JP6693584B2 - Heat-shrinkable polyester film and package - Google Patents

Description

  The present invention relates to a heat-shrinkable polyester film suitable for heat-shrinkable label applications, and a package using the label.

  In recent years, polyester-based heat that has high heat resistance, is easy to incinerate, and has excellent solvent resistance for label packaging, cap sealing, integrated packaging, etc. that also protects glass bottles or plastic bottles and displays the product Shrinkable films have come to be widely used as shrink labels, and the usage amount thereof tends to increase with the increase of PET (polyethylene terephthalate) bottle containers and the like.

  Heretofore, as a heat-shrinkable polyester film, a film which greatly shrinks in the width direction has been widely used. It is also known that the shrinkage ratio in the longitudinal direction, which is the non-shrinkage direction, is set to a minus value (so-called expansion by heating) in order to improve the shrink finish property (Patent Document 1). The heat-shrinkable polyester film whose width direction is the main shrinkage direction is stretched at a high ratio in the width direction in order to express shrinkage characteristics in the width direction, but in the longitudinal direction orthogonal to the main shrinkage direction. Often, it is only stretched at a low magnification, and some are not stretched. Such a film stretched at a low ratio in the longitudinal direction or a film stretched only in the width direction has a drawback that mechanical strength in the longitudinal direction is poor. Further, when the film is stretched in the longitudinal direction in order to improve the mechanical strength in the longitudinal direction, the mechanical strength in the longitudinal direction increases, but the shrinkage ratio in the longitudinal direction also increases, resulting in poor shrink finish.

  By the way, the conventional heat-shrinkable film has been produced by adjusting the composition and stretching conditions of the polyester so that the hot-water heat shrinkage at 90 ° C. is 40 to 60% (Patent Document 2). Further, even with higher shrinkage, the hot water heat shrinkage at 90 ° C. is 40 to 80% (Patent Document 3), and a high shrinkage film exceeding 80% has not been produced.

  However, recently, there is a demand to cover most of the container with a label for the purpose of protecting the contents and improving the design. Therefore, there has been a demand for a highly shrinkable film having a shrinkage ratio in the width direction of more than 80%. Further, if the shrinkage rate in the longitudinal direction is high, the length of the label in the longitudinal direction becomes short, which is contrary to the desire to cover most of the container with the label. Therefore, there is an increasing demand for a shrinkage ratio in the longitudinal direction of 0 or minus (extend). However, films having high mechanical strength in the longitudinal direction, such as Patent Document 2 and Patent Document 3, do not have a negative shrinkage ratio in the longitudinal direction.

  It is difficult to reduce the shrinkage ratio in the longitudinal direction to a negative value while maintaining the high mechanical strength in the longitudinal direction because it is contradictory to each other. Also has a high shrinkage rate, resulting in poor shrink finish.

Japanese Patent Publication No. 5-33895 Japanese Patent No. 5240387 Japanese Patent No. 5339061

  The present invention solves the above problems, has a high heat shrinkage ratio in the width direction, shows a small heat shrinkage ratio in the longitudinal direction, has a large mechanical strength in the longitudinal direction, has good perforation openability, and shrinks. An object of the present invention is to provide a heat-shrinkable polyester film having excellent finish.

  The present invention which solved the above-mentioned subject is a biaxially stretched heat-shrinkable polyester film characterized by satisfying the following requirements (1) to (5).

(1) Using 1,4-cyclohexanedimethanol as an amorphous monomer in an amount of 5 mol% to 30 mol% in 100 mol% of an alcohol component,
(2) When the film is immersed in hot water of 98 ° C. for 10 seconds, the hot water heat shrinkage ratio is 60% or more and 90% or less in the width direction, which is the main shrinking direction of the film,
(3) The hot water heat shrinkage rate when the film is immersed in hot water of 98 ° C. for 10 seconds is −5% or more% or less in the longitudinal direction which is the direction orthogonal to the main shrinkage direction of the film,
(4) The right-angled tear strength per unit thickness in the direction orthogonal to the main shrinkage direction after shrinking 10% in the main shrinkage direction in warm water of 80 ° C. is 180 N / mm or more and 350 N / mm or less.
(5) The maximum shrinkage stress in the main shrinkage direction of the film measured with hot air at 90 ° C. is 2 MPa or more and 10 MPa or less, and the shrinkage stress after 30 seconds from the start of measurement is 60% or more and 100% or less of the maximum shrinkage stress. ..

  It is also preferable that the heat-shrinkable polyester film of the present invention has a difference of 10% or less in hot water heat shrinkage in the main shrinkage direction at 70 ° C. before and after aging treatment at 30 ° C. and 65% RH for 672 hours. Is.

It is very preferable that the specific heat capacity difference ΔC _p before and after Tg when the reverse heat flow is measured by the temperature modulation DSC is 0.1 J / (g · ° C.) or more and 0.7 J / (g · ° C.) or less. It becomes a shrinkable polyester film.

  The heat-shrinkable polyester film of the present invention is biaxially stretched in a main shrinkage direction and a direction orthogonal to the main shrinkage direction.

  The present invention also includes a label obtained from the heat-shrinkable polyester film, and a package formed by heat-shrinking at least a part of the outer periphery of a packaging target with the label.

  INDUSTRIAL APPLICABILITY In the present invention, it is possible to provide a heat-shrinkable film having a heat shrinkage ratio in the main shrinkage direction (width direction) larger than that in the past and less shrinkage in the direction (longitudinal direction) orthogonal to the main shrinkage direction.

  Further, since the longitudinal-transverse biaxial stretching is performed, the mechanical strength in the longitudinal direction orthogonal to the width direction is also high. Therefore, when it is used as a label for PET bottles or the like, it can be used for a short time in containers such as bottles. It can be mounted very efficiently inside, and when heat-shrinked, a good finish with extremely few wrinkles and insufficient shrinkage can be developed. Further, since the film strength is large, the processing characteristics when printing or tubing are good.

  Furthermore, since the shrinkage stress attenuation rate is small and the shrinkage stress is high after 30 seconds from the start of shrinkage, the followability is good even if the container thermally expands during heating in the label mounting process, and the label does not loosen easily and has a good appearance. Is obtained. In addition, the perforation opening property as a label is good, and when the label is opened, it can be cut cleanly along the perforations from the start of tearing to the completion of tearing.

  Moreover, since the heat-shrinkable polyester film of the present invention is produced by biaxially stretching in the longitudinal and lateral directions, it can be produced very efficiently. Further, the heat-shrinkable polyester film of the present invention has an extremely high adhesive strength when the front and back surfaces (or the same surfaces) are bonded by a solvent, and is suitable for various coated labels such as labels such as PET bottles. Can be used.

  The package wrapped with the label obtained from the heat-shrinkable polyester film of the present invention has a beautiful appearance.

It is explanatory drawing which shows the shape of the test piece for measuring right-angled tear strength. 3 is a shrinkage stress curve of the films of Example 1 and Comparative Example 3. 4 is a reverse heat flow of the film of Example 1 measured by temperature modulation DSC.

  The polyester used in the heat-shrinkable polyester film of the present invention has an ethylene terephthalate unit as a main constituent component. The ethylene terephthalate unit is preferably 50 mol% or more, more preferably 60 mol% or more, still more preferably 70 mol% or more in 100 mol% of the polyester constituent unit.

  Other dicarboxylic acid components constituting the polyester of the present invention include aromatic dicarboxylic acids such as isophthalic acid, orthophthalic acid and 2,6-naphthalenedicarboxylic acid, and fats such as adipic acid, azelaic acid, sebacic acid and decanedicarboxylic acid. Group dicarboxylic acids and alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid and the like can be mentioned. Among these, the details will be described later, but the amount of change from movable amorphous to rigid amorphous due to the stretching process and heat treatment is small, and the change from rigid amorphous to movable amorphous due to relaxation treatment etc. in the stretching process. Examples of the monomer (amorphous monomer) that can be a large amount of amorphous component include isophthalic acid and orthophthalic acid, and more preferable one is isophthalic acid.

  Further, it is preferable that the polyester does not contain a trivalent or higher polyvalent carboxylic acid (for example, trimellitic acid, pyromellitic acid, and their anhydrides). With the heat-shrinkable polyester film obtained by using the polyester containing these polyvalent carboxylic acids, it becomes difficult to achieve the required high shrinkage ratio.

  As the diol component constituting the polyester, in addition to ethylene glycol, 1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol Fats such as 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, 1,4-butanediol, hexanediol, neopentyl glycol and hexanediol Examples thereof include group diols, alicyclic diols such as 1,4-cyclohexanedimethanol, and aromatic diols such as bisphenol A.

  Among these, amorphous components that have a small amount of change from movable amorphous to rigid amorphous due to the stretching process or heat treatment, and have a large amount of change from rigid amorphous to movable amorphous due to relaxation treatment etc. in the stretching process. In the present invention, 1,4-cyclohexanedimethanol is essentially used as an amorphous monomer that can become 5 to 30 mol% in 100 mol% of the alcohol component (requirement (1)). The amount of 1,4-cyclohexanedimethanol is preferably 5 to 28 mol%, more preferably 7 to 27 mol%, and further preferably 10 to 27 mol%. This 1,4-cyclohexanedimethanol also has the effect of reducing the difference in hot water shrinkage in the main shrinkage direction at 70 ° C. before and after aging treatment for 672 hours in an atmosphere of 30 ° C. and humidity of 65% RH%. Therefore, the heat-shrinkable polyester film of the present invention has a small natural shrinkage rate. Further, as another amorphous monomer, a cyclic diol or a diol having 3 to 6 carbon atoms (for example, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, hexanediol, etc.) is used. Of these, neopentyl glycol and 1,4-butanediol are particularly preferable.

  Further, in the polyester, the total amount of the amorphous components in 100 mol% of the polyhydric alcohol component and 100 mol% of the polycarboxylic acid component (that is, in the total 200 mol%) in all the polyester resins is preferably 17 mol% or more, preferably Is 18 mol% or more, more preferably 19 mol% or more, and particularly preferably 20 mol% or more. The upper limit of the total amount of amorphous components is not particularly limited, but 30 mol% is preferable. Thereby, a polyester having a glass transition point (Tg) adjusted to 60 to 80 ° C. is obtained.

  It should be noted that the polyester should not contain a diol having 8 or more carbon atoms (eg octane diol etc.) or a polyhydric alcohol having 3 or more valences (eg trimethylol propane, trimethylol ethane, glycerin, diglycerin etc.). Is preferred. A heat-shrinkable polyester film obtained by using a polyester containing these diols or polyhydric alcohols is difficult to achieve the required high shrinkage ratio. It is also preferable that the polyester contains as little diethylene glycol, triethylene glycol, or polyethylene glycol as possible.

  Among the resins that form the heat-shrinkable polyester film of the present invention, various additives such as waxes, antioxidants, antistatic agents, crystal nucleating agents, viscosity reducing agents, and heat stabilizers are added as needed. Agents, coloring pigments, anti-coloring agents, ultraviolet absorbers and the like can be added.

  In the resin forming the heat-shrinkable polyester film of the present invention, it is preferable to add fine particles as a lubricant for improving the workability (sliding property) of the film. As the fine particles, any one can be selected, for example, as the inorganic fine particles, silica, alumina, titanium dioxide, calcium carbonate, kaolin, barium sulfate, etc., and as the organic fine particles, for example, acrylic resin. Examples thereof include particles, melamine resin particles, silicone resin particles and crosslinked polystyrene particles. The average particle size of the fine particles is in the range of 0.05 to 3.0 μm (when measured with a Coulter counter) and can be appropriately selected as necessary.

  As a method of blending the above particles in the resin forming the heat-shrinkable polyester film, for example, the particles may be added at any stage of producing the polyester resin, but the esterification stage or the transesterification reaction may be performed. After the completion, it is preferable to add it as a slurry dispersed in ethylene glycol or the like at the stage before the start of the polycondensation reaction to proceed the polycondensation reaction. Further, a method of blending a slurry of particles dispersed in ethylene glycol or water with a polyester resin raw material using a kneading extruder with a vent, or using a kneading extruder, dried particles and a polyester resin raw material It is also preferable to carry out by a method of blending with.

  The heat-shrinkable polyester film of the present invention may be subjected to corona treatment, coating treatment, flame treatment or the like in order to improve the adhesiveness of the film surface.

  Next, the characteristics of the heat-shrinkable polyester film of the present invention will be described. The heat-shrinkable polyester film of the present invention is immersed in hot water of 98 ° C. for 10 seconds in an unloaded state, and immediately immersed in water of 25 ° C. ± 0.5 ° C. for 10 seconds. From the length, the heat shrinkage in the width direction (main shrinkage direction) of the film calculated by the following formula 1 (that is, the heat shrinkage of hot water at 98 ° C) is 60% or more and 90% or less (requirement (2)). ..

Thermal shrinkage rate = {(length before shrinkage-length after shrinkage) / length before shrinkage} × 100 (%) Equation 1
If the hot water heat shrinkage ratio in the width direction at 98 ° C. is less than 60%, it is not possible to meet the demand for a high shrinkage film that covers the entire container (so-called full label) and the shrinkage amount is small, so when used as a label. After heat shrinking, the label may be distorted, insufficiently shrunk, wrinkled or loosened. The heat shrinkage of hot water at 98 ° C. is preferably 70% or more, more preferably 75% or more. Since the demand for a film having a hot water heat shrinkage in the width direction at 98 ° C of more than 90% is low, the upper limit of the hot water heat shrinkage was set to 90%.

  The heat-shrinkable polyester film of the present invention has a hot water heat-shrinkage rate of 98 ° C. in the film longitudinal direction (direction orthogonal to the main shrinkage direction) measured in the same manner as above, −5% or more and 12% or less. (Requirement (3)). When the hot water heat shrinkage ratio in the longitudinal direction at 98 ° C. is smaller than −5%, the amount of the film stretched by heating is too large to obtain a good shrinkage appearance when used as a label for a bottle, which is preferable. On the contrary, if the heat shrinkage ratio of hot water in the longitudinal direction at 98 ° C exceeds 12%, the label after heat shrinking becomes shorter (the label height decreases) and the label area becomes smaller, which is not preferable as a full label. In addition, the label tends to be distorted after heat shrinkage, which is not preferable. The hot water heat shrinkage in the longitudinal direction at 98 ° C. is preferably 10% or less, more preferably 7% or less, further preferably 3% or less, particularly preferably 0% or less, most preferably less than 0%.

  In Patent Documents 2 and 3, the shrinkage ratio in the longitudinal direction is adjusted to 0% or more (minimum 4% in the example), 12% or less, or 15% or less by controlling the intermediate heat treatment temperature and the condition of relaxation in the longitudinal direction. Was. That is, in the methods described in these documents, since the film is stretched in the longitudinal direction, it was very difficult to make the hot water heat shrinkage force in the longitudinal direction negative. This is because, when the film is stretched in the width direction after the longitudinal stretching, the necking force acts in the longitudinal direction due to the transverse stretching stress, and the film shrinks slightly in the longitudinal direction. Therefore, the present inventors have succeeded in increasing the amount of movable amorphous material by more appropriately adjusting the intermediate heat treatment temperature and the relaxation rate in the longitudinal direction. Since the movable amorphous is completely amorphous, if there are many movable amorphouss, the necking stress at the time of transverse stretching becomes small, and the shrinkage ratio in the longitudinal direction can be made small. It is considered that the present invention could provide a film having a negative shrinkage ratio in the longitudinal direction even if the film was stretched in the longitudinal direction.

  The heat-shrinkable polyester film of the present invention has a tensile breaking strength in the longitudinal direction of 70 MPa or more and 200 MPa or less (requirement (4)). The method for measuring the tensile fracture strength will be described in Examples. If the tensile strength at break is less than 70 MPa, the "hip" (stiffness) when the label is attached to a bottle or the like becomes weak, which is not preferable. Moreover, it is difficult for the stretching method of the present invention to have a tensile breaking strength of more than 200 MPa. The tensile strength at break is more preferably 90 MPa or higher, and even more preferably 110 MPa or higher. The tensile breaking strength in the longitudinal direction cannot be in the above range unless the longitudinal stretching step is performed.

  The heat-shrinkable polyester film of the present invention has a maximum shrinkage stress of 2 MPa or more and 10 MPa or less in the film width direction measured with hot air of 90 ° C., and a shrinkage stress after 30 seconds from the start of measurement is 60% of the maximum shrinkage stress. % Or more and 100% or less (requirement (5)). The shrinkage stress is measured by the method described in the examples.

  When the maximum shrinkage stress at 90 ° C. in the film width direction is less than 2 MPa, the label may loosen and may not adhere to the bottle when used as a label for a bottle, which is not preferable. The maximum shrinkage stress at 90 ° C. is preferably 3.5 MPa or more, more preferably 5 MPa or more. On the contrary, when the maximum shrinkage stress at 90 ° C. exceeds 10 MPa, the label after heat shrinkage is likely to be distorted. The maximum shrinkage stress at 90 ° C. is preferably 9.5 MPa or less.

  The shrinkage stress after 30 seconds from the start of measurement in hot air at 90 ° C. is 60% or more and 100% or less with respect to the maximum shrinkage stress. That is, the heat-shrinkable polyester film of the present invention exhibits a unique heat-shrink characteristic of exhibiting a shrink stress similar to the maximum heat-shrink stress even 30 seconds after the start of heat shrink. When the shrinkage stress after 30 seconds / maximum shrinkage stress (hereinafter, stress ratio) is less than 60%, when the bottle is covered with the label and heat-shrinked, the followability of the label when the bottle is expanded by heating is poor. If the temperature of the bottle decreases and the thermal expansion disappears after shrinkage, the label becomes loose, which is not preferable. The stress ratio is more preferably 75% or more, further preferably 80% or more, particularly preferably 90% or more. The larger the stress ratio, the better the followability, which is preferable. However, the shrinkage stress after 30 seconds cannot exceed the maximum shrinkage stress, so the upper limit is 100%.

  The heat-shrinkable polyester film of the present invention has a right-angled tear strength in the longitudinal direction when the right-angled tear strength per unit thickness in the longitudinal direction of the film is obtained after shrinking 10% in the width direction in warm water at 80 ° C. The strength is preferably 180 N / mm or more and 350 N / mm or less. The method for measuring the right-angled tear strength in the longitudinal direction will be described in Examples.

  If the right-angled tear strength is less than 180 N / mm, it may be easily broken by an impact such as a drop during transportation when used as a label, which is not preferable. If it is larger than 350 N / mm, the cut property (tearability) at the time of tearing the label becomes poor, which is not preferable. The right-angled tear strength is more preferably 250 N / mm or more, further preferably 280 N / mm or more, and more preferably 330 N / mm or less.

  The heat-shrinkable polyester film of the present invention has a difference in hot water heat shrinkage in the main shrinkage direction at 70 ° C. of 10% or less before and after aging treatment for 672 hours in an atmosphere of 30 ° C. and a humidity of 65% RH. Preferably. The difference in the heat shrinkage rate of hot water is a value (%) obtained by subtracting the shrinkage rate after aging from the shrinkage rate before aging.

  The aging treatment conditions described above assume that the heat-shrinkable film is stored in a warehouse that is not air-conditioned under an atmosphere with a temperature of around 30 ° C. If the shrinking temperature condition during use is not changed according to the film after aging, there is a problem that the shrinking finish is deteriorated. Further, when the film is stored in the above-mentioned warehouse, it is necessary to manage the shrinking temperature condition separately for a film having a long storage period and a film having a short storage period, which is complicated. Therefore, the difference in hot water heat shrinkage at 70 ° C. before and after aging is preferably 10% or less, more preferably 8% or less, and further preferably 5% or less. The effect of reducing the difference in shrinkage ratio before and after aging is mainly an effect of 1,4-cyclohexanedimethanol. For this reason also, in the present invention, 1,4-cyclohexanedimethanol is essentially used in an amount of 5 to 30 mol% in 100 mol% of the alcohol component (requirement (1)). When the content of 1,4-cyclohexanedimethanol is less than 5 mol%, the difference in shrinkage ratio before and after the aging exceeds 10%, which is not preferable.

The heat-shrinkable polyester film of the present invention has a specific heat capacity difference ΔC _p before and after Tg of 0.1 J / (g · ° C.) or more and 0.7 J / (g · ° C.) when reverse heat flow is measured by temperature modulation DSC. ) It is preferable that it is the following. The specific heat capacity difference ΔC _p before and after Tg, which will be described in detail later, corresponds to the amount of mobile amorphous (conventional completely amorphous) in which the molecular chains start to move near Tg. This movable amorphous material can be distinguished from rigid amorphous material in which the molecular chains cannot move unless the temperature becomes higher than Tg. The present inventors have found that the amount of this movable amorphous material affects the heat shrinkage rate. In order to obtain a film with a high thermal shrinkage and which does not easily shrink in the longitudinal direction, it is important to do not change the movable amorphous to the rigid amorphous, or to change most of the rigid amorphous to the movable amorphous. The present invention has been completed, and succeeded in providing a film satisfying all of the above five requirements, and completed the present invention.

When the reverse heat flow of the film sample is measured by the temperature modulation DSC, the baseline shifts at a temperature corresponding to Tg as shown in FIG. The difference between the values before and after the shift is called the specific heat capacity difference ΔC _p , which is said to correspond to the amount of movable amorphous. If ΔC _p is smaller than 0.1 J / (g · ° C.), a high amount of heat-shrinkage cannot be achieved because the amount of movable amorphous is small. ΔC _p is preferably 0.15 J / (g · ° C.) or more, more preferably 0.2 J / (g · ° C.) or more, further preferably 0.3 J / (g · ° C.) or more, and 0.33 J / ( g · ° C.) or higher is particularly preferable. ΔC _p may exceed 0.7 J / (g · ° C.), but the upper limit of the film forming method of the present invention is about 0.7 J / (g · ° C.). is there.

  The heat-shrinkable polyester film of the present invention is not particularly limited, but preferably has a thickness of 10 μm or more and 70 μm or less and a haze value of 2% or more and 13% or less. If the haze value exceeds 13%, the transparency becomes poor and the appearance may be deteriorated during label production, which is not preferable. The haze value is more preferably 11% or less, and particularly preferably 9% or less. Further, the smaller the haze value is, the more preferable. However, considering that it is necessary to add a predetermined amount of lubricant to the film for the purpose of imparting the slipperiness necessary for practical use, the lower limit is about 2%.

  The heat-shrinkable polyester film of the present invention, the polyester raw material described above is melt-extruded by an extruder to form an unstretched film, and the unstretched film is biaxially stretched and heat-treated by a predetermined method shown below. Can be obtained by The polyester can be obtained by polycondensing the above-mentioned suitable dicarboxylic acid component and diol component by a known method. Further, usually, two or more kinds of chip-shaped polyester are mixed and used as a raw material of a film.

  When the raw material resin is melt-extruded, 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, it is melted at a temperature of 200 to 300 ° C. and extruded into a film using an extruder. For extrusion, any existing method such as a T-die method or a tubular method can be adopted.

  Then, an unstretched film can be obtained by rapidly cooling the sheet-shaped molten resin after extrusion. As a method of rapidly cooling the molten resin, a method of obtaining a substantially unoriented resin sheet by casting the molten resin from a die onto a rotating drum and rapidly solidifying it can be suitably adopted.

  Further, the resulting unstretched film, as described below, stretched in the width direction under predetermined conditions, after the longitudinally stretched film is annealed and then rapidly cooled, then heat-treated, the heat-treated film The heat-shrinkable polyester film of the present invention can be obtained by cooling the film under predetermined conditions, stretching it in the width direction under predetermined conditions, and then heat-treating it again. Hereinafter, a preferable film forming method for obtaining the heat-shrinkable polyester film of the present invention will be described.

[Method for forming heat-shrinkable polyester film of the present invention]
In order to obtain a heat-shrinkable polyester film having high mechanical strength in the longitudinal direction and excellent perforation opening property, as described in Patent Document 2 and Patent Document 3, the present inventors It was found that it is necessary to allow "molecules that are oriented but do not contribute to the shrinkage force" to be present in the film, and as a result, the film is stretched in the machine direction (longitudinal direction) and then in the width direction. -The transverse stretching method is adopted. In this longitudinal-transverse stretching method, after the longitudinal stretching, an intermediate heat treatment is performed before the transverse stretching in order to relax the longitudinal shrinkage force.

  One of the methods for obtaining a film with higher shrinkage is to increase the amount of an amorphous monomer (amorphous component) that constitutes a unit that can be amorphous in the film. In the film obtained by the conventional transverse uniaxial stretching method, it has been recognized that by increasing the amount of the amorphous component, the shrinkage ratio corresponding to it is increased. However, it was found that the film obtained by the above-mentioned longitudinal-transverse stretching method found by the present inventors did not show an increase in shrinkage ratio commensurate with the increased amount even if the amount of the amorphous component was increased. If the amount of the amorphous component is further increased, the thickness unevenness becomes large and the productivity deteriorates.

  Further, as a result of examination by the present inventors, it was found that there is almost no correlation between the crystallinity and the heat shrinkage, or the heat of fusion and the heat shrinkage. From these, it is considered that the polyester is not divided into two phases, a crystalline phase and an amorphous phase, but is divided into a crystalline phase and three phases, a movable amorphous phase and a rigid amorphous phase. It was

  This rigid amorphous is an intermediate state between crystalline and movable amorphous (conventional completely amorphous), and the molecular motion is frozen even at a glass transition temperature (Tg) or higher, and becomes a fluid state at a temperature higher than Tg. Amorphous (for example, Minoru Toki, "DSC (3) -Glass transition behavior of polymers-", Textile Society of Japan (Fiber and Industry), Vol. 65, No. 10 (2009)). The rigid amorphous amount (ratio) can be expressed by 100% -crystallinity-movable amorphous amount.

  Then, when the relationship between the amount of movable amorphous and the thermal contraction rate was examined, it was found that there was a correlation between them. Furthermore, when the movable amorphous amount of the unstretched sheet, the film after longitudinal stretching, the film after the final heat treatment, etc. was measured, the movable amorphous amount was higher than that of the unstretched film among the films after longitudinal stretching and intermediate heat treatment. It was considered that the film with a large decrease in C could not exhibit a high heat shrinkage, and the mobile amorphous had changed to a rigid amorphous.

  Therefore, the present inventors have examined the conditions for longitudinal stretching and intermediate heat treatment, and the relaxation conditions in the longitudinal direction, and have studied the amorphous component with a small rate of change from movable amorphous to rigid amorphous, or movable from rigid amorphous. He continued to study to find an amorphous component having a large rate of change to an amorphous state, and succeeded in obtaining a film satisfying all the above five requirements.

The heat-shrinkable polyester film of the present invention is formed by the following procedure.
(1) Control of longitudinal stretching conditions (2) Intermediate heat treatment after longitudinal stretching (3) Natural cooling (interruption of heating) between intermediate heat treatment and transverse stretching
(4) Forced cooling of the film after natural cooling (5) Control of transverse stretching conditions (6) Heat treatment after transverse stretching and relaxation in the width direction (7) Relax in the longitudinal direction twice or more during the above manufacturing process Providing Steps Hereinafter, each of the above means will be sequentially described.

(1) Control of longitudinal stretching conditions In the production of the film by the longitudinal-transverse stretching method of the present invention, the stretching temperature is Tg or more and Tg + 30 ° C. or less, and longitudinal stretching is performed so as to be 3.3 times or more and 4.6 times or less. There is a need. As the longitudinal stretching, either one-stage stretching or two-stage or more multi-stage stretching can be used.

  If the stretching temperature is too high or the total longitudinal stretching ratio is increased during stretching in the longitudinal direction, the amorphous molecules are stretched, and the heat shrinkage ratio in the longitudinal direction tends to increase. Further, if the longitudinal stretching ratio is too large, the oriented crystallization of the film after longitudinal stretching proceeds, the movable amorphous changes to rigid amorphous, and the rigid amorphous is crystallized, so that breakage easily occurs in the transverse stretching process. However, the shrinkage ratio in the transverse direction after transverse stretching is also reduced, which is not preferable. Therefore, the upper limit of the longitudinal stretching ratio is 4.6 times. The longitudinal stretching ratio is more preferably 4.5 times or less, further preferably 4.4 times or less. On the other hand, if the longitudinal stretching ratio is too small, the shrinkage ratio in the longitudinal direction becomes small, but the degree of molecular orientation in the longitudinal direction also becomes small, the right-angled tear strength in the longitudinal direction becomes large, and the tensile fracture strength becomes small, which is preferable. Absent. The longitudinal stretching ratio is preferably 3.3 times or more, more preferably 3.4 times or more, and further preferably 3.5 times or more.

(2) Intermediate heat treatment after longitudinal stretching In order to thermally relax the molecules oriented in the longitudinal direction, heat treatment is performed after longitudinal stretching. At this time, after the unstretched film was longitudinally stretched, in a state where both ends in the width direction were gripped by clips in a tenter, at a temperature of Tg + 40 ° C. or higher and Tg + 65 ° C. or lower for a time of 6.0 seconds or more and 12.0 seconds or less. It is necessary to perform heat treatment (hereinafter referred to as intermediate heat treatment).

  In addition, the temperature of the intermediate heat treatment is more preferably Tg + 41 ° C. or higher, further preferably Tg + 42 ° C. or higher, more preferably Tg + 63 ° C. or lower, and further preferably Tg + 60 ° C. or lower. If the temperature of the intermediate heat treatment is too high, the molecular chains oriented by the longitudinal stretching change into crystals, and it becomes impossible to obtain a high heat shrinkage rate after the lateral stretching. On the other hand, the time of the intermediate heat treatment needs to be appropriately adjusted within the range of 6.0 seconds or more and 12.0 seconds or less according to the raw material composition. The amount of heat given to the film is important for the intermediate heat treatment, and if the temperature of the intermediate heat treatment is low, the intermediate heat treatment for a long time is required. However, if the intermediate heat treatment time is too long, the equipment becomes huge, so it is preferable to appropriately adjust the temperature and time.

  By maintaining the temperature of the intermediate heat treatment at Tg + 40 ° C. or higher, it is possible to increase the degree of molecular orientation in the longitudinal direction, and it is possible to keep the tensile breaking strength in the longitudinal direction large while keeping the right-angled tear strength small. .. On the other hand, by controlling the temperature of the intermediate heat treatment to Tg + 65 ° C. or lower, the crystallization of the film can be suppressed, and the shrinkage ratio in the longitudinal direction can be reduced not by crystallization but by conversion from movable amorphous to rigid amorphous. To do. Since crystals are in a very tightly oriented state in which molecular chains are folded, once crystallized, the amount of crystals does not decrease even if the stretching method is changed thereafter. However, since rigid amorphous is in an orientation state in which the constraint is looser than that of crystals, it can be changed from rigid amorphous to movable amorphous by relaxation (relaxation) in the subsequent stretching step. Therefore, by setting the temperature of the intermediate heat treatment to Tg + 65 ° C. or lower, crystallization can be suppressed and the shrinkage ratio in the width direction can be increased. Further, by controlling the temperature of the intermediate heat treatment to Tg + 65 ° C. or lower, crystallization of the surface layer of the film can be suppressed, the solvent adhesive strength can be kept high, and the thickness unevenness in the longitudinal direction can be reduced.

(3) Natural cooling (interruption of heating) between intermediate heat treatment and transverse stretching
In the production of the film by the longitudinal-transverse stretching method of the present invention, it is necessary to perform an intermediate heat treatment after the longitudinal stretching, but after the longitudinal stretching and the intermediate heat treatment, a time period of 0.5 seconds or more and 3.0 seconds or less is required. It is necessary to pass the film through an intermediate zone that does not perform an aggressive heating operation. That is, an intermediate zone is provided in front of the transverse stretching zone of the tenter for transverse stretching, the film after the intermediate heat treatment after longitudinal stretching is introduced into the tenter, and after passing through this intermediate zone for a predetermined time, the transverse It is preferable to carry out stretching. In addition, in the intermediate zone, when a strip-shaped piece of paper hangs down without passing through the film, the accompanying flow and cooling zone accompanying the running of the film so that the piece of paper hangs almost completely in the vertical direction. It is preferable to block the hot air from. If the time for passing through the intermediate zone is less than 0.5 seconds, the transverse stretching becomes a high temperature stretching, and the transverse shrinkage cannot be sufficiently increased, which is not preferable. On the contrary, it is sufficient that the time for passing through the intermediate zone is as long as 3.0 seconds, and it is not preferable to set the length longer than that because the equipment is wasted. The time for passing through the intermediate zone is more preferably 0.7 seconds or more, further preferably 0.9 seconds or more, more preferably 2.8 seconds or less, and further preferably 2.6 seconds or less.

(4) Forced cooling of the film after natural cooling In the production of the film by the longitudinal-transverse stretching method of the present invention, the naturally cooled film is not laterally stretched as it is, but the temperature of the film is Tg or more and Tg + 40 ° C or less. Therefore, it is necessary to actively perform forced cooling. By performing such forced cooling treatment, it becomes possible to obtain a film having a good perforation opening property when it is used as a label. The temperature of the film after forced cooling is more preferably Tg + 2 ° C. or higher, further preferably Tg + 4 ° C. or higher, more preferably Tg + 35 ° C. or lower, still more preferably Tg + 30 ° C. or lower.

  When the film is forcibly cooled and the temperature of the film after the forcible cooling is still higher than Tg + 40 ° C., the shrinkage ratio of the film in the width direction becomes low, and the shrinkability when used as a label becomes insufficient. However, by controlling the temperature of the film after the forced cooling to be Tg + 40 ° C. or lower, it is possible to maintain a large shrinkage ratio in the width direction of the film. Further, if the temperature of the film after forced cooling remains higher than Tg + 40 ° C., the stress of transverse stretching performed after cooling becomes small, the shrinkage stress in the width direction becomes small, and the followability to the bottle deteriorates. By carrying out forced cooling so that the temperature of the film after cooling becomes Tg + 40 ° C. or lower, it becomes possible to maintain a large shrinkage stress in the width direction.

  Further, when the film is forcibly cooled and the temperature of the film after the forcible cooling is still higher than Tg + 40 ° C., the stress of the lateral stretching performed after the cooling becomes small and the thickness unevenness in the width direction tends to become large. However, by performing forced cooling so that the temperature of the film after cooling becomes Tg + 40 ° C. or less, it is possible to increase the stress of transverse stretching performed after cooling and reduce the thickness unevenness in the width direction.

(5) Control of transverse stretching conditions The transverse stretching is performed in a tenter while holding both ends in the width direction with clips at a temperature of Tg + 10 ° C. or higher and Tg + 40 ° C. or lower so that the ratio is from 3 times to 7 times. There is a need. By transversely stretching under such a predetermined condition, it becomes possible to orient the molecules in the width direction and develop a high shrinkage force in the width direction, and to obtain a film having good perforation opening properties when used as a label. Is possible. The transverse stretching temperature is more preferably Tg + 13 ° C or higher, further preferably Tg + 16 ° C or higher, more preferably Tg + 37 ° C or lower, and further preferably Tg + 34 ° C or lower. On the other hand, the transverse stretching ratio is more preferably 3.5 times or more, further preferably 4 times or more, more preferably 6.5 times or less, and further preferably 6 times or less.

  When stretching in the transverse direction, if the stretching temperature exceeds Tg + 40 ° C, the shrinkage ratio in the width direction becomes small, but by controlling the stretching temperature to Tg + 40 ° C or less, the shrinkage ratio in the width direction should be increased. Is possible. If the stretching temperature is higher than Tg + 40 ° C, the lateral stretching stress is reduced, the shrinking stress in the width direction is reduced, and the followability to the bottle is deteriorated. By controlling the transverse stretching temperature to be Tg + 40 ° C. or lower, the shrinkage stress in the width direction can be increased. Furthermore, when the temperature of the film exceeds Tg + 40 ° C., the stretching stress in the transverse stretching tends to be small, and thickness unevenness in the width direction tends to be large. By controlling the transverse stretching temperature to be Tg + 40 ° C. or lower, the stress of transverse stretching can be increased and the thickness unevenness in the width direction can be reduced.

  On the other hand, when the stretching temperature is lower than Tg + 10 ° C., the degree of molecular orientation in the width direction becomes too large, and the film tends to break during transverse stretching, and the voids inside the film increase, so that the haze of the film increases. Is not preferable.

(6) Heat treatment after lateral stretching (final heat treatment) and relaxation in the width direction The film after transverse stretching is held at a temperature of Tg ° C or higher and Tg + 50 ° C or lower in a state in which the widthwise ends of the film are held by clips. The final heat treatment is required for a time period of 1 second or more and 9 seconds or less. When the heat treatment temperature is higher than Tg + 50 ° C., the number of movable amorphous materials decreases, the shrinkage ratio in the width direction decreases, and the heat shrinkage ratio at 98 ° C. becomes less than 60%, which is not preferable. Further, if the heat treatment temperature is lower than Tg, it cannot be sufficiently relaxed in the width direction, and when the final product is stored at room temperature, the shrinkage in the width direction with time (so-called natural shrinkage rate) becomes large, which is not preferable. Further, the longer the heat treatment time is, the better, but if the heat treatment time is too long, the equipment becomes huge.

  In the present invention, it is preferable to relax in the width direction during the heat treatment in the width direction. The heat treatment with a fixed length is not preferable because the movable amorphous material is converted into the rigid amorphous material, the rigid amorphous material amount increases, and the shrinkage stress in the width direction becomes too high. Conventionally, it has been thought that when the width direction is relaxed, the shrinkage rate in the width direction is reduced. However, as a result of examination by the present inventors, it has been found that at a relaxation rate of 1 to 6%, the number of movable amorphous particles in the width direction increases, and the shrinkage rate in the width direction does not decrease but only the contraction stress decreases. Was given. Although the shrinkage rate is determined by the amount of mobile amorphous and the molecular orientation, the relaxation in the width direction decreases the molecular orientation, but the amount of mobile amorphous increases, so the shrinkage rate in the width direction does not decrease and only the shrinkage stress Is considered to have decreased.

(7) Longitudinal relaxation (relaxation) step In order to increase the number of movable amorphous particles and reduce the longitudinal shrinkage, the molecules oriented in the longitudinal direction by longitudinal stretching are thermally relaxed (relaxed). Is preferred. If the residual shrinkage stress in the longitudinal direction of the film after longitudinal stretching is large, the hot water heat shrinkage ratio in the longitudinal direction of the film after transverse stretching becomes large, and there is a drawback that the shrinkage finish property deteriorates. Heat treatment in the transverse stretching step is effective in reducing the hot water heat shrinkage in the longitudinal direction of the film, but relaxation by heat alone increases the number of crystals in the film and increases the shrinkage in the width direction. Not suitable.

  Therefore, as a result of examination by the present inventors, it was discovered that the bulk, which has been changed from movable amorphous to rigid amorphous by stretching or heat treatment, can be changed from rigid amorphous to movable amorphous by relaxation. Therefore, in order to increase the shrinkage ratio in the width direction and decrease the shrinkage ratio in the longitudinal direction, one of the effective means is to stretch in the longitudinal direction and then relax in the longitudinal direction. In addition, a means for controlling the right-angled tear strength and the tensile fracture strength in the longitudinal direction was studied by imparting a certain amount of rigid amorphous or crystal to the molecular chain in the longitudinal direction even if it relaxes in the longitudinal direction. Then, they have found that the film can be controlled by relaxing the film in the longitudinal direction by the means shown below. In addition, it is desirable to perform any two steps or all three steps of the following (i) to (iii).

  (i) The film after longitudinal stretching is heated at a temperature of Tg or more and Tg + 60 ° C. or less, and a roll having a speed difference is used, and in a time of 0.05 seconds or more and 5 seconds or less, 10% or more and 50% or less in the longitudinal direction. The process of performing relaxation. As the heating means, any of temperature control roll, near infrared ray, far infrared ray, hot air heater and the like can be used.

  (ii) In the intermediate heat treatment step, by shortening the distance between the gripping clips in the facing tenter, Tg + 40 ° C. or more and Tg + 60 ° C. or less, 0.1 second or more and 12 seconds or less, and 21% or more 40% in the longitudinal direction. % Or less The process of performing relaxation.

  (iii) In the final heat treatment step, by shortening the distance between the gripping clips in the opposing tenter, Tg or more and Tg + 50 ° C. or less, and 0.1% or more and 9 seconds or less, and 21% or more and 40% in the longitudinal direction. Below is the process of performing relaxation.

  Each step will be described below.

(i) Relaxation after longitudinal stretching The film after longitudinal stretching is heated at a temperature of Tg or more and Tg + 60 ° C. or less, and in a longitudinal direction for 0.05 seconds or more and 5.0 seconds or less using a roll having a speed difference. It is desirable to perform relaxation of 10% or more and 50% or less. If the temperature is lower than Tg, the film after longitudinal stretching does not shrink and relaxation cannot be performed, which is not preferable. On the other hand, if the temperature is higher than Tg + 60 ° C., the film is crystallized and the transparency and the like deteriorate, which is not preferable. The film temperature during relaxation is more preferably Tg + 10 ° C. or higher and Tg + 55 ° C. or lower, and even more preferably Tg + 20 ° C. or higher and Tg + 50 ° C. or lower.

  The time for relaxing the film in the longitudinal direction after longitudinal stretching is preferably 0.05 seconds or more and 5 seconds or less. If it is less than 0.05 seconds, the relaxation becomes short, and if the temperature is not higher than Tg + 60 ° C., relaxation unevenness occurs, which is not preferable. If the relaxation time is longer than 5 seconds, the film can be relaxed at a low temperature and there is no problem as a film, but since the equipment becomes huge, it is preferable to appropriately adjust the temperature and time. The relaxation time is more preferably 0.1 seconds or more and 4.5 seconds or less, and further preferably 0.5 seconds or more and 4 seconds or less.

  If the longitudinal relaxation rate of the film after longitudinal stretching is less than 10%, the molecular orientation in the longitudinal direction cannot be sufficiently relaxed, and the amount of change from rigid amorphous to movable amorphous is small, which is not preferable. If the relaxation rate in the longitudinal direction of the film after longitudinal stretching is larger than 50%, the right-angled tear strength in the longitudinal direction increases and the tensile breaking strength decreases, which is not preferable. After the longitudinal stretching, the relaxation rate of the film is more preferably 15% or more and 45% or less, still more preferably 20% or more and 40% or less.

  As a means for relaxing the film after longitudinal stretching, a method in which the film after longitudinal stretching is heated by a heating device (heating furnace) arranged between rolls, and the method is carried out by a speed difference between the rolls, or a film after longitudinal stretching Is heated by a heating device (heating furnace) arranged between the roll and the transverse stretching machine, and the speed of the transverse stretching machine is slower than that of the roll. As the heating device (heating furnace), any one of a temperature control roll, a near infrared heater, a far infrared heater, a hot air heater and the like can be used.

(ii) Relaxation in the intermediate heat treatment step In the intermediate heat treatment step, the distance between the gripping clips in the opposing tenter is shortened to reduce the distance from 0.1% to 12 seconds in the longitudinal direction to 21% to 40%. The following relaxations are recommended. If the relaxation rate is less than 21%, the molecular orientation in the longitudinal direction cannot be sufficiently relaxed, and the amount of change from rigid amorphous to movable amorphous is small, which is not preferable. If the relaxation rate is greater than 40%, the right-angled tear strength in the longitudinal direction increases and the tensile fracture strength decreases, which is not preferable. The relaxation rate is more preferably 22% or more, more preferably 38% or less, and further preferably 36% or less.

  The time for relaxing in the longitudinal direction in the intermediate heat treatment step is preferably 0.1 seconds or more and 12 seconds or less. If it is less than 0.1 seconds, the relaxation becomes short, and if the temperature is not higher than Tg + 60 ° C., relaxation unevenness occurs, which is not preferable. Further, if the relaxation time is longer than 12 seconds, there is no problem as a film, but since the equipment becomes huge, it is preferable to appropriately adjust the temperature and time. The relaxation time is more preferably 0.3 seconds or more and 11 seconds or less, and further preferably 0.5 seconds or more and 10 seconds or less.

(iii) Relaxation in the final heat treatment step In the final heat treatment step, the distance between the gripping clips in the opposing tenter is shortened so that 21% or more and 40% in the longitudinal direction in the time of 0.1 seconds or more and 9 seconds or less. The following relaxations are recommended. If the relaxation rate is less than 21%, the molecular orientation in the longitudinal direction cannot be sufficiently relaxed, and the amount of change from rigid amorphous to movable amorphous is small, which is not preferable. If the relaxation rate is greater than 40%, the right-angled tear strength in the longitudinal direction increases and the tensile fracture strength decreases, which is not preferable. The relaxation rate is more preferably 22% or more, more preferably 38% or less, and further preferably 36% or less.

  Further, the time for relaxing in the longitudinal direction in the final heat treatment step is preferably 0.1 seconds or more and 9 seconds or less. If it is less than 0.1 seconds, the relaxation becomes short, and if the temperature is not higher than Tg + 50 ° C., relaxation unevenness occurs, which is not preferable. Further, if the relaxing time is longer than 9 seconds, there is no problem as a film, but since the equipment becomes huge, it is preferable to appropriately adjust the temperature and time. The relaxation time is more preferably 0.3 seconds or more and 8 seconds or less, and further preferably 0.5 seconds or more and 7 seconds or less.

  The package of the present invention is one in which a label having perforations or notches obtained from the heat-shrinkable polyester film of the present invention is formed by covering at least a part of the outer periphery of a packaging target and thermally shrinking the label. Is. Examples of the object to be packaged include PET bottles for beverages, various bottles, cans, plastic containers such as confectionery and bento, and paper boxes. In general, when a label obtained from a heat-shrinkable polyester film is coated on these packaging objects by heat-shrinking, the label is heat-shrinked by about 5 to 70% and brought into close contact with the package. .. The label covered with the object to be packaged may be printed or may not be printed.

  As a method for producing a label, an organic solvent is applied slightly inward from one end of a rectangular film, and the film is immediately rolled to form a label by laminating and adhering the ends, or a roll. The organic solvent is applied a little inward from the edge of one side of the film wound into a roll, the film is immediately rolled and the edges are overlapped and bonded, and the tube is cut into a label. .. As an organic solvent for adhesion, cyclic ethers such as 1,3-dioxolane or tetrahydrofuran are preferable. In addition, aromatic hydrocarbons such as benzene, toluene, xylene and trimethylbenzene, halogenated hydrocarbons such as methylene chloride and chloroform, phenols such as phenol and mixtures thereof can be used.

  Next, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to the modes of these Examples, and may be appropriately performed without departing from the spirit of the present invention. It is possible to change. The evaluation method of the film is shown below.

[Heat Shrinkage (Hot Water Heat Shrinkage)]
The film is cut into squares of 10 cm x 10 cm, immersed in warm water of 98 ° C ± 0.5 ° C for 10 seconds in a no-load state to cause heat shrinkage, and then immersed in water of 25 ° C ± 0.5 ° C for 10 seconds. Then, the film was taken out from the water, the longitudinal and lateral dimensions of the film were measured, and the heat shrinkage rate was calculated according to the following formula 1. The direction in which the heat shrinkage was large was defined as the main shrinkage direction.
Thermal shrinkage rate = {(length before shrinkage-length after shrinkage) / length before shrinkage} × 100 (%) Equation 1

[Difference in shrinkage before and after aging]
The hot water heat shrinkage of the film before aging in the main shrinkage direction of 70 ° C. was obtained in the same manner as above except that hot water of 70 ° C. ± 0.5 ° C. was used. Similarly, for the film after aging for 672 hours, the hot water heat shrinkage in the main shrinkage direction of 70 ° C is obtained, and the hot water heat shrinkage after aging is subtracted from the hot water heat shrinkage before aging to obtain the difference in shrinkage. (%) Was calculated.

[Shrinkage stress]
A sample with a length of 200 mm in the main shrinkage direction and a width of 20 mm was cut out from the heat-shrinkable film, and a strong elongation measuring machine with a heating furnace manufactured by Toyo Baldwin Co., Ltd. (currently, Orientec Co., Ltd.) (Tensilon (registered trademark of Orientec Co. Ltd. )). The heating furnace was heated to 90 ° C. in advance, and the chuck distance was 100 mm. The air blowing of the heating furnace was once stopped, the door of the heating furnace was opened, the sample was attached to the chuck, and then the door of the heating furnace was quickly closed to restart the air blowing. The shrinkage stress was measured for 30 seconds or more, the shrinkage stress (MPa) after 30 seconds was determined, and the maximum value during the measurement was defined as the maximum shrinkage stress (MPa). Further, the ratio (percentage) of the shrinkage stress after 30 seconds to the maximum shrinkage stress was defined as the stress ratio (%).

[Right angle tear strength]
The film is mounted in a rectangular frame having a predetermined length in a loosened state (that is, both ends of the film are held by the frame). Then, the film was shrunk by 10% in the width direction by immersing the film in warm water at 80 ° C. for about 5 seconds until the film became strained in the frame (until the slack disappeared). A test piece having the shape shown in FIG. 1 was cut out from the film after 10% shrinkage according to JIS-K-7128-3. When the test piece was cut out, the longitudinal direction of the film was set to the tearing direction. Further, in FIG. 1, the unit of length is mm, and R represents a radius. Next, a universal tensile tester (“Autograph” manufactured by Shimadzu Corporation) was used to grasp both ends (width direction) of the test piece, and a tensile test was performed at a pulling speed of 200 mm / min to completely tear the film in the longitudinal direction. The maximum load was measured. This maximum load was divided by the thickness of the film to calculate the right-angled tear strength per unit thickness.

[Tensile fracture strength]
A strip-shaped test piece having a measuring direction (longitudinal direction of the film) of 140 mm and a direction (film width direction) orthogonal to the measuring direction of 20 mm was prepared. Using a universal tensile tester "DSS-100" (manufactured by Shimadzu Corp.), hold both ends of the test piece with chucks by 20 mm on each side (distance between chucks: 100 mm), conditions of atmospheric temperature 23 ° C, pulling speed 200 mm / min The tensile test was conducted at and the strength (stress) at the time of tensile fracture was defined as the tensile fracture strength.

[Label shrinkage distortion]
Both ends of each of the heat-shrinkable films before and after aging were adhered with dioxolane to produce a cylindrical label (a label having the main shrinkage direction of the heat-shrinkable film in the circumferential direction). A 500 ml square PET bottle (body circumference 215 mm, minimum neck length 87 mm) is covered with a label, and it is put in a Fuji Astec Inc steam tunnel (model; SH-1500-L) at a zone temperature of 90 ° C. in 5 seconds. The label was heat-shrinked by passing it and attached to the bottle. In addition, at the time of mounting, the neck portion was adjusted so that a portion having a peripheral length of 103 mm (position at a label height of 170 mm) was one end of the label. As an evaluation of the finishability after shrinkage, the strain in the 360 ° direction on the upper side of the attached label was measured using a gauge, and the maximum strain value was obtained. It evaluated according to the following criteria.
◎: Maximum strain less than 2.0 mm ○: Maximum strain 2.0 mm or more and less than 3.0 mm ×: Maximum strain 3.0 mm or more

[Label adhesion]
The label was attached to the PET bottle under the same conditions as the above-described contraction strain condition of the label. Label adhesion was evaluated according to the following criteria.
⊚: There is no slack between the mounted label and the PET bottle, and the label does not move when the bottle cap is fixed and the label is twisted.
A: The label does not move when the bottle cap is fixed and the label is twisted, but there is some slack between the label and the PET bottle.
X: The label is displaced when the bottle cap is fixed and the label is twisted.

[Label wrinkles]
The label was attached to a PET bottle under the same conditions as the contraction strain of the label described above, and the state of occurrence of wrinkles was evaluated according to the following criteria.
A: The number of wrinkles having a size of 2 mm or more is zero.
◯: The number of wrinkles having a size of 2 mm or more is 1 or more and 2 or less.
X: The number of wrinkles having a size of 2 mm or more is 3 or more.

[Label height]
A label (height: 170 mm) was attached to a PET bottle under the same conditions as the label shrinkage strain described above. The height of the label was measured and evaluated according to the following criteria.
◎: Label height is 169 mm or more ○: Label height is 167 mm or more and less than 169 mm ×: Label height is less than 167 mm

[Open perforation]
The label in which the perforation was made in the direction orthogonal to the main shrinkage direction in advance was mounted on the PET bottle under the same conditions as the shrinkage strain of the label described above. However, perforations were formed by inserting holes having a length of 1 mm at intervals of 1 mm, and two perforations were provided in the lengthwise direction (height direction) of the label with a width of 22 mm and a length of 185 mm. Then, fill this bottle with 500 ml of water, refrigerate at 5 ° C, tear the perforations on the label of the bottle immediately after taking it out from the refrigerator with your fingertips, do not tear it cleanly along the perforations in the vertical direction, or The number that could not be removed from the bottle was counted, and the perforation opening failure rate (%) for all 50 samples was calculated. If the perforation opening failure rate is 20% or less, it is practically acceptable.

[Specific heat capacity difference before and after Tg ΔC _p ]
Using a temperature modulation differential scanning calorimeter (TM DSC) "Q100" (manufactured by TA instruments), 10 mg of the film was weighed in a hermetic aluminum pan, and in a heat-only mode, an average heating rate of 1 ° C / min and a modulation cycle of 40. Get the reverse heat flow in seconds. The difference between the values of the obtained reverse heat flow before and after Tg was defined as the specific heat capacity difference ΔC _p .

<Preparation of polyester raw material>
In a stainless steel autoclave equipped with a stirrer, a thermometer and a partial reflux condenser, 100 mol% of dimethyl terephthalate (DMT) as a dibasic acid component and 100 mol% of ethylene glycol (EG) as a glycol component were mixed with ethylene. The glycol was charged so that the molar ratio would be 2.2 times that of dimethyl terephthalate, and 0.05 mol% of zinc acetate (based on the acid component) was used as the transesterification catalyst to distill off the produced methanol out of the system. While carrying out the transesterification reaction. After that, 0.025 mol% of antimony trioxide (based on the acid component) was added as a polycondensation catalyst, and the polycondensation reaction was performed at a reduced pressure of 280 ° C. and 26.6 Pa (0.2 torr) to obtain an intrinsic viscosity. 0.70 dl / g polyester (A) was obtained. This polyester is polyethylene terephthalate. In the production of the polyester (A), SiO ₂ (Silysia 266 manufactured by Fuji Silysia Chemical Ltd.) was added as a lubricant at a ratio of 8,000 ppm with respect to the polyester. Further, the polyesters (B, C, D, E, F) shown in Table 1 were synthesized by the same method as above. In the table, IPA is isophthalic acid, CHDM is 1,4-cyclohexanedimethanol, NPG is neopentyl glycol, and BD is 1,4-butanediol. The intrinsic viscosities of polyesters A, B, C, D, E and F are 0.70 dl / g, 0.70 dl / g, 0.73 dl / g, 0.73 dl / g, 0.70 dl / g and 0, respectively. It was 0.80 dl / g. Each polyester was appropriately made into a chip shape.

  Tables 1 and 2 show the compositions of the polyester raw materials used in Examples and Comparative Examples, the resin compositions of the films in Examples and Comparative Examples, and the production conditions.

Example 1
The above-mentioned polyester A, polyester B and polyester C were mixed in a mass ratio of 5:15:80 and charged into an extruder. This mixed resin was melted at 280 ° C., extruded from a T-die, wound on a rotating metal roll cooled to a surface temperature of 30 ° C., and rapidly cooled to obtain an unstretched film having a thickness of 211 μm. At this time, the take-up speed of the unstretched film (the rotation speed of the metal roll) was about 20 m / min. The Tg of the unstretched film was 75 ° C.

  The obtained unstretched film was guided to a longitudinal stretching machine in which a plurality of roll groups were continuously arranged, and was stretched 4.3 times in the longitudinal direction at 78 ° C. by utilizing the difference in rotation speed of the rolls.

  The film immediately after longitudinal stretching was passed through a heating furnace. The inside of the heating furnace was heated by a hot air heater, and the set temperature was 100 ° C. Using the difference in speed between the rolls at the inlet and outlet of the heating furnace, 30% relaxation treatment was performed in the longitudinal direction. The relaxation processing time was 0.6 seconds.

  The relaxed film was introduced into a transverse stretching machine (tenter) and continuously passed through an intermediate heat treatment zone, an intermediate zone (natural cooling zone), a cooling zone (forced cooling zone), a transverse stretching zone and a final heat treatment zone. In the intermediate zone of the tenter, when a strip-shaped piece of paper is hung in a state where the film is not passed, so that the piece of paper hangs almost completely in the vertical direction, hot air from the intermediate heat treatment zone, from the cooling zone Shut off the cooling air. When the film was running, the distance between the film and the blocking plate was adjusted so that most of the accompanying flow accompanying the running of the film was blocked by the blocking plate provided between the intermediate heat treatment zone and the intermediate zone. In addition, when the film was running, the distance between the film and the blocking plate was adjusted so that most of the accompanying flow accompanying the running of the film was blocked by the blocking plate at the boundary between the intermediate zone and the cooling zone.

  The relaxed film after longitudinal stretching guided by a tenter was heat-treated at 128 ° C. for 8 seconds in an intermediate heat treatment zone. At this time, the relaxation rate in the longitudinal direction was set to 28.6%. Next, the film after the intermediate heat treatment was guided to the intermediate zone and naturally cooled by passing through the intermediate zone (passing time = about 1 second). Subsequently, the film after natural cooling is guided to a cooling zone, and actively cooled by blowing low-temperature air until the surface temperature of the film reaches 100 ° C., and then at 96 ° C. in the width direction (transverse direction). It was stretched 5 times.

  The laterally stretched film was guided to a final heat treatment zone, and in the final heat treatment zone, heat treatment was performed at 97 ° C. for 5 seconds at a relaxation rate of 0% in the longitudinal direction and a relaxation rate of 2% in the width direction. Then, the biaxially stretched film having a thickness of 20 μm was continuously manufactured over a predetermined length by cooling, cutting and removing both edges, and winding the film into a roll with a width of 500 mm. The characteristics of the obtained film were evaluated by the methods described above. The evaluation results are shown in Table 3. Further, the contraction stress curve is shown in FIG. 2, and the reverse heat flow measured by the temperature modulation DSC is shown in FIG.

Example 2
A film having a thickness of 20 μm was produced in the same manner as in Example 1 except that the above polyester A, polyester B, polyester C and polyester D were mixed in a mass ratio of 5: 15: 70: 10. The Tg of the unstretched film was 75 ° C. The evaluation results are shown in Table 3.

Example 3
A film having a thickness of 20 μm was produced in the same manner as in Example 2 except that polyester E was used instead of polyester D. The Tg of the unstretched film was 75 ° C. The evaluation results are shown in Table 3.

Example 4
Polyester A, polyester B, polyester C and polyester F were mixed in a mass ratio of 5: 5: 80: 10, the thickness of the unstretched film was 190 μm, the longitudinal stretching temperature was 75 ° C., and the relaxation rate of the intermediate heat treatment step was 0. %, And a film having a thickness of 20 μm was manufactured in the same manner as in Example 1 except that the relaxation rate in the longitudinal direction of the final heat treatment step was 35.7%. The Tg of the unstretched film was 67 ° C. The evaluation results are shown in Table 3.

Example 5
Polyester A, polyester C, polyester E and polyester F were mixed in a mass ratio of 5: 60: 25: 10, the thickness of the unstretched film was 266 μm, the longitudinal stretching temperature was 75 ° C., and the relaxing temperature after longitudinal stretching was 95. 20 μm in the same manner as in Example 1, except that the relaxation rate of the intermediate heat treatment step was 35.7%, the transverse stretching temperature was 95 ° C., the transverse stretching ratio was 7 times, and the final heat treatment temperature was 96 ° C. A film was produced. The Tg of the unstretched film was 67 ° C. The evaluation results are shown in Table 3.

Example 6
The temperature of the heating furnace after longitudinal stretching was changed from 100 ° C to 50 ° C, and the relaxation rate in the longitudinal direction in the heating furnace after longitudinal stretching was changed from 30% to 0% (that is, no relaxation was performed). Example except that the longitudinal relaxation rate in the intermediate heat treatment step was changed from 28.6% to 30%, and the longitudinal relaxation rate in the final heat treatment step was changed from 0% to 28.6%. A film having a thickness of 20 μm was produced in the same manner as in 1. The evaluation results are shown in Table 3.

Example 7
The longitudinal relaxation rate in the heating furnace after longitudinal stretching was changed from 30% to 18%, and the longitudinal relaxation rate in the intermediate heat treatment step was changed from 28.6% to 22%. A film having a thickness of 20 μm was produced in the same manner as in Example 1 except that the relaxation rate in the longitudinal direction in Example 2 was changed from 0% to 21.8%. The evaluation results are shown in Table 3.

Comparative Example 1
Using polyester D instead of polyester C, the thickness of the unstretched film was 200 μm, the longitudinal stretching ratio was 4 times, the relaxation temperature after longitudinal stretching was 95 ° C., the intermediate heat treatment temperature was 123 ° C., the transverse stretching temperature was 95 ° C., A film having a thickness of 20 μm was produced in the same manner as in Example 4 except that the final heat treatment temperature was 98 ° C. and the relaxation in the width direction was not performed. The Tg of the unstretched film was 67 ° C. The evaluation results are shown in Table 3.

Comparative example 2
A 20 μm-thick film was produced in the same manner as in Example 4 except that Polyester A, Polyester B, Polyester C, and Polyester D were mixed in a mass ratio of 5: 15: 10: 70. The Tg of the unstretched film was 67 ° C. The evaluation results are shown in Table 3.

Comparative Example 3
Example except that the thickness of the unstretched film was 98 μm, longitudinal stretching and relaxation in the longitudinal direction were not performed, the temperature of the intermediate heat treatment was 100 ° C., the transverse stretching temperature was 78 ° C., and the final heat treatment temperature was 80 ° C. A film having a thickness of 20 μm was produced in the same manner as in 1. The evaluation results are shown in Table 3. The shrinkage stress curve is shown in FIG.

  Since the heat-shrinkable polyester film of the present invention has a high heat-shrinkage rate and excellent properties as described above, it can be suitably used for label applications such as bottles. A package such as a bottle obtained by using the heat-shrinkable polyester film of the present invention as a label has a beautiful appearance.

Claims (3)

A biaxially stretched heat-shrinkable polyester film, which satisfies the following requirements (1) to (5).
(1) Using 1,4-cyclohexanedimethanol as an amorphous monomer in an amount of 5 mol% to 30 mol% in 100 mol% of an alcohol component,
(2) When the film is immersed in hot water of 98 ° C. for 10 seconds, the hot water heat shrinkage ratio is 60% or more and 90% or less in the width direction, which is the main shrinking direction of the film,
(3) The hot water heat shrinkage rate when the film is immersed in hot water of 98 ° C. for 10 seconds is −5% or more and 5% or less in the longitudinal direction which is a direction orthogonal to the main shrinkage direction of the film,
(4) The right-angled tear strength per unit thickness in the direction orthogonal to the main shrinkage direction after shrinking 10% in the main shrinkage direction in warm water of 80 ° C. is 180 N / mm or more and 350 N / mm or less.
(5) The maximum shrinkage stress in the main shrinkage direction of the film measured with hot air at 90 ° C. is 2 MPa or more and 10 MPa or less, and the shrinkage stress after 30 seconds from the start of measurement is 60% or more and 100% or less of the maximum shrinkage stress. ..   The heat-shrinkable polyester film according to claim 1, wherein a difference in hot water heat shrinkage in the main shrinkage direction at 70 ° C. before and after aging treatment for 672 hours at a temperature of 30 ° C. and a humidity of 65% RH is 10% or less. The specific heat capacity difference ΔC _p before and after Tg when the reverse heat flow is measured by temperature modulation DSC is 0.1 J / (g · ° C.) or more and 0.7 J / (g · ° C.) or less. The heat-shrinkable polyester film according to any one of claims.