Classifications

• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
  • Y02W30/00—Technologies for solid waste management
  • Y02W30/50—Reuse, recycling or recovery technologies
  • Y02W30/80—Packaging reuse or recycling, e.g. of multilayer packaging

Definitions

• the present invention relates to a heat-shrinkable polyester film suitable for label applications and container packaging. Specifically, it is suitable for use in labels for beverage bottles and banding for containers such as lunch boxes by shrinking in the longitudinal direction, and is particularly excellent in productivity and shrink finish.
• heat-shrinkable films have come to be widely used for applications such as label packaging that combines the protection of glass bottles or plastic bottles and product display, cap sealing, stacked packaging, banding for bundling lunch boxes, etc.
• polyvinyl chloride films have problems such as low heat resistance, generation of hydrogen chloride gas when incinerated, and being a source of dioxin.
• Polystyrene-based films have poor solvent resistance, and require the use of ink with a special composition when printing, and in addition, they have the problem of needing to be incinerated at high temperatures, which produces a large amount of black smoke accompanied by an unpleasant odor when incinerated.
• polyester-based heat-shrinkable films which have high heat resistance, are easy to incinerate, and have excellent solvent resistance, tend to be widely used as shrink labels.
• the film can be unwound from a roll and directly wrapped around the bottle or lunch box, etc., and heat-sealed, which has the advantage of speeding up the attachment process, and automating the process of attaching ring-shaped labels, which was previously done by hand.
• Patent Document 1 discloses a technology for producing a polyester film that heat-shrinks in the longitudinal direction.
• Patent Document 1 describes a film that is stretched only in the longitudinal direction, and the stretching ratio described in the examples is at most 5 times, leaving room for improvement in productivity.
• heat-shrinkable films that are uniaxially stretched only in the longitudinal direction tend to shrink faster, leaving room for improvement in shrink finish.
• Patent Document 2 discloses a polyester film that is stretched about 4 times in the transverse direction, then stretched about 2 times in the longitudinal direction, and then heat-shrunk in the longitudinal direction. Patent Document 2 improves productivity because the area ratio (the product of transverse and longitudinal stretching) is about 12 times.
• the equipment required for the transverse-longitudinal sequential biaxial stretching method disclosed in Patent Document 2 is different from the longitudinal-transverse sequential biaxial stretching machine table generally used for producing films, and after the transverse-longitudinal stretching is completed, it is necessary to pass the film through a heater such as a tenter or oven for heat treatment again, so the equipment tends to be large.
• Patent Document 3 discloses a polyester film that shrinks in the longitudinal direction by sequential biaxial stretching in the longitudinal and transverse directions. However, in the examples of Patent Document 3, the area ratio of stretching is about 4.5, so the productivity is inferior to that of Patent Document 2, which is stretched only in the longitudinal direction. In addition, there is still room for improvement in the shrink finish due to the high shrink speed.
• the object of the present invention is to provide a heat-shrinkable polyester film that shrinks in the longitudinal direction and has excellent productivity and shrink finish.
• the present invention comprises the following configurations. 1.
• the shrinkage rate in the longitudinal direction of the film when immersed in 80°C hot water for 10 seconds is 20 to 70%
• the difference between the shrinkage rate in the longitudinal direction of the film when immersed in 80°C hot water for 10 seconds and the shrinkage rate when immersed for 3 seconds is 5 to 15%
• the seal strength when the films are heat sealed together at 130°C is 3 N/15 mm to 20 N/15 mm (4)
• the degree of planar orientation of the film is 0.03 to 0.08 (5)
• the difference in refractive index between the longitudinal direction and the width direction of the film is 0.01 to less than 0.04 2.
• the heat-shrinkable polyester heat-shrinkable film according to 1 characterized in that the shrinkage rate in the width direction when the film is immersed in 80°C hot water for 10 seconds is -2% to 18%. 3.
• the heat-shrinkable polyester film according to 1. or 2. characterized in that the shrinkage rate in the longitudinal direction when the film is immersed in 90° C. hot water for 10 seconds is 40% or more and 75% or less.
• 4. The heat-shrinkable polyester film according to any one of 1. to 3., wherein the reversible heat capacity difference ⁇ Cp of the film is 0.15 J/g ⁇ K or more and 0.28 J/g ⁇ K or less. 5.
• polyester component constituting the film contains 1 mol % to 30 mol % of one or more monomer components selected from the group consisting of isophthalic acid, neopentyl glycol, 1,4-cyclohexanedimethanol, 1,4-butanediol, and diethylene glycol.
• the heat-shrinkable polyester film according to any one of 1. to 5. characterized in that the raw material constituting the film is a mechanically recycled and/or chemically recycled polyester raw material.
• a heat-shrinkable label comprising at least a portion thereof made of the heat-shrinkable polyester film according to any one of 1. to 6.
• a packaging material comprising the heat-shrinkable polyester film according to any one of 1. to 6.
• a package comprising the label according to 7. above.
• the present invention provides a heat-shrinkable polyester film that shrinks in the longitudinal direction and has excellent productivity and shrink finish.
• 80°C 10-second heat shrinkage rate in the longitudinal direction The heat-shrinkable polyester film of the present invention is immersed in 80°C warm water for 10 seconds under no load, and then immediately immersed in 25°C ⁇ 0.5°C water for 10 seconds.
• the heat shrinkage rate in the longitudinal direction of the film calculated from the lengths before and after shrinkage according to the following formula 1 (hereinafter sometimes simply referred to as 80°C 10-second heat shrinkage rate in the longitudinal direction) must be 20% or more and 70% or less.
• Heat shrinkage rate ⁇ (length before shrinkage - length after shrinkage) / length before shrinkage ⁇ x 100 (%) Formula 1 If the 80°C 10-second heat shrinkage rate in the longitudinal direction is less than 20%, the shrinkage rate for the target object is insufficient, which is not preferable from the viewpoint of finish. If the 80°C 10-second heat shrinkage rate in the longitudinal direction is more than 70%, the value described below in [1-3] Difference between the 80°C 10-second heat shrinkage rate in the longitudinal direction and the 80°C 3-second heat shrinkage rate is likely to fall below 5% (the shrinkage rate becomes faster), which is not preferable.
• the 80°C 10-second heat shrinkage rate in the longitudinal direction is preferably 30% to 65%, more preferably 35% to 60%. That is, the 80°C 10-second heat shrinkage rate in the longitudinal direction is 20 to 70%, preferably 30 to 65%, more preferably 35 to 60%.
• the heat-shrinkable polyester film of the present invention is preferably immersed in 80°C warm water for 10 seconds under no load, and then immediately immersed in 25°C ⁇ 0.5°C water for 10 seconds, and then has a heat shrinkage in the width direction of the film calculated from the lengths before and after shrinkage according to the above formula 1 (hereinafter, sometimes simply referred to as 80°C 10-second heat shrinkage in the width direction) of -2% to 18%. If the 80°C 10-second heat shrinkage rate in the width direction falls below -2%, the effect of removing small wrinkles (grain wrinkles) that occur during shrink finishing is reduced, and the finishability is deteriorated, which is undesirable.
• the 80°C 10-second heat shrinkage in the width direction is preferably -1% to 17%, more preferably 0% to 16%. That is, the 80°C 10-second heat shrinkage in the width direction is preferably -2 to 18%, more preferably -1 to 17%, and even more preferably 0 to 16%.
• Difference in heat shrinkage rate 80°C 10-second heat shrinkage rate - 80°C 3-second heat shrinkage rate (%) Formula 2
• the difference in the thermal shrinkage rate is less than 5%, which means that the thermal shrinkage rate at the time of immersion for 3 seconds is close to that at the time of immersion for 10 seconds, and therefore the shrinkage speed at the time of shrink finishing is fast.
• the inventors have found that the difference in the thermal shrinkage rate has a large effect on the appearance of the shrink finishing. If the shrinkage speed is fast, problems such as distortion, wrinkles, and folding are likely to occur at the time of shrink finishing, and this is not preferable.
• the difference in the heat shrinkage rate is preferably 5.5% or more and 14.5% or less, and more preferably 6% or more and 14% or less. That is, the difference in the heat shrinkage rate is 5 to 15%, preferably 5.5 to 14.5%, and more preferably 6 to 14%.
• the heat-shrinkable polyester film of the present invention is preferably immersed in 90°C warm water for 10 seconds under no load, and then immediately immersed in 25°C ⁇ 0.5°C water for 10 seconds, and then has a heat shrinkage rate in the longitudinal direction of the film calculated from the lengths before and after shrinkage according to the above formula 1 (hereinafter, sometimes simply referred to as 90°C 10-second heat shrinkage rate in the longitudinal direction) of 40% or more and 75% or less.
• the shrinkage rate for the target object is insufficient, which is undesirable from the viewpoint of finish. If the 90°C 10-second heat shrinkage rate in the longitudinal direction is more than 75%, the value described in [1-3] above, which is the difference between the 80°C 10-second heat shrinkage rate in the longitudinal direction and the 80°C 3-second heat shrinkage rate, tends to fall below 5% (the shrinkage rate becomes faster), which is undesirable.
• the 90°C 10-second heat shrinkage rate in the longitudinal direction is preferably 45% to 70%, and more preferably 50% to 65%. That is, the 90°C 10-second heat shrinkage rate in the longitudinal direction is preferably 40 to 75%, more preferably 45 to 70%, and even more preferably 50 to 65%.
• the heat-shrinkable polyester film of the present invention is preferably immersed in 90°C warm water for 10 seconds under no load, and then immediately immersed in 25°C ⁇ 0.5°C water for 10 seconds, and then has a heat shrinkage in the width direction of the film calculated from the lengths before and after shrinkage according to the above formula 1 (hereinafter, sometimes simply referred to as 90°C 10-second heat shrinkage in the width direction) of -4% to 20%. If the 90°C 10-second heat shrinkage rate in the width direction is less than -4%, the effect of removing small wrinkles (grain wrinkles) that occur during shrink finishing is reduced, and the finishability is deteriorated, which is undesirable.
• the 90°C 10-second heat shrinkage in the width direction is preferably -2% to 19%, more preferably -1% to 18%. That is, the 90°C 10-second heat shrinkage in the width direction is preferably -4 to 20%, more preferably -2 to 19%, and even more preferably -1 to 18%.
• the heat-shrinkable polyester film of the present invention must have a seal strength (hereinafter sometimes simply referred to as 130°C seal strength) of 3 N/15 mm or more and 20 N/15 mm or less, as determined by heat-sealing the films together at 130°C, 0.2 MPa, and 2 seconds using a test sealer and then peeling them off using a tensile tester.
• 130°C seal strength 3 N/15 mm or more and 20 N/15 mm or less
• the 130°C seal strength is preferably 4 N/15 mm or more and 19 N/15 mm or less, and more preferably 5 N/15 mm or more and 18 N/15 mm or less. That is, the 130°C seal strength is 3 to 20 N/15 mm, preferably 4 to 19 N/15 mm, and more preferably 5 to 18 N/15 mm.
• refractive index difference between longitudinal and width directions
• the heat-shrinkable polyester film of the present invention needs to have a refractive index difference between the longitudinal and width directions (hereinafter, sometimes simply referred to as refractive index difference) calculated by the following formula 3 of 0.01 or more and less than 0.04.
• Difference in refractive index between the longitudinal direction and the width direction (refractive index in the longitudinal direction)-(refractive index in the width direction) Equation 3
• the refractive index difference 0.01 or more and less than 0.04
• the difference (shrinkage rate) between the 80° C. 10-second heat shrinkage rate and the 80° C. 3-second heat shrinkage rate in the longitudinal direction described in [1-3] above can be easily made 5% or more and 15%.
• the refractive index difference is preferably 0.011 or more and 0.039 or less, and more preferably 0.012 or more and 0.038 or less. That is, the refractive index difference is 0.01 to less than 0.04, preferably 0.011 to 0.039, and more preferably 0.012 to 0.038.
• Planar Orientation Degree The heat-shrinkable polyester film of the present invention must have a planar orientation degree, calculated from the following formula 4, of 0.03 to 0.08.
• Planar orientation degree ⁇ (refraction index in the longitudinal direction)+(refraction index in the width direction) ⁇ /2 ⁇ (refraction index in the thickness direction) Equation 4
• a planar orientation degree of less than 0.03 means that the sum of the stretching ratios in the longitudinal direction or the width direction (area ratio) is less than 5.0, which results in poor productivity.
• a planar orientation degree of more than 0.08 improves productivity, but the reversible heat capacity difference described below tends to fall below 0.15 g/J ⁇ K, which is undesirable because it results in a decrease in 130° C. seal strength.
• the degree of planar orientation is preferably 0.032 to 0.068, and more preferably 0.034 to 0.066. That is, the degree of planar orientation is 0.03 to 0.08, preferably 0.032 to 0.068, and more preferably 0.034 to 0.066.
• the heat-shrinkable polyester film of the present invention preferably has a reversible heat capacity difference before and after the glass transition temperature of 0.15 J/g ⁇ K or more and 0.28 J/g ⁇ K or less. If the reversible heat capacity difference exceeds 0.28 J/g ⁇ K, it means that the molecules constituting the completed film (after stretching) are not oriented, and the degree of planar orientation tends to fall below 0.03, which is undesirable as it deteriorates productivity. On the other hand, if the reversible heat capacity difference falls below 0.15 J/g ⁇ K, it is undesirable as it tends to cause the 130° C. seal strength to fall below 3 N/15 mm.
• the reversible heat capacity difference is more preferably 0.17 J/g K or more and 0.26 J/g K or less, and even more preferably 0.18 J/g K or more and 0.25 J/g K or less. That is, the reversible heat capacity difference is preferably 0.15 to 0.28 J/g K, more preferably 0.17 to 0.26 J/g K, and even more preferably 0.18 to 0.25 J/g K.
• the heat-shrinkable polyester film of the present invention preferably has a glass transition temperature of 50° C. or more and 100° C. or less. If the glass transition temperature is less than 50° C., the heat resistance of the heat-shrinkable label is poor, and the film may not be able to maintain its shape during shrink finishing. On the other hand, if the glass transition temperature is more than 100° C., the 80° C., 10-second heat shrinkage rate in the longitudinal direction tends to fall below 25%, which is undesirable.
• the glass transition temperature is more preferably 55° C. or higher and 95° C. or lower, and even more preferably 60° C. or higher and 90° C. or lower. That is, the glass transition temperature is preferably 50 to 100° C., more preferably 55 to 95° C., and even more preferably 60 to 90° C.
• the heat-shrinkable polyester film of the present invention preferably has a thickness of 4 ⁇ m or more and 100 ⁇ m or less.
• a thickness less than 4 ⁇ m is not preferred because the 130° C. seal strength tends to fall below 3 N/15 mm, whereas a thickness more than 100 ⁇ m is not preferred because the chemical costs increase more than necessary.
• the thickness is more preferably 6 ⁇ m or more and 98 ⁇ m or less, and even more preferably 8 ⁇ m or more and 96 ⁇ m or less. That is, the thickness is preferably 4 to 100 ⁇ m, more preferably 6 to 98 ⁇ m, and even more preferably 8 to 96 ⁇ m.
• polyester raw material used for the heat-shrinkable polyester film of the present invention is one having ethylene terephthalate units as a main constituent component.
• "Mainly" means 50 mol % or more, and the ethylene terephthalate unit preferably accounts for 50 mol % or more, more preferably 55 mol % or more, and even more preferably 60 mol % or more, of 100 mol % of the constituent units of the polyester.
• dicarboxylic acid components other than terephthalic acid that constitute 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, etc.
• 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
• alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, etc.
• isophthalic acid and orthophthalic acid are
• the content is preferably less than 3 mol % (based on 100 mol % of the dicarboxylic acid component). It is also preferable that the polyester does not contain a polyvalent carboxylic acid having a valence of three or more (e.g., trimellitic acid, pyromellitic acid, and anhydrides thereof, etc.), since a heat-shrinkable polyester film obtained by using a polyester containing such a polyvalent carboxylic acid will have difficulty in achieving a required shrinkage ratio.
• a polyvalent carboxylic acid having a valence of three or more
• diol components other than ethylene glycol that constitute the polyester of the present invention include alicyclic diols such as neopentyl glycol and 1,4-cyclohexanedimethanol, aliphatic diols such as 1,4-butanediol, diethylene glycol, 1,3-propanediol and hexanediol, and aromatic diols such as bisphenol A.
• alicyclic diols such as neopentyl glycol and 1,4-cyclohexanedimethanol
• aliphatic diols such as 1,4-butanediol
• diethylene glycol 1,3-propanediol and hexanediol
• aromatic diols such as bisphenol A.
• neopentyl glycol, 1,4-cyclohexanedimethanol, 1,4-butanediol and diethylene glycol are preferred.
• the dicarboxylic acid component other than terephthalic acid and/or the diol component other than ethylene glycol is contained in an amount of 1 mol % to 30 mol %.
• the copolymer contains at least one of isophthalic acid, neopentyl glycol, 1,4-cyclohexanedimethanol, 1,4-butanediol, and diethylene glycol.
• the film of the present invention may also contain a polyester elastomer, such as a copolymer of ⁇ -caprolactone and 1,4-butanediol, or polytetramethylene glycol.
• a polyester elastomer such as a copolymer of ⁇ -caprolactone and 1,4-butanediol, or polytetramethylene glycol.
• the use of recycled polyester raw materials from used waste such as PET bottles is also a preferred embodiment from the viewpoint of environmental friendliness of the present invention.
• polyester resins recycled from PET bottles include polyester resins obtained by a physical regeneration method in which used PET bottles collected from the market or society are sorted, crushed, and washed to thoroughly remove surface dirt and foreign matter, and then exposed to high temperatures to thoroughly wash contaminants remaining inside the resin, and then pelletized again (hereinafter, sometimes referred to as mechanically recycled polyester resins), and polyester resins obtained by decomposing polyester resins contained in used packaging containers to the monomer level, removing contaminants, and polymerizing them again (hereinafter, sometimes referred to as chemically recycled polyester resins).
• the recycled raw materials that can be preferably used in the present invention are mainly recycled containers mainly made of polyethylene terephthalate.
• recycled beverage containers for tea drinks, soft drinks, etc. can be preferably used.
• the content ratio of the recycled raw material is preferably 5% by weight or more and 100% by weight or less, within the range of 1 mol% or more and 30 mol% or less of the dicarboxylic acid component other than terephthalic acid and/or the diol component other than ethylene glycol. If the recycled raw material is less than 5% by weight, the recycled raw material ratio contained in the raw material used for film formation is very small, so the effect of reducing the environmental load is small.
• the content ratio of the recycled raw material is more preferably 6% by weight or more, and even more preferably 7% by weight or more.
• the upper limit of the recycled raw material used for film formation is 100% by weight.
• the raw materials recycled from the market or society including PET bottles, which can be preferably used, are polyesters manufactured and molded by normal polymerization and solid-phase polymerization, preferably mainly composed of polyethylene terephthalate, and may contain other polyester components and copolymer components. They may contain metal compounds such as antimony, germanium, and titanium as catalysts, and phosphorus compounds as stabilizers. Germanium is often used as a catalyst in polyesters for PET bottles, and if recycled PET bottle raw materials are used to make a film, the film will contain 1 ppm or more of germanium. However, since it is only the content of the catalyst, it is usually 100 ppm or less, and usually 50 ppm or less.
• additives such as waxes, antioxidants, antistatic agents, crystal nucleating agents, viscosity reducers, heat stabilizers, coloring pigments, coloring inhibitors, and ultraviolet absorbers, may be added to the resin forming the heat-shrinkable polyester film of the present invention, as necessary.
• fine particles as a lubricant to improve the workability (slipperiness) of the film.
• Any fine particles can be selected, but for example, inorganic fine particles can be silica, alumina, titanium dioxide, calcium carbonate, kaolin, barium sulfate, etc., and organic fine particles can be acrylic resin particles, melamine resin particles, silicone resin particles, crosslinked polystyrene particles, etc.
• the average particle size of the fine particles is preferably in the range of 0.05 to 3.0 ⁇ m.
• the average particle size of the fine particles is a value measured by a Coulter counter.
• the particle size is less than 0.05 ⁇ m, the smoothness required for handling may not be satisfied. On the other hand, if the particle size exceeds 3.0 ⁇ m, the particles may aggregate and become too coarse, resulting in foreign matter and extremely poor appearance quality.
• the particle size is more preferably 0.06 ⁇ m or more and 2.99 ⁇ m or less, and even more preferably 0.07 ⁇ m or more and 2.98 ⁇ m or less.
• the method of blending the above particles into the resin forming the heat-shrinkable polyester film of the present invention can be, for example, addition at any stage of producing the polyester resin, but it is preferable to add the particles as a slurry dispersed in ethylene glycol or the like at the stage of esterification or after the completion of the transesterification reaction and before the start of the polycondensation reaction, and proceed with the polycondensation reaction. It is also preferable to blend a slurry of the particles dispersed in ethylene glycol or water or the like with the polyester resin raw material using a vented kneading extruder, or to blend dried particles with the polyester resin raw material using a kneading extruder.
• the method of blending the fine particles in the polyester raw material is not particularly limited, and can be added at any stage of producing polyester resin, for example, but it is preferable to add the fine particles as a slurry dispersed in ethylene glycol or the like at the stage of esterification, or after the completion of transesterification reaction and before the start of polycondensation reaction, and proceed with polycondensation reaction. It may also be performed by a method of blending a slurry of the fine particles dispersed in ethylene glycol or water or the like with the polyester resin raw material using a vented kneading extruder; or a method of blending dried fine particles with the polyester resin raw material using a kneading extruder.
• the heat-shrinkable polyester film of the present invention can be obtained by melt-extruding the above-mentioned polyester raw material with an extruder to form an unstretched film, and stretching the unstretched film by a predetermined method described below.
• the stretching method there is no limitation on the stretching method as long as the above-mentioned [1] heat-shrinkable polyester film properties are satisfied, but the following describes sequential biaxial stretching, in which transverse stretching is performed after longitudinal stretching, as an example.
• the heat-shrinkable polyester film of the present invention may have a single layer structure or a multilayer structure of two or more layers. When the film has a multilayer structure, it is preferable that the film has five layers or less.
• polyester raw material When melt-extruding the raw resin, it is preferable to dry the polyester raw material using a dryer such as a hopper dryer or a paddle dryer, or a vacuum dryer. After drying the polyester raw material in this way, the polyester raw material is melted and extruded into a film using an extruder. If the raw material is not dried in advance, moisture can be removed by vacuuming through a vent in the extruder.
• the melting temperature when extruding the polyester raw material is preferably 200° C. or more and 300° C. or less. If the temperature is lower than 200° C., the extrusion pressure increases excessively, which is undesirable since it causes problems such as filter deformation.
• the melting temperature exceeds 300° C., the thermal decomposition of the raw material is promoted, which is likely to cause problems such as an increase in foreign matter in the film.
• the melting temperature is more preferably 205° C. or higher and 295° C. or lower, and even more preferably 210° C. or higher and 290° C. or lower. That is, the melting temperature is preferably 200 to 300° C., more preferably 205 to 295° C., and even more preferably 210 to 290° C.
• any existing method such as a T-die method or a tubular method can be used.
• the unstretched film can be obtained by quenching the sheet-like molten resin.
• a method for quenching the molten resin a method can be suitably adopted in which the molten resin is cast from a die onto a chill roll and rapidly solidified to obtain a substantially unoriented resin sheet (hereinafter, sometimes referred to as an unstretched film).
• the stretching ratio in the longitudinal direction (hereinafter sometimes referred to as machine-direction stretching) is preferably 3 to 6 times. If the machine-direction stretching ratio is less than 3 times, it is difficult to achieve a 80°C heat shrinkage ratio of 25% or more in the machine-direction. On the other hand, if the machine-direction stretching ratio exceeds 6 times, the 80°C heat shrinkage ratio difference (shrinkage speed) in the machine-direction tends to be less than 5%, which is not preferable.
• the longitudinal stretching ratio is more preferably 3.2 to 5.8 times, and even more preferably 3.4 to 5.6 times.
• the longitudinal stretching ratio is preferably 3 to 6 times, more preferably 3.2 to 5.8 times, and even more preferably 3.4 to 5.6 times.
• the longitudinal stretching temperature is more preferably Tg+5° C. or more and Tg+55° C. or less, and even more preferably Tg+10° C. or more and Tg+50° C. or less.
• the stretching temperature is preferably Tg to Tg+60° C., more preferably Tg+5° C. to Tg+55° C., and even more preferably Tg+10° C. to Tg+50° C.
• the longitudinal stretching may be either a single-stage stretching or a multi-stage stretching of two or more stages.
• the stretching temperature in the second half zone is preferably above Tg+25° C. and below Tg+50° C.
• Tg+25° C. and below Tg+50° C When a film is stretched transversely, the stretching stress tends to be greater in the latter half of stretching than in the first half. It is believed that by increasing the temperature of the latter half zone of transverse stretching as described above, the increase in the stretching stress can be suppressed, and the effect of suppressing the degree of molecular orientation in the width direction is exhibited.
• the temperature of the first half zone of transverse stretching is lower than Tg+5°C, or the temperature of the latter half zone of transverse stretching is equal to or lower than Tg+25°C, the degree of orientation in the width direction increases, and the refractive index difference between the longitudinal direction and the width direction tends to fall below 0.01, which is not preferable.
• the temperature of the first half zone of transverse stretching exceeds Tg+25°C, or the temperature of the latter half zone of transverse stretching exceeds Tg+50°C, the film is extremely heated, and the shrinkage rate in the longitudinal direction at 80°C or 90°C tends to fall below a specified range, which is not preferable.
• the stretching first half zone is more preferably Tg+7° C.
• the stretching first half zone is preferably Tg+5° C. to Tg+25° C., more preferably Tg+7° C. to Tg+23° C., and even more preferably Tg+9° C. to Tg+21° C.
• the latter half stretching zone is more preferably Tg+27° C. or more and Tg+48° C. or less, and even more preferably Tg+29° C. or more and Tg+46° C. or less. That is, the latter half stretching zone is preferably Tg+25° C.
• the film is preferably preheated to a temperature of Tg° C. or higher and Tg+40° C. or lower.
• the length of each of the first and second half transverse stretching zones is preferably 30% to 70% of the total transverse stretching zone. If the length of the first or second half zone is less than 30% of the total transverse stretching zone, it is difficult to make the actual film temperature in the corresponding zone reach the set temperature, which is not preferable. Note that the zone length of either the first or second half being less than 30% is synonymous with the zone length of the other being more than 70%.
• the length of the first or second half zone is more preferably 35% to 65% of the total transverse stretching zone, even more preferably 40% to 60% of the total transverse stretching zone, and particularly preferably 50% (the lengths of the first and second half are the same). That is, the length of the first or second half zone is preferably 30% to 70%, more preferably 35% to 65%, and even more preferably 40% to 60% of the total transverse stretching zone.
• the product of the first and second lateral stretching ratios is preferably 1.2 to 2.4 times. If the product of the transverse stretching ratios is less than 1.2 times, the productivity of the film is extremely reduced, which is not preferable. On the other hand, if the product of the transverse stretching ratios exceeds 2.4 times, the 80°C heat shrinkage in the width direction is likely to exceed 18%, which is not preferable.
• the stretching ratio in the first half of the transverse stretching is preferably 1.1 times or more and 1.8 times or less. If the stretching ratio in the first half of the transverse stretching is less than 1.1 times, the film is not substantially stretched, and there is no point in dividing the stretching zone.
• the stretching ratio in the first half of the transverse stretching exceeds 1.8 times, the stretching stress in the subsequent second half zone tends to increase, and the refractive index difference between the longitudinal direction and the width direction is likely to fall below 0.01, which is not preferable.
• the stretching ratio in the first half of the transverse stretching is more preferably 1.11 to 1.79 times, and even more preferably 1.12 to 1.78 times. That is, the stretching ratio in the first half of the transverse stretching is preferably 1.1 to 1.8 times, more preferably 1.11 to 1.79 times, and even more preferably 1.12 to 1.78 times.
• the stretching ratio in the latter half transverse stretching zone is preferably 1.1 times or more and 2.1 times or less.
• the stretch ratio in the latter half of the transverse stretching is less than 1.1 times, as described in the explanation of the first half of the stretching zone, there is no point in separating the stretching zones.
• the stretch ratio in the latter half of the transverse stretching is more than 2.1 times, even if the temperature of this zone is set to be higher than Tg+25°C and not higher than Tg+50°C, the refractive index difference between the longitudinal direction and the width direction is likely to be less than 0.01, which is not preferable.
• the stretching ratio in the latter half of the transverse stretching is more preferably 1.11 to 2.09 times, and even more preferably 1.12 to 2.08 times. That is, the stretching ratio in the latter half of the transverse stretching is preferably 1.1 to 2.1 times, more preferably 1.11 to 2.09 times, and even more preferably 1.12 to 2.08 times.
• the area ratio obtained by multiplying the ratios after successive stretching in the longitudinal direction and the width direction as described above is preferably 5.5 times or more and 14 times or less. By setting the area ratio to 5.5 times or more, the productivity of the film can be improved. On the other hand, if an attempt is made to set the area ratio to more than 14 times, the stretching ratios in the longitudinal direction and the width direction tend to exceed the predetermined range, which is undesirable because it tends to adversely affect various physical properties such as the shrinkage rate.
• the area magnification is more preferably 5.6 to 13.9 times, and even more preferably 5.7 to 13.8 times. That is, the area magnification is preferably 5.5 to 14 times, more preferably 5.6 to 13.9 times, and even more preferably 5.7 to 13.8 times.
• heat treatment means heat treatment at a temperature of 60°C to 120°C for a time of 1 to 9 seconds. This type of heat treatment is preferably used because it can adjust the heat shrinkage rate. If the heat treatment temperature is lower than 60°C, the above-mentioned effect of the heat treatment is not effectively exhibited. On the other hand, if the heat treatment temperature is higher than 120°C, the heat shrinkage rate in the longitudinal direction is likely to fall below the predetermined range, which is not preferable.
• relaxation in the width direction can be performed by shortening the distance between the gripping clips in the tenter in order to adjust the thermal shrinkage rate in the width direction.
• the relaxation rate is preferably 0% or more and 10% or less. A relaxation rate of 0% means that there is no relaxation.
• one or both of the surface layers may be subjected to a surface treatment.
• the surface treatment include corona treatment, plasma treatment, flame treatment, sandblasting, and coating.
• the purpose of these surface treatments includes improving adhesion and charging properties, and they can be applied within the scope of the present invention.
• the timing of carrying out the surface treatment may be during or after the film formation, and can be selected arbitrarily.
• the label of the present invention is at least partially made of the heat-shrinkable polyester film of the present invention, and may be made of the heat-shrinkable polyester film of the present invention alone or may be bonded to another film.
• the length (circumference) of the label and the number of bonded portions may be arbitrary.
• any conventionally known film can be used in any length.
• the material of the film can also be any material, such as polyester, polyolefin, polyamide, etc.
• the adhesion method required to produce the label of the present invention includes center sealing with a solvent, heat sealing, ultrasonic sealing, hot glue (hot melt) or cold glue, and the like, among which center sealing with a solvent, heat sealing or ultrasonic sealing is preferred.
• the type of solvent that can be used is 1,3-dioxolane, tetrahydrofuran, etc., but is not limited thereto.
• the heat seal strength varies depending on the temperature, pressure and sealing time of the heat seal bar (the surface that contacts the film), and is determined by the combination of these conditions. For example, even if the heat seal temperature is increased, if the sealing time is shortened, the temperature actually applied to the film will be lower.
• the heat sealing temperature is preferably 100° C. or higher and 180° C. or lower, more preferably 110° C. or higher and 170° C. or lower, and even more preferably 120° C. or higher and 160° C. or higher.
• the heat sealing pressure is preferably 0.05 MPa or more and 0.6 MPa or less, more preferably 0.1 MPa or more and 0.55 MPa or less, and even more preferably 0.15 MPa or more and 0.5 MPa or less. If the pressure falls below 0.05 MPa, the seal bar will have difficulty in transferring sufficient heat to the film.
• the heat sealing time is preferably from 0.1 to 3 seconds, more preferably from 0.2 to 2.9 seconds, and even more preferably from 0.3 to 2.8 seconds.
• objects to be packaged with the label of the present invention include plastic containers and PET bottles having a square or round shape.
• Heat shrinkage rate at 80°C for 10 seconds The heat-shrinkable film was cut into a 10 cm x 10 cm square, and immersed in warm water at 80 ⁇ 0.5°C for 10 seconds under no load to cause heat shrinkage. The film was then immersed in water at 25°C ⁇ 0.5°C for 10 seconds and pulled out of the water, after which the longitudinal and transverse dimensions of the film were measured and the heat shrinkage percentage was calculated according to the above formula 1.
• Heat shrinkage rate at 90°C for 10 seconds The heat-shrinkable film was cut into a 10 cm x 10 cm square, and immersed in warm water at 90 ⁇ 0.5°C for 10 seconds under no load to cause heat shrinkage. The film was then immersed in water at 25°C ⁇ 0.5°C for 10 seconds and pulled out of the water, after which the longitudinal and transverse dimensions of the film were measured and the heat shrinkage percentage was calculated according to the above formula 1.
• the length may be less than that (for example, 20 mm in the longitudinal direction and 10 mm in the transverse direction). If the longitudinal size is insufficient, the chuck distance may be 50 mm or less (for example, 10 mm in the transverse direction when the sample length is 20 mm) if one side of the chuck has a length of at least 5 mm to hold the sample.
• the size in the width direction is less than 15 mm, for example, a 5 mm piece is cut out in the width direction, the seal strength is measured, and the strength is converted to a strength per 15 mm width (multiplied by 3 when the width direction is 5 mm).
• the direction in which the seal strength is measured may be arbitrary.
• the refractive index was measured according to JIS K7105.
• the film was cut to a width of 2 cm and a length of 3 cm to prepare a sample.
• the sample was prepared by cutting the sample so that the longitudinal direction of the sample was parallel to the longitudinal direction of the film.
• the refractive index of the sample was measured in the longitudinal direction, width direction, and thickness direction of the film using an Abbe refractometer 4T manufactured by Atago Optical Co., Ltd.
• the solvent used in the measurement was diiodomethane, and the measurement conditions were 23°C and 60 RH%.
• the prepared samples were measured using a temperature-modulated differential scanning calorimeter (DSC) "DSC250" (manufactured by TA Instruments) in MDSC (registered trademark) heat-only mode at an average heating rate of 2°C/min and a modulation period of 40 seconds.
• the reverse heat flow was obtained.
• ⁇ Cp was calculated from the signal that changed stepwise from the baseline. Specifically, at two inflection points that changed stepwise from the baseline, An extension line of the baseline was drawn, and the intersection points with the tangent line at each inflection point (Tg) were determined, and the difference in the horizontal axis value between these intersection points was defined as ⁇ Cp.
• Glass transition temperature (Tg) The sample film was weighed out at 5.0 ⁇ 0.2 mg and placed in a TA Instruments T-zero pan or aluminum pan (flat dish shape), and the sample was melted by heating for 30 seconds on a hot plate heated to 300° C. The sample was then removed from the hot plate with tweezers and immediately immersed in liquid nitrogen for 1 minute to prepare a melt-quenched sample. When the sample was sealed in the pan, the film was layered and punched into a circle (diameter 4.5 mm) with a punch to ensure good adhesion to the bottom of the pan.
• Good adhesion to the bottom of the pan means that when the sample is sealed in the pan, the film sample is not bent in the pan and there is no space between the overlapping films that are firmly pressed down with a lid. It is acceptable for the film before punching to have wrinkles, but it is preferable to stretch the wrinkles before punching the sample.
• the shape and size of the punched sample (punch) are not limited to the above, and it is sufficient that the sample fits into the bottom of the pan without bending.
• the prepared melt-quenched sample was measured using a temperature-modulated differential scanning calorimeter (DSC) "DSC250" (manufactured by TA Instruments) in MDSC (registered trademark) heat-only mode at an average heating rate of 2°C/min and a modulation period of 40 seconds to obtain reverse heat flow.
• DSC temperature-modulated differential scanning calorimeter
• MDSC registered trademark
• Tg was determined as a signal that changed stepwise from the baseline. Specifically, extensions of the baseline of each heat flow were drawn on the lower and higher sides of Tg, and the intersection with the tangent at the inflection point (Tg) was determined. The value on the horizontal axis at this intersection was read, and the average value of the lower and higher sides was determined as Tg.
• the shrinkage direction (lengthwise direction) of the film was set to the circumferential direction of the ring film, and the long sides of the noodle container were secured with the ring film, and the midpoint of the width direction of the ring film and the midpoint of the long side of the container were aligned.
• the amount of slack in the ring film relative to the container was set to 25%.
• the noodle container and the circular film were shrunk by heating for 10 seconds with hot air at a set temperature of 150°C using a hot air shrink tunnel (TORNAD 2500 manufactured by Japan Technology Solutions), and the shrink finish was evaluated.
• ⁇ Wrinkles> The number of wrinkles in the heat-shrunk film was visually counted and rated according to the following criteria. ⁇ : 5 or less wrinkles ⁇ : 6 or more wrinkles
• Distortion amount is 2mm or less
• Distortion amount is more than 2mm
• polyester raw material A a mechanically recycled polyester raw material was prepared by the following procedure. After washing out the remaining beverage and other foreign matter from the PET beverage bottle, the bottle was crushed to obtain flakes. The obtained flakes were washed by stirring in the presence of 3.5 wt% sodium hydroxide solution at a flake concentration of 10 wt% at 85°C for 30 minutes. After the alkaline washing, the flakes were taken out and washed with distilled water under stirring at a flake concentration of 10 wt% at 25°C for 20 minutes. This water washing was repeated two more times by replacing the distilled water.
• the flakes were dried, melted in an extruder, filtered twice more using filters with successively smaller mesh sizes to remove finer foreign matter, and filtered a third time using a filter with the smallest mesh size of 50 ⁇ m to obtain a polyester raw material A having an intrinsic viscosity of 0.75 dl/g and an isophthalic acid content of 2 mol%.
• polyester raw materials C, D, G to I Polyester raw materials C, D, and G to I having the compositions shown in Table 1 were obtained in the same manner as in polyester raw material B. Note that silica (Silysia 266 manufactured by Fuji Silysia Corporation; average particle size 1.5 ⁇ m) was added as a lubricant to polyester raw material C in an amount of 10,000 ppm.
• polyester raw material E a chemically recycled polyester raw material was prepared by the following procedure. From the recovered polyester products, accessories made of materials other than polyester were removed to obtain recovered bales. The recovered bales were put into a wet grinder and immersed in a reducing agent aqueous solution (100°C) containing 1.0 wt% hydrosulfite and 0.3 wt% thiourea dioxide as reducing agents for 60 minutes, whereby deinking treatment was performed by reduction washing. After that, after being finely cut, the bales were fed into a melt extruder, melted at 260-270°C, and unnecessary residues were removed through a screen changer.
• reducing agent aqueous solution 100°C
• the polymer was discharged from the nozzle of the extruder, and the strand-shaped polymer was passed through a water chute and pelletized by a pelletizer.
• the first batch reactor was charged with 13 wt% of the recovered pellets, 61 wt% polyester resin, 25.93 wt% ethylene glycol (EG), and 0.07 wt% tetraethylammonium hydroxide (EAH), and the temperature was raised simultaneously with the charging of the raw materials, and a depolymerization reaction was performed under normal pressure.
• the polyester low polymer produced by this depolymerization reaction was transferred to a second batch reactor and subjected to a polycondensation reaction at 290° C. under reduced pressure (1 mmHg or less) to obtain a chemically recycled polyester raw material E.
• Table 1 The composition is shown in Table 1.
• polyester raw material F By the same method as for polyester raw material E, chemically recycled polyester raw material F having the composition shown in Table 1 was obtained.
• TPA is terephthalic acid
• IPA is isophthalic acid
• EG is ethylene glycol
• NPG is neopentyl glycol
• CHDM is 1,4-cyclohexanedimethanol
• DEG diethylene glycol (which may contain by-products from polymerization)
• BD 1,4-butanediol.
• the intrinsic viscosities of the polyesters were A: 0.75 dl/g, B: 0.72 dl/g, C: 0.72 dl/g, D: 0.75 dl/g, E: 0.75 dl/g, F: 0.75 dl/g, G: 0.75 dl/g, H: 0.78 dl/g, and I: 1.20 dl/g.
• Each polyester was appropriately cut into chips.
• Example 1 Polyester C and polyester F were mixed in a mass ratio of 5:95 and melted in an extruder by heating to 270° C.
• the molten resin was extruded from a T-die and taken up while being cooled on a chill roll set at a surface temperature of 25° C. to obtain an unstretched film.
• the obtained unstretched film was introduced into a longitudinal stretching machine having a plurality of rolls arranged in series, and preheated with a preheating roll until the film temperature reached 105°C. After that, the film was stretched 4.8 times in the longitudinal direction by utilizing the difference in rotation speed between a low-speed rotating roll set to a surface temperature of 105°C and a high-speed rotating roll set to a surface temperature of 30°C.
• the film after the longitudinal stretching was introduced into a transverse stretching machine (tenter), and preheated to a film temperature of 95° C. with both ends of the film held by clips. Thereafter, the film was stretched in the width direction at 80° C. in the first half stretching zone, and at 105° C. in the second half stretching zone to 1.4 times, and transversely stretched to 1.8 times in total in the first and second half stretching zones. The length of each stretching zone was set to 50% of the total zone. After stretching, the film was heat-treated at 95° C. for 5 seconds with the clip interval kept constant. Next, the biaxially stretched film with the main shrinkage direction of about 30 ⁇ m as the longitudinal direction was wound into a roll while cutting and removing both edges of the film. The properties of the obtained film were evaluated by the above-mentioned method. The film-forming conditions and evaluation results are shown in Table 2.
• Example 2 Except for changing various conditions, the same method as in Example 1 was used to produce a biaxially stretched film having a thickness of 13 ⁇ m or 30 ⁇ m, which was then wound into a roll. The properties of the obtained film were evaluated by the above-mentioned methods. The film production conditions and the evaluation results are shown in Table 2.
• the film was stretched twice in the longitudinal direction by utilizing the difference in rotation speed between a low-speed rotating roll set to a surface temperature of 95°C and a high-speed rotating roll set to a surface temperature of 30°C.
• both edges of the film were cut and removed, and the uniaxially stretched film with the main shrinkage direction of about 12 ⁇ m as the longitudinal direction was wound into a roll.
• the properties of the obtained film were evaluated by the above-mentioned method.
• the film formation conditions and the evaluation results are shown in Table 2.
• Example 7 A film was produced in the same manner as in Example 1, except that various conditions were changed, and a biaxially stretched film having a thickness of 30 ⁇ m was wound into a roll. The properties of the obtained film were evaluated by the above-mentioned methods. The film production conditions and the evaluation results are shown in Table 2.
• polyester-based heat-shrinkable films of the examples of the present invention all satisfied the required characteristics and were excellent in productivity and shrink finish.
• Comparative Example 1 was not only inferior in productivity but also lacked the necessary heat shrinkability, making it unsuitable as a heat shrinkable film.
• Comparative Examples 2 to 4 were uniaxially stretched in the machine direction, and therefore not only were the productivity poor, but the difference in the thermal shrinkage rate in the machine direction at 80° C. for 10 seconds and 3 seconds was low, resulting in films with poor shrink finish.
• Comparative Example 5 Although the film was sequentially biaxially stretched in the longitudinal and transverse directions, the difference in refractive index between the longitudinal and transverse directions exceeded the specified range, and thus the film had poor shrink finish properties, similar to Comparative Examples 2 to 4.
• Comparative Example 6 the 130° C. seal strength was low, so that it was not possible to prepare an annular label for evaluating the shrink finish.
• Comparative Example 7 lacked the necessary heat shrinkability and was therefore unsuitable as a heat shrinkable film.
• the present invention makes it possible to provide a heat-shrinkable polyester film that has high productivity and excellent shrink finish.

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