Copolymer polyester raw materials for films, heat-shrinkable polyester films, heat-shrinkable labels, and packaging materials

Abstract

To provide polyester film raw materials with excellent stretchability, and to provide heat-shrinkable polyester films that can reduce problems in processing steps such as printing and shrinkage using these raw materials. [Solution] A copolymer polyester raw material that satisfies 1) to 5) and is used in the manufacture of films with a thickness of 10 μm or more and whose width direction is the main shrinkage direction. 1) The total polyester resin components contain 20 to 30 mol% or less of constituent units derived from diethylene glycol. 2) The material contains 0 to 5 mol% of constituent units that can become amorphous components. The monomer components that can become amorphous components are selected from branched glycols such as neopentyl glycol, 1,4-cyclohexanedimethanol, and 2,2-diethyl-1,3-propanediol, and the acid component is terephthalic acid. 3) The Tg of the raw material is between 65°C and 73°C. 4) The intrinsic viscosity of the raw material is 0.60 or higher and 0.85 dl / g or lower. 5) The raw material has a shear rate of 6080 / S and a melt viscosity of 200 Pa·S or less at 255°C.

Description

Technical Field

[0001] The present invention relates to a copolymerized polyester raw material for films excellent in stretchability, and a heat-shrinkable polyester film, a heat-shrinkable label, and a package using the same. Background Art

[0002] In recent years, heat-shrinkable polyester-based labels obtained from polyester-based heat-shrinkable films, which have high heat resistance, are easy to incinerate and excellent in solvent resistance, have been widely used for applications such as label packaging that serves both for protecting glass bottles, plastic bottles and the other containers and displaying product information, cap sealing, collective packaging and the like, and the usage amount thereof tends to increase along with the increase in the number of PET (polyethylene terephthalate) bottle containers and the like. However, since heat-shrinkable labels become garbage after being used, recently, from the environmental perspective, there is a need to reduce the amount of garbage, and thin heat-shrinkable labels (thinned heat-shrinkable labels) have begun to be used. In addition, in order to accommodate various containers, there are many demands for heat-shrinkable films with high shrinkage. For this reason, there is an increasing tendency to form heat-shrinkable films using raw materials with increased amorphous content.

[0003] In order to produce heat-shrinkable films with increased shrinkage so as to be adaptable to various containers, it is necessary to increase the draw ratio in the shrinking direction. However, as a disadvantage, when the draw ratio is increased and the film thickness is reduced for environmental friendliness, problems are likely to occur in that the film breaks during production, causing production stoppage (so-called breaking). In Patent Document 1, heat-shrinkable films are produced by adding polybutylene terephthalate or polypropylene terephthalate, which has a glass transition temperature (hereinafter sometimes referred to as Tg) lower than that of PET and can suppress stretching stress to facilitate stretching. However, polybutylene terephthalate and polypropylene terephthalate have different bulk densities compared to PET raw materials, which causes raw material segregation during the supply to the extruder after raw material mixing, resulting in variation in the raw material blending ratio in the longitudinal direction of the film, and there is a concern that physical properties differ in the longitudinal direction of the film. Patent Document 2 describes equipment for a raw material supply method in which two or more raw materials with different bulk densities and angles of repose are supplied to the extrusion process without segregation, resulting in small variations in physical properties along the longitudinal direction of the film. However, this requires capital investment, which is undesirable. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 4552097 [Patent Document 2] Patent No. 6544492 [Overview of the project] [Problems that the invention aims to solve]

[0005] The present invention aims to provide a raw material for a polyester film with excellent stretchability. Furthermore, it aims to provide a heat-shrinkable polyester film using the aforementioned raw material that can reduce problems in processing steps such as printing and shrinkage. [Means for solving the problem]

[0006] The present invention, which solves the above problems, has the following configuration. 1. A copolymer polyester raw material for film that satisfies the following requirements (1) to (5) and is used for film manufacturing. (1) The total polyester resin components contain 5 mol% to 40 mol% of diethylene glycol-derived constituent units in 100 mol% of the total amount of glycol components. (2) Contains 0 mol% to 5 mol% of constituent units derived from monomer components that can become amorphous components in the total polyester resin components. (3) The glass transition temperature of the raw material is 73°C or lower. (4) The intrinsic viscosity of the raw material is 0.60 dl / g or more and 0.85 dl / g or less. (5) The melt viscosity of the raw material measured at a shear rate of 6080 / s and 255°C is 200 Pa·s or less. 2. The copolymer polyester raw material for film described in item 1 above, wherein the acid component in the total polyester resin components is terephthalic acid, and the glycol component is ethylene glycol and diethylene glycol. 3. A heat-shrinkable polyester film containing the copolymer polyester raw material described in 1 or 2 above, and satisfying the following requirements (6) to (10). (6) When the film is immersed in 98°C hot water for 10 seconds, the thermal shrinkage rate in the main shrinkage direction of the film is 40% to 85%. (7) When the film is immersed in 98°C hot water for 10 seconds, the thermal shrinkage rate in the hot water is -5% to 15% in the direction perpendicular to the main shrinkage direction of the film. (8) When the film is immersed in 70°C hot water for 10 seconds, the thermal shrinkage rate in the direction perpendicular to the main shrinkage direction of the film is -5% or more and 5% or less. (9) The intrinsic viscosity of the film is 0.57 dl / g or more and 0.82 dl / g or less. (10) The average number of defects of 1 mm or larger in the longitudinal or widthwise direction of the film per 100 square meters of film is 1.1 or less. 4. A heat-shrinkable label using the heat-shrinkable polyester film described in item 3 above. 5. A packaging body characterized by being formed by covering at least a portion of the outer circumference of the object to be packaged with the heat-shrinkable label described in 4 above and then heat-shrinking it. [Effects of the Invention]

[0007] The copolymer polyester raw material of the present invention exhibits excellent stretchability, allowing for high stretch ratios and thus superior productivity. Furthermore, the heat-shrinkable film using the copolymer polyester raw material of the present invention exhibits small differences in shrinkage rates along the longitudinal direction of the film and contains fewer foreign matter particles. Therefore, problems in processing steps such as printing and shrinkage can be reduced.

[0008] For a film that shrinks in width due to heat, the non-shrinking direction is the longitudinal direction of the film. Therefore, tension is applied in the longitudinal direction of the film during printing and processing, and a predetermined tensile elongation in the longitudinal direction of the film is required to obtain excellent processability. The heat-shrinkable polyester film produced with the copolymer polyester raw material of the present invention has a tensile elongation of 20% or more in the non-shrinking direction after aging, so even after aging, there is no film breakage during processing steps such as printing, and it has excellent processability.

[0009] Furthermore, the heat-shrinkable polyester film of the present invention includes not only a single layer of heat-shrinkable polyester film, but also laminated heat-shrinkable films having a heat-shrinkable polyester film layer of the present invention and laminated with a different resin layer.

[0010] Furthermore, a package wrapped with a label obtained from the heat-shrinkable polyester film of the present invention has a beautiful appearance. [Modes for carrying out the invention]

[0011] The copolymer polyester raw material for film (hereinafter sometimes referred to as "raw material") and the heat-shrinkable polyester film of the present invention will be described in detail below. The manufacturing method of the heat-shrinkable polyester film will be described in detail later, but the heat-shrinkable film is usually obtained by conveying it using a roll or the like and stretching it. In this case, the direction in which the film is conveyed is called the longitudinal direction, and the direction perpendicular to the longitudinal direction is called the film width direction. Therefore, the width direction of the heat-shrinkable polyester film as shown below is the direction perpendicular to the roll unwinding direction, and the longitudinal direction of the film is the direction parallel to the roll unwinding direction.

[0012] The raw material of the present invention contains 5 mol% to 40 mol% of diethylene glycol-derived constituent units in a total glycol component amount of 100 mol%. As described later, diethylene glycol-derived constituent units cause the generation of foreign matter during film manufacturing, and therefore, their use has generally been avoided as much as possible when considering film quality. However, the raw material of the present invention has a low melt viscosity even at a resin temperature of 250°C, making it possible to extrude at a lower temperature than ordinary polyester raw materials. Therefore, despite containing a large amount of diethylene glycol, with diethylene glycol-derived constituent units at a concentration of 5 mol% to 40 mol% in a total glycol component amount of 100 mol%, it is possible to reduce the number of defects with a size of 1 mm or more in the longitudinal or widthwise direction of the film to an average of 1.1 or less per 100 square meters of film when it is made into a 40 μm thick film.

[0013] One method for obtaining a more highly shrinkable heat-shrinkable polyester film is to increase the amount of monomer components (hereinafter sometimes simply referred to as amorphous components) that constitute units that can become amorphous components in a film whose main component is ethylene terephthalate. In films obtained by the conventional transverse uniaxial stretching method, an increase in the amount of amorphous components was observed to result in a corresponding increase in shrinkage rate. However, neopentyl glycol and cyclohexanedimethanol, which are used as amorphous components as described in Patent Document 2, have the problem of being expensive. Furthermore, the Tg does not decrease even when neopentyl glycol or cyclohexanedimethanol is added. For this reason, when produced at industrially high stretch ratios, breakage may occur during production due to fluctuations in stretching temperature, etc., which can lead to a deterioration in productivity. In order to improve such disadvantages, Patent Document 2 discloses production by adding polybutylene terephthalate or polypropylene terephthalate, which has a glass transition temperature lower than that of polyethylene terephthalate (PET) and can suppress stretching stress. However, polybutylene terephthalate and polypropylene terephthalate have different bulk densities compared to PET raw materials, which leads to raw material segregation during feeding to an extruder after raw material mixing, resulting in variation in the raw material blending ratio in the longitudinal direction of the film, and there is a concern that physical properties vary in the longitudinal direction of the film. Accordingly, the present inventors focused on diethylene glycol (hereinafter sometimes simply referred to as "DEG").

[0014] When the content of diethylene glycol in a film increases, heat resistance deteriorates and discharge of foreign matter increases during melt extrusion, so diethylene glycol has not been actively used until now. However, the present inventors found that when diethylene glycol is used as a constituent unit of a polyester resin, the Tg of the film decreases, the stretching stress during film stretching decreases, and furthermore, the decrease in shrinkage measured at a low temperature of about 70°C after aging can be suppressed.

[0015] The copolyester used for producing a film such as the heat-shrinkable polyester-based film of the present invention preferably contains an ethylene terephthalate unit as a main constituent component. Here, the expression "as a main constituent component" means that the content is 50 mol% or more of all constituent components. The content of ethylene terephthalate units is preferably 50 mol% or more, more preferably 60 mol% or more, and still more preferably 70 mol% or more, based on 100 mol% of all constituent units of the polyester.

[0016] Examples of dicarboxylic acid components other than terephthalic acid constituting the polyester of the present invention include aromatic dicarboxylic acids such as isophthalic acid, orthophthalic acid, and 2,6-naphthalenedicarboxylic acid; aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid; and alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid. In the present invention, it is preferable that no dicarboxylic acid component other than terephthalic acid is contained.

[0017] In the present invention, the term "monomer unit" refers to a repeating unit that constitutes a polymer derived from one polyhydric alcohol molecule and one polycarboxylic acid molecule.

[0018] When a monomer unit composed of terephthalic acid and ethylene glycol (ethylene terephthalate unit) is the main monomer unit constituting the polymer, examples of other monomer units include a monomer unit composed of isophthalic acid and ethylene glycol, a monomer unit composed of terephthalic acid and neopentyl glycol, a monomer unit composed of terephthalic acid and 1,4-cyclohexanedimethanol, and a monomer unit composed of isophthalic acid and butanediol. In the present invention, it is preferable that the aforementioned other monomer units are not contained.

[0019] It is also preferable that trivalent or higher polyhydric carboxylic acids (for example, trimellitic acid, pyromellitic acid, anhydrides thereof, and the like) are not contained in the polyester. A heat-shrinkable polyester film obtained by using a polyester containing such polyhydric carboxylic acids makes it difficult to achieve the required high shrinkage ratio.

[0020] Examples of diol components other than ethylene terephthalate units constituting polyester include aliphatic diols such as 1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, 1,4-butanediol, hexanediol, neopentyl glycol, and hexanediol; alicyclic diols such as 1,4-cyclohexanedimethanol; and aromatic diols such as bisphenol A. Diethylene glycol was used as the diol component other than ethylene terephthalate units constituting the copolyester of the present invention.

[0021] The copolymer polyester used for manufacturing the heat-shrinkable polyester film of the present invention must contain diethylene glycol-derived constituent units. The diethylene glycol-derived constituent units are preferably present in an amount of 5 mol% or more, more preferably 7 mol% or more, and even more preferably 9 mol% or more, based on 100 mol% of the polyester constituent units. The upper limit of the diethylene glycol-derived constituent units is preferably 40 mol% or less, more preferably 38 mol% or less, and even more preferably 36 mol% or less. The diethylene glycol-derived constituent units have the effect of lowering the glass transition temperature of the polyester and improving film-forming properties. Furthermore, when the diethylene glycol-derived constituent units are present in an amount of 5 mol% or more, the effects of the present invention, such as a reduction in shrinkage rate and shrinkage stress measured at 70°C after aging, are improved, making it preferable. On the other hand, when the diethylene glycol component is present in an amount greater than 40 mol%, the resin softens, making it more likely to stick to the cooling roll during the cooling and solidification process after melt extrusion, thus worsening productivity, which is undesirable.

[0022] Among the monomer components mentioned above, examples of monomers that can become amorphous components include neopentyl glycol, 1,4-cyclohexanedimethanol, isophthalic acid, 1,4-cyclohexanedicarboxylic acid, 2,6--naphthalenedicarboxylic acid, 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, and hexanediol. The content of the monomers that can become amorphous components in the copolymerized polyester is preferably 0 mol% or more and 5 mol% or less, and it is more preferable that there is no content (i.e., 0 mol%).

[0023] Furthermore, by adjusting the amount of constituent units derived from diethylene glycol within the above range, polyesters with a glass transition temperature (Tg) of 55 to 73°C can be obtained. If the Tg is lower than 55°C, the film molecules will move and the film properties will change during storage at room temperature in warehouses, etc., especially in the summer, so a Tg of 57°C or higher is preferable, and a Tg of 59°C or higher is even more preferable. Also, if the Tg is high, the stretchability during film production will be poor, so a Tg of 71°C or lower is preferable, and a Tg of 69°C or lower is even more preferable.

[0024] Furthermore, it is preferable that the polyester does not contain diols with 8 or more carbon atoms (e.g., octanediol) or polyhydric alcohols with a valency of 3 or higher (e.g., trimethylolpropane, trimethylolethane, glycerin, diglycerin). Heat-shrinkable polyester films obtained using polyesters containing these diols or polyhydric alcohols are less likely to achieve the required high shrinkage rate. It is also preferable that the polyester contains as little triethylene glycol and polyethylene glycol as possible. Furthermore, copolymerization of diethylene glycol in polyester is preferable. Copolymerization eliminates concerns about raw material segregation and prevents changes in film properties due to fluctuations in the film raw material composition. Moreover, copolymerization promotes transesterification (resulting in random copolymerization), which reduces crystallinity and is advantageous for increasing the shrinkage rate in the main shrinkage direction.

[0025] The resin forming the heat-shrinkable polyester film of the present invention may contain various additives as needed, such as waxes, antioxidants, antistatic agents, nucleating agents, viscosity reducers, heat stabilizers, coloring pigments, color inhibitors, and ultraviolet absorbers.

[0026] In the resin forming the heat-shrinkable polyester film 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 4 μm (measured with a Coulter counter) and can be appropriately selected as needed. For example, if the silica content is between 50 ppm and 3000 ppm, it is possible to adjust the average particle size of the fine particles to the above range. The silica content is preferably 200 ppm or more, and more preferably 300 ppm or more. If the silica content is too high, transparency will be impaired, so for films that require transparency, the silica content is preferably 2000 ppm or less, and more preferably 1500 ppm or less.

[0027] As for how to incorporate the above particles into the resin that forms the heat-shrinkable polyester film, 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 kneading extruder with a vent, or to blend the dried particles with the polyester resin raw material using a kneading extruder.

[0028] The heat-shrinkable polyester film of the present invention can also be subjected to corona treatment, coating treatment, flame treatment, etc., to improve the adhesion of the film surface.

[0029] Next, the properties of the copolymer polyester raw material and the heat-shrinkable polyester film of the present invention will be described.

[0030] The intrinsic viscosity of the copolymer polyester raw material of the present invention is preferably 0.60 dl / g or more and 0.85 dl / g or less. By combining this range of intrinsic viscosity with the melt extrusion conditions described later, it is possible to adjust the intrinsic viscosity of the heat-shrinkable polyester film to 0.57 dl / g or more and 0.82 dl / g or less. If the intrinsic viscosity of the heat-shrinkable polyester film is less than 0.57 dl / g, the tensile elongation at break in the longitudinal direction of the film after aging will be less than 5%, which is undesirable. The intrinsic viscosity of the heat-shrinkable polyester film is preferably 0.60 dl / g or more, and more preferably 0.63 dl / g or more. Note that the requirements for films with an intrinsic viscosity higher than 0.82 dl / g are low, so the upper limit of the hot water heat shrinkage rate was set to 0.82 dl / g.

[0031] The melt viscosity of the amorphous copolymer polyester raw material of the present invention is preferably 200 Pa·S or less when measured at a shear rate of 6080 / S and 255°C. If the melt viscosity is high, extrusion becomes difficult unless the resin temperature is raised, but in raw materials with a high diethylene glycol content, as in the present invention, a high resin temperature is undesirable as it results in a large amount of foreign matter in the film or sheet after extrusion. Therefore, the resin temperature is preferably 265°C or lower, and more preferably 260°C or lower. A lower resin temperature is preferable, but since unmelted material will be produced at low temperatures, the lower limit is set at 235°C or lower. Furthermore, if the melt viscosity measured at 255°C is 200 Pa·s or higher, it is undesirable because it increases the load on the machine that melts and extrudes the raw material, leading to the need for larger equipment. Preferably, it is 190 Pa·s or less, and more preferably 180 Pa·s or less. Furthermore, if the viscosity is too low, the shear stress at the molten resin discharge point will be low, which can cause uneven thickness and is undesirable. The melt viscosity measured at 255°C is preferably 100 Pa·s or higher, and more preferably 110 Pa·s or higher.

[0032] The heat-shrinkable film obtained using the copolymer polyester raw material of the present invention preferably has 1.1 or fewer defects per 100 square meters in the longitudinal or widthwise direction of the film when it is made into a film with a thickness of, for example, 40 μm. If there are more than 1.1 defects, the areas of the defects (foreign matter) will become ink-bleeding during printing, which is undesirable as it impairs the appearance of the printed label. More preferably, the number of defects per 100 square meters in the longitudinal or widthwise direction of the film is 1 or fewer, and even more preferably 0.5 or fewer.

[0033] The heat-shrinkable polyester film of the present invention is subjected to immersion in 98°C hot water for 10 seconds under no load, followed immediately by immersion in 25°C ± 0.5°C water for 10 seconds. The heat shrinkage rate in the width direction (main shrinkage direction) of the film (i.e., the 98°C hot water heat shrinkage rate), calculated from the length before and after shrinkage using the following formula 1, is between 40% and 85%. Thermal shrinkage rate = {(length before shrinkage - length after shrinkage) / length before shrinkage} × 100 (%) (Equation 1)

[0034] If the hot water shrinkage rate in the main shrinkage direction at 98°C is less than 40%, it cannot meet the requirements for high-shrinkage films that cover the entire container (so-called full labels). Furthermore, because the amount of shrinkage is small, when used as a label, the label after heat shrinkage may suffer from distortion, insufficient shrinkage, wrinkles, sagging, etc. A hot water shrinkage rate of 45% or more at 98°C is preferable, and 50% or more is more preferable. Since there is little demand for films with a hot water shrinkage rate exceeding 85% in the main shrinkage direction at 98°C, the upper limit for the hot water shrinkage rate was set at 85%.

[0035] Furthermore, the heat-shrinkable polyester film of the present invention has a hot water shrinkage rate at 98°C in the direction perpendicular to the main shrinkage direction of the film (longitudinal direction), measured in the same manner as described above, which is between -5% and 15%. If the hot water shrinkage rate at 98°C in the direction perpendicular to the main shrinkage direction is less than -5%, the amount of stretching of the film due to heating is too great, making it undesirable as a good shrinkage appearance cannot be obtained when used as a label for a container. Conversely, if the hot water shrinkage rate at 98°C in the direction perpendicular to the main shrinkage direction exceeds 15%, the label becomes shorter after heat shrinkage (label height decreases), and the label area becomes smaller, which is undesirable for a full label, and is also undesirable as it makes the label more prone to distortion after heat shrinkage. Regarding the upper limit of the hot water shrinkage rate at 98°C in the direction perpendicular to the main shrinkage direction, 12% or less is preferred, and 9% or less is more preferred.

[0036] Furthermore, if the hot water shrinkage rate in the direction perpendicular to the main shrinkage direction at 98°C is lower than -5%, the label height will increase after shrinkage, resulting in excess material becoming loose and wrinkled. Therefore, the lower limit was set at -5%.

[0037] The heat-shrinkable polyester film of the present invention is subjected to immersion in 70°C hot water for 10 seconds under no load, followed immediately by immersion in 25°C ± 0.5°C water for 10 seconds. The heat shrinkage rate in the longitudinal direction (i.e., the 70°C hot water heat shrinkage rate), calculated from the length before and after shrinkage using Formula 1 above, is between -5% and 5%. If the hot water heat shrinkage rate in the direction perpendicular to the main shrinkage direction at 70°C is less than -5%, the film stretches too much due to heating, making it undesirable to obtain a good shrunk appearance when used as a label for a container. Conversely, if the hot water heat shrinkage rate in the direction perpendicular to the main shrinkage direction at 70°C exceeds 5%, distortion occurs in the label after heat shrinkage, which is undesirable. Regarding the upper limit of the hot water heat shrinkage rate in the direction perpendicular to the main shrinkage direction at 70°C, 4% or less is preferable, and 3% or less is more preferable.

[0038] The heat-shrinkable polyester film of the present invention is not particularly limited, but it is preferably 10 μm or more and 60 μm or less in thickness. A more preferable lower limit for thickness is 15 μm.

[0039] The heat-shrinkable polyester film of the present invention can be obtained by melt-extruding the above-mentioned polyester raw material using an extruder to form an unstretched film, and then stretching the unstretched film in the width direction. The polyester can be obtained by polycondensing the above-mentioned suitable dicarboxylic acid component and diol component using a known method. In addition, chip-shaped polyester is usually used as the raw material for the film.

[0040] When melt-extruding the raw material resin, it is preferable to dry the polyester raw material using a dryer such as a hopper dryer or paddle dryer, or a vacuum dryer. After drying the polyester raw material in this way, it is melted at a temperature of 235 to 265°C using an extruder and extruded into a film. In extruders, preventing raw material degradation (foreign matter), stable resin discharge from the die due to appropriate melt viscosity, and the progress of transesterification are crucial. As mentioned above, extruding at a temperature of 235-265°C is to reduce foreign matter caused by resin degradation. At 235-265°C and a shear rate of 5000-8000 / S, the melt viscosity is preferably between 100 Pa·S and 200 Pa·S. As mentioned above, this range reduces the load on the extrusion machine and minimizes thickness unevenness. The shear rate was determined according to the following equation (2). The raw material discharge rate and die lip gap are adjusted to achieve the aforementioned shear rate.

[0041] Shear rate γ = 6Q / (W × H) 2 ) γ; Shear rate (sec -1 ) Q: Discharge volume of raw material from the extruder (cm²) 3 / sec) W; Width of the die exit opening (cm) H; Lip gap of the die (cm) Equation (2)

[0042] To promote transesterification, it is common to raise the extruder temperature and lengthen the resin residence time, but this method can cause resin degradation and lead to the formation of foreign matter. Therefore, to promote transesterification even in a short time, it is preferable to use an extruder with 2 to 32 screws. Increasing the number of screws increases the shear during mixing, which promotes transesterification. While a larger number of screws promotes transesterification, too many screws increase the maintenance requirements of the machine, so the upper limit is set at 32 screws.

[0043] Then, an unstretched film can be obtained by rapidly cooling the sheet-like molten resin after 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.

[0044] (Transverse stretching and relaxation after transverse stretching) By employing the following methods (1) and (2), the performance of the copolymerized polyester of this application can be more favorably expressed, and therefore is preferable. From the viewpoint of simplifying production equipment, it is preferable to form the film by transverse uniaxial stretching.

[0045] (1) Control of lateral extension conditions For transverse stretching, the film is preheated to a temperature of Tg+10°C to Tg+40°C while being held at both ends in the width direction by clips inside a tenter. Then, it is preferable to stretch the film 3.5 to 6 times in the width direction while cooling it to a temperature of Tg-5°C to Tg+10°C. Stretching in the width direction while cooling increases the stress ratio (tensile stress at final stretch ÷ upper yield point stress) of the stress-strain curve, which reduces thickness unevenness in the width direction. After transverse stretching, it is preferable to heat treat the film at a temperature of stretching temperature +1°C to +15°C. If the heat treatment temperature is lower than the stretching temperature, the relaxation of molecular orientation is insufficient, and the film shrinks (so-called natural shrinkage) when stored in a warehouse after becoming a film product, which is undesirable. Also, if the heat treatment temperature is higher than the stretching temperature +15°C, the shrinkage rate in the width direction decreases, which is undesirable.

[0046] (2) Relaxation in the width direction after lateral stretching In the heat treatment process, it is preferable to relax the material by 0% to 5% in the width direction while holding both ends in the width direction with clips inside the tenter (0% means no relaxation). Relaxation slightly reduces the shrinkage rate in the width direction, but it relaxes the molecular orientation in the width direction, making it possible to reduce shrinkage stress and natural shrinkage rate. Furthermore, in the final heat treatment process, heat treatment at a temperature higher than the stretching temperature relaxes the molecular orientation, making it possible to reduce shrinkage stress and natural shrinkage rate.

[0047] The packaging of the present invention is formed by covering at least a portion of the outer circumference of an object to be packaged with a label having perforations or notches obtained from the heat-shrinkable polyester film of the present invention and then heat-shrinking it. Examples of objects to be packaged include PET bottles for beverages, various bottles, cans, plastic containers for confectionery and bento boxes, and paper boxes. When covering such objects to be packaged with a label obtained from the heat-shrinkable polyester film by heat shrinking, the label is usually heat-shrinked by about 5-70% to make it adhere tightly to the packaging. The label covering the object to be packaged may or may not have printing on it.

[0048] The method for producing labels from the heat-shrinkable polyester film of the present invention involves applying an organic solvent slightly inward from one end of a rectangular film, immediately rolling the film and overlapping and bonding the ends to form a label, or applying an organic solvent slightly inward from one end of a roll of film, immediately rolling the film and overlapping and bonding the ends to form a tube, which is then cut to form a label. Preferred organic solvents for bonding are cyclic ethers such as 1,3-dioxolane or tetrahydrofuran, or mixtures of these solvents with amorphous resins. Other usable solvents include aromatic hydrocarbons such as benzene, toluene, xylene, and trimethylbenzene, halogenated hydrocarbons such as methylene chloride and chloroform, phenols such as phenol, or mixtures thereof. Alternatively, the film may be heated and heat-bonded (so-called heat seal or heat-cut seal) to form a label. [Examples]

[0049] 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 as appropriate without departing from the spirit of the invention. The film evaluation method is shown below.

[0050] [Thermal shrinkage rate (hot water thermal shrinkage rate)] The film was cut into 10cm x 10cm squares, immersed in warm water at a specified temperature of ℃±0.5℃ for 10 seconds without load to cause thermal shrinkage, then immersed in water at 25℃±0.5℃ for 10 seconds, and after being removed from the water, the lengthwise and widthwise dimensions of the film were measured, and the thermal shrinkage rate was calculated according to the following formula (1). Thermal shrinkage rate = {(Length before shrinkage - Length after shrinkage) / Length before shrinkage} × 100 (%) Equation (1)

[0051] [Long-term tensile elongation at break after aging] After aging the film for 672 hours in an environmental test chamber at 40°C and 65% humidity, strip-shaped test pieces were prepared, measuring 140 mm in the longitudinal direction of the film and 20 mm in the direction perpendicular to the measurement direction (film width direction). Using a universal tensile testing machine "DSS-100" (manufactured by Shimadzu Corporation), both ends of the test piece were gripped with chucks, 20 mm on each side (chuck distance 100 mm), and a tensile test was performed under ambient temperature of 23°C and tensile speed of 200 mm / min. The elongation at tensile failure was defined as the tensile fracture elongation. Ten samples were measured, and the following evaluations were performed. ○: 9 or more pieces with a breaking elongation of 30% or more. ×: Eight or more pieces with a breaking elongation of less than 30%.

[0052] [Melting viscosity] Measurements were performed using a Capillograph 1D PMD-C (manufactured by Toyo Seiki Seisakusho Co., Ltd.) under conditions of a resin temperature of 255°C and a shear rate of 6080 / S, in accordance with JIS K7199.

[0053] [Intrinsic viscosity (IV)] 0.2 g of polyester was dissolved in 50 ml of a mixed solvent of phenol / 1,1,2,2-tetrachloroethane (60 / 40 (weight ratio)) and measured using an Ostwald viscometer at 30°C. The unit is dl / g.

[0054] [How to count the number of defects] The film was sampled to a size of 0.5m in the width direction and 5m in the length direction. The cut film was placed on a tabletop film orientation viewer (manufactured by Unitika) and polarized. Then, the number of defects larger than 1mm was counted using a 10x magnification loupe. The number of defects was counted in the same way for a total of 80 sheets (200 square meters) of film. The average number of defects per 100 square meters of film was then calculated using equation 3 below. Average number of defects = Total number of defects ÷ 2 (defects / 100 square meters) (Equation 3)

[0055] [Diethylene glycol content] A heat-shrinkable film was scraped off with a razor blade for sampling. Approximately 5 mg of the sampled film was dissolved in 0.7 ml of a mixed solution of deuterated chloroform and trifluoroacetic acid (volume ratio 9 / 1), and the amount of diethylene glycol units was calculated using 1H-NMR (Varian, UNITY50), and its molar percentage was determined.

[0056] [Tg (Glass transition temperature)] Using a differential scanning calorimeter (model: DSC220) manufactured by Seiko Electronics Industries, Ltd., 5 mg of unstretched film was heated from -40°C to 120°C at a heating rate of 10°C / min, and the endothermic curve obtained was used to determine the glass transition temperature (Tg). The temperature at the intersection of the extension of the baseline below the glass transition temperature and the tangent line showing the maximum slope in the transition region was defined as the glass transition temperature (Tg).

[0057] [Shrinkage properties] A heat-shrinkable film was pre-printed with three colors of inks (grass, gold, and white) from Toyo Ink Manufacturing Co., Ltd. Then, the ends of the printed film were bonded together with a solution of 1,3-dioxolane mixed with 10% PET resin (Byron 200, manufactured by Toyobo Co., Ltd.) to create a cylindrical label (a label with the main shrinkage direction of the heat-shrinkable film oriented circumferentially), which was then cut. The diameter of the label in the shrinkage direction was 70 mm. Subsequently, the label was heat-shrinked onto a 500 ml PET bottle (body diameter 62 mm, minimum neck diameter 25 mm) using a steam tunnel (model SH-1500-L) manufactured by Fuji Astec Inc., with a passage time of 4 seconds and a zone temperature of 90°C. During attachment, the neck portion was adjusted so that a 45 mm diameter section was one end of the label. The finish quality after shrinkage was evaluated visually, with the following criteria.

[0058] [Label shrinkage and distortion] To evaluate the finish after shrinkage, the strain in the 360-degree direction of the lower and upper parts of the attached label was measured using a gauge, and the maximum strain was determined separately for the lower and upper parts. The evaluation was performed according to the following criteria. ○: Maximum distortion less than 3mm ×: Maximum distortion of 3mm or more

[0059] [Insufficient label shrinkage] The label shrinkage state described above was evaluated according to the following criteria. ○: There is no slack between the attached label and the container; it is contracted. ×: There is looseness between the label and the container due to insufficient shrinkage.

[0060] [Label wrinkles] Under the same conditions as those for the shrinkage strain of the labels described above, the wrinkle formation was evaluated according to the following criteria. ○: There are two or fewer wrinkles that are 2mm or larger in size. ×: Three or more wrinkles larger than 2mm in size.

[0061] [productivity] Productivity was calculated as follows based on the number of fractures during a 2-hour film deposition process. ○: Breakdown 1 time / 2 hours or less ×: Breakage occurred twice in more than 2 hours.

[0062] <Preparation of polyester raw materials> Starting materials A to H were obtained by a known method involving polycondensation via transesterification using dimethyl terephthalate (DMT) and the glycol components described below. Raw material A: Polyester composed of 40 mol% diethylene glycol, 60 mol% ethylene glycol, and terephthalic acid. Intrinsic viscosity: 0.831 dl / g. Melt viscosity measured at a shear rate of 6080 rpm at 255°C: 170 Pa·s. Raw material B: A polyester composed of 7 mol% diethylene glyco, 93 mol% ethylene glycol, and terephthalic acid. Intrinsic viscosity: 0.631 dl / g. Melt viscosity measured at a shear rate of 6080 rpm at 255°C: 100 Pa·s. Raw material C: Polyester composed of 30 mol% diethylene glyco, 70 mol% ethylene glycol, and terephthalic acid. Intrinsic viscosity: 0.731 dl / g. Melt viscosity measured at a shear rate of 6080 rpm at 255°C: 130 Pa·s.

[0063] Raw material D: A polyester composed of 20 mol% diethylene glyco, 80 mol% ethylene glycol, and terephthalic acid. Intrinsic viscosity: 0.731 dl / g. Melt viscosity measured at a shear rate of 6080 rpm at 255°C: 140 Pa·s. Raw material E: A polyester composed of 3 mol% diethylene glyco, 97 mol% ethylene glycol, and terephthalic acid. Intrinsic viscosity: 0.731 dl / g. Melt viscosity measured at a shear rate of 6080 rpm at 255°C: 170 Pa·s. Raw material F: Polyester composed of 20 mol% diethylene glyco, 80 mol% ethylene glycol, and terephthalic acid. Intrinsic viscosity: 0.91 dl / g. Melt viscosity measured at a shear rate of 6080 rpm at 255°C: 215 Pa·s Raw material G: Polyester composed of 30 mol% diethylene glyco, 70 mol% ethylene glycol, and terephthalic acid. Intrinsic viscosity: 0.551 dl / g. Melt viscosity measured at a shear rate of 6080 rpm at 255°C: 88 Pa·s.

[0064] Raw material H: Polyester composed of 60 mol% diethylene glyco, 40 mol% ethylene glycol, and terephthalic acid. Intrinsic viscosity: 0.651 dl / g. Melt viscosity measured at a shear rate of 6080 rpm at 255°C: 110 Pa·s. Raw material I: Polyester composed of 60 mol% diethylene glyco, 40 mol% ethylene glycol, and terephthalic acid. Intrinsic viscosity: 0.651 dl / g. Melt viscosity measured at a shear rate of 6080 rpm at 255°C: 105 Pa·s

[0065] In the production of polyester raw materials A to G described above, SiO2 (Silysia 266, manufactured by Fuji Silysia Co., Ltd.) was added as a lubricant at a ratio of 700 ppm relative to the polyester. The same silica was added to raw material I at a ratio of 7200 ppm. In the table, TPA stands for terephthalic acid, EG for ethylene glycol, and DEG for diethylene glycol. Each polyester was processed into chips as appropriate.

[0066] The composition of the polyester raw materials used in the examples and comparative examples, as well as the resin composition and manufacturing conditions of the films in the examples and comparative examples, are shown in Tables 1 and 2, respectively. Hereinafter, Example 1 will be read as Reference Example 1, Example 2 as Reference Example 2, Example 5 as Reference Example 5, and Example 6 as Reference Example 6.

[0067] [Table 1]

[0068] [Table 2]

[0069] Example 1 Raw material A was fed into an extruder. This resin was melted at 255°C and extruded from a T-die. The film was then wound onto a rotating metal roll cooled to a surface temperature of 30°C and rapidly cooled to obtain an unstretched film with a thickness of 152 μm. The take-up speed (rotation speed of the metal roll) of the unstretched film at this time was 30 m / min. The Tg of the unstretched film was 62°C. The obtained unstretched film was guided to a tenter, preheated to a surface temperature of 120°C, and then stretched four times in the width direction while cooling to a surface temperature of 75°C. Next, the film was relaxed by 5% in the width direction while heating to a surface temperature of 76°C. After that, it was cooled, the edges were cut off, and the film was wound into a roll with a width of 500 mm to continuously produce a uniaxially oriented film with a thickness of 40 μm over a predetermined length. The properties of the obtained film were evaluated using the method described above. The evaluation results are shown in Table 3. The results were good.

[0070] Example 2 A 40 μm thick film was manufactured using the same method as in Example 1, except that raw material A was changed to raw material B. The evaluation results are shown in Table 3. The results were good, similar to Example 1.

[0071] Example 3 A 40 μm thick film was manufactured using the same method as in Example 1, except that raw material A was changed to raw material C. The evaluation results are shown in Table 3. The results were good, similar to Example 1.

[0072] Example 4 A 40 μm thick film was manufactured using the same method as in Example 1, except that raw material A was changed to raw material D. The evaluation results are shown in Table 3. The results were good, similar to Example 1.

[0073] Example 5 Raw material A was fed into an extruder. This resin was melted at 255°C and extruded from a T-die. The film was then wound onto a rotating metal roll cooled to a surface temperature of 30°C and rapidly cooled to obtain an unstretched film with a thickness of 198 μm. The take-up speed (rotation speed of the metal roll) of the unstretched film at this time was 30 m / min. The Tg of the unstretched film was 62°C. The obtained unstretched film was guided to a tenter, preheated to a surface temperature of 125°C, and then stretched six times in the width direction while cooling to a surface temperature of 78°C. Next, the film was relaxed by 5% in the width direction while heating to a surface temperature of 79°C. After that, it was cooled, the edges were cut off, and the film was wound into a roll with a width of 500 mm to continuously produce a uniaxially oriented film with a thickness of 40 μm over a predetermined length. The properties of the obtained film were evaluated using the method described above. The evaluation results are shown in Table 3. The results were good.

[0074] Example 6 A 40 μm thick film was manufactured using the same method as in Example 5, except that raw material A was changed to raw material B. The evaluation results are shown in Table 3. The results were good, similar to Example 5.

[0075] Comparative Example 1 The procedure was the same as in Example 5, except that raw material A was changed to raw material E. However, breakage occurred occasionally during film production, resulting in unstable productivity. The evaluation results of the obtained film are shown in Table 3. Compared to Example 5, the shrinkage rate in the width direction was low, the shrinkage rate in the longitudinal direction was high, and the shrinkage finish was inferior.

[0076] Comparative Example 2 A 40 μm thick film was manufactured using the same method as in Example 1, except that raw material A was changed to raw material F, and because raw material F has a high melt viscosity and increases the pressure load on the extruder, the resin temperature inside the extruder was increased from 255°C to 280°C. The evaluation results are shown in Table 3. Compared to Example 1, the number of defects was higher, and the result was inferior as a heat-shrinkable film that requires printing.

[0077] Comparative Example 3 A 40 μm thick film was manufactured using the same method as in Example 1, except that raw material A was changed to raw material G. The evaluation results are shown in Table 3. Due to the low longitudinal tensile break elongation after aging, breakage occurred repeatedly during printing, and it was not possible to obtain printing rolls.

[0078] Comparative Example 4 A 40 μm thick film was manufactured using the same method as in Example 1, except that raw material A was changed to raw material H:raw material I = 90:10 (weight ratio). The evaluation results are shown in Table 3. Compared to Example 1, the number of defects was higher, resulting in a lower performance as a heat-shrinkable film requiring printing. Also, possibly due to the high shrinkage rate in the main shrinkage direction at 70°C, the shrinkage finish was also inferior in terms of wrinkles.

[0079] [Table 3] [Industrial applicability]

[0080] The copolymer polyester raw material for films of the present invention is a suitable raw material for films that undergo shrinkage, molding, etc., including heat-shrinkable films. Furthermore, the heat-shrinkable polyester film produced using this copolymer polyester raw material is inexpensive, has good productivity and shrinkage finish, and the packaging such as containers obtained when used as labels has a beautiful appearance.

Claims

1. A copolymer polyester raw material for films that satisfies the following requirements (1) to (5), has a thickness of 10 μm or more, and is characterized by being used for the manufacture of films with the width direction as the main shrinkage direction. (1) The total amount of glycol components in the polyester resin contains 20 mol% to 30 mol% of constituent units derived from diethylene glycol. (2) The total polyester resin components contain 0 mol% to 5 mol% of constituent units derived from monomer components that can become amorphous components, and the monomer components that can become amorphous components are selected from the group consisting of neopentyl glycol, 1,4-cyclohexanedimethanol, 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, and hexanediol, and the acid component is terephthalic acid. (3) The glass transition temperature of the raw material is between 65°C and 73°C. (4) The intrinsic viscosity of the raw material is 0.60 dl / g or more and 0.85 dl / g or less. (5) The melt viscosity of the raw material measured at a shear rate of 6080 / s and 255°C is 200 Pa·s or less.

2. The copolymer polyester raw material for film according to claim 1, wherein the acid component in the total polyester resin components is terephthalic acid, and the glycol component is ethylene glycol and diethylene glycol.

3. A heat-shrinkable polyester film containing the copolymer polyester raw material described in claim 1 or 2, and satisfying the following requirements (6) to (10). (6) When the film is immersed in 98°C hot water for 10 seconds, the thermal shrinkage rate in the main shrinkage direction of the film is 40% or more and 85% or less. (7) When the film is immersed in 98°C hot water for 10 seconds, the thermal shrinkage rate in the direction perpendicular to the main shrinkage direction of the film is -5% to 15%. (8) When the film is immersed in 70°C hot water for 10 seconds, the thermal shrinkage rate in the direction perpendicular to the main shrinkage direction of the film is -5% or more and 5% or less. (9) The intrinsic viscosity of the film is 0.57 dl / g or more and 0.82 dl / g or less. (10) The average number of defects of 1 mm or larger in the longitudinal or widthwise direction of the film per 100 square meters of film is 1.1 or less.

4. A heat-shrinkable label using the heat-shrinkable polyester film described in claim 3.

5. A packaging body characterized by being formed by covering and heat-shrinking at least a portion of the outer circumference of the object to be packaged, using the heat-shrinkable label described in claim 4.

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