Heat-shrinkable polyester 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 formed by winding a heat-shrinkable polyester-based film. More specifically, it relates to a heat-shrinkable polyester-based film roll in which the occurrence of defects such as insufficient shrinkage, shrinkage marks, wrinkles, distortion, and vertical streaks generated due to variations in the heat shrinkage rate within the heat-shrinkable film roll is extremely low in post-processing steps.

Background Art

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

[0003] Furthermore, conventional heat-shrinkable polyester films that shrink significantly in the width direction are widely used. When used as label films for bottles or banding films for binding lunch boxes, the film must be made into a ring shape and attached to the bottle or lunch box before being heat-shrinkable in the circumferential direction. Therefore, when using a heat-shrinkable film that shrinks in the width direction as a banding film, a ring shape must be formed so that the width direction of the film is the circumferential direction, and then the ring shape must be cut to predetermined lengths and attached to the bottle or lunch box by hand. Consequently, it is difficult to attach label films or banding films made of heat-shrinkable films that shrink in the width direction to bottles or lunch boxes at high speed. For this reason, recently, films that shrink in the longitudinal direction have been invented that can be directly wrapped around bottles or lunch boxes from a film roll (the so-called wrap-around method) (for example, Patent Document 1). This eliminates the need for a center-sealing process to form and seal a film ring shape, as well as processing such as cutting and hand-covering, and also allows for high-speed attachment.

[0004] These heat-shrinkable films are often wound into rolls after manufacturing and used in this film roll form. These film rolls are cut to the size of labels used on the final product as needed, and both ends of the film (or both ends in the longitudinal direction if shrinking in the longitudinal direction) are sealed using solvent bonding or heat sealing to form an annular shape (hereinafter also referred to as a label). This label is then heated to adhere tightly to the container. Heating methods include a type that uses steam to induce heat shrinkage (steam tunnel) and a type that uses hot air to induce heat shrinkage (hot air tunnel). The heat shrinkage process is completed by passing the film through these heating tunnels on an attached conveyor belt.

[0005] Incidentally, since the heating conditions inside the tunnel are the same during this heat shrinkage process, if there is a large variation in the heat shrinkage rate for each label, it is likely that some labels will not exhibit the correct heat shrinkage rate. These will result in defects in appearance such as insufficient shrinkage, uneven shrinkage, wrinkles, distortion of the design, and sink marks, making them unsuitable as final products. Normally, the same label is produced from a single film roll. Therefore, if there is a large variation in the heat shrinkage rate of the film wound on a single film roll, the defect rate in the heat shrinkage process increases. These defects were a common problem with 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 in which the 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 in that the 85°C heat shrinkage rate in the maximum shrinkage direction (main shrinkage direction) along the longitudinal direction is 20% or more along the entire length of the roll. Patent Document 3 successfully suppresses fluctuations in the heat shrinkage rate along the entire length of the film roll by controlling the raw material supply method. However, all the examples in Patent Document 3 have the main shrinkage direction as the width direction, and do not mention means for controlling fluctuations in the shrinkage rate of a film roll where the 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 to be exhibited, so if the main shrinkage direction of a heat-shrinkable film is the longitudinal direction, it needs to be stretched in the longitudinal direction. In order to reduce fluctuations in the heat shrinkage rate in the longitudinal direction, it is necessary to control the method of stretching in the longitudinal direction in addition to the raw material supply method described above. Furthermore, Patent Document 3 is a technology disclosed more than 15 years ago, and there is now an even greater demand for reductions in heat shrinkage rate fluctuations. In other words, it was difficult to suppress fluctuations in the heat shrinkage rate in the longitudinal direction to the current required level with only the technology described in Patent Document 3. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2019-111824 [Patent Document 2] Japanese Patent Publication No. 2019-123252 [Patent Document 3] Japanese Patent Publication No. 2003-170494 [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention aims to provide a heat-shrinkable polyester film roll that can reduce defects in the heat shrinkage process caused by fluctuations in the heat shrinkage rate within the heat-shrinkable polyester film roll, where the main shrinkage direction is the longitudinal direction, particularly defects that occur when the film is attached to the object to be packaged using the wrap-around method and then heat-shrinked. [Means for solving the problem]

[0008] The present invention is as follows: 1. A heat-shrinkable polyester film roll comprising a heat-shrinkable polyester film whose main shrinkage direction is the longitudinal direction wound onto a core, characterized in that 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 has ethylene terephthalate as its main component and contains 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 (core) side is designated as the first end, and the end on the winding end (surface) side is designated as the second end. The first sample cutting section is provided within 2 m inside the second end at the center of the roll width direction, and the final sample cutting section is provided within 2 m inside the first end. Sample cutting sections are also provided approximately every 100 m from the first sample cutting section. A 10 cm x 10 cm square sample is cut from each sample cutting section, immersed in 90°C hot water for 10 seconds and then removed, and the longitudinal thermal shrinkage rate is 30% to 80% for all samples when immersed in 25°C water for 10 seconds and then removed. (3) When the thermal shrinkage rate in the longitudinal direction is measured by the method described in (2) above and the average of these is calculated, the thermal shrinkage rate in the longitudinal direction for all samples is ±3% or less of the average thermal shrinkage rate. 2. A heat-shrinkable polyester film roll as described in 1., which also satisfies the following requirements (4) and (5). (4) When the thermal shrinkage rate in the width direction is measured by the method described in (2) above, the thermal shrinkage rate in the width direction (direction perpendicular to the longitudinal direction) is -20% or more and 20% or less for all samples. (5) When the thermal shrinkage rate in the width direction is measured by the method described in (2) above and the average of these is calculated, the thermal shrinkage rate in the width direction for all samples is ±3% or less of the average thermal shrinkage rate. 3. A heat-shrinkable polyester film roll as described in 1. or 2., wherein the effective roll length of the film is 1,000 m or more and 20,000 m or less. 4. A heat-shrinkable polyester film roll as described in any of 1. to 3., with a film width of 300 mm or more and 2500 mm or less. 5. A heat-shrinkable polyester film roll as described in any of 1. to 4., with a film thickness of 5 μm or more and 100 μm or less. [Effects of the Invention]

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

[0010] [Figure 1] Schematic diagram illustrating an example of raw material mixing in the manufacturing process of a heat-shrinkable polyester film roll according to the present invention. [Figure 2] Partial enlarged view of Figure 1 [Figure 3] Schematic diagram of a plastic lunch container for evaluating wrinkles in film after shrinkage. [Figure 4] Schematic diagram of a plastic lunch container for evaluating sink marks of film after shrinkage. [Modes for carrying out the invention]

[0011] The inventors of the present invention investigated the fluctuations in the thermal shrinkage rate within the roll and found that there are mainly two causes for these fluctuations. Firstly, in the raw material supply process, two or more raw materials are used (polymer blend), and secondly, in the longitudinal stretching process, fluctuations in molecular orientation occur due to stretching. The inventors of the present invention found that the fluctuations in the thermal shrinkage rate are small, and therefore the above problems are less likely to occur. The present invention will be described in detail below. In this invention, "longitudinal direction" refers to the direction in which the film is wound on the film roll.

[0012] 1. Physical properties of film rolls 1.1. Thermal shrinkage rate in the longitudinal direction (main shrinkage direction) The heat-shrinkable polyester film roll of the present invention has a first end at the winding start side (core) and a second end at the winding end side (surface layer), with the first sample cutting section located within 2 m inside the second end at the center of the roll width direction, and the final cutting section located within 2 m inside the first end, and with sample cutting sections located approximately every 100 m from the first sample cutting section, each sample must meet the following requirements (2) and (3). (2) For each 10 cm × 10 cm square sample cut out from each of the sample cutting parts, when each sample is immersed in warm water at 90°C for 10 seconds and then pulled out, and then immersed in water at 25°C for 10 seconds and pulled out, the longitudinal thermal shrinkage rate of all the samples is 30% or more and 80% or less. (3) When the longitudinal thermal shrinkage rate is measured by the method described in (2) above and the average thereof is calculated, the longitudinal thermal shrinkage rate of all the samples is within ±3% of the average thermal shrinkage rate. For the film wound around one roll, when the end portion (core) on the starting side of the film winding is defined as the first end portion and the end portion on the finishing side (surface layer) is defined as the second end portion, a first sample cutting part is provided within 2 m from the inside of the first end portion, and a final cutting part is provided within 2 m from the inside of the first end portion. By providing sample cutting parts at approximately every 100 m from the first sample cutting part, samples are selected at substantially equal intervals over the entire length of the steady region of the film. Note that the phrase "about every 100 m" means that samples may be cut out at a position of about 100 m ± 1 m.

[0013] The above sampling method will be described in more detail. For example, when a heat-shrinkable film with a film length of 498 m is wound around a roll, within 2 m from the end of the film winding, the first sample A (10 cm × 10 cm) is cut out at the central part in the roll width direction. For the convenience of cutting, the cutting direction of the square is set such that it has a side along the longitudinal direction of the film and a side along the direction perpendicular to the longitudinal direction (width direction) (not cut diagonally). Subsequently, at a position approximately 100 m away from the cut-out part in the longitudinal direction, the second sample B is cut out at the central part in the roll width direction. Similarly, the third sample C is cut out at about the 200 m mark, the fourth sample D is cut out at about the 300 m mark, and the fifth sample E is cut out at about the 400 m mark. Here, since the remaining part is shorter than 100 m, the sixth (final) sample F is cut out from any part within 2 m from the start of the film winding.

[0014] Requirement (2) of the present invention is that the heat shrinkage rate at 90 °C in the longitudinal direction of all the samples cut out in this way is 30% or more. If the heat shrinkage rate in the longitudinal direction of the film is less than 30%, the heat shrinkage of the film is insufficient, so when it is shrink-wrapped onto a container or the like, it does not adhere closely to the container, resulting in poor appearance, which is not preferable. 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 more preferable it is as the versatility increases, but the upper limit of the technical level of the present invention is 80%. In practical use, an upper limit of 75% is sufficient.

[0015] And in the present invention, in requirement (3), when calculating the average value of the heat shrinkage rate in the longitudinal direction based on all the samples obtained from the above-mentioned cut-out parts, it is determined that the heat shrinkage rate in the longitudinal direction of all the samples is within the range of the average value ±3%. This range is preferably within ±2.8%, and more preferably within ±2.6%. The meaning of within this average ±3% will be explained in more detail. First, measure the heat shrinkage rate for each of the cut samples and calculate the average in the longitudinal direction. If the average value of the heat shrinkage rate in this longitudinal direction is X (%), and the heat shrinkage rate in the longitudinal direction of sample A above is Y1 (%), then |X - Y1| (the absolute value of X - Y1) is less than 3 (%), and similarly for the heat shrinkage rates Y2 to Y6 (%) in the longitudinal direction of samples B to F, |X - Yn| is all less than 3 (%), which is the meaning of within the average ±3%. In other words, if both the difference between the maximum value Ymax of Yn and X and the difference between the minimum value Ymin of Yn and X are within ±3%, the requirements of the present invention are satisfied. As is clear from the fact that the measurement temperature of the heat shrinkage rate is 90 °C, according to the present invention, since the variation of the heat shrinkage rate in the longitudinal direction at a temperature of 90 °C can be suppressed, even when an annular body is produced from the film roll, coated on the package (container), and heat-shrunk at about 90 °C, the occurrence of shrinkage failure can be prevented.

[0016] 1.2. Heat Shrinkage Rate in the Width Direction (Direction Orthogonal to the Main Shrinkage Direction) The heat-shrinkable polyester film wound on the heat-shrinkable polyester film roll of the present invention preferably satisfies the following requirements (4) and (5) for each sample obtained from 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 from each sample cutting section is immersed in 90°C hot water for 10 seconds and then removed, and then immersed in 25°C water for 10 seconds and removed, and the thermal shrinkage rate in the width direction for all samples is -20% or more and 20% or less. (5) When the thermal shrinkage rate in the width direction is measured by the method described in (1) above and the average value is calculated, the thermal shrinkage rate in the width direction for all samples is less than or equal to the average value ± 3%. For heat-shrinkable polyester films, it is desirable that the heat shrinkage rate in the width direction is close to zero after shrinking as an annular body, as this prevents changes in the dimensions in the direction where shrinkage is not desired (non-shrinking direction). If the heat shrinkage rate in the width direction of the film exceeds 20% (requirement (3) above), the length in the non-shrinking direction after being used as a label becomes 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 non-shrinking direction will stretch. If the heat shrinkage rate in the width direction falls below -20%, the dimensions in the non-shrinking direction will change after being shrunk as a label. A heat shrinkage rate in the width direction of -19% or more is preferable, and -18% or more is more preferable. Furthermore, in this invention, when the average value of the thermal shrinkage rate in the width direction is calculated based on all the samples obtained from each cut section, it is preferable that the thermal shrinkage rate in the width direction of all samples is within ±3% of the average value. This range is more preferably within ±2.8%, and even more preferably within ±2.6%. As is clear from the fact that the measurement temperature for the heat shrinkage rate is 90°C, according to the present invention, it is possible to suppress fluctuations in the heat shrinkage rate in the width direction at a temperature of 90°C. Therefore, even when an annular body is made from the film roll and this is used to cover a packaged object (container) and heat-shrink at approximately 90°C, it is possible to prevent the occurrence of shrinkage defects.

[0017] 1.3. Refractive Index The heat-shrinkable polyester film wound on the heat-shrinkable polyester film roll of the present invention is preferably calculated based on all samples obtained from the sampling method described in (2) of "1.1. Heat shrinkage rate in the longitudinal direction (main shrinkage direction)" above, and the average refractive index Nx in the longitudinal direction is calculated based on all samples, and it is preferable that the Nx of all samples is within the range of the average value ±0.01. 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 how much the film has been stretched. Generally, the higher the degree of orientation of the molecular chains caused by stretching, the higher the heat shrinkage rate of the heat-shrinkable polyester film tends to be. In other words, in the present invention, if the variation in Nx in the longitudinal direction of the film roll is small, it means that the variation 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, it is not economical as it simply increases the weight per unit area of ​​the film. On the other hand, if the thickness is less than 5 μm, the film becomes extremely thin, making it difficult to handle in processes such as forming an annular shape (poor handling properties). 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. Types and amounts of polyester raw materials that make up the film roll. The polyester raw material constituting the film of the present invention is one whose main component is ethylene terephthalate units. Here, "main component" means that when the total amount of components is 100 mol%, it contains 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 the polyester component units out of 100 mol%. The diol components constituting the polyester, other than ethylene glycol, must include at least one polyhydric alcohol selected from 1,4-cyclohexanedimethanol, neopentyl glycol, 1,4-butanediol, diethylene glycol, and 1,3-propanediol. These diol components are amorphous and necessary to achieve a thermal shrinkage rate of 30% or more at 90°C. Other components may include aromatic diols such as propylene glycol and bisphenol A, and aliphatic diols such as hexanediol.

[0020] The amount of these amorphous components is preferably 10 mol% or more, and more preferably 20 mol% or more, out of 100 mol% of the polyhydric alcohol components in the total 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 for the amount of amorphous components is 50 mol%, since ethylene terephthalate is the main component (50 mol%). If the amount of amorphous components is too high, there is a concern that the variation in molecular orientation that occurs during stretching in the longitudinal direction, as described later, will become large. The amount of amorphous components is preferably 45 mol% or less, and more preferably 40 mol% or less.

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

[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 incorporating aliphatic dicarboxylic acids (e.g., adipic acid, sebacic acid, decanedicarboxylic acid, etc.) into polyester, the content is preferably less than 3 mol% (out of 100 mol% of the dicarboxylic acid component). Heat-shrinkable polyester films obtained using polyester containing 3 mol% or more of these aliphatic dicarboxylic acids have insufficient stiffness when mounted at high speed. Furthermore, it is preferable not to include polycarboxylic acids with a valency of 3 or higher (for example, trimellitic acid, pyromellitic acid, and their anhydrides) in the polyester. Heat-shrinkable polyester films obtained using polyesters containing these polycarboxylic acids tend to have difficulty achieving the required shrinkage rate.

[0023] In the film resin forming the heat-shrinkable polyester film roll of the present invention, it is preferable to add fine particles as a lubricant 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, while examples of organic fine particles include acrylic resin particles, melamine resin particles, silicone resin particles, and cross-linked polystyrene particles. The average particle size of the fine particles is within the range of 0.05 to 3.0 μm (measured with a Coulter counter) and can be appropriately selected as needed. As for how to incorporate the above-mentioned fine particles, for example, they can be added at any stage in the production of the polyester resin, but it is preferable to add them as a slurry dispersed in ethylene glycol or the like at the esterification stage, or after the completion of the transesterification reaction but before the start of the polycondensation reaction, in order to proceed with the polycondensation reaction. It is also preferable to blend the slurry of particles dispersed in ethylene glycol or water with the polyester resin raw material using a vented kneading extruder, or to blend the dried particles with the polyester resin raw material using a kneading extruder. Furthermore, by keeping the amount of fine particles added in the film within the range of 300 to 1200 ppm, it is possible to achieve both good slipperiness (friction) and transparency.

[0024] 3. Method for manufacturing film rolls The heat-shrinkable polyester film of the present invention can be obtained by supplying the polyester raw materials described in "2.1. Types and amounts of polyester raw materials constituting the film roll" above to an extruder and melt-extruding them, and then obtaining the formed unstretched film through the following predetermined process. In this invention, the challenge is to suppress fluctuations in the thermal shrinkage rate within the film roll, which can be achieved by controlling the raw material supply and the method of stretching in the longitudinal direction. Below, the manufacturing method is described, highlighting the key technologies of this invention.

[0025] 3.1. Raw material mixing and supply In manufacturing the film roll of the present invention, as described in "2. Types and amounts of polyester raw materials" above, the film needs to contain monomers that can become amorphous components in addition to ethylene terephthalate units. In this case, two or more types of raw materials (polyester resin) are usually mixed and used. Conventionally, when two or more types of raw materials are mixed and fed into an extruder, variations (segregation) in the supply of raw materials occur, causing problems with fluctuations in the film composition. When the composition fluctuates within the film roll, it becomes difficult to keep the fluctuations in the thermal shrinkage rate within a predetermined range. To prevent raw material segregation, the following are effective: (1) optimizing the angle of repose of the polyester resin used as the raw material, (2) optimizing the shape of the hopper in the raw material supply line, (3) installing a stirring device directly above the extruder, (4) installing a conical cover at the bottom of the hopper (to cut powder pressure), and (5) installing an inner pipe in the final hopper. It is preferable to adopt at least one of these means to suppress fluctuations in the thermal shrinkage rate within the film roll. It is even more preferable to combine two or more of these means. These methods will be explained in detail below.

[0026] 3.1.(1) Angle of repose of polyester resin During the manufacturing of film rolls, as the resin in the final hopper directly above the extruder decreases, a phenomenon called segregation can easily occur, depending on the hopper's capacity and shape, resulting in a difference in the composition of the mixed resin supplied to the extruder. This problem is particularly pronounced when the angles of repose of the various resins differ. As a result, the thermal shrinkage rate within the film roll fluctuates. The angle of repose is the angle between the slope of a pile formed when a certain amount of resin is dropped from a certain height and the horizontal plane. This is determined by the shape and particle size of the resin; the larger the resin, the smaller the angle of repose tends to be, and the smaller the angle of repose of the resin, the less likely it is to remain in the hopper (it flows more easily). The angle of repose also changes depending on the slipperiness of the resin surface; the more slippery the resin surface, the lower the angle of repose (the more likely the pile is to collapse). When manufacturing the raw material resin, the usual method is to extrude it in a molten state in the form of strands (strings) after the polymerization process, immediately cool it with water, and then cut it with a strand cutter. Therefore, the shape of the resin is an elliptical cylinder, and its volume is determined by the major axis (mm), minor axis (mm), and height (mm) of the elliptical cross-section of the resin, which affects the angle of repose of the resin. The resin volume can be changed by the viscosity of the molten resin (swell at the strand die outlet), the strand extrusion speed, the rotation speed of the strand cutter, etc. Furthermore, the angle of repose is affected not only by the resin volume but also by its specific gravity. The specific gravity of the resin is also affected by the composition of the polyester component and the cooling rate of the molten resin. As mentioned above, the angle of repose of the resin varies depending on the various conditions when manufacturing the polyester, but it is usually between 30 and 45 degrees. When manufacturing by mixing two or more raw material resins, in order to obtain a film with minimal compositional variation, it is preferable to match the angles of repose of all resins used to suppress raw material segregation in the final hopper. By using the raw material with the largest quantity as the main raw material and using others with angles of repose within ±4 degrees relative to it, raw material segregation can be reduced. An angle of repose within ±3 degrees is more preferable.

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

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

[0029] 3.1.(4) Jinkasa installation As described in (1) above, the amount of raw material in the hopper is constantly fluctuating during the manufacturing of film rolls. Specifically, a raw material level gauge is installed in the hopper, and when the raw material is consumed and reaches the lowest level, the level gauge senses this and the raw material is refilled. In other words, the raw material is consumed and refilled repeatedly, and the powder pressure applied to the supply section directly above the extruder (lower part of the hopper) is constantly fluctuating depending on the amount of raw material filled in the hopper. When manufacturing film by mixing two or more types of raw material resins, fluctuations in powder pressure can also promote segregation of the raw material, so it is preferable to keep the powder pressure constant. Conventionally, measures have been taken to shorten the raw material charging cycle (set a higher minimum raw material level). However, shortening the raw material charging cycle leads to more frequent operation of mechanical parts, resulting in problems such as an increased frequency of breakdowns. Therefore, it is preferable to provide a conical shield at the bottom of the hopper to cut off the powder pressure from the top of the hopper. The shape of the conical shield is not particularly limited, but it is preferable to be a cone or a triangular pyramid. Furthermore, while there are no particular limitations on the size of the hopper cap, it must not exceed the diameter of the piping at the bottom of the hopper in order to ensure a smooth supply of raw materials.

[0030] 3.1.(5) Installation of the inner pipe If the angles of repose of two or more raw material resins differ drastically, raw material segregation may occur even if the measures described in 3.1.(2) to (4) above are taken. In this case, instead of using the mixed 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 sometimes referred to as "secondary materials"). This method is preferable because it can essentially avoid raw material segregation that occurs in the hopper. The amount of raw material supplied from the inner pipe must match the amount of raw material supplied from the final hopper. Figure 1 shows an example of a specific mixing procedure. Figure 1 shows an extruder 2 equipped with a hopper 1 and an injection This is a schematic diagram showing an example of the relationship with the nerpipe 3, and Figure 2 is an enlarged view of part A of Figure 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. And since the outlet 4 of the inner pipe 3 is directly above the extruder (exactly 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 following relationship of 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 indicates 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 indicates 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 greater 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 air entering the extruder and generating bubbles can be prevented.

[0031] The height H3 (= H2 - 0.5 × L / tanθ) of the mixing position of the auxiliary raw material is desirably 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. Polyester can be obtained by polycondensing the aforementioned suitable dicarboxylic acid and diol components using a known method. Furthermore, it is preferable to dry the raw resin using a dryer such as a hopper dryer or paddle dryer, or a vacuum dryer, before sending it to the final hopper.

[0032] 3.2. Molten Extrusion The raw materials mixed as described above are extruded into a film at a temperature of 200-280°C using an extruder. Any existing extrusion method, such as the T-die method or the tubular method, may be used. However, if the extrusion temperature exceeds 280°C, the intrinsic viscosity of the polyester resin decreases, making it more prone to breakage during the film-forming process and making it difficult to obtain a steady-state film, which is undesirable. If multiple layers of film are to be produced, multiple extruders, feed blocks, or multi-manifolds may be used. Subsequently, an unstretched film can be obtained by rapidly cooling the film melted by extrusion. As a method for rapidly cooling the molten resin, a method of casting the molten resin from a die onto a rotating drum and rapidly cooling and solidifying it to obtain a substantially unoriented resin sheet can be suitably employed. Furthermore, the shear rate when the molten resin is extruded from the die opening is preferably 100 sec⁻¹ or higher, and more preferably 150 sec⁻¹ or higher. The higher the shear rate, the more the variation in shrinkage rate in the longitudinal direction of the film can be suppressed. This is because the higher the shear rate, the more stable the resin extrusion pressure at the die opening (outlet). If the shear rate is less than 100 sec⁻¹, the resin extrusion pressure at the die outlet becomes unstable, and pulsation (thickness variation of the unstretched film in the longitudinal direction) is more likely to occur. As a result, the stretching in the longitudinal direction, which will be described later, will not be uniform, and the variation in thermal shrinkage rate in the longitudinal direction will become large.

[0033] On the other hand, if the shear rate is greater than 600 sec⁻¹, the polyester molecular chains are broken (decomposed), which not only reduces the intrinsic viscosity but also causes resin residue and other debris to adhere to the die's discharge portion, resulting in poor productivity, which is undesirable. The shear rate at the die exit was calculated using Equation 3 below.

[0034] γ=6Q / (W×H2) (Formula 3) γ; Shear rate (sec-1) Q: What is the raw material discharge rate (cm³ / sec) from the extruder? W; Width of the die opening (cm) H; Die opening gap (dimensions in cm)

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

[0036] 3.3. Extension in the width direction (lateral extension) First, the film is stretched in the width (lateral) direction. Lateral stretching is preferably performed at 65°C to 100°C for approximately 2.5 to 5 times its original length, while the film is held at both ends in the width direction by clips within a tenter (first tenter). Preheating is preferable before lateral stretching, and this preheating should be carried out until the film surface temperature reaches 60°C to 95°C. After lateral stretching, it is preferable to pass the film through an intermediate zone where no active heating is performed. If there is a temperature difference between the lateral stretching zone and the intermediate heat treatment zone of the first tenter, heat from the intermediate heat treatment zone (both hot air and radiant heat) may flow into the lateral stretching process, causing the temperature in the lateral stretching zone to become unstable and potentially leading to unstable film quality. Therefore, it is preferable to pass the film through the intermediate zone for a predetermined amount of time after lateral stretching and before intermediate heat treatment, and then perform the intermediate heat treatment. In this intermediate zone, a stable quality film can be obtained by blocking the accompanying flow associated with the film's movement, as well as the hot air from the lateral stretching zone and the intermediate heat treatment zone, so that when a strip of paper is hung down without passing through the film, the strip hangs almost completely vertically. A passage time of 1 to 5 seconds in the intermediate zone is sufficient. If it is shorter than 1 second, the length of the intermediate zone will be insufficient, resulting in inadequate heat insulation. While a longer intermediate zone is preferable, making it too long would increase the size of the equipment, so about 5 seconds is sufficient.

[0037] 3.4. Intermediate heat treatment After passing through the intermediate zone, an intermediate heat treatment is performed before longitudinal stretching. This intermediate heat treatment is to adjust the shrinkage rate in the width direction. Increasing the temperature of the intermediate heat treatment after transverse stretching tends to reduce the thermal shrinkage rate 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 thermal shrinkage rate in the width direction will not change at all compared to the thermal shrinkage rate after transverse stretching. If the temperature is higher than 140°C, the thermal shrinkage rate in the width direction will be even lower, but this is undesirable because it makes crystallization difficult and subsequent longitudinal stretching difficult. 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 is insufficient, making it difficult to adjust the thermal shrinkage rate in the transverse direction. A longer intermediate heat treatment zone is preferable, but about 20 seconds is sufficient. This results in a transversely uniaxially oriented film. During intermediate heat treatment, by reducing the distance between clips of the first tenter by an arbitrary factor in the film width direction (relaxation treatment), the molecular chains oriented in the width direction are relaxed without crystallization, thereby reducing the shrinkage rate in the width direction. It is preferable to perform relaxation of 3% or more after transverse stretching. On the other hand, 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 beyond this limit cannot be performed.

[0038] 3.5. Extension in the longitudinal direction (longitudinal extension) Next, the film is stretched lengthwise. In the stretching process, the film from the previous process is introduced into a stretching machine that has multiple rolls arranged in a continuous pattern. When stretching lengthwise, 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 become difficult to stretch in the lengthwise direction (i.e., it is more prone to tearing). On the other hand, if the temperature is higher than 120°C, the film tends to stick to the rolls, which may lead to premature roll contamination in continuous production. Once the film temperature reaches the aforementioned range, longitudinal stretching is performed. Longitudinal stretching is carried out by the difference in speed of the rolls. The stretching ratio is preferably 1.5 to 5 times. At this time, in addition to single-stage stretching using two rolls (low speed and high speed), the number of stretching stages can also be increased to two-stage stretching using three rolls (low speed, medium speed, and high speed) or three-stage stretching using four rolls (low speed, medium-low speed, medium-high speed, and high speed). The stretching speed should preferably be controlled within a range of, for example, 100% / second to 10000% / second. If the stretching speed is too fast, the film is likely to be underheated, and if the stretching speed is too slow, productivity will decrease. A stretching speed of 200% / second to 9900% / second is more preferable, and 300% / second to 9800% / second is even more preferable. The stretching speed can be calculated according to the following formula 4.

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

[0040] As heating rolls, for example, heating rolls made of metal material with hard chrome plating on the surface (hereinafter referred to as chrome-plated rolls), heating rolls made of ceramic material (hereinafter referred to as ceramic rolls), heating rolls made of fluororesin material (hereinafter referred to as fluororesin rolls), and heating rolls made of silicone rubber material (hereinafter referred to as silicone rubber rolls) can be selected. Chrome-plated rolls and ceramic rolls are particularly desirable to use during preheating, while fluororesin rolls and silicone rubber rolls are desirable to use when heating to the predetermined temperature after preheating. Chrome-plated rolls and ceramic rolls have relatively smooth surfaces and good adhesion to the film, so they are excellent at transferring heat to the film and can efficiently preheat the film. The surface roughness of the roll can be measured using average roughness (SRa), maximum protrusion height (SRmax), or ten-point average roughness (SRz), which can be measured using, for example, a small surface roughness meter such as the Surftest SJ-301 (manufactured by Mitutoyo Corporation). Chromium-plated rolls preferably have an SRz of 0.01 to 0.05, and more preferably 0.02 to 0.04. Ceramic rolls preferably have an SRmax of 1 to 8, and more preferably 1.5 to 7.5. On the other hand, fluororesin rolls and silicone rubber rolls have rough surfaces and excellent release properties, maintaining good release properties even when the film softens and becomes sticky due to heating. Fluororesin rolls preferably have an SRz of 0.1 to 2, and more preferably 0.2 to 1.9. Silicone rubber rolls preferably have an SRz of 2 to 12, and more preferably 3 to 11. For example, it is preferable to preheat the film using a group of preheating rolls consisting of chromium-plated rolls and / or fluororesin rolls, and then raise the film 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, heated to a predetermined temperature in this manner, can be stretched longitudinally by utilizing the speed difference between the heating roll and the stretching roll installed downstream of it.

[0041] 3.6. Final Heat Treatment Next, the film, after longitudinal stretching and cooling, is introduced into a second tenter for final heat treatment and relaxation. The final heat treatment step is a preferred embodiment because it allows for adjustment of the longitudinal and transverse shrinkage rates. Relaxation in the second tenter does not significantly change the longitudinal shrinkage rate, but the transverse shrinkage rate decreases. A relaxation rate of 0% to 50% is preferable. 0% is the lower limit of the relaxation rate. On the other hand, a high relaxation rate is undesirable because it has the disadvantage of shortening the width of the film product, so an upper limit of around 50% for the relaxation rate is preferable. The heat treatment (relaxation treatment) temperature is preferably between 65°C and 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, resulting in a film that does not shrink in either the longitudinal or transverse direction, making it undesirable as a heat-shrinkable film. Furthermore, from the viewpoint of reducing fluctuations in thermal shrinkage, it is preferable to control the range of fluctuation in the film surface temperature measured at arbitrary points in each step of the transverse stretching process, the intermediate heat treatment process, the preheating, stretching, and cooling process in the longitudinal stretching process, and the final heat treatment process, preferably within ±1°C of the average temperature, and more preferably within ±0.5°C of the average temperature. The range of fluctuation in the film surface temperature measured at the aforementioned arbitrary points refers to the range of fluctuation when the film surface temperature at a predetermined position during film manufacturing is continuously measured, for example, with an infrared non-contact surface thermometer.

[0042] 3.7. Winding In the present invention, the heat-shrinkable polyester film roll is preferably made by winding a heat-shrinkable film with a width of 300 mm to 2500 mm onto a winding core to a length of 1000 m to 20000 m. Typically, a wide master roll is made, and this master roll is slit to an arbitrary width and wound into a roll of arbitrary width and length to produce a film roll product. Film rolls with a width of less than 300 mm or a length of less than 1000 m have low 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, if the width of the heat-shrinkable film roll exceeds 2500 mm, the paper core tends to bend during winding, making it more prone to winding defects such as wrinkles in the film roll, which is undesirable. The width of the heat-shrinkable polyester film roll is more preferably 2450 mm or less, and even more preferably 2400 mm or less. Furthermore, the length of the heat-shrinkable film wound onto the roll is more preferably 400m or more, and even more preferably 500m or more. The longer the length of the heat-shrinkable film roll, the less the number of roll changes required when producing the ring-shaped body, thus improving productivity, which is preferable. However, in this invention, we have confirmed up to 20,000m, so this value was chosen. Furthermore, the winding core is not particularly limited and any known core can be used. Paper cores, plastic cores, or metal cores of 3 inches, 6 inches, 8 inches, etc., can be used. [Examples]

[0043] Next, the present invention will be specifically described using examples and comparative examples. However, the present invention is not limited in any way to the embodiments of these examples and can be modified without departing from the spirit of the invention.

[0044] [Sampling method for samples] In the 1000m long film rolls obtained in the examples and comparative examples described later, the first sample cutting section was set as the second end (0m from the surface) at the center of the roll width direction, and sample cutting sections were set every 100m from the first sample cutting section. The final sample cutting section was set as the first end of the film (0m from the core), and samples were taken from a total of 11 sample cutting sections. Ten samples were then cut from each sample cutting section, and the average value of the physical properties of the ten samples from each sample cutting section was taken as the physical property value of the sample from that section.

[0045] [Thermal shrinkage rate (hot water thermal shrinkage rate)] A polyester film was cut into 100mm x 100mm squares, immersed in 90°C ± 0.5°C hot water for 10 seconds under no load to induce heat shrinkage, then immersed in 25°C ± 0.5°C water for 10 seconds. After removing the film from the water, its longitudinal and widthwise dimensions were measured, and the heat shrinkage rate for each direction was calculated according to Equation 3 below. The direction with the largest heat shrinkage rate was defined as the primary shrinkage direction (longitudinal direction). Furthermore, the variation (average value, maximum value, minimum value) of the heat shrinkage rate in the longitudinal and widthwise directions between samples was investigated. Thermal shrinkage rate (%) = {(L0-L1) / L0} × 100 (Equation 5) L0; Film length before heat shrinkage (100mm) L1; Film length after heat shrinkage

[0046] [Component composition] Each sample was dissolved in a solvent mixture of chloroform D (Eurysop) and trifluoroacetic acid D1 (Eurysop) in a 10:1 volume ratio to prepare a sample solution. The proton NMR of the sample solution was measured using an NMR spectrometer "GEMINI-200" (Varian) at a temperature of 23 °C and with 64 cumulative measurements. In the NMR measurement, the peak intensity of a predetermined proton was calculated to determine the amount of the component in 100 mol% of polyhydric alcohol components. In the following examples and comparative examples, the most abundant alcohol component was ethylene glycol. Among the components other than ethylene glycol, the variation (mean, maximum, and minimum values) of the most abundant alcohol component (primary component) and the second most abundant alcohol component (secondary component) between samples 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 its viscosity was measured in dL / g using an Ostwald viscometer in a 30°C water bath.

[0048] [Evaluation of shrinkage finish (wrap-around)] For a plastic bento box container (150mm x 150mm sides, 100mm height), a 50mm wide film was wrapped around the container with the shrinkage direction in the circumferential direction, so that the film bonded the body and lid of the container. After sealing with an impulse sealer at 220°C, the film was heat-shrunk onto the plastic bento box container in a shrink tunnel at a set temperature of 90°C. In evaluating the shrinkage finish, wrinkles, sink marks, insufficient shrinkage, and sagging were considered defects and evaluated on a 5-point scale as follows. For wrinkles, in Figure 3, wrinkles with a length of 5cm or more extending along the sides of the bento box container were counted. For sink marks, in Figure 4 (a top view of the banding film and bento box container after shrinkage), L was defined as the length from one end of the film to the other, and R was defined as the difference between the maximum value Lmax and the minimum value Lmin when length L was measured at 5mm intervals along the circumferential direction of the bento box container. Sink marks were counted when R was greater than 10mm. Regarding insufficient shrinkage, we visually inspected the film after shrinkage to determine if there was any insufficient shrinkage. For sagging, we determined that the banding film did not adhere completely to the bento container after shrinkage, lacked tightness when touched, and had gaps in the film. 5: Excellent finish (no flaws) 4: Good finish (one flaw) 3: There are two drawbacks. 2: There are 3 to 5 flaws. 1: Has numerous flaws (more than 6) A score of 4 or higher was considered acceptable, and a score of 3 or lower was considered defective. The shrinkage finish defect rate (%) was calculated according to formula 6 below. Shrinkage 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 In a stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser, 100 mol% dimethyl terephthalate (DMT) as the dicarboxylic acid component and 100 mol% ethylene glycol (EG) as the polyhydric alcohol component were charged so that the molar ratio of ethylene glycol was 2.2 times that of dimethyl terephthalate. 0.05 mol% zinc acetate relative to the acid component was added as a transesterification catalyst, and 0.225 mol% antimony trioxide relative to the acid component was added as a polycondensation catalyst. The transesterification reaction was carried out while distilling off the resulting methanol. Subsequently, a polycondensation reaction was carried out at 280°C under reduced pressure of 26.7 Pa. The obtained polyester was removed from the polymerization apparatus in a molten state in strand form, immediately cooled with water, 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 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, weight ratio) and using an Ostwald viscometer at 30°C. This polyester raw material A is polyethylene terephthalate. The monomer component composition 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 the total acid component, and the "Polyhydric alcohol component" column shows the content of each monomer component in 100 mol% of the total polyhydric alcohol component. The average size of polyester A resin was calculated from 100 resin samples. Assuming the resin was cylindrical, the major axis, minor axis, and height (cut length) of the elliptical cross-section were measured using calipers. 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 Polyester raw materials B to F with different monomer components were obtained using the same method as for polyester raw material A described above, as shown in Table 1. Polyester raw material B was produced by adding SiO2 (Silysia 266, manufactured by Fuji Silysia Co., Ltd.; average particle size 1.5 μm) as a lubricant at a ratio of 7,000 ppm to the polyester. Each polyester raw material was made into chips as appropriate. For polyester F, the resin shape was reduced by increasing the rotation speed of the strand cutter. In Table 1, TPA is terephthalic acid, EG is ethylene glycol, NPG is neopentyl glycol, CHDM is 1,4-cyclohexanedimethanol, BD is 1,4-butanediol, and DEG is 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 characteristics of each polyester raw material are shown in Table 1.

[0051] [Table 1]

[0052] Using the above 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 from a hopper installed directly above it. As shown in Figure 3, a cone and a stirring device were installed on the extruder. This mixed resin was melted at 280°C and extruded from a T-die at a shear rate of 120 sec⁻¹. The unstretched film was then wrapped around a rotating metal roll cooled to a surface temperature of 30°C and rapidly cooled to obtain the unstretched film. The obtained unstretched film was led to a transverse stretching machine (tenter) and preheated at 80°C for 5 seconds. After preheating, the film was continuously led to the transverse stretching zone and stretched transversely at 77°C until it was 3.8 times its original size. After transverse stretching, the film was continuously led to the intermediate heat treatment zone and heated at 107°C for 8 seconds. Subsequently, the film was guided to a longitudinal stretching machine, which had a continuous arrangement of rolls consisting of low-speed rolls made of chrome-plated rolls and ceramic rolls, and high-speed rolls made of fluororesin rolls and silicone rubber rolls. The film was preheated on a preheating roll until its temperature reached 95°C, and then stretched at 90°C to twice its original length in the longitudinal direction. The stretching speed at this time was 130% / second. After stretching, the longitudinally stretched film was cooled on a cooling roll with a surface temperature set to 25°C. The cooled film was then guided to a tenter (second tenter), where it was heat-treated for 10 seconds in a 92°C atmosphere and relaxed by 2% in the transverse direction (film width direction) before cooling. The edges were then trimmed to obtain a heat-shrinkable polyester film with a thickness of approximately 30 μm. Finally, the film was heat-treated in a heat treatment zone at 50°C for 3 seconds, then cooled, and the edges were trimmed to continuously produce a film over a length of more than 4000 m. During this process, the fluctuation range of the film surface temperature was within ±0.5°C of the average temperature in all stages, including the preheating and stretching processes for transverse stretching, the intermediate heat treatment process, the preheating, stretching, and cooling processes for longitudinal stretching, and the final heat treatment process. The obtained film was slit into strips 900 mm wide and 4000 m long, and wound into rolls on a 3-inch paper core to obtain the film of Example 1.

[0054] [Examples 2-4] Examples 2 to 4 involved manufacturing film rolls by changing various conditions from Example 1 as shown in Table 2. In Examples 3 and 4, only longitudinal stretching was performed, without transverse stretching or intermediate heat treatment. In Example 4, polyesters A, B, and C were mixed in a ratio of 20:8:53 by total weight and supplied to the raw material supply hopper. Furthermore, an inner pipe as shown in Figure 1 was installed inside the raw material supply hopper, and only polyester F was supplied directly to the extruder in an amount of 19% by total weight (the composition of polyesters A:B:C:F was 20:8:53:19 by mass ratio).

[0055] [Comparative Examples 1-4] Comparative Examples 1 to 4 were manufactured by changing various conditions from Example 1 as shown in Table 2. The characteristics of each film obtained in this way were evaluated using the method described above. These results are shown in Table 2.

[0056] [Table 2]

[0057] [Table 3]

[0058] The heat-shrinkable films of Examples 1 to 4, which satisfy the requirements of the present invention, exhibited good performance, with the variation in heat shrinkage rate within the film roll remaining within the specified range. In Comparative Example 1, compared to these examples, a chrome-plated roll was used as the roll material when stretching in the longitudinal direction. As a result, the film adhered to the roll, making uniform stretching difficult. Consequently, the variation in thermal shrinkage rate exceeded the specified range. In Comparative Example 2, since neither a stirring device, a conical casing, nor an inner pipe was used in the raw material supply process, the compositional variation within the film roll became large, resulting in a large variation in the thermal shrinkage rate. In Comparative Example 3, polyester F with an extremely small angle of repose was used, and an inner pipe was not used in the raw material supply process. As a result, the composition fluctuated significantly, similar to Comparative Example 2, and the thermal shrinkage rate exceeded the specified range. In Comparative Example 4, although a stirring device and a conical casing were used in the raw material supply process, the shear rate in the extrusion process was low, and the stretching rate in the longitudinal direction was also low, resulting in large fluctuations in the thermal shrinkage rate within the film roll. [Industrial applicability]

[0059] The heat-shrinkable polyester film roll of the present invention has high heat shrinkability in the longitudinal direction of the film as described above, and the variation in shrinkage in the width and longitudinal directions is extremely small. In particular, when the film is continuously attached to the object to be packaged using a wrap-around method and shrunk, the rate of defects such as wrinkles and distortion is extremely low, making it a heat-shrinkable polyester film roll with high industrial 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 comprising a heat-shrinkable polyester film having its main shrinkage direction in the longitudinal direction wound onto a core, 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 has ethylene terephthalate as its main component and contains 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 (core) side is designated as the first end, and the end on the winding end (surface) side is designated as the second end. The first sample cutting section is provided within 2 m inside the second end at the center of the roll width direction, and the final sample cutting section is provided within 2 m inside the first end. Sample cutting sections are also provided approximately every 100 m from the first sample cutting section. A 10 cm x 10 cm square sample is cut from each sample cutting section, immersed in 90°C hot water for 10 seconds and then removed, and the longitudinal thermal shrinkage rate is 30% to 80% for all samples when immersed in 25°C water for 10 seconds and then removed. (3) When the thermal shrinkage rate in the longitudinal direction is measured by the method described in (2) above and the average of these is calculated, the thermal shrinkage rate in the longitudinal direction for all samples is ±3% or less of the average thermal shrinkage rate. (4) For each sample obtained from 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 values ​​is calculated, the Nx for all samples is within the range of the average value ± 0.

01.

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

3. A heat-shrinkable polyester film roll according to claim 1 or 2, wherein the effective 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 claims 1 to 3, wherein the film width is 300 mm or more and 2500 mm or less.

5. A 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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