JP6835127B2 - Heat shrinkable polyester film and packaging - Google Patents

Description

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

In recent years, polyester-based heat with high heat resistance, easy incineration, and excellent solvent resistance has been applied to label packaging, cap seals, integrated packaging, etc. that protect glass bottles or plastic bottles and display products. Shrinkable films have come to be widely used as shrinkage labels, and the amount used tends to increase with the increase in PET (polyethylene terephthalate) bottle containers and the like.

So far, as a heat-shrinkable polyester-based film, a film that shrinks significantly in the width direction has been widely used. It is also known that the shrinkage rate in the longitudinal direction, which is the non-shrinkage direction, is set to minus (so-called stretching by heating) in order to improve the shrinkage finish (Patent Document 1). The heat-shrinkable polyester-based film whose width direction is the main shrinkage direction is stretched at a high magnification in the width direction in order to exhibit shrinkage characteristics in the width direction, but the longitudinal direction orthogonal to the main shrinkage direction is In many cases, only low-magnification stretching is applied, and some are not stretched. Such a film stretched at a low magnification in the longitudinal direction and a film stretched only in the width direction have a drawback that the mechanical strength in the longitudinal direction is inferior. Further, when the machine is stretched in the longitudinal direction in order to improve the mechanical strength in the longitudinal direction, the mechanical strength in the longitudinal direction is increased, but the shrinkage rate in the longitudinal direction is also increased and the shrinkage finish is deteriorated.

By the way, conventional heat-shrinkable films have been produced by adjusting the composition and stretching conditions of polyester so that the heat-shrinkability of hot water at 90 ° C. is 40 to 60% (Patent Document 2). Further, even if the film has a higher shrinkage, the heat shrinkage rate of hot water at 90 ° C. is 40 to 80% (Patent Document 3), and a film having a high shrinkage 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, a high shrinkage film having a shrinkage rate of more than 80% in the width direction has been required. Further, if the shrinkage rate in the longitudinal direction is high, the label length in the longitudinal direction becomes short, which is contrary to the desire to cover most of the container with the label. Therefore, there has been an increasing demand for the contraction rate in the longitudinal direction to be 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 rate in the longitudinal direction.

It is difficult to reduce the contraction rate in the longitudinal direction until it becomes negative while maintaining the mechanical strength in the longitudinal direction high, and it is difficult to increase the contraction rate in the width direction in the longitudinal direction. The shrinkage rate of the product is also high, and the shrinkage finish is inferior.

Special Fair 5-33895 Gazette Japanese Patent No. 5240387 Japanese Patent No. 5339061

The present invention solves the above problems, has a high heat shrinkage rate in the width direction, exhibits a small heat shrinkage rate in the longitudinal direction, has a large mechanical strength in the longitudinal direction, has good perforation opening property, and shrinks. An object of the present invention is to provide a heat-shrinkable polyester-based film having excellent finishability.

The present invention that solves the above problems is a biaxially stretched heat-shrinkable polyester-based film that satisfies the following requirements (1) to (5).

(1) Isophthalic acid is used as an amorphous monomer in an amount of 1 mol% or more and 30 mol% or less in 100 mol% of the acid component.
(2) The heat shrinkage rate of hot water when the film is immersed in warm water at 98 ° C. for 10 seconds is 60% or more and 90% or less in the main shrinkage direction of the film.
(3) The heat shrinkage rate of hot water when the film is immersed in warm water at 98 ° C. for 10 seconds is -5% or more and 12% or less in the direction orthogonal to the main shrinkage direction of the film.
(4) The right-angle tear strength per unit thickness in the direction orthogonal to the main contraction direction after shrinking 10% in the main contraction direction in warm water at 80 ° C. is 180 N / mm or more and 350 N / mm or less.
(5) Thickness unevenness in the main shrinkage direction per 1 m of film is 1% or more and 12% or less.

In the heat-shrinkable polyester film of the present invention, 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 14 MPa or less, and the shrinkage stress 30 seconds after the start of measurement is the maximum shrinkage stress. It is preferably 60% or more and 100% or less. It is also a preferred embodiment that the natural shrinkage rate after aging treatment at a temperature of 40 ° C. and a humidity of 65% RH for 672 hours is 0.3% or more and 1.0% or less.

As the amorphous monomer, it is preferable to use only isophthalic acid or isophthalic acid and neopentyl glycol and / or cyclohexanedimethanol. At this time, the specific heat capacity around Tg when the reverse heat flow is measured by the temperature-modulated DSC. When the difference ΔC _p is 0.1 J / (g · ° C.) or more and 0.7 J / (g · ° C.) or less, a very preferable heat-shrinkable polyester-based film is obtained.

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

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

In the present invention, it has been possible to provide a heat-shrinkable film having a larger heat-shrinkage rate in the main shrinkage direction (width direction) and less shrinkage in a direction orthogonal to the main-shrinkage direction.

In addition, since it is biaxially stretched vertically and horizontally, it has high mechanical strength in the longitudinal direction orthogonal to the width direction. Therefore, when it is used as a label for PET bottles and the like, it can be used in a container such as a bottle for a short time. It can be installed very efficiently inside, and when heat-shrinked, it is possible to develop a good finish with extremely few wrinkles and insufficient shrinkage. Further, since the film strength is high, the processing characteristics at the time of printing processing and tubing processing are good.

Furthermore, since the damping stress of the shrinkage stress is small and the shrinkage stress 30 seconds after the start of shrinkage is high, the followability is good even if the container thermally expands during the heating of the label mounting process, and the label is less likely to loosen and has a good appearance. Is obtained. In addition, the perforation opening property of the label is good, and when the label is opened, it can be cut neatly along the perforation from the start of tearing to the completion of tearing.

Further, since the heat-shrinkable polyester-based film of the present invention is produced by being stretched in both vertical and horizontal axes, it can be produced very efficiently. Further, the heat-shrinkable polyester film of the present invention has extremely high adhesive force when the front and back surfaces (or the same surfaces) are adhered to each other with a solvent, and is suitable for various coated labels such as labels for PET bottles and the like. Can be used.

The package packaged 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 the right-angled tear strength. It is a shrinkage stress curve of the film of Example 1 and Comparative Example 1. It is a reverse heat flow which measured the film of Example 1 by the temperature-modulated DSC.

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

Examples of 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 decandicarboxylic acid. Examples thereof include group dicarboxylic acids and alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid. Of these, isophthalic acid and orthophthalic acid are preferable. These are amorphous monomers constituting the amorphous part in polyester, but when movable amorphous and rigid amorphous (these contents will be described in detail later) were examined, they were not movable in the stretching step and the heat treatment step. The amount of change of crystals to rigid amorphous is small, and the amount of change from rigid amorphous to movable amorphous is large due to relaxation treatment in the stretching step. In particular, isophthalic acid has a smaller amount of moving amorphous components that change to rigid amorphous components than other amorphous components, so even a small amount of isophthalic acid can secure a sufficient amount of amorphous components in polyester and achieve a high shrinkage rate. Most preferable because it can be achieved.

Therefore, in the present invention, it is an essential requirement to use 1 to 30 mol% of isophthalic acid in 100 mol% of dicarboxylic acid as an amorphous monomer (amorphous component) (requirement (1)). The amount of isophthalic acid is more preferably 2 to 28 mol%, further preferably 3 to 27 mol%.

Further, it is preferable that the polyester does not contain a trivalent or higher valent carboxylic acid (for example, trimellitic acid, pyromellitic acid and anhydrides thereof). A heat-shrinkable polyester-based film obtained by using a polyester containing these multivalent carboxylic acids makes it difficult to achieve the required high shrinkage rate.

In addition to ethylene glycol, the diol components constituting polyester include 1,3-propanediol, 2,2-diethyl-1,3-propanediol, and 2-n-butyl-2-ethyl-1,3-propanediol. , 2,2-Isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, 1,4-butanediol, hexanediol, neopentyl glycol, hexanediol and other fats Examples thereof include group diols, alicyclic diols such as 1,4-cyclohexanedimethanol, and aromatic diols such as bisphenol A.

Among these, as an amorphous component that can be suitably used together with isophthalic acid, 1,4-cyclohexanedim as an amorphous monomer having a relatively large amount of change from rigid amorphous to movable amorphous by relaxation treatment in the stretching step. It is preferable to use a cyclic diol such as methanol or a diol having 3 to 6 carbon atoms (for example, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, hexanediol, etc.), and particularly 1, 4-Cyclohexanedimethanol, neopentyl glycol and 1,4-butanediol are more preferred, and 1,4-cyclohexanedimethanol and / or neopentyl glycol is even more preferred. However, since neopentyl glycol has a large amount of movable amorphous that changes to rigid amorphous by the stretching process or heat treatment, the heat shrinkage rate is slightly smaller and the thickness unevenness in the width direction is large when isophthalic acid is not used. Tends to be.

Further, in the polyester, the total amount of the amorphous components in 100 mol% of the polyhydric alcohol component and 100 mol% of the polyvalent carboxylic acid component (that is, 200 mol% in total) in the total polyester resin is 17 mol% or more, preferably. It 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 the amorphous components is not particularly limited, but is preferably about 30 mol%. If the amorphous component exceeds 30 mol%, the thickness unevenness in the width direction may become large. As a result, a polyester having a glass transition point (Tg) adjusted to 60 to 80 ° C. can be obtained.

The polyester should not contain a diol having 8 or more carbon atoms (for example, octane diol) or a polyhydric alcohol having 3 or more valences (for example, trimethylolpropane, trimethylolethane, glycerin, diglycerin, etc.). Is preferable. A heat-shrinkable polyester-based film obtained by using a polyester containing these diols or a polyhydric alcohol makes it difficult to achieve the required high shrinkage rate. It is also preferable that the polyester contains as little diethylene glycol, triethylene glycol, and polyethylene glycol as possible.

In the resin forming the heat-shrinkable polyester film of the present invention, various additives such as waxes, antioxidants, antistatic agents, crystal nucleating agents, thickeners, and heat-stabilizing agents are included as required. Agents, coloring pigments, anticoloring agents, ultraviolet absorbers and the like can be added.

It is preferable to add fine particles as a lubricant to improve the workability (slipperiness) of the film in the resin forming the heat-shrinkable polyester film of the present invention. Any fine particles can be selected. For example, the inorganic fine particles include silica, alumina, titanium dioxide, calcium carbonate, kaolin, barium sulfate, etc., and the organic fine particles include, for example, an acrylic resin. Examples thereof include particles, melamine resin particles, silicone resin particles, crosslinked polystyrene particles and the like. 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 needed.

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

The heat-shrinkable polyester-based film of the present invention can also be subjected to a corona treatment, a coating treatment, a 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 warm water at 98 ° C. for 10 seconds under no load, and the film is immediately immersed in water at 25 ° C. ± 0.5 ° C. for 10 seconds, and then before and after shrinkage. From the length, the heat shrinkage rate in the width direction (main shrinkage direction) of the film calculated by the following formula 1 (that is, the heat shrinkage rate of hot water at 98 ° C.) is 60% or more and 90% or less (requirement (2)). ..
Thermal shrinkage = {(length before shrinkage-length after shrinkage) / length before shrinkage} x 100 (%) Equation 1

If the heat shrinkage rate of hot water 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 that when used as a label. , The label after heat shrinkage is distorted, insufficient shrinkage, wrinkles, slack, etc. occur. The heat shrinkage rate 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 rate of more than 90% in the width direction at 98 ° C. is low, the upper limit of the hot water heat shrinkage rate is set to 90%.

Further, 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 described above of −5% or more and 12% or less. (Requirement (3)). If the thermal shrinkage of hot water in the longitudinal direction at 98 ° C. is less than -5%, the amount of elongation of the film when heated is too large, and a good shrinkage appearance can be obtained when used as a label for a bottle. On the contrary, if the heat shrinkage rate of hot water in the longitudinal direction at 98 ° C. exceeds 12%, the label after heat shrinkage becomes shorter (the label height decreases) and the label area becomes smaller, so that the label is used as a full label. Is not preferable, and the label is easily distorted after heat shrinkage. The thermal shrinkage rate of hot water 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, and most preferably less than 0%.

In Patent Documents 2 and 3, the shrinkage rate in the longitudinal direction is adjusted to 0% or more (minimum 4% in the examples), 12% or less, or 15% or less by controlling the intermediate heat treatment temperature and the relaxation condition in the longitudinal direction. Was there. That is, in the methods described in these documents, since the film is stretched in the longitudinal direction, it is very difficult to make the heat shrinkage force of hot water in the longitudinal direction negative. This is because when the film is stretched in the width direction after longitudinal stretching, a necking force acts in the longitudinal direction due to the transverse stretching stress, resulting in a film that contracts slightly in the longitudinal direction. Therefore, the present inventors have succeeded in increasing the amount of movable amorphous 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 amorphous, the necking stress at the time of lateral stretching becomes small, and the shrinkage rate in the vertical direction can be reduced. In the present invention, it is considered that a film having a negative shrinkage rate in the longitudinal direction can be provided even if the film is stretched in the longitudinal direction.

The heat-shrinkable polyester-based film of the present invention has a tensile fracture 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 fracture strength is less than 70 MPa, the "waist" (stiffness) when the label is attached to a bottle or the like becomes weak, which is not preferable. Further, in the stretching method of the present invention, it is difficult for the tensile fracture strength to exceed 200 MPa. The tensile fracture strength is more preferably 90 MPa or more, further preferably 110 MPa or more. The tensile fracture strength in the longitudinal direction cannot be in the above range unless the longitudinal stretching step is performed.

The heat-shrinkable polyester-based film of the present invention has a thickness unevenness of 1% or more and 12% or less in the width direction per 1 m of the film (requirement (5)). The heat-shrinkable polyester film of the present invention preferably has a thickness unevenness in the width direction (thickness unevenness when the measurement length is 1 m) of 12% or less. If the thickness unevenness in the width direction exceeds 12%, printing spots are likely to occur during printing during label production, and shrinkage spots after heat shrinkage are likely to occur, which is not preferable. The thickness unevenness in the width direction is more preferably 10% or less, and particularly preferably 8% or less. Further, the smaller the thickness unevenness in the width direction is, the more preferable it is, but the lower limit of the thickness unevenness in the width direction is sufficient to be about 1%.

In the heat-shrinkable polyester film of the present invention, the maximum shrinkage stress in the film width direction measured with hot air at 90 ° C. is 2 MPa or more and 14 MPa or less, and the shrinkage stress 30 seconds after the start of measurement is 60 of the maximum shrinkage stress. It is preferably% or more and 100% or less. The contraction stress shall be measured by the method described in the examples.

If the maximum shrinkage stress at 90 ° C. in the film width direction is less than 2 MPa, the label may loosen and do 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 more preferably 4 MPa or more, further preferably 5 MPa or more. On the contrary, if the maximum shrinkage stress at 90 ° C. exceeds 14 MPa, the label after heat shrinkage tends to be distorted, which is not preferable. The maximum shrinkage stress at 90 ° C. is more preferably 13.5 MPa or less, further preferably 13 MPa or less.

The contraction stress 30 seconds after the start of measurement in hot air at 90 ° C. is preferably 60% or more and 100% or less with respect to the maximum contraction stress. That is, the heat-shrinkable polyester-based film of the present invention exhibits a peculiar heat-shrinkability property that it shows a shrinkage stress equivalent to the maximum heat-shrink stress even 30 seconds after the start of heat-shrinkage. If the contraction stress / maximum contraction stress (hereinafter referred to as “stress ratio”) after 30 seconds is less than 60%, the label's followability when the bottle expands due to heating when the bottle is covered with the label and heat-shrinked is poor. If the temperature of the bottle drops after shrinkage and the thermal expansion disappears, the label will loosen, which is not preferable. The stress ratio is more preferably 75% or more, further preferably 80% or more, and particularly preferably 90% or more. A larger stress ratio is preferable because the followability is good, but the contraction stress after 30 seconds cannot exceed the maximum contraction stress, so the upper limit is 100%.

The heat-shrinkable polyester-based film of the present invention shrinks 10% in the width direction in warm water at 80 ° C., and then tears at right angles in the longitudinal direction when the right-angle tear strength per unit thickness in the longitudinal direction of the film is determined. 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, when used as a label, it may be easily torn by an impact such as dropping during transportation, which is not preferable. On the contrary, the right-angled tear strength is low. If it is larger than 350 N / mm, the cut property (easiness of tearing) when tearing the label becomes poor, which is not preferable. The right-angle tear strength is more preferably 250 N / mm or more, further preferably 280 N / mm or more, and even more preferably 330 N / mm or less.

Further, the heat-shrinkable polyester film of the present invention has a natural shrinkage rate of 0.3% or more and 1.0% or less in the main shrinkage direction after aging treatment at 40 ° C. and 65% RH for 672 hours. Is preferable. By indispensably using isophthalic acid in the present invention, the natural shrinkage rate could be reduced, although the reason is not clear. The natural shrinkage rate (%) is calculated by the following formula 2.
Natural shrinkage rate = {(length before aging-length after aging) / length before aging} x 100 (%) Equation 2
If the natural shrinkage rate exceeds 1.0%, the size in the width direction becomes shorter when the rolled-up product is stored, so that the width does not match during printing, or the desired pattern is not obtained. It is not preferable because it may be different or the film roll may be easily wrinkled.

In the heat-shrinkable polyester film of the present invention, the specific heat capacity difference ΔC _p before and after Tg when the reverse heat flow is measured by the temperature-modulated DSC is 0.1 J / (g · ° C) or more and 0.7 J / (g · ° C.). ) The following is preferable. The specific heat capacity difference ΔC _p before and after Tg corresponds to the amount of movable amorphous (conventional complete amorphous) in which the molecular chain starts to move in the vicinity of Tg, which will be described in detail later. This movable amorphous can be distinguished from a rigid amorphous in which the molecular chain cannot move unless the temperature is higher than Tg. In the present invention, the amount of the movable amorphous affects the heat shrinkage rate. It is important to do so, not to change the movable amorphous to rigid amorphous, or to change most of the rigid amorphous to movable amorphous in order to obtain a film with high thermal shrinkage and less shrinkage in the longitudinal direction. We found that there was, succeeded in providing a film satisfying all the above five requirements, and completed the present invention.

When the reverse heat flow of the film sample is measured by the temperature-modulated 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. When ΔC _p is smaller than 0.1 J / (g · ° C.), a high thermal shrinkage cannot be achieved because the amount of movable amorphous is small, and 0.15 J / (g · ° C.) or more is preferable, and 0.2 J / (. g · ° C.) or higher is more preferable. ΔC _p may exceed 0.7 J / (g · ° C.), but in the film forming method of the present invention in which the film is stretched biaxially, the upper limit 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 it is, but considering that a predetermined amount of lubricant must be added to the film for the purpose of imparting the slipperiness necessary for practical use, the lower limit is about 2%.

In the heat-shrinkable polyester-based 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. In addition, usually, two or more kinds of chip-shaped polyester are mixed and used as a raw material for 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 the polyester raw material is dried 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 the T-die method and the tubular method can be adopted.

Then, an unstretched film can be obtained by quenching the sheet-shaped molten resin after extrusion. As a method for rapidly cooling the molten resin, a method of casting the molten resin from a base onto a rotating drum and quenching and solidifying the molten resin to obtain a substantially unoriented resin sheet can be preferably adopted.

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

[Method for forming a heat-shrinkable polyester film of the present invention]
As described in Patent Documents 2 and 3, the present inventors have stated that in order to obtain a heat-shrinkable polyester-based film having high mechanical strength in the longitudinal direction and excellent perforation opening property, "in the longitudinal direction" We obtained the finding that it is necessary to have "molecules that are oriented but do not contribute to shrinkage force" in the film, and as a result, the film is stretched in the longitudinal direction (longitudinal direction) and then in the width direction, so-called longitudinal. -The transverse stretching method is adopted. In this longitudinal-lateral stretching method, after stretching in the longitudinal direction, an intermediate heat treatment is performed before stretching in the width direction in order to relax the contraction force in the longitudinal direction.

One of the methods for obtaining a film having higher shrinkage is to increase the amount of monomer components (hereinafter, simply amorphous components) constituting a unit that can be amorphous in the film. In the film obtained by the conventional lateral uniaxial stretching method, an increase in the shrinkage rate corresponding to the increase in the amount of the amorphous component was observed. However, it has been found that in the film obtained by the above-mentioned longitudinal-transverse stretching method found by the present inventors, even if the amount of amorphous components is increased, the shrinkage rate does not increase in proportion to the increased amount. 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 degree of crystallinity and the heat shrinkage rate, or the heat of fusion and the heat shrinkage rate. From these facts, it is considered that polyester is not divided into two phases, a crystalline phase and an amorphous phase, but is divided into a crystalline phase, a movable amorphous phase, and a rigid amorphous phase. It was.

This rigid amorphous is an amorphous state in which the molecular motion is frozen even at the glass transition temperature (Tg) or higher in the intermediate state between the crystal and the movable amorphous, and becomes a fluid state at a temperature higher than Tg (). For example, Minoru 10 o'clock, "DSC (3) -Glass transition behavior of polymers-", Journal of the Textile Society (Fiber and Industry), Vol. 65, No. 10 (2009)). The amount of rigid amorphous (rate) can be expressed as 100% -crystallinity-movable amorphous amount.

Then, when the relationship between the amount of movable amorphous and the heat shrinkage rate was examined, it was found that there was a correlation between the two. Furthermore, when the amount of movable non-crystals was measured for the unstretched sheet, the film after longitudinal stretching, the film after final heat treatment, etc., the amount of movable amorphous was compared with the unstretched film among the films after longitudinal stretching and intermediate heat treatment. The film in which the amount was significantly reduced could not show a high heat shrinkage rate, and it was considered that the movable acrystal was changed to a rigid acrystal.

Therefore, the present inventors have examined the conditions of longitudinal stretching and intermediate heat treatment, and have a small rate of change from movable amorphous to rigid amorphous, or a rate of change from rigid amorphous to movable amorphous. We continued to study finding a large amorphous component and succeeded in obtaining a film that satisfied all of 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 between intermediate heat treatment and transverse stretching (cutting off heating)
(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 more than once during the above manufacturing process Providing a Step Hereinafter, each of the above-mentioned means will be described in sequence.

(1) Control of longitudinal stretching conditions In the production of a film by the longitudinal-lateral stretching method of the present invention, the stretching temperature is set to Tg or more and Tg + 30 ° C. or less, and the film is vertically stretched 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-step stretching or multi-step stretching of two or more steps can be used.

When stretching in the longitudinal direction, if the stretching temperature is too high or the total longitudinal stretching ratio becomes large, the amorphous molecules are stretched, and the heat shrinkage rate in the longitudinal direction tends to increase. Further, if the longitudinal stretching ratio is too large, the orientational crystallization of the film proceeds after the longitudinal stretching, the movable amorphous changes to a rigid amorphous, and the rigid amorphous crystallizes, and breakage is likely to occur in the transverse stretching step. This is not preferable because the shrinkage rate in the lateral direction after lateral stretching also decreases. Therefore, the upper limit of the longitudinal stretching ratio is set to 4.6 times. The longitudinal stretching ratio is more preferably 4.5 times or less, and further preferably 4.4 times or less. On the other hand, if the longitudinal stretching ratio is too small, the shrinkage rate in the longitudinal direction becomes small, but the degree of molecular orientation in the longitudinal direction also becomes small, the right-angle 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 even more preferably 3.5 times or more.

(2) Intermediate heat treatment after longitudinal stretching In order to heat-relax molecules oriented in the longitudinal direction, heat treatment is performed after longitudinal stretching. At this time, after the unstretched film is vertically stretched, both ends in the width direction are gripped by clips in the tenter, and the temperature is Tg + 40 ° C. or higher and Tg + 70 ° C. or lower for 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).

The temperature of the intermediate heat treatment is more preferably Tg + 41 ° C. or higher, further preferably Tg + 42 ° C. or higher, further preferably Tg + 68 ° C. or lower, and further preferably Tg + 66 ° 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 thermal shrinkage rate after the transverse stretching. On the other hand, the time of the intermediate heat treatment needs to be appropriately adjusted according to the raw material composition within the range of 6.0 seconds or more and 12.0 seconds or less. 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, a long time intermediate heat treatment is required. However, if the intermediate heat treatment time is too long, the equipment becomes huge, so it is preferable to adjust the temperature and time appropriately.

By keeping 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 maintain a large tensile fracture strength in the longitudinal direction while keeping the right-angle tear strength small. .. On the other hand, by controlling the temperature of the intermediate heat treatment to Tg + 70 ° C or lower, crystallization of the film can be suppressed and the shrinkage rate in the longitudinal direction can be reduced by conversion from movable amorphous to rigid amorphous instead of crystallization. To do. Since the crystal is in a very constrained orientation state in which the molecular chains are folded, once crystallized, the amount of the crystal does not decrease even if the subsequent stretching method is changed. However, since the rigid amorphous is in a loosely constrained orientation state as compared with the crystal, it can be changed from the rigid amorphous to the movable amorphous by relaxation in the subsequent stretching step. Therefore, by setting the temperature of the intermediate heat treatment to Tg + 70 ° C. or lower, crystallization can be suppressed and the shrinkage rate in the width direction can be increased. Further, by suppressing the temperature of the intermediate heat treatment to Tg + 70 ° 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 between intermediate heat treatment and transverse stretching (cutting off heating)
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, the time is 0.5 seconds or more and 3.0 seconds or less. , The film needs to pass through an intermediate zone that does not perform an aggressive heating operation. That is, an intermediate zone is provided in front of the lateral stretching zone of the tenter for transverse stretching, the film after the intermediate heat treatment after the longitudinal stretching is guided to the tenter, passed through this intermediate zone over a predetermined time, and then laterally stretched. It is preferable to carry out stretching. In addition, in the intermediate zone, the accompanying flow and cooling zone accompanying the running of the film so that when the strip-shaped piece of paper hangs down without passing through the film, the piece of paper hangs down almost completely in the vertical direction. It is preferable to block hot air from. If the time for passing through the intermediate zone is less than 0.5 seconds, the lateral stretching becomes high temperature stretching, and the lateral shrinkage rate cannot be sufficiently increased, which is not preferable. On the contrary, 3.0 seconds is sufficient for passing through the intermediate zone, and setting the length longer than that is not preferable 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, further 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 temperature of the film is Tg or more and Tg + 40 ° C. or less instead of laterally stretching the naturally cooled film as it is. It is necessary to actively forcibly cool the film. By performing such a forced cooling treatment, it is possible to obtain a film having good perforation opening property when it is made into 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, further preferably Tg + 35 ° C. or lower, still more preferably Tg + 30 ° C. or lower.

When the film is forcibly cooled, if the temperature of the film after the forcible cooling remains above Tg + 40 ° C., the shrinkage rate in the width direction of the film becomes low, and the shrinkage when made into a label becomes insufficient. However, by controlling the temperature of the film after forced cooling to be Tg + 40 ° C. or lower, it is possible to maintain a large shrinkage rate in the width direction of the film. Further, if the temperature of the film after forced cooling remains above Tg + 40 ° C., the stress of lateral stretching performed after cooling becomes small, the shrinkage stress in the width direction becomes small, and the followability to the bottle becomes poor. By performing forced cooling so that the temperature of the film after cooling becomes Tg + 40 ° C. or lower, it is possible to maintain a large shrinkage stress in the width direction.

Further, when the film is forcibly cooled, if the temperature of the film after the forcible cooling remains above Tg + 40 ° C., the stress of 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 lateral stretching performed after cooling and reduce the thickness unevenness in the width direction.

(5) Control of lateral stretching conditions The lateral stretching is performed so that the magnification is 3 times or more and 7 times or less at a temperature of Tg + 10 ° C. or higher and Tg + 40 ° C. or lower in a state where both ends in the width direction are gripped by clips in the tenter. There is a need. By laterally stretching under such predetermined conditions, it is possible to orient the molecules in the width direction to develop a high contraction force in the width direction, and to obtain a film having good perforation opening property when made into a label. Is possible. The temperature of the transverse stretching is more preferably Tg + 13 ° C. or higher, further preferably Tg + 16 ° C. or higher, further preferably Tg + 37 ° C. or lower, and further preferably Tg + 34 ° C. or lower. On the other hand, the lateral stretching ratio is more preferably 3.5 times or more, further preferably 4 times or more, further preferably 6.5 times or less, still more preferably 6 times or less.

When stretching in the lateral direction, if the stretching temperature exceeds Tg + 40 ° C., the shrinkage rate in the width direction becomes small, but by controlling the stretching temperature to Tg + 40 ° C. or less, the shrinkage rate in the width direction is increased. Is possible. Further, when the stretching temperature exceeds Tg + 40 ° C., the stress of lateral stretching becomes small, the contraction stress in the width direction becomes small, and the followability to the bottle becomes poor. By controlling the transverse stretching temperature to be Tg + 40 ° C. or lower, it is possible to increase the contraction stress in the width direction. Further, when the temperature of the film exceeds Tg + 40 ° C., the stretching stress of lateral stretching tends to be small, and the thickness unevenness in the width direction tends to be large. By controlling the transverse stretching temperature to Tg + 40 ° C. or lower, the stress of the 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, the film is easily broken during lateral stretching, and the voids inside the film increase, so that the haze of the film becomes large. Therefore, it is not preferable.

(6) Heat treatment after transverse stretching and relaxation in the width direction The film after transverse stretching is 1 second or more and 9 seconds at a temperature of Tg or more and Tg + 50 ° C. or less with clips on both ends in the width direction in the tenter. It is necessary that the final heat treatment is performed over the following time. When the heat treatment temperature is higher than Tg + 50 ° C., the number of movable amorphous is reduced, the shrinkage rate in the width direction is lowered, and the heat shrinkage rate at 98 ° C. is smaller 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 (so-called natural shrinkage rate) becomes large with time, which is not preferable. Further, the longer the heat treatment time is, the more preferable it is, but if it is too long, the equipment becomes huge, so it is preferably 9 seconds or less.

In the present invention, it is preferable to relax in the width direction during the heat treatment in the width direction. Heat treatment with a constant length is not preferable because the movable amorphous is converted into rigid amorphous, the amount of rigid amorphous increases, and the contraction stress in the width direction becomes too high. Conventionally, it has been considered that relaxing in the width direction reduces the contraction rate in the width direction. However, as a result of examination by the present inventors, it was found that at a relaxation rate of 1 to 6%, movable amorphous in the width direction increases, and only the contraction stress decreases without decreasing the contraction rate in the width direction. Was done. The shrinkage rate is determined by the amount of movable amorphous and the molecular orientation, but by relaxing in the width direction, the molecular orientation decreased but the amount of movable amorphous increased, so the shrinkage rate in the width direction did not decrease and only the shrinkage stress. Is considered to have decreased.

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

Therefore, as a result of studies, the present inventors have discovered that the bulk 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 contraction rate in the width direction and decrease the contraction rate in the longitudinal direction, it is one of the effective means to stretch in the longitudinal direction and then relax in the longitudinal direction. In addition, we investigated means for controlling the right-angle tear strength and tensile fracture strength in the longitudinal direction 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 found that the film can be controlled by relaxing in the longitudinal direction by the means shown below. It is desirable to perform any two steps or all three steps from 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 using a roll having a speed difference, 10% or more and 50% or less in the longitudinal direction in a time of 0.05 seconds or more and 5 seconds or less. The process of relaxing. As the heating means, any of a temperature control roll, near infrared rays, far infrared rays, 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 higher and Tg + 70 ° C. or lower, 0.1 seconds or more and 12 seconds or less, 21% or more and 40 in the longitudinal direction. % Or less The process of relaxing.

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

Hereinafter, each step will be described.

(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 using rolls having different speeds, in the longitudinal direction in a time of 0.05 seconds or more and 5.0 seconds or less. It is desirable to carry out 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 crystallizes and the transparency and the like deteriorate, which is not preferable. The film temperature at the time of relaxation is more preferably Tg + 10 ° C. or higher and Tg + 55 ° C. or lower, and further 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, relaxation will be short, and if the temperature is not higher than Tg, relaxation unevenness will occur, which is not preferable. Further, if the relaxing time is longer than 5 seconds, it is possible to relax 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.

Further, if the relaxation rate in the longitudinal direction 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. Further, if the relaxation rate in the longitudinal direction of the film after longitudinal stretching is larger than 50%, the right-angle tear strength in the longitudinal direction increases and the tensile fracture strength decreases, which is not preferable. The relaxation rate of the film after longitudinal stretching is more preferably 15% or more and 45% or less, and further 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 speed is different between the rolls, or a film after longitudinal stretching is performed. 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 made slower than that of the roll. As the heating device (heating furnace), any 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, by shortening the distance between the gripping clips in the facing tenter, 21% or more and 40% in the longitudinal direction in a time of 0.1 second or more and 12 seconds or less. It is desirable to carry out the following relaxation. 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. Further, when the relaxation rate is larger than 40%, the right-angle tear strength in the longitudinal direction becomes large and the tensile fracture strength becomes small, which is not preferable. The relaxation rate is more preferably 22% or more, more preferably 38% or less, still more preferably 36% or less.

Further, 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, relaxation will be short, and if the temperature is not higher than Tg + 40 ° C., relaxation unevenness will occur, which is not preferable. Further, if the relaxing 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, by shortening the distance between the gripping clips in the facing tenter, 21% or more and 40% in the longitudinal direction in a time of 0.1 seconds or more and 9 seconds or less. It is desirable to carry out the following relaxation. 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. Further, when the relaxation rate is larger than 40%, the right-angle tear strength in the longitudinal direction becomes large and the tensile fracture strength becomes small, which is not preferable. The relaxation rate is more preferably 22% or more, more preferably 38% or less, still more preferably 36% or less.

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, relaxation will be short, and if the temperature is not higher than Tg, relaxation unevenness will occur, 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 formed by heat-shrinking a label having perforations or notches obtained from the heat-shrinkable polyester film of the present invention by covering at least a part of the outer periphery of the object to be packaged. Is. Examples of the packaging object include PET bottles for beverages, various bottles, cans, plastic containers such as confectionery and lunch boxes, and paper boxes. Normally, when a label obtained from a heat-shrinkable polyester film is heat-shrinked and coated on those packaging objects, the label is heat-shrinked by about 5 to 70% and brought into close contact with the package. .. The label coated on the object to be packaged may or may not be printed.

As a method of producing a label, an organic solvent is applied slightly inward from one end of a rectangular film, and the film is immediately rolled and the ends are overlapped and adhered to form a label, or a roll. Apply an organic solvent slightly inward from one end of the film wound into a shape, immediately roll the film, overlap the ends and bond them together, and cut the tube-shaped film into a label shape. .. As the 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 phenols 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 aspects of these Examples, and is appropriate as long as it does not deviate from the gist of the present invention. It is possible to change. The film evaluation method is shown below.

[Heat shrinkage rate (hot water heat shrinkage rate)]
The film is cut into 10 cm × 10 cm squares, immersed in warm water at 98 ° C ± 0.5 ° C for 10 seconds under no load, heat-shrinked, and then immersed in water at 25 ° C ± 0.5 ° C for 10 seconds. Then, the film was drawn out of water, the vertical and horizontal dimensions of the film were measured, and the heat shrinkage rate was determined according to the following formula 1. The direction in which the heat shrinkage rate was large was defined as the main shrinkage direction.
Thermal shrinkage = {(length before shrinkage-length after shrinkage) / length before shrinkage} x 100 (%) Equation 1

[Shrink stress]
A sample with a length of 200 mm and a width of 20 mm in the main shrinkage direction is cut out from the heat-shrinkable film, and a strength elongation measuring machine with a heating furnace manufactured by Toyo Baldwin (currently Orientec) (Tensilon (registered trademark of Orientec) )) Was measured. The heating furnace was preheated to 90 ° C., and the distance between the chucks was set to 100 mm. The ventilation of the heating furnace was temporarily 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 closed promptly, and the ventilation was restarted. The contraction stress was measured for 30 seconds or more, the contraction stress (MPa) after 30 seconds was determined, and the maximum value during the measurement was defined as the maximum contraction stress (MPa). Further, the ratio (percentage) of the contraction stress after 30 seconds to the maximum contraction stress was defined as the stress ratio (%).

[Tensile fracture strength]
A strip-shaped test piece having a measurement direction (film longitudinal direction) of 140 mm and a direction orthogonal to the measurement direction (film width direction) of 20 mm was produced. Using a universal tensile tester "DSS-100" (manufactured by Shimadzu Corporation), grip both ends of the test piece with chucks by 20 mm on each side (distance between chucks is 100 mm), and the conditions are an atmospheric temperature of 23 ° C. and a tensile speed of 200 mm / min. The tensile test was carried out at, and the strength (stress) at the time of tensile failure was defined as the tensile failure strength.

[Right-angle tear strength]
The film is attached to a rectangular frame having a predetermined length in a loosened state in advance (that is, both ends of the film are gripped by the frame). Then, the film was shrunk by 10% in the width direction by immersing the loose film in warm water at 80 ° C. for about 5 seconds until the loose film became tense in the frame (until the loose film disappeared). A test piece having the shape shown in FIG. 1 was cut out from the film after shrinking by 10% according to JIS-K-7128-3. When cutting out the test piece, 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, grasp both ends (width direction) of the test piece with a universal tensile tester ("Autograph" manufactured by Shimadzu Corporation), perform a tensile test under the condition of a tensile speed of 200 mm / min, and the film tears completely in the longitudinal direction. The maximum load was measured when the load was removed. This maximum load was divided by the film thickness to calculate the right-angle tear strength per unit thickness.

[Thickness unevenness in the width direction]
The film was sampled to 1 m in the width direction and 40 mm in the longitudinal direction, and the thickness in the width direction was continuously along the longitudinal direction of the film sample at 5 m / s using a continuous contact type thickness gauge manufactured by Micron Measuring Instruments Co., Ltd. Was measured. The maximum thickness at the time of measurement was Tmax., The minimum thickness was Tmin., And the average thickness was Tave., And the thickness unevenness in the film width direction was calculated from the following equation 3.
Thickness unevenness = {(Tmax.-Tmin.) /Tave.} × 100 (%) Equation 3

[Natural shrinkage rate after aging]
After aging treatment for 672 hours in an environment of 40 ° C. and 65% RH, the value obtained by the above formula 2 was taken as the natural shrinkage rate (%).

[Label shrinkage distortion]
By adhering both ends of the heat-shrinkable film with dioxolane, a cylindrical label (a label whose main shrinkage direction of the heat-shrinkable film is the circumferential direction) was produced. A 500 ml square PET bottle (body circumference 215 mm, minimum straight neck 87 mm) is covered with a label, and a steam tunnel (model; SH-1500-L) manufactured by Fuji Astick Inc with a zone temperature of 90 ° C. is used in 5 seconds. By passing it through, the label was heat-shrinked and attached to the bottle. At the time of mounting, the neck portion was adjusted so that the portion having a circumference of 103 mm (position of the label height of 170 mm) was one end of the label. As an evaluation of the finish after shrinkage, the strain in the 360-degree direction of the upper part of the attached label was measured using a gauge, and the maximum value of the strain was obtained. Evaluation was made according to the following criteria.
⊚: Maximum distortion less than 2.0 mm ○: Maximum distortion 2.0 mm or more and less than 3.0 mm ×: Maximum distortion 3.0 mm or more

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

[Label wrinkles]
The label was attached to the PET bottle under the same conditions as the shrinkage distortion condition of the label described above, and the wrinkle generation state was evaluated according to the following criteria.
⊚: The number of wrinkles with 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 with a size of 2 mm or more is 3 or more.

[Label height]
A label (height 170 mm) was attached to the 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

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

[Specific heat capacity difference before and after Tg ΔC _p ]
Using a temperature-modulated differential scanning calorimeter (TM DSC) "Q100" (manufactured by TA instruments), weigh 10 mg of the film in a hermetic aluminum pan, and in heat-only mode, the average temperature rise rate is 1 ° C./min and the modulation cycle is 40. I got a 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, thermometer and partial recirculation cooler, 100 mol% of dimethyl terephthalate (DMT) as a dibasic acid component and 100 mol% of ethylene glycol (EG) as a glycol component are added to ethylene. Glycol was charged so as to be 2.2 times the molar ratio of dimethyl terephthalate, and 0.05 mol% (relative to the acid component) of zinc acetate was used as a transesterification catalyst to distill off the produced methanol. However, the transesterification reaction was carried out. Then, 0.025 mol% of antimony trioxide (relative to the acid component) was added as a polycondensation catalyst, and the polycondensation reaction was carried out at 280 ° C. under a reduced pressure of 26.6 Pa (0.2 toll) to obtain the intrinsic viscosity. 0.70 dl / g of polyester (A) was obtained. This polyester is polyethylene terephthalate. In the production of the polyester (A), SiO ₂ (Silicia 266 manufactured by Fuji Silysia Chemical Ltd.) was added as a lubricant at a ratio of 8,000 ppm to the polyester. Further, the polyesters (B, C, D, E, F, G) shown in Table 1 were synthesized by the same method as described above. In the table, IPA is isophthalic acid, NPG is neopentyl glycol, CHDM is 1,4-cyclohexanedimethanol, and BD is 1,4-butanediol. The intrinsic viscosities of polyesters A, B, C, D, E, F and G are 0.70 dl / g, 0.70 dl / g, 0.73 dl / g, 0.73 dl / g and 0.70 dl / g, respectively. , 0.70 dl / g and 0.80 dl / g. In addition, each polyester was appropriately formed into chips.

The composition of the polyester raw material used in Examples and Comparative Examples, the resin composition of the films in Examples and Comparative Examples, and the production conditions are shown in Tables 1 and 2, respectively.

Example 1
The polyester A, polyester B, polyester E and polyester G described above were mixed at a mass ratio of 5:15:70:10 and charged into an extruder. This mixed resin was melted at 280 ° C., extruded from a T-die, wound around a rotating metal roll cooled to a surface temperature of 30 ° C., and rapidly cooled to obtain an unstretched film having a thickness of 194 μm. The take-up speed of the unstretched film (rotational speed of the metal roll) at this time was about 20 m / min. The Tg of the unstretched film was 67 ° C.

The obtained unstretched film was guided to a longitudinal stretching machine in which a plurality of roll groups were continuously arranged, and stretched four 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 95 ° C. A 30% relaxation treatment was performed in the longitudinal direction by utilizing the speed difference between the rolls at the inlet and the outlet of the heating furnace. The relaxation processing time was 0.6 seconds.

The film after the relaxation treatment was guided to a transverse heat treatment machine (tenter), and was 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, the hot air from the intermediate heat treatment zone and the cooling zone so that when the strip-shaped piece of paper hangs down without passing through the film, the piece of paper hangs down almost completely in the vertical direction. The cooling air was cut off. When the film was running, the distance between the film and the shielding plate was adjusted so that most of the accompanying flow accompanying the running of the film was blocked by the shielding 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 shielding plate was adjusted so that most of the accompanying flow accompanying the running of the film was blocked by the shielding plate at the boundary between the intermediate zone and the cooling zone.

The relaxed film after longitudinal stretching guided by the tenter was heat-treated at 130 ° C. for 5 seconds in the 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 naturally cooled film is guided to a cooling zone, and the film is actively forcibly cooled by blowing low-temperature wind until the surface temperature of the film reaches 100 ° C., and then in the width direction (horizontal direction) at 95 ° C. It was stretched 5 times.

The film after the transverse stretching was led to a final heat treatment zone, and the film was heat-treated at 98 ° C. at 98 ° C. for 5 seconds with a relaxation rate of 0% in the longitudinal direction and a relaxation rate of 3% in the width direction. Then, it was cooled, both edges were cut and removed, and the film was wound into a roll with a width of 500 mm to continuously produce a biaxially stretched film having a thickness of 20 μm over a predetermined length. The properties of the obtained film were evaluated by the method described above. The evaluation results are shown in Table 3. The contraction stress curve is shown in FIG. 2, and the reverse heat flow measured by the temperature-modulated DSC is shown in FIG.

Example 2
Polyester A, polyester B, polyester F and polyester G in mass ratio 5:
A film having a thickness of 20 μm was produced in the same manner as in Example 1 except that the setting was 15:70:10. The Tg of the unstretched film was 67 ° 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 1 except that polyester A, polyester B, polyester C, polyester E and polyester G were mixed at a mass ratio of 5:15:60:10:10. The Tg of the unstretched film was 67 ° C. The evaluation results are shown in Table 3.

Example 4
A film having a thickness of 20 μm was produced in the same manner as in Example 1 except that polyester A, polyester B, polyester D, polyester E and polyester G were mixed at a mass ratio of 5:15:60:10:10. The Tg of the unstretched film was 67 ° C. The evaluation results are shown in Table 3.

Example 5
A film having a thickness of 20 μm was produced in the same manner as in Example 1 except that polyester A, polyester B, polyester E and polyester G were mixed at a mass ratio of 25: 5: 60: 10. The Tg of the unstretched film was 67 ° C. The evaluation results are shown in Table 3.

Example 6
A film having a thickness of 20 μm was produced by the same method as in Example 2 except that the thickness of the unstretched film was 232 μm, the temperature of the intermediate heat treatment was 125 ° C., the time was 8 seconds, and the transverse stretching ratio was 6 times. .. The Tg of the unstretched film was 67 ° C. The evaluation results are shown in Table 3.

Example 7
The thickness of the unstretched film is 260 μm, the longitudinal stretch ratio is 4.2 times, the relaxation rate in the intermediate heat treatment is 0%, the transverse stretch ratio is 7 times, and the relaxation rate in the longitudinal direction in the final heat treatment step is 33.3%. A film having a thickness of 20 μm was produced by the same method as in Example 6 except that the relaxation rate in the width direction was set to 5%. The Tg of the unstretched film was 67 ° C. The evaluation results are shown in Table 3.

Example 8
A film having a thickness of 20 μm was produced in the same manner as in Example 1 except that the thickness of the unstretched film was 181 μm, the temperature of the intermediate heat treatment was 135 ° C., and the relaxation rate in the longitudinal direction was 33.3%. The Tg of the unstretched film was 67 ° C. The evaluation results are shown in Table 3.

Example 9
A film having a thickness of 20 μm was produced in the same manner as in Example 1 except that polyester A, polyester B, polyester D, polyester F and polyester G were mixed at a mass ratio of 5:15:10:60:10. The Tg of the unstretched film was 67 ° C. The evaluation results are shown in Table 3.

Example 10
The temperature of the heating furnace after longitudinal stretching was changed from 95 ° 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). Examples 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 11
The relaxation rate in the longitudinal direction in the heating furnace after longitudinal stretching was changed from 30% to 18%, the relaxation rate in the longitudinal direction in the intermediate heat treatment step was changed from 28.6% to 22%, and the final heat treatment step. 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 was changed from 0% to 21.8%. The evaluation results are shown in Table 3.

Comparative Example 1
The thickness of the unstretched film was 97 μm, and the temperature of the intermediate heat treatment was changed to 100 ° C., the time was 8 seconds, the transverse stretching temperature was changed to 70 ° C., and the final heat treatment temperature was changed to 80 ° C. without longitudinal stretching and relaxation in the longitudinal direction. A film having a thickness of 20 μm was produced in the same manner as in Example 1 except for the above. The evaluation results are shown in Table 3. The film had a small stress ratio and a large difference between the maximum shrinkage stress and the shrinkage stress after 30 seconds (see FIG. 2).

Comparative Example 2
Polyester A, polyester B, polyester C and polyester G are mixed at a mass ratio of 5: 5: 80: 10, the thickness of the unstretched film is 200 μm, the temperature of the intermediate heat treatment is 123 ° C., the time is 8 seconds, and the final heat treatment. 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 width direction was set to 0%. The Tg of the unstretched film was 67 ° C. The evaluation results are shown in Table 3.

Since the heat-shrinkable polyester film of the present invention has a high heat-shrinkability and excellent properties as described above, it can be suitably used for labeling 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 (6)

A biaxially stretched heat-shrinkable polyester film that satisfies the following requirements (1) to (5), has a thickness of 10 μm or more and 70 μm or less, and has a haze value of 2% or more and 13% or less.
(1) Isophthalic acid is used as an amorphous monomer in an amount of 1 mol% or more and 30 mol% or less in 100 mol% of the acid component.
(2) The heat shrinkage rate of hot water when the film is immersed in warm water at 98 ° C. for 10 seconds is 60% or more and 90% or less in the main shrinkage direction of the film.
(3) The heat shrinkage rate of hot water when the film is immersed in warm water at 98 ° C. for 10 seconds is -5% or more and 3% or less in the direction orthogonal to the main shrinkage direction of the film.
(4) The right-angle tear strength per unit thickness in the direction orthogonal to the main contraction direction after shrinking 10% in the main contraction direction in warm water at 80 ° C. is 180 N / mm or more and 295 N / mm or less.
(5) Thickness unevenness in the main shrinkage direction per 1 m of film is 1% or more and 12% or less. Claim 1 that the maximum shrinkage stress in the film main shrinkage direction measured with hot air at 90 ° C. is 2 MPa or more and 14 MPa or less, and the shrinkage stress 30 seconds after the start of measurement is 60% or more and 100% or less of the maximum shrinkage stress. The heat-shrinkable polyester-based film described in. The heat according to claim 1 or 2, wherein the natural shrinkage rate in the main shrinkage direction after aging treatment at a temperature of 40 ° C. and a humidity of 65% RH for 672 hours is 0.3% or more and 1.0% or less. Shrinkable polyester film. The heat-shrinkable polyester-based film according to any one of claims 1 to 3, wherein only isophthalic acid or isophthalic acid and neopentyl glycol and / or cyclohexanedimethanol are used as the amorphous monomer. _{Claims 1 to 4 in which the specific heat capacity difference ΔC p} around Tg when the reverse heat flow is measured by the temperature-modulated DSC is 0.1 J / (g · ° C) or more and 0.7 J / (g · ° C) or less. The heat-shrinkable polyester-based film according to any one. A packaging obtained from the heat-shrinkable polyester-based film according to any one of claims 1 to 5, wherein the label is formed by covering at least a part of the outer periphery of the object to be packaged and heat-shrinking the label. body.