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-based film that uses recycled PET bottle raw materials, has high shrinkability, low shrinkage stress, excellent solvent adhesion, and has few defects such as insufficient shrinkage, uneven shrinkage, distortion, and vertical streaks during use.

Background Art

[0002] In recent years, stretched films (so-called heat-shrinkable films) made of polyvinyl chloride-based resins, polystyrene-based resins, polyester-based resins, etc. have been widely used for applications such as label packaging, cap sealing, and integrated packaging that combine the protection of glass bottles and PET bottles with product display. Among such heat-shrinkable films, polyvinyl chloride-based films have problems such as low heat resistance and the generation of hydrogen chloride gas during incineration or being a cause of dioxins. In addition, polystyrene-based films are inferior in solvent resistance, require the use of inks with special compositions during printing, and need to be incinerated at high temperatures, resulting in problems such as the generation of a large amount of black smoke with a strange odor during incineration. Therefore, polyester-based heat-shrinkable films with high heat resistance, easy incineration, and excellent solvent resistance have come to be widely used as shrink labels, and with the increasing circulation volume of PET containers (PET bottles), the usage amount has a tendency to increase.

[0003] However, on the other hand, due to the dramatic increase in the usage amount of PET bottles, waste problems and resource conservation have become social issues. As one of the countermeasures, there is an active movement to collect used PET bottles and reuse them as resources (recycle). Recycling technologies mainly include mechanical recycling, chemical recycling, thermal recycling, etc. Among them, mechanical recycling is the most widely spread. Used containers are sorted, crushed, washed, and then made into resin chips again by an extruder, and then processed and used again as PET bottles or fibers and films.

[0004] Even with heat-shrinkable polyester film labels, using recycled PET bottle materials as described above can contribute to the entire lifecycle of PET, from production to use and disposal, and thus contribute to reducing environmental impact.

[0005] While much remains unknown about the molecular structure governing the shrinkage behavior of films, it is believed that oriented amorphous molecules are involved in the shrinkage characteristics. In the state of an unstretched film formed by melt molding, the molecular chains are not oriented (random coil state), but stretching causes the molecular chains to align mainly in the stretching direction. It is thought that some of the oriented amorphous molecular chains become mobile when heat above the glass transition temperature is applied, and a force acts to return them 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 needs to be highly amorphous, or in other words, low in crystallinity. It is known that if the crystallinity is high, orientation crystallization occurs when stretching occurs, but the crystallized molecular chains do not move even when heat is applied, thus inhibiting thermal shrinkage.

[0006] On the other hand, there is a demand to cover most of the container with a label for the purpose of protecting the contents and improving the design. Also, container shapes are diversifying among companies to improve design and differentiation. For this reason, heat-shrinkable films used for labels require a high shrinkage rate.

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

[0008] Conventional heat-shrinkable polyester films that shrink significantly in the width direction are widely used. These films are stretched using methods such as tenter stretching to create wide master rolls, which are then slit to the desired width and wound into rolls of the desired length to produce film roll products. The film is then subjected to a printing process in roll form to add design elements or for product labeling purposes. After printing, the film is slit again to the required width and wound into rolls, then subjected to a center sealing process using solvent bonding to form tubes, which are then wound into rolls (becoming label rolls).

[0009] Labels, formed into tubes and wound up, are cut to the required length as they are unwound from the roll, forming a ring-shaped label. The ring-shaped label is then attached to the packaged item by methods such as hand-covering, and shrinks through a steam tunnel or hot air tunnel to become a finished label.

[0010] If the shrinkage stress during shrinkage is too high, heat-shrinkable polyester films can cause delamination at the adhesive joint of the tube due to shrinkage, resulting in a significant deterioration of appearance and potentially impairing the protective function of the packaged goods. Furthermore, if the solvent adhesive strength of the center seal is low, delamination will similarly occur at the adhesive joint due to shrinkage. Delamination of the adhesive joint is thought to occur when the adhesive strength is weaker than the shrinkage stress; therefore, a low shrinkage stress and high solvent adhesive strength are ideal. When the raw materials constituting a heat-shrinkable polyester film have high crystallinity, the stretch stress increases due to oriented crystallization during stretching, resulting in high shrinkage stress. Furthermore, when the film has high crystallinity, the polymer molecular chains are less likely to swell with solvents, leading to lower solvent adhesion strength. The increased crystallinity resulting from the incorporation of recycled PET bottle materials can be an inhibiting factor in achieving 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 amorphous copolymer components. However, Patent Document 1 does not provide 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 copolymer state is not achieved, the crystallinity is not sufficiently reduced, and the necessary shrinkage is not obtained when it is made into a heat-shrinkable film, resulting in high shrinkage stress and low solvent adhesion. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] Patent No. 5320737 [Overview of the project] [Problems that the invention aims to solve]

[0013] The present invention aims to provide a heat-shrinkable polyester film that has sufficient shrinkage properties, low shrinkage stress, and high solvent adhesion strength, even when containing recycled PET bottle materials. [Means for solving the problem]

[0014] The inventors of this invention have diligently studied and, as a result, completed the present invention in order to solve the above problems. That is, the present invention has the following configuration. 1. A heat-shrinkable polyester film composed of polyester containing 5% to 50% by mass of recycled PET bottle material and isophthalic acid components, characterized in that it satisfies the following requirements (1) to (5). (1) The shrinkage rate of the film in the principal shrinkage direction when immersed in 98°C hot water for 10 seconds must be 50% or more. (2) The maximum shrinkage stress in the principal shrinkage direction of the film, measured in 90°C hot air, must be between 3 MPa and 15 MPa. (3) The heat of fusion ΔHm of the sample after the film has been melted and rapidly cooled is 0 J / g or more and 32 J / g or less, as measured by a differential scanning calorimetry (DSC). (4) The solvent adhesion strength of the film when 1,3-dioxolane is used as the adhesive solvent is 2.9 N / 15 mm or higher. (5) The intrinsic viscosity of the film is 0.59 dl / g or more and 0.75 dl / g or less.

[0015] 2. The heat-shrinkable polyester film according to 1, characterized in that, in a sample in which the film has been melted once and then rapidly cooled, the change in specific heat capacity ΔCp before and after the glass transition, when measured by reverse heat flow measurement using temperature-modulated DSC, is 0.20 J / (g·℃) or more and 0.35 J / (g·℃) or less. 3. A heat-shrinkable polyester film according to either of 1. or 2., characterized in that the tensile elongation at break in a direction perpendicular to the principal 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 ratio of 0.1 mol% or more and 3.0 mol% or less in 100 mol% of the total acid components. 5. A heat-shrinkable polyester film according to any one of 1 to 4, characterized in that the polyester constituting the heat-shrinkable polyester film has ethylene terephthalate as its main component.

[0016] 6. A heat-shrinkable label using a heat-shrinkable polyester film as described in any of items 1 to 5 above. 7. A package in which the heat-shrinkable label described in 6. above covers at least a portion of the outer circumference of the object to be packaged. [Modes for carrying out the invention]

[0017] The heat-shrinkable polyester film of the present invention is a heat-shrinkable polyester film composed of a polyester containing 5% by mass or more and 50% by mass or less of a PET bottle recycling raw material and 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 warm water at 98 °C 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 measured by a differential scanning calorimeter (DSC) for a sample obtained by melting and rapidly cooling the film once is 0 J / g or more and 32 J / g or less. (4) The solvent adhesion strength of the film when 1,3-dioxolane is used as an adhesive solvent is 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 has ethylene terephthalate as a main constituent. That is, it contains 50 mol% or more, preferably 60 mol% or more of ethylene terephthalate based on 100 mol% of all the constituent components of the polyester. Examples of other 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 (for example, adipic acid, sebacic acid, decanedicarboxylic acid, etc.) is contained, the content is preferably less than 3 mol%. Using a heat-shrinkable polyester film obtained using a polyester containing 3 mol% or more of these aliphatic dicarboxylic acids is not preferable because the film strength becomes insufficient and problems occur in slitting and post-processing. ]

[0020] Moreover, it is preferable not to contain a polyvalent carboxylic acid having a valence of 3 or more (for example, trimellitic acid, pyromellitic acid, and their anhydrides, etc.). In a heat-shrinkable polyester-based film obtained using a polyester containing these polyvalent carboxylic acids, it becomes difficult to achieve the required high shrinkage rate.

[0021] Examples of the diol component other than ethylene glycol that constitutes 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-based film of the present invention preferably contains one or more of cyclic diols such as 1,4-cyclohexanedimethanol and diols having 3 to 6 carbon atoms (for example, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, hexanediol, diethylene glycol, etc.), and is a polyester having a glass transition point (Tg) adjusted to 60 to 80°C.

[0023] Furthermore, the polyester used in the heat-shrinkable polyester film of the present invention preferably contains 8 mol% or more of one or more monomer components that can become amorphous components in 100 mol% of polyhydric alcohol components or 100 mol% of polyhydric carboxylic acid components in the total polyester resin, more preferably 10 mol% or more, and particularly preferably 13 mol% or more. In addition, the total of one or more monomer components that can become amorphous components preferably contains 45 mol% or less, more preferably 40 mol% or less, and particularly preferably 35 mol% or less. Here, 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. Among these, neopentyl glycol, diethylene glycol, 1,4-cyclohexanedimethanol, and isophthalic acid are preferred.

[0024] It is preferable that the polyester used in the heat-shrinkable polyester film of the present invention does not contain diols with 8 or more carbon atoms (e.g., octanediol) or polyhydric alcohols with a valency of 3 or higher (e.g., trimethylolpropane, trimethylolethane, glycerin, diglycerin). Heat-shrinkable polyester films obtained using polyesters containing these diols or polyhydric alcohols make it difficult to achieve the required high shrinkage rate.

[0025] Furthermore, various additives, such as waxes, antioxidants, antistatic agents, nucleating agents, viscosity reducers, heat stabilizers, coloring pigments, color inhibitors, and UV absorbers, may be added to the resin forming the heat-shrinkable polyester film of the present invention as needed. It is preferable to improve the workability (slipperiness) of the polyethylene terephthalate resin film by adding fine particles as a lubricant to the resin forming the heat-shrinkable polyester film of the present invention. 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 is within the range of 0.05 to 3.0 μm (measured with a Coulter counter) and can be appropriately selected as needed. The amount of fine particles added to the film can be within the range of 300 to 1200 ppm to achieve both good slipperiness (friction) and transparency.

[0026] As for how to incorporate the above particles into the resin that forms the heat-shrinkable polyester film, for example, they can be added 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 esterification stage, or after the completion of the transesterification reaction but before the start of the polycondensation reaction, in order to proceed with the polycondensation reaction. It is also preferable to blend the slurry of particles dispersed in ethylene glycol or water with the polyester resin raw material using a kneading extruder with a vent, or to blend the dried particles with the polyester resin raw material using a kneading extruder.

[0027] Furthermore, the heat-shrinkable polyester film of the present invention can be subjected to corona treatment, coating treatment, flame treatment, etc., in order to improve the adhesion of the film surface.

[0028] The heat-shrinkable polyester film of the present invention contains 5% to 50% by mass of recycled PET bottle material. The polyester used in PET bottles contains a few percent of isophthalic acid as a dicarboxylic acid component to improve moldability, but the other components are terephthalic acid, and in many cases the diol component is mostly ethylene glycol. In other words, it is composed of crystalline raw materials, and its recycled raw material (recycled PET bottle material) is also crystalline. As a method to reduce the crystallinity of the polyester constituting the heat-shrinkable polyester film, which contains recycled PET bottle material, a method of blending it with a highly amorphous polyester material is employed. A highly amorphous material is a material that has monomer components that can become amorphous components as described above. By blending the recycled PET bottle material with the highly amorphous material, the amount of monomer components that can become the desirable amorphous components described above is adjusted. The preferred range for the content of recycled PET bottle material is 5% by mass or more and 50% by mass. If the content is less than 5% by mass, the contribution to reducing environmental impact is extremely small. If the content exceeds 50% by mass, it is necessary to make the amorphous properties of materials other than recycled PET bottle material extremely high, which is uneconomical as it increases the polymerization time of the materials and is therefore undesirable. The heat-shrinkable polyester film of the present invention may be a single-layer structure or a laminated structure of two or more layers, but it is preferable that each layer constituting the film contains recycled PET bottle material within the above content range.

[0029] In a sample of the heat-shrinkable polyester film of the present invention that has been melted and then rapidly cooled, the enthalpy of fusion (ΔHm) measured by differential scanning calorimetry (DSC) must be between 0 J / g and 32 J / g. The above enthalpy of fusion (ΔHm) is an indicator of the high crystallinity of all polyester constituting the heat-shrinkable polyester film of the present invention. The enthalpy of fusion is the enthalpy at which crystalline components that have undergone thermal crystallization due to heating in a DSC device melt. A large value indicates that there are many components that easily crystallize, and it is thought that stretch crystallization during film formation and crystallization due to heat treatment are likely to occur. A smaller enthalpy of fusion is preferable because it indicates higher amorphousness, which makes it easier to obtain a high shrinkage rate in the heat-shrinkable polyester film, resulting in lower shrinkage stress and higher solvent adhesion strength. If the enthalpy of melting exceeds 32 J / g, the crystallinity is too high, making stretch crystallization and crystallization due to heat treatment more likely. This results in insufficient shrinkage, increased stretch stress, and high shrinkage stress, leading to lower solvent adhesion strength. A lower enthalpy of melting is preferable, with 0 J / g being the lower limit (no melting peak). A more preferable range is 0 J / g to 30 J / g, an even more preferable range is 0 J / g to 27 J / g, and a particularly preferable range is 0 J / g to 24 J / g.

[0030] Mixing a highly amorphous polyester raw material with a crystalline PET bottle recycling raw material reduces its crystallinity, which in turn reduces the enthalpy of fusion (ΔHm) mentioned above. Generally, increasing the copolymer component in a homopolymer reduces its steric regularity, leading to a decrease in crystallinity. However, this effect is more pronounced when the polyester monomer components undergo transesterification, resulting in random copolymerization. If crystallinity is simply reduced by increasing the copolymer component, and the randomization necessary for random copolymerization is not sufficiently advanced, sufficient solvent adhesion strength may not be achieved. In this invention, a crystalline raw material (recycled PET bottle material) is dry-blended with a highly amorphous raw material, and the transesterification process is carried out while melt-extruding the material in an extruder. If the transesterification reaction is insufficient, crystalline components remain, and the enthalpy of fusion increases. Methods for promoting transesterification within the extruder will be described later.

[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., the 98°C hot water heat shrinkage rate) of 50% or more, calculated from the length before and after shrinkage using the formula 1 below when treated in 98°C hot water for 10 seconds under no load. Thermal shrinkage rate = {(length before shrinkage - length after shrinkage) / length before shrinkage} × 100 (%) · Equation 1 If the shrinkage rate at 98°C is less than 50%, the amount of shrinkage is insufficient, resulting in wrinkles or insufficient shrinkage of the label after heat shrinkage, making it undesirable as a heat-shrinkable film. There is no specific upper limit for the shrinkage rate, but around 80% is considered the upper limit.

[0032] The heat-shrinkable polyester film of the present invention preferably has a maximum shrinkage stress in the main shrinkage direction of 3 MPa to 15 MPa, measured under hot air at 90°C. The shrinkage stress should be measured by the method described in the examples. If the maximum shrinkage stress at 90°C in the main shrinkage direction exceeds 15 MPa, it is undesirable because it can cause lifting or peeling of the label edges when shrinking, or cause shrinkage in the non-shrinkage direction, resulting in a poor appearance. If it falls below 3 MPa, it is undesirable because the label may sag and not adhere properly to the container when used as a label. Shrinkage stress is considered to be the residual force applied to the film during stretching and correlates with tensile stress. When highly crystalline raw materials are used, oriented crystallization is likely to occur during stretching, and tensile stress increases significantly with increasing tensile strain. By suppressing crystallinity, crystallization due to stretching is inhibited, the tensile stress decreases, and the shrinkage stress of the film is also thought to decrease. A more preferable range for shrinkage stress is 4 MPa to 14 MPa, and an even more preferable range is 5 MPa to 13 MPa.

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

[0034] While a higher solvent adhesion strength is preferable, we believe the upper limit is approximately 15.0 (N / 15mm). If the solvent adhesion strength is too high, it can lead to unnecessary adhesion of two films when bonding them together to form a label, potentially reducing label productivity. Therefore, a strength of 10.0 (N / 15mm) or less is practically acceptable.

[0035] The intrinsic viscosity of the film is preferably between 0.59 dl / g and 0.75 dl / g. If the intrinsic viscosity is less than 0.59 dl / g, the strength of the film decreases, making it prone to breakage during film formation. Furthermore, the longitudinal elongation at break of the resulting film becomes low, which is undesirable as it increases the likelihood of breakage problems in subsequent processes such as printing. If the intrinsic viscosity exceeds 0.75 dl / g, the pressure during extrusion becomes too high, which is undesirable as it increases the likelihood of equipment failure. More preferably, it is between 0.60 dl / g and 0.75 dl / g, and even more preferably between 0.61 dl / g and 0.73 dl / g.

[0036] In a sample of the heat-shrinkable polyester film of the present invention, which was melted and then rapidly cooled, the change in specific heat capacity ΔCp before and after the glass transition, as measured by reverse heat flow using temperature-modulated DSC, was between 0.20 J / (g·°C) and 0.35 J / (g·°C). Polyester is divided into a crystalline phase and an amorphous phase, and the amorphous phase is further divided into a rigid amorphous phase and a mobile amorphous phase. 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 the heat-shrinkable polyester film. On the other hand, the rigid amorphous phase is an amorphous phase in which molecular motion is constrained even during the glass transition. The above-mentioned change in specific heat capacity ΔCp is considered to correspond to the amount of mobile amorphous. In other words, the larger ΔCp, the greater the amount of mobile amorphous that contributes to shrinkage, and the higher the thermal shrinkage rate of the film is considered to be. If the change in specific heat capacity ΔCp is less than 0.2 J / (g·°C), the required shrinkage rate cannot be obtained, which is undesirable. More preferably, the concentration is 0.22 J / (g·℃) or higher, and even more preferably 0.24 or higher. ΔCp may be 0.35 or higher, but since it contains crystalline PET bottle recycled material, the upper limit is approximately 0.35 J / (g·℃). Note that maintaining a random copolymer state contributes to increasing the amount of movable amorphous material.

[0037] The polyester constituting the heat-shrinkable polyester film of the present invention has an isophthalic acid content ratio of 0.1 mol% to 3.0 mol% in 100 mol% of the total acid components. In order to improve the appearance of the bottle, the polyester used in PET bottles is subject to control of its crystallinity, and as a result, polyester containing 6 mol% or less of isophthalic acid is generally used. In the present invention, since recycled PET bottle material is contained at a rate of 50% by mass or less, the upper limit of the isophthalic acid content ratio is preferably 3.0 mol% or less. More preferably, it is 2.0 mol% or less, and even more preferably 1.0 mol% or less. The lower limit of the isophthalic acid content is preferably 0.1 mol%, more preferably 0.3 mol%, and even more preferably 0.6 mol%. The isophthalic acid content ratio will be measured and calculated by NMR measurement, as described later.

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

[0039] The film thickness is preferably 5 μm to 40 μm. A thickness of less than 5 μm increases the risk of breakage during film formation, and also reduces the firmness of the label, making it prone to wrinkling, which is undesirable. While a thicker film tends to result in more stable film formation and increased firmness, thus reducing problems such as wrinkling, this is undesirable because it contradicts the environmentally friendly objective of the present invention, which is to reduce waste, and also from the perspective of volume reduction. More preferably, the film thickness is 8 μm to 37 μm, and even more preferably 11 μm to 34 μm.

[0040] The following describes a preferred method for manufacturing the heat-shrinkable polyester fill of the present invention. The manufacturing process for the heat-shrinkable polyester film of the present invention comprises (1) raw material mixing and supply, (2) melt extrusion, (3) casting of an unstretched sheet, (4) transverse stretching, and (5) final heat treatment. In particular, to obtain a film with the characteristics of the present invention, it is important to mix a highly amorphous raw material with the recycled PET bottle raw material and to promote transesterification between polyester raw materials during the extrusion process to reduce crystallinity. The specific method is described below.

[0041] (1) Mixing and supply of raw materials While heat-shrinkable films generally require amorphous components as raw materials, the heat-shrinkable polyester film of the present invention uses recycled PET bottle raw material chips, and therefore inevitably uses at least two or more types of raw material chips, including recycled PET bottle raw materials. A blending method is common for this use, and this is also adopted in the present invention.

[0042] (2) Melt extrusion In the extruder, the recycled PET bottle material and amorphous raw material are melted and mixed, undergoing transesterification to create a random copolymer polyester, which is crucial for enhancing amorphous properties. Transesterification is affected by factors such as the degree of resin mixing, temperature, and time within the extruder. A molten extruder mainly consists of a cylinder and a screw, but it is preferable to use a twin-screw extruder, which has two screws. This is because the rotation by the two screws promotes the distribution and mixing of the molten resin, increasing the interface area between resins of different components, and allowing for efficient transesterification. In the case of a single-screw extruder, the distribution and mixing capacity is small, and methods such as raising the resin temperature or increasing the residence time in the extruder are necessary to promote transesterification. However, raising the temperature or increasing the residence time also promotes the thermal decomposition of the resin, which is undesirable because it leads to a decrease in intrinsic viscosity (decrease in molecular weight). Furthermore, while multi-screw extruders can have screws rotating in either the same direction or in opposite directions, it is preferable to use the same-direction rotation. This is also to increase the distribution and mixing capacity, as mentioned above. Furthermore, it is preferable to use a screw with two or three threads. A single-start screw is undesirable because its shear strength is weak and transesterification is not promoted. However, while a triple-start screw is preferable from the standpoint of promoting transesterification, its resin transport capacity is reduced, which may become a bottleneck in film manufacturing as speeds increase. Therefore, the most preferable option is to use a screw with two threads.

[0043] In the molten mixing section near the middle of the extruder, it is preferable to use a kneading disc as the screw element. Kneading discs come in various types, such as those with a feeding capability (forward feed), those with a return capability (reverse feed), and those without a feeding capability (neutral), but it is more preferable to use a combination of these types. The residence time of the resin inside the extruder is determined by the screw shape, rotation speed, etc., but is preferably between 60 seconds and 300 seconds. Less than 60 seconds is undesirable because transesterification is insufficient and the crystallinity cannot be reduced. More than 300 seconds is undesirable because the decomposition of the resin progresses and the intrinsic viscosity decreases. More preferably it is between 80 seconds and 280 seconds, and even more preferably between 100 seconds and 260 seconds. The ratio of the extruder's discharge rate to the screw rotation speed (Q / N), expressed by equation (2), is called the filling rate, and is preferably between 1.0 and 5.0. Q is the discharge rate (kg / h), and N is the screw rotation speed (rpm). If the filling rate exceeds 5.0, the mixing of the resins is insufficient, transesterification is not promoted, and the crystallinity cannot be reduced. Also, if the filling rate is less than 1.0, the resin is prone to degradation, which is undesirable as it can lead to a decrease in intrinsic viscosity and the presence of foreign matter. More preferably, it is between 1.2 and 4.8, and even more preferably between 1.4 and 4.6. Filling rate = Discharge rate (kg / h) ÷ Screw rotation speed (rpm) ... Equation (2)

[0044] An extruder is divided into a feed section, a melting and mixing section, and an extrusion section from the raw material supply side. The cylinder temperature in each section is preferably 200°C to 270°C in the feed section. Below 200°C is undesirable because some of the resin (especially recycled PET bottle material) does not melt completely. Above 270°C is undesirable because the resin tends to wrap around the screw (especially with highly amorphous materials). More preferably 210°C to 260°C. In the melting and mixing section, the temperature is preferably 260°C to 330°C. Below 260°C is undesirable because the transesterification reaction is not promoted. Above 330°C is undesirable because the decomposition of the resin progresses and the intrinsic viscosity decreases. More preferably 270°C to 310°C. In the extrusion section, the temperature is preferably 230°C to 300°C. Below 230°C is undesirable because the melt viscosity is too high, resulting in high resin pressure and causing failure of subsequent piping and foreign matter filters. A temperature exceeding 300 is undesirable because it lowers the melt viscosity, leading to defects such as pulsation during subsequent extrusion from the die. More preferably, the temperature is between 240°C and 290°C. It is preferable to install 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. Specifically, four-screw extruders, eight-screw extruders, sixteen-screw extruders, etc., can be suitably used.

[0045] (3) Casting process of unstretched sheets Unstretched sheets are prepared by extruding them into a sheet using existing methods such as the T-die method or the tubular method. Then, by rapidly cooling the sheet extruded by melt extrusion in an extruder, an unstretched film can be obtained. As a method for rapidly cooling the molten resin, a method in which the molten resin is cast from a die onto a rotating drum and rapidly cooled and solidified to obtain a substantially unoriented resin sheet can be suitably employed.

[0046] (4) Lateral stretching process For stretching the film, transverse uniaxial stretching, where stretching is performed only in the width direction, is preferable. Although it is possible to use a method in which longitudinal stretching is performed as a pre-process for transverse stretching, this is undesirable because it results in a long production machine. The unstretched sheet obtained as described above is guided to a tenter device that can grip both ends of the sheet with clips and heat it, and after heating the film to a predetermined temperature with hot air, it is stretched by increasing the distance between the clips while conveying it in the longitudinal direction. The film temperature during widthwise stretching is preferably between Tg + 5°C and Tg + 40°C. If the film temperature is below Tg + 5°C, the stretching force becomes too high, increasing the risk of breakage, which is undesirable. If the film temperature exceeds Tg + 40°C, the stretching force is too low, and the film cannot be given sufficient shrinkage, which is undesirable. The stretching ratio is preferably between 3 and 7 times. If it is less than 3 times, the required shrinkage rate cannot be obtained, or the stretching unevenness becomes large, which is undesirable. Stretching of 7 times or more is undesirable because the risk of breakage is high. More preferably, it is 3.5 times or more and 6.5 times or less, and even more preferably 4 times or more and 6 times or less.

[0047] (3) Final heat treatment process After transverse stretching, the film is preferably held at both ends in the width direction with clips inside the tenter and then subjected to a final heat treatment at a temperature of transverse stretching temperature + 5°C to 45°C for a period of 5 to 10 seconds. If the temperature is higher than the lateral stretching temperature + 45°C, the shrinkage rate in the width direction decreases, making it undesirable as the required shrinkage characteristics cannot be obtained. Also, if the temperature is lower than the lateral stretching temperature + 5°C, when the final product is stored at room temperature, the shrinkage in the width direction (so-called natural shrinkage rate) over time increases, which is undesirable. [Examples]

[0048] Next, the present invention will be specifically described using examples and comparative examples. However, the present invention is not limited in any way to the embodiments of these examples, and can be modified as appropriate without departing from the spirit of the invention.

[0049] [Thermal shrinkage rate in the main shrinkage direction] The film was cut into 10cm x 10cm squares and subjected to heat shrinkage by being treated in hot water at a temperature of 98℃ ± 0.5℃ for 10 seconds under no load. After that, the dimensions of the film in the longitudinal and width directions (main shrinkage direction) were measured, and the heat shrinkage rate was calculated according to the following formula (1). Thermal shrinkage rate = ((Length before shrinkage - Length after shrinkage) / Length before shrinkage) × 100 (%) Equation (1)

[0050] [Contraction stress] A sample measuring 200 mm in length and 20 mm in width in the main shrinkage direction was cut from a heat-shrinkable polyester film and measured using a Tensilon (a registered trademark of Orientec Co., Ltd.) heating furnace equipped stretch measuring instrument 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 set to 100 mm. The airflow to the heating furnace was temporarily stopped, the door of the heating furnace was opened, the sample was attached to the chuck, and then the door of the heating furnace was quickly closed and the airflow was restarted. The shrinkage stress was measured for 30 seconds or more, and the shrinkage stress (MPa) after 30 seconds was determined, with the maximum value during measurement being taken as the maximum shrinkage stress (MPa).

[0051] [Solvent bonding strength] Apply 1,3-dioxolane to a heat-shrinkable polyester film at a rate of 5±0.3 g / m². 2 The two pieces were sealed by applying the adhesive in a width of 5±1 mm and bonding them together. Subsequently, a 15 mm wide strip was cut in a direction perpendicular to the sealing direction, and this strip was set in a Baldwin Corporation STM-50 universal tensile testing machine with a 20 mm gap between the chucks. The strip was then subjected to tensile peeling at a tensile speed of 200 mm / min, and the peel resistance force in T-shaped peeling (90-degree peeling) was measured. The strength at that time was defined as the solvent adhesive strength.

[0052] [Tg (Glass transition temperature)] A differential scanning calorimetry analyzer (TAInstructions, DSC250) was used to measure the temperature of a 5 mg sample of unstretched film. The sample was placed in a sample pan, covered, and heated from -40°C to 300°C at a rate of 10°C / min under a nitrogen atmosphere. Tg(°C) was determined according to JIS-K7121-1987.

[0053] [Enthalpy of Melting] A 5 mg sample of the film after deposition was placed in a sample pan, covered, and heated to 300°C at a rate of 10°C / min under a nitrogen atmosphere using a differential scanning calorimetry analyzer. The sample was then held at 300°C for 2 minutes. After that, the sample pan was removed and rapidly cooled with liquid nitrogen. The rapidly cooled sample was returned to room temperature and heated again from 30°C to 300°C at a rate of 10°C / min using a differential scanning calorimetry analyzer, and the DSC was measured. The enthalpy of fusion was determined from the endothermic peak area where the sample melted. If two melting peaks were observed, they were combined and integrated to determine the enthalpy of fusion. If no melting peak was observed, the enthalpy of fusion was set to 0.

[0054] [Change in specific heat capacity] Similarly to the above, in samples that were rapidly melted and cooled, a differential scanning calorimetry analyzer was used to measure temperatures from 30°C to 300°C in temperature modulation mode, with a heating rate of 2°C / min and a modulation period of 40 Hz, and a reverse heat flow DSC curve was obtained. The difference in specific heat capacity values ​​before and after the obtained reverse heat flow Tg was defined as the specific heat capacity difference ΔCp. If two Tg values ​​were observed, ΔCp was calculated from the start of the glass transition on the low-temperature side to the end of the glass transition on the high-temperature 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 measured using an Ostwald viscometer at 30°C. The unit is dl / g.

[0056] [Composition analysis] Each sample was dissolved in a solvent mixture of chloroform D (Eurysop) and trifluoroacetic acid D1 (Eurysop) in a 10:1 volume ratio to prepare a sample solution. The proton NMR of the sample solution was measured using an NMR spectrometer "GEMINI-200" (Varian) at a temperature of 23°C and with 64 integration cycles. In the NMR measurement, the peak intensity of a predetermined proton was calculated to determine the amount of the diacid component in 100 mol% and the diol component in 100 mol%.

[0057] [Tensile test] In accordance with JIS-K-7127, a rectangular sample was prepared as a test specimen, measuring 50 mm in the longitudinal direction of the film and 20 mm in the principal shrinkage direction (film width direction). A universal tensile testing machine (Autograph®, manufactured by Shimadzu Corporation) was used to grip both ends of the test specimen (both ends in the longitudinal direction) and perform a tensile test at a tensile speed of 200 mm / min. The elongation at the time of breakage was defined as the elongation at break.

[0058] [Shrinkage finish evaluation] A cylindrical label (a label with the main shrinkage direction of the heat-shrinkable film as the circumferential direction) was created by bonding both ends of the film with dioxolane, and then cut. The diameter of the label in the shrinkage direction was 70 mm. Subsequently, the label was attached to a 500 ml PET bottle (body diameter 62 mm, minimum neck diameter 25 mm) by heat shrinking using a steam tunnel (model: SH-1500-L) manufactured by Fuji Astec Inc., with a passage time of 4 seconds and a zone temperature of 90°C. During attachment, the neck portion was adjusted so that a 30 mm diameter section was one end of the label. The finish quality after shrinkage was evaluated visually, and the criteria were as follows. 4: Excellent finish 3: There are a few minor flaws (1-2 places) 2: Has flaws (3-5 places) 1: Many flaws (6 or more) Defects here included wrinkles, folded edges on labels, uneven shrinkage, insufficient shrinkage, and peeling of adhesive. A score of 4 or higher was considered acceptable, while a score of 3 or lower was considered poor.

[0059] <Recycled PET bottle material (Polyester A)> Polyester A is made from recycled PET bottles, using recycled material chips manufactured by Utsumi Recycling Systems Co., Ltd. It contains 2 mol% 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> In a stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser, 100 mol% dimethyl terephthalate (DMT) as the dicarboxylic acid component, 63 mol% ethylene glycol (EG), 26 mol% neopentyl glycol (NPG), and 11 mol% diethylene glycol were charged as polyhydric alcohol components, so that the polyhydric alcohols were 2.2 times the molar ratio of dimethyl terephthalate. 0.05 mol% zinc acetate (relative to the acid component) was added as a transesterification catalyst, and 0.225 mol% antimony trioxide (relative to the acid component) was added as a polycondensation catalyst. The transesterification reaction was carried out while distilling off the resulting methanol. Subsequently, a 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 it consisted of 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 it consisted of 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 volume> The discharge rate of the extruder was determined by measuring the weight of the resin obtained after operating the extruder under specified conditions for one hour, and this was expressed as the discharge rate (kg / h).

[0065] <Dwelling time inside the extruder> Residence time was measured using white chips (polyethylene terephthalate containing titanium dioxide). While continuously extruding polyester resin, a small amount (1 kg) of white chips was fed into the extruder from the supply port. Unstretched sheets obtained from the extrusion were sampled every 10 seconds, and the color L value of the center of the sheet was measured. The time when the white chips were introduced was set as 0, and the color L value against the sampling time of the unstretched sheet was plotted. Since residence time exhibits a distribution, the time at which the L value is maximum was defined as the residence time. The color was measured using a Nippon Denshoku ZE6000 colorimeter.

[0066] <Method for manufacturing heat-shrinkable polyester film> [Example 1] The polyester A and polyester B raw materials described above were mixed and fed into a hopper directly above the extruder. At this time, the mixing ratio of the raw materials was polyester A:polyester B = 15:85. A twin-screw extruder was used. The screw had a kneading disc and a 2-start thread. The screw rotation speed was set to 200 rpm. The cylinder temperature of the feed section of the extruder was set to 210°C, the cylinder temperature of the melting and mixing section to 300°C, and the cylinder temperature of the extrusion section to 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 rate was 2.1. The resin extruded from the extruder was then extruded through a T-die and rapidly cooled to obtain an unstretched film with a thickness of 120 μm. The glass transition temperature of the unstretched film at this time was 66°C. The unstretched film was guided into a tenter and preheated until the film temperature reached 76°C. Then, by widening the clip spacing, the film was stretched 4.0 times in the width direction at 76°C. Furthermore, it was guided into a final heat treatment zone and heat-treated at 83°C. The thickness of the stretched film was 30 μm. The film was continuously wound onto a paper tube to obtain a film roll. The manufacturing method and film evaluation results are shown in Table 2. The evaluation results showed that by mixing with amorphous raw materials and promoting transesterification during melt extrusion, a highly amorphous film was produced, exhibiting sufficient shrinkage in the width direction, low shrinkage stress, and high solvent adhesion strength, resulting in a film with excellent shrinkage finish.

[0067] [Example 2] The procedure was the same as in Example 1, except that the gear pump was adjusted to a discharge rate of 473 kg / h, resulting in an unstretched film thickness of 135 μm and a tenter stretching ratio of 4.5 times. The manufacturing method and film evaluation results are shown in Table 2. The evaluation results showed that by mixing with amorphous raw materials and promoting transesterification during melt extrusion, a highly amorphous film was produced, exhibiting sufficient shrinkage in the width direction, low shrinkage stress, and high solvent adhesion strength, resulting in a film with excellent shrinkage finish.

[0068] [Example 3] The process was the same as in Example 1, except that the gear pump was adjusted to a discharge rate of 525 kg / h, resulting in an unstretched film thickness of 150 μm, and the tenter's stretching ratio was changed to 5.0 times. The manufacturing method and film evaluation results are shown in Table 2. The evaluation results showed that by mixing with amorphous raw materials and promoting transesterification during melt extrusion, a highly amorphous film was produced, exhibiting sufficient shrinkage in the width direction, low shrinkage stress, and high solvent adhesion strength, resulting in a film with excellent 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. Except for the above, the procedure was the same as in Example 2. The manufacturing method and film evaluation results are shown in Table 2. The evaluation results showed that by mixing with amorphous raw materials and promoting transesterification during melt extrusion, a highly amorphous film was produced, exhibiting sufficient shrinkage in the width direction, low shrinkage stress, and high solvent adhesion strength, resulting in a film with excellent shrinkage finish.

[0070] [Example 5] The mixing ratio of polyester A to polyester B was set to 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 procedure was the same as in Example 2. Except for the above, the procedure was the same as in Example 2. The manufacturing method and film evaluation results are shown in Table 2. The evaluation results showed that by mixing with amorphous raw materials and promoting transesterification during melt extrusion, a highly amorphous film was produced, exhibiting sufficient shrinkage in the width direction, low shrinkage stress, and high solvent adhesion strength, resulting in a film with excellent shrinkage finish.

[0071] [Example 6] The procedure was carried out in the same manner as in Example 4, except that the mixing ratio of polyester A and polyester C was set to polyester A:polyester B = 25:75. The manufacturing method and film evaluation results are shown in Table 2. The evaluation results showed that by mixing with amorphous raw materials and promoting transesterification during melt extrusion, a highly amorphous film was produced, exhibiting sufficient shrinkage in the width direction, low shrinkage stress, and high solvent adhesion strength, resulting in a film with excellent shrinkage finish.

[0072] [Example 7] The mixing ratio of polyester A to polyester B was set to 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 procedure was the same as in Example 2. Except for the above, the procedure was the same as in Example 2. The manufacturing method and film evaluation results are shown in Table 2. The evaluation results showed that by mixing with amorphous raw materials and promoting transesterification during melt extrusion, a highly amorphous film was produced, exhibiting sufficient shrinkage in the width direction, low shrinkage stress, and high solvent adhesion strength, resulting in a film with excellent shrinkage finish.

[0073] [Example 8] The mixing ratio of polyester A and polyester C was set to 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 procedure was the same as in Example 4. Except for the above, the procedure was the same as in Example 2. The manufacturing method and film evaluation results are shown in Table 2. The evaluation results showed that by mixing with amorphous raw materials and promoting transesterification during melt extrusion, a highly amorphous film was produced, exhibiting sufficient shrinkage in the width direction, low shrinkage stress, and high solvent adhesion strength, resulting in a film with excellent shrinkage finish.

[0074] [Example 9] The procedure was carried out in the same manner as in Example 8, except that the mixing ratio of polyester A and polyester C was set to polyester A:polyester B = 45:55. The manufacturing method and film evaluation results are shown in Table 2. The evaluation results showed that by mixing with amorphous raw materials and promoting transesterification during melt extrusion, a highly amorphous film was produced, exhibiting sufficient shrinkage in the width direction, low shrinkage stress, and high solvent adhesion strength, resulting in a film with excellent shrinkage finish.

[0075] [Comparative Example 1] The mixing ratio of polyester A and polyester C was set to 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. Except for the above, the procedure was carried out in the same manner as in Example 9. The manufacturing method and film evaluation results are shown in Table 2. The evaluation revealed that, compared to recycled PET bottle material, the amount of amorphous raw material added was insufficient, resulting in high crystallinity, insufficient shrinkage rate, low solvent adhesion strength, and poor shrinkage finish.

[0076] [Comparative Example 2] The process was the same as in Comparative Example 1, except that the gear pump was adjusted to a discharge rate of 525 kg / h, resulting in an unstretched film thickness of 150 μm, and the tenter stretching ratio was changed to 5.0 times. The manufacturing method and film evaluation results are shown in Table 2. The evaluation revealed that, compared to recycled PET bottle material, the amount of amorphous raw material added was insufficient, resulting in high crystallinity, insufficient shrinkage rate, high shrinkage stress, low solvent adhesion strength, and poor shrinkage finish.

[0077] [Example 10] The procedure was carried out in the same manner as in Example 9, except that polyester A and polyester D were used, and the mixing ratio was polyester A:polyester D = 25:75. The manufacturing method and film evaluation results are shown in Table 2. The evaluation results showed that by mixing with amorphous raw materials and promoting transesterification during melt extrusion, a highly amorphous film was produced, exhibiting sufficient shrinkage in the width direction, low shrinkage stress, and high solvent adhesion strength, resulting in a film with excellent 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 adjusted to a screw rotation speed of 80 rpm and a discharge volume of 420 kg. At this time, the filling rate 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. The evaluation revealed that insufficient transesterification in the extruder resulted in high overall film crystallinity, insufficient shrinkage, low solvent adhesion strength, and poor shrinkage finish.

[0079] [Comparative Example 4] The procedure was the same as in Example 9, except that the extruder was changed to a single-screw extruder, and the screw rotation speed was adjusted to 70 rpm and the discharge volume 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. The evaluation revealed that insufficient transesterification in the extruder resulted in high overall film crystallinity, insufficient shrinkage, low solvent adhesion strength, and poor shrinkage finish.

[0080] [Comparative Example 5] The procedure was carried out in the same manner as in Example 9, except that the cylinder temperature of the feed section of the extruder was set to 240°C, the cylinder temperature of the melt mixing section to 350°C, and the cylinder temperature of the extrusion section to 280°C. The manufacturing method and film evaluation results are shown in Table 2. The evaluation revealed that while the film as a whole exhibited high amorphousness, sufficient shrinkage rate and low shrinkage stress, and adequate solvent adhesion strength, its low intrinsic viscosity and low longitudinal tensile elongation made it prone to breakage problems during post-processing.

[0081] [Table 2A]

[0082] [Table 2B] [Industrial applicability]

[0083] Despite containing a predetermined amount of recycled PET bottle material as described above, the heat-shrinkable polyester film of the present invention exhibits high shrinkage in the width direction, low shrinkage stress, and high solvent adhesion strength, resulting in excellent shrinkage finish and making it suitable for use in beverage bottle labels and the like. Furthermore, because it contains recycled PET bottle material, it can also contribute to reducing environmental impact.

Claims

1. A heat-shrinkable polyester film comprising a polyester containing 5% to 50% by mass of recycled PET bottle material and an isophthalic acid component, wherein the polyester is characterized in that the total amount of 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 is 8 mol% or more of the polyhydric alcohol component or 100 mol% of the polyhydric carboxylic acid component in the total polyester resin, and satisfies the following requirements (1) to (5). (1) The shrinkage rate of the film in the main shrinkage direction 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 of the sample after the film has been melted and rapidly cooled is 0 J / g or more and 32 J / g or less, as measured by a differential scanning calorimetry (DSC). (4) The solvent adhesion strength of the film when 1,3-dioxolane is used as the adhesive solvent is 2.9 N / 15 mm or more. (5) The tensile elongation at break in the direction perpendicular to the principal shrinkage direction of the film is 100% or more.

2. The heat-shrinkable polyester film according to claim 1, characterized in that, in a sample in which the film has been melted once and then rapidly cooled, the change in specific heat capacity ΔCp before and after the glass transition, when measured by reverse heat flow measurement using temperature-modulated DSC, is 0.20 J / (g·°C) or more and 0.35 J / (g·°C) or less.

3. The heat-shrinkable polyester film according to claim 1 or 2, characterized in that the polyester constituting the film has an isophthalic acid content ratio of 0.1 mol% or more and 3.0 mol% or less in 100 mol% of the total acid components.

4. A heat-shrinkable polyester film according to any one of claims 1 to 3, characterized in that the polyester constituting the heat-shrinkable polyester film has ethylene terephthalate as its main component.

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

6. A package in which the heat-shrinkable label described in claim 5 covers at least a portion of the outer circumference of the object to be packaged.

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