Heat-shrinkable polyester film roll

Abstract

To provide a heat-shrinkable polyester film roll that reduces the occurrence of defects such as wrinkles and vertical sink marks during the heat shrinkage process caused by fluctuations in the heat shrinkage rate within the film roll, even when containing recycled PET bottle materials. [Solution] A heat-shrinkable polyester film roll made of a polyester containing 5% to 50% by mass of recycled PET bottle material and an isophthalic acid component, characterized in that it satisfies the following requirements (1) to (3). (1) When film samples taken at 100m intervals along the longitudinal direction of the roll are immersed in 90°C hot water for 10 seconds, the average shrinkage rate in the main shrinkage direction is 40% or more, and the shrinkage rate for all samples is within ±3% of the average. (2) In film samples taken at 100m intervals along the length of the roll, the isophthalic acid content ratio of the polyester constituting the film is all within ±0.3 mol% of its average value in 100 mol% of the total acid components. (3) The thickness variation in the longitudinal direction of the roll must be 20% or less.

Description

Technical Field

[0001] The present invention relates to a film roll formed by winding a heat-shrinkable polyester film. More specifically, while using recycled PET bottle raw materials, it has high shrinkability, has little variation in shrinkage physical properties in the longitudinal direction of the film roll, and has few defects such as insufficient shrinkage, shrinkage unevenness, distortion, and vertical draw in the subsequent process. It relates to a heat-shrinkable polyester film roll.

Background Art

[0002] In recent years, stretched films (so-called heat-shrinkable films) made of polyvinyl chloride resins, polystyrene resins, polyester 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 and product display. Among such heat-shrinkable films, polyvinyl chloride films have problems such as low heat resistance, generation of hydrogen chloride gas during incineration, and being a cause of dioxins. In addition, polystyrene 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 accompanied by a strange smell 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 increase in the 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 use of PET bottles, the problems of waste and resource conservation have become social issues. As one of the countermeasures, the movement to collect used PET bottles and reuse them as resources (recycle) is active. Recycling technologies mainly include mechanical recycling, chemical recycling, and thermal recycling, but mechanical recycling is the most widely used. In this method, used containers are sorted, crushed, and washed, then extruded back into resin chips, which are then processed again into PET bottles, fibers, or films for reuse.

[0004] Even with heat-shrinkable polyester film labels, using recycled PET bottle raw 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] Generally, to achieve high shrinkability in heat-shrinkable polyester films, it is necessary to reduce the crystallinity of the polyester that makes up the film. However, recycled PET bottles are highly crystalline raw materials. Therefore, when using recycled PET bottles, it is essential to mix them with at least two other raw materials, including a highly amorphous raw material.

[0006] After manufacturing, the heat-shrinkable film is wound into a roll and sent in film roll form to the printing process for various designs. After printing is complete, it is slit as needed to match the size of the labels used in the final product, and the left and right ends of the film are overlapped and sealed by means of solvent bonding or other methods to form a tube. The tube is then cut and processed into labels, bags, etc. These labels or bags are then attached to a container and passed through a shrink tunnel (hot air tunnel) on a belt conveyor or similar device, where steam is blown in to cause heat shrinkage and ensure a tight fit to the container.

[0007] However, in this heat shrinkage process, if the heat shrinkage rate of each individual label or bag varies significantly, since the heating conditions inside the tunnel are the same, some labels or bags will not exhibit the correct heat shrinkage rate. These will result in defects in appearance such as insufficient shrinkage, uneven shrinkage, wrinkles, distortion of the design, and vertical sink marks, making them unsuitable for final production. Here, vertical sink marks refer to uneven lengths of labels after shrinkage, causing the upper edge of the label to curve downwards or the lower edge to curve upwards. It has a cosmetic defect.

[0008] Such fluctuations in the thermal shrinkage rate are largely influenced by variations in the polyester composition that makes up the film in the longitudinal direction of the roll. Typically, heat-shrinkable polyester films are produced by feeding various raw material chips into an extruder, melting them, and extruding the molten resin through a die to obtain an unstretched base roll, which is then stretched. However, compositional variations occur before the various raw material chips are supplied to the extruder; in other words, it is thought that compositional variations occur because the mixing of the various raw material chips is not uniform and is segregated.

[0009] Segregation can be avoided by using raw material chips with a single composition containing all the necessary components for polyester film (using only one type of raw material chip). However, as mentioned above, when using recycled PET bottles, it is necessary to mix at least two types of raw material chips, and the risk of segregation exists. In other words, as long as recycled PET bottles are used, there is a risk of fluctuations in the thermal shrinkage rate in the longitudinal direction. For example, it is not impossible to obtain a single-composition raw material chip containing all the necessary components for film by adding amorphous polyester when crushing, washing, and re-chip-recycled PET bottles, but this is not practical because recycled materials are used for purposes other than film. Furthermore, the inventors of this invention have found that recycled PET bottles are often recycled by randomly mixing various PET bottles, and their molecular weight and other properties decrease due to repeated use. In addition, additives such as high crystallization nucleating agents are often used, and when used as a raw material for film, the impact on film properties due to variations in the blending amount caused by segregation is greater than with other raw materials.

[0010] Patent Document 1 describes a heat-shrinkable polyester film using recycled PET bottle material, but it does not describe the variation in the thermal shrinkage rate in the longitudinal direction. Patent Document 2 describes a heat-shrinkable polyester film containing a high proportion of recycled PET bottle material. However, it is difficult to obtain a shrinkage rate of 45% or more at 90°C using the method described, and there is no description of the variation in the thermal shrinkage rate in the longitudinal direction. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Patent No. 5320737 [Patent Document 2] Patent No. 6402954 [Overview of the project] [Problems that the invention aims to solve]

[0012] The present invention aims to provide a heat-shrinkable polyester film roll that reduces the occurrence of defects such as wrinkles and vertical sink marks during the heat shrinkage process caused by fluctuations in the heat shrinkage rate within the film roll, even when containing recycled PET bottle materials. [Means for solving the problem]

[0013] 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.

[0014] 1. A heat-shrinkable polyester film roll made 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 (3). (1) When film samples taken at 100m intervals along the longitudinal direction of the roll are immersed in 90°C hot water for 10 seconds, the average shrinkage rate in the main shrinkage direction is 40% or more, and all samples are within ±3% of the average. (2) In film samples taken at 100m intervals along the length of the roll, the isophthalic acid content ratio of the polyester constituting the film must be within ±0.3 mol% of the average value in all cases. (3) The thickness variation in the longitudinal direction of the roll must be 20% or less. 2. The heat-shrinkable polyester film roll according to claim 1, characterized in that the heat-shrinkable polyester film is formed from a mixture of at least recycled PET bottle material and one or more polymer chips of different compositions. 3. The heat-shrinkable polyester film roll according to 1. or 2., characterized in that the polyester constituting the heat-shrinkable polyester film has ethylene terephthalate as its main component. 4. A heat-shrinkable polyester film roll according to any one of 1 to 3, characterized in that, in film samples taken at 100m intervals along the longitudinal direction of the roll, the average value of the isophthalic acid content ratio in 100 mol% of the total acid components of the polyester constituting the film is 0.3 mol% or more and 3.0 mol% or less. 5. A heat-shrinkable polyester film roll according to any one of 1 to 4, characterized in that the length of the heat-shrinkable polyester film roll is 1000m or more. 6. The shrinkage rate when a film sample collected at a pitch of 100 m in the roll longitudinal direction is immersed in warm water at 90°C for 10 seconds has an average value in the direction orthogonal to the main shrinkage direction of 0% or more and 15% or less, and the shrinkage rate of all samples is within the average value ±3%. The heat-shrinkable polyester film roll according to any one of 1. to 5., characterized in that.

Advantages of the Invention

[0015] Even when the heat-shrinkable polyester film roll of the present invention is used by mixing recycled PET bottle raw materials, the variation in the heat shrinkage rate within the film roll is small, and it is possible to extremely reduce the occurrence of defects such as wrinkles and vertical streaks in the heat shrinkage process caused by this.

Brief Description of the Drawings

[0016] [Figure 1] It is a schematic diagram showing an example of the relationship between an extruder 2 provided with a hopper 1 and an inner pipe. [Figure 2] It is an enlarged view showing the part A of FIG. 1.

Embodiments for Carrying Out the Invention

[0017] The polyester used in the heat-shrinkable polyester film constituting the heat-shrinkable polyester film roll of the present invention (hereinafter sometimes referred to as 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 with respect to 100 mol% of all the constituent components of the polyester. Further, as described later, the polyester contains an isophthalic acid component. 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.

[0018] When including aliphatic dicarboxylic acids (for example, adipic acid, sebacic acid, decanedicarboxylic acid, etc.), 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 stiffness, leading to problems during slitting and post-processing.

[0019] Furthermore, it is preferable not to include polycarboxylic acids with a valency of 3 or higher (for example, trimellitic acid, pyromellitic acid, and their anhydrides). Heat-shrinkable polyester films obtained using polyesters containing these polycarboxylic acids tend to have difficulty achieving the required high shrinkage rate.

[0020] 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, aromatic diols such as bisphenol A, and diethylene glycol.

[0021] The polyester used in the heat-shrinkable polyester film of the present invention is preferably a polyester that contains 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.) and has its glass transition temperature (Tg) adjusted to 60 to 80°C.

[0022] Furthermore, the polyester used in the heat-shrinkable polyester film of the present invention preferably contains 14 mol% or more of one or more monomer components that can become amorphous components in 100 mol% of the polyhydric alcohol component or 100 mol% of the polyhydric carboxylic acid component in the total polyester resin, more preferably 16 mol% or more, and particularly preferably 18 mol% or more. Examples of monomers that can become amorphous components include neopentyl glycol, 1,4-cyclohexanedimethanol, 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, but among these, neopentyl glycol or 1,4-cyclohexanedimethanol is preferred. The upper limit of the total amount of monomer components that can become amorphous components is preferably 40 mol% or less. More preferably, it is 38 mol% or less, and even more preferably 36 mol% or less.

[0023] 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.

[0024] The intrinsic viscosity of the heat-shrinkable polyester film of the present invention is preferably 0.55 dl / g or more and 1.50 dl / g or less. If the intrinsic viscosity is less than 0.55 dl / g, the strength of the film is significantly reduced, making it prone to breakage during film formation and processing, which is undesirable. Also, if the intrinsic viscosity exceeds 1.50 dl / g, stretching becomes difficult, which can cause breakage, which is also undesirable. More preferably, it is 0.58 dl / g or more and 1.47 dl / g or less, and even more preferably 0.61 dl / g or more and 1.44 dl / g or less.

[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 is within the range of 300 to 1200 ppm, which allows for 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. Below 5% by mass, the contribution to reducing environmental impact is extremely small, and the effects of the present invention are not exhibited. When used in amounts exceeding 50% by mass, it is necessary to make the amorphous nature (amount of amorphous components) of raw materials other than recycled PET bottle material extremely high, which is uneconomical as it increases the polymerization time of the raw materials. A more preferable content of recycled PET bottle material is 10% to 45% by mass, and even more preferably 20% to 40% by mass.

[0029] In this invention, film is sampled at 100m intervals along the longitudinal direction of a film roll, and the shrinkage rate in 90°C hot water (90°C hot water shrinkage rate) is measured for each film sample. The average shrinkage rate in the main shrinkage direction is 40% or more, and the shrinkage rate of all samples is within ±3% of the average. The hot water shrinkage rate is calculated using the following formula 1, based on the length before and after shrinkage when treated in 90°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 average shrinkage rate is less than 40%, the amount of shrinkage is insufficient, resulting in wrinkles or insufficient shrinkage in the label after heat shrinking, making it undesirable for heat-shrinkable film. There is no specific upper limit set for the shrinkage rate, but around 80% is considered the upper limit. Furthermore, if the shrinkage rate of the film sampled at 100m intervals exceeds the range of ±3% of the average value, when processed into labels, the variation in shrinkage rate for each label becomes large, making it more likely for labels to develop appearance defects such as wrinkles when finished in a shrink tunnel, which is undesirable. More preferably, the average value is ±2.5%, even more preferably ±2.0%, particularly preferably ±1.5% or less, and most preferably ±1.0% or less. Furthermore, in this invention, when film samples are taken at 100m intervals along the longitudinal direction of the roll and the shrinkage rate in 90°C hot water (90°C hot water shrinkage rate) is measured for each film sample, the shrinkage rate in the direction perpendicular to the main shrinkage direction for all samples is within the range of ±3% of the average value. If the shrinkage rate in the direction perpendicular to the main shrinkage direction of the film sampled at 100m intervals exceeds the range of ±3% of the average value, when processed into labels, the variation in shrinkage rate for each label will be large, and when finished in a shrink tunnel, the height of each label will differ, which is undesirable. More preferably, the average value is ±2.5%, even more preferably ±2.0%, particularly preferably ±1.5% or less, and most preferably ±1.0% or less. In addition, the upper limit of the average value of the shrinkage rate in the direction perpendicular to the main shrinkage direction for all samples is 20%. If the average value exceeds 20%, the vertical sink marking during shrinkage finishing will be large, which is undesirable. More preferably, it is 17% or less, and even more preferably 14% or less. Furthermore, it is preferable that the shrinkage rate in the direction perpendicular to the principal shrinkage direction is as low as possible.

[0030] In the heat-shrinkable polyester film roll of the present invention, it is preferable that the isophthalic acid content ratio in film samples taken at 100m intervals along the longitudinal direction of the roll is within ±0.3 mol% of the average value in all cases. The isophthalic acid content ratio is measured and calculated by NMR measurement as described later. If the isophthalic acid content fluctuates beyond the average value range of ±0.3 mol%, the variation in composition will lead to significant variations in thermal shrinkage. As a result, when the material is processed into labels, the shrinkage rate will vary from label to label, making it more likely for cosmetic defects such as wrinkles to occur, which is undesirable. The film roll of the present invention uses recycled PET bottle material, but as will be described later, recycled PET bottle material generally contains a small amount of isophthalic acid as an acid component. Fluctuations in the ratio of isophthalic acid mean that the chips of recycled PET bottle material and chips of other materials are segregated. As mentioned above, recycled PET bottle material often contains additives such as high crystallization nucleating agents, and its molecular weight and other properties decrease with repeated use, so the impact of segregation on the variation in physical properties within the film roll is greater than with other materials. Methods for reducing segregation will be described later. A more preferred range for the isophthalic acid ratio is an average value of ±0.2 mol%, and even more preferably an average value of ±0.1 mol%.

[0031] Furthermore, the average content ratio of isophthalic acid is preferably 0.3 mol% to 3.0 mol% of the total acid components of the polyester (100 mol%). In order to improve the appearance of the bottle, the polyester used in PET bottles is subjected to crystallinity control, and as a result, polyester containing 10 mol% or less of isophthalic acid is generally used. In the present invention, since recycled PET bottle material is contained at 50% by mass or less, the upper limit of the average value of the isophthalic acid content ratio is preferably 3.0 mol% or less. More preferably 2.8 mol% or less, even more preferably 2.6 mol% or less, and particularly preferably 2.4 mol% or less. The lower limit of the average value of the isophthalic acid content is preferably 0.3 mol%, more preferably 0.4 mol%, even more preferably 0.5 mol%, and particularly preferably 0.6 mol%.

[0032] Furthermore, the thickness variation in the longitudinal direction of the heat-shrinkable polyester film roll of the present invention is 20% or less, as shown in equation 2 below. If the thickness variation in the longitudinal direction is poor, the thickness of each label will differ when processed into labels. If the thickness of the labels differs, the way heat is applied to the labels inside the steam tunnel (hot air tunnel) will differ, which is undesirable as it is more likely to cause appearance defects such as wrinkles. Preferably, it is 18% or less, and more preferably 15% or less. The smaller the value of the thickness variation, the better. Thickness variation = {(Maximum thickness - Minimum thickness) ÷ Average thickness} × 100 (%) ··(Equation 2)

[0033] Furthermore, the thickness of the heat-shrinkable polyester film of the present invention 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 formation, and also reduces the stiffness 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 stiffness, thus reducing problems such as wrinkling, this is undesirable because it contradicts the objective of the present invention, which is to reduce environmental impact and reduce volume. More preferably, the film thickness is 8 μm or more and 37 μm or less, and even more preferably 11 μm or more and 34 μm or less.

[0034] The width of the heat-shrinkable polyester film roll of the present invention is preferably 500 mm or more, more preferably 1000 mm or more, and particularly preferably 1500 mm or more. The length of the film roll is preferably 2000 m or more, more preferably 4000 m or more, and particularly preferably 8000 m or more.

[0035] The following describes a preferred method for manufacturing the heat-shrinkable polyester film roll of the present invention. The heat-shrinkable polyester film roll of the present invention is manufactured by a process of storing and supplying raw material resin, extruding the resin while melting it, converting the extruded resin into an unstretched sheet, stretching the unstretched sheet, and winding up the resulting stretched film. Furthermore, in order to obtain a film roll with the characteristics of the present invention, it is important to suppress variations in the film composition. Specific methods are described below.

[0036] <Methods for suppressing variations in film composition> 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 requires the use of at least two types of raw material chips, including recycled PET bottle raw materials. Blending is a common method of use, but this method tends to cause segregation of the raw material chips. Therefore, in the present invention, it is preferable to suppress the segregation of raw material chips in the blending method by various methods and combinations of methods as shown below.

[0037] (a) Uniformity of tip shape In the blending method, multiple raw material polyester chips with different compositions are typically blended inside a hopper, then melted and kneaded, and extruded into a film using an extruder. In this invention, recycled PET bottle raw material chips and other amorphous raw material chips are supplied continuously or intermittently and mixed inside a hopper. Finally, the mixed raw material chips are supplied to a hopper directly above the extruder (final hopper), and the raw material is supplied in accordance with the extrusion rate of the extruder to form a film. However, it has been found that depending on the capacity or shape of the hopper in which the raw materials are mixed and the final hopper, the mixing ratio of the chips supplied to the subsequent hopper or extruder differs depending on whether the amount of chips in the hopper is large or small. This problem is particularly pronounced when the shapes and specific gravities of various polyester raw material chips differ. As a result, the isophthalic acid content fluctuates in this invention. In order to obtain a film roll with minimal variation in longitudinal shrinkage rate and isophthalic acid content according to the present invention, it is preferable to suppress the segregation phenomenon of raw materials inside the hopper by adjusting the shape of the raw material chips used as a means to reduce compositional variations of the polyester constituting the film.

[0038] Polyester raw material chips are removed in a molten state as strands from the polymerization apparatus after passing through and polymerization, immediately cooled with water, and then cut and shaped with a strand cutter. In the case of recycled PET bottles, the PET bottles are sorted, crushed, and washed to obtain flake-like polyester, which is then extruded again in an extruder, removed as strands, immediately cooled with water, and cut and shaped with a strand cutter. As a result, polyester chips usually have an elliptical cross-section. At this time, it is preferable that the average major axis (mm), average minor axis (mm), and average chip length (mm) of the elliptical cross-section of the polyester chips be within ±20% of each other. Furthermore, it is even more preferable that these average values ​​be within ±15% of each other. The average major axis and average minor axis of the elliptical cross-section can be adjusted by adjusting the size of the nozzle hole of the die when extruding in strand form, and the chip length can be adjusted by adjusting the amount of strand extruded, the strand conveying speed, and the rotation speed of the strand cutter. When there are differences in the size of the wood chips, smaller chips tend to fall first as the chip mixture falls through the hopper. As a result, as the amount of chips remaining in the hopper decreases, the proportion of larger chips increases, which causes material segregation. However, by using material chips within the specified range, it is possible to suppress this material segregation.

[0039] Another indicator of the particle fluidity, or ease of falling, of raw material chips is the angle of repose. The angle of repose is the angle between the slope of the mound formed when a certain amount of raw material chips are dropped from a certain height and the horizontal plane. The angle of repose is determined by the shape and particle size of the chips; the smaller the chip, the smaller the angle of repose tends to be, and the smaller the angle of repose of the resin, the easier it tends to fall. It is preferable that the difference between the angle of repose of the resin with the smallest angle of repose and the chip with the largest angle of repose be 5 degrees or less. It is more preferable that the angle is 4 degrees or less, as using raw material chips within the above range makes it possible to suppress these material segregation issues.

[0040] (b) Hopper shape optimization Optimizing the hopper shape as described above is also a desirable measure to address raw material segregation. By using a funnel-shaped hopper for the hopper into which the mixed chips are placed, and setting its inclination angle to 65° or more, larger chips can be dropped in at the same rate as smaller chips, and the upper end of the contents descends while maintaining a horizontal plane, which is effective in reducing raw material segregation. A more preferable inclination angle is 70° or more. The inclination angle of the hopper is the angle between the slanted side of the funnel shape and the horizontal line segment.

[0041] (c) Optimization of hopper capacity To reduce raw material segregation within the hopper, optimizing the hopper capacity is also a desirable measure. Here, an appropriate hopper capacity is within the range of 15 to 120% by mass of the extruder's hourly discharge volume. The reason for setting the hopper capacity within the above range is that if the hopper capacity is less than 15% by mass of the discharge volume, it becomes difficult to ensure a stable supply of raw materials, and if the hopper is too large, the raw material chip mixture will remain in the hopper for a long time, which may cause chip segregation. More preferably, the hopper capacity is within the range of 20 to 100% by mass of the extruder's hourly discharge volume.

[0042] (d) Reduction of fine powder Reducing the proportion of fine powder generated by the abrasion of the raw material chips used is also a preferred means to suppress raw material segregation. Fine powder gets between the chips, and the reduced friction between the chips makes it easier for smaller chips to fall, thus promoting segregation. It is preferable to remove the fine powder generated during the process to reduce the proportion of fine powder contained in the hopper. The proportion of fine powder contained is preferably controlled to within 1% by mass throughout the entire process in which the raw material chips enter the extruder, and more preferably to within 0.5% by mass. Specifically, fine powder can be removed by methods such as passing the material through a sieve during chip formation with a strand cutter, or by passing the raw material chips through a cyclone-type air filter when pneumatically transporting them.

[0043] (e) Use of uncrystallized raw materials Segregation of raw materials is more likely to occur when there is a large difference in specific gravity among the multiple raw material chips used. In other words, chips with a higher specific gravity (heavier chips) tend to fall first as the chip mixture falls, thus promoting segregation. In this invention, recycled PET bottle raw material chips and amorphous raw material chips are used in a mixture, but since recycled PET bottle raw material is a crystalline raw material, its specific gravity is higher than that of amorphous raw material, resulting in differences in specific gravity among the chips. On the other hand, the raw material chips undergo a drying process to reduce the moisture content of the resin before being fed into the extruder, or separately dried raw material chips are fed into the hopper. In order to shorten the drying time for recycled PET bottles, the chips are heated to about 160°C to dry them. At this time, the polyester crystallizes, and the specific gravity increases compared to the chips before drying. Therefore, the difference in specific gravity between the heated and dried recycled PET bottle raw material chips and the amorphous raw material chips increases further, promoting segregation. Therefore, it is preferable to use a method in which the raw material chips used in the present invention are dried at room temperature under vacuum to reduce the moisture content in order to prevent crystallization. Alternatively, it is preferable to use raw material chips that have not undergone crystallization without drying them at all, and to use a twin-screw extruder with a vent to perform melt extrusion while removing moisture from the vent.

[0044] (f) Agitation inside the hopper It is also effective to reduce material segregation by stirring the inside of the hopper containing the mixture of raw material chips. For example, by installing a stirring device with blades or a stirring device with a spiral ribbon in the hopper, the resins can be stirred and mixed together while being supplied to the next process (hopper or extruder), thereby reducing material segregation. The location of the hopper with stirring function is not particularly limited, but it is more preferable to have it be a hopper close to the extruder, and it is especially preferable to stir it in the final hopper directly above the extruder.

[0045] (g) Installation of cone baffle The fall of raw material chips at the bottom of the hopper is affected by the pressure (so-called powder pressure) caused by the weight of the raw material chips above them. While film is usually produced continuously, the supply of raw material chips to the hopper is often intermittent. Continuous supply of raw resin would require the chip transport system to be constantly running, increasing the frequency of malfunctions. Furthermore, it would be necessary to balance the supply amount with the consumption amount, making accurate weighing difficult for resin chips with low raw material supply quantities. Intermittent supply means that when the raw material inside the hopper is consumed and falls below a certain capacity level, a certain amount of raw material chips are supplied, the supply stops when it reaches a certain level, and then resumes when consumption progresses. In this case, the hopper's capacity level is constantly fluctuating, and therefore the powder pressure at the bottom of the hopper also fluctuates. Fluctuations in powder pressure are undesirable because they promote raw material segregation. Therefore, it is preferable to install a cone baffle (cone-shaped baffle) at the bottom of the hopper to cut off the pressure from the raw material chips at the top of the hopper. By setting the minimum capacity level above the cone baffle, it becomes possible to maintain a constant powder pressure on the raw material chips below the cone baffle at the bottom of the hopper, thereby reducing raw material segregation. The shape of the cone baffle is not particularly limited, but it is preferably conical or triangular pyramidal.

[0046] (h) Mixing directly above the extruder Another preferred method is to insert piping into the hopper (final hopper) directly above the extruder and mix the chips immediately before extrusion. Since the raw material chips that are prone to segregation are mixed just before the extruder, the opportunity for segregation to occur is extremely low, making it effective in reducing segregation. However, it is necessary to use equipment that satisfies at least the following equation 3. An example of a specific mixing procedure is shown in Figure 1. Figure 1 is a schematic diagram showing an example of the relationship between an extruder 2 equipped with a hopper 1 and an inner pipe, and Figure 2 is an enlarged view of part A in Figure 1. As shown in Figures 1 and 2, the raw material chips to be mixed are supplied from the inner pipe 3, and other raw material chips are supplied from the top of the hopper 1. And since the outlet 4 of the inner pipe 3 is directly above the extruder (more precisely, directly above the raw material chip supply port 5 of the extruder 2), the mixing ratio of the raw material mixed chips can be kept constant. The height (H2) of the outlet 4 of the inner pipe 3 preferably satisfies the relationship of the following formula 3, and more preferably satisfies the relationships of both formulas 3 and 4. H2 < H1 ··· (Formula 3) (In the formula, H1 represents the height of the portion where the inner wall of the hopper is vertical (see Figure 2)) 0.5 × L / tanθ < H2 ··· (Formula 4) (In the formula, L represents the inner diameter of the outlet 4 of the inner pipe 3 (see Figure 2). θ is the angle of repose of the raw material chips that have entered the hopper before mixing.) By satisfying Formula 3, the position (H3) where the raw material chips are mixed can be made above the extruder, and it is possible to prevent air from entering the extruder and generating bubbles. The height H3 (= H2 - 0.5 × L / tanθ) of the mixing position of the raw material chips is preferably higher than 0 m and less than 2 m. Making it higher than 0 m is preferable because it can prevent air from entering the extruder. Also, making it less than 2 m can shorten the distance to the extruder and prevent raw material segregation. The height H3 is preferably 0.3 m or more and 1.7 m or less, and more preferably 0.6 m or more and 1.4 m or less.

[0047] In order to obtain a film roll with small variations in the longitudinal thermal shrinkage rate and variations in the isophthalic acid ratio of the present invention by adopting the blending method, it is preferable to perform all of the above (a) to (d). However, even if all of (a) to (d) are implemented, it is insufficient to reduce raw material segregation, and it is preferable to adopt one or more of the four means (e) to (h), and more preferably to adopt two or more. Alternatively, without adopting the above blending method, the following means (i) can be adopted.

[0048] (i) Use of a twin-screw extruder and a side feeder In addition to the above method, as a method of using the raw material chips without blending, a method using a twin-screw extruder and a side feeder can be preferably used. Specifically, when using two types of raw materials, amorphous raw material chips and recycled PET bottle raw material chips, it is preferable to supply amorphous raw material chips to twin-screw extruder 1, melt them in the extruder, then supply recycled PET bottle raw material chips to another twin-screw extruder (hereinafter referred to as twin-screw extruder 2), melt them, and directly introduce them into twin-screw extruder 1 via piping using a side-feed method, after which the two types of raw materials are mixed inside twin-screw extruder 1. Since there is no process of mixing the raw materials in chip form, the aforementioned concern about segregation of raw material chips is essentially eliminated. The mixing ratio of the raw materials can be precisely adjusted by controlling the rotation speed of the screw feeder or other means at which the raw material chips fed into the twin-screw extruder 2 (side feeder) are supplied. Therefore, it is possible to minimize variations in composition along the longitudinal direction of the film.

[0049] The twin-screw extruder 1 preferably has a venting function. To prevent the inclusion of air bubbles when raw materials are introduced by the side feeder, it is preferable to provide a vent at the starting position where the raw materials are mixed to remove air. It is preferable that the raw material chips supplied to twin-screw extruders 1 and 2 are each single-type. This is to eliminate the process of mixing the raw material chips before supplying them to the extruders, thereby essentially eliminating segregation of the raw material chips. When using three or more types of raw materials, it is preferable to provide another twin-screw extruder 3 and directly introduce the raw materials into the twin-screw extruder 1 using a side-feed method.

[0050] The manufacturing process for the heat-shrinkable polyester film of the present invention is described below, for each of the following steps: (1) melt extrusion and casting of an unstretched sheet, (2) transverse stretching, and (3) final heat treatment.

[0051] (1) Melt extrusion and casting process of unstretched sheets Regarding the mixing and supply of raw materials, the measures to prevent raw material segregation described above are implemented, and the material is extruded into a sheet using an extruder at a temperature of 220-280°C, using existing methods such as the T-die method or the tubular method. Note that if the extrusion temperature exceeds 280°C, the intrinsic viscosity of the polyester resin decreases, making it more prone to breakage during the film-forming process and making it difficult to obtain a steady-state film, which is undesirable. If the temperature falls below 220°C, some of the raw materials remain unmelted, which can overload the machine, and the unmelted resin can become the starting point for breakage during film-forming, which is also undesirable. Subsequently, an unstretched film can be obtained by rapidly cooling the film melted by extrusion. As a method for rapidly cooling the molten resin, a method of casting the molten resin from a die onto a rotating drum and rapidly cooling and solidifying it to obtain a substantially unoriented resin sheet can be suitably employed. Furthermore, the shear rate when the molten resin is extruded from the die opening is preferably 100 sec⁻¹ or higher, and more preferably 150 sec⁻¹ or higher. The higher the shear rate, the more the variation in shrinkage rate and thickness unevenness in the longitudinal direction of the film can be suppressed. This is because the higher the shear rate, the more stable the resin extrusion pressure at the die opening (outlet). If the shear rate is less than 100 sec⁻¹, the resin extrusion pressure at the die outlet becomes unstable, and pulsation (thickness variation of the unstretched film in the longitudinal direction) is more likely to occur. As a result, the stretching in the longitudinal direction, which will be described later, will not be uniform, leading to larger variations in thermal shrinkage rate and thickness unevenness in the longitudinal direction. On the other hand, if the shear rate is greater than 600 sec⁻¹, the polyester molecular chains are broken (decomposed), which not only reduces the intrinsic viscosity but also causes resin residue and other debris to adhere to the die's discharge portion, resulting in poor productivity, which is undesirable.

[0052] The shear rate at the die exit was calculated using Equation 5 below. γ=6Q / (W×H2) (Formula 5) γ; Shear rate (sec -1 ) Q: Raw material discharge volume from extruder (cm²) 3 / sec) W; Width of the die opening (cm) H; Die opening gap (dimensions in cm)

[0053] (2) Lateral stretching process For stretching the film, uniaxial stretching, which stretches only in the width direction, is preferred. Although it is possible to perform longitudinal stretching 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 hold both ends of the sheet with clips and heat it. In the preheating process, the film is heated to a predetermined temperature with hot air, and then in the stretching process, 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. 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 also undesirable because the stretching force is too low, preventing the film from being sufficiently shrinkable.

[0054] (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 transverse 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 transverse stretching temperature + 5°C, when the final product is stored at room temperature, the shrinkage in the width direction over time (so-called natural shrinkage rate) becomes large, which is undesirable. Furthermore, a longer heat treatment time is preferable, but if it is too long, the equipment will become enormous, so a time of 10 seconds or less is preferable. Furthermore, from the viewpoint of reducing fluctuations in thermal shrinkage rate, it is preferable to control the range of fluctuations in the film surface temperature measured at arbitrary points in each of the preheating, stretching, and final heat treatment processes in the transverse stretching process and the final heat treatment process, preferably within ±1°C of the average temperature, and more preferably within ±0.5°C of the average temperature. [Examples]

[0055] 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.

[0056] [Sampling method for evaluation samples] The surface layer was defined as the portion of the film obtained by removing 1 meter of film from the film roll, and the first sample was cut from the center in the width direction. Subsequently, while unwinding the film roll using a winding machine, samples were cut from the center in the width direction every 100 meters. Sampling was stopped when the remaining length of the film roll was less than 100 meters, and the samples collected up to that point were evaluated.

[0057] [Thermal shrinkage rate] The film was cut into 10cm x 10cm squares and subjected to heat shrinkage by being treated in hot water at a temperature of 90℃ ± 0.5℃ for 10 seconds under no load. After that, the dimensions of the film in the longitudinal direction (direction perpendicular to the main shrinkage direction) and the width direction (main shrinkage direction) were measured, and the heat shrinkage rate was calculated according to the following formula (1). Furthermore, regarding the variation (variation) in shrinkage rate, the thermal shrinkage rate was measured for samples sampled using the method described above, and the average, maximum, and minimum values ​​were determined. Thermal shrinkage rate = ((Length before shrinkage - Length after shrinkage) / Length before shrinkage) × 100 (%) Equation (1)

[0058] [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 cumulative measurements. In the NMR measurement, the peak intensity of a predetermined proton was calculated to determine the amount of the component in 100 mol% of the diacid component. The average, maximum, and minimum values ​​of the isophthalic acid component ratio (mol%) of the samples sampled every 100 m in the longitudinal direction as described above were determined.

[0059] [Thickness variations in the longitudinal direction] A long roll of film, measuring 100 m in length and 40 mm in width, was sampled and measured at a speed of 5 m / min using a continuous contact thickness gauge manufactured by Micron Measuring Instruments Co., Ltd. The maximum thickness during measurement was defined as Tmax., the minimum thickness as Tmin., and the average thickness as Tave. The thickness variation in the film width direction was calculated using the following formula (2). Thickness unevenness = {(Tmax.-Tmin.) / Tave.} × 100 (%) Equation (2)

[0060] [Tg (Glass transition temperature)] A differential scanning calorimetry analyzer (Seiko Electronics Industries, Ltd., DSC220) 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 120°C at a rate of 10°C / min under a nitrogen gas atmosphere. Tg(°C) was determined according to JIS-K7121-1987.

[0061] [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.

[0062] [Shrinkage finish evaluation] By bonding both ends of the film with dioxolane, cylindrical labels (labels with the main shrinkage direction of the heat-shrinkable film as the circumferential direction) were created, and 3000 labels were produced by cutting them. The diameter of the labels in the shrinkage direction was 70 mm. Subsequently, the labels were attached to 500 ml PET bottles (body diameter 62 mm, minimum neck diameter 25 mm) by heat shrinking using a Fuji Astec Inc. steam tunnel (model: SH-1500-L) 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. 5: Best finish 4: Good finish 3: There are a few minor flaws (two or fewer). 2: Has flaws (3-5 places) 1: Many flaws (6 or more) The drawbacks here are wrinkles, folded edges on the label, uneven shrinkage, and insufficient shrinkage. A score of 4 or higher was considered acceptable, and a score of 3 or lower was considered unacceptable. 3000 samples were evaluated. The shrinkage finish defect rate (%) was calculated according to the following formula. Shrinkage defect rate (%) = Number of defective samples / Total number of samples × 100

[0063] <Measuring the angle of repose> A stainless steel funnel with an 18mm inner diameter at the tip outlet was placed directly above a horizontal stainless steel plate, with a distance (height) of 200mm from the tip to the plate. 3kg of raw material chips were poured into the funnel and dropped from the tip onto the stainless steel plate. At this time, the chips were dropped at a rate of approximately 50g / min. The dropped raw material chips formed a conical mound and stabilized. The angle between the slope of the mound and the stainless steel plate at this time was measured using a protractor and defined as the angle of repose.

[0064] <Preparation of amorphous polyester raw material (polyester A) 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, 55 mol% ethylene glycol (EG), 30 mol% neopentyl glycol (NPG), and 15 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 1 with an intrinsic viscosity of 0.77 dl / g. The average size of polyester A resin was calculated from 100 resin samples. Assuming the resin was elliptical in shape, the major axis, minor axis, and length (strand cut length) of the elliptical cross-section were measured using calipers. The results showed a major axis of 3.1 mm, a minor axis of 2.1 mm, a height of 3.3 mm, and an angle of repose of 37 degrees. The composition, tip size, and angle of repose are shown in Table 1.

[0065] <Recycled PET bottle material (Polyester B)> Polyester B 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 resin size was measured using the same method as described above, and the results were a major diameter of 2.9 mm, a minor diameter of 2.0 mm, and a length of 3.4 mm, with an angle of repose of 36 degrees. The major diameter was -6% compared to polyester A, the minor diameter was -5% compared to polyester A, and the length was +3% compared to polyester A. The intrinsic viscosity of polyester B was 0.68 dl / g.

[0066] <Preparation of amorphous polyester raw material (polyester C) chips> Polyester C was polymerized in the same way as polyester A, and the resin size was changed by altering the die pore size and cutter speed when forming the strands. Calculating the average size of polyester C resin from 100 samples, the result was a major axis of 3.8 mm, a minor axis of 2.5 mm, a height of 4.3 mm, and an angle of repose of 43 degrees. The major axis was ±31% compared to polyester B, the minor axis was +25% compared to polyester B, and the length was +26% compared to polyester B. The intrinsic viscosity of polyester C was 0.77 dl / g.

[0067] [Table 1]

[0068] <Method for manufacturing heat-shrinkable film> [Example 1] The polyester A raw material chips described above were dried at room temperature under vacuum to a moisture content of less than 100 ppm. On the other hand, the polyester B raw material chips were heated at 150°C under vacuum to a moisture content of less than 100 ppm. The raw material chips were mixed while being supplied separately from the hopper where they were stored to the final hopper directly above the extruder using a quantitative screw feeder. The supply was performed by pneumatic transport, and fine powder was removed using a cyclone-type air filter. The mixing ratio of the raw materials was polyester A:polyester B = 70:30. The raw material chips were stirred in the final hopper. The stirring device used was a type in which a spiral ribbon rotated to stir the raw material chips. The capacity of the final hopper was 190 kg, and the supply rate to the extruder was 500 kg per hour. The hopper tilt angle was 70°. Subsequently, the mixed raw material chips were supplied from the final hopper to the extruder, and melt extrusion was performed using a single-screw extruder at an extrusion temperature of 280°C to extrude the molten resin from the T-die. After that, it was rapidly cooled to obtain an unstretched film with a thickness of 135 μm. The shear rate at this time was 180 sec. -1 Furthermore, the glass transition temperature of the unstretched film was 65°C. The unstretched film was guided into a tenter and preheated until the film temperature reached 90°C. Then, by widening the clip spacing, the film was stretched 4.5 times in the width direction at a film temperature of 90°C. Furthermore, it was guided into a final heat treatment zone and heat-treated at a film temperature of 100°C for 6 seconds. During this process, the temperature fluctuation of the film remained within ±0.5°C of the average temperature in the preheating, stretching, and final heat treatment stages. After heat treatment, the film was cooled, and both ends were continuously cut and wound into a roll to obtain a master roll. The thickness of the stretched film was 30 μm. The master roll obtained as described above was used in a slitter to produce a slit roll with a width of 800 mm and a length of 4000 m, thereby obtaining a heat-shrinkable polyester film roll. The manufacturing method is shown in Table 2, and the film evaluation results are shown in Table 3. The evaluation results showed that the film roll was suitable if it had sufficient shrinkage in the width direction, small variation in shrinkage rate and isophthalic acid ratio in the longitudinal direction, good shrinkage finish, and an extremely low defect rate.

[0069] [Example 2] A heat-shrinkable polyester film roll was manufactured in the same manner as in Example 1, except that stirring was not performed in the final hopper and a cone-shaped baffle was provided. The manufacturing method is shown in Table 2, and the film evaluation results are shown in Table 3. The evaluation results showed that the film roll was suitable if it had sufficient shrinkage in the width direction, small variation in shrinkage rate and isophthalic acid ratio in the longitudinal direction, good shrinkage finish, and an extremely low defect rate.

[0070] [Example 3] A heat-shrinkable polyester film roll was manufactured in the same manner as in Example 1, except that stirring was not performed in the final hopper, and the raw material chips of polyester A and polyester B were mixed via an inner pipe just before the extruder. In this case, the raw material chips of polyester A were supplied from the top of the final hopper, and the raw material chips of polyester B were supplied via an inner pipe. At this time, the inner diameter of the inner pipe was 0.2m, and in Figures 1 and 2, height H1 was 5m, height H2 was 1.5m, and height H3 was 1.37m. The manufacturing method is shown in Table 2, and the film evaluation results are shown in Table 3. The evaluation results showed that the film roll was suitable if it had sufficient shrinkage in the width direction, small variation in shrinkage rate and isophthalic acid ratio in the longitudinal direction, good shrinkage finish, and an extremely low defect rate.

[0071] [Example 4] Polyester raw materials A and B were chipped and then placed into their respective hoppers without drying. They were then supplied to an extruder in the same manner as in Example 2. A twin-screw extruder with a vent was used, and while removing moisture from the raw material chips by degassing through the vent, melt extrusion was performed to produce film rolls in the same manner as in Example 2. The manufacturing method is shown in Table 2, and the film evaluation results are shown in Table 3. The evaluation results showed that the film roll was suitable if it had sufficient shrinkage in the width direction, small variation in shrinkage rate and isophthalic acid ratio in the longitudinal direction, good shrinkage finish, and an extremely low defect rate.

[0072] [Example 5] Similar to Example 1, the raw material chips were dried and placed into their respective hoppers. Afterward, without mixing the raw material chips in the hoppers, the polyester A raw material chips were fed into a twin-screw extruder 1 with a vent. Meanwhile, the polyester B raw material chips were fed into a separate twin-screw extruder 2, and the molten polyester B resin discharged from the tip of twin-screw extruder 2 was side-fed into twin-screw extruder 1. Each raw material chip was fed into the extruder from the hopper using a screw feeder, and the feeder rotation speed was adjusted so that the raw material mixing ratio was polyester A:polyester B = 70:30. A vent was designed in twin-screw extruder 1 at the point where the resins from twin-screw extruder 2 merged, and degassing was performed. Polyester A and polyester B were mixed inside twin-screw extruder 1 while being melt-extruded, then extruded from the T-die, and then rapidly cooled to obtain an unstretched sheet. The subsequent manufacturing method was the same as in Example 1. The manufacturing method is shown in Table 2, and the film evaluation results are shown in Table 3. The evaluation results showed that the film roll was suitable if it had sufficient shrinkage in the width direction, small variation in shrinkage rate and isophthalic acid ratio in the longitudinal direction, good shrinkage finish, and an extremely low defect rate.

[0073] [Example 6] The mixing ratio of polyester raw materials was set to polyester A:polyester B = 80:20. The procedure was carried out under the same conditions as in Example 5, except that the transverse stretching temperature in the tenter was set to 87°C and the final heat treatment temperature was set to 96°C. At this time, the Tg of the unstretched film was 62°C, the thickness of the unstretched film was 135 μm, and the thickness of the stretched film was 30 μm. The manufacturing method is shown in Table 2, and the film evaluation results are shown in Table 3. The evaluation results showed that the film roll was suitable if it had sufficient shrinkage in the width direction, small variation in shrinkage rate and isophthalic acid ratio in the longitudinal direction, good shrinkage finish, and an extremely low defect rate.

[0074] [Example 7] The mixing ratio of polyester raw materials was set to polyester A:polyester B = 60:40. The procedure was carried out under the same conditions as in Example 5, except that the transverse stretching temperature in the tenter was set to 94°C and the final heat treatment temperature was set to 103°C. At this time, the Tg of the unstretched film was 69°C, the thickness of the unstretched film was 135 μm, and the thickness of the stretched film was 30 μm. The manufacturing method is shown in Table 2, and the film evaluation results are shown in Table 3. The evaluation results showed that the film roll was suitable if it had sufficient shrinkage in the width direction, small variation in shrinkage rate and isophthalic acid ratio in the longitudinal direction, good shrinkage finish, and an extremely low defect rate.

[0075] [Comparative Example 1] Polyester B and polyester C raw material chips were mixed in a mixing ratio of polyester B:polyester C = 30:70 inside the final hopper. All other conditions were the same as in Example 2. The manufacturing method is shown in Table 2, and the film evaluation results are shown in Table 3. The evaluation revealed that although the film roll had sufficient shrinkage in the width direction, large differences in raw material chip size and angle of repose led to raw material segregation. As a result, there was considerable variation in shrinkage rates and isophthalic acid ratios in both the width and length directions. While the shrinkage finish was sometimes good, the film roll had a high defect rate.

[0076] [Comparative Example 2] The method was the same as in Example 2, except that the supply rate to the extruder was changed to 120 kg per hour. The manufacturing method is shown in Table 2, and the film evaluation results are shown in Table 3. The evaluation revealed that although the film roll had sufficient shrinkage in the width direction, the excessively long residence time in the final hopper caused raw material segregation. As a result, there was significant variation in shrinkage rates and isophthalic acid ratios in both the width and length directions. While the shrinkage finish was sometimes good, the film roll had a high defect rate.

[0077] [Example 3] The procedure was the same as in Example 2, except that the inclination angle of the final hopper was changed to 50°. The manufacturing method is shown in Table 2, and the film evaluation results are shown in Table 3. The evaluation revealed that although the film roll had sufficient shrinkage in the width direction, the small tilt angle of the hopper caused raw material segregation, resulting in large variations in shrinkage rates and isophthalic acid ratios in both the width and length directions. While the shrinkage finish was sometimes good, the film roll had a high defect rate.

[0078] [Example 4] The procedure was the same as in Example 3, except that the height H2 of the inner pipe was changed to 7m. In this case, the height H3 was 6.87m. The manufacturing method is shown in Table 2, and the film evaluation results are shown in Table 3. The evaluation revealed that although the film roll had sufficient shrinkage in the width direction, it did not satisfy equations 3 and 4 for the inner pipe, resulting in raw material segregation. Due to the large variation in shrinkage rates and isophthalic acid ratios in both the width and longitudinal directions, the shrinkage finish was sometimes good, but the defect rate was high.

[0079] [Table 2]

[0080] [Table 3] [Industrial applicability]

[0081] The heat-shrinkable polyester film roll of the present invention contains a predetermined amount of recycled PET bottle material as described above, and has high shrinkage in the width direction. Furthermore, because the variation in composition in the longitudinal direction of the roll is small, the variation in shrinkage in both the width and longitudinal directions is extremely small. As a result, when it is continuously processed into beverage labels and the like and used after shrinking, the occurrence rate of defects such as wrinkles and distortions is extremely low.

Claims

1. A film roll made of a heat-shrinkable polyester film, characterized in that it contains 5% to 45% by mass of recycled PET bottle raw materials and is composed of a polyester containing isophthalic acid components, the polyester contains 50 mol% or more of ethylene terephthalate per 100 mol% of all components, and contains one or more monomer components selected from the group consisting of neopentyl glycol, 1,4-cyclohexanedimethanol, 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 an amount such that the total amount of these monomers per 100 mol% of the polyhydric alcohol component or per 100 mol% of the polyhydric carboxylic acid component is 14 mol% or more, and satisfies the following requirements (1) to (4). (1) When film samples taken at 100m intervals along the longitudinal direction of the roll are immersed in 90°C hot water for 10 seconds, the average shrinkage rate in the main shrinkage direction is 40% or more, and all samples are within ±3% of the average value. (2) In film samples taken at 100m intervals along the length of the roll, the polyester constituting the film must all have an isophthalic acid content ratio within 100 mol% of the total acid components that is within ±0.3 mol% of its average value. (3) The thickness variation in the longitudinal direction of the roll is 20% or less. (4) When film samples taken at 100m intervals along the longitudinal direction of the roll are immersed in 90°C hot water for 10 seconds, the shrinkage rate in the direction perpendicular to the main shrinkage direction shall be within ±3% of the average value for all samples.

2. The heat-shrinkable polyester film roll according to claim 1, characterized in that the heat-shrinkable polyester film is formed from a mixture of at least recycled PET bottle material and one or more polymer chips of different compositions.

3. The heat-shrinkable polyester film roll according to claim 1 or 2, characterized in that the polyester constituting the heat-shrinkable polyester film has ethylene terephthalate as its main component.

4. A heat-shrinkable polyester film roll according to any one of claims 1 to 3, characterized in that, in film samples taken at 100m intervals along the longitudinal direction of the roll, the average value of the isophthalic acid content ratio in 100 mol% of the total acid components of the polyester constituting the film is 0.3 mol% or more and 3.0 mol% or less.

Images