JP6740577B2 - Heat-shrinkable polyester film and package - Google Patents

Description

The present invention relates to a heat-shrinkable polyester film that shrinks in the longitudinal direction and a packaging body, and more specifically, it is suitable for label applications, banding applications for binding lunch boxes, etc. In addition to the excellent natural shrinkage resistance caused by the above, the reduction in shrinkage rate at high temperature storage is small, so the product is a problem unique to the film that shrinks in the longitudinal direction due to paper tube crushing and surface wrinkles that occur when stored at high temperature. The present invention relates to a heat-shrinkable polyester film capable of eliminating shrinkage loss and shrink-finishing at a constant heat-shrinking temperature throughout the year.

In recent years, a stretched film made of polyvinyl chloride resin, polystyrene resin, polyester resin or the like (so-called, so-called, for the purpose of label packaging, cap seal, integrated packaging, etc., that also protects glass bottles and PET bottles and displays products Heat-shrinkable films) have become widely used. Among such heat-shrinkable films, polyvinyl chloride-based films have problems such as low heat resistance and the generation of dioxin during incineration. Further, the polystyrene-based film is inferior in solvent resistance, an ink having a special composition must be used for printing, and there is a problem that a large amount of black smoke is generated with an offensive odor during incineration. Therefore, polyester-based heat-shrinkable films, which have high heat resistance, are easy to incinerate, and have excellent solvent resistance, have been widely used in shrink-wrapping applications.

As a general heat-shrinkable polyester film, a film that shrinks in the width direction is widely used. Here, when it is used as a label film for a bottle or a banding film for binding a lunch box container or the like, the film must be formed into an annular shape and attached to the bottle or lunch box container, and then heat-shrinked in the circumferential direction. Therefore, when mounting a heat-shrinkable film that heat-shrinks in the width direction as a banding film, after forming an annular body so that the width direction of the film is the circumferential direction, the annular body is set at a predetermined length. It must be cut and attached to the bottle or lunch container by hand. Therefore, it is difficult to attach a label film or a banding film made of a heat-shrinkable film that heat-shrinks in the width direction to a bottle or a lunch box at high speed. Therefore, recently, there has been a demand for a film that is heat-shrinkable in the longitudinal direction such that it can be shrink-wrapped by being wound around a bottle or a bento container and mounted directly from a film roll and heated. By having the property of heat shrinking in the longitudinal direction, the center sealing step of forming and sealing the film annular body and the processing such as cutting and covering with a hand are unnecessary, and it can be mounted at high speed.

In banding film applications for bento containers, at the time of shrinking the film in the longitudinal direction by heating, to prevent the container from being deformed by the heat, and in order to perform shrink wrapping at high speed, at a low temperature and a small amount of heat. Sufficient shrinkage must be obtained. Therefore, a heat-shrinkable film in the longitudinal direction having high low-temperature shrinkability is required. A heat-shrinkable polyester film stretched in the longitudinal direction is widely used as such a film that contracts in the longitudinal direction and has a high low-temperature shrinkage ratio. However, the film has a high natural shrinkage ratio, and the film tends to shrink when stored in a season when the outside air temperature is high, such as in the summer, or when it is stored in a high temperature environment such as a truck bed during transportation. .. As a result, there is a problem that a paper tube is crushed in the film roll and surface wrinkles are generated, which makes it difficult to use as a packaging film and causes a loss. Furthermore, when the film is generally stored in a high-temperature environment, its inherent heat shrinkability deteriorates, so that the shrinkage is insufficient during shrink-finishing with hot air, resulting in an external appearance. There is a problem that becomes worse. Therefore, it is necessary to suppress the occurrence of natural shrinkage and reduction of heat shrinkability by using a cold storage warehouse or a cold storage vehicle, especially during transportation and storage in seasons when the outside air temperature rises, which is one of the factors that increase costs. Has become.

A heat-shrinkable polyester film having improved natural shrinkage resistance has been proposed so far. For example, in Patent Document 1, the shrinkage rate in the main shrinkage direction is 10% or more and less than 80% under the shrinkage condition of 80° C. for 10 seconds by controlling the film forming conditions, and the natural shrinkage rate is under the condition of 60° C. for 8 hours. Films of 2.0% or less are disclosed.

However, since the main shrinking direction of the film is the width direction, it cannot be heat-shrinked by being wound around the bottle or lunch box container directly from the film roll. Further, since the shrinkage ratio of the film in the main shrinkage direction at 70° C. is substantially 3% or less at 70° C. for 10 seconds, there is a problem that the low-temperature shrinkability is low and the shrink finish with hot air cannot be accelerated.

As a method for forming a heat-shrinkable polyester film that has a good natural shrinkage in the longitudinal direction, Patent Document 2 achieves a good natural shrinkage by controlling the cooling speed of the film after stretching in the longitudinal direction. ing.

However, this film forming method uses a biaxial stretching film forming method in which the width direction is first stretched and then the longitudinal direction is stretched. Therefore, for a uniaxially stretched heat-shrinkable film that is stretched only in the longitudinal direction, the orientation of the width direction becomes larger, and the entanglement of molecules becomes stronger, which greatly contributes to the effect of suppressing the natural shrinkage rate. It is estimated that However, there is a problem that cost is increased because large-scale equipment for biaxial stretching is required. Therefore, the inventors considered that there is an urgent need to develop a longitudinally stretched heat-shrinkable polyester film which has a large longitudinal orientation and a high low-temperature shrinkage ratio but is excellent in natural shrinkage resistance.

Japanese Patent No. 5249996 Japanese Patent No. 4411556

The object of the present invention relates to a heat-shrinkable polyester film that shrinks in the longitudinal direction and a package, and more specifically, it is suitable for label applications, banding applications for binding lunch boxes and the like, while being a long-term shrinkable film. It has excellent natural shrinkage resistance caused by high-temperature storage, and at the same time has a small decrease in shrinkage rate at high-temperature storage, it is a problem peculiar to the film that shrinks in the longitudinal direction. The present invention aims to provide a longitudinally stretched heat-shrinkable polyester film capable of shrink-finishing at a constant heat-shrinking temperature throughout the year by eliminating loss of product defects.

That is, the present invention has the following configurations.
1. A heat-shrinkable polyester film having ethylene terephthalate as a main constituent, which satisfies the following requirements (1) to (3).
(1) Hot water shrinkage in the main shrinkage direction when immersed in hot water at 70°C for 10 seconds is 20% or more and 60% or less (2) Nature of the main shrinkage direction when stored in 55°C, 35% RH atmosphere for 48 hours Shrinkage is less than 6% (3) Refractive index difference shown by the following formula is 0.06 or more Refractive index difference=(refractive index in main shrinkage direction)-(refractive index in direction orthogonal to main shrinkage direction)
2. The heat-shrinkable polyester film according to the first aspect, which has a maximum shrinkage stress in the main shrinkage direction of 15 MPa or less measured under hot air of 90°C.
3. 3. The heat-shrinkable polyester film according to the above 1 or 2, wherein the main shrinkage direction is the longitudinal direction.
4. Regarding the hot water shrinkage in the main shrinkage direction when immersed in hot water at 70° C. for 10 seconds, the shrinkage difference shown by the following formula is 15% or less. The heat-shrinkable polyester film described.
Shrinkage difference = (Hot water shrinkage before storage in 55°C 35%RH atmosphere for 48 hours)-(Hot water shrinkage after storage in 55°C 35%RH atmosphere for 48 hours)
5. A package obtained by covering at least a part of the outer periphery of an object to be packaged with the heat-shrinkable film according to any one of the first to fourth aspects, and then heat-shrinking the heat-shrinkable film.

As a result of intensive studies by the present inventors, stretching in the longitudinal direction is performed to obtain low-temperature shrinkability, and the natural shrinkage resistance that deteriorates when the orientation is increased is that stretching temperature is increased to stretch in the longitudinal direction. The present invention was found to be able to improve by relaxing the tension of molecules oriented in the longitudinal direction by performing a heat treatment at a temperature equal to or higher than the stretching temperature with equipment such as a roll or an IR heater after stretching in the longitudinal direction and ..

That is, according to the present invention, it relates to a heat-shrinkable polyester film shrinkable in the longitudinal direction and a packaging body, specifically, it is suitable for label applications, banding applications for binding lunch boxes, etc., and is a long-direction shrinkable film. However, since it is excellent in natural shrinkage resistance that occurs during high temperature storage, and at the same time, the reduction in shrinkage rate during high temperature storage is small, it is a problem peculiar to the film that shrinks in the longitudinal direction. It is possible to provide a longitudinally stretched heat-shrinkable polyester film capable of eliminating a product defect loss due to generation and performing shrink finish at a constant heat shrinkage temperature throughout the year.

Hereinafter, the heat-shrinkable polyester film of the present invention will be described in detail. The method for producing the heat-shrinkable polyester film will be described in detail later, but the film is usually obtained by transporting using a roll or the like and stretching. At this time, the transport direction of the film is referred to as a longitudinal direction, and the direction orthogonal to the longitudinal direction is referred to as a film width direction. Therefore, the width direction of the heat-shrinkable polyester film shown below is a direction perpendicular to the roll unwinding direction, and the film longitudinal direction is a direction parallel to the roll unwinding direction. The main shrinkage direction in the heat-shrinkable polyester films obtained in Examples and Comparative Examples is the longitudinal direction.

The heat-shrinkable polyester film of the present invention whose main shrinkage direction is the longitudinal direction has a natural shrinkage ratio of less than 6% in the main shrinkage direction when stored in a 55° C. 35% RH atmosphere for 48 hours, preferably 4%. Less, more preferably less than 2%. When the natural shrinkage in the main shrinkage direction is 6% or more when stored in an atmosphere of 55°C and 35% RH for 48 hours, thermal shrinkage of the film occurs due to temperature rise during storage, and the paper tube of the film roll It is not preferable because it is difficult to use due to deformation of the film and wrinkles on the surface of the film, resulting in loss of product defects. Furthermore, the shrinkage rate of the film after storage becomes large, which is not preferable.

In order to suppress the natural shrinkage rate in the main shrinkage direction to less than 6% when stored in an atmosphere of 55° C. and 35% RH for 48 hours, it is useful to control the stretching conditions in the longitudinal direction of the film. For example, when the film is drawn in the longitudinal direction by using the speed difference of rolls, it is necessary to control the drawing temperature or the heat treatment temperature. With regard to the stretching temperature, the natural shrinkage during storage at high temperature can be suppressed by performing stretching at a temperature as high as possible within the range in which the thickness unevenness in the longitudinal direction after stretching does not deteriorate. Regarding the heat treatment, by performing the heat treatment at a temperature equal to or higher than the stretching temperature, the natural shrinkage rate during high temperature storage can be suppressed. As described above, by controlling the stretching temperature and the heat treatment temperature, the tension of the molecules oriented in the longitudinal direction can be relaxed, and the natural shrinkage rate during high temperature storage can be suppressed.

The heat-shrinkable polyester film of the present invention has a hot water shrinkage in the main shrinkage direction of 20% or more and 60% or less, preferably 25% or more and 55% or less, more preferably 50% or less, when it is immersed in hot water of 70° C. for 10 seconds. It is 30% or more and 50% or less.

When the hot water shrinkage in the main shrinkage direction when immersed in 70° C. hot water for 10 seconds is less than 20%, the hot air temperature required for heat shrink finish with hot air becomes high, and the package such as a lunch box container is It may hurt by heat and is not preferable. Furthermore, the heating time required for shrink finish is long and the productivity is deteriorated, which is not preferable. Further, if the hot water shrinkage in the main shrinkage direction when immersed in hot water at 70° C. for 10 seconds is higher than 60%, the natural shrinkage of the film becomes high, which is not preferable.

The heat-shrinkable polyester film of the present invention has a refractive index difference represented by the following formula (1) of 0.06 or more, preferably 0.07 or more, and more preferably 0.08 or more. When the difference in refractive index is smaller than 0.06, the low temperature shrinkability becomes low and the shrink finish with hot air deteriorates, which is not preferable.
Refractive index difference=(refractive index in main shrinkage direction)-(refractive index in direction orthogonal to main shrinkage direction) Equation (1)

The heat-shrinkable polyester film of the present invention has a maximum shrinkage stress in the main shrinkage direction of the film of 15 MPa or less, preferably 14 MPa or less, and more preferably 13 MPa or less, as measured under hot air of 90°C. When the maximum shrinkage stress in the main shrinkage direction of the film measured under hot air of 90° C. is larger than 15 MPa, crushing of the paper tube and wrinkling of the surface layer are likely to occur when the film roll is stored at high temperature, which is not preferable.

The heat shrinkable polyester film of the present invention has a shrinkage difference of 15% or less as expressed by the following formula (2) with respect to hot water shrinkage in the main shrinkage direction when immersed in 70° C. hot water for 10 seconds. preferable. If the difference in shrinkage ratio is larger than 15%, the shrinkage finish with hot air is deteriorated, and therefore the shrinking finish temperature needs to be adjusted each time, which is not preferable, more preferably 13% or less, and further preferably 12% or less. ..
Shrinkage difference = (Hot water shrinkage before storage in 55°C 35%RH atmosphere for 48 hours)-(Hot water shrinkage after storage in 55°C 35%RH atmosphere for 48 hours) Equation (2)

The maximum shrinkage stress of the film can be controlled by the material and components of the film and the stretching conditions. As the material of the film that shrinks in the longitudinal direction, polyvinyl chloride or polyolefin resin is used, but in order to achieve the effect of the present invention, the natural shrinkage rate is lower than that of the above materials, and the low temperature shrinkability is excellent. It is important that it is a polyester resin. As a component constituting the polyester film, a film component having high crystallinity causes a high shrinkage stress, and therefore it is preferable to use a film component that suppresses crystallinity. Regarding the stretching conditions, the shrinkage stress can be controlled by adjusting the stretching temperature and the heat treatment temperature. Among them, the stretching temperature has a particular influence, and the shrinking stress can be suppressed by increasing the stretching temperature.

Examples of the dicarboxylic acid component constituting the polyester used in the present invention include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid and orthophthalic acid, and aliphatic compounds such as adipic acid, azelaic acid, sebacic acid and decanedicarboxylic acid. Examples thereof include dicarboxylic acid and alicyclic dicarboxylic acid.

When an aliphatic dicarboxylic acid (eg, adipic acid, sebacic acid, decanedicarboxylic acid, etc.) is contained, the content is preferably less than 3 mol %. A heat-shrinkable polyester film obtained by using a polyester containing these aliphatic dicarboxylic acids in an amount of 3 mol% or more cannot provide stable wearability due to insufficient rigidity of the film during high-speed wear.

Further, it is preferable not to 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 polycarboxylic acids, it becomes difficult to achieve the required high shrinkage ratio.

Examples of the diol component constituting the polyester used in the present invention include aliphatic diols such as ethylene glycol, 1-3 propanediol, 1-4 butanediol, neopentyl glycol and hexanediol, and 1,4-cyclohexanedimethanol. Examples thereof include alicyclic diols and aromatic diols such as bisphenol A.

The polyester used in the heat-shrinkable polyester film of the present invention is a cyclic diol such as 1,4-cyclohexanedimethanol or a diol having 3 to 6 carbon atoms (for example, 1-3 propanediol, 1-4 butanediol). , Neopentyl glycol, hexanediol, etc.), and a polyester having a glass transition point (Tg) adjusted to 60 to 80° C. is preferable.

In addition, the polyester used for the heat-shrinkable polyester film of the present invention is such that the total amount of one or more kinds of monomer components that can be an amorphous component in 100 mol% of the polyhydric alcohol component in the total polyester resin is 10 mol% or more. It is necessary to be present, preferably 15 mol% or more, more preferably 17 mol% or more, and particularly preferably 20 mol% or more. Here, examples of the monomer that can be an amorphous component include neopentyl glycol, 1,4-cyclohexanediol, and isophthalic acid.

Here, the interpretation of the above-mentioned "can be an amorphous component" will be described in detail.

In the present invention, the “amorphous polymer” specifically refers to a case where it has no endothermic peak due to melting as measured by a DSC differential scanning calorimeter. Amorphous polymers are not substantially crystallized and cannot be in a crystalline state, or have an extremely low crystallinity even when crystallized.

Further, in the present invention, the "crystalline polymer" means a substance which is not the above "amorphous polymer", that is, a case where it has an endothermic peak due to melting as measured by a DSC differential scanning calorimeter. A crystalline polymer is one that has the property of being crystallizable, crystallizable, or already crystallized when the polymer is heated.

Generally, for polymers in which a large number of monomer units are bound, the stereoregularity of the polymer is low, the symmetry of the polymer is poor, the side chains of the polymer are large, the branching of the polymer is large, the intermolecular between the polymers When it has various conditions such as a low cohesive force, it becomes an amorphous polymer. However, depending on the existing state, crystallization may proceed sufficiently to form a crystalline polymer. For example, even if the polymer has a large side chain, when the polymer is composed of a single monomer unit, crystallization may proceed sufficiently to become crystalline. Therefore, even with the same monomer unit, the polymer may be crystalline or amorphous in some cases. Therefore, the expression “monomer capable of becoming an amorphous component” is used in the present invention.

Here, in the present invention, a monomer unit is a repeating unit that constitutes a polymer derived from one polyhydric alcohol molecule and one polycarboxylic acid molecule, and in the case of ε-caprolactone, a lactone. The structural units obtained by ring opening are shown.

When the monomer unit consisting of terephthalic acid and ethylene glycol is the main monomer unit constituting the polymer, a monomer unit consisting of isophthalic acid and ethylene glycol, a monomer unit consisting of terephthalic acid and neopentyl glycol, terephthalic acid and 1.4-cyclohexane A monomer unit composed of dimethanol, a monomer unit composed of isophthalic acid and butanediol, and the like are mentioned as the above-mentioned monomer which can be an amorphous component.

Among the polyesters used in the heat-shrinkable polyester film of the present invention, diols having 8 or more carbon atoms (eg octane diol etc.) or polyhydric alcohols having 3 or more valences (eg trimethylol propane, trimethylol ethane, glycerin). , Diglycerin, etc.) is preferably not contained. With the heat-shrinkable polyester film obtained by using the polyester containing these diols or polyhydric alcohols, it becomes difficult to achieve the required high shrinkage ratio.

The layer structure of the heat-shrinkable polyester film of the present invention is not limited, and may be a single layer film or a laminated film. In the case of a laminated film, the material and the number of layers of the film to be laminated are not particularly limited as long as the requirements of the present invention are satisfied, and it may be the same or different material as the film of the present invention. I do not care. However, in order to maintain the excellent low natural shrinkage characteristic of the present film, each layer in the case of a laminated film is preferably made of a polyester resin. The thickness of the present film in the case of a laminated film is not particularly limited, but if it is 50% or more with respect to the thickness of all layers, it is difficult to impair the natural shrinkage resistance, which is preferable.

The heat-shrinkable polyester film of the present invention is not limited in any way with respect to its manufacturing method, for example, the polyester raw material described above is melt-extruded by an extruder to form an unstretched film, and the unstretched film is formed. It can be obtained by stretching according to the method described below.

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 and 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 such 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 on a rotating drum from a die and rapidly solidifying it can be suitably used.

Further, the obtained unstretched film is preferably reheated by an appropriate method such as hot air, warm water, infrared ray or the like, and uniaxially stretched in the longitudinal direction by a roll method, a tenter method, a tubular method or the like. Among them, the roll method is more preferable because it is inexpensive as an apparatus. The stretching temperature needs to be changed depending on the glass transition temperature (Tg) of each resin constituting the heat-shrinkable film and the required properties, but from the viewpoint of productivity and shrinkage properties, it is generally a temperature of Tg+18°C or higher and Tg+40°C or lower. It is necessary to carry out so that the magnification is 2.5 times or more and 6.0 times or less. If the stretching temperature is lower than Tg+18° C., it is not preferable because breakage easily occurs during stretching, and the natural shrinkage rate and shrinkage stress are further increased, which is not preferable. On the other hand, when the temperature exceeds Tg+40° C., the thickness unevenness in the longitudinal direction becomes worse, which is not preferable. The lower limit of the stretching temperature is preferably Tg+20°C or higher, and more preferably Tg+22°C or higher. Moreover, the upper limit of the stretching temperature is preferably Tg+37° C. or lower, and more preferably Tg+34° C. or lower. On the other hand, if the draw ratio is less than 2.5 times, not only the productivity is poor, but also sufficient shrinkage cannot be obtained, and the thickness unevenness in the longitudinal direction is also unfavorable. On the other hand, if it exceeds 6.0 times, breakage is likely to occur during stretching, the shrinkage stress increases, and the natural shrinkage ratio increases, which is not preferable. The lower limit of the draw ratio is preferably 3.0 times or more, and more preferably 3.5 times or more. The upper limit of the draw ratio is preferably 5.5 times or less, more preferably 5.0 times or less.

The stretched film is preferably heat-treated in the heat treatment step for the purpose of suppressing the natural shrinkage rate. For the heat treatment, any known method such as roll, tenter, and IR heater may be adopted, but the roll and IR heater are more preferable because they are inexpensive as an apparatus. The heat treatment condition is not particularly limited, but from the viewpoint of productivity and shrinkage characteristics, it is preferable to perform the treatment at a stretching temperature or higher and a stretching temperature +40° C. or lower for 1 to 5 seconds. When the heat treatment temperature is lower than the stretching temperature, a sufficient heat treatment effect cannot be obtained, which is not preferable. Further, when the heat treatment temperature is higher than the stretching temperature +40° C., a rapid shrinkage behavior of the film occurs and the thickness unevenness of the film deteriorates, which is not preferable. When the heat treatment time is less than 1 second, a sufficient heat treatment effect cannot be obtained, which is not preferable. Further, if the heat treatment time is longer than 5 seconds, it is not preferable because it is necessary to reduce the production rate and the productivity is deteriorated, or large-scale equipment is required, which causes a cost increase.

As a result of intensive studies by the present inventors, stretching in the longitudinal direction is performed to obtain low-temperature shrinkability, and the natural shrinkage resistance that deteriorates when the orientation is increased is that stretching temperature is increased to stretch in the longitudinal direction. The present invention was found to be able to improve by relaxing the tension of molecules oriented in the longitudinal direction by performing a heat treatment at a temperature equal to or higher than the stretching temperature with equipment such as a roll or an IR heater after stretching in the longitudinal direction and .. From the viewpoint of improving the natural shrinkage resistance, for the step of increasing the stretching temperature and stretching in the longitudinal direction and the step of performing heat treatment at a temperature equal to or higher than the stretching temperature with equipment such as a roll or an IR heater after stretching in the longitudinal direction, , You need to do at least one.

The thickness of the heat-shrinkable polyester film of the present invention is not particularly limited, but is preferably 5 to 100 μm, more preferably 10 to 95 μm as a heat-shrinkable film for label use and banding use.

The packaging of the present invention is formed by heat-shrinking the banding film (and label) obtained from the heat-shrinkable polyester film of the present invention by covering at least a part of the outer periphery of the packaging target. is there. Examples of the objects to be packaged include PET bottles for beverages, various bottles, cans, confectionery, plastic containers such as lunch boxes, and paper boxes. In addition, when the label obtained from the heat-shrinkable polyester film is heat-shrinked to cover the packaging object, the banding film (and the label) is usually heat-shrinked by about 5 to 70%. Adhere closely to the package. The banding film (and the label) covered with the object to be packaged may be printed or may not be printed.

The banding film (and label) can be produced by rolling a rectangular film in the lengthwise direction and stacking the ends and adhering it to form a label, or by winding a roll into a roll lengthwise film. It is rounded in the direction and the ends are overlapped and adhered to the film to form a tube-shaped body that is cut into a label. As a method for adhering the films to each other, known methods such as fusing sealing, solvent adhesion, adhesion with a hot melt adhesive, and adhesion with an energy ray-curable adhesive can be used.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the modes of the Examples, and can be appropriately modified without departing from the gist of the present invention. is there. The measured values and evaluations shown in the examples were carried out as follows.

[Tg (glass transition point)]
It was determined based on JIS-K7121-1987 using a differential scanning calorimeter (manufactured by Seiko Denshi Kogyo KK, DSC220). 5 mg of an unstretched film was placed in a sample pan, the pan was covered with a lid, and the temperature was raised from -40°C to 120°C at a temperature increase rate of 10°C/min in a nitrogen gas atmosphere. .. The glass transition temperature was defined as the temperature at the intersection of the base line extension below the glass transition temperature and the tangent line showing the maximum slope at the transition.

[Shrinkage rate (heat shrinkage rate of hot water)]
The film was cut into a square of 10 cm×10 cm, immersed in hot water of 70±0.5° C. for 10 seconds under no load for heat shrinkage, and then immersed in water of 25°±0.5° C. for 10 seconds. Then, the film was pulled out from water, the dimension in the longitudinal direction of the film was measured, and the heat shrinkage rate was calculated according to the following formula 1.
Heat shrinkage rate={(length before shrinkage-length after shrinkage)/length before shrinkage}×100(%)

[Maximum contraction stress]
A strip-shaped film sample with a length of 150 mm in the longitudinal direction and a length of 20 mm in the width direction was cut out from the heat-shrinkable film, and a strong elongation measuring machine with a heating furnace (Tesilon PTM) manufactured by Toyo Baldwin Co., Ltd. The shrinkage stress was measured using -250 (registered trademark of Orientec Co.). The heating furnace of the strong elongation measuring machine was heated in advance to 90° C. and the distance between chucks for gripping the film sample was 100 mm. When attaching the sample to the chuck of the strength/elongation measuring machine, temporarily stop the air flow of the heating furnace, open the door of the heating furnace, and sandwich both 25 mm of both ends of the sample of 150 mm in the length direction between the chucks. The distance between the chucks was set to 100 mm, and the length direction of the sample was aligned, and the sample was fixed without loosening so that it was horizontal. After attaching the sample to the chuck, the door of the heating furnace was promptly closed and the blowing was restarted. The time when the door of the heating furnace is closed and the air flow is restarted is the contraction stress measurement start time, and the maximum value of the contraction stress measurement value from the contraction stress measurement start time to 30 seconds after the measurement start is the maximum contraction stress value. (Maximum shrinkage stress (MPa)).

[Refractive index]
Using an "Abbe refractometer 4T type" manufactured by Atago Co., each sample film was allowed to stand in an atmosphere of 23° C. and 65% RH for 2 hours or more and then measured.

[Natural shrinkage rate]
The obtained film is cut into a size of main shrinkage direction×orthogonal direction=200 mm×30 mm and left in an atmosphere of 55° C. and 35% RH for 48 hours (high temperature storage), and then the longitudinal dimension of the film is measured, The natural shrinkage ratio was calculated by the following formula (3).
Natural shrinkage={(length before high temperature storage-length after high temperature storage)/length before high temperature storage}×100(%) ··· Equation (3)

[Shrinkage difference after high temperature storage]
A film roll having a width of 50 mm and a length of 4000 m was prepared from the obtained film, left for 48 hours (stored at high temperature) in an atmosphere of 55° C. and 35% RH, and then a film of 10 m was removed from the surface layer of the roll. Then, a film having a length of 30 cm was sampled from the surface layer of the obtained film roll, and the shrinkage rate when immersed in hot water at 70° C. for 10 seconds was determined by the above shrinkage rate evaluation method, and the shrinkage rate was calculated from the following formula (4). The rate difference (decrease in shrinkage rate after high temperature storage) was determined.
Shrinkage rate difference=(Hot water shrinkage rate before storage in 55° C. 35% RH atmosphere for 48 hours)−(Hot water shrinkage rate after storage in 55° C. 35% RH atmosphere for 48 hours) Equation (4)

[Shrink finish (wrap round)]
For a plastic container of bento (side 150 x 150 mm, height 100 mm), a film with a width of 50 mm is stretched in the circumferential direction of the container (longitudinal direction) so that the body and lid of the container are bound by the film. ), wound and sealed at 170° C., and then heated in a hot air tunnel at a set temperature of 90° C. for heat shrink finish. Regarding the evaluation of wrinkles, in FIG. 1, the number of wrinkles with a length of 5 cm or more entering the side of the lunch container was judged, and the criteria were as follows: 0: 4 to 4 △: 5 to 14 ×: 15 or more

Insufficient shrinkage was judged based on whether shrinkage was insufficient after finishing shrinkage, and the criteria were as follows.
○: No shrinkage is insufficient ×: Shrinkage is insufficient

[Stability of shrink finish (wrap round)]
Using the high-temperature storage film roll after evaluation of shrinkage reduction after high-temperature storage, shrink-finishing is carried out in the same manner as the above-mentioned shrinkage finish evaluation, and comparison with the finish before high-temperature treatment is performed, shrinking finish The stability of sex was evaluated. The standard of stability of shrinkage finish was as follows.
○: Equal to or more than before high temperature storage ×: Worse than before high temperature storage

[Paper tube crash]
The dimension of the inner diameter of the paper tube of the high temperature storage film roll prepared by the evaluation of the shrinkage reduction after the high temperature storage was measured and judged from the reduction amount of the paper tube inner diameter obtained from the following formula 4. The criteria are as follows.
Reduction of inner diameter of paper tube = inner diameter before high temperature storage-inner diameter after high temperature storage ··· Equation 4
◯: Reduction of inner diameter is less than 1 mm ×: Reduction of inner diameter is 1 mm or more

[Surface wrinkles]
The surface wrinkles of the high temperature storage film roll prepared by the above-described evaluation of shrinkage reduction after high temperature storage were confirmed and judged. The criteria are as follows.
○: No wrinkles occurred ×: Wrinkles occurred

The composition of the raw materials used in the following Examples and Comparative Examples is shown in Table 1, the ratio of the mixed raw materials used in each layer is shown in Table 2, the film production conditions are shown in Table 3, and the evaluation results in Examples and Comparative Examples are shown in Table 1. It shows in Table 4.

<Preparation of polyester raw material>
Synthesis example 1
In a stainless steel autoclave equipped with a stirrer, a thermometer and a partial reflux condenser, dimethyl terephthalate (DMT) 100 mol% as a dicarboxylic acid component and ethylene glycol (EG) 100 mol% as a polyhydric alcohol component, Ethylene glycol was added so that the molar ratio was 2.2 times that of dimethyl terephthalate, zinc acetate was 0.05 mol% (based on the acid component) as a transesterification catalyst, and antimony trioxide was 0.225 mol as a polycondensation catalyst. % (Based on the acid component) was added, and the transesterification reaction was performed while distilling off the produced methanol to the outside of the system. Then, a polycondensation reaction was performed under a reduced pressure condition of 280° C. and 26.7 Pa to obtain a polyester 1 having an intrinsic viscosity of 0.75 dl/g. The composition is shown in Table 1.
Synthesis examples 2-3
By the same method as in Synthesis Example 1, polyesters 2 and 3 shown in Table 1 were obtained. In the table, NPG is neopentyl glycol, BD is 1,4-butanediol, and DEG is by-product diethylene glycol. The intrinsic viscosity of each polyester was 2:0.74 dl/g and 3:1.20 dl/g, respectively. Each polyester was appropriately made into a chip shape.

Example 1
The above polyester 1, polyester 2 and polyester 3 were mixed in a mass ratio of 30:60:10 to obtain a resin mixture for the skin layer. The above polyester 1, polyester 2, and polyester 3 were mixed in a mass ratio of 30:30:40 to obtain a resin mixture for the core layer. The resin mixture for each layer of the skin layer and the core layer was coextruded at a temperature of 280° C. using a T-die mold equipped with a two-layer multi-manifold by using two twin-screw extruders, and immediately After cooling with a cooling roll, an unstretched film having a thickness of 48 μm in two layers of skin layer/core layer was obtained. The Tg of the unstretched film was 62°C. At this time, co-extrusion was performed so that the thickness ratio of the skin layer and the core layer was skin layer:core layer=1:4. Then, the unstretched film is introduced into a longitudinal stretching machine in which a plurality of roll groups are continuously arranged, heated in a preheating roll state until the film temperature reaches 95° C., and then the stretching ratio in the longitudinal direction is 4. by a roll stretching method. The film was longitudinally stretched 0 times so that the thickness of the film after stretching was 12 μm. After the longitudinal stretching, it was cooled with a cooling roll whose surface temperature was set to 25° C., and then wound into a roll. The characteristics of the obtained film were evaluated by the above methods. The evaluation results are shown in Table 3. As a result of the evaluation, it was a good result that it had sufficient shrinkability, had good shrink finish before and after high temperature storage, and did not suffer from crushing of paper tubes and wrinkles due to high temperature storage.

[Example 2]
The same procedure as in Example 1 was carried out except that the stretching temperature in the longitudinal direction was 80° C., and after the stretching in the longitudinal direction, heat treatment was performed with a roll at 80° C. for 5 seconds. As a result of the evaluation, it was a good result that it had sufficient shrinkability, had good shrink finish before and after high temperature storage, and did not suffer from crushing of paper tubes and wrinkles due to high temperature storage.

[Example 3]
The same procedure as in Example 1 was carried out except that the stretching temperature in the longitudinal direction was 80° C., and after the stretching in the longitudinal direction, heat treatment was performed for 1 second with an IR heater. At this time, the film temperature after the heat treatment was 100°C. As a result of the evaluation, it was a good result that it had sufficient shrinkability, had good shrink finish before and after high temperature storage, and did not suffer from crushing of paper tubes and wrinkles due to high temperature storage.

[Example 4]
The above polyester 1, polyester 2 and polyester 3 were mixed at a mass ratio of 30:60:10 and charged into an extruder. Then, the 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 48 μm. The Tg of the unstretched film was 68°C. Next, the sheet was heated to 95° C. and longitudinally stretched by a roll stretching method so that the stretching ratio in the longitudinal direction was 4.0 times and the total thickness of the stretched film was 12 μm. After the longitudinal stretching, it was cooled with a cooling roll and then wound into a roll. The characteristics of the obtained film were evaluated by the above methods. As a result of the evaluation, it was a good result that it had sufficient shrinkability, had good shrink finish before and after high temperature storage, and did not suffer from crushing of paper tubes and wrinkles due to high temperature storage.

[Example 5]
The same procedure as in Example 4 was performed, except that the stretching temperature in the longitudinal direction was 80° C., and after the stretching in the longitudinal direction, heat treatment was performed with a roll at 80° C. for 5 seconds. As a result of the evaluation, it was a good result that it had sufficient shrinkability, had good shrink finish before and after high temperature storage, and did not suffer from crushing of paper tubes and wrinkles due to high temperature storage.

[Example 6]
The same procedure as in Example 4 was carried out except that the stretching temperature in the longitudinal direction was set to 80° C., and after the stretching in the longitudinal direction, heat treatment was performed for 1 second with an IR heater. At this time, the film temperature after the heat treatment was 100°C. As a result of the evaluation, it was a good result that it had sufficient shrinkability, had good shrink finish before and after high temperature storage, and did not suffer from crushing of paper tubes and wrinkles due to high temperature storage.

[Example 7]
The same procedure as in Example 4 was carried out except that the stretching ratio in the longitudinal direction was 5.0 times, and after the stretching in the longitudinal direction, heat treatment was performed with an IR heater for 1 second. At this time, the film temperature after the heat treatment was 110°C. As a result of the evaluation, it was a good result that it had sufficient shrinkability, had good shrink finish before and after high temperature storage, and did not suffer from crushing of paper tubes and wrinkles due to high temperature storage.

Comparative Example 1
Example 1 was repeated except that the stretching temperature in the longitudinal direction was 80°C. As a result of the evaluation, the film before the high temperature storage had a good shrink finish, but after the high temperature storage, the finish deteriorated and paper tube crushing and surface wrinkling occurred.

[Comparative Example 2]
Same as Example 4 except that the stretching temperature in the longitudinal direction was 80°C. As a result of the evaluation, the film before the high temperature storage had a good shrink finish, but after the high temperature storage, the finish deteriorated and paper tube crushing and surface wrinkling occurred.

[Comparative Example 3]
Example 4 was the same as Example 4 except that the stretching temperature in the longitudinal direction was 120°C. As a result of the evaluation, the paper tube crushing and the surface layer wrinkles did not occur after the high temperature storage, but the low temperature shrinkability was low before the high temperature storage, and the shrink finish defect occurred.

[Comparative Example 4]
After stretching in the longitudinal direction, the same procedure as in Example 5 was carried out except that heat treatment was performed with a roll at 70° C. for 5 seconds. As a result of the evaluation, the film before the high temperature storage had a good shrink finish, but after the high temperature storage, the finish deteriorated and paper tube crushing and surface wrinkling occurred.

[Comparative Example 5]
After stretching in the longitudinal direction, the same procedure as in Example 6 was carried out except that the film temperature after heat treatment for 1 second with an IR heater was changed to 75°C. As a result of the evaluation, the film before the high temperature storage had a good shrink finish, but after the high temperature storage, the finish deteriorated and paper tube crushing and surface wrinkling occurred.

Since the heat-shrinkable polyester film of the present invention has excellent properties as described above, it can be suitably used for label applications and banding applications for binding lunch boxes and the like. The bottle obtained by using the heat-shrinkable polyester film of the present invention as a label and the package such as a lunch box container used as a banding film have a beautiful appearance.

Claims (4)

Ethylene terephthalate is the main constituent component, and the total of one or more monomer components that can be amorphous components in 100 mol% of the polyhydric alcohol component in all polyester resins is 10 mol% or more, and the main shrinkage direction is the longitudinal direction. A heat-shrinkable polyester-based film that satisfies the following requirements (1) to (3) and is used for application by winding around a bottle or a container.
(1) Hot water shrinkage in the main shrinkage direction when immersed in hot water at 70°C for 10 seconds is 20% or more and 60% or less (2) Nature of the main shrinkage direction when stored in 55°C, 35% RH atmosphere for 48 hours Shrinkage is less than 4 % (3) Refractive index difference shown by the following formula is 0.06 or more Refractive index difference = (refractive index in main shrinkage direction)-(refractive index in direction orthogonal to main shrinkage direction) The maximum shrinkage stress in the main shrinkage direction measured under hot air of 90° C. is 15 MPa or less, and the heat-shrinkable polyester film according to claim 1. Regarding the hot water shrinkage in the main shrinkage direction when immersed in hot water at 70° C. for 10 seconds, the shrinkage difference shown by the following formula is 15% or less, and the shrinkage difference is 15% or less. Heat-shrinkable polyester film.
Shrinkage difference = (Hot water shrinkage before storage in 55°C 35%RH atmosphere for 48 hours)-(Hot water shrinkage after storage in 55°C 35%RH atmosphere for 48 hours) A package obtained by covering at least a part of the outer periphery of an object to be packaged with the heat-shrinkable film according to claim 1, and then heat-shrinking the heat-shrinkable film.