Heat shrink polyester film rolls

Abstract

[Problem] To provide a heat-shrinkable polyester film roll wherein the occurrence of defects in a heat-shrinking step, such as wrinkles and vertical shrinkages caused by heat shrinkage rate variations within a film roll, is reduced even when containing a PET bottle recycled raw material. [Solution] The present invention provides a heat-shrinkable polyester film roll comprising a heat-shrinkable polyester-based film constituted by a polyester containing an isophthalic acid ingredient while containing between 5% by mass and 50% by mass inclusive of a PET bottle recycled raw material, the film roll being characterized by satisfying requirements (1) to (3). (1) The shrinkage rate in the main shrinking direction for film samples collected at a 100 m pitch in the roll length direction and immersed in hot water at 90°C for 10 seconds has a mean value of 40% or higher in the main shrinking direction, and the shrinkage rate for all samples falls within the mean value ± 3% inclusive. (2) The ratios of isophthalic acid contained within 100% by mole of all acid ingredients in the polyester constituting the film in film samples collected at a 100 m pitch in the roll length direction all fall within the mean value thereof ± 0.3% by mole inclusive. (3) The unevenness of thickness in the roll length direction is 20% or less.

Description

Heat-shrinkable polyester film roll

[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.

[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 serve to protect glass bottles, PET bottles, etc. and display product information. 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 easily incinerated, 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 solution, there has been a growing movement to collect used PET bottles and reuse them as resources (recycling). Recycling techniques mainly include mechanical recycling, chemical recycling, and thermal recycling, but mechanical recycling is the most widespread. Used containers are sorted, crushed, and washed, and then re-formed into resin chips in an extruder. These are then reprocessed into PET bottles or fibers or films for reuse.

[0004] Heat-shrinkable polyester film labels can also be made partially from recycled (regenerated) PET bottle materials, contributing to the life cycle of PET, from production to use and disposal, and helping to reduce the environmental impact.

[0005] In general, heat-shrinkable polyester films require a low crystallinity of the polyester constituting 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) of the type that causes thermal shrinkage by blowing steam, whereby they are thermally shrunk and adhered to the container.

[0007] 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, bags, etc. that do not exhibit the appropriate heat shrinkage rate, and these will suffer from poor appearance due to insufficient shrinkage, uneven shrinkage, wrinkles, distorted patterns, vertical sink marks, etc., and will therefore not be usable as final products. Vertical sink marks are appearance defects caused by labels having uneven lengths after shrinkage, such as the upper edge of the label curving downward or the lower edge curving upward.

[0008] The fluctuation of the heat shrinkage rate is largely influenced by the fluctuation of the polyester composition constituting the film in the longitudinal direction of the roll. Usually, 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 sheet, which is then stretched. However, the fluctuation of the composition occurs before the various raw material chips are fed into the extruder. In other words, it is thought that the fluctuation of the composition occurs because the various raw material chips are not mixed uniformly and segregated.

[0009] Segregation does not occur when the components necessary for polyester film are prepared as raw material chips of a single composition (using only one type of raw material chip). However, as mentioned above, when using recycled PET bottles, a mixture of at least two types of raw material chips is required, which poses a risk of segregation. In other words, using recycled PET bottles carries the risk of variations in longitudinal thermal shrinkage. For example, it is possible to add amorphous polyester during the PET bottle recycling process, which involves crushing, cleaning, and re-chipping the bottles, to obtain raw material 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 discovered that recycled PET bottles are often recycled by randomly mixing various PET bottles, which reduces the molecular weight and other properties due to repeated use. Furthermore, they often contain additives such as high-crystallization nucleating agents. Therefore, when used as a raw material for film, variations in the blending amount due to segregation have a greater impact on the film's physical properties than with other raw materials.

[0010] Patent Document 1 describes a heat-shrinkable polyester film made from recycled PET bottle materials, but does not mention variations 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 materials, but with the described method, it is difficult to achieve a shrinkage rate of 45% or more at 90°C, and does not mention variations in the heat shrinkage rate in the longitudinal direction.

[0011] Patent No. 5320737 Patent No. 6402954

[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.

[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 heat-shrinkable polyester film roll comprising a heat-shrinkable polyester film containing 5% to 50% by mass of recycled PET bottle material and made of a polyester containing an isophthalic acid component, the heat-shrinkable polyester film roll being characterized by satisfying the following requirements (1) to (3): (1) 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 shrinkage rate in the main shrinkage direction is an average of 40% or more, and is within ±3% of the average value for all samples; (2) In film samples taken at 100 m intervals in the longitudinal direction of the roll, the polyester constituting the film has an isophthalic acid content of 100 mol% of all acid components that is within ±0.3 mol% of the average value; and (3) the thickness variation in the longitudinal direction of the roll is 20% or less. 2. The 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 material and one or more polymer chips having different compositions. 3. 1. A heat-shrinkable polyester film roll according to 1. or 2., characterized in that the polyester constituting the heat-shrinkable polyester film is primarily composed of ethylene terephthalate. 4. A heat-shrinkable polyester film roll according to any one of 1. to 3., characterized in that, in film samples collected 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% to 3.0 mol% in 100 mol% of all acid components. 5. A heat-shrinkable polyester film roll according to any one of 1. to 4., characterized in that the heat-shrinkable polyester film roll has a wound length of 1,000 m or more. 6. A heat-shrinkable polyester film roll according to any one of 1. to 5., characterized in that, when film samples collected 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% to 15%, and the shrinkage rates of all samples are within ±3% of the average value.

[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.

[0016] Fig. 2 is a schematic diagram showing an example of the relationship between an extruder 2 equipped with a hopper 1 and an inner pipe. Fig. 3 is an enlarged view showing a portion A in Fig. 1.

[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 polyester components. Furthermore, 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 (e.g., adipic acid, sebacic acid, decanedicarboxylic acid, etc.) 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 contain trivalent or higher polycarboxylic acids (e.g., trimellitic acid, pyromellitic acid, and anhydrides thereof), since a heat-shrinkable polyester film obtained using a polyester containing such polycarboxylic acids will have difficulty achieving the required high shrinkage percentage.

[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 and 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 one or more amorphous monomer components in a total content of 14 mol% or more, more preferably 16 mol% or more, and particularly preferably 18 mol% or more, based on 100 mol% of the polyhydric alcohol components or 100 mol% of the polycarboxylic acid components in the entire 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. Of these, neopentyl glycol or 1,4-cyclohexanedimethanol is preferred. The upper limit of the total content 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] Furthermore, 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. Furthermore, the amount of fine particles added is within the range of 300 to 1,200 ppm of the film, which allows for both good slipperiness (friction) and transparency.

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

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

[0028] The heat-shrinkable polyester film of the present invention contains 5% by mass or more and 50% by mass or less 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 the content exceeds 50% by mass, the amorphousness (amount of amorphous components) of raw materials other than the recycled PET bottle raw materials must be extremely high, which is uneconomical because it increases the polymerization time of the raw materials. The content of recycled PET bottle raw materials is more preferably 10% by mass or more and 45% by mass or less, and even more preferably 20% by mass or more and 40% by mass or less.

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

[0030] In the heat-shrinkable polyester film roll of the present invention, it is preferable that the isophthalic acid content of all film samples taken at 100-m intervals along the roll longitudinal direction be within ±0.3 mol% of the average value of the total acid components of the polyester. The isophthalic acid content is measured and calculated by NMR measurement as described below. If the isophthalic acid content fluctuates beyond the range of ±0.3 mol% of the average value, the variation in composition will result in significant variations in heat shrinkage. As a result, when processed into labels, the shrinkage rate will vary from label to label, making it more likely to develop appearance defects such as wrinkles, which is undesirable. The film roll of the present invention uses recycled PET bottle material, which, as described below, generally contains a small amount of isophthalic acid as an acid component. Fluctuations in the isophthalic acid content indicate segregation of chips from recycled PET bottle material and chips from other raw materials. As mentioned above, recycled PET bottle materials often contain additives such as high-crystallization nucleating agents, and their molecular weights decrease with repeated use. Therefore, segregation has a greater impact on physical property variations within the film roll than other raw materials. Methods for reducing segregation will be described later. The isophthalic acid ratio is more preferably within the average value ±0.2 mol%, and even more preferably within 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 PET bottle recycled raw materials are contained in an amount of 50 mass% or less, 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 content of isophthalic acid 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 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 way the heat is applied to the label inside the steam tunnel (hot air tunnel) will differ, which is undesirable as it will easily cause 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 unevenness = {(maximum thickness - minimum thickness) / average thickness} x 100 (%) (formula 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 when made into a label, making it prone to wrinkling, which is undesirable. Although a thicker film tends to make film production more stable and improve stiffness, making it less prone to problems such as wrinkling, this is undesirable because it goes against the environmentally friendly objective of the film of the present invention, namely, volume reduction. 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, 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 be described below. The heat-shrinkable polyester film roll of the present invention is produced through the steps of storing and supplying 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 are described below.

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

[0037] (a) Uniform Chip Shape: In the blending method, multiple raw polyester chips with different compositions are typically blended in a hopper, melt-kneaded, and extruded into a film using an extruder. In the present invention, recycled PET bottle chips and other amorphous raw chips are continuously or intermittently fed into the hopper and mixed. The mixed raw chips are then finally fed into a hopper (final hopper) directly above the extruder, where the raw materials are fed according to 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 the chips fed to the subsequent hopper or extruder can vary 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 the various polyester raw 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 bottle raw materials, polyester flakes obtained by sorting, crushing, and washing PET bottles are extruded again through an extruder, removed in the form of strands, immediately cooled with water, and then cut with a strand cutter for molding. Therefore, polyester chips usually 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 each within a range of ±20%. Furthermore, it is more preferable that these average values ​​are each within a range of ±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 of 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 described above is also a preferred measure to prevent raw material segregation. The hopper that receives the mixed chips is a funnel-shaped hopper. By setting its inclination angle to 65° or more, large chips can be dropped as easily as small chips, and the upper end of the contents descends while remaining horizontal, which is effective in 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) Optimization of Hopper Capacity One 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. The hopper capacity must be within the above range because stable supply of raw materials is difficult if the hopper does not have a capacity of at least 15% by mass of the output. 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 result in chip segregation. It is more preferable that the hopper capacity be within the range of 20 to 100% by mass of the extruder's hourly output.

[0042] (d) Reducing Fine Powder Reducing the proportion of fine powder generated by scraping of the raw material chips used is also a preferred means for suppressing raw material segregation. Fine powder gets between the chips, reducing friction between the chips and making it easier for small chips to fall, thereby promoting segregation. It is preferable to remove 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 from when the raw material chips enter 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 them.

[0043] (e) Use of Uncrystallized Raw Material 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 higher specific gravity (heavier) tend to fall first as 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. However, because PET bottle recycled raw material is a crystalline raw material, it has a higher specific gravity than the amorphous raw material, resulting in a difference in specific gravity between the chips. Meanwhile, 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. PET bottle recycled raw material chips are dried by heating to approximately 160°C to shorten the drying time. During this process, the polyester crystallizes, increasing its specific gravity compared to the chips before drying. As a result, the difference in specific gravity between the heated and dried PET bottle recycled raw material chips and the amorphous raw material chips further increases, promoting segregation. Therefore, the raw material chips used in the present invention are preferably dried at room temperature by vacuuming to reduce the moisture content, in order to prevent crystallization. Alternatively, it is preferable to use raw material chips without drying, i.e., in a state where no crystallization has occurred, and to use a twin-screw extruder equipped with a vent to perform melt extrusion while removing moisture from the vent.

[0044] (f) Stirring inside the hopper Stirring inside the hopper into which the raw material chip mixture is placed is also effective in reducing raw material segregation. For example, by providing 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. The location of the hopper with a stirring function is not particularly limited, 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 directly above the extruder.

[0045] (g) Installation of a Cone Baffle: The falling of raw chips from the bottom of the hopper is affected by the pressure (so-called powder pressure) caused by the weight of the raw chips above them. Films are typically produced continuously, but raw chips are often supplied intermittently to the hopper. Continuous supply of raw resin requires the chip transport device to be constantly running, increasing the frequency of breakdowns. Furthermore, the supply amount must be balanced with the consumption amount, making accurate metering difficult for resin chips with a small raw material supply. Intermittent supply means that when the raw material in the hopper is consumed and falls below a certain capacity level, a certain amount of raw chips is supplied, the supply stops when it reaches a certain level, and then the supply resumes as consumption progresses. However, in this case, the hopper's capacity level constantly fluctuates, which means that the powder pressure at the bottom of the hopper also fluctuates. Fluctuations in powder pressure are undesirable because they promote raw material segregation. Therefore, installing a cone baffle (jinbaori) at the bottom of the hopper is preferred as a means to cut off the pressure from the raw chips above 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 located 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 is preferably conical or triangular pyramidal.

[0046] (h) Mixing Directly Above the Extruder Another preferred method involves inserting a pipe into the hopper (final hopper) directly above the extruder and mixing the chips immediately before extrusion. Because raw chips that 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. An example of a specific mixing procedure is shown in FIG. 1. FIG. 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 FIG. 2 is an enlarged view of portion A in FIG. 1. As shown in FIGS. 1 and 2, raw chips to be mixed are supplied from the inner pipe 3, and other raw chips are supplied from the top of the hopper 1. Furthermore, since the outlet 4 of the inner pipe 3 is located directly above the extruder (specifically, directly above the raw chip supply port 5 of the 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 both the relationships of formulas 3 and 4. H2

[0047] ​To obtain a film roll of the present invention with small variations in the thermal shrinkage rate and isophthalic acid ratio in the longitudinal direction by using a blending method, it is preferable to perform all of the above (a) to (d). However, even if all of (a) to (d) are performed, it is not sufficient to reduce raw material segregation, so it is preferable to further adopt one or more of the four measures (e) to (h), and more preferably to adopt two or more of them. Alternatively, the above blending method can be omitted and the following measure (i) can be adopted.

[0048] (i) Use of a Twin-Screw Extruder and Side Feeder In addition to the above methods, a method using a twin-screw extruder and side feeder can be suitably used as a method for using raw material chips without blending them. Specifically, when using two types of raw material chips, amorphous raw material chips and recycled PET bottle chips, a preferred method is to feed the amorphous raw material chips into twin-screw extruder 1 and melt them therein, and then feed and melt the recycled PET bottle chips into another twin-screw extruder (hereinafter referred to as twin-screw extruder 2), which is then directly introduced into the middle of twin-screw extruder 1 via a pipe using a side feed method, and then mix the two raw materials inside twin-screw extruder 1. Since there is no process of mixing the raw materials in chip form, the aforementioned concerns about raw material chip segregation are essentially eliminated. The raw material mixing ratio can be accurately adjusted by adjusting the rotation speed of a screw feeder or the like for the raw material chips fed into twin-screw extruder 2 (side feeder). This makes it possible to extremely minimize compositional variations in the film's longitudinal direction.

[0049] Twin-screw extruder 1 preferably has a vent function. In order to prevent the introduction of air bubbles 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 and degas them. It is preferable that the raw material chips supplied to twin-screw extruders 1 and 2 are each a single type. This is because the process of mixing the raw material chips before feeding the raw materials to the extruder is eliminated, thereby essentially eliminating segregation of the raw material chips. When three or more types of raw materials are used, it is preferable to provide another twin-screw extruder 3 and introduce the raw materials directly into twin-screw extruder 1 using 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 described below.

[0051] (1) Melt Extrusion and Unstretched Sheet Casting Process The raw materials are mixed and fed with the above-described measures to prevent raw material segregation. The material is then extruded into a sheet using an extruder at a temperature of 220 to 280°C using conventional methods such as the T-die method or the tubular method. Note that temperatures exceeding 280°C during extrusion are undesirable because the intrinsic viscosity of the polyester resin decreases, making breakage more likely during the film-forming 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, overloading the machine and causing breakage during film formation. The unmelted resin can then be rapidly cooled to obtain an unstretched film. A suitable method for rapidly cooling the molten resin is to cast the molten resin from a die onto a rotating drum and rapidly solidify it to obtain a substantially unoriented resin sheet. 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 longitudinal direction of the film can be suppressed. This is because the resin discharge pressure at the die opening (exit) becomes more stable as the shear rate increases. If the shear rate is less than 100 sec-1, the resin discharge pressure at the die outlet becomes unstable, and pulsation (thickness fluctuation of the unstretched film in the longitudinal direction) is more likely to occur. This results in non-uniform longitudinal stretching, as described below, and increases the heat shrinkage fluctuation and thickness unevenness in the longitudinal direction. On the other hand, if the shear rate is greater than 600 sec-1, not only will the polyester molecular chain be scission (decomposition) and the intrinsic viscosity decrease, but resin residue and the like will adhere to the die outlet, reducing productivity, which is undesirable.

[0052] The shear rate at the die outlet 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: distance between die openings (lip gap) (cm)

[0053] (2) Transverse Stretching Process The film is preferably stretched transversely uniaxially, in which the film is stretched only in the width direction. Although it is possible to perform longitudinal stretching in a process prior to transverse stretching, 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. The film is heated to a predetermined temperature with hot air in a preheating process, and then stretched by increasing the distance between the clips while conveying the film in the longitudinal direction in a stretching process. The film temperature during widthwise stretching is preferably at least Tg + 5°C and up to Tg + 40°C. A film temperature below Tg + 5°C is not preferred because the stretching force becomes too high, increasing the risk of breakage. A film temperature above Tg + 40°C is not preferred because the stretching force is too low and the film cannot be imparted with sufficient shrinkability.

[0054] (3) Final Heat Treatment Step The transversely stretched film is preferably finally heat-treated in a tenter with both ends in the width direction held with clips at a temperature of 5°C to 45°C above the transverse stretching temperature for 5 to 10 seconds. A temperature higher than the transverse stretching temperature +45°C is undesirable because the shrinkage rate in the width direction decreases and the required shrinkage characteristics cannot be obtained. A temperature lower than the transverse stretching temperature +5°C is undesirable because, when the final product is stored at room temperature, shrinkage in the width direction (so-called natural shrinkage rate) increases over time, which is undesirable. A longer heat treatment time is preferable, but if it is too long, the equipment becomes large, so a time of 10 seconds or less is preferred. In the transverse stretching step and the final heat treatment step, 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, preferably within ±1°C of the average temperature, more preferably within ±0.5°C of the average temperature, from the viewpoint of reducing fluctuations in heat shrinkage rate.

[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 1 m length of film was removed from the film roll to form the surface layer, and the first sample was cut out from the center position in the width direction. Thereafter, while the film roll was unwound using a winding machine or the like, samples were cut out from the center position in the width direction every 100 m. Sampling was stopped when the remaining length of the film roll became less than 100 m, and the samples taken up to that point were evaluated.

[0057] [Heat Shrinkage Ratio] The film was cut into a 10 cm x 10 cm square and heat-shrunk in hot water at 90°C ± 0.5°C for 10 seconds under no load. The dimensions of the film were then measured in the longitudinal direction (direction perpendicular to the main shrinkage direction) and width direction (main shrinkage direction), and the heat shrinkage ratio was calculated according to the following formula (1). Regarding fluctuations (variations) in the shrinkage ratio, the heat shrinkage ratios of samples sampled by the above-mentioned method were measured, and the average, maximum, and minimum values ​​were calculated. Heat Shrinkage Ratio = ((Length before shrinkage - Length after shrinkage) / Length before shrinkage) x 100 (%) Formula (1)

[0058] [Composition Analysis] Each sample was dissolved in a solvent containing a 10:1 (volume ratio) mixture of chloroform D (manufactured by Eurisop) and trifluoroacetic acid D1 (manufactured by Eurisop) to prepare a sample solution. The proton NMR of the sample solution was measured using an NMR "GEMINI-200" (manufactured by Varian) at a temperature of 23°C and an accumulation of 64 times. In the NMR measurement, the peak intensity of a predetermined proton was calculated to measure the amount of the component in 100 mol % of the diacid component. The average, maximum, and minimum values ​​of the component ratio (mol %) of isophthalic acid were determined for the samples sampled every 100 m in the longitudinal direction as described above.

[0059] [Longitudinal Thickness Unevenness] A long roll of 100 m in the longitudinal direction of the film and 40 mm in width was sampled and 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 width direction of the film was calculated using the following formula (2): Thickness Unevenness = {(Tmax. - Tmin.) / Tave.} × 100 (%) Formula (2)

[0060] [Tg (glass transition point)] Using a differential scanning calorimeter (DSC220, manufactured by Seiko Instruments Inc.), 5 mg of the 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 in a nitrogen gas atmosphere to measure Tg (° C.). 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 intrinsic viscosity was measured using an Ostwald viscometer at 30° C. The unit is dl / g.

[0062] [Evaluation of Shrinkage Finish] Cylindrical labels (labels with the main shrinkage direction of the heat-shrinkable film as the circumferential direction) were prepared by adhering both ends of the film with dioxolane, and then cut into 3,000 labels. The diameter of the labels in the shrinkage 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 using a steam tunnel (model: SH-1500-L) manufactured by Fuji Astec Inc., at a zone temperature of 90°C for 4 seconds. During attachment, the neck was adjusted so that the 30 mm diameter was at one end of the label. The finish after shrinkage was evaluated visually, using the following criteria: 5: Best finish 4: Good finish 3: A few defects (up to 2 places) 2: Defects (3-5 places) 1: Many defects (6 places or more) Defects here include wrinkles, folded label edges, uneven shrinkage, and insufficient shrinkage. An evaluation result of 4 or more was considered acceptable, and 3 or less was considered defective. 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 material 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 material 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, so that the molar ratio of the polyhydric alcohol was 2.2 times that of the dimethyl terephthalate. 0.05 mol% (relative to the acid component) of zinc acetate as a transesterification catalyst and 0.225 mol% (relative to the acid component) of antimony trioxide as a polycondensation catalyst were added, and a transesterification reaction was carried out while the resulting methanol was distilled out of the system. 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 resin size of Polyester A was calculated as an average value from 100 resins. Assuming that the resin was elliptical cylindrical, 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] <PET bottle recycled material (Polyester B)> Polyester B is a recycled PET bottle material, and recycled material chips manufactured by Utsumi Recycle Systems Co., Ltd. were used. It contains 2 mol% isophthalic acid relative to the total dicarboxylic acid components constituting 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 manner as polyester A, and the resin size was changed by changing the die hole size and cutter speed when forming the strands. The average resin size of polyester C was calculated from 100 resin particles, 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% of polyester B, the minor axis was +25% of polyester B, and the length was +26% of polyester B. The intrinsic viscosity of polyester C was 0.77 dl / g.

[0067]

[0068] <Method for Manufacturing Heat-Shrinkable Film> [Example 1] The polyester A raw material chips described above were dried under vacuum at room temperature to a moisture content of less than 100 ppm. Meanwhile, polyester B raw material chips were heated under vacuum at 150°C 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, with fine powder 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°. Then, the mixed raw material chips were fed from the final hopper to the extruder, and melt-extruded using a single-screw extruder at an extrusion temperature of 280°C. 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. －１The 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. The clip distance was then widened, allowing the film to be stretched 4.5 times in the width direction at a film temperature of 90°C. The film was then introduced into a final heat treatment zone and heat-treated at a film temperature of 100°C for 6 seconds. The film temperature fluctuation range was within the average temperature range of ±0.5°C in all of the preheating, stretching, and final heat treatment steps. 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 above was slit into a slit roll with a width of 800 mm and a wound length of 4,000 m, yielding 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 that had sufficient shrinkability in the width direction, small variations in the shrinkage rate and isophthalic acid ratio in the longitudinal direction, good shrink 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 through an inner pipe. 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 through the inner pipe. The inner diameter of the inner pipe was 0.2 m, and the heights H1, H2, and H3 in Figures 1 and 2 were 5 m, 1.5 m, and 1.37 m, respectively. The production method is shown in Table 2, and the film evaluation results are shown in Table 3. The evaluation results indicated that the film roll had sufficient shrinkability in the width direction, small variations in the shrinkage rate and isophthalic acid ratio in the longitudinal direction, good shrinkage finish, and an extremely low reject rate.

[0071] [Example 4] After being chipped, 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, and melt extrusion was carried out while removing moisture contained in the raw material chips from the extruder by degassing through the vent, 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. The evaluation results showed that the film rolls had sufficient shrinkability in the width direction, small variations in the shrinkage rate and isophthalic acid ratio in the longitudinal direction, good shrinkage finish, and an extremely low defect rate.

[0072] Example 5: The raw material chips were dried and placed into their respective hoppers in the same manner as in Example 1. Thereafter, without mixing the raw material chips in the hopper, the polyester A raw material chips were placed into a vented twin-screw extruder 1. Meanwhile, the polyester B raw material chips were placed 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 midway through twin-screw extruder 1. Each raw material chip was metered from the hopper into the extruder using a screw feeder, and the feeder rotation speed was adjusted to achieve a raw material mixing ratio of polyester A:polyester B = 70:30. Twin-screw extruder 1 was designed with a vent at the confluence point of the resin from twin-screw extruder 2, and degassing was performed. Polyester A and polyester B were melt-extruded while being mixed inside 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 manufacturing 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 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. The evaluation results indicated that the film roll had sufficient shrinkability in the width direction, small variations in the longitudinal shrinkage rate and isophthalic acid ratio, good shrinkage finish, and an extremely low reject rate.

[0074] [Example 7] The blend ratio of 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. The unstretched film had a Tg of 69°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. The evaluation results indicated that the film roll had sufficient shrinkability in the width direction, small variations in the longitudinal shrinkage rate and isophthalic acid ratio, good shrinkage finish, and an extremely low reject rate.

[0075] Comparative Example 1 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. All other conditions were the same as in Example 2. The production method is shown in Table 2, and the film evaluation results are shown in Table 3. The evaluation results showed that although the film had sufficient shrinkability in the width direction, the raw material chips had large differences in size and angle of repose, which caused raw material segregation, and the shrinkage rates and isophthalic acid ratio in the width and length directions varied greatly, resulting in a film roll with a high reject rate, although the shrinkage finish was sometimes good.

[0076] Comparative Example 2 The procedure was the same as in Example 2, except that the amount of material fed 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. The evaluation results showed that although the film had sufficient shrinkability in the width direction, the retention time in the final hopper was too long, causing raw material segregation, and the shrinkage rates and isophthalic acid ratio in the width and length directions varied greatly, resulting in a film roll with a high reject rate, although the shrinkage finish was sometimes good.

[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 evaluation results of the film are shown in Table 3. As a result of the evaluation, although the film had sufficient shrinkability in the width direction, the small inclination angle of the hopper caused raw material segregation, and there were large variations in the shrinkage rate and the isophthalic acid ratio in the width and length directions, so that although the shrinkage finish was good in some cases, 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. The height H3 at this time 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 had sufficient shrinkability in the width direction, raw material segregation occurred because the inner pipe did not satisfy formulas 3 and 4, and the shrinkage rate and isophthalic acid ratio in the width and length directions varied greatly, so that the film roll had a high defect rate, although the shrinkage finish was sometimes good.

[0079]

[0080]

[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. A heat-shrinkable polyester film roll is a film roll made from a polyester composite material containing isophthalic acid and 5% by mass or more and 50% by mass or less recycled PET bottle material, and meets the following conditions (1) to (3): (1) The shrinkage rate in the main shrinkage direction when the film sample is immersed for 10 seconds in 90°C hot water is an average of 40% or more and the total sample is within the average (plus or minus) 3%. (2) The ratio of isophthalic acid in the film sample that is 100% by mole of total acid isophthalic acid is within the average (plus or minus) 0.3% by mole of total isophthalic acid in the total isophthalic acid component of the total isophthalic acid. (3) The thickness unevenness in the longitudinal direction of the roll is 20% or less.

3. Heat-shrink polyester film rolls specified in Patent 1 or 2 are characterized by a polyester composite film with ethylene terephthalate as the primary component.

4. Heat-shrink polyester film rolls specified in any one of the Patents 1 through 3 are characterized by a polyester composite film in film samples collected at a pitch of 100 meters in the longitudinal direction of the roll, with an average ratio of isophthalic acid within 100% of the total acid components being 0.3% by mol or greater and 3.0% by mol or less.