Heat-shrinkable polyester film roll

Abstract

Provided is a heat-shrinkable polyester film roll capable of reducing defects in a heat-shrinking process caused by variation in heat shrinkage in a heat-shrinkable polyester film roll whose main shrinkage direction is the length direction, particularly when the film is heat-shrunk after being fitted to a packaging object by winding. A heat-shrinkable polyester film roll, which is a heat-shrinkable polyester film roll whose main shrinkage direction is the length direction and is wound around a core, satisfies a prescribed polyester composition, and for all samples, the heat shrinkage in the length direction after immersion in 90°C warm water for 10 seconds when samples are collected every 100 m is 30% or more and 80% or less, and is ±3% or less of the average heat shrinkage.

Description

Technical Field

[0001] This invention relates to film rolls formed by winding heat-shrinkable polyester films, and more specifically, to heat-shrinkable polyester film rolls that minimize defects such as insufficient shrinkage, uneven shrinkage, wrinkles, deformation, and longitudinal depressions in subsequent processing due to variations in the heat shrinkage rate within the heat-shrinkable film roll. Background Technology

[0002] In recent years, stretch films (so-called heat-shrinkable films) made of polyvinyl chloride (PVC), polystyrene (PS), and polyester resins have become increasingly widely used for protective packaging of glass and PET bottles, as well as for labeling, cap sealing, and integrated packaging. Among these heat-shrinkable films, PVC-based films suffer from low heat resistance and produce hydrogen chloride gas or dioxins when burned. Additionally, PPS films have poor solvent resistance, requiring specially formulated inks for printing and high-temperature incineration, resulting in unpleasant odors and large amounts of black smoke during combustion. Therefore, polyester-based heat-shrinkable films, with their high heat resistance, easy combustion, and excellent solvent resistance, are widely used for shrink labels, and their usage tends to increase with the growing volume of PET containers.

[0003] Furthermore, heat-shrinkable polyester films are commonly used, and these films shrink significantly in the width direction. When used as label films for bottles, banding films for wrapping bento containers, etc., the film must be formed into a ring and then heat-shrink in the circumferential direction after being assembled into the bottle or bento container. Therefore, when assembling a heat-shrinkable film that shrinks along the width direction as a banding film, a ring must be formed so that the width direction of the film is circumferential, and this ring must be cut at predetermined lengths and assembled into the bottle or bento container by hand covering. Therefore, it is difficult to assemble label films and banding films formed from heat-shrinkable films that shrink along the width direction into bottles or bento containers at high speed. Therefore, a film that shrinks in the length direction can recently be invented (e.g., Patent Document 1) that can be directly wound from a film roll and assembled around a bottle or bento container (so-called winding method). It eliminates the need for a central sealing process of forming a film ring and sealing, cutting, hand covering, etc., and enables high-speed assembly.

[0004] These heat-shrinkable films are temporarily rolled into rolls after manufacturing, and are mostly used in the form of film rolls. The film roll is cut to fit the dimensions of labels, etc., used in the final product, and then the two ends of the film (the two ends along the length when shrinking in the length direction) are sealed using solvent bonding, heat sealing, or other methods to form a ring (hereinafter also referred to as a label). Then, the label is heated to seal it to a container. As for the heating method, there are types that shrink by blowing steam (steam tunnels) and types that shrink by blowing hot air (hot air tunnels). The heat-shrinking process is completed by placing the interior of these heated tunnels on an attached conveyor belt and passing them through.

[0005] However, in this heat shrinking process, the heating conditions inside the tunnel are the same. Therefore, if the heat shrinkage rate of each of the aforementioned labels varies greatly, it is easy to produce materials that do not exhibit the appropriate heat shrinkage rate. These can cause appearance defects such as insufficient shrinkage, uneven shrinkage, wrinkles, pattern deformation, and dents, thus making it impossible to produce a final product.

[0006] Typically, identical labels are made from a single film roll. Therefore, when the heat shrinkage rate of the film wound on a single film roll varies greatly, the defect rate in the heat shrinking process increases. These defects are common to any raw material, such as vinyl chloride resin, polystyrene resin, and polyester resin. For example, Patent Document 2 discloses a heat-shrinkable polyester film roll with the main shrinkage direction being the length direction. However, Patent Document 2 does not describe the variation in shrinkage rate within the roll.

[0007] Patent Document 3 discloses a heat-shrinkable polyester film roll, characterized in that the heat shrinkage rate at 85°C in the maximum shrinkage direction (main shrinkage direction) along the length is 20% or more over the entire length of the roll. Patent Document 3 successfully suppresses the variation in heat shrinkage rate along the entire length of the film roll by controlling the supply of raw materials. However, the embodiments in Patent Document 3 all have the main shrinkage direction in the width direction, and do not mention methods for controlling the shrinkage rate variation of film rolls where the main shrinkage direction is the length direction. Heat-shrinkable films typically need to be stretched in the direction where the desired heat shrinkage rate is desired; therefore, when the main shrinkage direction of the heat-shrinkable film is set to the length direction, stretching in the length direction is necessary. To reduce the variation in heat shrinkage rate along the length direction, it is necessary to control the stretching method along the length direction in addition to controlling the aforementioned raw material supply method. Furthermore, Patent Document 3 is a technology disclosed more than 15 years ago, and now a further reduction in heat shrinkage rate variation is sought. That is, if the heat shrinkage rate variation along the length direction is to be suppressed to the current required level, it is difficult to achieve this solely using the technical content of Patent Document 3.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2019-111824

[0011] Patent Document 2: Japanese Patent Application Publication No. 2019-123252

[0012] Patent Document 3: Japanese Patent Application Publication No. 2003-170494 Summary of the Invention

[0013] The problem the invention aims to solve

[0014] The objective of this invention is to provide a heat-shrinkable polyester film roll capable of reducing defects in the heat-shrinkage process caused by variations in the heat shrinkage rate within a heat-shrinkable polyester film roll whose main shrinkage direction is the length direction, particularly defects that occur when the film is heat-shrinked after being assembled onto a packaged object by a winding method.

[0015] Solution for solving the problem

[0016] The present invention is as follows.

[0017] 1. A heat-shrinkable polyester film roll, characterized in that it is formed by winding a heat-shrinkable polyester film with the main shrinkage direction being the length direction onto a core, and the heat-shrinkable polyester film and the heat-shrinkable polyester film roll satisfy the following conditions (1) to (3).

[0018] (1) The polyester constituting the film is mainly composed of polyethylene terephthalate and contains at least one polyol selected from the group consisting of 1,4-cyclohexanediol, neopentyl glycol, 1,4-butanediol, diethylene glycol and 1,3-propanediol.

[0019] (2) The thermal shrinkage rate in the length direction when the sample is immersed in warm water at 90°C for 10 seconds and then lifted out, and then immersed in water at 25°C for 10 seconds and lifted out, is more than 30% and less than 80% in all samples. The sample is obtained as follows: the end of the film roll at the beginning of winding (core) is taken as the first end, the end of the roll at the end of winding (surface) is taken as the second end, and a first sample cutout is set at the center position in the roll width direction within 2m inside the aforementioned second end. In addition, a final sample cutout is set at the inner 2m inside the aforementioned first end. Furthermore, a sample cutout is set every approximately 100m from the first sample cutout, and a 10cm×10cm square shape is cut out from each sample cutout.

[0020] (3) When the thermal shrinkage rate in the length direction is determined by the method described in (2) above and their average value is calculated, the thermal shrinkage rate in the length direction of all samples is less than ±3% of the average thermal shrinkage rate described above.

[0021] 2. The heat-shrinkable polyester film roll according to 1. also satisfies the following conditions (4) and (5).

[0022] (4) When the heat shrinkage rate in the width direction is determined by the method described in (2) above, the heat shrinkage rate in the width direction (the direction orthogonal to the length direction) of all samples is more than -20% and less than 20%.

[0023] (5) When the heat shrinkage rate in the width direction is determined by the method described in (2) above and their average value is calculated, the heat shrinkage rate in the width direction of all samples is less than ±3% of the average heat shrinkage rate described above.

[0024] 3. The heat-shrinkable polyester film roll according to 1. or 2, wherein the effective roll length of the film is more than 1000m and less than 20000m.

[0025] 4. The 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.

[0026] 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.

[0027] The effects of the invention

[0028] The heat-shrinkable polyester film roll of the present invention, whose main shrinkage direction is the length direction, has little variation in heat shrinkage rate within the roll, thus reducing defects in the final product. Attached Figure Description

[0029] Figure 1 This is a schematic diagram illustrating an example of raw material mixing in the manufacturing process of the heat-shrinkable polyester film roll of the present invention.

[0030] Figure 2 yes Figure 1 Enlarged portion

[0031] Figure 3 This is a schematic diagram of a plastic bento container used to evaluate the wrinkles of a shrunken film.

[0032] Figure 4 This is a schematic diagram of a plastic bento container used to evaluate the indentation of the film after shrinkage. Detailed Implementation

[0033] The inventors' research on the variation in heat shrinkage rate within the roll revealed two main causes. First, the use of two or more raw materials (polymer blending) in the raw material supply process; second, the change in molecular orientation due to stretching during the length-direction stretching process. Furthermore, it was found that the variation in heat shrinkage rate is smaller in the heat-shrinkable polyester film roll described in this invention, thus minimizing the aforementioned adverse effects. The invention will now be described in detail.

[0034] It should be noted that the "length direction" in this invention refers to the winding direction of the film in the film roll.

[0035] 1. Physical properties of film rolls

[0036] 1.1. Thermal shrinkage rate along the length direction (main contraction direction)

[0037] In the heat-shrinkable polyester film roll of the present invention, the end of the winding start side (core) is designated as the first end, and the end of the winding end side (surface layer) is designated as the second end. At the center position in the roll width direction, a first sample cutout portion is provided within 2m inside the second end.

[0038] In addition, the final cut-out portion is provided within 2m inside the first end mentioned above, and when the sample cut-out portion is provided every approximately 100m from the first sample cut-out portion, the following conditions (2) and (3) must be met for each sample.

[0039] (2) For each 10cm×10cm square sample cut from the cut-out part of the aforementioned sample, when the sample is immersed in warm water at 90°C for 10 seconds and then lifted out, and then immersed in water at 25°C for 10 seconds and lifted out, the thermal shrinkage rate of all samples in the length direction is more than 30% and less than 80%.

[0040] (3) When the thermal shrinkage rate in the length direction is determined by the method described in (2) above and their average value is calculated, the thermal shrinkage rate in the length direction of all samples is less than ±3% of the average thermal shrinkage rate described above.

[0041] For a film rolled into a single roll, with the end of the film at the beginning of winding (core) as the first end and the end at the end of winding (surface) as the second end, a first sample cutout is provided within 2m of the first end. A final cutout is also provided within 2m of the first end. Furthermore, sample cutouts are provided approximately every 100m from the first sample cutout, thus selecting samples at approximately equal intervals across the entire length of the film's normal region. It should be noted that "approximately every 100m" means cutting samples at approximately 100m ± 1m intervals.

[0042] The above sampling method will be explained in more detail. For example, when a heat-shrinkable film with a length of 498m is wound into a roll, the initial sample A (10cm × 10cm) is cut at the center of the roll width direction within 2m from the end of the winding. It should be noted that, for convenience, the cut is made in a square cutting direction with an edge along the length direction of the film and an edge along the direction orthogonal to the length direction (width direction) (not at an angle). Next, at a point approximately 100m from the cut portion in the length direction, the second sample B is cut at the center of the roll width direction. Similarly, the third sample C is cut at approximately 200m, the fourth sample D at approximately 300m, and the fifth sample E at approximately 400m. Here, the remaining length is less than 100m, therefore, the sixth (final) sample F is cut at any point within 2m from the beginning of the winding of the film.

[0043] The aforementioned condition (2) of the present invention is that the 90°C heat shrinkage rate of all samples cut in this manner is 30% or more along the length. If the heat shrinkage rate of the film along the length is less than 30%, the film's heat shrinkage is insufficient, and therefore, it will not seal tightly to the container when covered or shrunken, resulting in poor appearance, which is not preferable. The heat shrinkage rate along the length is more preferably 35% or more, and even more preferably 40% or more. On the other hand, a higher heat shrinkage rate along the length increases versatility and is preferred, but as the technical level of the present invention, the upper limit is 80%. In practical terms, even an upper limit of 75% is sufficient.

[0044] Furthermore, in this invention, under the aforementioned condition (3), when calculating the average value of the thermal shrinkage rate in the length direction based on all samples obtained from the cut portion, the thermal shrinkage rate in the length direction of all samples is defined as being within ±3% of the average value. This range is preferably within ±2.8%, and more preferably within ±2.6%. The meaning of this average value within ±3% will be explained in more detail.

[0045] First, the heat shrinkage rate is measured for each cut sample, and the average value along the length direction is calculated. This average value of the heat shrinkage rate along the length direction is denoted as X (%). When the heat shrinkage rate along the length direction of sample A is denoted as Y1 (%), |X-Y1| (the absolute value of X-Y1) is less than 3 (%). Similarly, for the heat shrinkage rates Y2-Y6 (%) along the length direction of samples B to F, |X-Yn| is less than 3 (%), meaning an average of ±3%. In other words, if the difference between the maximum value Ymax and X and the difference between the minimum value Ymin and X are both within ±3%, the conditions of this invention are met. Since the heat shrinkage rate is measured at 90°C, it is clear that according to this invention, variations in the heat shrinkage rate along the length direction can be suppressed at 90°C. Therefore, when a ring-shaped body is made from the aforementioned film roll, covered with it, and heat-shrinked at approximately 90°C, poor shrinkage can also be prevented.

[0046] 1.2. Thermal shrinkage rate in the width direction (direction orthogonal to the main shrinkage direction)

[0047] Regarding the heat-shrinkable polyester film wound on the heat-shrinkable polyester film roll of the present invention, each sample obtained by the sampling method described in (1) of “1.1. Heat shrinkage rate in the length direction (main shrinkage direction)” above preferably satisfies the following conditions (4) and (5).

[0048] (4) For each 10cm×10cm square sample cut from the cut-out part of the aforementioned sample, when the sample is immersed in warm water at 90°C for 10 seconds and then lifted out, and then immersed in water at 25°C for 10 seconds and lifted out, the thermal shrinkage rate in the width direction of all samples is more than -20% and less than 20%.

[0049] (5) When the thermal shrinkage rate in the width direction is determined by the method described in (1) above and their average value is calculated, the thermal shrinkage rate in the width direction of all samples is less than the average value ±3%.

[0050] Ideally, when a heat-shrinkable polyester film shrinks in a ring-like shape, the closer the heat shrinkage rate in the width direction is to zero, the less the dimension of the direction where shrinkage is not desired (the non-shrinkage direction) changes, which is therefore desirable. If the heat shrinkage rate in the width direction of the film exceeds 20% (condition (3) above), the length of the non-shrinkage direction after the label is made becomes extremely short. The heat shrinkage rate in the width direction is more preferably 19% or less, and even more preferably 18% or less. On the other hand, if the heat shrinkage rate in the width direction becomes negative, the non-shrinkage direction will elongate. If the heat shrinkage rate in the width direction is less than -20%, the dimension of the non-shrinkage direction will still change after the label is made and shrunk. The heat shrinkage rate in the width direction is preferably -19% or more, and more preferably -18% or more.

[0051] Furthermore, in this invention, when calculating the average value of the heat shrinkage rate in the width direction based on all samples obtained from each cut portion, the heat shrinkage rate in the width direction of all samples is preferably within ±3% of the average value. This range is more preferably within ±2.8%, and even more preferably within ±2.6%.

[0052] It is clear from the fact that the temperature for measuring the heat shrinkage rate is 90°C that, according to the present invention, the variation of the heat shrinkage rate in the width direction at a temperature of 90°C can be suppressed. Therefore, when the aforementioned film roll is made into an annular body, which is then covered on the packaged body (container) and heat-shrinked at about 90°C, poor shrinkage can also be prevented.

[0053] 1.3. Refractive Index

[0054] Regarding the heat-shrinkable polyester film wound in the heat-shrinkable polyester film roll of the present invention, for each sample obtained by the sampling method described in (2) of "1.1. Heat shrinkage rate in the length direction (main shrinkage direction)" above, the average value of the refractive index Nx in the length direction is calculated based on all samples, and the Nx of all samples is preferably within the range of ±0.01 of the average value. This range is preferably within ±0.009, more preferably within ±0.008. The refractive index indicates the degree of orientation of the polymer chains constituting the film and becomes an indicator of the degree of film stretching. Generally speaking, heat-shrinkable polyester films tend to have a higher degree of thermal shrinkage rate as the degree of orientation of the molecular chains generated by stretching increases. That is, in the present invention, if the deviation of Nx in the length direction of the film roll is small, the variation of thermal shrinkage rate within the film roll is suppressed.

[0055] 1.4. Thickness

[0056] The thickness of the heat-shrinkable polyester film wound on the heat-shrinkable polyester film roll of the present invention is preferably 5 μm or more and 100 μm or less. If the thickness exceeds 100 μm, it will only increase the weight per unit area of ​​the film, which is uneconomical. On the other hand, if the thickness is less than 5 μm, the film becomes extremely thin, and therefore, it is difficult to process in processes such as forming rings (poor processability). The thickness is preferably 7 μm or more and 98 μm or less, more preferably 9 μm or more and 96 μm or less.

[0057] 2. Types and proportions of polyester raw materials constituting the film roll

[0058] Regarding the type of polyester raw material constituting the film of the present invention, polyethylene terephthalate (PET) units are used as the main constituent component. Here, "main constituent component" means that when the total amount of all constituent components is set to 100 mol%, it contains 50 mol% or more. PET is a unit formed from 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, more preferably 60 mol% or more, of the polyester structural units in 100 mol% of the film.

[0059] The diol component, other than ethylene glycol, constituting the polyester must contain at least one polyol selected from 1,4-cyclohexanediol, neopentyl glycol, 1,4-butanediol, diethylene glycol, and 1,3-propanediol. This diol component must be capable of forming amorphous materials and is essential for achieving a heat shrinkage rate of 30% or more at 90°C. In addition, it may also contain aromatic diols such as propylene glycol and bisphenol A, and aliphatic diols such as hexanediol.

[0060] The amorphous component content is preferably 10 mol% or more, more preferably 20 mol% or more, out of 100 mol% of the polyol content in the total polyester resin. If it is less than 10%, the necessary shrinkage rate will not be obtained, and the final product will have insufficient shrinkage. On the other hand, since polyethylene terephthalate is the main component (50 mol%), the upper limit of the amorphous component content is 50 mol%. If the amorphous component content is too high, there is a concern that the change in molecular orientation due to stretching in the length direction (described later) will be greater. The amorphous component content is preferably 45 mol% or less, more preferably 40 mol% or less.

[0061] Regarding the heat-shrinkable polyester film wound on the heat-shrinkable polyester film roll of the present invention, for each sample obtained by the sampling method described in (2) of "1.1. Heat shrinkage rate in the length direction (main shrinkage direction)" above, the composition ratio (mol%) is calculated based on all samples, and the amorphous component content in all samples is preferably within an average of ±2 mol%. By setting the amorphous component content to within an average of ±2 mol%, the variation in the heat shrinkage rate of the heat-shrinkable polyester film roll can be set to a predetermined range. The amorphous component content is more preferably within an average of ±1.5 mol%, and even more preferably within an average of ±1 mol%.

[0062] 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, naphthalic acid, and phthalic acid; aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid; and alicyclic dicarboxylic acids.

[0063] When polyester contains aliphatic dicarboxylic acids (such as adipic acid, sebacic acid, decanedicarboxylic acid, etc.), the content is preferably less than 3 mol% (in 100 mol% of dicarboxylic acid content). In heat-shrinkable polyester films obtained using polyesters containing more than 3 mol% of these aliphatic dicarboxylic acids, the film strength is insufficient during high-speed assembly.

[0064] In addition, the preferred polyester does not contain more than three polycarboxylic acids (such as trimellitic acid, pyromellitic acid and their anhydrides). Heat-shrinkable polyester films obtained using polyesters containing these polycarboxylic acids are difficult to achieve the necessary shrinkage rate.

[0065] In the film resin used to form the heat-shrinkable polyester film roll of the present invention, it is preferable to add microparticles as a lubricant to improve the operability (slipability) of the film. Any type of microparticle can be selected; for example, inorganic microparticles include silica, alumina, titanium dioxide, calcium carbonate, kaolin, and barium sulfate, while organic microparticles include acrylic resin particles, melamine resin particles, silicone resin particles, and cross-linked polystyrene particles. The average particle size can be in the range of 0.05 to 3.0 μm (when measured using a Coulter counter), and can be appropriately selected as needed.

[0066] As a method for compounding the aforementioned microparticles, they can be added at any stage of manufacturing the polyester resin, for example. Preferably, they are added in the form of a slurry dispersed in ethylene glycol, etc., after the transesterification reaction has ended and before the polycondensation reaction begins, and then the polycondensation reaction is carried out. Alternatively, it is preferable to use methods such as: using a compounding extruder with ventilation holes to blend a slurry of particles dispersed in ethylene glycol or water with the polyester resin raw material; or using a compounding extruder to blend dried particles with the polyester resin raw material. Furthermore, by setting the amount of microparticles added to be in the range of 300 to 1200 ppm in the film, both good slip properties (friction) and transparency can be achieved.

[0067] 3. Method for manufacturing film rolls

[0068] The heat-shrinkable polyester film of the present invention can be obtained by feeding the polyester raw material described in "2.1. Type and amount of polyester raw material constituting the film roll" to an extruder and melting and extruding it, and then subjecting the resulting unstretched film to the prescribed steps shown below.

[0069] In this invention, suppressing variations in the thermal shrinkage rate within the film roll is a challenge, which can be achieved by controlling the raw material supply and stretching along the length direction. Hereinafter, the manufacturing method will be described while illustrating the key techniques.

[0070] 3.1. Raw material mixing and supply

[0071] When manufacturing the film roll of the present invention, as described in "2. Types and amounts of polyester raw materials" above, it is necessary for the film to contain monomers that can form amorphous components in addition to polyethylene terephthalate units. In this case, two or more raw materials (polyester resins) are usually mixed and used. Conventionally, if two or more raw materials are mixed and fed into the extruder, the supply of raw materials will be biased (segregation), resulting in a problem of film composition variation. If composition variation occurs within the film roll, it is difficult to set the variation of heat shrinkage rate within a specified range. To prevent raw material segregation, it is effective to: (1) optimize the stationary angle of the polyester resin that becomes the raw material, (2) optimize the shape of the hopper in the raw material supply line, (3) install a stirring device directly above the extruder, (4) install a helmet-shaped helmet (to relieve powder pressure) in the lower part of the hopper, and (5) install an inner tube in the final hopper. By employing at least one of these means, it is possible to suppress the variation of heat shrinkage rate within the film roll, and therefore preferred. It is even more preferred to combine two or more of these means. These means will be described in detail below.

[0072] 3.1.(1) Angle of repose of polyester resin

[0073] During the manufacturing of film rolls, if the resin in the final hopper directly above the extruder is consumed and becomes insufficient, segregation can easily occur due to variations in the composition of the mixed resin supplied to the extruder, depending on the hopper's capacity and shape. This problem becomes more pronounced when the resting angles of the various resins differ. Consequently, the thermal shrinkage rate within the film roll varies.

[0074] The angle of repose is the angle between the slope of a hill formed when a certain amount of resin falls from a certain height and the horizontal. It is determined by the shape and particle size of the resin; there is a tendency for the angle of repose to decrease as the resin becomes larger, and a smaller angle of repose indicates that the resin is less likely to remain in the hopper (it flows easily). Furthermore, the angle of repose also varies due to the slipperiness of the resin surface; the easier the resin surface is to slip, the lower the angle of repose (the hill is more likely to collapse). In manufacturing resin as raw material, the following method is typically used: after the polymerization process, it is discharged in a molten state as a strand (rope), immediately water-cooled, and then cut using a wire cutter. Therefore, the resin shape is elliptical cylindrical, and its volume is determined by the major axis (mm), minor axis (mm), and height (mm) of the elliptical cross-section, which affects the angle of repose. The resin volume can vary depending on the viscosity of the molten resin (expansion at the outlet of the wire die), the discharge speed of the strand, and the rotation speed of the wire cutter. In addition, 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 and the cooling rate of the molten resin. As mentioned above, the angle of repose of the resin also varies depending on the various conditions during polyester manufacturing, and is usually mostly between 30 and 45 degrees.

[0075] When manufacturing by mixing two or more raw material resins, in order to obtain a film with minimal compositional variation, it is preferable to suppress raw material segregation in the final hopper based on the settling angle of all the resins used. If the raw material used in the largest quantity is used as the main raw material, and a substance with a settling angle within ±4 degrees relative to it is used, raw material segregation can be reduced. A settling angle within ±3 degrees is more preferable.

[0076] 3.1.(2) Optimization of hopper shape

[0077] As described above, in addition to controlling the settling angle of the resin that becomes the raw material, optimizing the shape of the final hopper can also yield a uniformly composed elongated film, which is therefore a preferred method. Specifically, setting the tilt angle of the funnel-shaped hopper (the angle between the inclined side of the funnel and the horizontal line) to 60 degrees or more can suppress raw material segregation, which is therefore preferred. When the tilt angle is less than 60 degrees, the resin does not follow the tilt of the hopper, therefore, only the resin with the smaller settling angle falls first. A tilt angle of 62 degrees or more is more preferable. On the other hand, if the tilt angle exceeds 75 degrees, the hopper capacity is limited (the capacity becomes extremely small), which is not preferred. A tilt angle of 73 degrees or less is preferred.

[0078] 3.1.(3) Setting of stirring device

[0079] When using two or more resins as raw materials, it is preferable to match the stationary angle as described in (1) above. However, depending on the resin used, there are cases where the stationary angle cannot be controlled within ±4 degrees. In this case, in order to eliminate raw material segregation that occurs during the process of supplying raw materials to the extruder, a mixer can be installed on the piping or hopper directly above the extruder to mix the raw materials uniformly.

[0080] 3.1.(4) The setting of the conical helmet

[0081] As described in (1) above, the amount of raw material in the hopper constantly changes during the manufacturing of the film roll. Specifically, a raw material level gauge is installed in the hopper, and if the raw material is consumed and reaches the minimum level, the level gauge senses this and refills the hopper. In other words, the 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 constantly changes according to the amount of raw material filled in the hopper. When two or more raw material resins are mixed to manufacture a film, the change in powder pressure also promotes raw material segregation, so it is preferable to keep the powder pressure constant. As a means of this, the countermeasure of shortening the raw material filling cycle (setting the minimum raw material level high) has been adopted in the past. However, if the raw material filling cycle is shortened, the operation of the associated mechanical parts also becomes more frequent, thus increasing the frequency of failures. Therefore, in order to relieve the powder pressure from the upper part of the hopper, it is preferable to install a helmet-shaped cap at the lower part of the hopper. The shape of the helmet-shaped cap is not particularly limited, but a cone or a triangular cone is preferred. In addition, there is no particular limitation on the size of the conical helmet. In order to ensure the smooth supply of raw materials, the diameter should not exceed the diameter of the pipe at the bottom of the hopper.

[0082] 3.1.(5) Installation of inner tubes

[0083] When the stationary angles of two or more raw material resins are extremely different, even with the countermeasures described in 3.1.(2) to (4) above, raw material segregation sometimes occurs. In this case, instead of using the raw materials mixed in the final hopper, a pipe (inner pipe) can be inserted into a hopper filled only with the main raw material to directly add the raw materials with different stationary angles (hereinafter sometimes referred to as "secondary raw materials"). This method can essentially avoid raw material segregation occurring in the hopper, and is therefore preferred. The amount of raw material added from the inner pipe needs to match the amount of raw material supplied from the final hopper.

[0084] An example of a specific mixing step is shown below. Figure 1 . Figure 1 This is a schematic diagram illustrating an example of the relationship between an extruder 2 equipped with a hopper 1 and an inner tube 3. Figure 2 The aforementioned Figure 1 An enlarged view of part A. (See image below.) Figure 1 , 2As shown, 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. Moreover, the outlet 4 of the inner pipe 3 is directly above the extruder (precisely, directly above the resin supply port 5 of the extruder 2), so that the mixing ratio of the raw materials can be kept constant.

[0085] The height (H2) of the outlet 4 of the aforementioned inner pipe 3 preferably satisfies the relationship of the following formula 1, and more preferably satisfies the relationships of both formula 1 and formula 2.

[0086] H2 < H1 (Formula 1)

[0087] ※In Formula 1, H1 represents the height of the part where the inner wall of the hopper is vertical (refer to Figure 2 ).

[0088] 0.5×L / tanθ < H2 (Formula 2)

[0089] ※In Formula 2, L represents the inner diameter of the outlet 4 of the inner pipe 3 (refer to Figure 2 ).

[0090] In addition, θ is the static angle of other resin chips.

[0091] By making the height of H2 greater than 0.5×L / tanθ, the mixing position (H3; refer to Figure 2 ) of the auxiliary raw material and the main raw material can be outside the extruder, and air can be prevented from entering the extruder to generate bubbles.

[0092] The height H3 of the mixing position of the auxiliary raw material (=H2 - 0.5×L / tanθ) is preferably higher than 0 m and less than 2 m. By being higher than 0 m, air intrusion into the extruder can be prevented. In addition, by being set 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.

[0093] As the metering device, a known metering device such as a table feeder can be used. In addition, not only one inner pipe but also two or more inner pipes can be used, and various raw materials can be added from one inner pipe. In order to supply the raw materials with good accuracy, the method of supplying one kind of raw material from one inner pipe is preferred.

[0094] It should be noted that the polyester can be obtained by subjecting the aforementioned suitable dicarboxylic acid component and diol component to polycondensation by a known method. In addition, before transporting the raw material resin to the final hopper, it is preferably dried in advance using a dryer such as a hopper dryer, paddle dryer, or vacuum dryer.

[0095] 3.2. Melting and Extrusion

[0096] The above-mentioned mixed raw materials are extruded into a film using an extruder at a temperature of 200–280°C. Extrusion can be performed using any existing method, such as the T-die method or the tubular method. It should be noted that if the extrusion temperature exceeds 280°C, the intrinsic viscosity of the polyester resin decreases, making it prone to breakage during the film-forming process and difficult to obtain a stable film; therefore, this method is not preferred. When producing multilayer films, multiple extruders, feed blocks, and manifolds can be used.

[0097] Subsequently, by quenching the film that has melted during extrusion, an unstretched film can be obtained. It should be noted that, as a method for quenching the molten resin, a method can be suitably adopted that involves casting the molten resin from the nozzle onto a rotating drum and then quenching and solidifying it to obtain a substantially unoriented resin sheet.

[0098] Furthermore, the shear rate at which the molten resin is discharged from the mold opening is preferably 100 sec⁻¹ or more, and more preferably 150 sec⁻¹. -1 The higher the shear rate, the better it suppresses shrinkage variations along the film's length. This is because a higher shear rate results in more stable resin discharge pressure at the die opening (exit). If the shear rate is less than 100 seconds... -1 If this happens, the resin discharge pressure at the mold exit becomes unstable and prone to pulsation (thickness variation of the unstretched film along its length). Consequently, the stretching along the length will not be uniform, resulting in a larger variation in the thermal shrinkage rate along the length.

[0099] On the other hand, if the shear rate is greater than 600 seconds -1 If this happens, not only will the polyester molecular chains be broken (decomposed), resulting in a decrease in intrinsic viscosity, but resin debris will also adhere to the discharge part of the mold, leading to a decrease in productivity. Therefore, this method is not preferred.

[0100] It should be noted that the shearing speed at the mold exit is calculated using Equation 3 below.

[0101] γ=6Q / (W×H2) (Equation 3)

[0102] γ: Shear rate (sec) -1 )

[0103] Q: Amount of raw material discharged from the extruder (cm³) 3 / sec)

[0104] W: Width of the mold opening (cm)

[0105] H: Spacing at the mold opening (lip spacing) (cm)

[0106] Films can be formed by any of the following methods: no stretching, uniaxial stretching (stretching in the length direction), and biaxial stretching. From the viewpoint of mechanical strength and productivity, uniaxial stretching is preferred, and biaxial stretching is more preferred. Hereinafter, the sequential biaxial stretching method, which is based on initially performing stretching in the width direction (sometimes referred to as transverse stretching) followed by stretching in the length direction (sometimes referred to as longitudinal stretching), can be described. However, the order of transverse stretching-longitudinal stretching can be reversed, or the biaxial stretching method can be performed simultaneously in both the longitudinal and transverse directions.

[0107] 3.3. Stretching in the width direction (lateral stretching)

[0108] First, the film is stretched in the width (lateral) direction. The lateral stretching is preferably performed within a tenter frame (first tenter frame) with the film held at both ends in the width direction by clamps, at a temperature of 65°C to 100°C for approximately 2.5 to 5 times the normal stretch. Preheating is preferable before lateral stretching, and can be performed until the film surface temperature reaches 60°C to 95°C. After lateral stretching, the film is preferably passed through an intermediate zone where no active heating is applied. Because a temperature difference exists between the lateral stretching zone and the intermediate heat treatment zone in the first tenter frame, heat (hot air itself, radiant heat) from the intermediate heat treatment zone flows into the lateral stretching process. This temperature instability in the lateral stretching zone can sometimes lead to inconsistent film quality. Therefore, it is preferable to perform intermediate heat treatment after the film has been laterally stretched and passed through the intermediate zone for a predetermined time, followed by intermediate heat treatment. Within this intermediate zone, when a short strip of paper is allowed to hang without the film passing through, if the accompanying flow accompanying the film's movement, the hot air from the transverse stretching zone, or the intermediate heat treatment zone is blocked, causing the paper to hang almost entirely vertically, a film of stable quality can be obtained. A passage time of approximately 1 to 5 seconds in the intermediate zone is sufficient. If it is less than 1 second, the length of the intermediate zone is insufficient, resulting in inadequate heat blocking. Furthermore, a relatively long intermediate zone is preferable; if it is too long, the equipment becomes larger. Therefore, approximately 5 seconds is sufficient.

[0109] 3.4. Intermediate heat treatment

[0110] After passing through the intermediate region, an intermediate heat treatment is performed before longitudinal stretching. This is because the intermediate heat treatment is used to adjust the shrinkage rate in the width direction. If the temperature of the intermediate heat treatment after transverse stretching is increased, there is a tendency for the thermal shrinkage rate in the width direction to decrease. The temperature of the intermediate heat treatment is preferably 60 to 140°C. When the temperature of the intermediate heat treatment region is less than 60°C, the thermal shrinkage rate in the width direction does not show any change relative to the thermal shrinkage rate after transverse stretching. Furthermore, if the temperature is higher than 140°C, the thermal shrinkage rate in the width direction decreases further, crystallization occurs, and it is difficult to perform subsequent longitudinal stretching, so this is not preferred. In addition, the passage time of the intermediate heat treatment region is preferably 2 to 20 seconds. If it is less than 2 seconds, the length of the intermediate heat treatment region is insufficient, and it is difficult to adjust the thermal shrinkage rate in the transverse direction. In addition, the intermediate heat treatment region is preferably longer, but about 20 seconds is sufficient. This yields a transversely uniaxially stretched film.

[0111] During intermediate heat treatment, by shortening the distance between the clamps of the first tenter frame at any ratio in the film width direction (relaxation treatment), the molecular chains oriented in the width direction are prevented from crystallizing and are instead moderated, thereby reducing the shrinkage rate in the width direction. Relaxation after transverse stretching is preferably 3% or more. On the other hand, the upper limit of the relaxation rate after transverse stretching depends on the raw materials used, the stretching conditions in the width direction, and the heat treatment temperature. Relaxation cannot be performed beyond these limits.

[0112] 3.5. Tension in the length direction (longitudinal tension)

[0113] Next, longitudinal stretching is performed. In the longitudinal stretching process, the film up to the previous step is fed into a longitudinal stretching machine with multiple rolls arranged continuously. During longitudinal stretching, it is preferable to preheat the film using a preheating roller until the film temperature reaches 65°C to 120°C. If the film temperature is below 65°C, there is a tendency for it to be difficult to stretch longitudinally (i.e., it is prone to breakage). On the other hand, if the temperature is above 120°C, the film is prone to sticking to the roller, which may lead to roll contamination in the early stages of continuous production.

[0114] After the film temperature reaches the aforementioned range, longitudinal stretching is performed. Longitudinal stretching is based on the speed difference of the rollers. The stretching ratio is preferably set to 1.5 to 5 times. In addition, at this time, not only can the stretching be performed with two rollers of low speed / high speed (i.e., one-stage stretching), but also with three rollers of low speed / medium speed / high speed (i.e., two-stage stretching), or with four rollers of low speed / medium-low speed / medium-high speed / high speed (i.e., three-stage stretching), the number of stretching stages can be increased.

[0115] The stretching speed is preferably controlled to, for example, a range of 100% / second or more and 10,000% / second or less. If the stretching speed is too fast, insufficient heating of the film may occur; if the stretching speed is too slow, productivity will decrease. A stretching speed is more preferably 200% / second or more and 9,900% / second or less, and even more preferably 300% / second or more and 9,800% / second or less. It should be noted that the stretching speed can be calculated according to Formula 4 below.

[0116] Tension speed = λ / T (Equation 4)

[0117] λ: Tensile strain (%)

[0118] T: Time required for stretching (sec)

[0119] As heating rollers, options include, for example, heating rollers made of metallic raw materials with hard chrome plating on the surface (hereinafter referred to as chrome-plated rollers), heating rollers made of ceramic raw materials (hereinafter referred to as ceramic rollers), heating rollers made of fluoropolymer raw materials (hereinafter referred to as fluoropolymer rollers), and heating rollers made of silicone rubber raw materials (hereinafter referred to as silicone rubber rollers). Chrome-plated rollers and ceramic rollers are particularly preferred for use during preheating, while fluoropolymer rollers and silicone rubber rollers are preferred for use after preheating and when heating to a specified temperature. Chrome-plated rollers and ceramic rollers have relatively smooth surface roughness and good adhesion to the film; therefore, they are excellent for heat conduction to the film and can preheat the film with good efficiency. The surface roughness of the roll can be measured using the average roughness (SRa), maximum protrusion height (SRmax), and ten-point average roughness (SRz), and can be measured using, for example, a small surface roughness meter such as the Surftest SJ-301 (manufactured by MITUTOYO). The SRz of the chrome-plated roller is preferably 0.01 or more and 0.05 or less, more preferably 0.02 or more and 0.04 or less. The Srmax of the ceramic roller is preferably 1 or more and 8 or less, more preferably 1.5 or more and 7.5 or less. On the other hand, fluoropolymer rollers and silicone rubber rollers have rough surfaces and excellent peelability. When heated, the film is softened, and even if it is easily bonded, good peelability is maintained. The SRz of the fluoropolymer roller is preferably 0.1 or more and 2 or less, more preferably 0.2 or more and 1.9 or less. The SRz of the silicone rubber roller is preferably 2 or more and 12 or less, more preferably 3 or more and 11 or less. For example, it is preferable to preheat the film using a preheating roller group composed of chrome-plated rollers and / or fluoropolymer rollers, and then use one or more main heating rollers composed of ceramic rollers and / or silicone rubber rollers to heat the film to a predetermined temperature. It should be noted that the aforementioned preheating rollers can be either freely rotating or driven. The aforementioned main heating rollers are typically driven. It should be noted that the film heated to the specified temperature in this manner can be longitudinally stretched by utilizing the speed difference between the aforementioned main heating roller and the stretching roller located downstream of it.

[0120] 3.6. Final Heat Treatment

[0121] Next, the longitudinally stretched and cooled film is fed into a second tenter for final heat treatment, where it undergoes heat treatment and relaxation. The final heat treatment process allows for adjustment of both longitudinal and transverse shrinkage rates, making it a preferred embodiment. During relaxation in the second tenter, the longitudinal shrinkage rate shows almost no change, but the transverse shrinkage rate decreases. The relaxation rate is preferably 0% to 50%. The lower limit of the relaxation rate is 0%. On the other hand, a high relaxation rate results in a shorter film width, which is not preferred; the upper limit of the relaxation rate is suitable at around 50%.

[0122] The heat treatment (relaxation) temperature is preferably 65°C to 120°C. If the heat treatment temperature is less than 65°C, the shrinkage rate of the film does not change. On the other hand, if the heat treatment temperature is higher than 120°C, the film crystallizes, forming a film that does not shrink in either the longitudinal or transverse directions. Therefore, it is not preferred as a heat-shrinkable film.

[0123] It should be noted that, from the viewpoint of reducing the variation in heat shrinkage rate, it is preferable to control the variation range of the film surface temperature measured at any point in each of the aforementioned transverse stretching process (preheating / stretching step), intermediate heat treatment step, longitudinal stretching process (preheating / stretching / cooling step), and final heat treatment step to preferably be within ±1°C of the average temperature, and more preferably within ±0.5°C of the average temperature. The variation range of the film surface temperature measured at any point refers to the variation range when the film surface temperature at a specified location is continuously measured using, for example, an infrared non-contact surface thermometer during film manufacturing.

[0124] 3.7. Winding

[0125] The heat-shrinkable polyester film roll of the present invention is preferably obtained by winding a heat-shrinkable film with a width of 300 mm or more and 2500 mm or less onto a winding core (core) for a length of 1000 m or more and 20000 m or less. Typically, for film rolls, a wide master roll is made, and while cutting the master roll to any width, it is wound into a roll of any width and length to produce a film roll product. Rolls of films with a width of less than 300 mm and a length of less than 1000 m have low industrial utilization 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 tube is prone to bending during winding, and the film roll is prone to wrinkles and other winding defects, so it is not preferred. 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 roll length of the heat-shrinkable film wound on the roll is more preferably 400 m or more, and even more preferably 500 m or more. The longer the roll length of the heat-shrinkable film, the fewer times the roll needs to be replaced when making the ring, thus increasing productivity, which is preferable. In this invention, the roll length is set to 20,000 m.

[0126] In addition, there are no particular restrictions on the winding core; any known core can be used. 3-inch, 6-inch, 8-inch, etc., paper tubes, plastic cores, and metal cores can be used.

[0127] Example

[0128] Next, the present invention will be specifically described using examples and comparative examples, but the present invention is not limited to these examples at all, and changes can be made without departing from the spirit of the present invention.

[0129] [Sample Sampling Method]

[0130] In the 1000m long film roll obtained in the embodiments and comparative examples described later, a first sample cutout was set as the second end (0m from the surface layer) at the center position in the roll width direction, and sample cutouts were set every 100m from the first sample cutout. The final sample cutout was set as the first end of the film (0m from the core), and samples were collected from all 11 sample cutouts. Then, 10 samples were cut from each sample cutout, and the average value of the physical properties of the 10 samples from each sample cutout was taken as the physical property value of the sample from that cutout.

[0131] [Heat shrinkage rate (hot water heat shrinkage rate)]

[0132] Polyester films were cut into 100mm × 100mm squares and immersed in hot water at 90℃ ± 0.5℃ without load for 10 seconds to induce heat shrinkage. Then, they were immersed in water at 25℃ ± 0.5℃ for 10 seconds. The films were then pulled out of the water, and the length and width dimensions were measured. The heat shrinkage rate was calculated using Formula 3. The direction with the largest heat shrinkage rate was designated as the main shrinkage direction (length direction). Furthermore, the variation (average, maximum, and minimum) of the heat shrinkage rates in the length and width directions was investigated among the samples.

[0133] Heat shrinkage rate (%) = {(L0-L1) / L0} × 100 (Equation 5)

[0134] L0: Film length before heat shrinking (100mm)

[0135] L1: Length of the film after heat shrinkage

[0136] [Ingredients]

[0137] Each sample was dissolved in a solvent prepared by mixing chloroform D (manufactured by Eurisotop) and trifluoroacetic acid D1 (manufactured by Eurisotop) in a 10:1 (volume ratio) solution to prepare a sample solution. The NMR of the protons in the sample solution was measured using an NMR spectrometer "GEMINI-200" (manufactured by Varian) at 23°C for a cumulative measurement of 64 times. In the NMR measurement, the peak intensity of the specified protons was calculated, and the amount of the polyol component in 100 mol% was determined. In the examples and comparative examples described below, the most abundant alcohol component was ethylene glycol. The variation (average, maximum, minimum) of the content of the most abundant alcohol component (most abundant component) and the second most abundant alcohol component (second most abundant component) among the components other than ethylene glycol was investigated.

[0138] [Intrinsic Viscosity (IV)]

[0139] 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 solution was measured in dL / g using an Orstau viscometer in a water bath at 30 °C.

[0140] [Evaluation of contraction completion (entanglement)]

[0141] For the bento box's plastic container (150mm x 150mm sides, 100mm height), a 50mm wide film is wound around the container's body and lid, with the container's circumference as the film's shrinkage direction. After sealing with a pulse sealer at 220°C, the film is heated and shrunk in a shrink tunnel at a set temperature of 90°C until it reaches the bento box's plastic container size. In evaluating the completeness of shrinkage, wrinkles, dents, insufficient shrinkage, and looseness are considered defects and evaluated in five stages as follows. It should be noted that regarding wrinkles... Figure 3 In the middle, count the wrinkles that are 5cm or longer along the edge of the bento container. Regarding dents, in... Figure 4 (In the diagram showing the shrunken binding film and bento container viewed from above), the length from one end of the film to the other end is denoted as L. The difference between the maximum and minimum values ​​of L (Lmax and Lmin) when measuring length L 5mm along the circumference of the bento container is denoted as R. A value greater than 10mm is considered a depression. Insufficient shrinkage is determined visually after shrinkage. Looseness is defined as the shrunken binding film not completely sealing the bento container, feeling loose to the touch, or floating up.

[0142] 5: Best completion (no flaws)

[0143] 4: Good completion (with a defect in one area)

[0144] 3: There are defects in two parts.

[0145] 2: Defects exist in 3 to 5 locations.

[0146] 1. It has multiple defects (more than 6 parts).

[0147] Set 4 or above as acceptable level and 3 or below as unacceptable level. Calculate the shrinkage completion failure rate (%) according to Formula 6 below.

[0148] Shrinkage completion failure rate = 100 × number of defective samples ÷ total number of samples (Equation 6)

[0149] Synthesis of Polyester Raw Materials

[0150] Synthesis of polyester raw material A

[0151] In a stainless steel autoclave equipped with a stirrer, thermometer, and partial circulating cooler, 100 mol% dimethyl terephthalate (DMT) as a dicarboxylic acid and 100 mol% ethylene glycol (EG) as a polyol were added as transesterification catalysts, with zinc acetate at 0.05 mol% relative to the acid content as a polycondensation catalyst, and antimony trioxide at 0.225 mol% relative to the acid content. The transesterification reaction was carried out while the generated methanol was distilled off the system. Subsequently, a polycondensation reaction was carried out at 280°C and a reduced pressure of 26.7 Pa. The resulting polyester was removed from the polymerization apparatus in a molten state as a strand, immediately water-cooled, and then cut using a wire cutter to obtain polyester raw material A. It should be noted that the intrinsic viscosity of polyester raw material A is 0.70 dL / g. Regarding intrinsic viscosity, the intrinsic viscosity (dL / g) was determined 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 Orthau viscometer at 30°C. The polyester raw material A is polyethylene terephthalate. The monomer composition of polyester raw material A is shown in Table 1. In Table 1, the "Acid Components" column indicates the content of each monomer component in 100 mol% of the total acid components, and the "Polyol Components" column indicates the content of each monomer component in 100 mol% of the total polyol components.

[0152] The resin dimensions of polyester A were calculated as an average of 100 resin samples. Assuming the resin is cylindrical, the major and minor axes, and height (cut length) of the elliptical cross-section were measured using vernier calipers. Polyester A has 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 mm². 3 .

[0153] Synthesis of polyester raw materials B-F

[0154] Using the same method as polyester raw material A described above, polyester raw materials B to F with different monomer compositions were obtained as shown in Table 1. It should be noted that polyester raw material B was manufactured by adding SiO2 (SILYSIA 266 manufactured by FUJI SILYSIA; 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 formed into small flakes. Regarding polyester F, the resin shape was reduced by increasing the rotation speed of the wire cutting machine. In Table 1, TPA is terephthalic acid, EG is ethylene glycol, NPG is neopentyl glycol, CHDM is 1,4-cyclohexanediol, BD is 1,4-butanediol, and DEG is diethylene glycol as a byproduct. The intrinsic viscosities of each polyester raw material are: B: 0.70 dl / g, C: 0.75 dl / g, D: 0.74 dl / g, E: 1.20 dl / g, F: 1.20 dl / g. The characteristics of each polyester raw material are shown in Table 1.

[0155] [Table 1]

[0156]

[0157] Using the above-mentioned polyester raw materials A to F, various polyester films as shown in Table 2 were obtained.

[0158] [Example 1]

[0159] Polyesters B, C, and E are mixed in a mass ratio of 10:66:24 and fed into the extruder from a hopper located directly above it. In the extruder, as... Figure 3 The helmet and stirring device are arranged as shown. The mixed resin is melted at 280°C and extracted from the T-mold in 120 seconds. -1 The film is extruded at a shear rate and wound onto a rotating metal roller cooled to 30°C for rapid cooling, thereby obtaining an unstretched film.

[0160] The resulting unstretched film is fed into a transverse stretching machine (tentorial stretcher) and preheated at 80°C for 5 seconds. The preheated film is then continuously fed into the transverse stretching zone and stretched transversely to 3.8 times its original length at 77°C. The transversely stretched film is then continuously fed into the intermediate heat treatment zone and heated at 107°C for 8 seconds.

[0161] Subsequently, the film is fed into a longitudinal stretching machine continuously equipped with roller sets consisting of low-speed rolls including chrome-plated and ceramic rollers, and high-speed rolls including fluoropolymer and silicone rubber rollers. After preheating on the preheating rollers to a film temperature of 95°C, it is stretched along its length (longitudinal direction) to 2.0 times its original length at 90°C. It should be noted that the stretching speed at this point is 130% / second. After stretching, the longitudinally stretched film is cooled on cooling rollers with a surface temperature set to 25°C.

[0162] The cooled film is then fed into a tenter frame (second tenter frame), where it is heat-treated at 92°C for 10 seconds. After a 2% relaxation in the transverse direction (film width direction), it is cooled and the two edges are trimmed off, resulting in a heat-shrinkable polyester film with a thickness of approximately 30 μm. Finally, it is heat-treated at 50°C for 3 seconds in the heat treatment zone, cooled, and the two edges are trimmed off, allowing for continuous film production of over 4000 m.

[0163] At this point, the variation in film surface temperature is within ±0.5℃ in the preheating / stretching process of transverse stretching, the intermediate heat treatment process, the preheating / stretching / cooling process of longitudinal stretching, and the final heat treatment process.

[0164] The resulting film was cut into pieces 900 mm wide and 4000 m long, and wound into rolls on 3-inch paper tubes to obtain the film of Example 1.

[0165] [Examples 2-4]

[0166] In Examples 2 to 4, various conditions were changed from those in Example 1 as shown in Table 2 to manufacture film rolls.

[0167] It should be noted that Examples 3 and 4 do not undergo transverse stretching and intermediate heat treatment, but only longitudinal stretching.

[0168] Regarding Example 4, polyesters A, B, and C are mixed in a total weight ratio of 20:8:53 and fed into a raw material supply hopper. Furthermore, a [material / material] is placed inside the raw material supply hopper. Figure 1 Such an inner tube directly supplies polyester F to the extruder at a weight of 19% of the total weight (the composition of polyester A:B:C:F is 20:8:53:19 by mass).

[0169] [Comparative Examples 1-4]

[0170] In Comparative Examples 1 to 4, various conditions were changed from those in Example 1 as shown in Table 2 to manufacture film rolls.

[0171] The properties of the thin films obtained by this operation were evaluated using the methods described above. The results are recorded in Table 2.

[0172] [Table 2]

[0173]

[0174] [Table 3]

[0175]

[0176] Regarding the heat-shrinkable films of Examples 1 to 4 that meet the conditions of the present invention, the variation in heat shrinkage rate in the film roll falls within the specified range, which is good.

[0177] Compared to these embodiments, in Comparative Example 1, a chrome-plated roller was used as the roller material for stretching in the length direction. As a result, the film adhered to the roll and was difficult to stretch uniformly. Consequently, the variation in heat shrinkage exceeded the specified range.

[0178] In Comparative Example 2, no stirring device, helmet, or inner tube was used in the raw material supply process. As a result, the composition of the film roll varied more, and consequently, the heat shrinkage rate varied more.

[0179] In Comparative Example 3, polyester F with a very small rest angle was used, and an inner tube was not used in the raw material supply process. Therefore, similar to Comparative Example 2, the composition changed significantly, and the heat shrinkage rate exceeded the specified range.

[0180] In Comparative Example 4, a stirring device and a helmet were used in the raw material supply process, but the shearing speed in the extrusion process was low and the stretching speed in the length direction was also low. Therefore, the thermal shrinkage rate variation in the film roll was large.

[0181] Industrial availability

[0182] As described above, the heat-shrinkable polyester film roll of the present invention has high heat shrinkage in the length direction of the film, and minimal variation in shrinkage in the width and length directions. In particular, when the film is continuously wound and assembled onto the packaged object and then shrunk, the occurrence rate of defects such as wrinkles and deformation is extremely low, making it highly valuable for industrial applications.

[0183] Explanation of reference numerals in the attached figures

[0184] 1: Hopper

[0185] 2: Extruder

[0186] 3: Inner tube

[0187] 4: Inner pipe outlet

[0188] 5: Resin supply port

[0189] 6: Bento container

[0190] 7: Film

[0191] 8: Wrinkles

[0192] 9: Bento container

[0193] 10: Film

Claims

1. A heat-shrinkable polyester film roll, characterized in that, It is formed by winding a heat-shrinkable polyester film with the main shrinkage direction being the length direction onto a core. The heat-shrinkable polyester film and the roll of heat-shrinkable polyester film satisfy the following conditions (1) to (3) and (6): (1) The polyester constituting the film is mainly composed of polyethylene terephthalate and contains at least one polyol selected from the group consisting of 1,4-cyclohexanediol, neopentyl glycol, 1,4-butanediol, diethylene glycol and 1,3-propanediol. (2) The thermal shrinkage rate in the length direction when the sample is immersed in warm water at 90°C for 10 seconds and then lifted out, and then immersed in water at 25°C for 10 seconds and lifted out, is more than 30% and less than 80% in all samples. The sample is obtained as follows: the end of the film roll at the starting side of the winding is taken as the first end, the end of the winding at the ending side is taken as the second end, and a first sample cutout is set at the center position in the roll width direction within 2m inside the second end. In addition, a final sample cutout is set within 2m inside the first end. Furthermore, a sample cutout is set every 100m from the first sample cutout, and a 10cm×10cm square is cut from each sample cutout. The starting side of the film roll is the core side, and the ending side of the winding is the surface side. (3) When the thermal shrinkage rate in the length direction is determined by the method described in (2) and their average value is calculated, the thermal shrinkage rate in the length direction of all samples is less than ±3% of the average thermal shrinkage rate. (6) The heat-shrinkable polyester film contains 300 to 1200 ppm of particles.

2. The heat-shrinkable polyester film roll according to claim 1, further satisfies the following conditions (4) and (5): (4) When the method described in (2) is used to determine the thermal shrinkage rate in the width direction, the thermal shrinkage rate in the width direction of all samples is more than -20% and less than 20%. (5) When the heat shrinkage rate in the width direction is determined by the method described in (2) and their average value is calculated, the heat shrinkage rate in the width direction of all samples is less than ±3% of the average heat shrinkage rate.

3. The heat-shrinkable polyester film roll according to claim 1 or 2, wherein, The effective roll length of the film is more than 1,000m and less than 20,000m.

4. The heat-shrinkable polyester film roll according to claim 1 or 2, wherein, The film width is 300mm or more and 2500mm or less.

5. The heat-shrinkable polyester film roll according to claim 1 or 2, wherein, The film thickness is greater than 5 μm and less than 100 μm.

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