Heat-shrinkable polyester-based film roll

Abstract

To provide a heat-shrinkable polyester-based film roll which can reduce defects caused during a heat shrinking step due to the variation of a heat shrinkage rate in the heat-shrinkable polyester-based film roll having the longitudinal direction as the main shrinkage direction, specifically, defects that occur after the film has been applied to an object by the wrap-around method and subsequently heat-shrunk.SOLUTION: A heat-shrinkable polyester-based film roll, comprises a core and a heat-shrinkable polyester-based film having a longitudinal direction as a main shrinkage direction that is wound around the core, wherein the film roll satisfies a predetermined polyester composition, and the heat shrinkage rate in the longitudinal direction, measured after immersing each sample taken every about 100 m in hot water at 90°C for 10 seconds, is 30% or more and 80% or less for all samples, and within ±3% of the average heat shrinkage rate.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a film roll obtained by winding up a heat-shrinkable polyester film, and more particularly to a heat-shrinkable polyester film roll that is extremely free from defects such as insufficient shrinkage, shrinkage spots, wrinkles, distortions, and vertical sink marks that occur in post-processing steps due to fluctuations in the heat shrinkage rate within the heat-shrinkable film roll. [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, the generation of hydrogen chloride gas when incinerated, and the production of dioxins. Polystyrene films, on the other hand, have poor solvent resistance, require the use of inks with special compositions when printed, 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 is on the rise as the distribution volume of PET containers increases.

[0003] Furthermore, typical heat-shrinkable polyester films widely used are those that shrink significantly in the width direction. When used as a label film for bottles or a banding film for bundling lunch boxes, the film must be formed into a ring and attached to the bottle or lunch box, and then heat-shrunk in the circumferential direction. Therefore, when attaching a heat-shrinkable film that heat-shrinks in the width direction as a banding film, a ring must be formed so that the width direction of the film is the circumferential direction, and the ring must then be cut to a predetermined length and attached to the bottle or lunch box by hand or other means. Therefore, it is difficult to attach a label film or banding film made of a heat-shrinkable film that heat-shrinks in the width direction to a bottle or lunch box at high speed. Therefore, recently, a film that heat-shrinks in the length direction has been invented that can be wrapped around a bottle or lunch box directly from a film roll (the so-called wrap-around method) and attached to the bottle or lunch box (e.g., Patent Document 1). This eliminates the need for a center-sealing process for forming and sealing a film ring, as well as cutting, hand-attaching, and other processes, and allows for high-speed attachment.

[0004] These heat-shrinkable films are often wound into a roll after production and used in this form. If necessary, this film roll is cut to the size of the label or the like to be used in the final product, and then both ends of the film (both longitudinal ends in the case of longitudinal shrinkage) are sealed by solvent bonding, heat sealing, or other means to form a ring-shaped body (hereinafter also referred to as a label). This label is then heated to adhere to the container. Heating methods include a type that uses steam to cause thermal shrinkage (steam tunnel) and a type that uses hot air to cause thermal shrinkage (hot air tunnel). The heat-shrinking process is completed by passing the film through the heating tunnel on an attached belt conveyor.

[0005] However, because the heating conditions in the tunnel are the same during this heat shrinking process, if the heat shrinkage rate varies greatly from label to label, some labels will not exhibit the appropriate heat shrinkage rate. These labels will have poor appearance due to insufficient shrinkage, shrinkage spots, wrinkles, distortion of the design, sink marks, etc., and will therefore not be usable as a final product. Since identical labels are usually produced from a single film roll, if the heat shrinkage rate of the film wound on a single film roll varies greatly, there is a problem of an increased reject rate during the heat shrinkage process. These defects are common to all materials, including the aforementioned vinyl chloride resin, polystyrene resin, and polyester resin. For example, Patent Document 2 discloses a heat-shrinkable polyester film roll whose main shrinkage direction is the longitudinal direction. However, Patent Document 2 does not describe the variation in shrinkage rate within the roll. Patent Document 3 discloses a heat-shrinkable polyester film roll characterized by having an 85°C heat shrinkage rate in the maximum shrinkage direction (main shrinkage direction) of 20% or more throughout the entire length of the roll. Patent Document 3 successfully suppresses heat shrinkage rate fluctuations throughout the entire length of the film roll by controlling the raw material supply method. However, all of the examples in Patent Document 3 have a main shrinkage direction in the width direction, and no mention is made of means for controlling shrinkage rate fluctuations in a film roll whose main shrinkage direction is the longitudinal direction. Heat-shrinkable films usually need to be stretched in the direction in which the heat shrinkage rate is desired. Therefore, if the main shrinkage direction of the heat-shrinkable film is set to the longitudinal direction, stretching in the longitudinal direction is necessary. To reduce heat shrinkage rate fluctuations in the longitudinal direction, it is necessary to control not only the raw material supply method described above but also the method of longitudinal stretching. Furthermore, Patent Document 3 was disclosed more than 15 years ago, and there is currently a greater demand for reducing heat shrinkage rate fluctuations. In other words, it would be difficult to suppress heat shrinkage rate fluctuations in the longitudinal direction to the currently required level using the technology disclosed in Patent Document 3 alone. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-111824 [Patent Document 2] Japanese Patent Application Publication No. 2019-123252 [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-170494 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a heat-shrinkable polyester film roll that can reduce defects during the heat-shrinking process due to variations in the heat-shrinkage rate within the heat-shrinkable polyester film roll whose main shrinkage direction is the longitudinal direction as described above, particularly defects that occur when the film is attached to an object to be packaged using the wrap-around method and then heat-shrunk. [Means for solving the problem]

[0008] The present invention is as follows. 1. A heat-shrinkable polyester film roll obtained by winding a heat-shrinkable polyester film whose main shrinkage direction is the longitudinal direction around a core, wherein the heat-shrinkable polyester film and the heat-shrinkable polyester film roll satisfy the following requirements (1) to (3): (1) The polyester constituting the film contains ethylene terephthalate as a main component and at least one polyhydric alcohol selected from the group consisting of 1,4-cyclohexanedimethanol, neopentyl glycol, 1,4-butanediol, diethylene glycol, and 1,3-propanediol. (2) The end of the film roll on the winding start side (core) is defined as the first end, and the end on the winding end side (surface layer) is defined as the second end. The first sample cut-out is located within 2 m inside the second end at the center position in the roll width direction, and the final sample cut-out is located within 2 m inside the first end. Sample cut-outs are also located approximately every 100 m from the first sample cut-out. Samples cut into 10 cm x 10 cm squares from each sample cut-out are immersed in 90°C warm water for 10 seconds, pulled out, and then immersed in 25°C water for 10 seconds and pulled out. When the thermal shrinkage in the longitudinal direction is 30% or more and 80% or less for all samples, (3) When the heat shrinkage rates in the longitudinal direction are measured by the method described in (2) above and the average is calculated, the heat shrinkage rates in the longitudinal direction for all samples are within ±3% of the average heat shrinkage rate. 2. A heat-shrinkable polyester film roll according to 1., further satisfying the following requirements (4) and (5): (4) When the thermal shrinkage in the width direction is measured by the method described in (2) above, the thermal shrinkage in the width direction (the direction perpendicular to the longitudinal direction) for all samples is -20% or more and 20% or less. (5) When the heat shrinkage rates in the width direction are measured by the method described in (2) above and the average is calculated, the heat shrinkage rates in the width direction for all samples are within ±3% of the average heat shrinkage rate. 3. A heat-shrinkable polyester film roll according to 1. or 2., wherein the effective wound length of the film is 1,000 m or more and 20,000 m or less. 4. A heat-shrinkable polyester film roll according to any one of 1. to 3., wherein the film width is 300 mm or more and 2500 mm or less. 5. The heat-shrinkable polyester film roll according to any one of 1. to 4., wherein the film thickness is 5 μm or more and 100 μm or less. [Effects of the Invention]

[0009] The heat-shrinkable polyester film roll of the present invention, whose main shrinkage direction is the longitudinal direction, exhibits little variation in the heat shrinkage rate within the roll, thereby reducing defects in the final product. [Brief explanation of the drawings]

[0010] [Figure 1] Schematic diagram illustrating an example of mixing raw materials in the process for producing a heat-shrinkable polyester film roll of the present invention. [Figure 2] Enlarged view of part of Figure 1 [Figure 3] Schematic diagram of a plastic lunch box container for evaluating wrinkles in film after shrinkage [Figure 4] Schematic diagram of a plastic lunch box container for evaluating film sink marks after shrinkage DETAILED DESCRIPTION OF THE INVENTION

[0011] The present inventors have investigated the variation in heat shrinkage rate within the roll and found that there are two main causes for this variation. First, this is because two or more raw materials are used (polymer blend) in the raw material supply process, and second, this is because the molecular orientation varies due to stretching in the longitudinal direction during the stretching process. They have also found that the heat-shrinkable polyester film roll according to the present invention has small variations in heat shrinkage rate and is therefore less likely to cause the above-mentioned problems. The present invention will be described in detail below. In the present invention, the "longitudinal direction" refers to the direction in which the film is wound up in the film roll.

[0012] 1. Physical properties of film rolls 1.1.Heat shrinkage rate in the longitudinal direction (main shrinkage direction) The heat-shrinkable polyester film roll of the present invention has the end at the start of winding (core) as the first end and the end at the end of winding (surface layer) as the second end, with the first sample cut-out section located within 2 m inside the second end at the center position in the roll width direction, and the final sample cut-out section located within 2 m inside the first end, and sample cut-out sections located approximately every 100 m from the first sample cut-out section. When each sample is cut out, it must meet the following requirements (2) and (3). (2) Each 10cm x 10cm square sample cut out from each of the sample cutouts is immersed in 90°C warm water for 10 seconds, pulled out, and then immersed in 25°C water for 10 seconds and pulled out. When this is done, the thermal shrinkage rate in the longitudinal direction for all samples is 30% or more and 80% or less. (3) When the heat shrinkage rates in the longitudinal direction are measured by the method described in (2) above and the average is calculated, the heat shrinkage rates in the longitudinal direction for all samples are within ±3% of the average heat shrinkage rate. For a film wound on a single roll, the end at the beginning of winding (core) of the film is defined as the first end, and the end at the end of winding (surface layer) is defined as the second end. The first sample cutout is located within 2 m of the first end, and the final sample cutout is located within 2 m of the first end. Samples are selected at approximately equal intervals along the entire length of the steady-state region of the film by cutting out sample sections approximately 100 m from the first sample cutout. Note that "approximately every 100 m" means that samples may be cut out at intervals of approximately 100 m ± 1 m.

[0013] The above sampling method will be explained in more detail. For example, if a 498-m-long heat-shrinkable film is wound on a roll, the first sample A (10 cm x 10 cm) is cut from the center of the roll width direction within 2 m of the end of the film. For convenience, the square cut is made so that it has one side along the longitudinal direction of the film and one side along the direction perpendicular to the longitudinal direction (width direction) (no diagonal cuts). Next, the second sample B is cut from the center of the roll width direction approximately 100 m longitudinally away from the cut portion. In the same manner, the third sample C is cut at approximately 200 m, the fourth sample D at approximately 300 m, and the fifth sample E at approximately 400 m. Since the remaining length is shorter than 100 m, the sixth (final) sample F is cut from anywhere within 2 m of the start of the film winding.

[0014] The requirement (2) of the present invention is that all samples cut in this manner have a heat shrinkage rate of 30% or more in the longitudinal direction at 90°C. If the heat shrinkage rate of the film in the longitudinal direction is less than 30%, the film will not heat shrink sufficiently, and when shrunk to cover a container or the like, it will not adhere to the container, resulting in poor appearance, which is undesirable. A more preferable heat shrinkage rate in the longitudinal direction is 35% or more, and even more preferably 40% or more. On the other hand, the higher the heat shrinkage rate in the longitudinal direction, the greater the versatility and the more preferable it is, but the technical level of the present invention is 80% as the upper limit. In practice, an upper limit of 75% is sufficient.

[0015] In the present invention, the requirement (3) stipulates that when the average value of the thermal shrinkage percentages in the longitudinal direction is calculated based on all the samples obtained from the cut-out portions, the thermal shrinkage percentages in the longitudinal direction of all the samples must be within ±3% of the average value. This range is preferably within ±2.8%, and more preferably within ±2.6%. The meaning of "within ±3% of the average" will be explained in more detail. First, the heat shrinkage of each cut sample was measured and the longitudinal average was calculated. If this longitudinal heat shrinkage average is X (%) and the longitudinal heat shrinkage of Sample A is Y1 (%), then |X-Y1| (the absolute value of X-Y1) is less than 3%. Similarly, for the longitudinal heat shrinkages Y2 to Y6 (%) of Samples B to F, |X-Yn| is less than 3%. This average ±3% means that the difference between the maximum value Ymax of Yn and X, and the difference between the minimum value Ymin and X are all less than ±3%. As is clear from the fact that the heat shrinkage measurement temperature is 90°C, the present invention can suppress fluctuations in the longitudinal heat shrinkage at a temperature of 90°C. Therefore, even when a ring-shaped body is made from the film roll, wrapped around a packaged object (container), and heat-shrunk at approximately 90°C, poor shrinkage can be prevented.

[0016] 1.2. Heat shrinkage rate in the width direction (direction perpendicular to the main shrinkage direction) The heat-shrinkable polyester film wound around the heat-shrinkable polyester film roll of the present invention preferably satisfies the following requirements (4) and (5) for each sample obtained by the sampling method described in (1) of "1.1. Heat shrinkage rate in the longitudinal direction (main shrinkage direction)" above. (4) Each 10cm x 10cm square sample cut out from each of the sample cutouts is immersed in 90°C warm water for 10 seconds, pulled out, and then immersed in 25°C water for 10 seconds and pulled out. When this is done, the thermal shrinkage rate in the width direction for all samples is between -20% and 20%. (5) When the thermal shrinkage rates in the width direction are measured by the method described in (1) above and the average value is calculated, the thermal shrinkage rates in the width direction for all samples are the average value ±3% or less. When a heat-shrinkable polyester film is shrunk as a ring, the closer the heat shrinkage rate in the width direction to zero, the less the dimension in the direction where shrinkage is not desired (the non-shrinkage direction) changes, which is desirable. If the heat shrinkage rate in the width direction of the film exceeds 20% (requirement (3) above), the length in the non-shrinkage direction after being made into a label will be extremely short. A more preferable heat shrinkage rate in the width direction is 19% or less, and even more preferably 18% or less. On the other hand, if the heat shrinkage rate in the width direction is negative, the film will stretch in the non-shrinkage direction. If the heat shrinkage rate in the width direction is below -20%, the dimension in the non-shrinkage direction will change after being shrunk into a label. The heat shrinkage rate in the width direction is preferably -19% or more, and more preferably -18% or more. In the present invention, when the average thermal shrinkage in the width direction is calculated based on all the samples obtained from each cut-out portion, the thermal shrinkage in the width direction of all the samples is preferably within ±3% of the average value, more preferably within ±2.8%, and even more preferably within ±2.6%. As is clear from the fact that the measurement temperature for the thermal shrinkage rate is 90°C, according to the present invention, fluctuations in the thermal shrinkage rate in the width direction at a temperature of 90°C can be suppressed, and therefore, even when a ring-shaped body is made from the film roll, this is applied to a packaged item (container), and the body is thermally shrunk at about 90°C, poor shrinkage can be prevented.

[0017] Refractive Index The heat-shrinkable polyester film wound into the heat-shrinkable polyester film roll of the present invention is preferably such that the average refractive index Nx in the longitudinal direction of all samples obtained by the sampling method described in (2) of "1.1. Heat shrinkage rate in the longitudinal direction (main shrinkage direction)" is calculated based on all samples, and the Nx of all samples is within ±0.01 of the average value. This range is preferably within ±0.009, and more preferably within ±0.008. The refractive index indicates the degree of orientation of the polymer chains constituting the film and serves as an indicator of the extent to which the film has been stretched. Generally, the higher the degree of molecular chain orientation caused by stretching, the higher the heat shrinkage rate of the heat-shrinkable polyester film. In other words, in the present invention, if the variation in Nx in the longitudinal direction of the film roll is small, the fluctuation in the heat shrinkage rate within the film roll is suppressed.

[0018] 1.4.Thickness The heat-shrinkable polyester film wound on the heat-shrinkable polyester film roll of the present invention preferably has a thickness of 5 μm or more and 100 μm or less. If the thickness exceeds 100 μm, the weight per area of the film simply increases, which is uneconomical. On the other hand, if the thickness is less than 5 μm, the film becomes extremely thin, making it difficult to handle (poor handling) during processes such as forming into a ring. The thickness is preferably 7 μm or more and 98 μm or less, and more preferably 9 μm or more and 96 μm or less.

[0019] 2.Type and amount of polyester raw material that makes up the film roll The polyester raw material constituting the film of the present invention is one whose main constituent is ethylene terephthalate units. Here, "mainly composed of" means that the total amount of constituent components is 100 mol % and the ethylene terephthalate unit accounts for 50 mol % or more. Ethylene terephthalate is a unit composed of ethylene glycol and terephthalic acid. The heat-shrinkable polyester film wound on the heat-shrinkable polyester film roll of the present invention preferably contains 55 mol % or more, and more preferably 60 mol % or more, of 100 mol % of polyester constituent units. The diol component other than ethylene glycol that constitutes the polyester must contain at least one polyhydric alcohol selected from 1,4-cyclohexanedimethanol, neopentyl glycol, 1,4-butanediol, diethylene glycol, and 1,3-propanediol. The diol component can be amorphous and is necessary to achieve a heat shrinkage rate of 30% or more at 90°C. In addition to these, aromatic diols such as propylene glycol and bisphenol A, and aliphatic diols such as hexanediol, etc. may also be contained.

[0020] The total amount of these amorphous components is preferably 10 mol% or more, more preferably 20 mol% or more, based on 100 mol% of the polyhydric alcohol components in the entire polyester resin. If it is less than 10%, the required shrinkage rate cannot be obtained, resulting in insufficient shrinkage in the final product. On the other hand, the upper limit of the amount of amorphous components is 50 mol% because ethylene terephthalate is the main constituent (50 mol%). If the amount of amorphous components is too high, there is a concern that the fluctuation in molecular orientation caused by longitudinal stretching, as described below, will increase. The amount of amorphous components is preferably 45 mol% or less, more preferably 40 mol% or less.

[0021] The heat-shrinkable polyester film wound into the heat-shrinkable polyester film roll of the present invention is obtained by the sampling method described in (2) of "1.1. Heat shrinkage rate in the longitudinal direction (main shrinkage direction)" above, and the composition ratio (mol %) is calculated based on all samples. It is preferable that the amount of amorphous components in all samples is within ±2 mol % on average. By keeping the amount of amorphous components within ±2 mol % on average, the fluctuation in the heat shrinkage rate of the heat-shrinkable polyester film roll can be kept within a predetermined range. The amount of amorphous components is more preferably within ±1.5 mol % on average, and even more preferably within ±1 mol % on average.

[0022] Examples of dicarboxylic acid components other than terephthalic acid that constitute the polyester of the present invention include aromatic dicarboxylic acids such as isophthalic acid, naphthalenedicarboxylic acid, and orthophthalic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid, and alicyclic dicarboxylic acids. When an aliphatic dicarboxylic acid (e.g., adipic acid, sebacic acid, decanedicarboxylic acid, etc.) is contained in the polyester, the content is preferably less than 3 mol % (based on 100 mol % of the dicarboxylic acid component). Heat-shrinkable polyester films obtained using polyesters containing 3 mol % or more of these aliphatic dicarboxylic acids have insufficient film stiffness when applied at high speed. It is also preferable that the polyester does not contain trivalent or higher polycarboxylic acids (e.g., trimellitic acid, pyromellitic acid, and anhydrides thereof), since heat-shrinkable polyester films obtained using polyesters containing these polycarboxylic acids have difficulty achieving the required shrinkage ratio.

[0023] It is preferable to add fine particles as a lubricant to the film resin forming the heat-shrinkable polyester film roll of the present invention to improve the workability (slipperiness) of the film. Any fine particles can be selected, but examples of inorganic fine particles include silica, alumina, titanium dioxide, calcium carbonate, kaolin, and barium sulfate, and 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 appropriately selected as needed within the range of 0.05 to 3.0 μm (measured with a Coulter counter). The method of blending the above-mentioned fine particles can be, for example, added at any stage of polyester resin production. Preferably, they are added 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 the polycondensation reaction is then carried out. Alternatively, a method of blending a slurry of particles dispersed in ethylene glycol or water with the polyester resin raw material using a vented kneading extruder, or a method of blending dried particles with the polyester resin raw material using a kneading extruder, is also preferred. Furthermore, by adding the fine particles in an amount within the range of 300 to 1200 ppm in the film, both good slip properties (friction) and transparency can be achieved.

[0024] 3. Film roll manufacturing method The heat-shrinkable polyester film of the present invention can be obtained by supplying the polyester raw material described above in "2.1. Types and component amounts of polyester raw materials constituting the film roll" to an extruder, melt-extruding the resulting unstretched film, and then subjecting the resulting unstretched film to the following predetermined steps. In the present invention, the objective is to suppress the fluctuation of the thermal shrinkage rate within the film roll, which can be achieved by controlling the method of raw material supply and longitudinal stretching. Below, the production method will be described while showing the key technologies of the present invention.

[0025] 3.1. Raw material mixing and supply As described above in "2. Types and Amounts of Polyester Raw Materials," when manufacturing the film roll of the present invention, it is necessary to incorporate a monomer capable of forming an amorphous component in addition to the ethylene terephthalate unit. In this case, two or more raw materials (polyester resins) are typically mixed together. Conventionally, mixing two or more raw materials into an extruder has resulted in uneven raw material supply (segregation), which in turn leads to fluctuations in the film composition. Fluctuations in composition within the film roll make it difficult to maintain the thermal shrinkage within a specified range. Effective methods for preventing raw material segregation include (1) optimizing the angle of repose of the raw polyester resin, (2) optimizing the shape of the hopper in the raw material supply line, (3) installing a mixer directly above the extruder, (4) installing a bellows in the lower part of the hopper (to reduce powder pressure), and (5) installing an inner pipe in the final hopper. Using at least one of these methods is preferable because it can suppress fluctuations in the thermal shrinkage within the film roll. A combination of two or more of these methods is even more preferable. These means are described in detail below.

[0026] 3.1.(1) Angle of repose of polyester resin During the production of film rolls, if the resin in the final hopper directly above the extruder becomes low due to consumption, the composition of the mixed resin supplied to the extruder can easily become different (segregation), depending on the capacity and shape of the hopper. This problem becomes more pronounced when the angles of repose of the various resins are different. As a result, the thermal shrinkage rate within the film roll varies. The angle of repose is the angle between the horizontal and the slope of the cone formed when a certain amount of resin is dropped from a certain height. This angle is determined by the resin's shape and particle size. The larger the resin, the smaller the angle of repose. The smaller the angle of repose of a resin, the less likely it is to remain in the hopper (the easier it is to flow). The angle of repose also depends on the slipperiness of the resin surface; the slipperier the resin surface, the lower the angle of repose (the more likely it is to collapse). When producing raw resin, the resin is typically extruded in a molten state into strands after polymerization, immediately cooled in water, and then cut with a strand cutter. This results in an elliptical cylindrical shape, and its volume is determined by the major axis (mm), minor axis (mm), and height (mm) of the resin cross-sectional ellipse, which in turn affects the angle of repose of the resin. Resin volume can be controlled by the viscosity of the molten resin (swell at the strand die outlet), the extrusion speed of the strands, and the rotation speed of the strand cutter. The angle of repose is affected not only by the volume of the resin but also by its specific gravity. The specific gravity of the resin is also affected by the composition of the polyester components and the cooling rate of the molten resin. As mentioned above, the angle of repose of the resin varies depending on the various conditions used when manufacturing the polyester, but is usually between 30 and 45 degrees. When mixing two or more raw resins, it is preferable to match the angles of repose of all resins used to prevent raw material segregation in the final hopper in order to obtain a film with minimal compositional variation. Raw material segregation can be reduced by using the raw material used in the largest amount as the main raw material and using a raw material with an angle of repose within ±4 degrees of that. An angle of repose within ±3 degrees is more preferable.

[0027] 3.1.(2) Hopper shape optimization As mentioned above, in addition to controlling the angle of repose of the resin raw material, optimizing the shape of the final hopper is also a preferred method for obtaining a long film with a uniform composition. Specifically, setting the inclination angle of the funnel-shaped hopper (the angle between the hypotenuse of the funnel and the horizontal line) to 60 degrees or more is preferable because it suppresses raw material segregation. If the inclination angle is less than 60 degrees, the hopper is not inclined, and only resin with a small angle of repose falls first. An inclination angle of 62 degrees or more is more preferable. On the other hand, an inclination angle of more than 75 degrees is undesirable because it limits the hopper capacity (it becomes extremely small). An inclination angle of 73 degrees or less is preferable.

[0028] 3.1.(3) Installation of agitator As mentioned in (1) above, when using two or more resins as raw materials, it is preferable to match the angles of repose, but depending on the resin used, there are cases where it is not possible to keep the angle of repose within ±4 degrees. In this case, in order to eliminate raw material segregation that occurs during the process of supplying the raw materials to the extruder, a mixer can be installed in the piping or hopper directly above the extruder to mix the raw materials uniformly.

[0029] 3.1.(4) Jinkasa installation As described in (1) above, the amount of raw material in the hopper constantly fluctuates during the production of film rolls. Specifically, the hopper is equipped with a raw material level meter, which detects when the raw material is consumed and reaches a minimum level, triggering the refill of raw material. In other words, raw material is repeatedly consumed and refilled, and the powder pressure applied to the supply section (lower part of the hopper) directly above the extruder fluctuates depending on the amount of raw material filled in the hopper. When producing film by mixing two or more raw resins, fluctuations in powder pressure can also promote raw material segregation, so maintaining a constant powder pressure is desirable. A conventional approach to this end has been to shorten the raw material charging cycle (by setting the minimum raw material level high). However, shortening the raw material charging cycle increases the frequency of mechanical component operation, resulting in problems such as increased breakdowns. Therefore, it is preferable to install a bellows below the hopper to cut off the powder pressure from the upper part of the hopper. The shape of the bellows is not particularly limited, but a cone or a triangular pyramid is preferable. The size of the hopper is not particularly limited, but in order to ensure smooth supply of raw materials, the diameter must not exceed the diameter of the pipe below the hopper.

[0030] 3.1.(5) Installing the inner pipe When two or more raw resin materials have significantly different angles of repose, raw material segregation may occur even after taking the measures described in 3.1.(2) to (4) above. In this case, instead of using a mixture of raw materials in the final hopper, it is possible to insert a pipe (inner pipe) into a hopper filled with only the main raw material and directly add raw materials with different angles of repose (hereinafter referred to as "auxiliary raw materials"). This method is preferable because it essentially prevents raw material segregation within the hopper. The amount of raw material added through the inner pipe needs to be the same as the amount of raw material being fed from the final hopper. An example of a specific mixing procedure is shown in Figure 1. Figure 1 shows an extruder 2 equipped with a hopper 1 and an inlet 2 is an enlarged view of part A in FIG. 1. As shown in FIGS. 1 and 2, the main raw material is supplied from the upper part of the hopper 1, and the auxiliary raw material is supplied through the inner pipe 3. Since the outlet 4 of the inner pipe 3 is directly above the extruder (specifically, directly above the resin supply port 5 of the extruder 2), the mixing ratio of the raw materials can be kept constant. The height (H2) of the outlet 4 of the inner pipe 3 satisfies the relationship of the following formula 1 which is preferable, and it is more preferable to satisfy the relationships of both formula 1 and formula 2. H2 < H1 (Formula 1) ※ In Formula 1, H1 represents the height of the portion where the inner wall of the hopper is vertical (see FIG. 2). 0.5 × L / tanθ < H2 (Formula 2) ※ In Formula 2, L represents the inner diameter of the outlet 4 of the inner pipe 3 (see FIG. 2). Also, θ is the angle of repose of other resin chips. By making the height of H2 larger than 0.5 × L / tanθ, the position (H3; see FIG. 2) where the auxiliary raw material is mixed with the main raw material can be made outside the extruder, and the entry of air into the extruder and the generation of air bubbles can be prevented.

[0031] The height H3 (= H2 - 0.5 × L / tanθ) of the mixing position of the auxiliary raw material is preferably higher than 0 m and less than 2 m. By making it higher than 0 m, the intrusion of air into the extruder can be prevented. Also, by making it less than 2 m, the distance to the extruder can be kept short, and raw material segregation can be prevented. 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. As the metering device, a known one such as a table feeder can be adopted. Also, not only one inner pipe but two or more inner pipes may be used, and a plurality of types of raw materials may be added from one inner pipe. In order to supply the raw materials accurately, a method of supplying one type of raw material from one inner pipe is preferable. The polyester can be obtained by polycondensing the above-mentioned suitable dicarboxylic acid component and diol component by a known method. Before transferring the raw resin to the final hopper, it is preferable to dry it using a dryer such as a hopper dryer or a paddle dryer, or a vacuum dryer.

[0032] 3.2.Melt extrusion The mixed raw materials are extruded into a film at a temperature of 200 to 280°C using an extruder. Any existing method, such as the T-die method or tubular method, may be used for extrusion. However, if the extrusion temperature exceeds 280°C, the intrinsic viscosity of the polyester resin decreases, making it more likely to break during the film-forming process and making it difficult to obtain a steady-state film, which is not desirable. When forming a film with multiple layers, multiple extruders, feed blocks, or multi-manifolds may be used. 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 discharged 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 fluctuation in the shrinkage rate in the longitudinal direction of the film can be suppressed. This is because the higher the shear rate, the more stable the resin discharge pressure at the die mouth (exit). If the shear rate is less than 100 sec-1, the resin discharge pressure at the die outlet becomes unstable, making pulsation (fluctuation in the thickness of the unstretched film in the longitudinal direction) more likely to occur. This results in non-uniform longitudinal stretching, as described below, and therefore greater fluctuation in the thermal shrinkage rate in the longitudinal direction.

[0033] On the other hand, if the shear rate is higher than 600 sec-1, not only will the polyester molecular chains be cut (decomposed) and the intrinsic viscosity decrease, but resin residue will adhere to the discharge part of the die, reducing productivity, which is undesirable. The shear rate at the die exit was calculated using the following formula 3.

[0034] γ=6Q / (W×H2) (Formula 3) γ: Shear rate (sec-1) Q: Amount of raw material discharged from the extruder (cm3 / sec) W: width of die opening (cm) H: Die mouth gap (lip gap) (cm)

[0035] The film may be produced by any of the following methods: unstretched, uniaxially stretched (stretched in the longitudinal direction), and biaxially stretched. From the viewpoints of mechanical strength and productivity, uniaxial stretching is preferred, and biaxial stretching is more preferred. The following description focuses on a sequential biaxial stretching method using transverse stretching-transverse stretching, in which stretching in the width direction (sometimes referred to as transverse stretching) is first performed, and then stretching in the longitudinal direction (sometimes referred to as longitudinal stretching). However, the order may be reversed (transverse stretching-longitudinal stretching), or a simultaneous biaxial stretching method in which stretching is performed in the longitudinal and transverse directions simultaneously may also be used.

[0036] 3.3. Stretching in the width direction (transverse stretching) First, the film is stretched in the width (transverse) direction. The transverse stretching is preferably performed in a tenter (first tenter) at 65°C to 100°C and approximately 2.5 to 5 times its original size while both widthwise edges of the film are held with clips. Preheating is preferably performed before transverse stretching, and preheating is preferably performed until the film surface temperature reaches 60°C to 95°C. After transverse stretching, the film is preferably passed through an intermediate zone where no active heating operation is performed. If there is a temperature difference between the transverse stretching zone and the intermediate heat treatment zone of the first tenter, heat from the intermediate heat treatment zone (hot air itself or radiant heat) may flow into the transverse stretching step, resulting in an unstable temperature in the transverse stretching zone and unstable film quality. Therefore, it is preferable to pass the film after transverse stretching but before intermediate heat treatment through the intermediate zone for a predetermined time and then perform intermediate heat treatment. In this intermediate zone, when a strip of paper is dropped without passing through the film, the accompanying flow caused by the film running and the hot air from the transverse stretching zone and intermediate heat treatment zone are blocked so that the paper hangs almost completely vertically, resulting in a film of stable quality. A passage time through the intermediate zone of about 1 to 5 seconds is sufficient. If it is shorter than 1 second, the length of the intermediate zone will be insufficient and the heat blocking effect will be insufficient. Furthermore, a longer intermediate zone is preferable, but if it is too long, the equipment will become larger, so about 5 seconds is sufficient.

[0037] 3.4.Intermediate heat treatment After passing through the intermediate zone, intermediate heat treatment is performed before longitudinal stretching. This intermediate heat treatment is used to adjust the shrinkage in the width direction. Increasing the temperature of the intermediate heat treatment after transverse stretching tends to reduce the heat shrinkage in the width direction. The temperature of the intermediate heat treatment is preferably 60 to 140°C. If the temperature of the intermediate heat treatment zone is lower than 60°C, the heat shrinkage in the width direction does not change at all compared to the heat shrinkage after transverse stretching. On the other hand, if the temperature is higher than 140°C, the heat shrinkage in the width direction will be lower, but this is not preferred because crystallization will occur and subsequent longitudinal stretching will become difficult. Furthermore, the passage time through the intermediate heat treatment zone is preferably 2 to 20 seconds. If it is shorter than 2 seconds, the length of the intermediate heat treatment zone will be insufficient, making it difficult to adjust the heat shrinkage in the transverse direction. Furthermore, a longer intermediate heat treatment zone is preferable, but about 20 seconds is sufficient. This results in a transversely uniaxially stretched film. During the intermediate heat treatment, the distance between the clips of the first tenter is reduced by a desired factor in the film width direction (relaxation treatment), which relaxes the molecular chains oriented in the width direction without crystallizing, thereby reducing the shrinkage rate in the width direction. Relaxation after transverse stretching is preferably performed by 3% or more. Meanwhile, the upper limit of the relaxation rate after transverse stretching is determined by the raw materials used, the stretching conditions in the width direction, and the heat treatment temperature. Relaxation cannot be performed beyond this limit.

[0038] 3.5. Stretching in the longitudinal direction (longitudinal stretching) Next, longitudinal stretching is performed. In the longitudinal stretching process, the film from the previous process is introduced into a longitudinal stretching machine in which multiple roll groups are arranged in series. For longitudinal stretching, it is preferable to preheat the film using preheating rolls until the film temperature reaches 65°C to 120°C. If the film temperature is lower than 65°C, it tends to be difficult to stretch in the longitudinal direction (i.e., it is more likely to break). On the other hand, if the film temperature is higher than 120°C, the film tends to stick to the rolls, and there is a risk of roll contamination occurring early in continuous production. Once the film temperature reaches the above range, longitudinal stretching is performed. Longitudinal stretching is performed by varying the roll speed. A stretching ratio of 1.5 to 5 times is preferred. The number of stretching stages can be increased, not only through one-stage stretching, where the rolls used for stretching are low-speed and high-speed, but also through two-stage stretching, where the rolls are low-speed, medium-speed, and high-speed, or through three-stage stretching, where the rolls used for stretching are low-speed, medium-low speed, medium-high speed, and high speed. The stretching speed is preferably controlled within the range of, for example, 100% / sec or more and 10,000% / sec or less. If the stretching speed is too fast, the film is likely to be insufficiently heated, and if the stretching speed is too slow, productivity decreases. The stretching speed is more preferably 200% / sec or more and 9,900% / sec or less, and even more preferably 300% / sec or more and 9,800% / sec or less. The stretching speed can be calculated according to the following formula 4.

[0039] Stretching speed = λ / T (Formula 4) λ: Elongation strain (%) T: Time required for stretching (sec)

[0040] Examples of suitable heating rolls include a metal heating roll with a hard chrome-plated surface (hereinafter referred to as a chrome-plated roll), a ceramic heating roll (hereinafter referred to as a ceramic roll), a fluororesin heating roll (hereinafter referred to as a fluororesin roll), and a silicone rubber heating roll (hereinafter referred to as a silicone rubber roll). Chrome-plated rolls and ceramic rolls are particularly suitable for preheating, while fluororesin rolls and silicone rubber rolls are suitable for heating to a predetermined temperature after preheating. Chrome-plated rolls and ceramic rolls have a relatively smooth surface and good adhesion to the film, making them excellent at transferring heat to the film and enabling efficient preheating of the film. The surface roughness of the roll is measured using the average roughness (SRa), maximum peak height (SRmax), and ten-point mean roughness (SRz), which can be measured using a small surface roughness meter such as the Surftest SJ-301 (manufactured by Mitutoyo Corporation). The SRz of the chrome-plated roll is preferably 0.01 to 0.05, more preferably 0.02 to 0.04. The SRmax of the ceramic roll is preferably 1 to 8, more preferably 1.5 to 7.5. On the other hand, fluororesin rolls and silicone rubber rolls have a rough surface and excellent releasability, maintaining good releasability even when the film softens and becomes sticky due to heating. The SRz of the fluororesin roll is preferably 0.1 to 2, more preferably 0.2 to 1.9. The SRz of the silicone rubber roll is preferably 2 to 12, more preferably 3 to 11. For example, after preheating the film using a group of preheating rolls consisting of chrome-plated rolls and / or fluororesin rolls, the film is preferably heated to a predetermined temperature using one or more main heating rolls consisting of ceramic rolls and / or silicone rubber rolls. The preheating rolls may be free-rotating or driven. The main heating rolls are usually driven.The film thus heated to a predetermined temperature can be longitudinally stretched by utilizing the speed difference between the main heating roll and a stretching roll disposed downstream of the main heating roll.

[0041] 3.6. Final heat treatment Next, the film after longitudinal stretching and cooling is introduced into a second tenter for final heat treatment, where it is subjected to heat treatment and relaxation treatment. The final heat treatment step is a preferred embodiment because it allows adjustment of the longitudinal and transverse shrinkage rates. Relaxation in the second tenter does not significantly change the longitudinal shrinkage rate, but decreases the transverse shrinkage rate. A relaxation rate of 0% to 50% is preferred. The lower limit of the relaxation rate is 0%. On the other hand, a high relaxation rate is undesirable because it has the disadvantage of shortening the width of the film product, and the upper limit of the relaxation rate is preferably around 50%. The heat treatment (relaxation treatment) temperature is preferably 65°C to 120°C. If the heat treatment temperature is lower than 65°C, the shrinkage rate of the film will not change. On the other hand, if the heat treatment temperature is higher than 120°C, the film will crystallize and will not shrink in either the longitudinal or transverse direction, which is not preferable as a heat-shrinkable film. 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 step in the transverse stretching step, the intermediate heat treatment step, the preheating-stretching-cooling step in the longitudinal stretching step, and the final heat treatment step to preferably within ±1°C of the average temperature, more preferably within ±0.5°C of the average temperature. The fluctuation range of the film surface temperature measured at any point refers to the fluctuation range when the film surface temperature at a predetermined position during film production is continuously measured, for example, with an infrared non-contact surface thermometer.

[0042] 3.7. Winding The heat-shrinkable polyester film roll of the present invention is preferably a heat-shrinkable film having a width of 300 mm to 2500 mm and wound around a winding core to a length of 1000 m to 20,000 m. Typically, a wide-width master roll is produced, and the master roll is then slit to a desired width and wound into a roll of desired width and length to produce a film roll product. Film rolls having a width of less than 300 mm or a length of less than 1000 m are of little industrial value. The width of the heat-shrinkable film roll is more preferably 350 mm or more, and even more preferably 400 mm or more. On the other hand, a width of more than 2500 mm is undesirable because the paper core is prone to bending during winding, which can lead to winding defects such as wrinkles in the film roll. The width of the heat-shrinkable polyester film roll is more preferably 2450 mm or less, and even more preferably 2400 mm or less. The length of the heat-shrinkable film wound around the roll is more preferably 400 m or more, and even more preferably 500 m or more. The longer the length of the heat-shrinkable film roll, the less the number of times the roll needs to be replaced when producing the annular body, which improves productivity, and this is preferable. In the present invention, however, lengths up to 20,000 m have been confirmed, and this value was set as the length. The winding core is not particularly limited, and any known core can be used. A 3-inch, 6-inch, 8-inch, or other paper tube, a plastic core, or a metal core can be used. [Example]

[0043] 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 modified within the scope of the present invention.

[0044] [Sample sampling method] In a 1000 m long film roll obtained in the Examples and Comparative Examples described below, the first sample cutout was set at the center position in the roll width direction, with the second end (0 m from the surface layer portion) and sample cutouts set every 100 m from the first sample cutout. The final sample cutout was set at the first end (0 m from the core) of the film, and samples were taken from a total of 11 sample cutouts. Ten samples were cut out from each sample cutout, and the average of the physical properties of the 10 samples at each sample cutout was used as the physical property value of the sample at that cutout.

[0045] [Heat shrinkage rate (hot water heat shrinkage rate)] The polyester film was cut into a 100 mm x 100 mm square and immersed in hot water at 90°C ± 0.5°C for 10 seconds without load to allow it to shrink. It was then immersed in water at 25°C ± 0.5°C for 10 seconds, removed from the water, and the dimensions of the film in the longitudinal and transverse directions were measured, and the thermal shrinkage ratios for each direction were calculated according to the following formula 3. The direction with the largest thermal shrinkage ratio was designated the main shrinkage direction (longitudinal direction). Variation (average, maximum, and minimum values) between samples was also investigated for the thermal shrinkage ratios in the longitudinal and transverse directions. Heat shrinkage rate (%) = {(L0-L1) / L0} × 100 (Equation 5) L0: Film length before heat shrinking (100mm) L1: Film length after heat shrinkage

[0046] [Component composition] 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 subjected to proton NMR measurement using a GEMINI-200 NMR spectrometer (Varian) at 23°C and 64 cycles of accumulation. In the NMR measurement, the peak intensity of a specific proton was calculated to determine the amount of the component in 100 mol% of the polyhydric alcohol component. In the following examples and comparative examples, the most abundant alcohol component was ethylene glycol. Among the components other than ethylene glycol, the variation (average, maximum, and minimum values) between samples in the content of the most abundant alcohol component (most abundant component) and the second most abundant alcohol component (second abundant component) was investigated.

[0047] [Intrinsic viscosity (IV)] 0.2 g of polyester was dissolved in 50 mL of a mixed solvent of phenol / 1,2,2-tetrachloroethane (weight ratio 60 / 40), and the viscosity was measured in dL / g using an Ostwald viscometer in a water bath at 30°C.

[0048] [Evaluation of shrinkage finish (wrap-around)] A 50-mm-wide film was wrapped around a plastic lunch box container (150 mm x 150 mm, 100 mm high) with the film oriented in the shrink direction around the container's circumference, binding the body and lid of the container. The film was then heat-sealed using an impulse sealer at 220°C, and then heat-shrunk onto the plastic lunch box container in a shrink tunnel set at 90°C. The shrink finish was evaluated based on defects: wrinkles, sink marks, insufficient shrinkage, and sagging. The evaluation was based on a five-point scale. Regarding wrinkles, wrinkles of 5 cm or more along the sides of the lunch box container were counted in Figure 3. Regarding sink marks, in Figure 4 (a top view of the shrunk banding film and lunch box container), the length from one edge of the film to the other edge of the film was defined as L, and the difference between the maximum value Lmax and the minimum value Lmin when measuring length L 5 mm around the circumference of the lunch box was defined as R. A sink mark was counted if the R was greater than 10 mm. Regarding insufficient shrinkage, the presence or absence of insufficient shrinkage after the shrinkage was judged visually. Regarding sagging, if the banding film after shrinkage was not completely adhered to the lunch box container, it was not tight when touched with the hand, and the film was floating, it was judged as sagging. 5: Best finish (no defects) 4: Good finish (one defect) 3: There are two flaws 2: 3 to 5 defects 1: Many defects (6 or more) A score of 4 or more was considered acceptable, and a score of 3 or less was considered unacceptable, and the shrinkage finish defect rate (%) was calculated according to the following formula 6. Shrinkage finish defect rate = 100 × number of defective samples ÷ total number of samples (Equation 6)

[0049] <Synthesis of polyester raw materials> Synthesis of polyester raw material A A stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser was charged with 100 mol% dimethyl terephthalate (DMT) as the dicarboxylic acid component and 100 mol% ethylene glycol (EG) as the polyhydric alcohol component, with the ethylene glycol being 2.2 times the molar ratio of dimethyl terephthalate. 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 from the system while the transesterification reaction was carried out. The polycondensation reaction was then carried out at 280°C under a reduced pressure of 26.7 Pa. The resulting polyester was removed from the polymerization reactor in a molten state in the form of a strand, immediately water-cooled, and then cut with a strand cutter to obtain polyester raw material A. The intrinsic viscosity of polyester raw material A was 0.70 dL / g. The intrinsic viscosity (dL / g) was measured by dissolving 0.2 g of polyester in 50 mL of a mixed solvent of phenol / 1,1,2,2-tetrachloroethane (60 / 40 by weight), and using an Ostwald viscometer at 30°C. This polyester raw material A is polyethylene terephthalate. The composition of the monomer components of polyester raw material A is shown in Table 1. In Table 1, the "Acid component" column shows the content of each monomer component in 100 mol% of all acid components, and the "Polyhydric alcohol component" column shows the content of each monomer component in 100 mol% of all polyhydric alcohol components. The resin size of this Polyester A was calculated as an average value from 100 resin pieces. Assuming that the resin was cylindrical, the major and minor axes of the elliptical cross section and the height (cut length) were measured with a vernier caliper. Polyester A had a major axis of 3.7 mm, a minor axis of 2.6 mm, a height of 3.7 mm, and a volume of 28 mm3.

[0050] Synthesis of polyester raw materials B to F Using the same method as for polyester raw material A, polyester raw materials B to F were obtained with different monomer components, as shown in Table 1. Polyester raw material B was produced by adding SiO2 (Sylysia 266 manufactured by Fuji Silysia Corporation; average particle size 1.5 μm) as a lubricant at a ratio of 7,000 ppm relative to the polyester. Each polyester raw material was appropriately cut into chips. For polyester F, the rotation speed of the strand cutter was increased to reduce the resin size. In Table 1, TPA represents terephthalic acid, EG represents ethylene glycol, NPG represents neopentyl glycol, CHDM represents 1,4-cyclohexanedimethanol, BD represents 1,4-butanediol, and DEG represents the by-product diethylene glycol. The intrinsic viscosities of each polyester raw material were B: 0.70 dl / g, C: 0.75 dl / g, D: 0.74 dl / g, E: 1.20 dl / g, and F: 1.20 dl / g, respectively. The properties of each polyester raw material are shown in Table 1.

[0051] [Table 1]

[0052] Using the polyester raw materials A to F, various polyester films listed in Table 2 were obtained.

[0053] [Example 1] Polyesters B, C, and E were mixed in a mass ratio of 10:66:24 and fed into the extruder via a hopper installed directly above the extruder. The extruder was equipped with a bellows and a stirrer, as shown in Figure 3. This mixed resin was melted at 280°C and extruded through a T-die at a shear rate of 120 sec-1. The extruder was then wound around a rotating metal roll cooled to a surface temperature of 30°C and quenched to obtain an unstretched film. The resulting unstretched film was introduced into a transverse stretching machine (tenter) and preheated at 80°C for 5 seconds. After preheating, the film was continuously introduced into the transverse stretching zone and transversely stretched to 3.8 times its original size at 77°C. After transverse stretching, the film was continuously introduced into the intermediate heat treatment zone and heated at 107°C for 8 seconds. The film was then introduced into a longitudinal stretching machine, which had a series of rolls consisting of a low-speed roll made of a chrome-plated roll and a ceramic roll, and a high-speed roll made of a fluororesin roll and a silicone rubber roll. The film was preheated on a preheating roll until the film temperature reached 95°C, and then stretched in the longitudinal (machine) direction to 2.0 times its original size at 90°C. The stretching speed was 130% / sec. After stretching, the longitudinally stretched film was cooled on a cooling roll whose surface temperature was set to 25°C. The cooled film was then introduced into a tenter (second tenter), where it was heat-treated for 10 seconds in an atmosphere of 92°C and relaxed 2% in the transverse direction (film width direction), then cooled, and both edges were cut and removed to obtain a heat-shrinkable polyester film with a thickness of approximately 30 μm.Finally, it was heat-treated for 3 seconds at 50°C in a heat treatment zone, cooled, and both edges were cut and removed to produce a continuous film of more than 4000 m. In this case, the fluctuation range of the film surface temperature was within the average temperature ±0.5°C in the preheating and stretching processes of the transverse stretching, the intermediate heat treatment process, the preheating, stretching and cooling processes of the longitudinal stretching, and the final heat treatment process. The obtained film was slit into a width of 900 mm and a length of 4000 m, and wound into a roll on a 3-inch paper tube to obtain the film of Example 1.

[0054] [Examples 2 to 4] In Examples 2 to 4, various conditions were changed from those in Example 1 as shown in Table 2 to produce film rolls. In Examples 3 and 4, only longitudinal stretching was carried out without transverse stretching and intermediate heat treatment. In Example 4, polyesters A, B, and C were mixed in a total weight ratio of 20:8:53 and fed to a raw material feed hopper. Furthermore, an inner pipe as shown in FIG. 1 was provided in the raw material feed hopper, and only polyester F was fed directly to the extruder in an amount of 19% of the total weight (the composition of polyesters A:B:C:F was 20:8:53:19 in mass ratio).

[0055] [Comparative Examples 1 to 4] In Comparative Examples 1 to 4, various conditions were changed from those in Example 1 as shown in Table 2 to produce film rolls. The properties of each film thus obtained were evaluated by the methods described above, and the results are shown in Table 2.

[0056] [Table 2]

[0057] [Table 3]

[0058] The heat-shrinkable films of Examples 1 to 4, which satisfied the requirements of the present invention, showed good results, with the fluctuation in heat shrinkage rate within the film roll falling within the specified range. In contrast to these Examples, in Comparative Example 1, a chrome-plated roll was used as the roll material for longitudinal stretching, which caused the film to stick to the roll, making uniform stretching difficult, resulting in fluctuations in the thermal shrinkage rate exceeding the specified range. In Comparative Example 2, since no stirring device, no bellows, or no inner pipe was used in the raw material supplying step, the composition in the film roll fluctuated greatly, resulting in large fluctuations in the thermal shrinkage rate. In Comparative Example 3, Polyester F, which has an extremely small angle of repose, was used, and an inner pipe was not used in the raw material supply process, so the composition fluctuated significantly, as in Comparative Example 2, and the heat shrinkage rate exceeded the specified range. In Comparative Example 4, although a stirring device and a jinbaori were used in the raw material supply process, the shear rate in the extrusion process was low and the longitudinal stretching rate was also low, resulting in large fluctuations in the thermal shrinkage rate within the film roll. [Industrial Applicability]

[0059] As described above, the heat-shrinkable polyester film roll of the present invention has high heat shrinkability in the longitudinal direction of the film, and exhibits extremely small fluctuations in shrinkability in the width and longitudinal directions. In particular, when the film is continuously applied to packaging objects using a wrap-around method and then shrunk to finish before use, the rate of occurrence of defects such as wrinkles and distortion is extremely small, making it a heat-shrinkable polyester film roll with great industrial utility value. [Explanation of symbols]

[0060] 1: Hopper 2: Extruder 3: Inner pipe 4: Inner pipe outlet 5: Resin supply port 6: Lunch box container 7: Film 8: Wrinkles 9: Lunch box container 10: Film

Claims

1. A heat-shrinkable polyester film roll is obtained by winding a heat-shrinkable polyester film whose main shrinkage direction is a longitudinal direction around a core, and is characterized in that the heat-shrinkable polyester film and the heat-shrinkable polyester film roll satisfy the following requirements (1) to (4): (1) The polyester constituting the film contains ethylene terephthalate as a main component and at least one polyhydric alcohol selected from the group consisting of 1,4-cyclohexanedimethanol, neopentyl glycol, 1,4-butanediol, diethylene glycol, and 1,3-propanediol. (2) The end of the film roll on the winding start side (core) is defined as the first end, and the end on the winding end side (surface layer) is defined as the second end. A first sample cutout is provided at the center position in the roll width direction, within 2 m inside the second end, and a final sample cutout is provided at a position within 2 m inside the first end. Sample cutouts are also provided approximately every 100 m from the first sample cutout. Samples cut into 10 cm x 10 cm squares from each sample cutout are immersed in 90°C warm water for 10 seconds, pulled out, and then immersed in 25°C water for 10 seconds and pulled out. When these samples are cut out, the thermal shrinkage in the longitudinal direction is 30% or more and 80% or less. (3) When the heat shrinkage rates in the longitudinal direction are measured by the method described in (2) above and the average is calculated, the heat shrinkage rates in the longitudinal direction for all samples are within ±3% of the average heat shrinkage rate. (4) For each sample obtained by the sampling method described in (2) above, the refractive index Nx in the longitudinal direction is measured for all samples, and when the average value of these is calculated, Nx for all samples is within the range of the average value ±0.

01.

2. The heat-shrinkable polyester film roll according to claim 1, further satisfying the following requirements (5) and (6): (5) When the thermal shrinkage in the width direction is measured by the method described in (2) above, the thermal shrinkage in the width direction (direction perpendicular to the longitudinal direction) for all samples is -20% or more and 20% or less. (6) When the heat shrinkage rates in the width direction are measured by the method described in (2) above and the average is calculated, the heat shrinkage rates in the width direction for all samples are within ±3% of the average heat shrinkage rate.

3. 3. The heat-shrinkable polyester film roll according to claim 1, wherein the effective wound length of the film is 1,000 m or more and 20,000 m or less.

4. The heat-shrinkable polyester film roll according to any one of claims 1 to 3, wherein the film width is 300 mm or more and 2500 mm or less.

5. The heat-shrinkable polyester film roll according to any one of claims 1 to 4, wherein the film thickness is 5 µm or more and 100 µm or less.

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