Heat-shrinkable polyester film

Abstract

To provide a heat-shrinkable polyester film having sufficient shrinkability, low shrinkage stress and high solvent adhesive strength even if a PET bottle recycled raw material is contained.SOLUTION: A heat-shrinkable polyester-based film comprising a polyester containing 5% by mass or more and 50% by mass or less of a PET bottle recycled raw material and containing an isophthalic acid component, wherein the heat-shrinkable polyester-based film satisfies the following requirements (1) to (5): (1) a shrinkage ratio in the main shrinkage direction of the film when immersed in hot water at 98 °C for 10 seconds is 50% or more, (2) a maximum shrinkage stress in the main shrinkage direction of the film measured in hot air at 90 °C is 3MPa or more and 15MPa or less, (3) a sample obtained by melting the film once and rapidly cooling the film is subjected to: A melting calorie Δ Hm measured by a differential scanning calorimeter (DSC) is 0J / g or more and 32J / g or less, (4) a solvent-bonding strength of the film when 1, 3-dioxolane is used as a bonding solution is 2. 9N / 15mm or more, and (5) an intrinsic viscosity of the film is 0. 59dl / g or more and 0. 75dl / g or less SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a heat-shrinkable polyester film that uses recycled PET bottle materials and yet has high shrinkage, low shrinkage stress, excellent solvent adhesion, and little occurrence of defects such as insufficient shrinkage, uneven shrinkage, distortion, and longitudinal shrinkage during use. [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 low heat resistance, generating hydrogen chloride gas when incinerated, and being a source of dioxins. 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 has tended to increase with the increase in the distribution volume of PET containers (PET bottles).

[0003] However, the dramatic increase in the use of PET bottles has made waste problems and resource conservation social issues. As one of the countermeasures, there is a growing movement to collect used PET bottles and reuse them as resources (recycling). Recycling technologies include mechanical recycling, chemical recycling, and thermal recycling, but mechanical recycling is the most widespread method, in which used containers are sorted, crushed, and washed, and then re-formed into resin chips in an extruder. These are then processed into PET bottles or fibers or films for reuse.

[0004] Heat-shrinkable polyester film labels can also contribute to the life cycle of PET, from production, use, to disposal, by using some of the recycled PET bottle materials as described above, thereby contributing to reducing the environmental impact.

[0005] Although many details of the molecular structure that governs the shrinkage behavior of films remain unclear, it is believed that oriented amorphous molecules are involved in the shrinkage characteristics. In the unstretched melt-molded film state, the molecular chains are not oriented (random coil state), but upon stretching, the molecular chains become aligned and oriented mainly in the direction of stretching. When heat above the glass transition temperature is applied, some of the oriented amorphous molecular chains become mobile, and they act to return to their original random coil state, causing the entire film to shrink. In other words, the polyester that makes up the heat-shrinkable polyester film must be highly amorphous, or in other words, have low crystallinity. It is known that when the polyester has high crystallinity, oriented crystallization occurs when stretched, but the crystallized molecular chains do not move even when heat is applied, which inhibits heat shrinkage.

[0006] On the other hand, there is a demand for labels to cover most of the container to protect the contents and improve design. Furthermore, container shapes are becoming more diverse among manufacturers to improve design and differentiate products. Therefore, the heat-shrinkable film used for labels must have a high shrinkage rate.

[0007] However, the polyester raw material used in beverage bottles is highly crystalline to ensure the thermal stability of the container, and recycled PET bottle raw material is also a crystalline raw material, so when used in heat-shrinkable film, it is difficult to achieve a high shrinkage rate due to its crystallinity.

[0008] 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 produce a wide master roll. The master roll is then slit to the desired width and wound into a roll of the desired length to produce a film roll product. The roll is then printed in its original form to impart a design to the film or to display the product. After printing, the film is re-slit to the required width and wound into a roll. It then undergoes a center-sealing process using solvent bonding, is made into a tubular bag, and is wound into a roll (to produce a label roll).

[0009] 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 packaged item by hand or other methods, and passed through a steam tunnel or hot air tunnel to shrink and become a label.

[0010] If the shrinkage stress of a heat-shrinkable polyester film is too high during shrinkage, peeling may occur at the adhesive joint of the tube, significantly deteriorating the appearance and possibly impairing the function of protecting the packaged items. Furthermore, if the solvent adhesive strength of the center seal is low, peeling may also occur at the adhesive joint due to shrinkage. Peeling at the adhesive joint is thought to occur when the adhesive strength is weaker than the shrinkage stress, and it is ideal for the shrinkage stress to be low and the solvent adhesive strength to be high. If the raw material constituting the heat-shrinkable polyester film is highly crystalline, the stretching stress increases due to oriented crystallization caused by stretching, resulting in high shrinkage stress. Also, if the film is highly crystalline, the polymer molecular chains are less likely to swell in solvents, resulting in low solvent adhesion strength. The increased crystallinity caused by blending recycled PET bottle materials is an inhibitor of low shrinkage stress and strong adhesion.

[0011] Patent Document 1 describes a method for reducing the crystallinity of recycled PET bottle raw materials by adding an amorphous copolymer component. However, Patent Document 1 does not provide any specific indicators for crystallinity. Furthermore, the present inventors have found that when two or more raw materials are dry-blended and fed into an extruder, a random copolymerization state is not achieved, the crystallinity is not sufficiently reduced, and the required shrinkability cannot be obtained when the material is made into a heat-shrinkable film, resulting in high shrinkage stress and poor solvent adhesion. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Patent No. 5320737 Summary of the Invention [Problem to be solved by the invention]

[0013] An object of the present invention is to provide a heat-shrinkable polyester film that has sufficient shrinkability, low shrinkage stress, and high solvent adhesive strength even when it contains recycled PET bottle raw materials. [Means for solving the problem]

[0014] The present inventors have conducted extensive research to solve the above problems and have completed the present invention, which comprises the following features. 1. A heat-shrinkable polyester film that contains 5% by mass or more and 50% by mass or less of recycled PET bottle raw materials and is made of a polyester containing an isophthalic acid component, and that satisfies the following requirements (1) to (5): (1) The shrinkage rate in the main shrinkage direction of the film when immersed in 98°C hot water for 10 seconds is 50% or more. (2) The maximum shrinkage stress in the main shrinkage direction of the film measured in 90°C hot air is 3 MPa or more and 15 MPa or less. (3) The heat of fusion ΔHm measured by a differential scanning calorimeter (DSC) after the film is melted and then rapidly cooled is between 0 J / g and 32 J / g. (4) When 1,3-dioxolane is used as an adhesive solvent, the film has a solvent adhesive strength of 2.9 N / 15 mm or more. (5) The intrinsic viscosity of the film is 0.59 dl / g or more and 0.75 dl / g or less.

[0015] 2. A heat-shrinkable polyester film according to 1, characterized in that when a sample of the film is melted and then rapidly cooled and subjected to reverse heat flow measurement by temperature-modulated DSC, the change in specific heat capacity ΔCp before and after the glass transition is 0.20 J / (g·°C) or more and 0.35 J / (g·°C) or less. 3. The heat-shrinkable polyester film according to any one of 1. and 2., wherein the tensile elongation at break in the direction perpendicular to the main shrinkage direction of the film is 40% or more. 4. A heat-shrinkable polyester film according to any one of 1. to 3., characterized in that the polyester constituting the film has an isophthalic acid content of 0.1 mol % or more and 3.0 mol % or less in 100 mol % of all acid components. 5. The heat-shrinkable polyester film according to any one of 1. to 4., wherein the polyester constituting the heat-shrinkable polyester film is composed mainly of ethylene terephthalate.

[0016] 6. A heat-shrinkable label using the heat-shrinkable polyester film described in any one of 1. to 5. 7. A package in which the heat-shrinkable label described in 6. above covers at least a portion of the outer periphery of the object to be packaged. DETAILED DESCRIPTION OF THE INVENTION

[0017] The heat-shrinkable polyester film of the present invention is a heat-shrinkable polyester film that contains 5% by mass or more and 50% by mass or less of recycled PET bottle raw materials and is composed of a polyester containing an isophthalic acid component, and is characterized by satisfying the following requirements (1) to (5): (1) The shrinkage rate in the main shrinkage direction of the film when immersed in 98°C hot water for 10 seconds is 50% or more. (2) The maximum shrinkage stress in the main shrinkage direction of the film measured in 90°C hot air is 3 MPa or more and 15 MPa or less. (3) The heat of fusion ΔHm measured by a differential scanning calorimeter (DSC) after the film is melted and then rapidly cooled is between 0 J / g and 32 J / g. (4) When 1,3-dioxolane is used as an adhesive solvent, the film has a solvent adhesive strength of 2.9 N / 15 mm or more. (5) The intrinsic viscosity of the film is 0.59 dl / g or more and 0.75 dl / g or less.

[0018] The polyester constituting the heat-shrinkable polyester film of the present invention is a polyester mainly composed of ethylene terephthalate. That is, the polyester contains 50 mol % or more, preferably 60 mol % or more, of ethylene terephthalate relative to 100 mol % of all constituent components. Examples of dicarboxylic acid components other than terephthalic acid and isophthalic acid constituting the polyester of the present invention include aromatic dicarboxylic acids such as naphthalenedicarboxylic acid and orthophthalic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and decanedicarboxylic acid, and alicyclic dicarboxylic acids.

[0019] When an aliphatic dicarboxylic acid (such as adipic acid, sebacic acid, or decanedicarboxylic acid) is contained, the content is preferably less than 3 mol %. Heat-shrinkable polyester films obtained using polyesters containing 3 mol % or more of these aliphatic dicarboxylic acids are undesirable because they have insufficient film stiffness and cause problems during slitting and post-processing.

[0020] It is also preferable not to include trivalent or higher polycarboxylic acids (for example, trimellitic acid, pyromellitic acid, and anhydrides thereof), as heat-shrinkable polyester films obtained using polyesters containing these polycarboxylic acids will have difficulty achieving the required high shrinkage ratio.

[0021] Examples of diol components other than ethylene glycol that constitute the polyester used in the present invention include aliphatic diols such as 1,3-propanediol, 1,4-butanediol, neopentyl glycol, and hexanediol; alicyclic diols such as 1,4-cyclohexanedimethanol and diethylene glycol; and aromatic diols such as bisphenol A.

[0022] The polyester used in the heat-shrinkable polyester film of the present invention is preferably a polyester whose glass transition temperature (Tg) is adjusted to 60 to 80°C by containing one or more cyclic diols such as 1,4-cyclohexanedimethanol or diols having 3 to 6 carbon atoms (for example, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, hexanediol, diethylene glycol, etc.).

[0023] The polyester used in the heat-shrinkable polyester film of the present invention preferably contains one or more amorphous monomer components in 100 mol % of the polyhydric alcohol component or 100 mol % of the polycarboxylic acid component in the entire polyester resin, in total, of 8 mol % or more, more preferably 10 mol % or more, and particularly preferably 13 mol % or more. The total of the amorphous monomer components is preferably 45 mol % or less, more preferably 40 mol % or less, and particularly preferably 35 mol % or less. Examples of monomers that can become amorphous components include neopentyl glycol, 1,4-cyclohexanedimethanol, diethylene glycol, 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, 1,4-butanediol, and hexanediol. Of these, neopentyl glycol, diethylene glycol, 1,4-cyclohexanedimethanol, and isophthalic acid are preferably used.

[0024] The polyester used in the heat-shrinkable polyester film of the present invention preferably does not contain a diol having 8 or more carbon atoms (e.g., octanediol, etc.) or a polyhydric alcohol having a valence of 3 or more (e.g., trimethylolpropane, trimethylolethane, glycerin, diglycerin, etc.). A heat-shrinkable polyester film obtained using a polyester containing such a diol or polyhydric alcohol will have difficulty achieving the required high shrinkage percentage.

[0025] In addition, various additives, such as waxes, antioxidants, antistatic agents, crystal nucleating agents, viscosity reducers, heat stabilizers, coloring pigments, color inhibitors, and UV absorbers, can be added to the resin forming the heat-shrinkable polyester film of the present invention as needed. 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 polyethylene terephthalate resin film. Any fine particles can be selected, but examples of inorganic fine particles include silica, alumina, titanium dioxide, calcium carbonate, kaolin, and barium sulfate. 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 selected appropriately within the range of 0.05 to 3.0 μm (as measured with a Coulter counter) as needed. The amount of fine particles added is within the range of 300 to 1,200 ppm in the film, which allows for both good slipperiness (friction) and transparency.

[0026] The method of incorporating the particles into the resin that forms the heat-shrinkable polyester film includes adding the particles at any stage in the production of the polyester resin, but it is preferable to add the particles 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. It is also preferable to use a vented kneading extruder to blend a slurry of the particles dispersed in ethylene glycol or water with the polyester resin raw material, or a kneading extruder to blend dried particles with the polyester resin raw material.

[0027] Furthermore, the heat-shrinkable polyester film of the present invention may be subjected to corona treatment, coating treatment, flame treatment, or the like in order to improve the adhesiveness of the film surface.

[0028] The heat-shrinkable polyester film of the present invention contains 5% to 50% by mass of recycled PET bottle raw materials. While polyesters used in PET bottles contain a few percent of isophthalic acid as a dicarboxylic acid component to improve moldability, the other components are terephthalic acid, and most of the diol components are ethylene glycol. In other words, the film is made up of crystalline raw materials, and the recycled raw materials (recycled PET bottle raw materials) are also crystalline. As a method for reducing the crystallinity of the polyester that constitutes the heat-shrinkable polyester film containing recycled PET bottle material, a method of blending with a highly amorphous polyester material is adopted. The highly amorphous material is a material containing a monomer component that can become the above-mentioned amorphous component. By blending the recycled PET bottle material with the highly amorphous material, the amount of the monomer component that can become the above-mentioned preferred amorphous component is adjusted. The preferred range of the content of recycled PET bottle raw materials is 5% by mass or more and 50% by mass. If the content is less than 5% by mass, the contribution to reducing the environmental load is extremely small. If more than 50% by mass is used, the amorphousness of the raw materials other than the recycled PET bottle raw materials must be extremely high, which is uneconomical as it increases the polymerization time of the raw materials. The heat-shrinkable polyester film of the present invention may have either a single layer structure or a laminate structure of two or more layers, but it is preferable that each layer constituting the film contains recycled PET bottle raw materials within the above content range.

[0029] When a sample of the heat-shrinkable polyester film of the present invention is melted and then rapidly cooled, the melting enthalpy (ΔHm) must be 0 J / g or more and 32 J / g or less when measured using a differential scanning calorimeter (DSC). The melting enthalpy (ΔHm) is an index showing the degree of crystallinity of all polyesters constituting the heat-shrinkable polyester film of the present invention. The melting enthalpy is the enthalpy required when crystalline components thermally crystallized by heating in a DSC device melt. A larger value can be interpreted as meaning that there are more components that are easily crystallized, and it is thought that crystallization due to stretching during film formation or heat treatment is more likely to occur. A smaller melting enthalpy is preferred because it results in higher amorphousness, making it easier to achieve a high shrinkage rate in the heat-shrinkable polyester film, lower shrinkage stress, and higher solvent adhesion strength. If the melting enthalpy exceeds 32 J / g, the crystallinity is too high, so stretching crystallization or crystallization due to heat treatment is likely to occur, and sufficient shrinkage cannot be obtained. In addition, the stretching stress increases, which leads to high shrinkage stress and low solvent adhesion strength. The lower the melting enthalpy, the better, with 0 J / g being the lower limit (no melting peak). A more preferable range is 0 J / g or more and 30 J / g or less, an even more preferable range is 0 J / g or more and 27 J / g or less, and an especially preferable range is 0 J / g or more and 24 J / g or less.

[0030] Mixing highly amorphous polyester raw materials with crystalline recycled PET bottle raw materials reduces the crystallinity, which in turn reduces the melting enthalpy (ΔHm) mentioned above. Generally, increasing the copolymerization component of a homopolymer reduces stereoregularity and therefore crystallinity. However, this effect becomes more pronounced when the polyester monomer components undergo transesterification to form a random copolymer. If the copolymerization component is simply increased to reduce crystallinity, sufficient solvent adhesion strength may not be obtained if the randomization required for a random copolymerization is not sufficiently advanced. In the present invention, a crystalline raw material (recycled PET bottle raw material) is dry-blended with a highly amorphous raw material, and transesterification proceeds while melt-extruding in an extruder. If the transesterification reaction is insufficient, crystalline components remain, resulting in a high enthalpy of fusion. Methods for promoting transesterification in the extruder are described below.

[0031] 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 98°C) of 50% or more when treated in 98°C hot water for 10 seconds under no load, calculated from the lengths before and after shrinkage using the following formula 1: Heat shrinkage rate = {(length before shrinkage - length after shrinkage) / length before shrinkage} x 100 (%) Formula 1 If the hot water shrinkage rate at 98°C is less than 50%, the shrinkage amount is so small that the label after heat shrinkage will have wrinkles or will not shrink enough, making it undesirable as a heat shrinkable film. There is no upper limit to the shrinkage rate, but the upper limit is about 80%.

[0032] The heat-shrinkable polyester film of the present invention preferably has a maximum shrinkage stress in the main shrinkage direction measured under hot air at 90°C of 3 MPa or more and 15 MPa or less. The shrinkage stress is measured by the method described in the Examples. If the maximum shrinkage stress in the main shrinkage direction at 90°C exceeds 15 MPa, the label edge may lift or peel off at the bonded portion during shrinkage, or sink marks may occur in the non-shrinkage direction, deteriorating the appearance, which is undesirable. If the maximum shrinkage stress is less than 3 MPa, the label may slacken and not adhere tightly to the container when used as a label for the container, which is undesirable. Shrinkage stress is thought to be the residual force applied to the film during stretching, and is correlated with stretching stress. When highly crystalline raw materials are used, orientation crystallization is likely to occur during stretching, and stretching stress increases significantly with increasing stretching strain. It is thought that suppressing crystallinity will suppress crystallization due to stretching, reducing stretching stress and therefore shrinkage stress of the film. The shrinkage stress is more preferably in the range of 4 MPa or more and 14 MPa or less, and even more preferably in the range of 5 MPa or more and 13 MPa or less.

[0033] The heat-shrinkable polyester film of the present invention preferably has a solvent adhesive strength of 2.9 (N / 15 mm) or more when 1,3-dioxolane is used as the adhesive solvent. If the solvent adhesive strength is less than 2.9 (N / 15 mm), the solvent-adhered portion is likely to peel off due to the shrinkage force when the label is heat-shrunk, which is undesirable. The solvent adhesive strength is more preferably 3.0 (N / 15 mm) or more, particularly preferably 4.0 (N / 15 mm) or more, and most preferably 6.0 (N / 15 mm) or more. Solvent adhesion is thought to occur when the polymer chains on the film surface swell with the solvent, increasing the mobility of the molecular chains and causing the polymer chains on the surface to become entangled, resulting in adhesion. When the film is highly crystalline, the polymer chains are densely packed, making it difficult for solvent molecules to penetrate between the molecular chains, and it is thought that swelling is therefore difficult. As a result, entanglement of polymer chains on the film surface is difficult, resulting in low adhesive strength. Conversely, when the film is highly amorphous and in a random copolymer state, swelling by the solvent and entanglement of molecular chains are more likely to occur, resulting in high solvent adhesive strength.

[0034] Although a higher solvent adhesive strength is preferable, we believe that the upper limit of the solvent adhesive strength is approximately 15.0 (N / 15 mm). If the solvent adhesive strength is too high, when two films are solvent-bonded to form a label, the films are more likely to be unnecessarily bonded together, which may reduce label productivity. Therefore, a solvent adhesive strength of 10.0 (N / 15 mm) or less is acceptable for practical use.

[0035] The intrinsic viscosity of the film is preferably 0.59 dL / g or more and 0.75 dL / g or less. If the intrinsic viscosity is less than 0.59 dL / g, the strength of the film decreases and it is prone to breakage during film formation. Furthermore, the longitudinal breaking elongation of the obtained film decreases, which is undesirable because it is prone to breakage problems in subsequent processes such as printing. An intrinsic viscosity exceeding 0.75 dL / g is undesirable because the pressure during extrusion becomes too high, making the equipment prone to breakdown. It is more preferably 0.60 dL / g or more and 0.75 dL / g or less, and even more preferably 0.61 dL / g or more and 0.73 dL / g or less.

[0036] When a sample of the heat-shrinkable polyester film of the present invention is melted and then rapidly cooled, and subjected to reverse heat flow measurement using temperature-modulated DSC, the change in specific heat capacity (ΔCp) before and after the glass transition is 0.20 J / (g·°C) or more and 0.35 J / (g·°C) or less. Polyesters are divided into crystalline and amorphous phases, and the amorphous phase is further divided into rigid amorphous and mobile amorphous phases. The mobile amorphous phase is a phase in which molecular motion increases near the glass transition temperature and is thought to contribute to the shrinkage of heat-shrinkable polyester films. On the other hand, the rigid amorphous phase is an amorphous phase in which molecular motion is restricted even at the glass transition. The change in specific heat capacity (ΔCp) is considered to correspond to the mobile amorphous amount. In other words, the larger the ΔCp, the greater the mobile amorphous amount contributing to shrinkage, and the higher the heat shrinkage rate of the film. A change in specific heat capacity (ΔCp) of less than 0.2 J / (g·°C) is not preferable because the required shrinkage rate cannot be achieved. It is more preferably 0.22 J / (g·°C) or higher, and even more preferably 0.24 or higher. ΔCp can be 0.35 or higher, but because it contains crystalline recycled PET bottle raw materials, the upper limit is approximately 0.35 J / (g·°C). Note that random copolymerization contributes to an increase in the mobile amorphous content.

[0037] The polyester constituting the heat-shrinkable polyester film of the present invention has an isophthalic acid content of 0.1 mol % or more and 3.0 mol % or less, based on 100 mol % of all acid components. The crystallinity of polyesters used in PET bottles is controlled to improve the bottle appearance, and as a result, polyesters containing 6 mol % or less of isophthalic acid are generally used. In the present invention, since recycled PET bottle raw materials are contained in an amount of 50 mass % or less, the upper limit of the isophthalic acid content is preferably 3.0 mol % or less. It is more preferably 2.0 mol % or less, and even more preferably 1.0 mol % or less. The lower limit of the content of isophthalic acid is preferably 0.1 mol %, more preferably 0.3 mol %, and even more preferably 0.6 mol %. The content of isophthalic acid is measured and calculated by NMR measurement as described below.

[0038] The heat-shrinkable polyester film of the present invention has a tensile breaking elongation in a direction perpendicular to the main shrinkage direction of 40% or more. If the breaking elongation is less than 40%, the risk of breakage due to longitudinal tension in post-processing steps such as printing and label production increases, which is undesirable. It is more preferably 50% or more, even more preferably 60% or more, particularly preferably 100% or more, and most preferably 300% or more. The higher the breaking elongation, the better, but the upper limit is 900% at most.

[0039] The thickness of the film is preferably 5 μm or more and 40 μm or less. A thickness of less than 5 μm increases the risk of breakage during film production, and also reduces stiffness when made into a label, making it prone to wrinkling, which is undesirable. Although a thicker film tends to make film production more stable and improve stiffness, making it less prone to problems such as wrinkling, this is undesirable because it goes against the objective of the film of the present invention, which is environmentally friendly, and the need to reduce volume. The film thickness is more preferably 8 μm or more and 37 μm or less, and even more preferably 11 μm or more and 34 μm or less.

[0040] A preferred method for producing the heat-shrinkable polyester film of the present invention will now be described. The manufacturing process of the heat-shrinkable polyester film of the present invention includes (1) mixing and supplying raw materials, (2) melt extrusion, (3) casting the unstretched sheet, (4) transverse stretching, and (5) final heat treatment. Among these, in order to obtain a film having the characteristics of the present invention, it is important to mix a highly amorphous raw material with recycled PET bottle raw material and to promote transesterification between polyester raw materials in the extrusion process to reduce crystallinity. Specific methods are described below.

[0041] (1) Mixing and supply of raw materials Heat-shrinkable films generally require an amorphous component as a raw material, but the heat-shrinkable polyester film of the present invention uses recycled PET bottle chips, so it is necessary to use at least two or more types of raw material chips, including recycled PET bottle chips. A blending method is commonly used, and this method is also adopted in the present invention.

[0042] (2) Melt extrusion The recycled PET bottle material and the amorphous material are melt-mixed in the extruder while undergoing transesterification to form a random copolymerized polyester, which is important for enhancing amorphousness. Transesterification is affected by the mixing condition of the resins in the extruder, temperature, time, etc. A melt extruder is primarily composed of a cylinder and a screw, but it is preferable to use a twin-screw extruder with two screws. This is because the rotation of the two screws promotes distributive mixing of the molten resin, increasing the interfacial area between resins of different components and making transesterification more efficient. In the case of a single-screw extruder, the distributive mixing capacity is low, so methods such as increasing the resin temperature or extending the residence time in the extruder are necessary to promote transesterification. However, increasing the temperature or extending the residence time also promotes thermal decomposition of the resin, which leads to the problem of a decrease in intrinsic viscosity (reduction in molecular weight), and is therefore undesirable. In addition, the multi-screw extruder can have co-rotating or counter-rotating screws, but it is preferable to use co-rotating screws, as this also increases the distributive mixing capacity as described above. Additionally, it is preferable to use a two-start or three-start screw. A single-start screw is undesirable because it has weak shear and does not promote transesterification. However, a three-start screw is preferable from the perspective of promoting transesterification, but it has a lower resin transport capacity, which can become a bottleneck in film production, which is becoming increasingly fast. Therefore, it is most preferable to use a two-start screw.

[0043] In the melt mixing section near the middle of the extruder, it is preferable to use kneading discs as screw elements. There are various types of kneading discs, such as a type with forward feeding capability (forward feeding), a type with return capability (reverse feeding), and a type without forward feeding capability (neutral), and it is more preferable to use a combination of these types. The residence time of the resin inside the extruder is determined by factors such as the screw shape and rotation speed, but is preferably 60 to 300 seconds. A residence time of less than 60 seconds is undesirable because transesterification is insufficient and crystallinity cannot be reduced. A residence time of more than 300 seconds is undesirable because decomposition of the resin progresses and the intrinsic viscosity decreases. A residence time of more than 80 to 280 seconds is more preferable, and a residence time of even more preferably 100 to 260 seconds is even more preferable. The ratio of the extruder's output to the screw rotation speed (Q / N), as expressed by formula (2), is called the filling ratio, and is preferably 1.0 or more and 5.0 or less. Q is the output (kg / h), and N is the screw rotation speed (rpm). If the filling ratio exceeds 5.0, the resins are not mixed sufficiently, which prevents the transesterification from being promoted and prevents the crystallinity from being reduced. Furthermore, if the filling ratio is less than 1.0, the resin is prone to deterioration, which can lead to a decrease in intrinsic viscosity and the formation of foreign matter, and is therefore undesirable. A filling ratio of 1.2 or more and 4.8 or less is more preferable, and a ratio of 1.4 or more and 4.6 or less is even more preferable. Filling rate = Discharge rate (kg / h) ÷ Screw rotation speed (rpm) Equation (2)

[0044] The extruder is divided into a feed section, a melt-mixing section, and an extrusion section from the raw material supply side. The cylinder temperature in each section is preferably 200°C or higher and 270°C or lower in the feed section. Temperatures below 200°C are undesirable because some of the resin (especially recycled PET bottle raw materials) will not completely melt. Temperatures above 270°C are undesirable because the resin tends to wrap around the screw (especially highly amorphous raw materials). A more preferable temperature is 210°C or higher and 260°C or lower. Furthermore, a temperature of 260°C or higher and 330°C or lower in the melt-mixing section is preferable. Temperatures below 260°C are undesirable because the transesterification reaction is not promoted. Temperatures above 330°C are undesirable because the resin decomposes and the intrinsic viscosity decreases. A more preferable temperature is 270°C or higher and 310°C or lower. Temperatures of 230°C or higher and 300°C or lower in the extrusion section are preferable. Temperatures below 230°C are undesirable because the melt viscosity is too high, increasing the resin pressure and causing failure of downstream piping and foreign matter filters. If the temperature exceeds 300, the melt viscosity will be low, which is undesirable as it will cause defects such as pulsation when the resin is subsequently extruded from the die. A temperature of 240°C or higher and 290°C or lower is more preferable. It is preferable to provide a gear pump after the extruder to adjust the supply amount and ensure supply stability. The extruder may be a multi-screw extruder having two or more screws, and specifically, a 4-screw extruder, an 8-screw extruder, a 16-screw extruder, etc. may be suitably used.

[0045] (3) Casting process of unstretched sheet The unstretched sheet is produced by extruding the resin into a sheet using a conventional method such as the T-die method or the tubular method. The melt-extruded sheet is then quenched in an extruder to obtain an unstretched film. A suitable method for quenching 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.

[0046] (4) Lateral stretching process The film is preferably stretched in a transverse uniaxial stretching process, in which the film is stretched only in the width direction. While it is possible to perform longitudinal stretching before the transverse stretching process, this method is not preferred due to the length of the production machine. The unstretched sheet obtained as described above is introduced into a tenter device that can heat the film by holding both ends of the sheet with clips. The film is heated to a predetermined temperature with hot air, and then stretched by increasing the distance between the clips while transporting the film in the longitudinal direction. The film temperature during width direction stretching is preferably at least Tg+5°C and not more than Tg+40°C. A film temperature below Tg+5°C is undesirable because the stretching force becomes too high, increasing the risk of breakage. A film temperature above Tg+40°C is undesirable because the stretching force is too low and the film cannot be imparted with sufficient shrinkability. The stretching ratio is preferably 3x to 7x. A stretching ratio of less than 3x is undesirable because the required shrinkage rate cannot be obtained or the stretching unevenness becomes large. Stretching of more than 7x is undesirable because of the high risk of breakage. More preferably, it is 3.5 times or more and 6.5 times or less, and even more preferably, it is 4 times or more and 6 times or less.

[0047] (3) Final heat treatment process After transverse stretching, the film is preferably finally heat-treated in a tenter at a temperature of transverse stretching temperature +5°C or higher and 45°C or lower for 5 seconds or longer and 10 seconds or shorter, while both ends in the width direction are held with clips. If the temperature is higher than the transverse stretching temperature + 45°C, the shrinkage rate in the width direction will decrease and the required shrinkage characteristics will not be obtained, which is not preferable. Also, if the temperature is lower than the transverse stretching temperature + 5°C, when the final product is stored at room temperature, shrinkage in the width direction (so-called natural shrinkage rate) will increase over time, which is not preferable. [Example]

[0048] Next, the present invention will be specifically explained using examples and comparative examples, but the present invention is not limited to the aspects of these examples and can be appropriately modified within the scope of the invention.

[0049] [Heat shrinkage rate in the main shrinkage direction] The film was cut into a 10 cm x 10 cm square and heat-shrunk by immersing it in warm water at 98°C ± 0.5°C for 10 seconds under no load. After that, the dimensions of the film in the longitudinal direction and width direction (main shrinkage direction) were measured, and the heat shrinkage rate was calculated according to the following formula (1). Heat shrinkage rate = ((length before shrinkage - length after shrinkage) / length before shrinkage) × 100 (%) Formula (1)

[0050] [Shrinkage stress] A sample measuring 200 mm in length in the main shrinkage direction and 20 mm in width was cut from the heat-shrinkable polyester film and measured using a tensilon (registered trademark of Orientec Co., Ltd.) with a heating furnace manufactured by Toyo Baldwin Co., Ltd. (now Orientec Co., Ltd.). The heating furnace was preheated to 90°C, and the distance between the chucks was 100 mm. The airflow to the heating furnace was stopped, the door of the heating furnace was opened, and the sample was attached to the chuck. The door was then quickly closed and the airflow was resumed. The shrinkage stress was measured for 30 seconds or more, and the shrinkage stress (MPa) after 30 seconds was determined. The maximum value during the measurement was taken as the maximum shrinkage stress (MPa).

[0051] [Solvent adhesive strength] Heat-shrinkable polyester film coated with 1,3-dioxolane at a rate of 5±0.3g / m 2 The adhesive was applied over a width of 5±1 mm and the two sheets were then bonded together to form a seal. Then, a 15 mm wide strip was cut out in the direction perpendicular to the sealing direction, and this was placed in a Baldwin STM-50 universal tensile tester with a chuck distance of 20 mm. The strip was then subjected to a tensile peel test at a speed of 200 mm / min, and the peel resistance in a T-type peel (90-degree peel) was measured. The strength measured at this point was taken as the solvent adhesive strength.

[0052] [Tg (glass transition temperature)] Using a differential scanning calorimeter (TA Instruments, DSC250), 5 mg of unstretched film was placed in a sample pan, the pan was covered, and the temperature was increased from -40°C to 300°C at a rate of 10°C / min under a nitrogen gas atmosphere. Tg (°C) was determined in accordance with JIS-K7121-1987.

[0053] [Enthalpy of fusion] Five milligrams of the film after film formation was placed in a sample pan, the pan was covered, and the sample was heated to 300°C at a rate of 10°C / min in a nitrogen gas atmosphere using a differential scanning calorimeter. After heating, 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 rate of 10°C / min using a differential scanning calorimeter, and DSC was measured. The enthalpy of fusion was calculated from the area of ​​the endothermic peak where the sample melted. If two melting peaks were observed, they were integrated together. If no melting peak was observed, the enthalpy of fusion was set to 0.

[0054] [Change in specific heat capacity] Similarly to the above, the melt-quenched sample was measured using a differential scanning calorimeter in temperature modulation mode from 30°C to 300°C at a heating rate of 2°C / min and a modulation frequency of 40 Hz, to obtain a reverse heat flow DSC curve. The difference in specific heat capacity values ​​before and after the obtained reverse heat flow Tg was taken as the specific heat capacity difference ΔCp. When two Tg's were observed, ΔCp was calculated from the start of the glass transition on the lower side to the end of the glass transition on the higher side.

[0055] [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.

[0056] [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 (Varian) at 23°C and 64 cycles of accumulation. In the NMR measurement, 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 diol component were measured.

[0057] [Tensile test] In accordance with JIS-K-7127, a rectangular sample measuring 50 mm in the longitudinal direction of the film and 20 mm in the main shrinkage direction (film width direction) was taken as a test piece, and a tensile test was performed using a universal tensile tester (Autograph (registered trademark) manufactured by Shimadzu Corporation) by gripping both ends (both ends in the longitudinal direction) of the test piece at a tensile speed of 200 mm / min, and the elongation at break was taken as the breaking elongation.

[0058] [Shrinkage finish evaluation] Both ends of the film were bonded with dioxolane to create a cylindrical label (with the main shrinkage direction of the heat-shrinkable film aligned circumferentially). This was then cut. The diameter of the label in the shrinking direction was 70 mm. The label was then attached to a 500 ml PET bottle (body diameter 62 mm, minimum neck diameter 25 mm) by heat shrinking it using a Fuji Astec Inc. steam tunnel (model: SH-1500-L) at a zone temperature of 90°C for 4 seconds. The neck was adjusted so that the 30 mm diameter was located at one end of the label. The finished quality after shrinkage was evaluated visually, using the following criteria: 4: Good finish 3: Minor imperfections (1-2 places) 2: Flaws present (3-5 places) 1: Many defects (6 or more) The defects were wrinkles, bent edges of the label, uneven shrinkage, insufficient shrinkage, and peeling of adhesive areas. Evaluation results of 4 or more were considered acceptable, and 3 or less were considered unacceptable.

[0059] <Recycled PET bottle material (Polyester A)> Polyester A is made from recycled PET bottles, and recycled material chips manufactured by Utsumi Recycle Systems Co., Ltd. It contains 2 mol % of isophthalic acid relative to the total dicarboxylic acid components that make up the polyester. The intrinsic viscosity was 0.60 dl / g.

[0060] <Preparation of amorphous polyester raw material (polyester B) chips> A stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser was charged with 100 mol% dimethyl terephthalate (DMT) as a dicarboxylic acid component, 63 mol% ethylene glycol (EG), 26 mol% neopentyl glycol (NPG), and 11 mol% diethylene glycol as polyhydric alcohol components, with the polyhydric alcohol 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, and the polycondensation reaction was carried out at 280°C under reduced pressure of 26.7 Pa to obtain Polyester B with an intrinsic viscosity of 0.77 dL / g.

[0061] <Preparation of amorphous polyester raw material (polyester C) chips> It was prepared in the same manner as Polyester B, except that the contents were 85 mol % ethylene glycol (EG), 10 mol % neopentyl glycol (NPG), and 5 mol % diethylene glycol. The intrinsic viscosity was 0.76 dl / g.

[0062] <Preparation of amorphous polyester raw material (polyester C) chips> It was prepared in the same manner as Polyester B, except that the contents were 90 mol % ethylene glycol (EG), 7 mol % neopentyl glycol (NPG), and 3 mol % diethylene glycol. The intrinsic viscosity was 0.76 dl / g.

[0063] [Table 1]

[0064] <Extruder Discharge Rate> The extruder discharge rate (kg / h) was determined by measuring the weight of the resin obtained after operating the extruder under specified conditions for 1 hour.

[0065] <Residence time in extruder> The residence time was measured using white chips (polyethylene terephthalate containing titanium oxide). While the polyester resin was continuously extruded, a small amount (1 kg) of white chips was fed into the extruder through the feed port. The unstretched sheet obtained by extrusion was sampled every 10 seconds, and the color L value of the center of the sheet was measured. The time when the white chips were added was set to 0, and the color L value of the unstretched sheet was plotted against the sampling time. Since there is a distribution of residence times, the time at which the L value reached its maximum was taken as the residence time. The color was measured using a Nippon Denshoku ZE6000 color difference meter.

[0066] <Method for producing heat-shrinkable polyester film> [Example 1] The above-mentioned polyester A raw material and polyester B raw material were mixed and charged into a hopper immediately above the extruder, and then fed to the extruder at a mixing ratio of polyester A:polyester B=15:85. A twin-screw extruder was used. The screw had a kneading disc and had two threads. The screw rotation speed was 200 rpm. The cylinder temperature in the feed section of the extruder was 210°C, the cylinder temperature in the melt mixing section was 300°C, and the cylinder temperature in the extrusion section was 260°C. A gear pump was installed after the extruder, and the discharge rate was adjusted to 420 kg / h. The resin residence time when extruded under the above conditions was 270 seconds. The filling ratio was 2.1. The resin extruded from the extruder was extruded through a T-die and then rapidly cooled to obtain an unstretched film with a thickness of 120 μm. The glass transition temperature of the unstretched film was 66° C. This unstretched film was introduced into a tenter and preheated to a film temperature of 76°C. The clip spacing was then widened, allowing the film to be stretched 4.0 times in the width direction at a film temperature of 76°C. The film was then introduced into the final heat treatment zone, where it was heat-treated at a film temperature of 83°C. The thickness of the stretched film was 30 μm. The film was continuously wound around a paper tube to obtain a film roll. The manufacturing method and film evaluation results are shown in Table 2. As a result of the evaluation, it was found that by mixing with amorphous raw materials and promoting ester exchange during melt extrusion, a highly amorphous film was formed, which had sufficient shrinkability in the width direction, low shrinkage stress, and high solvent adhesion strength, resulting in a film with good shrink finish.

[0067] [Example 2] The same procedure as in Example 1 was carried out except that the gear pump was adjusted to a discharge rate of 473 kg / h to make the thickness of the unstretched film 135 μm and the stretching ratio of the tenter was changed to 4.5 times. The manufacturing method and film evaluation results are shown in Table 2. As a result of the evaluation, it was found that by mixing with amorphous raw materials and promoting ester exchange during melt extrusion, a highly amorphous film was formed, which had sufficient shrinkability in the width direction, low shrinkage stress, and high solvent adhesion strength, resulting in a film with good shrink finish.

[0068] [Example 3] The gear pump was adjusted to a discharge rate of 525 kg / h to make the thickness of the unstretched film 150 μm, and the stretching ratio of the tenter was changed to 5.0 times, but the same procedures were followed as in Example 1. The production method and film evaluation results are shown in Table 2. As a result of the evaluation, it was found that by mixing with amorphous raw materials and promoting ester exchange during melt extrusion, a highly amorphous film was formed, which had sufficient shrinkability in the width direction, low shrinkage stress, and high solvent adhesive strength, resulting in a film with good shrinkage finish.

[0069] [Example 4] The raw materials used were polyester A and polyester C, with a mixing ratio of polyester A:polyester C = 15:85. The Tg of the unstretched film was 71°C. The film temperature during tenter stretching was 81°C, and the final heat treatment temperature was 88°C. Other than the above, the same method as in Example 2 was used. The manufacturing method and film evaluation results are shown in Table 2. As a result of the evaluation, it was found that by mixing with amorphous raw materials and promoting ester exchange during melt extrusion, a highly amorphous film was formed, which had sufficient shrinkability in the width direction, low shrinkage stress, and high solvent adhesive strength, resulting in a film with good shrinkage finish.

[0070] [Example 5] The blend ratio of polyester A and polyester B was polyester A:polyester B = 25:75. The Tg of the unstretched film was 67°C. The film temperature during tenter stretching was 77°C, and the final heat treatment temperature was 84°C. Except for the above, the same method as in Example 2 was carried out. Except for the above, the same method as in Example 2 was carried out. The manufacturing method and film evaluation results are shown in Table 2. As a result of the evaluation, it was found that by mixing with amorphous raw materials and promoting ester exchange during melt extrusion, a highly amorphous film was formed, which had sufficient shrinkability in the width direction, low shrinkage stress, and high solvent adhesive strength, resulting in a film with good shrinkage finish.

[0071] [Example 6] The same procedure as in Example 4 was carried out, except that the mixing ratio of polyester A to polyester C was polyester A:polyester B=25:75. The manufacturing method and film evaluation results are shown in Table 2. As a result of the evaluation, it was found that by mixing with amorphous raw materials and promoting ester exchange during melt extrusion, a highly amorphous film was formed, which had sufficient shrinkability in the width direction, low shrinkage stress, and high solvent adhesive strength, resulting in a film with good shrinkage finish.

[0072] [Example 7] The blend ratio of polyester A and polyester B was polyester A:polyester B = 40:60. The Tg of the unstretched film was 68°C. The film temperature during tenter stretching was 78°C, and the final heat treatment temperature was 85°C. Except for the above, the same method as in Example 2 was carried out. Except for the above, the same method as in Example 2 was carried out. The manufacturing method and film evaluation results are shown in Table 2. As a result of the evaluation, it was found that by mixing with amorphous raw materials and promoting ester exchange during melt extrusion, a highly amorphous film was formed, which had sufficient shrinkability in the width direction, low shrinkage stress, and high solvent adhesive strength, resulting in a film with good shrinkage finish.

[0073] [Example 8] The blend ratio of polyester A and polyester C was polyester A:polyester B = 40:60. The Tg of the unstretched film was 72°C. The film temperature during tenter stretching was 82°C, and the final heat treatment temperature was 89°C. Except for the above, the same method as in Example 4 was carried out. Except for the above, the same method as in Example 2 was carried out. The manufacturing method and film evaluation results are shown in Table 2. As a result of the evaluation, it was found that by mixing with amorphous raw materials and promoting ester exchange during melt extrusion, a highly amorphous film was formed, which had sufficient shrinkability in the width direction, low shrinkage stress, and high solvent adhesive strength, resulting in a film with good shrinkage finish.

[0074] [Example 9] The same procedure as in Example 8 was carried out, except that the mixing ratio of polyester A to polyester C was polyester A:polyester B=45:55. The manufacturing method and film evaluation results are shown in Table 2. As a result of the evaluation, it was found that by mixing with amorphous raw materials and promoting ester exchange during melt extrusion, a highly amorphous film was formed, which had sufficient shrinkability in the width direction, low shrinkage stress, and high solvent adhesive strength, resulting in a film with good shrinkage finish.

[0075] [Comparative Example 1] The blend ratio of polyester A and polyester C was polyester A:polyester B = 55:45. The Tg of the unstretched film was 73°C. The film temperature during tenter stretching was 83°C, and the final heat treatment temperature was 90°C. Other than the above, the same method as in Example 9 was used. The manufacturing method and film evaluation results are shown in Table 2. As a result of the evaluation, it was found that the amount of amorphous raw material added was small compared to the amount of recycled PET bottle raw material, resulting in high crystallinity, insufficient shrinkage, low solvent adhesive strength, and poor shrinkage finish.

[0076] Comparative Example 2 The gear pump was adjusted to a discharge rate of 525 kg / h to make the thickness of the unstretched film 150 μm, and the stretching ratio of the tenter was changed to 5.0 times, but the same procedures were performed as in Comparative Example 1. The production method and film evaluation results are shown in Table 2. As a result of the evaluation, it was found that the amount of amorphous raw material added was small compared to the amount of recycled PET bottle raw material, resulting in high crystallinity, insufficient shrinkage rate, high shrinkage stress, low solvent adhesive strength, and poor shrinkage finish.

[0077] [Example 10] The same procedure as in Example 9 was carried out, except that polyester A and polyester D were used in a mixing ratio of polyester A:polyester D=25:75. The manufacturing method and film evaluation results are shown in Table 2. As a result of the evaluation, it was found that by mixing with amorphous raw materials and promoting ester exchange during melt extrusion, a highly amorphous film was formed, which had sufficient shrinkability in the width direction, low shrinkage stress, and high solvent adhesive strength, resulting in a film with good shrinkage finish.

[0078] Comparative Example 3 The procedure was the same as in Example 9, except that the screw of the twin-screw extruder was changed and the screw rotation speed was adjusted to 80 rpm and the discharge rate to 420 kg. At this time, the filling ratio was 5.3. The residence time of the resin in the extruder was 40 seconds. The manufacturing method and film evaluation results are shown in Table 2. As a result of the evaluation, it was found that the ester exchange in the extruder was insufficient, so the film as a whole had high crystallinity, an insufficient shrinkage rate was not obtained, the solvent adhesive strength was low, and the shrink finish was poor.

[0079] Comparative Example 4 The procedure was the same as in Example 9, except that the extruder was changed to a single-screw extruder, the screw rotation speed was adjusted to 70 rpm, and the discharge rate was adjusted to 420 kg. At this time, the filling rate was 6.0. The residence time of the resin in the extruder was 50 seconds. The manufacturing method and film evaluation results are shown in Table 2. As a result of the evaluation, it was found that the ester exchange in the extruder was insufficient, so the film as a whole had high crystallinity, an insufficient shrinkage rate was not obtained, the solvent adhesive strength was low, and the shrink finish was poor.

[0080] Comparative Example 5 The same procedure as in Example 9 was carried out except that the cylinder temperature in the feed section of the extruder was 240°C, the cylinder temperature in the melt mixing section was 350°C, and the cylinder temperature in the extrusion section was 280°C. The manufacturing method and film evaluation results are shown in Table 2. As a result of the evaluation, it was found that the film as a whole was highly amorphous, had a sufficient shrinkage rate with low shrinkage stress, and had sufficient solvent adhesive strength; however, due to its low intrinsic viscosity and low longitudinal tensile elongation at break, it was prone to breakage problems during post-processing.

[0081] [Table 2A]

[0082] [Table 2B] [Industrial Applicability]

[0083] The heat-shrinkable polyester film of the present invention, despite containing a predetermined amount of recycled PET bottle raw material as described above, has high shrinkability in the width direction, low shrinkage stress, and high solvent adhesive strength, resulting in excellent shrink finish, and is suitable for use in beverage bottle labels, etc. Furthermore, since it contains recycled PET bottle raw material, it can also contribute to reducing the environmental load.

Claims

1. A heat-shrinkable polyester film comprising 5% by mass or more and 50% by mass or less of recycled PET bottle material and composed of a polyester containing an isophthalic acid component, wherein the polyester contains one or more monomer components selected from the group consisting of neopentyl glycol, 1,4-cyclohexanedimethanol, diethylene glycol, 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, 1,4-butanediol, and hexanediol in total, of 8 mol % or more of the polyhydric alcohol components or 8 mol % or more of the polycarboxylic acid components in 100 mol % of the total polyester resin, and the heat-shrinkable polyester film satisfies the following requirements (1) to (5): (1) The shrinkage rate in the main shrinkage direction of the film when immersed in 98°C hot water for 10 seconds is 50% or more. (2) The maximum shrinkage stress in the main shrinkage direction of the film measured in hot air at 90°C is 3 MPa or more and 15 MPa or less. (3) The heat of fusion ΔHm of the film, measured by a differential scanning calorimeter (DSC) after the film is melted and then rapidly cooled, is 0 J / g or more and 32 J / g or less. (4) The film has a solvent adhesive strength of 2.9 N / 15 mm or more when 1,3-dioxolane is used as an adhesive solvent. (5) The tensile elongation at break in the direction perpendicular to the main shrinkage direction of the film is 100% or more.

2. 2. The heat-shrinkable polyester film according to claim 1, wherein the film is melted and then rapidly cooled, and when a reverse heat flow measurement is performed using temperature-modulated DSC on the sample, the change in specific heat capacity ΔCp between before and after the glass transition is 0.20 J / (g ° C) or more and 0.35 J / (g ° C) or less.

3. 3. The heat-shrinkable polyester film according to claim 1, wherein the polyester constituting the film has an isophthalic acid content of 0.1 mol % or more and 3.0 mol % or less in 100 mol % of all acid components.

4. 4. The heat-shrinkable polyester film according to claim 1, wherein the polyester constituting the heat-shrinkable polyester film is composed mainly of ethylene terephthalate.

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

6. A package in which the heat-shrinkable label according to claim 5 covers at least a part of the outer periphery of an object to be packaged.

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