylic acid, and phthalic 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.

[0041] When aliphatic dicarboxylic acids (such as adipic acid, sebacic acid, decanedicarboxylic acid, etc.) are included, the content is preferably less than 3 mol%. For heat-shrinkable polyester films obtained by using polyesters containing more than 3 mol% of these aliphatic dicarboxylic acids, the film elasticity is insufficient during high-speed installation.

[0042] Furthermore, it is preferable that the film does not contain more than three polycarboxylic acids (such as trimellitic acid, pyromellitic acid, and their anhydrides). For heat-shrinkable polyester films obtained using polyesters containing these polycarboxylic acids, it is difficult to achieve the necessary shrinkage.

[0043] Of the 100 mol% of the polyol component of the polyester used in the film of the present invention, diethylene glycol needs to be 5 mol% or more and 40 mol% or less. High heat shrinkage can be imparted by containing diethylene glycol in an amount within the aforementioned range. If the diethylene glycol is less than 5 mol%, it is difficult to obtain a film with a high shrinkage rate of 70% or more when heated to 90°C, and therefore this is not preferred. More preferably, the diethylene glycol is 6 mol% or more, and particularly preferably 8 mol% or more. Even a high upper limit for diethylene glycol is not a problem, but if it is too high, it may lead to reduced activation during polymerization, foaming, or foreign matter in the melt extrusion process during film formation. Therefore, in the present invention, the upper limit is set to 40 mol%.

[0044] Examples of polyols other than ethylene glycol and diethylene glycol that constitute the polyester used in this invention include 1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, 1,4-butanediol, neopentyl glycol, hexanediol and other aliphatic diols, 1,4-cyclohexanediol and other alicyclic diols, bisphenol A and other aromatic diols.

[0045] Preferably, the product does not contain diols with 8 or more carbon atoms (e.g., octanediol) or polyols with 3 or more carbon atoms (e.g., trimethylolpropane, trimethylolethane, glycerol, diglycerol, etc.). For heat-shrinkable polyester films obtained using polyesters containing these diols or polyols, it is difficult to achieve the necessary high shrinkage.

[0046] Various additives, such as waxes, antioxidants, antistatic agents, crystal nucleating agents, detackifiers, heat stabilizers, pigments for coloring, color inhibitors, and ultraviolet absorbers, can be added to the resin in which the heat-shrinkable polyester film of the present invention is formed, as needed.

[0047] In the resin forming the heat-shrinkable polyester film of the present invention, fine particles are preferably added as a lubricant to improve the workability (slipability) of the film. Any type of fine particle can be selected; for example, inorganic fine particles include silica, alumina, titanium dioxide, calcium carbonate, kaolin, and barium sulfate; organic fine particles include, for example, acrylic resin particles, melamine resin particles, silicone resin particles, and cross-linked polystyrene particles. The average particle size of the fine particles can be appropriately selected as needed, within the range of 0.05 to 3.0 μm (when measured using a Coulter counter).

[0048] As a method for compounding the aforementioned particles into the resin that forms a heat-shrinkable polyester film, the particles can be added at any stage of the polyester resin manufacturing process. Preferably, they are added in the form of a slurry dispersed in ethylene glycol or the like during the esterification stage, or after the transesterification reaction and before the start of the polycondensation reaction, to carry out the polycondensation reaction. Alternatively, it is preferable to use a compounding extruder with venting holes to mix the slurry of particles dispersed in ethylene glycol or water with the polyester resin raw material, or to use a compounding extruder to mix dried particles with the polyester resin raw material.

[0049] It should be noted that, among the aforementioned monomeric components, monomers capable of forming amorphous components may include, for example, neopentyl glycol, 1,4-cyclohexanediethanol, isophthalic acid, 1,4-cyclohexanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, and hexanediol. The content of this monomer capable of forming amorphous components in the copolyester is preferably 0 mol% or more and 5 mol% or less, more preferably none (i.e., 0 mol%).

[0050] When the heat-shrinkable polyester film of the present invention is treated in hot water at 90°C under no-load conditions for 10 seconds, the heat shrinkage rate of the film in the main shrinkage direction (i.e., the heat shrinkage rate of hot water at 90°C), calculated from the length before and after shrinkage using Formula 1, is preferably 40% or more and 80% or less.

[0051] Heat shrinkage rate = {(length before shrinkage - length after shrinkage) / length before shrinkage} × 100 (%) Equation 1

[0052] If the hot water shrinkage rate in the main shrinkage direction at 90°C is less than 40%, the shrinkage will be small when used for beverage labeling or as film for boxed meal packaging. This will result in wrinkles and loosening of the label after heat shrinkage, making it undesirable. A hot water shrinkage rate of 43% or more is more preferred, 46% or more is particularly preferred, and 50% or more is most preferred.

[0053] Even if the hot water thermal shrinkage rate in the main shrinkage direction at 90°C is higher than 80%, there is no problem. However, in this invention, it is not possible to obtain a film with a hot water thermal shrinkage rate of higher than 80% at 90°C. Therefore, the upper limit is set to 80%.

[0054] The heat-shrinkable polyester film of the present invention preferably has a hot water shrinkage rate of -5% or more and 15% or less in the longitudinal direction orthogonal to the main shrinkage direction at 90°C. If the hot water shrinkage rate in the longitudinal direction at 90°C is less than -5%, the label will elongate and the label height in the PET bottle will increase when used for beverage labeling, which is therefore undesirable. A hot water shrinkage rate in the longitudinal direction at 90°C is more preferably -4% or more, and particularly preferably -3% or more.

[0055] If the shrinkage rate in hot water at 90°C along the length direction is greater than 15%, the label will shorten when used for beverage labeling, resulting in a shorter label height in the PET bottle, which is undesirable. Furthermore, it also contributes to label deformation after shrinkage. A shrinkage rate in hot water at 90°C along the length direction is more preferably 13% or less, further preferably 11% or less, particularly preferably 8% or less, and most preferably 5% or less.

[0056] The heat-shrinkable polyester film of the present invention preferably has a puncture strength of 0.2 N / μm or more and 0.6 N / μm or less. It should be noted that the puncture strength is measured using the method described in the examples. If the puncture strength is less than 0.2 N / μm, for beverage PET bottle labels using thin heat-shrinkable films, the label may break if dropped during purchase from a vending machine, which is therefore undesirable. A puncture strength of 0.25 N / μm or more is more preferred, and particularly preferred is 0.3 N / μm or more. Even if the puncture strength is higher than 0.6 N / μm, there is no problem, but films with a puncture strength higher than 0.6 N / μm cannot be obtained in the present invention, therefore the upper limit is set to 0.6 N / μm.

[0057] The heat-shrinkable polyester film of the present invention preferably has a puncture strength of 0.1 N / μm or more and 0.5 N / μm or less after shrinking the film by 10% in the width direction. Heat-shrinkable polyester films are typically used through heat shrinking, therefore, the 10% shrunk film is the envisioned film for the shrunk label. If the puncture strength is less than 0.1 N / μm, for beverage PET bottle labels using thin heat-shrinkable films, the label could break the bag if it falls during purchase from a vending machine, which is undesirable. The puncture strength of the 10% shrunk film is more preferably 0.15 N / μm or more, and particularly preferably 0.2 N / μm or more. Even if the puncture strength of the 10% shrunk film is higher than 0.5 N / μm, it is not a problem, but in the present invention, a film with a puncture strength higher than 0.5 N / μm after 10% shrinkage cannot be obtained; therefore, the upper limit is set to 0.5 N / μm.

[0058] The heat-shrinkable polyester film of the present invention preferably has a refractive index of 1.575 or less along its length. It should be noted that the refractive index was determined using the method described in the examples.

[0059] Generally, a higher refractive index increases the tensile strength of a thin film, but decreases its elongation at break. A lower elongation at break means the film is difficult to stretch (becomes brittle). Therefore, for beverage PET bottle labels using thin heat-shrinkable films, if the label falls from a vending machine during purchase, the label will break the bottle, making it undesirable. Especially since the film's length direction is not the shrinkage direction, perforations and notches are often formed in ways that make the label easy to open; therefore, the refractive index in the length direction is important. A refractive index in the length direction is more preferably 1.572 or less, and particularly preferably 1.569 or less. There is no specified lower limit for the refractive index in the length direction; even for unstretched films, the refractive index in the length direction is around 1.55 to 1.56, and therefore will not be lower than 1.55.

[0060] The heat-shrinkable polyester film of the present invention preferably has a density of 1.33 g / cm³. 3The above. If it is less than 1.330 g / cm³ 3 For labels using thin heat-shrink film, insufficient elasticity during installation onto PET beverage bottles can cause breakage or prevent the label from being properly secured, making it less desirable. A film density of 1.340 g / cm³ is more preferred. 3 Above, with a preferred concentration of 1.350 g / cm³ 3 The above. When the film density is high, it is preferable in terms of elasticity, preferably 1.385 g / cm³. 3 The following is because if it exceeds 1.385 g / cm³... 3 If the film crystallizes, the 90°C width-direction shrinkage rate described above will not be achieved. A more preferable density for heat-shrinkable polyester films is 1.384 g / cm³. 3 The following is a preferred value: 1.383 g / cm³ 3 the following.

[0061] The thickness of the heat-shrinkable polyester film of the present invention is not particularly limited, but for heat-shrinkable films used for labeling and lunchbox packaging, 15 to 50 μm is preferred. If the film thickness is less than 15 μm, the elasticity of the film is significantly reduced, and wrinkles are easily formed during rolling, so it is not preferred. On the other hand, even if the film thickness is thick, there is no problem with the film roll, and from a cost point of view, thinner film is preferred. The film thickness is more preferably 17 to 45 μm, and particularly preferably 20 to 40 μm.

[0062] The heat-shrinkable polyester film of the present invention preferably has a haze value of 2% or more and 10% or less when the film thickness is 20 μm. Since heat-shrinkable films are designed for aesthetic purposes, a haze value higher than 10% would prevent the contents from being clearly visible when forming labels for PET bottles, reducing the design flexibility and therefore is not preferred. A haze value of 8% or less, and particularly preferably 6% or less, when the film thickness is 20 μm, is more preferably preferred.

[0063] Even if the haze is less than 2% when the film thickness is 20μm, there is no problem. In this invention, if the haze value is less than 2%, the sliding properties of the film will deteriorate. Therefore, the lower limit is set to 2%.

[0064] The heat-shrinkable polyester film of the present invention can be obtained by melt-extruding the above-mentioned polyester raw material using an extruder to form an unstretched film, and then stretching the unstretched film in the width direction. It should be noted that the polyester can be obtained by polycondensing the aforementioned suitable dicarboxylic acid component and diol component using a known method. Furthermore, fragmented polyester is typically used as the raw material for the film.

[0065] 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 is melted in an extruder at a temperature of 230–270°C and extruded in a thin film. During extrusion, any existing method can be used, such as the T-die method or the tubular method.

[0066] Next, by rapidly cooling the extruded sheet of molten resin, an unstretched film can be obtained. It should be noted that, as a method for rapidly cooling the molten resin, a suitable approach is to cast the molten resin from the spinneret onto a rotating drum and rapidly cool and solidify it to obtain a substantially unoriented resin sheet.

[0067] Furthermore, by stretching the obtained unstretched film in the width direction under specified conditions as described below, the heat-shrinkable polyester film of the present invention can be obtained. The preferred stretching method for obtaining the heat-shrinkable polyester film of the present invention will be described below.

[0068] Conventional heat-shrinkable polyester films are manufactured by stretching an unstretched film in the desired shrinkage direction. Alternatively, there are biaxial stretching methods that involve longitudinal stretching followed by transverse stretching, which require large-scale equipment. In this invention, uniaxial stretching is performed in the width direction, which is the main shrinkage direction. It should be noted that the manufacturing method using uniaxial stretching in the width (transverse) direction has the advantage of being able to be manufactured with simple equipment because it does not require stretching equipment in the length direction.

[0069] For stretching in the width direction, the unstretched film is guided to a tenter frame that can hold and heat both ends of the film with clamps. After the film is heated to a specified temperature by hot air, the distance between the clamps is increased while the film is being transported in the length direction, thereby stretching the film.

[0070] The preheating temperature of the unstretched film is preferably above Tg+30°C and below Tg+80°C. More preferably, it is above Tg+20°C and below Tg+60°C. Below Tg+30°C, the tensile force increases due to insufficient preheating temperature, making it prone to breakage, which is not preferred. In addition, if heating is carried out at a temperature above Tg+80°C, the tensile force of the unstretched sheet in the width direction decreases, and the thickness accuracy (thickness unevenness) in the width direction deteriorates, which is also not preferred. More preferably, it is above Tg+40°C and below Tg+70°C.

[0071] The film temperature during width-direction stretching is preferably above Tg℃ and below Tg+30℃. If the film temperature is below Tg, the tensile force is too high, which can easily cause the film to break, and therefore this is not preferred. If the film temperature exceeds Tg+30℃, the tensile force is too low, and therefore the width-direction thermal shrinkage rate measured at 90℃ as described above is reduced, and therefore this is not preferred. More preferably, the temperature is above Tg+3℃ and below +25℃, and even more preferably, the temperature is above Tg+5℃ and below +25℃.

[0072] The stretching ratio in the width direction is preferably 3.5 times or more and 6 times or less. If the stretching ratio is less than 3.5 times, the stretching force is insufficient, and the thickness accuracy (so-called thickness unevenness) in the width direction of the film deteriorates. In addition, if the stretching ratio exceeds 6 times, the risk of film breakage during film formation increases, and the equipment becomes larger, so it is not preferred. More preferably, it is 3.7 times or more and 5.5 times or less. In addition, although there is no particular limitation, heat treatment can be performed after stretching in the width direction to adjust the shrinkage rate. The film temperature during heat setting (heat treatment) is preferably above the film stretching temperature in the width direction and below Tg+50°C. If the film temperature is lower than the film stretching temperature in the width direction, the molecular relaxation in the width direction is insufficient, and there is no heat setting effect, so it is not preferred. If the film temperature exceeds Tg+50°C, the film crystallizes and the shrinkage rate decreases, so it is not preferred. More preferably, it is above the film stretching temperature in the width direction +1°C and below Tg+45°C, and even more preferably, it is above the film stretching temperature in the width direction +2°C and below Tg+40°C.

[0073] When stretching in the width direction, it is preferable to relax in the length direction. Thermal shrinkage in the length direction is caused by residual stress (so-called necking force) generated during stretching in the width direction relative to the stress in the direction orthogonal to the stretching direction. Therefore, by relaxing in the length direction during stretching in the width direction, the residual stress in the length direction is alleviated, and the thermal shrinkage rate in the length direction can be reduced. Relaxation in the length direction is performed while shortening the distance between the clips. The relaxation rate in the length direction is preferably 0% or more and 4% or less. Even if the relaxation rate in the length direction is 0%, there is no problem if the thermal shrinkage rate in the length direction is as targeted. If the relaxation rate in the length direction is higher than 4%, the amount of relaxation increases compared to the amount of film shortening, resulting in insufficient relaxation and poor planarity, which is therefore undesirable. More preferably, it is 1% or more and 3% or less. If a relaxation rate within this range is achieved, a film with a particularly high thermal shrinkage rate in the width direction and a low thermal shrinkage rate in the length direction can be obtained.

[0074] Example

[0075] The present invention will be described in more detail below through embodiments, but the present invention is not limited in any way by the above embodiments, and appropriate changes can be made without departing from the spirit of the present invention.

[0076] In addition, the evaluation method for thin films is described below.

[0077] [Intrinsic Viscosity (IV)]

[0078] 0.2 g of polyester was dissolved in 50 ml of a mixed solvent of phenol and 1,1,2,2-tetrachloroethane (60 / 40 by weight), and the viscosity was measured using an Ostwald viscometer at 30 °C. The unit is dl / g.

[0079] [Heat shrinkage rate (hot water heat shrinkage rate)]

[0080] The film was cut into 10cm×10cm squares and immersed in hot water at a specified temperature ±0.5℃ for 10 seconds under no load to shrink it. Then, it was immersed in water at 25℃±0.5℃ for 10 seconds. The film was then removed from the water and the longitudinal and transverse dimensions were measured. The heat shrinkage rate was calculated according to the following formula (1). The direction with the larger heat shrinkage rate was taken as the main shrinkage direction.

[0081] Heat shrinkage rate = {(length before shrinkage - length after shrinkage) / length before shrinkage} × 100 (%) Equation 1

[0082] [Piercing strength of the film]

[0083] The value determined by the test method according to JIS-Z1707 is calculated by converting to 1 μm using the following formula (2).

[0084] Puncture strength = Actual measured puncture strength / Film thickness (N / μm) Equation 2

[0085] [Puncture strength of the film after 10% shrinkage]

[0086] Prepare a rectangular frame with a gap of 200mm (the gap between the frames is 200mm wide and 250mm high). Adhere the film to the frame with a 23mm relaxation in the main shrinkage direction (width direction) (the film length between the frames is 223mm). The length direction is not fixed at this time; a length of 200mm is used. Immerse the film adhered to the frame in hot water heated to 80℃±0.5℃. Immediately after the film has relaxed, remove it and immerse it in water at 25℃±0.5℃ for 10 seconds. Remove it from the water, wipe off the water with a towel, and then determine the puncture strength of the film using the method described above. The puncture strength after 10% shrinkage is calculated using formula (2).

[0087] [Thickness of the thin film]

[0088] The determination was performed using a dial gauge according to JIS K7130-1999 Method A.

[0089] [Density of the thin film]

[0090] The density of a sample approximately 3 mm square was determined using the density gradient tube method according to JIS-K-7112 and an aqueous solution of calcium nitrate.

[0091] [Refractive index along the length]

[0092] Using the JIS K 7142-1996A method, sodium D-rays were used as the light source and the contact liquid as the contact fluid. Diiodomethane was used, and the refractive index of the thin film along its length was determined using an Abbe refractometer.

[0093] [Haze of the thin film]

[0094] According to JIS K7361-1, the film was cut into a square shape with 10cm sides, and the haze was measured using a NDH2000 haze meter manufactured by Nippon Densho Co., Ltd. The measurement was performed at 3 locations, and the average value was taken as the actual haze measurement value. The haze converted to 20μm was calculated by the following formula (3).

[0095] Haze = Actual measured haze value × 20 / Film thickness (%) (20 μm) Equation 3

[0096] [Tg (glass transition temperature)]

[0097] Tg was determined using a differential scanning calorimeter (DSC220) manufactured by Seiko Instruments Inc., according to JIS-K7121-1987. Specifically, 10 mg of an unstretched film was heated from -40 °C to 120 °C at a heating rate of 10 °C / min, and the endothermic curve was measured. Tangents were plotted before and after the inflection point of the obtained endothermic curve, and the intersection point was taken as the glass transition temperature (Tg, °C).

[0098] [Shrinkage finish]

[0099] The ends of the heat-shrinkable film were welded using a pulse sealer (manufactured by FUJI IMPULSE CO.,LTD.) to obtain a cylindrical label with the width direction as the circumferential direction. Additionally, 0.5mm holes were formed at 3mm intervals along the length of the film. Furthermore, similarly, 0.5mm holes were formed at 3mm intervals along the length of the film at 10mm intervals (the so-called perforation lines for easy-to-peel labels). The diameter of the label in the shrinkage direction was 68mm. This label was then placed over a commercially available 500ml PET bottle (containing contents, body diameter 62mm, minimum neck diameter 25mm), and heat-shrinked using a Fuji Astec Inc. steam channel (model: SH-1500-L) adjusted to 90°C (channel passage time 5 seconds). The shrinkage finish of the label was evaluated visually according to the following standards. A 5-level evaluation was performed based on the following visual standards. The defects described below refer to flying, wrinkling, insufficient shrinkage, label end folding, shrinkage whitening, etc. A score of 3 or higher is considered passing.

[0100] 5: Excellent machinability (no drawbacks)

[0101] 4: Good machinability (1 defect exists)

[0102] 3: There are 2 shortcomings.

[0103] 2: There are 3 to 5 defects.

[0104] 1. It has many shortcomings (more than 6).

[0105] [Evaluation of the outcome when the bag is placed]

[0106] In the aforementioned 500ml PET bottle, the label was dropped horizontally with the perforation line facing downwards from a height of 1.2m onto concrete. The label was then visually evaluated according to the following criteria.

[0107] 〇: In the evaluation of 10 bags, the number of bags with broken labels is less than 1.

[0108] ×: In the evaluation of 10 bags, more than 2 bags were found to be broken.

[0109] [Evaluation of the opening during bag placement]

[0110] Similarly, in a 500ml PET bottle, the label was dropped horizontally with the perforation line facing downwards from a height of 1.2m onto concrete. The dropped label was then visually evaluated according to the following criteria.

[0111] 〇: In the evaluation of 10 bags, the label with a hole is less than 1.

[0112] ×: In the evaluation of 10 bags, more than 2 bags had perforated labels.

[0113] <Manufacturing of Polyester Raw Materials>

[0114] [Synthesis example 1]

[0115] A stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux cooler was used to add 100 mol% dimethyl terephthalate (DMT) as a dicarboxylic acid and 100 mol% ethylene glycol (EG) as a polyol, at a molar ratio of 2.2 times that of dimethyl terephthalate. Zinc acetate (0.05 mol% relative to the acid component) and antimony trioxide (0.225 mol% relative to the acid component) as a polycondensation catalyst were also added. The transesterification reaction was carried out simultaneously with the distillation removal of the generated methanol from the system. Polycondensation was then carried out at 280 °C under reduced pressure of 26.7 Pa to obtain polyester A with an intrinsic viscosity of 0.70 dl / g. The composition is shown in Table 1.

[0116] [Synthesis Examples 2 to 4]

[0117] Polyesters B to D, as shown in Table 1, were obtained using the same method as in Synthesis Example 1. During the manufacture of polyester B, SiO2 (manufactured by FUJI SILYSIA CHEMICAL LTD., SYLYSIA 266; average particle size 1.5 μm) was added as a lubricant at a ratio of 20,000 ppm relative to the polyester. It should be noted that the intrinsic viscosity of all polyesters was 0.70 dl / g.

[0118] It should be noted that each polyester is appropriately formed into fragments. The composition of each polyester is shown in Table 1.

[0119] [Table 1]

[0120]

[0121] ※DMT: Dimethyl terephthalate

[0122] EG: Ethylene glycol

[0123] DEG: Diethylene glycol

[0124] [Example 1]

[0125] Polyester A, Polyester B, and Polyester C were mixed in a mass ratio of 17:3:80 and fed into an extruder. The mixed resin was then melted at 270°C using a quadrupole screw, cooled to 260°C, and extruded through a T-die. The mixture was then quenched by winding it onto a rotating metal roller cooled to a surface temperature of 20°C, resulting in an unstretched film with a thickness of 99 μm. The Tg of the unstretched film was 50°C. This unstretched film was then guided to a tenter frame, preheated to a film temperature of 90°C (Tg + 40°C) while holding the film at both ends with clamps, and then stretched 5 times in the transverse direction at a film temperature of 55°C (Tg + 5°C). At this point, the distance between the clamps in the length direction was shortened to allow for a 1% relaxation in the length direction. The film stretched in the width direction was then heat-set at 57°C (Tg + 7°C). The two edges of the stretched film were cut off, thereby continuously producing uniaxially stretched films of approximately 20 μm in length, resulting in film rolls formed from heat-shrinkable polyester films. The properties of the obtained films were then evaluated using the method described above. The film-forming conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[0126] The film has no problems in practical application, both in terms of shrinkage finish and bagging evaluation.

[0127] [Example 2]

[0128] Polyester A, polyester B, and polyester C were mixed in a mass ratio of 7:3:90 and fed into an extruder to obtain an unstretched film with a thickness of 99 μm, similar to Example 1. The Tg of the unstretched film was 48°C. The unstretched film was guided to a tenter frame and preheated to a film temperature of 88°C (Tg+40°C) while holding the film at both ends with clamps. Then, it was stretched 5 times in the transverse direction at a film temperature of 53°C (Tg+5°C). At this time, the distance between the clamps in the length direction was shortened to allow for a 1% relaxation in the length direction. The film stretched in the width direction was then heat-set at 55°C (Tg+7°C). The two edges of the stretched film were cut off, thereby continuously producing uniaxially stretched films of approximately 20 μm in length to obtain film rolls formed from heat-shrinkable polyester films. The properties of the obtained films were then evaluated using the above method. The film-making conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[0129] The film has no problems in practical application, both in terms of shrinkage finish and bagging evaluation.

[0130] [Example 3]

[0131] Polyester A, polyester B, and polyester C were mixed in a mass ratio of 57:3:40 and fed into an extruder to obtain an unstretched film with a thickness of 99 μm, similar to Example 1. The Tg of the unstretched film was 63°C. The unstretched film was guided to a tenter frame and preheated to a film temperature of 103°C (Tg+40°C) while holding the film at both ends with clamps. Then, it was stretched 5 times in the transverse direction at a film temperature of 68°C (Tg+5°C). At this time, the distance between the clamps in the length direction was shortened to allow for a 1% relaxation in the length direction. The film stretched in the width direction was heat-set at 70°C (Tg+7°C). The two edges of the stretched film were cut off, thereby continuously producing uniaxially stretched films of approximately 20 μm in length to obtain film rolls formed from heat-shrinkable polyester films. The properties of the obtained films were then evaluated using the above method. The film-making conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[0132] The film has no problems in practical application, both in terms of shrinkage finish and bagging evaluation.

[0133] [Example 4]

[0134] Polyester A, polyester B, and polyester C were mixed in a mass ratio of 77:3:20 and fed into an extruder to obtain an unstretched film with a thickness of 79 μm, similar to Example 1. The Tg of the unstretched film was 70°C. The unstretched film was guided to a tenter frame and preheated to a film temperature of 115°C (Tg+45°C) while holding the film at both ends with clamps. Then, it was stretched 4 times in the transverse direction at a film temperature of 75°C (Tg+5°C). At this time, the distance between the clamps in the length direction was shortened to allow for a 2% relaxation in the length direction. The film stretched in the width direction was then heat-set at 77°C (Tg+7°C). The two edges of the stretched film were cut off, thereby continuously producing uniaxially stretched films of approximately 20 μm in length to obtain film rolls formed from heat-shrinkable polyester films. The properties of the obtained films were then evaluated using the above method. The film-making conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[0135] The film has no problems in practical application, both in terms of shrinkage finish and bagging evaluation.

[0136] [Example 5]

[0137] Polyester A, polyester B, and polyester C were mixed in a mass ratio of 57:3:40 and fed into an extruder to obtain an unstretched film with a thickness of 118 μm, similar to Example 1. The Tg of the unstretched film was 63°C. The unstretched film was guided to a tenter frame and preheated to a film temperature of 103°C (Tg+40°C) while holding the film at both ends with clamps. Then, it was stretched 6 times in the transverse direction at a film temperature of 68°C (Tg+5°C). At this time, the distance between the clamps in the length direction was shortened to allow for a 2% relaxation in the length direction. The film stretched in the width direction was heat-set at 70°C (Tg+7°C). The two edges of the stretched film were cut off, thereby continuously producing uniaxially stretched films of approximately 20 μm in length to obtain film rolls formed from heat-shrinkable polyester films. The properties of the obtained films were then evaluated using the above method. The film-making conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[0138] The film has no problems in practical application, both in terms of shrinkage finish and bagging evaluation.

[0139] [Example 6]

[0140] Polyester A, polyester B, and polyester C were mixed in a mass ratio of 57:3:40 and fed into an extruder to obtain an unstretched film with a thickness of 79 μm, similar to Example 1. The Tg of the unstretched film was 63°C. The unstretched film was guided to a tenter frame and preheated to a film temperature of 103°C (Tg+40°C) while holding the film at both ends with clamps. Then, it was stretched 4 times in the transverse direction at a film temperature of 68°C (Tg+5°C). At this time, the distance between the clamps in the length direction was shortened to allow for a 1% relaxation in the length direction. The film stretched in the width direction was then heat-set at 70°C (Tg+7°C). The two edges of the stretched film were cut off, thereby continuously producing uniaxially stretched films of approximately 20 μm in length to obtain film rolls formed from heat-shrinkable polyester films. The properties of the obtained films were then evaluated using the above method. The film-making conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[0141] The film has no problems in practical application, both in terms of shrinkage finish and bagging evaluation.

[0142] [Example 7]

[0143] The extrusion rate of the extruder was reduced, and the molten resin was wound onto a rotating metal roll for rapid cooling, thereby changing the thickness to 74 μm. Otherwise, a film roll with a thickness of 15 μm was obtained using the same method as in Example 1. The properties of the obtained film were then evaluated using the above method. The film-forming conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[0144] The film has no problems in practical application, both in terms of shrinkage finish and bagging evaluation.

[0145] [Example 8]

[0146] The extrusion rate of the extruder was reduced, and the molten resin was wound onto a rotating metal roll for rapid cooling, thereby changing the thickness to 198 μm. Otherwise, a film roll with a thickness of 40 μm was obtained using the same method as in Example 1. The properties of the obtained film were then evaluated using the above method. The film-forming conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[0147] The film has no problems in practical application, both in terms of shrinkage finish and bagging evaluation.

[0148] [Comparative Example 1]

[0149] Polyester A, polyester B, and polyester C were mixed in a mass ratio of 42:3:55 and fed into an extruder. The mixed resin was then melted at 270°C using a quadrupole screw, cooled to 260°C, and extruded through a T-die. The mixture was then quenched by winding it onto a rotating metal roller cooled to a surface temperature of 20°C, resulting in an unstretched film with a thickness of 130 μm. The Tg of the unstretched film was 57°C. This unstretched film was then guided to a tenter frame and preheated to a film temperature of 97°C (Tg + 40°C) while holding the film at both ends with clamps. It was then stretched 6.5 times in the transverse direction at a film temperature of 62°C (Tg + 5°C). The stretched film was then heat-set at 64°C (Tg + 7°C). The two edges of the stretched film were trimmed off, thereby continuously producing uniaxially stretched films of approximately 20 μm in length, resulting in film rolls formed from heat-shrinkable polyester films. The properties of the obtained film were then evaluated using the methods described above. The film-forming conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[0150] It has the problem of high refractive index in the length direction, which can cause bag breakage during bag evaluation.

[0151] [Comparative Example 2]

[0152] Polyester A, polyester B, and polyester C were mixed in a mass ratio of 77:3:20 and fed into an extruder to obtain an unstretched film with a thickness of 80 μm, similar to Example 1. The Tg of the unstretched film was 70°C. The unstretched film was guided to a tenter frame and preheated to a film temperature of 75°C (Tg+5°C) while holding the film at both ends with clamps. Then, it was stretched 4 times in the transverse direction at a film temperature of 75°C (Tg+5°C). The film stretched in the width direction was heat-set at 77°C (Tg+7°C). The two edges of the stretched film were cut off, thereby continuously producing uniaxially stretched films of approximately 20 μm in length to obtain film rolls formed from heat-shrinkable polyester films. The properties of the obtained films were then evaluated using the above method. The film-making conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[0153] It has problems such as low puncture strength, high refractive index in the length direction, and bag breakage and holes in bag evaluation.

[0154] [Comparative Example 3]

[0155] Polyester A, polyester B, and polyester D were mixed in a mass ratio of 17:3:80 and fed into an extruder. The aim was to obtain an unstretched film with a thickness of 80 μm, similar to Example 1. However, the Tg was low at 38°C, so the film adhered to the cooling roller and could not be obtained continuously, thus preventing film evaluation.

[0156] [Comparative Example 4]

[0157] Polyester A, polyester B, and polyester C were mixed in a mass ratio of 92:3:5 and fed into an extruder to obtain an unstretched film with a thickness of 99 μm, similar to Example 1. The Tg of the unstretched film was 75°C. The unstretched film was guided to a tenter frame and preheated to a film temperature of 115°C (Tg+40°C) while holding the film at both ends with clamps. Then, it was stretched 5 times in the transverse direction at a film temperature of 80°C (Tg+5°C). At this time, the distance between the clamps in the length direction was shortened to allow for a 1% relaxation in the length direction. The film stretched in the width direction was then heat-set at 82°C (Tg+7°C). The two edges of the stretched film were cut off, thereby continuously producing uniaxially stretched films of approximately 20 μm in length to obtain film rolls formed from heat-shrinkable polyester films. The properties of the obtained films were then evaluated using the above method. The film-making conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[0158] The width-direction hot water shrinkage rate measured at 90℃ for 10 seconds is low, resulting in insufficient shrinkage in the shrinkage finishing evaluation, and it cannot be used for shrinkage finishing performance or bag evaluation.

[0159] [Comparative Example 5]

[0160] Polyester A, polyester B, and polyester C were mixed in a mass ratio of 17:3:80 and fed into an extruder to obtain an unstretched film with a thickness of 101 μm, similar to Example 1. The Tg of the unstretched film was 50°C. The unstretched film was guided to a tenter frame and preheated to a film temperature of 90°C (Tg+40°C) while holding the film at both ends with clamps. Then, it was stretched 5 times in the transverse direction at a film temperature of 55°C (Tg+5°C). At this time, the distance between the clamps in the length direction was increased, and the length direction was stretched by 2%. The film, stretched 5 times in the width direction and 1.02 times in the length direction, was heat-set at 57°C (Tg+7°C). The two edges of the stretched film were cut off, thereby continuously producing uniaxially stretched films of approximately 20 μm in length, resulting in a film roll formed from a heat-shrinkable polyester film. The properties of the obtained film were then evaluated using the above method. The film-making conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[0161] It has the problem of high refractive index in the length direction, which can cause bag breakage during bag evaluation.

[0162] [Table 2]

[0163]

[0164] [Table 3]

[0165]

[0166] Industrial availability

[0167] The heat-shrinkable polyester film of the present invention, despite its high heat shrinkage rate, also exhibits excellent bag-holding properties, making it suitable for labeling applications such as containers. Containers and other packaging obtained using the heat-shrinkable polyester film of the present invention as labels possess an attractive appearance and excellent bag-holding durability.

Claims

1. A heat-shrinkable polyester film, characterized in that, It contains 60 mol% to 95 mol% of ethylene terephthalate units in 100 mol% of all ester units, 5 mol% to 40 mol% of diethylene glycol in 100 mol% of polyol components, and 0 mol% to 5 mol% of constituent units derived from monomer components capable of becoming amorphous components in all polyester resin components, and satisfies the following conditions (1) to (5). (1) The hot water thermal shrinkage rate of the film when immersed in hot water at 90°C for 10 seconds is more than 40% and less than 80% in the width direction of the film. (2) The hot water thermal shrinkage rate of the film when immersed in hot water at 90℃ for 10 seconds is greater than -5% and less than 15% in the length direction of the film. (3) The puncture strength of the film is above 0.2 N / μm and below 0.6 N / μm. (4) The density of the film is 1.330 g / cm³. 3 Above and 1.385 g / cm 3 the following, (5) The refractive index along the length of the thin film is below 1.

575. The monomeric components that can become amorphous components are neopentyl glycol, 1,4-cyclohexanediethanol, isophthalic acid, 1,4-cyclohexanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, or hexanediol.

2. The heat-shrinkable polyester film according to claim 1, characterized in that, The thickness of the film is greater than 15 μm.

3. The heat-shrinkable polyester film according to claim 1 or 2, characterized in that, The haze is above 2% and below 10% when the film thickness is 20μm.

4. The heat-shrinkable polyester film according to claim 1 or 2, characterized in that, The puncture strength of the film after shrinking by 10% in the width direction is above 0.1 N / μm and below 0.5 N / μm.

5. The heat-shrinkable polyester film according to claim 3, characterized in that, The puncture strength of the film after shrinking by 10% in the width direction is above 0.1 N / μm and below 0.5 N / μm.

6. A heat-shrinkable label using the heat-shrinkable polyester film according to any one of claims 1 to 5.

7. A packaging body, characterized in that, It is formed by covering at least a portion of the outer periphery of the packaged object with the heat-shrinkable label as described in claim 6 and causing it to heat-shrink.

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