Heat-shrinkable polyester film, heat-shrinkable label, and packaging material

Abstract

To provide a heat-shrinkable polyester-based film that has a high heat shrinkage rate in the main shrinkage direction and can be recycled together with used beverage plastic bottles to obtain good recycled PET resin.SOLUTION: A heat-shrinkable polyester-based film contains: in 100 mol% of the dicarboxylic acid component, dicarboxylic acid of 95 mol% or more and 100 mol% or less and isophthalic acid of 0 mol% or more and 5 mol% or less; in a total ester unit 100 mol%, an ethylene terephthalate unit of 85 mol% or more and 98 mol% or less; and in 100 mol% of a polyhydric alcohol component, diethylene glycol of 2 mol% or more and 15 mol% or less. heat-shrinkable polyester-based film having a predetermined hot water heat shrinkage rate, melts the film using a differential scanning calorimeter (DSC), and then quenches and heats the same again, and a melting peak temperature, a crystallization calorific value, and a melting calorimetric value are measured and all of these fall within a predetermined range.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a heat-shrinkable polyester film, and more particularly to a heat-shrinkable polyester film, a heat-shrinkable label, and a packaging material that can be mixed with PET bottles in the PET bottle recycling process to produce recycled PET resin that can be recycled without any problems. [Background technology]

[0002] In recent years, stretched films (so-called heat-shrinkable films) made of polyvinyl chloride resins, polystyrene resins, polyester resins, etc. have come into widespread use for label packaging, cap seals, and stacked packaging, which combine the protection of glass bottles, PET bottles, etc. with product labeling. Among these heat-shrinkable films, polyvinyl chloride films have problems such as poor heat resistance and the generation of hydrogen chloride gas upon incineration, which can cause dioxin emissions. Polystyrene films, on the other hand, have poor solvent resistance, require the use of inks with special compositions for printing, and require incineration at high temperatures, resulting in the generation of large amounts of black smoke accompanied by an unpleasant odor upon incineration. Therefore, polyester-based heat-shrinkable films, which have high heat resistance, are easy to incinerate, and have excellent solvent resistance, have come to be widely used as shrink labels, and their usage is on the rise as the distribution volume of PET containers increases.

[0003] Conventional heat-shrinkable polyester films that shrink significantly in the width direction are widely used. This film is stretched using a tenter stretching method or similar to create a wide-width master roll. The master roll is then slit to the desired width and wound into a roll of the desired length to create a film roll product. This film is then given a design and printed in roll form for product display purposes. After printing, the film is re-slit to the required width and wound into a roll, after which it is center-sealed using solvent bonding, formed into a tubular bag, and wound into a roll (to become a label roll).

[0004] The labels are rolled up into a tube, cut to the required length as they are unwound from the roll, and then attached to the package by hand or other methods, and passed through a steam tunnel or hot air tunnel to shrink and become a label.

[0005] In recent years, there has been a growing demand for environmental friendliness. For example, PET bottle containers are recycled and regenerated as recycled PET resin, which is used in various plastic products. Due to the growing demand for environmental friendliness, the amount of recycled PET resin used is increasing, and the recycling rate of PET bottles is also increasing.

[0006] PET beverage bottles are recycled once their contents are gone and are made into recycled PET resin, but the labels that give the beverage bottles their decorative appeal are generally not recycled. Polystyrene-based heat-shrinkable film labels, such as those described in Patent Document 1, are incompatible with PET, the raw material for PET bottles. Therefore, if polystyrene-based heat-shrinkable film is mixed in during the process of making recycled PET resin, the transparency of the recycled PET resin will be lost, which is undesirable. The polyester and polystyrene laminate film described in Patent Document 2 is also undesirable because it contains a mixture of PET and polystyrene, which is incompatible with PET. Patent Document 3 is an invention of a polyester-based heat-shrinkable film, but cyclic olefins and the like are mixed in to create voids, and as with the above, olefin-based raw materials that are incompatible with PET are mixed in, which is undesirable.

[0007] Patent Document 4 describes a transparent polyester-based heat-shrinkable film that does not contain any incompatible materials with PET, ensuring transparency during the process of producing recycled PET resin. However, polyester-based heat-shrinkable films are generally produced from amorphous PET raw materials, to which amorphous monomers are added to develop heat-shrink properties. The raw material used in PET bottles is homo-PET, which is a crystalline raw material. Therefore, if amorphous polyester-based heat-shrinkable film is mixed during the process of producing recycled PET resin, the resulting recycled PET resin becomes difficult to reuse as homo-PET raw material and cannot be used to produce PET bottles again. Furthermore, because the densities of crystalline and amorphous raw materials are different, when the two raw materials are mixed to produce recycled resin, the amorphous raw material is not extruded uniformly, which can lead to problems such as pulsation and tow breakage in the die after melt extrusion, which is undesirable. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 5286763 [Patent Document 2] International Publication No. WO2020 / 021948 [Patent Document 3] Patent No. 5625912 [Patent Document 4] Patent No. 5633808 Summary of the Invention [Problem to be solved by the invention]

[0009] The heat-shrinkable polyester film of the present invention has a high heat shrinkage rate in the main shrinkage direction, and is also intended to provide a heat-shrinkable polyester film that can be recycled together with used PET beverage bottles to yield a good recycled PET resin. [Means for solving the problem]

[0010] The present invention, which has solved the above problems, has the following configuration. 1. A heat-shrinkable polyester film containing 95 mol% to 100 mol% of dicarboxylic acids and 0 mol% to 5 mol% of isophthalic acid out of 100 mol% of dicarboxylic acid components, and containing 85 mol% to 98 mol% of ethylene terephthalate units out of 100 mol% of all ester units, and containing 2 mol% to 15 mol% of diethylene glycol out of 100 mol% of polyhydric alcohol components, wherein the heat-shrinkable polyester film satisfies the following requirements (1) to (5): (1) When the film is immersed in 90°C hot water for 10 seconds, the hot water shrinkage rate is 40% or more and 70% or less in the width direction of the film. (2) When the film is immersed in 90°C hot water for 10 seconds, the hot water shrinkage rate is between -5% and 15% in the longitudinal direction of the film. (3) Using a differential scanning calorimeter (DSC), the film is heated to 300°C, melted, then rapidly cooled, and heated again to 300°C. The endothermic peak temperature due to melting is 245°C or higher and 260°C or lower. (4) Film thickness: 15 μm to 50 μm (5) Using a differential scanning calorimeter (DSC), the film is heated to 300°C, melted, then rapidly cooled, and heated again to 300°C. The endothermic heat due to melting is 10 mJ / mg or more. 2. The density of the film is 1.33 g / cm 3 More than 1.39g / cm 3 1. The heat-shrinkable polyester film according to 1., characterized in that: 3. The heat-shrinkable polyester film according to 1 or 2, characterized in that the haze at a film thickness of 20 μm is 2% or more and 10% or less. 4. A heat-shrinkable label using the heat-shrinkable polyester film described in any one of 1. to 3. 5. A package formed by covering at least a portion of the outer periphery of an object to be packaged with the heat-shrinkable label described in 4 above and then heat-shrinking it. 6. The heat-shrinkable polyester film according to any one of 1. to 3., which is used for a heat-shrinkable label and then used as a raw material for recycling PET bottles. [Effects of the Invention]

[0011] The heat-shrinkable polyester film of the present invention has a high heat shrinkage rate in the main shrinkage direction, and the raw material components used are similar to those used in PET beverage bottles. In addition, the melting point, heat release amount, and heat absorption amount of the film measured by a differential scanning calorimeter (hereinafter sometimes referred to as DSC) are similar to those of the raw materials used in PET bottles. Therefore, recycled PET resin can be obtained even if the heat-shrinkable polyester film is recycled together with PET bottles. [Brief explanation of the drawings]

[0012] [Figure 1] 1 shows an example of measurement of the endothermic peak temperature, the amount of heat generated by crystallization, and the amount of endothermic heat generated by melting of a film using DSC in the present invention. [Figure 2] 1 is a top view showing an example of a TD (transverse direction stretching) pattern in the process of producing a heat-shrinkable polyester film of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] The heat-shrinkable polyester film of the present invention will be described in detail below. The method for producing the heat-shrinkable polyester film will be described in detail later, but the heat-shrinkable film is usually obtained by transporting and stretching the film using rolls or the like. Here, the transport direction of the film is referred to as the longitudinal direction, and the direction perpendicular to the longitudinal direction is referred to as the width direction of the film. Therefore, the width direction of the heat-shrinkable polyester film described below refers to the direction perpendicular to the unwinding direction of the roll, and the longitudinal direction of the film refers to the direction parallel to the unwinding direction of the roll.

[0014] The heat-shrinkable polyester film of the present invention contains 85 mol% to 98 mol% of ethylene terephthalate units out of 100 mol% of all ester units, 95 mol% to 100 mol% of dicarboxylic acids and 0 mol% to 5 mol% of isophthalic acid out of 100 mol% of dicarboxylic acid components, and 2 mol% to 15 mol% of diethylene glycol out of 100 mol% of polyhydric alcohol components, and is a heat-shrinkable polyester film characterized by satisfying the following requirements (1) to (5): (1) When the film is immersed in 90°C hot water for 10 seconds, the hot water shrinkage rate is 40% or more and 70% or less in the width direction of the film. (2) When the film is immersed in 90°C hot water for 10 seconds, the hot water shrinkage rate is between -5% and 15% in the longitudinal direction of the film. (3) Using a differential scanning calorimeter (DSC), the film is heated to 300°C, melted, then rapidly cooled, and heated again to 300°C. The endothermic peak temperature due to melting is 245°C or higher and 260°C or lower. (4) Using a differential scanning calorimeter (DSC), the film is heated to 300°C, melted, then rapidly cooled, and heated again to 300°C, resulting in crystallization with a calorific value of 10 mJ / mg or more. (5) Using a differential scanning calorimeter (DSC), the film is heated to 300°C, melted, then rapidly cooled, and heated again to 300°C. The endothermic heat due to melting is 10 mJ / mg or more.

[0015] The present inventors analyzed the raw material composition of commercially available PET beverage bottles (PET beverage bottles sold by Coca-Cola, Suntory, Ito En, Kirin, and Asahi) using 1H-NMR (Varian, UNITY50). Of 100 mol% of dicarboxylic acid components, 97-98.5 mol% of dicarboxylic acid and 1.5-3 mol% of isophthalic acid were contained. Furthermore, of 100 mol% of ester units, 97-99 mol% of ethylene terephthalate units were contained, and of 100 mol% of polyhydric alcohol components, 1-3 mol% of diethylene glycol was contained. It is believed that isophthalic acid is intentionally added to prevent whitening of the neck of the PET bottle during PET bottle molding. Diethylene glycol is believed to be a by-product of the polymerization of the raw materials.

[0016] Therefore, for heat-shrinkable polyester films, raw materials containing only dicarboxylic acid and isophthalic acid as dicarboxylic acid components and ethylene terephthalate units and diethylene glycol as ester units are preferred, as this makes recycling with PET bottles easier. The weight ratio of the PET bottle to the label was also compared using 500 ml PET beverage bottles. The weight ratio of the PET bottle was 1, with the label being 0.05 to 0.2, meaning the weight ratio of the label was low. Thus, the inventors discovered that even though the weight ratio of the label is low when the PET bottle and label are mixed for recycling, the composition and properties of the label are factors that cause variations in the resin size and other properties during the recycling process.

[0017] In order to achieve high shrinkability in heat-shrinkable polyester films, it is common to copolymerize other polycarboxylic acid components or other polyhydric alcohol components with a homopolymer (PET) made of, for example, ethylene terephthalate. Examples of polyhydric alcohol components that can be used as copolymerization components include neopentyl glycol and 1,4-cyclohexanediethanol, which are widely used. Films copolymerized with these components have a different raw material composition from the raw materials used in the aforementioned PET beverage bottles, which is undesirable because it reduces recyclability with the PET bottles.

[0018] Polyethylene terephthalate (hereinafter sometimes simply referred to as PET) can be produced by any of a variety of polymerization methods, including a direct polymerization method in which terephthalic acid is directly reacted with ethylene glycol, and, if necessary, other dicarboxylic acid components and diol components, and an ester exchange method in which a dimethyl ester of terephthalic acid (containing, if necessary, a methyl ester of another dicarboxylic acid) is subjected to an ester exchange reaction with ethylene glycol (containing, if necessary, another diol component).

[0019] Examples of dicarboxylic acid components other than terephthalic acid that constitute polyester include aromatic dicarboxylic acids such as isophthalic acid, naphthalenedicarboxylic acid, and orthophthalic acid; aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid; and alicyclic dicarboxylic acids. In the heat-shrinkable polyester film of the present invention, isophthalic acid, the same component as the raw material for PET bottles, is preferably used. The content of the isophthalic acid component is 0 mol% or more, preferably 1 mol% or more, based on 100 mol% of the polycarboxylic acid component, and more preferably 1.5 mol% or more, which is the same composition as the raw material for PET bottles. Since the weight of the label is 5 to 20% of the PET bottle, an upper limit of 15 mol%, which is five times the isophthalic acid content of the PET bottle, is not preferable. Isophthalic acid is amorphous, and a high content of isophthalic acid increases the amorphous nature, which is undesirable because it can cause problems such as pulsation when mixed with PET bottles to produce recycled PET raw materials. The content of isophthalic acid is 5 mol % or less, preferably 4 mol % or less, and more preferably 3 mol % or less, the same as that of the raw material for PET bottles.

[0020] It is necessary that the content of diethylene glycol is 2 mol % or more and 15 mol % or less out of 100 mol % of the polyhydric alcohol component constituting the polyester used in the film of the present invention. If the diethylene glycol content is less than 2 mol %, it is difficult to exhibit the shrinkage properties required for a heat shrinkable film, which is undesirable.The diethylene glycol content is preferably 3 mol % or more, and more preferably 4 mol % or more. On the other hand, as mentioned above, the upper limit for the label weight is 5-20% of the PET bottle weight. Therefore, even if it is mixed with the PET bottle during the recycling process, the diethylene glycol content will be 1 / 5-1 / 20 or less. As mentioned above, the raw materials for PET bottles contain 1-3 mol% diethylene glycol, so if the diethylene glycol content in recycled PET resin is 15 mol% or less, it will fall within the range of diethylene glycol for PET bottle resin when it becomes recycled PET resin. Diethylene glycol should preferably be 13 mol% or less, and more preferably 11 mol% or less.

[0021] It is preferable not to contain diols having 8 or more carbon atoms (e.g., octanediol, etc.) or trihydric or higher polyhydric alcohols (e.g., trimethylolpropane, trimellitolethane, glycerin, diglycerin, etc.). Heat-shrinkable polyester films obtained using polyesters containing these diols or polyhydric alcohols are unlikely to achieve the required high shrinkage.

[0022] Various additives, such as waxes, antioxidants, antistatic agents, crystal nucleating agents, viscosity reducers, heat stabilizers, coloring pigments, color inhibitors, and ultraviolet absorbers, may be added to the resin forming the heat-shrinkable polyester film of the present invention, as needed.

[0023] It is preferable to add fine particles as a lubricant to the resin forming the heat-shrinkable polyester film of the present invention to improve the workability (slipperiness) of the film. Any fine particles can be selected, but examples of inorganic fine particles include silica, alumina, titanium dioxide, calcium carbonate, kaolin, and barium sulfate, and examples of organic fine particles include 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 (as measured with a Coulter counter).

[0024] The method of incorporating the particles into the resin that forms the heat-shrinkable polyester film can be, for example, adding them at any stage in the production of the polyester resin, but it is preferable to add them as a slurry dispersed in ethylene glycol or the like at the stage of esterification or after the completion of the transesterification reaction and before the start of the polycondensation reaction, and then proceed with the polycondensation reaction. Also preferred is a method of blending a slurry of particles dispersed in ethylene glycol or water or the like with a polyester resin raw material using a vented kneading extruder, or a method of blending dried particles with a polyester resin raw material using a kneading extruder.

[0025] The heat-shrinkable polyester film of the present invention preferably has a heat shrinkage rate in the main shrinkage direction of the film (i.e., hot water heat shrinkage rate at 90°C) calculated from the lengths before and after shrinkage using the following formula 1 when treated in 90°C hot water for 10 seconds under no load, of 40% or more and 70% or less. Heat shrinkage rate = {(length before shrinkage - length after shrinkage) / length before shrinkage} x 100 (%) Formula 1

[0026] If the hot water shrinkage rate in the main shrinkage direction at 90°C is less than 40%, when the film is used for beverage labels or as a film for lunch box packaging, the shrinkage amount is so small that wrinkles and sagging of the label occur after heat shrinkage, which is undesirable. The hot water shrinkage rate at 90°C is more preferably 43% or more, particularly preferably 46% or more, and most preferably 50% or more. There is no problem if the hot water heat shrinkage rate in the main shrinkage direction at 90°C is higher than 70%, but in the present invention, it was not possible to obtain a film with a hot water heat shrinkage rate at 90°C higher than 70%, so the upper limit was set at 70%.

[0027] The heat-shrinkable polyester film of the present invention preferably has a hot water shrinkage rate at 90°C in the longitudinal direction perpendicular to the main shrinkage direction of -5% to 15%. If the hot water shrinkage rate at 90°C in the longitudinal direction is less than -5%, when used as a beverage label, the label will stretch, undesirably increasing the label height on a PET bottle. The hot water shrinkage rate at 90°C in the longitudinal direction is more preferably -4% or more, and particularly preferably -3% or more. If the hot water shrinkage rate at 90°C in the longitudinal direction is greater than 15%, the label will shrink when used as a beverage label, shortening the label height on the PET bottle, which is undesirable. It may also cause distortion of the label after shrinkage. The hot water shrinkage rate at 90°C in the longitudinal direction is more preferably 13% or less, even more preferably 11% or less, particularly preferably 8% or less, and most preferably 5% or less.

[0028] The heat-shrinkable polyester film of the present invention preferably has an endothermic peak temperature of 245°C to 260°C when heated to 300°C using a differential scanning calorimeter (DSC), melted, cooled, and then heated again to 300°C. When a PET bottle was measured using the same method, the peak heat of fusion was in the range of 250 to 260°C. Therefore, if the peak heat of fusion differs significantly from that of a PET bottle, problems such as pulsation will occur during the melt extrusion process when recycled PET resin is produced, which is undesirable. A temperature of 247°C to 260°C is more preferable, and a temperature of 250°C to 255°C is particularly preferable.

[0029] The heat-shrinkable polyester film of the present invention is preferably crystallized by heating it to 300°C using a DSC, melting it, cooling it, and then heating it again to 300°C to obtain a calorific value of 10 mJ / mg or more. When a PET bottle was measured using the same method, the calorific value was in the range of 25 to 55 mJ / mg. If the amorphous content of the heat-shrinkable polyester film is high, the calorific value will not be displayed, which is undesirable because it will cause problems such as pulsation during the melt extrusion process when producing recycled PET resin. Therefore, the amount of heat generated by crystallization is preferably 10 mJ / mg or more, more preferably 20 mJ / mg or more, and particularly preferably 25 mJ / mg or more. There is no specific upper limit for the amount of heat generated by crystallization, but it will not exceed 60 mJ / mg for polyester raw materials.

[0030] The heat-shrinkable polyester film of the present invention preferably has an endothermic value of 10 mJ / mg or more when heated to 300°C using a DSC, melted, cooled, and then heated again to 300°C. When a PET bottle was measured using the same method, the endothermic value was in the range of 30 to 65 mJ / mg. If the heat-shrinkable polyester film has a high amorphous content, it will not exhibit an endothermic value, which is undesirable because it will cause problems such as pulsation during the melt extrusion process when producing recycled PET resin. Therefore, the endothermic heat due to melting is preferably 10 mJ / mg or more, more preferably 20 mJ / mg or more, and particularly preferably 30 mJ / mg or more. There is no specific upper limit for the amount of heat absorbed by melting, but for polyester raw materials, it will not exceed 70 mJ / mg.

[0031] The heat-shrinkable polyester film of the present invention has a density of 1.33 g / cm 3 Density has been reported in many reports as an index of crystallinity. Therefore, a low density indicates low crystallinity and a high amorphous content. Density is 1.33g / cm 3 If the viscosity is less than 1.34 g / cm, problems such as pulsation will occur during the melt extrusion process when producing recycled PET resin, which is not preferable. 3 More preferably, it is 1.35 g / cm or more. 3 It is particularly preferable that the above value is satisfied. On the other hand, if the density is too high, it will crystallize and the shrinkage characteristics described above will not be obtained, which is not desirable. 3 It is more preferable that it is 1.37 g / cm or less. 3 It is particularly preferred that:

[0032] The thickness of the heat-shrinkable polyester film of the present invention is not particularly limited, but is preferably 15 to 50 μm for use as a heat-shrinkable film for label applications or lunch box packaging. If the film thickness is less than 15 μm, the stiffness of the film will be significantly reduced, making the roll prone to wrinkles, which is undesirable. On the other hand, even if the film is thick, there is no problem with the film roll, but from a cost perspective, it is preferable to make it thinner. The film thickness is more preferably 17 to 45 μm, and particularly preferably 20 to 40 μm.

[0033] The heat-shrinkable polyester film of the present invention preferably has a haze value of 2% or more and 10% or less at a thickness of 20 μm. Since heat-shrinkable films are films that add design, a haze value higher than 10% is undesirable because when used as a label for a PET bottle, the contents become difficult to see clearly, reducing the design. The haze at a film thickness of 20 μm is more preferably 8% or less, and particularly preferably 6% or less. Although there is no problem with a haze of less than 2% for a film thickness of 20 μm, in the present invention, the slipperiness of the film deteriorates when the haze value is less than 2%, so the lower limit is set to 2%.

[0034] 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. The polyester can be obtained by polycondensing the above-mentioned suitable dicarboxylic acid component and diol component using a known method. In addition, chip-like polyester is usually used as the raw material for the film.

[0035] When melt-extruding the raw material resin, it is preferable to dry the polyester raw material using a dryer such as a hopper dryer or a paddle dryer, or a vacuum dryer. After drying the polyester raw material in this way, it is melted at a temperature of 230 to 270°C using an extruder and extruded into a film. For extrusion, any existing method such as a T-die method or a tubular method can be used.

[0036] The extruded sheet-like molten resin can then be rapidly cooled to obtain an unstretched film. A suitable method for rapidly cooling the molten resin is to cast the molten resin from a die onto a rotating drum and rapidly cool and solidify it to obtain a substantially unoriented resin sheet.

[0037] The unstretched film thus obtained can be stretched in the width direction under predetermined conditions to obtain the heat-shrinkable polyester film of the present invention. Preferred stretching methods for obtaining the heat-shrinkable polyester film of the present invention are described below.

[0038] Ordinary heat-shrinkable polyester films are produced by stretching an unstretched film in the direction of desired shrinkage. In the present invention, the film is biaxially stretched within the range of stretch ratios described below, since stretching in the longitudinal direction also increases the production speed and improves productivity.

[0039] Longitudinal stretching is preferably performed using rolls with different speeds, using a roll stretching method. The rolls are preheated with a surface temperature between Tg and Tg + 20°C, and stretched at a ratio of 1.1 to 1.3. Surface temperatures below Tg are not preferred because the stretching stress increases and the film breaks. Temperatures higher than Tg + 20°C are also not preferred because the film sticks to the roll, causing scratches. The roll surface temperature is preferably between Tg + 3°C and Tg + 17°C, and particularly preferably between Tg + 5°C and Tg + 15°C. A stretching ratio of less than 1.1 times is not preferred because the improvement in productivity is small. It is preferably 1.15 times or more, and 1.2 times or more is particularly preferred. A longitudinal stretching ratio of more than 1.3 times is not preferred because the shrinkage rate in the longitudinal direction increases. It is preferably 1.28 times or less, and 1.25 times or less is particularly preferred.

[0040] For widthwise stretching, the film stretched in the longitudinal direction is introduced into a tenter device that can heat the film by holding both ends of the film with clips, and the film is heated to a predetermined temperature with hot air.The film is then stretched by widening the distance between the clips while being transported in the longitudinal direction. The preheating temperature of the longitudinally stretched film is preferably Tg+30°C or more and Tg+80°C or less. A preheating temperature lower than Tg+30°C is undesirable because the preheating temperature is insufficient, resulting in high stretching force and increased susceptibility to breakage. Heating at a temperature higher than Tg+80°C is also undesirable because the stretching force in the width direction of the unstretched sheet decreases, resulting in poor thickness accuracy (thickness deviation) in the width direction. A more preferable temperature is Tg+40°C or more and Tg+70°C or less.

[0041] The film temperature during width direction stretching is preferably Tg+5°C or more and Tg+30°C or less. If the film temperature is less than Tg+5°C, the stretching force becomes too high, which is undesirable as the film is prone to breakage. If the film temperature exceeds Tg+30°C, the stretching force is too low, which is undesirable as the heat shrinkage in the width direction measured at 90°C as described above decreases. A more preferable temperature is Tg+8°C or more and Tg+25°C or less.

[0042] The stretching ratio in the width direction is preferably 3.4 times or more and 5 times or less. If the stretching ratio is less than 3.4 times, the stretching force will be insufficient, resulting in poor thickness accuracy in the width direction of the film (so-called uneven thickness). Furthermore, if the stretching ratio exceeds 5 times, the risk of breakage during film production increases and the equipment becomes long and bulky, which is undesirable. A more preferable range is 3.5 times or more and 4.8 times or less. Furthermore, although not particularly limited, heat treatment may be performed after stretching in the width direction to adjust the shrinkage rate.

[0043] When stretching in the width direction, it is desirable to stretch in two or more stages. In the present invention, a crystalline polyester raw material is weakly stretched in the longitudinal direction, and then the film is stretched in the width direction. It is common for the molecules of a film to be oriented in the stretching direction, resulting in reduced molecular orientation in the direction perpendicular to the stretching direction. Therefore, by initially stretching in the width direction at a low stretch ratio of 1.2 to 1.7 times, the molecular orientation in the longitudinal direction of the film can be reduced, thereby reducing the thermal shrinkage in the longitudinal direction. Furthermore, after the first-stage stretching in the width direction, relaxation in the width direction at a ratio of 5% to 20% in the width direction (so-called TD relaxation) in a tenter apparatus also relaxes the molecules in the longitudinal direction, thereby effectively reducing the thermal shrinkage in the longitudinal direction. It is preferable to stretch the film to a fixed length in the tenter apparatus after relaxation in the width direction, and then perform the second-stage stretching at a ratio of 2 to 4.2 times. After the second stage of stretching, it is preferable to heat treat the film in a tenter at a temperature above the stretching temperature and not higher than the stretching temperature +18°C. If the heat treatment temperature is lower than the stretching temperature, the purpose of the heat treatment step, which is to relax the molecular chains, will not be achieved. Furthermore, if the heat treatment temperature is higher than the stretching temperature +18°C, the heat shrinkage rate will decrease, making it undesirable as a heat-shrinkable film. More preferably, it is between the stretching temperature +1°C and the stretching temperature +15°C. [Example]

[0044] The present invention will be described in more detail below using examples, but the present invention is not limited to the embodiments of these examples and can be modified as appropriate within the scope of the invention.

[0045] The film was evaluated as follows.

[0046] [Intrinsic viscosity (IV)] 0.2 g of polyester was dissolved in 50 ml of a mixed solvent of phenol / 1,1,2,2-tetrachloroethane (60 / 40 (weight ratio)), and the viscosity was measured using an Ostwald viscometer at 30° C. The unit is dl / g.

[0047] [Composition analysis] Each sample was dissolved in a 10:1 (volume ratio) mixture of chloroform D (Eurisop) and trifluoroacetic acid D1 (Eurisop) to prepare a sample solution. The sample solution was then subjected to NMR measurement of protons using a GEMINI-200 NMR spectrometer (Varian) at 23°C and 64 cycles of accumulation. The peak intensity of a given proton was calculated, and the amount of the component in 100 mol% of the diacid component and the amount of the component in 100 mol% of the polyhydric alcohol component were measured.

[0048] [Heat shrinkage rate (hot water heat shrinkage rate)] The film was cut into a 10 cm x 10 cm square and immersed in warm water of a specified temperature ±0.5°C for 10 seconds without load to allow it to shrink, then immersed in water at 25°C ±0.5°C for 10 seconds and removed from the water, measuring the longitudinal and transverse dimensions of the film, and calculating the thermal shrinkage rate according to the following formula (1). The direction with the largest thermal shrinkage rate was defined as the main shrinkage direction. Heat shrinkage rate = {(length before shrinkage - length after shrinkage) / length before shrinkage} x 100 (%) Formula 1

[0049] [Tg (glass transition temperature)] Tg was determined according to JIS-K7121-1987 using a differential scanning calorimeter (model: DSC220) manufactured by Seiko Instruments Inc. Specifically, 10 mg of unstretched film was heated from -40°C to 120°C at a heating rate of 10°C / min, and an endothermic curve was measured. Tangent lines were drawn before and after the inflection point of the obtained endothermic curve, and the intersection point was defined as the glass transition point (Tg; °C).

[0050] [Endothermic peak temperature] [Endothermic amount] The DSC was measured using a differential scanning calorimeter (model: DSC220) manufactured by Seiko Electronics Co., Ltd., in accordance with JIS-K7121-1987. Five milligrams of the film after film formation was placed in a sample pan, the pan was covered, and the temperature was increased to 300°C at a heating rate of 10°C / min under a nitrogen gas atmosphere. After the temperature increase, the sample was held at 300°C for 2 minutes. The sample pan was then removed and rapidly cooled with liquid nitrogen. The rapidly cooled sample was returned to room temperature and again heated from 30°C to 300°C at a heating rate of 10°C / min using a differential scanning calorimeter, and DSC was measured. The endothermic peak at which the sample melted was taken as the endothermic peak temperature. The endothermic amount of melting was calculated from the endothermic peak area. If no melting peak was observed, the melting peak temperature was recorded as zero, and the endothermic amount was recorded as zero.

[0051] [Heat output] The calorific value was determined according to JIS-K7121-1987 using a differential scanning calorimeter (model: DSC220) manufactured by Seiko Electronics Co., Ltd. 5 mg of the film after film formation was placed in a sample pan, the pan was covered, and the temperature was increased to 300°C at a heating rate of 10°C / min under a nitrogen gas atmosphere. After the temperature increase, the sample was held at 300°C for 2 minutes. The sample pan was then removed and rapidly cooled with liquid nitrogen. The rapidly cooled sample was returned to room temperature and again heated from 30°C to 300°C at a heating rate of 10°C / min using a differential scanning calorimeter, and DSC was measured. The calorific value was determined from the area of ​​the exothermic peak where the sample generated heat. If there was no exothermic peak, the exothermic peak temperature was absent and the calorific value was recorded as 0.

[0052] [Film thickness] Measurement was carried out using a dial gauge in accordance with JIS K7130-1999 Method A.

[0053] [Film Density] The density of a sample approximately 3 mm square was measured using a calcium nitrate aqueous solution according to the density gradient tube method of JIS-K-7112.

[0054] [Film Haze] According to JIS K7361-1, the film was cut into a square with a side length of 10 cm, and the haze was measured using a haze meter NDH2000 manufactured by Nippon Denshoku Co., Ltd. Measurements were taken at three locations, and the average value was used as the actual haze measurement value, and the haze converted to 20 μm was calculated using the following formula (2): Haze = measured haze value x 20 / film thickness (% / 20μm) Formula 2

[0055] [Shrinkage finish] The edges of the heat-shrinkable film were welded using an impulse sealer (manufactured by Fuji Impulse Co., Ltd.) to obtain a cylindrical label with the width direction as the circumferential direction. The diameter of the label in the shrinking direction was 68 mm. This label was placed on a commercially available 500 ml PET bottle (filled; body diameter 62 mm, minimum neck diameter 25 mm) and heat-shrunk by passing it through steam using a Fuji Astec Inc. steam tunnel (model: SH-1500-L) adjusted to 90°C (tunnel passage time: 5 seconds). The shrinkage finish of the label was visually evaluated according to the following criteria. A 5-point scale was used visually according to the following criteria. The defects described below include jumping, wrinkles, insufficient shrinkage, label edge folding, and shrinkage whitening. A score of 3 or higher was considered acceptable. 5: Best finish (no defects) 4: Good finish (one defect) 3: There are two flaws 2: 3 to 5 defects 1: Many defects (6 or more)

[0056] [Variation in recycled PET resin] The contents of the 500 ml PET bottles that had been evaluated for shrinkage finish were removed and washed with water. The PET bottles and labels were then crushed into pieces 8 to 10 mm in size using a crusher (Fujitex Co., Ltd., Model 48) to produce fluff. The resulting fluff was melted at 280°C in a pelletizer (Nihon Yuki SRH-V55 / 48) and pellets were produced at a rate of 120 kg per hour for 30 minutes to produce recycled PET resin. The recycled PET resin was then cut to a length of 3±0.8 mm (2.2-3.8 mm) and a particle weight of 30±10 mg / piece (20-40 mg / piece). Five, 15, and 25 minutes after the start of granulation, 300 particles of recycled PET resin were sampled (a total of 900 particles) and their size was measured. Evaluation was performed using the following method, with a "good" indicating a pass. Good: Resin of the wrong size (length, particle weight) accounts for less than 10% of the total, and there are no problems during granulation due to pulsation, etc. △: Resin of the wrong size (length, particle weight) accounts for less than 30% of the total, and problems during granulation due to pulsation, etc., occurred less than twice. ×: Resin that is out of size (length, particle weight) is more than 30% of the total, and problems during granulation due to pulsation, etc. have occurred three or more times.

[0057] <Preparation of polyester raw materials> [Synthesis Example 1] A stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser was charged with 100 mol% dimethyl terephthalate (DMT) as the dicarboxylic acid component and 100 mol% ethylene glycol (EG) as the polyhydric alcohol component, with the ethylene glycol being 2.2 times the molar ratio of dimethyl terephthalate. 0.05 mol% (relative to the acid component) zinc acetate was added as a transesterification catalyst, and 0.225 mol% (relative to the acid component) antimony trioxide was added as a polycondensation catalyst. The resulting methanol was distilled off while the transesterification reaction was carried out. Polycondensation was then carried out at 280°C under reduced pressure of 26.7 Pa, yielding Polyester A with an intrinsic viscosity of 0.75 dL / g. The composition is shown in Table 1.

[0058] [Synthesis Examples 2 to 5] Polyesters B to D shown in Table 1 were obtained in the same manner as in Synthesis Example 1. When producing polyester B, SiO2 (Sylysia 266 manufactured by Fuji Silysia Ltd.; average particle size 3 μm) was added as a lubricant at a ratio of 20,000 ppm relative to the polyester. The intrinsic viscosity of the polyesters was all 0.75 dL / g. Each polyester was appropriately cut into chips. The composition of each polyester is shown in Table 1.

[0059] [Table 1]

[0060] [Example 1] The above-mentioned polyester A, polyester B, and polyester C were mixed in a weight ratio of 67:3:30 and charged into an extruder. The mixed resin was then melted at 273°C using a four-screw, extruded through a T-die while cooling to 260°C, and quenched by being wound around a rotating metal roll cooled to a surface temperature of 20°C, to obtain an unstretched film with a thickness of 201 μm. The Tg of the unstretched film was 65°C. The unstretched film was introduced into a longitudinal stretching machine, preheated with rolls having a surface temperature of Tg+10°C (75°C), and stretched 1.2 times in the longitudinal (machine) direction using the speed difference between the rolls. The uniaxially stretched film in the machine direction was introduced into a tenter, and while both ends of the film were held with clips, the film was preheated until the film temperature reached Tg+45°C (110°C). The film was then stretched 1.5 times in the transverse direction in the first stage at Tg+10°C (75°C), and then relaxed 10% in the width direction at Tg+10°C (75°C). After relaxation in the width direction, the film was stretched 3.1 times (total stretch ratio of 4.2 times) in the second stage at Tg+10°C (75°C). The film after stretching in the width direction was heat-set at Tg+12°C (77°C). After stretching, both edges of the film were cut and removed to continuously produce a biaxially stretched film of approximately 40 μm over a predetermined length, yielding a film roll made of heat-shrinkable polyester film. The properties of the resulting film were evaluated using the methods described above. The film-forming conditions are shown in Table 2, and the evaluation results are shown in Table 3. The film had no practical problems with shrinkage finish or variations in recycled PET.

[0061] [Example 2] Polyester A, polyester B, and polyester C were mixed in a weight ratio of 77:3:20 and charged into an extruder to obtain an unstretched film having a thickness of 201 μm in the same manner as in Example 1. The Tg of the unstretched film was 70°C. The unstretched film was stretched in the same manner as in Example 1 to obtain a film roll made of a heat-shrinkable polyester film with a thickness of 40 μm. However, since the Tg was different from that in Example 1, the temperature conditions for stretching were changed to Tg+10°C (80°C), Tg+45°C (115°C), and Tg+12°C (82°C). The properties of the obtained film were evaluated using the methods described above. The film formation conditions are shown in Table 2, and the evaluation results are shown in Table 3. The film had no practical problems with shrinkage finish or variations in recycled PET.

[0062] [Example 3] Polyester A, polyester B, and polyester C were mixed in a weight ratio of 92:3:5 and charged into an extruder to obtain an unstretched film having a thickness of 201 μm in the same manner as in Example 1. The Tg of the unstretched film was 74°C. The unstretched film was stretched in the same manner as in Example 1 to obtain a film roll made of a heat-shrinkable polyester film with a thickness of 40 μm. However, since the Tg differed from that in Example 1, the temperature conditions for stretching were changed to Tg+10°C (84°C), Tg+45°C (119°C), and Tg+12°C (86°C). The properties of the obtained film were evaluated using the methods described above. The film formation conditions are shown in Table 2, and the evaluation results are shown in Table 3. The film had no practical problems with shrinkage finish or variations in recycled PET.

[0063] [Example 4] Polyester A, polyester B, polyester C, and polyester D were mixed in a weight ratio of 52:3:5:40 and charged into an extruder to obtain an unstretched film having a thickness of 201 μm in the same manner as in Example 1. The Tg of the unstretched film was 74°C. The unstretched film was stretched in the same manner as in Example 1 to obtain a film roll made of a heat-shrinkable polyester film with a thickness of 40 μm. However, since the Tg differed from that in Example 1, the temperature conditions for stretching were changed to Tg+10°C (84°C), Tg+45°C (119°C), and Tg+12°C (86°C). The properties of the obtained film were evaluated using the methods described above. The film formation conditions are shown in Table 2, and the evaluation results are shown in Table 3. The film had no practical problems with shrinkage finish or variations in recycled PET.

[0064] [Example 5] Polyester A, polyester B, polyester C, and polyester D were mixed in a weight ratio of 57:3:30:10 and charged into an extruder to obtain an unstretched film having a thickness of 201 μm in the same manner as in Example 1. The Tg of the unstretched film was 65° C. The unstretched film was stretched in the same manner as in Example 1 to obtain a film roll made of a heat-shrinkable polyester film having a thickness of 40 μm. The film formation conditions are shown in Table 2, and the evaluation results are shown in Table 3. The film had no practical problems with shrinkage finish or variations in recycled PET.

[0065] [Example 6] Polyester A, polyester B, polyester C, and polyester D were mixed in a weight ratio of 67:3:20:10 and charged into an extruder to obtain an unstretched film having a thickness of 201 μm in the same manner as in Example 1. The Tg of the unstretched film was 70°C. The unstretched film was stretched in the same manner as in Example 1 to obtain a film roll made of a heat-shrinkable polyester film with a thickness of 40 μm. However, since the Tg was different from that in Example 1, the temperature conditions for stretching were changed to Tg+10°C (80°C), Tg+45°C (115°C), and Tg+12°C (82°C). The properties of the obtained film were evaluated using the methods described above. The film formation conditions are shown in Table 2, and the evaluation results are shown in Table 3. The film had no practical problems with shrinkage finish or variations in recycled PET.

[0066] [Comparative Example 1] The above-mentioned polyester A, polyester B, and polyester C were mixed in a weight ratio of 47:3:50 and charged into an extruder. The mixed resin was then melted at 273°C using a four-screw, extruded through a T-die while cooling to 260°C, and quenched by being wound around a rotating metal roll cooled to a surface temperature of 20°C, to obtain an unstretched film with a thickness of 201 μm. The Tg of the unstretched film was 58°C. The unstretched film was introduced into a longitudinal stretching machine, preheated with rolls having a surface temperature of Tg+10°C (68°C), and stretched 1.2 times in the longitudinal (machine) direction using the speed difference between the rolls. The uniaxially stretched film in the machine direction was introduced into a tenter, and while both ends of the film were held with clips, the film was preheated until the film temperature reached Tg+45°C (103°C). The film was then stretched 1.5 times in the transverse direction in the first stage at Tg+10°C (68°C), and then relaxed 10% in the width direction at Tg+10°C (68°C). After relaxation in the width direction, the film was stretched 3.1 times (total stretch ratio of 4.2 times) in the second stage at Tg+10°C (68°C). The film after stretching in the width direction was heat-set at Tg+12°C (70°C). After stretching, both edges of the film were cut and removed to continuously produce a biaxially stretched film of approximately 40 μm over a predetermined length, yielding a film roll made of heat-shrinkable polyester film. The properties of the resulting film were evaluated using the methods described above. The film-forming conditions are shown in Table 2, and the evaluation results are shown in Table 3. The shrinkage finish was a film that had no practical problems, but the recycled PET resin mixed with PET bottles had a large variation in size, and there was one defect that occurred during granulation due to pulsation.

[0067] Comparative Example 2 Polyester B, polyester C, and polyester D were mixed in a weight ratio of 3:7:90 and charged into an extruder to obtain an unstretched film having a thickness of 201 μm in the same manner as in Example 1. The Tg of the unstretched film was 73°C. The unstretched film was stretched in the same manner as in Example 1 to obtain a film roll made of a heat-shrinkable polyester film with a thickness of 40 μm. However, since the Tg was different from that in Example 1, the temperature conditions for stretching were changed to Tg + 10°C (83°C), Tg + 45°C (118°C), and Tg + 12°C (85°C). The properties of the obtained film were evaluated using the methods described above. The film formation conditions are shown in Table 2, and the evaluation results are shown in Table 3. The shrinkage finish was a film that had no practical problems, but the recycled PET resin mixed with PET bottles had a large variation in size, and there were two defects that occurred during granulation due to pulsation.

[0068] Comparative Example 3 Polyester A, polyester B, polyester C, and polyester E were mixed in a weight ratio of 12:3:5:80 and charged into an extruder to obtain an unstretched film having a thickness of 201 μm in the same manner as in Example 1. The Tg of the unstretched film was 74°C. The unstretched film was stretched in the same manner as in Example 1 to obtain a film roll made of a heat-shrinkable polyester film with a thickness of 40 μm. However, since the Tg was different from that in Example 1, the temperature conditions for stretching were changed to Tg + 10°C (83°C), Tg + 45°C (118°C), and Tg + 12°C (85°C). The properties of the obtained film were evaluated using the methods described above. The film formation conditions are shown in Table 2, and the evaluation results are shown in Table 3. The film had good shrinkage finish, but the recycled PET resin mixed with PET bottles had a large variation in size, and there were repeated defects due to problems during granulation caused by pulsation.

[0069] [Table 2A]

[0070] [Table 2B]

[0071] [Table 3] [Industrial Applicability]

[0072] The heat-shrinkable polyester film of the present invention has a high heat shrinkage rate, but the raw material components used are similar to those used in PET beverage bottles. Therefore, even if the heat-shrinkable polyester film used as a label is mixed in during the process of recycling PET bottles to produce recycled PET resin, recycled PET resin can be produced with stable quality.

Claims

1. A heat-shrinkable polyester film containing 95 mol% to 100 mol% of dicarboxylic acid and 0 mol% to 5 mol% of isophthalic acid, based on 100 mol% of dicarboxylic acid components, and containing 85 mol% to 98 mol% of ethylene terephthalate units, based on 100 mol% of all ester units, and containing 2 mol% to 15 mol% of diethylene glycol, based on 100 mol% of polyhydric alcohol components, wherein the heat-shrinkable polyester film satisfies the following requirements (1) to (5): (1) When the film is immersed in 90°C hot water for 10 seconds, the hot water shrinkage rate is 40% or more and 70% or less in the film width direction. (2) When the film is immersed in 90°C hot water for 10 seconds, the hot water shrinkage rate is between -5% and 15% in the longitudinal direction of the film. (3) Using a differential scanning calorimeter (DSC), the film is heated to 300°C, melted, then rapidly cooled, and heated again to 300°C. The endothermic peak temperature due to melting is 245°C or higher and 260°C or lower. (4) Film thickness is 15 μm or more and 50 μm or less (5) Using a differential scanning calorimeter (DSC), the film is heated to 300°C, melted, then rapidly cooled, and heated again to 300°C, and the endothermic heat due to melting is 10 mJ / mg or more.

2. The density of the film is 1.33 g / cm ３ 1.39g / cm or more ３ 2. The heat-shrinkable polyester film according to claim 1, wherein the heat-shrinkable polyester film is:

3. 3. The heat-shrinkable polyester film according to claim 1, wherein the haze at a film thickness of 20 μm is 2% or more and 10% or less.

4. A heat-shrinkable label using the heat-shrinkable polyester film according to any one of claims 1 to 3.

5. A method for producing a package, comprising covering at least a part of the outer periphery of an object to be packaged with the heat-shrinkable label according to claim 4 and then heat-shrinking the object.

6. 4. The heat-shrinkable polyester film according to claim 1, which is used for a heat-shrinkable label and then used as a recycled PET bottle material.

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