Heat-shrinkable polyester film roll

Abstract

To provide a heat shrinkable polyester film roll that reduces occurrence of defects such as wrinkles or vertical recesses in a heat shrinkage process, which are caused by variation of a heat shrinkage rate within a film roll, even when a PET bottle-recycled raw material is contained.SOLUTION: A film roll is made of a heat-shrinkable polyester-based film composed of polyester containing 5 to 50 mass% of a recycled PET material and iso-phthalic acid components, characterized by satisfying the following requirements (1) to (3): (1) when a film sample taken at a pitch of 100 m in the roll's longitudinal direction is immersed in 90°C warm water for 10 seconds, the shrinkage rate in the main shrinkage direction is at least 40% on average, and the shrinkage rates of all samples are within the average ±3%; (2) in the film samples taken at a pitch of 100 m in the roll's longitudinal direction, the ratio of iso-phthalic acid in the total acid components of 100 mol% in the polyester that constitutes the film is within the average ±0.3 mol% for all samples; (3) the thickness variation in the roll's longitudinal direction is 20% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a film roll obtained by winding up a heat-shrinkable polyester film. More specifically, the present invention relates to a heat-shrinkable polyester film roll that uses recycled PET bottles as raw materials and yet has high shrinkability, small variations in shrinkage properties in the longitudinal direction of the film roll, and little occurrence of defects such as insufficient shrinkage, uneven shrinkage, distortion, and longitudinal shrinkage in post-processing. [Background technology]

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

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

[0004] Heat-shrinkable polyester film labels can also contribute to the life cycle of PET, from production to use and disposal, by using some of the above-mentioned recycled (regenerated) PET bottle raw materials, thereby helping to reduce the environmental impact.

[0005] Heat-shrinkable polyester films generally require a low crystallinity of the polyester that makes up the film to achieve high shrinkage. However, recycled PET bottle materials are highly crystalline. Therefore, when using recycled PET bottle materials, it is essential to mix at least two types of raw materials, including a highly amorphous raw material.

[0006] After production, heat-shrinkable film is wound up into a roll and sent in the form of a film roll to a process for printing various designs, and after printing is completed, it is slit as necessary to fit the size of the label or the like to be used in the final product, and then the left and right ends of the film are overlapped and sealed by means of solvent bonding or the like to form a tubular body, which is then cut and processed into labels, bags, etc. The labels or bags are then attached to containers and passed on a belt conveyor or the like through a shrink tunnel (hot air tunnel) that blows steam to cause thermal shrinkage, causing them to adhere tightly to the container.

[0007] However, in this heat shrinking process, if the heat shrinkage rate varies from one label or bag to another, that is, if there is a large variation, the heating conditions in the tunnel will be the same, resulting in labels or bags that do not exhibit the appropriate heat shrinkage rate, which will cause poor appearance due to insufficient shrinkage, uneven shrinkage, wrinkles, distortion of the design, vertical sink marks, etc., and will not be usable as a final product. Vertical sink marks here refer to uneven lengths of labels after shrinkage, causing the upper edge of the label to curve downward or the lower edge to curve upward. The appearance is poor.

[0008] Such fluctuations in the heat shrinkage rate are largely influenced by fluctuations in the polyester composition constituting the film in the longitudinal direction of the roll. Typically, heat-shrinkable polyester films are made by feeding various raw material chips into an extruder, melting them, and extruding the molten resin through a die to obtain an unstretched raw film, which is then stretched.However, variations in composition occur before the various raw material chips are fed into the extruder.In other words, it is thought that the variations in composition occur because the various raw material chips are not mixed uniformly and segregate.

[0009] Segregation does not occur when the components necessary for polyester film are made into raw chips of a single composition (using only one type of raw chip). However, as mentioned above, when using recycled PET bottles, at least two types of raw chips must be mixed, which creates the risk of segregation. In other words, using recycled PET bottles carries the risk of variations in the thermal shrinkage rate in the longitudinal direction. For example, during the PET bottle recycling process, it is possible to add amorphous polyester when crushing, cleaning, and re-chipping PET bottles to obtain raw chips of a single composition containing all the components necessary for film. However, this is not practical because recycled materials are also used for purposes other than film. Furthermore, the inventors have found that recycled PET bottle raw materials are often made by randomly mixing various PET bottles, and that repeated use reduces the molecular weight, etc., of the raw materials. In addition, additives such as high-crystallization nucleating agents are often used. When used as a raw material for film, the inventors have found that this has the disadvantage that fluctuations in the blending amount due to segregation have a greater impact on the physical properties of the film than with other raw materials.

[0010] Patent Document 1 describes a heat-shrinkable polyester film made from recycled PET bottle materials, but does not describe fluctuations in the heat shrinkage rate in the longitudinal direction. Patent Document 2 describes a heat-shrinkable polyester film containing a high proportion of recycled PET bottle raw materials, but the method described makes it difficult to achieve a shrinkage rate of 45% or more at 90°C, and there is no description of fluctuations in the heat shrinkage rate in the longitudinal direction. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent No. 5320737 [Patent Document 2] Patent No. 6402954 Summary of the Invention [Problem to be solved by the invention]

[0012] An object of the present invention is to provide a heat-shrinkable polyester film roll that reduces the occurrence of defects such as wrinkles and vertical sink marks during a heat-shrinking process due to variations in the heat shrinkage rate within the film roll, even when the film contains recycled PET bottle raw materials. [Means for solving the problem]

[0013] The present inventors have conducted extensive research to solve the above problems and have completed the present invention, which comprises the following features.

[0014] 1. A film roll made of a heat-shrinkable polyester film that contains 5% by mass or more and 50% by mass or less of recycled PET bottle raw materials and is made of a polyester containing an isophthalic acid component, and that satisfies the following requirements (1) to (3): (1) Film samples taken at 100m intervals along the length 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 average value for all samples is within ±3%. (2) In film samples taken at 100m intervals along the roll length, the polyester constituting the film has an isophthalic acid content of 100 mol% of the total acid components, all of which are within the average value ±0.3 mol%. (3) The thickness variation in the longitudinal direction of the roll is 20% or less. 2. A heat-shrinkable polyester film roll according to 1., characterized in that the heat-shrinkable polyester film is formed from a mixture of at least recycled PET bottle materials and one or more polymer chips with different compositions. 3. A heat-shrinkable polyester film roll according to 1. or 2., characterized in that the polyester constituting the heat-shrinkable polyester film is composed mainly of ethylene terephthalate. 4. A heat-shrinkable polyester film roll according to any one of 1. to 3., characterized in that in film samples taken at 100 m intervals in the longitudinal direction of the roll, the polyester constituting the film has an average isophthalic acid content of 0.3 mol% or more and 3.0 mol% or less in 100 mol% of all acid components. 5. The heat-shrinkable polyester film roll according to any one of 1. to 4., wherein the heat-shrinkable polyester film roll has a wound length of 1000 m or more. 6. A heat-shrinkable polyester film roll according to any one of 1. to 5., characterized in that when film samples taken at 100 m intervals in the longitudinal direction of the roll are immersed in 90°C hot water for 10 seconds, the average shrinkage rate in a direction perpendicular to the main shrinkage direction is 0% or more and 15% or less, and the shrinkage rates of all samples are within ±3% of the average value. [Effects of the Invention]

[0015] Even when the heat-shrinkable polyester film roll of the present invention is mixed with recycled PET bottle 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 sink marks during the heat shrinkage process. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic diagram showing an example of the relationship between an extruder 2 equipped with a hopper 1 and an inner pipe. [Figure 2] FIG. 2 is an enlarged view showing a portion A in FIG. DETAILED DESCRIPTION OF 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) is a polyester primarily composed of ethylene terephthalate. That is, the polyester contains 50 mol% or more, preferably 60 mol% or more, of ethylene terephthalate relative to 100 mol% of all constituent components of the polyester. As described below, the polyester also contains an isophthalic acid component. Examples of dicarboxylic acid components other than terephthalic acid and isophthalic acid that constitute 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 an aliphatic dicarboxylic acid (such as adipic acid, sebacic acid, or decanedicarboxylic acid) is contained, the content is preferably less than 3 mol %. Heat-shrinkable polyester films obtained using polyesters containing 3 mol % or more of these aliphatic dicarboxylic acids are undesirable because they have insufficient film stiffness and cause problems during slitting and post-processing.

[0019] It is also preferable not to include trivalent or higher polycarboxylic acids (for example, trimellitic acid, pyromellitic acid, and anhydrides thereof), as heat-shrinkable polyester films obtained using polyesters containing these polycarboxylic acids will have difficulty achieving the required high shrinkage ratio.

[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 whose glass transition temperature (Tg) is adjusted to 60 to 80°C by containing one or more cyclic diols such as 1,4-cyclohexanedimethanol or diols having 3 to 6 carbon atoms (for example, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, hexanediol, diethylene glycol, etc.).

[0022] Furthermore, the polyester used in the heat-shrinkable polyester film of the present invention preferably contains at least 14 mol%, more preferably at least 16 mol%, and particularly preferably at least 18 mol% of one or more amorphous monomer components relative to 100 mol% of the polyhydric alcohol or polycarboxylic acid components in the total polyester resin. Examples of monomers that can form 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. Among these, neopentyl glycol or 1,4-cyclohexanedimethanol is preferred. The upper limit of the total amount of amorphous monomer components is preferably 40 mol% or less. It is more preferably 38 mol % or less, and even more preferably 36 mol % or less.

[0023] The polyester used in the heat-shrinkable polyester film of the present invention preferably does not contain a diol having 8 or more carbon atoms (e.g., octanediol, etc.) or a polyhydric alcohol having a valence of 3 or more (e.g., trimethylolpropane, trimethylolethane, glycerin, diglycerin, etc.). A heat-shrinkable polyester film obtained using a polyester containing such a diol or polyhydric alcohol will have difficulty achieving the required high shrinkage percentage.

[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. Furthermore, if the intrinsic viscosity exceeds 1.50 dL / g, stretching becomes difficult, which may cause breakage, which is also undesirable. The intrinsic viscosity is more preferably 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] In addition, various additives, such as waxes, antioxidants, antistatic agents, crystal nucleating agents, viscosity reducers, heat stabilizers, coloring pigments, color inhibitors, and UV absorbers, can be added to the resin forming the heat-shrinkable polyester film of the present invention as needed. It is preferable to add fine particles as a lubricant to the resin forming the heat-shrinkable polyester film of the present invention to improve the workability (slipperiness) of the polyethylene terephthalate resin film. Any fine particles can be selected, but examples of inorganic fine particles include silica, alumina, titanium dioxide, calcium carbonate, kaolin, and barium sulfate. Examples of organic fine particles include acrylic resin particles, melamine resin particles, silicone resin particles, and cross-linked polystyrene particles. The average particle size of the fine particles can be selected appropriately within the range of 0.05 to 3.0 μm (as measured with a Coulter counter) as needed. The amount of fine particles added is within the range of 300 to 1,200 ppm of the film, which can achieve both good slipperiness (friction) and transparency.

[0026] The method of incorporating the particles into the resin that forms the heat-shrinkable polyester film includes adding the particles at any stage in the production of the polyester resin, but it is preferable to add the particles as a slurry dispersed in ethylene glycol or the like at the stage of esterification or after the completion of the transesterification reaction and before the start of the polycondensation reaction, and then proceed with the polycondensation reaction. It is also preferable to use a vented kneading extruder to blend a slurry of the particles dispersed in ethylene glycol or water with the polyester resin raw material, or a kneading extruder to blend dried particles with the polyester resin raw material.

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

[0028] The heat-shrinkable polyester film of the present invention contains 5% to 50% by mass of recycled PET bottle raw materials. If the content is less than 5% by mass, the contribution to reducing the environmental impact is extremely small, and the effects of the present invention are not achieved. If more than 50% by mass is used, the amorphousness (amount of amorphous components) of raw materials other than the recycled PET bottle raw materials must be extremely high, which is uneconomical as it increases the polymerization time of the raw materials, making it undesirable. The content of recycled PET bottle raw materials is more preferably 10% to 45% by mass, and even more preferably 20% to 40% by mass.

[0029] In the present invention, when film is sampled at 100 m intervals in the longitudinal direction of the 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 rates of all samples are within the average value ±3%. The hot water shrinkage is calculated from the length before and after shrinkage when treated in hot water at 90°C for 10 seconds under no load, using the following formula 1. Heat shrinkage rate = {(length before shrinkage - length after shrinkage) / length before shrinkage} × 100 (%) (Equation 1) If the average shrinkage rate is less than 40%, the shrinkage amount is so small that the label after heat shrinkage will wrinkle or shrink insufficiently, making it undesirable as a heat shrinkable film. There is no particular upper limit for the shrinkage rate, but the upper limit is about 80%. Furthermore, if the shrinkage rate of the film sampled at 100 m intervals exceeds the range of the average value ±3%, when processed into labels, the shrinkage rate will vary greatly for each label, making it more likely that the labels will have poor appearances such as wrinkles when finished in a shrink tunnel. A more preferred range is the average value ±2.5%, even more preferred is the average value ±2.0%, particularly preferred is the average value ±1.5%, and most preferred is the average value ±1.0%. Furthermore, in the present invention, when film samples are sampled at 100-m intervals along the longitudinal direction of the roll and the shrinkage rate (90°C hot water shrinkage rate) of each film sample is measured, the shrinkage rate in the direction perpendicular to the main shrinkage direction of all samples is within the range of the average value ±3%. If the shrinkage rate in the direction perpendicular to the main shrinkage direction of the film sampled at 100-m intervals exceeds the range of the average value ±3%, when processed into labels, the shrinkage rate for each label will vary greatly, resulting in different label heights when finished in a shrink tunnel, which is undesirable. More preferably, it is within the range of the average value ±2.5%, even more preferably the average value ±2.0%, particularly preferably the average value ±1.5%, and most preferably the average value ±1.0%. Furthermore, the upper limit of the average shrinkage rate in the direction perpendicular to the main shrinkage direction of all samples is 20%. If the average value exceeds 20%, it is undesirable because vertical sink marks will increase during shrink finishing. More preferably, it is within the range of 17% or less, and even more preferably 14% or less. The shrinkage rate in the direction perpendicular to the main shrinkage direction is preferably as low as possible.

[0030] In the heat-shrinkable polyester film roll of the present invention, it is preferable that the content of isophthalic acid in 100 mol % of all polyester acid components is within ±0.3 mol % of the average value in film samples taken at 100 m intervals in the longitudinal direction of the roll. The content of isophthalic acid is measured and calculated by NMR measurement as described below. If the content of isophthalic acid varies beyond the range of the average value ±0.3 mol%, the fluctuation in composition will result in large variations in thermal shrinkage, and as a result, when processed into labels, the shrinkage rate will vary from label to label, making them more likely to suffer from appearance defects such as wrinkles, which is undesirable. The film roll of the present invention uses recycled PET bottle materials, which generally contain a small amount of isophthalic acid as an acid component, as described below. Fluctuations in the ratio of isophthalic acid mean that chips from recycled PET bottle materials and chips from other raw materials segregate. As described above, recycled PET bottle materials often contain additives such as high-crystallization nucleating agents, and their molecular weights decrease with repeated use. Therefore, the impact of segregation on physical property variations within the film roll is greater than with other raw materials. Methods for reducing segregation will be described below. A more preferred range of the isophthalic acid ratio is the average value ±0.2 mol %, and even more preferred is the average value ±0.1 mol %.

[0031] The average content of isophthalic acid is preferably 0.3 mol% or more and 3.0 mol% or less, based on 100 mol% of the total acid components of the polyester. The crystallinity of polyesters used in PET bottles is controlled to improve the bottle appearance, and as a result, polyesters containing 10 mol% or less of isophthalic acid are generally used. In the present invention, since 50% or less of recycled PET bottle raw materials are contained, the upper limit of the average content of isophthalic acid is preferably 3.0 mol% or less. It is 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 %, still more preferably 0.5 mol %, and particularly preferably 0.6 mol %.

[0032] Furthermore, the thickness unevenness in the longitudinal direction of the heat-shrinkable polyester film roll of the present invention is 20% or less as expressed by the following formula 2. If the thickness unevenness in the longitudinal direction is poor, the thickness of each label will vary when processed into labels. If the label thickness varies, the labels will be heated differently inside the steam tunnel (hot air tunnel), which is undesirable as it makes them more susceptible to appearance defects such as wrinkles. The thickness unevenness is preferably 18% or less, and more preferably 15% or less. The smaller the thickness unevenness value, the better. Thickness variation = {(maximum thickness - minimum thickness) ÷ average thickness} × 100 (%) (Equation 2)

[0033] 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 production, and also reduces stiffness and makes labels more prone to wrinkling, which is undesirable. Although a thicker film tends to make film production more stable and improve stiffness, making it less prone to problems such as wrinkling, this is undesirable because it goes against the environmentally friendly objective of the film of the present invention, namely, volume reduction. The film thickness is more preferably 8 μm or more and 37 μm or less, and even more preferably 11 μm or more and 34 μm or less.

[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, and the wound 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] A preferred method for producing the heat-shrinkable polyester film roll of the present invention will now be described. The heat-shrinkable polyester film roll of the present invention is produced through the steps of storing and supplying a raw resin, extruding the resin while melting it, forming 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 having the characteristics of the present invention, it is important to suppress fluctuations in the film composition. Specific methods for doing so are described below.

[0036] <Method for suppressing fluctuations in film composition> Heat-shrinkable films generally require an amorphous component as a raw material. However, the heat-shrinkable polyester film of the present invention uses recycled PET bottle chips, so it is necessary to use at least two or more types of raw material chips, including recycled PET bottle chips. Blending is a common method, but this tends to cause segregation of the raw material chips. Therefore, in the present invention, it is preferable to suppress the segregation of the raw material chips in the blending method by using the following various methods and combinations of these methods.

[0037] (a) Uniform chip shape In the blending method, multiple raw polyester chips with different compositions are usually blended in a hopper, melt-kneaded, and extruded into a film using an extruder. In the present invention, PET bottle recycled raw material chips and other amorphous raw material chips are continuously or intermittently fed and mixed in the hopper, and finally the mixed raw material chips are fed to a hopper (final hopper) directly above the extruder, where raw materials are fed in accordance with the extrusion rate of the extruder to form a film. However, depending on the capacity or shape of the hopper where the raw materials are mixed and the final hopper, the mixing ratio of chips fed to the subsequent hopper or extruder may differ depending on whether the amount of chips in the hopper is large or small. This problem becomes more pronounced when the shapes and specific gravities of various polyester raw material chips are different. As a result, the isophthalic acid content varies in the present invention. In order to obtain the film roll of the present invention with little variation in the longitudinal shrinkage rate and the isophthalic acid content, it is preferable to match the shape of the raw material chips used as a means for reducing compositional variation of the polyester constituting the film, thereby suppressing the phenomenon of raw material segregation inside the hopper.

[0038] After polymerization, polyester raw material chips are removed in a molten state from the polymerization apparatus in the form of strands, immediately cooled with water, and then cut with a strand cutter for molding. In the case of recycled PET bottles, the polyester flakes are extruded again through an extruder after sorting, crushing, and washing PET bottles, and then removed in the form of strands. These strands are immediately cooled with water and cut with a strand cutter for molding. Therefore, polyester chips typically have an elliptical cylindrical cross-section. The average major axis (mm), average minor axis (mm), and average chip length (mm) of the cross-sectional ellipse of the polyester chips are preferably within ±20%. Furthermore, it is more preferable that these average values are within ±15%. The average major axis and average minor axis of the cross-sectional ellipse can be adjusted by adjusting the size of the nozzle hole in the die used for extrusion into strands, and the chip length can be adjusted by adjusting the extrusion rate of the strand, the strand conveying speed, and the rotation speed of the strand cutter. When chips vary in size, the smaller chips tend to fall first as the chip mixture falls through the hopper. As a result, when the amount of chips remaining in the hopper decreases, the proportion of larger chips increases, which can cause raw material segregation. However, by using raw material chips within the above range, it is possible to suppress this raw material segregation.

[0039] The angle of repose is also an indicator of the granular fluidity of raw material chips, i.e., the ease with which they fall. The angle of repose is the angle between the horizontal plane and the slope of the mountain formed when a certain amount of raw material chips is dropped from a certain height. The angle of repose is determined by the shape and particle size of the chips; the smaller the chips, 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 in the angle of repose between the resin with the smallest angle of repose and the largest chip is 5 degrees or less. By using raw material chips within the above range, it is possible to suppress these raw material segregations, and it is more preferable that it is 4 degrees or less.

[0040] (b) Hopper shape optimization Optimizing the hopper shape as mentioned above is also a preferred measure to prevent raw material segregation. Using a funnel-shaped hopper for the mixed chips and setting its inclination angle to 65° or more allows large chips to fall just as easily as small chips, and the upper end of the contents descends while remaining horizontal, effectively reducing raw material segregation. A more preferred inclination angle is 70° or more. The inclination angle of the hopper is the angle between the hypotenuse of the funnel and the horizontal line.

[0041] (c) Hopper capacity optimization Another preferred method for reducing raw material segregation within the hopper is to optimize the capacity of the hopper used. The appropriate hopper capacity is within the range of 15 to 120% by mass of the extruder's hourly output. If the hopper does not have a capacity equal to or greater than 15% by mass of this output, stable supply of raw materials becomes difficult. Furthermore, if the hopper is too large, the raw material chip mixture will remain in the hopper for a long period of time, which may cause chip segregation. The hopper capacity is more preferably within the range of 20 to 100% by mass of the extruder's hourly output.

[0042] (d) Reduction of fine powder Reducing the proportion of fine powder generated by scraping of the raw material chips used is also a preferred method for suppressing raw material segregation. Fine powder gets into the gaps between chips, reducing friction between the chips and making it easier for small chips to fall, which promotes segregation. It is preferable to remove the fine powder generated during the process and 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 of the raw material chips entering the extruder, and more preferably within 0.5% by mass. Specifically, fine powder can be removed by passing the raw material chips through a sieve when forming chips with a strand cutter, or by passing the raw material chips through a cyclone air filter when air-transporting the raw material chips.

[0043] (e) Use of uncrystallized raw materials Raw material segregation is also likely to occur when there is a large difference in specific gravity between the multiple raw material chips used. In other words, chips with a large specific gravity (heavy) tend to fall first when the chip mixture falls, promoting segregation. In the present invention, PET bottle recycled raw material chips and amorphous raw material chips are mixed and used, but since PET bottle recycled raw material is a crystalline raw material, it has a higher specific gravity than the amorphous raw material, and there is a difference in specific gravity between the chips. Meanwhile, the raw chips undergo a drying process to reduce the moisture content of the resin before being fed into the extruder, or separately dried raw chips are fed into the hopper. To shorten the drying time for recycled PET bottles, the chips are heated to around 160°C and dried, but at this time the polyester crystallizes and its specific gravity increases compared to the chips before drying. This further increases the difference in specific gravity between the heated and dried recycled PET bottle chips and the amorphous raw chips, promoting segregation. Therefore, the raw material chips used in the present invention are preferably dried by vacuuming at room temperature to reduce the moisture content, without causing crystallization. Alternatively, it is preferable to use raw material chips in a state where no crystallization has occurred, without performing drying itself, and to use a twin-screw extruder with a vent as the extruder, while performing melt extrusion and removing moisture from the vent.

[0044] (f) Mixing inside the hopper It is also effective to reduce raw material segregation by stirring the inside of the hopper that contains the mixture of raw material chips. For example, by installing a stirrer with blades or a stirrer with a spiral ribbon in the hopper, the resins can be stirred and mixed while being fed to the next process (hopper or extruder), thereby reducing raw material segregation. There are no particular restrictions on the location of the hopper with stirring function, but it is more preferable for it to be a hopper close to the extruder, and it is particularly preferable for it to be stirred in the final hopper immediately above the extruder.

[0045] (g) Installation of cone baffles The falling of the 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 it. Film is typically produced continuously, but raw chips are often fed intermittently to the hopper. Continuous feeding of raw resin requires the chip transport device to be constantly running, increasing the frequency of breakdowns. Furthermore, the feed rate must be balanced with the consumption rate, making accurate metering difficult for resin chips with a small raw material supply. Intermittent feeding means that when the raw material in the hopper falls below a certain capacity level, a certain amount of raw chips is fed, then stops when the level is reached, and then feed resumes as consumption progresses. In this case, the hopper's capacity level is constantly fluctuating, which in turn causes fluctuations in the powder pressure at the bottom of the hopper. Fluctuations in powder pressure are undesirable because they promote raw material segregation. Therefore, it is preferable to install a cone baffle at the bottom of the hopper to cut 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 a cone or a triangular pyramid.

[0046] (h) Mixing directly above the extruder Another preferred method is to insert a pipe into the hopper (final hopper) directly above the extruder and mix the chips immediately before extrusion. Because the raw chips, which tend to segregate, are mixed immediately before the extruder, the opportunity for actual segregation is extremely low, making this method effective in reducing segregation. However, it is necessary to use equipment that satisfies at least the following formula 3. Figure 1 shows an example of a specific mixing procedure. 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 portion A in Figure 1. As shown in Figures 1 and 2, raw chips to be mixed are supplied through inner pipe 3, and other raw chips are supplied from the top of hopper 1. Furthermore, because the outlet 4 of inner pipe 3 is located directly above the extruder (specifically, directly above the raw chip supply port 5 of extruder 2), the mixing ratio of the raw chip mixture can be maintained 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 the intrusion of air into 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 material chips, amorphous raw material chips and PET bottle recycled raw material chips, it is preferable to supply the amorphous raw material chips to twin-screw extruder 1 and melt them inside the extruder, and then supply the PET bottle recycled raw material chips to another twin-screw extruder (hereinafter, this other twin-screw extruder will be referred to as twin-screw extruder 2), melt them, and introduce them directly into the middle of twin-screw extruder 1 via piping using a side feed method, and then mix the two types of raw materials inside twin-screw extruder 1. Since there is no process of mixing the raw materials in chip form, the concern about segregation of the raw material chips as mentioned above is essentially eliminated. The mixing ratio of the raw materials can be precisely adjusted by adjusting the rotation speed of the screw feeder, etc., for the raw material chips fed into the twin-screw extruder 2 (side feeder). This makes it possible to minimize compositional variations in the longitudinal direction of the film.

[0049] The twin-screw extruder 1 preferably has a vent function. In order to prevent air bubbles from being mixed in when the raw materials are introduced by the side feeder, it is preferable to provide a vent at the starting position where the raw materials start to mix together for degassing. It is preferable that the raw material chips fed to twin-screw extruders 1 and 2 are each a single material, in order to eliminate the step of mixing the raw material chips before feeding them to the extruders and essentially eliminate segregation of the raw material chips. When three or more kinds of raw materials are used, it is preferable to provide another twin-screw extruder 3 and introduce the raw materials directly into the twin-screw extruder 1 by a side feed method.

[0050] The manufacturing process of the heat-shrinkable polyester film of the present invention comprises (1) a melt extrusion and casting step of an unstretched sheet, (2) a transverse stretching step, and (3) a final heat treatment step. Each step will be explained below.

[0051] (1) Melt extrusion and unstretched sheet casting process The raw materials are mixed and fed with the above-mentioned measures to prevent raw material segregation, and then extruded into a sheet using an extruder at a temperature of 220-280°C using existing methods such as the T-die method or tubular method. Temperatures above 280°C during extrusion are undesirable because they reduce the intrinsic viscosity of the polyester resin, making it more susceptible to breakage during the film-making process and making it difficult to obtain a steady-state film. Temperatures below 220°C are undesirable because some of the raw materials remain unmelted, causing an overload on the machine and the unmelted resin becoming the starting point for breakage during film-making. The film melted by extrusion is then quenched to obtain an unstretched film. As a method for quenching 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. Furthermore, the shear rate when the molten resin is extruded from the die mouth is preferably 100 sec-1 or higher, and more preferably 150 sec-1 or higher. The higher the shear rate, the more the shrinkage fluctuation and thickness unevenness in the film's longitudinal direction can be suppressed. This is because the resin extrusion pressure at the die mouth (exit) becomes more stable as the shear rate increases. If the shear rate is less than 100 sec-1, the resin extrusion pressure at the die outlet becomes unstable, making pulsation (thickness fluctuation of the unstretched film in the longitudinal direction) more likely to occur. This results in non-uniform stretching in the longitudinal direction, as described below, and therefore increases the heat shrinkage fluctuation and thickness unevenness in the longitudinal direction. On the other hand, if the shear rate is higher than 600 sec-1, not only will the polyester molecular chains be cut (decomposed) to reduce the intrinsic viscosity, but resin residue will adhere to the discharge part of the die, reducing productivity, which is undesirable.

[0052] The shear rate at the die exit was calculated using the following formula 5. γ=6Q / (W×H2) (Formula 5) γ: Shear rate (sec -1 ) Q: Amount of raw material discharged from the extruder (cm 3 / sec) W: width of die opening (cm) H: Die mouth gap (lip gap) (cm)

[0053] (2) Lateral stretching process The film is preferably stretched in a transverse uniaxial stretching method, in which the film is stretched only in the width direction. A method of performing longitudinal stretching before the transverse stretching method can also be used, but this is not preferred because it requires a long production machine. The unstretched sheet obtained as described above is introduced into a tenter device that can heat the sheet by holding both ends with clips, and the film is heated to a predetermined temperature with hot air in a preheating step. After that, the film is stretched by widening the distance between the clips while being transported in the longitudinal direction in the stretching step. The film temperature during width direction stretching is preferably at least Tg+5°C and not more than Tg+40°C. If the film temperature is less than Tg+5°C, the stretching force becomes too high, increasing the risk of breakage, which is not preferred. If the film temperature exceeds Tg+40°C, the stretching force is too low, making it difficult to impart sufficient shrinkability to the film, which is not preferred.

[0054] (3) Final heat treatment process After transverse stretching, the film is preferably finally heat-treated in a tenter at a temperature of transverse stretching temperature +5°C or higher and 45°C or lower for 5 seconds or longer and 10 seconds or shorter, while both ends in the width direction are held with clips. If the temperature is higher than the transverse stretching temperature + 45°C, the shrinkage rate in the width direction will decrease and the required shrinkage characteristics will not be obtained, which is undesirable. Also, if the temperature is lower than the transverse stretching temperature + 5°C, when the final product is stored at room temperature, shrinkage in the width direction (the so-called natural shrinkage rate) will increase over time, which is undesirable. Furthermore, the longer the heat treatment time, the better, but if it is too long, the equipment will become large, so a time of 10 seconds or less is preferable. From the viewpoint of reducing fluctuations in heat shrinkage, it is preferable to control the fluctuation range of the film surface temperature measured at any point in each of the preheating, stretching, and final heat treatment steps in the transverse stretching step and the final heat treatment step to preferably within ±1°C of the average temperature, and more preferably within ±0.5°C of the average temperature. [Example]

[0055] Next, the present invention will be specifically explained using examples and comparative examples, but the present invention is not limited to the aspects of these examples and can be appropriately modified within the scope of the invention.

[0056] [Sampling method for evaluation samples] A 1m length of film removed from the film roll was used as the surface layer, and the first sample was cut out from the center position in the width direction. After that, while the film roll was unwound using a winding machine, samples were cut out from the center position in the width direction every 100m. Sampling was stopped when the remaining length of the film roll was less than 100m, and the samples taken up to that point were evaluated.

[0057] [Heat shrinkage rate] The film was cut into a 10 cm x 10 cm square and heat-shrunk by placing it in hot water at 90°C ± 0.5°C 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 width direction (main shrinkage direction) were measured, and the heat shrinkage rate was calculated according to the following formula (1). Regarding fluctuations (variations) in shrinkage rate, the heat shrinkage rates of the samples sampled by the above-mentioned method were measured, and the average, maximum, and minimum values were calculated. Heat shrinkage rate = ((length before shrinkage - length after shrinkage) / length before shrinkage) × 100 (%) Formula (1)

[0058] [Composition analysis] Each sample was dissolved in a 10:1 (volume ratio) mixture of chloroform D (Eurisop) and trifluoroacetic acid D1 (Eurisop) to prepare a sample solution. The sample solution was then subjected to NMR measurement of protons using a GEMINI-200 NMR (Varian) at a temperature of 23°C and 64 cycles of accumulation. The peak intensity of a specific proton was calculated to determine the amount of the diacid component in 100 mol %. The average, maximum, and minimum values of the isophthalic acid component ratio (mol %) were determined for the samples sampled every 100 m in the longitudinal direction as described above.

[0059] [Thickness variation in the longitudinal direction] A long roll measuring 100 m in length and 40 mm in width was sampled in the longitudinal direction of the film, and the thickness was measured at a speed of 5 m / min using a continuous contact thickness meter 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 unevenness in the film width direction was calculated using the following formula (2). Thickness unevenness = {(Tmax. - Tmin.) / Tave.} × 100 (%) Formula (2)

[0060] [Tg (glass transition temperature)] Using a differential scanning calorimeter (DSC220, manufactured by Seiko Instruments Inc.), 5 mg of unstretched film was placed in a sample pan, the pan was covered, and the temperature was increased from -40°C to 120°C at a rate of 10°C / min under a nitrogen gas atmosphere. Tg (°C) was determined in accordance with 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 the viscosity was measured using an Ostwald viscometer at 30° C. The unit is dl / g.

[0062] [Shrinkage finish evaluation] Both ends of the film were bonded with dioxolane to create cylindrical labels (labels with the main shrinkage direction of the heat-shrinkable film aligned circumferentially). These were then cut into 3,000 labels. The diameter of the labels in the shrinking direction was 70 mm. The labels were then attached to 500 ml PET bottles (body diameter 62 mm, minimum neck diameter 25 mm) by heat shrinking them using a Fuji Astec Inc. steam tunnel (model: SH-1500-L) at a zone temperature of 90°C for 4 seconds. The labels were attached to the bottles by adjusting the neck so that the 30 mm diameter was located at one end of the label. The finished appearance after shrinkage was evaluated visually, using the following criteria: 5: Best finish 4: Good finish 3: Minor defects (up to 2 places) 2: Flaws present (3-5 places) 1: Many defects (6 or more) Defects here include wrinkles, folded label edges, uneven shrinkage, and insufficient shrinkage. An evaluation result of 4 or more was considered pass, and 3 or less was considered fail, and 3,000 samples were evaluated. The shrinkage finish defect rate (%) was calculated according to the following formula: Shrinkage finish defect rate (%) = Number of defective samples / Total number of samples x 100

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

[0064] <Preparation of amorphous polyester raw material (polyester A) chips> A stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser was charged with 100 mol% dimethyl terephthalate (DMT) as a dicarboxylic acid component, 55 mol% ethylene glycol (EG), 30 mol% neopentyl glycol (NPG), and 15 mol% diethylene glycol as polyhydric alcohol components (a molar ratio of 2.2:DMT). Zinc acetate (0.05 mol% relative to the acid component) was added as a transesterification catalyst, and antimony trioxide (0.225 mol% relative to the acid component) was added as a polycondensation catalyst. The resulting methanol was distilled off, and the resulting polycondensation reaction was carried out at 280°C under reduced pressure of 26.7 Pa to yield polyester 1 with an intrinsic viscosity of 0.77 dL / g. The resin size of Polyester A was calculated as an average value from 100 pieces of resin. Assuming that the resin was an elliptical cylinder, the major and minor axes of the elliptical cross section and the length (cut length of the strand) were measured using a vernier caliper. The results were 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, chip 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, and recycled chips manufactured by Utsumi Recycle Systems Co., Ltd. are used. 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 above, and the results were a major axis of 2.9 mm, a minor axis of 2.0 mm, a length of 3.4 mm, and an angle of repose of 36 degrees. The major axis was -6% compared to Polyester A, the minor axis 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 changing the die hole size when forming the strands and the cutter speed. The average resin size of Polyester C was calculated from 100 pieces of resin, and the results were 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% relative to polyester B, the minor axis was +25% relative to polyester B, and the length was +26% relative 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 were dried at room temperature under vacuum to a moisture content of less than 100 ppm. Meanwhile, 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 by feeding them separately from the hoppers in which they were stored using a fixed-rate screw feeder to the final hopper directly above the extruder. The feed was carried out air-fed, and fine powder was removed using a cyclone air filter. The raw material mixing ratio was polyester A:polyester B = 70:30. The raw material chips were mixed in the final hopper. The mixing device used a system in which a spiral ribbon rotated to mix the raw material chips. The final hopper had a capacity of 190 kg, and the feed rate to the extruder was 500 kg per hour. The inclination angle of the hopper was 70°. The mixed raw material chips were then fed from the final hopper to the extruder, melt-extruded using a single-screw extruder at an extrusion temperature of 280°C, and the molten resin was extruded from a T-die and then quenched to obtain an unstretched film with a thickness of 135 μm. The shear rate at this time was 180 sec -1 The glass transition temperature of the unstretched film was 65°C. This unstretched film was introduced into a tenter and preheated to a film temperature of 90°C, after which the clip spacing was widened to stretch the film 4.5 times in the width direction at a film temperature of 90°C, followed by introduction into the final heat treatment zone where it was heat-treated at a film temperature of 100°C for 6 seconds. The film temperature fluctuations were within ±0.5°C of the average temperature in the preheating, stretching, and final heat treatment steps. After the 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 above was slit into a slit roll having a width of 800 mm and a wound length of 4000 m using a slitter, to obtain a heat-shrinkable polyester film roll. The production method is shown in Table 2, and the film evaluation results are shown in Table 3. As a result of the evaluation, the film roll was made from a film having sufficient shrinkability in the width direction, small variations in the shrinkage rate and isophthalic acid ratio in the length direction, good shrinkage finish, and an extremely small defective rate.

[0069] [Example 2] A heat-shrinkable polyester film roll was produced in the same manner as in Example 1, except that stirring was not performed in the final hopper and a conical cone baffle was provided. The production method is shown in Table 2, and the film evaluation results are shown in Table 3. As a result of the evaluation, the film roll was made from a film having sufficient shrinkability in the width direction, small variations in the shrinkage rate and isophthalic acid ratio in the length direction, good shrinkage finish, and an extremely small defective rate.

[0070] [Example 3] A heat-shrinkable polyester film roll was produced in the same manner as in Example 1, except that no stirring was performed in the final hopper and raw material chips of Polyester A and Polyester B were mixed immediately before the extruder using an inner pipe. At this time, raw material chips of Polyester A were supplied from the top of the final hopper, and raw material chips of Polyester B were supplied using the inner pipe. At this time, the inner diameter of the inner pipe was 0.2 m, the height H1 in Figures 1 and 2 was 5 m, the height H2 was 1.5 m, and the height H3 was 1.37 m. The production method is shown in Table 2, and the film evaluation results are shown in Table 3. As a result of the evaluation, the film roll was made from a film having sufficient shrinkability in the width direction, small variations in the shrinkage rate and isophthalic acid ratio in the length direction, good shrinkage finish, and an extremely small defective rate.

[0071] [Example 4] After being cut into chips, polyester raw material A and polyester raw material B were charged into their respective hoppers without drying. They were then fed into an extruder in the same manner as in Example 2. A vented twin-screw extruder was used as the extruder, and melt extrusion was carried out while degassing through the vent to remove moisture contained in the raw material chips from the extruder, to produce a film roll in the same manner as in Example 2. The production method is shown in Table 2, and the film evaluation results are shown in Table 3. As a result of the evaluation, the film roll was made from a film having sufficient shrinkability in the width direction, small variations in the shrinkage rate and isophthalic acid ratio in the length direction, good shrinkage finish, and an extremely small defective rate.

[0072] [Example 5] The raw material chips were dried as in Example 1 and charged into their respective hoppers. Thereafter, the raw material chips were not mixed in the hopper, and the polyester A raw material chips were charged into a vented twin-screw extruder 1. Meanwhile, the polyester B raw material chips were charged into a separate twin-screw extruder 2, and the molten polyester B resin discharged from the tip of the twin-screw extruder 2 was side-fed into the twin-screw extruder 1. Each raw material chip was metered from the hopper by a screw feeder and charged into the extruder, and the feeder rotation speed was adjusted so that the raw material mixing ratio was polyester A:polyester B = 70:30. The twin-screw extruder 1 was designed to have a vent at the confluence point of the resin from the twin-screw extruder 2, and degassing was performed. Polyester A and polyester B were melt-extruded while being mixed inside the twin-screw extruder 1, then extruded through a T-die and quenched to obtain an unstretched sheet. The subsequent manufacturing method was the same as in Example 1. The production method is shown in Table 2, and the film evaluation results are shown in Table 3. As a result of the evaluation, the film roll was made from a film having sufficient shrinkability in the width direction, small variations in the shrinkage rate and isophthalic acid ratio in the length direction, good shrinkage finish, and an extremely small defective rate.

[0073] [Example 6] The blend ratio of the polyester raw materials was polyester A:polyester B = 80:20. The same conditions as in Example 5 were used, except that the transverse stretching temperature in the tenter was 87°C and the final heat treatment temperature was 96°C. The unstretched film had a Tg of 62°C, a thickness of 135 μm, and a thickness of 30 μm after stretching. The production method is shown in Table 2, and the film evaluation results are shown in Table 3. As a result of the evaluation, the film roll was made from a film having sufficient shrinkability in the width direction, small variations in the shrinkage rate and isophthalic acid ratio in the length direction, good shrinkage finish, and an extremely small defective rate.

[0074] [Example 7] The blend ratio of the polyester raw materials was polyester A:polyester B = 60:40. The same conditions as in Example 5 were used, except that the transverse stretching temperature in the tenter was 94°C and the final heat treatment temperature was 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 film after stretching was 30 μm. The production method is shown in Table 2, and the film evaluation results are shown in Table 3. As a result of the evaluation, the film roll was made from a film having sufficient shrinkability in the width direction, small variations in the shrinkage rate and isophthalic acid ratio in the length direction, good shrinkage finish, and an extremely small defective rate.

[0075] [Comparative Example 1] The raw material chips of polyester B and polyester C were mixed in the final hopper at a mixing ratio of polyester B:polyester C=30:70. The other conditions were the same as those in Example 2. The production method is shown in Table 2, and the film evaluation results are shown in Table 3. As a result of the evaluation, although the film roll had sufficient shrinkability in the width direction, there was a large difference in the size of the raw material chips, and a large difference in the angle of repose, which caused raw material segregation, and there was a large variation in the shrinkage rate and the isophthalic acid ratio in the width direction and length direction, so although the shrinkage finish was sometimes good, the film roll had a high defect rate.

[0076] Comparative Example 2 The same procedure as in Example 2 was carried out except that the amount of feed to the extruder was changed to 120 kg per hour. The production method is shown in Table 2, and the film evaluation results are shown in Table 3. As a result of the evaluation, although the film roll had sufficient shrinkability in the width direction, the retention time in the final hopper was too long, which caused raw material segregation, and large variations in the shrinkage rate and isophthalic acid ratio in the width and length directions. Therefore, although the shrinkage finish was sometimes good, the film roll had a high reject rate.

[0077] [Example 3] The same procedure as in Example 2 was carried out except that the inclination angle of the final hopper was changed to 50°. The production method is shown in Table 2, and the film evaluation results are shown in Table 3. As a result of the evaluation, although the film roll had sufficient shrinkability in the width direction, raw material segregation occurred due to the small inclination angle of the hopper, and the shrinkage rate and isophthalic acid ratio in the width direction and length direction varied greatly, so that although the shrinkage finish was sometimes good, the film roll had a high reject rate.

[0078] [Example 4] The same procedure as in Example 3 was carried out except that the height H2 of the inner pipe was changed to 7 m. At this time, the height H3 was 6.87 m. The production method is shown in Table 2, and the film evaluation results are shown in Table 3. As a result of the evaluation, although the film roll had sufficient shrinkage in the width direction, it did not satisfy formulas 3 and 4 for the inner pipe, which caused raw material segregation, and there was a large variation in the shrinkage rate and isophthalic acid ratio in the width and length directions, so although the shrinkage finish was sometimes good, the film roll had a high reject rate.

[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 raw materials as described above, and has high shrinkability in the width direction. In addition, since the composition of the film varies little in the longitudinal direction of the roll, the variation in shrinkability in the width direction and the longitudinal direction is extremely small. Therefore, when the film roll is continuously processed into beverage labels, etc., and then shrunk and used, the rate of occurrence of defects such as wrinkles and distortion is extremely small.

Claims

1. The polyester contains 5% by mass or more and 45% by mass or less of recycled PET bottle raw materials and is composed of a polyester containing an isophthalic acid component, and the polyester contains 50% by mole or more of ethylene terephthalate relative to 100% by mole of all constituent components, and also contains 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, and 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 one or more monomer components selected from the group consisting of 2,2-di-n-butyl-1,3-propanediol, 1,4-butanediol, and hexanediol is 14 mol % or more relative to 100 mol % of polyhydric alcohol components or 100 mol % of polycarboxylic acid components, and the film roll is made of a heat-shrinkable polyester film having a thickness of 5 μm to 40 μm and containing no trivalent or higher polycarboxylic acid components, and the film roll is characterized by satisfying the following requirements (1) to (3): (1) Film samples taken at 100m intervals along the length 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 100 m intervals in the longitudinal direction of the roll, the content ratio of isophthalic acid in 100 mol% of the total acid components of the polyester constituting the film is within the average value ±0.3 mol%. (3) The thickness variation in the longitudinal direction of the roll is 20% or less.

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

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

4. 4. The heat-shrinkable polyester film roll according to claim 1, wherein in film samples taken at 100 m intervals in the longitudinal direction of the roll, the polyester constituting the film has an average isophthalic acid content of 0.3 mol% or more and 3.0 mol% or less, based on 100 mol% of all acid components.

Images