KR102463003B1 - Heat-shrinkable polyester film and packaging material - Google Patents

Abstract

(4) 필름 주 수축방향의 굴절률이 1.600 이상인 것을 특징으로 한다.The present invention has sufficient heat shrinkage characteristics in the main shrinkage direction, which is the longitudinal direction, has a low rate of heat shrinkage in the width direction orthogonal to the main shrinkage direction, the shrinkage stress in the main shrinkage direction is not too high, and the reduction of the shrinkage stress is An object of the present invention is to provide a heat-shrinkable polyester film that is small in size and has high followability to a container, which is an object to be packaged, during shrinkage, and is less likely to become loose.
In order to solve the above problems, the heat-shrinkable polyester film of the present invention is a heat-shrinkable polyester film in which the main shrinkage direction is a longitudinal direction,
(1) In the case of treatment in 98°C hot water for 10 seconds, the shrinkage rate of hot water in the main shrinking direction of the film is 40% or more and 80% or less,
(2) When treated in 98°C hot water for 10 seconds, the shrinkage rate of hot water in the direction perpendicular to the main shrinkage direction of the film is -5% or more and 15% or less,
(3) With respect to the shrinkage stress in the main shrinking direction of the film measured under hot wind at 90°C, the shrinkage stress ratio expressed by the following formula is 0.6 or more and 1.0 or less,

(4) It is characterized in that the refractive index in the main shrinkage direction of the film is 1.600 or more.

Description

Heat-shrinkable polyester film and packaging material {Heat-shrinkable polyester film and packaging material}

The present invention relates to a heat-shrinkable polyester film and a package, and in particular, it is very suitable for a label use or a banding use that binds a lunch box, etc. It relates to a heat-shrinkable polyester film that can be finished with a small load.

Recently, stretched films made of polyvinyl chloride-based resin, polystyrene-based resin, polyester-based resin, etc. (so-called heat-shrinkable) are used for label packaging, cap seal, and integrated packaging that serves as both protection of glass and PET bottles and product display. film) is widely used. Among these heat-shrinkable films, polyvinyl chloride-based films not only have low heat resistance, but also have problems such as generating hydrogen chloride gas during incineration or causing dioxins. In addition, the polystyrene-based film has poor solvent resistance, it is necessary to use ink of a special composition during printing, and it is necessary to incinerate it at a high temperature, and there is a problem that it accompanies a bad smell and a large amount of black smoke is generated during incineration. For this reason, heat-shrinkable polyester films with high heat resistance, easy incineration and excellent solvent resistance have been widely used as shrink labels, and their usage tends to increase with the increase in the circulation of PET containers.

Moreover, as a normal heat-shrinkable polyester film, the thing which shrink|contracts greatly in the width direction is widely used. When used as a banding film for binding the label film of a bottle or a lunch box, etc., the film must be heat-shrinked in the circumferential direction after being mounted on a bottle or lunch box in a ring shape. When mounting as a film, after forming the annular body so that the width direction of the film becomes the circumferential direction, the annular body must be cut at predetermined lengths and mounted on a bottle or a lunch box by hand. Therefore, it is difficult to mount a label film or a banding film made of a heat-shrinkable film heat-shrinkable in the width direction to a bottle or a lunch box at high speed. For this reason, in recent years, the film heat-shrinkable in the longitudinal direction which can be directly wound around a bottle or a lunch box from a film roll and can be attached is calculated|required. The center sealing process of forming and sealing the film ring-shaped body, cutting, and processing such as hand covering are unnecessary, so that it is possible to mount the film at high speed.

As a demand for a shrink film, it is required to follow the shape of the object to be packaged during shrinkage and to have a feeling of tightness after shrinkage. In the case of a beverage bottle label, if the label does not follow the shape and does not feel tight, the label rotates and is difficult to open when the consumer holds the bottle body and opens the bottle cap. In addition, in the case of bending of the lunch box, a tight finish of the shrink film is required to prevent the contents of the lunch box from overflowing and to prevent the mixing of foreign substances.

As a method of imparting tautness after finishing shrinkage, it can be considered to increase the shrinkage stress, but if the shrinkage stress is too high, there is a problem that the container is deformed when packaged in a thin and soft beverage bottle or lunch box. In addition, there is a problem in that the adhesive portion of the tubular label or the banding film is peeled off due to high shrinkage stress.

For example, in Patent Document 1, after stretching in the longitudinal direction, intermediate heat treatment is performed, and then stretching in the width direction. A small heat-shrinkable film is described, and it is described that it has good followability to a container in label applications, is less likely to loosen after finishing, and has a good appearance.

However, in the case of the method described in Patent Document 1, there is a problem in that a large-scale facility for biaxial stretching is required and the cost increases. In addition, as described above, it is difficult to mount the film shrinking in the width direction to a bottle or a lunch box at high speed.

Japanese Patent No. 5240387 publication

An object of the present invention is to have sufficient heat shrinkage characteristics in the main shrinkage direction, which is the longitudinal direction, to have a low rate of heat shrinkage in the width direction orthogonal to the main shrinkage direction, and not to have excessively high shrinkage stress in the main shrinkage direction. An object of the present invention is to provide a heat-shrinkable polyester film that has high followability to a container, which is an object to be packaged, in shrinkage due to small damping, and is less likely to become loose.

That is, the present invention consists of the following configuration.

1. A heat-shrinkable polyester film whose main shrinkage direction is in the longitudinal direction, characterized in that it satisfies the following requirements (1) to (4).

(1) In the case of treatment in 98°C hot water for 10 seconds, the shrinkage rate of hot water in the main shrinkage direction of the film is 40% or more and 80% or less.

(2) When treated in 98°C hot water for 10 seconds, the shrinkage rate of hot water in the direction orthogonal to the main shrinkage direction is -5% or more and 15% or less

(3) With respect to the shrinkage stress in the main shrinkage direction of the film measured under hot wind at 90°C, the shrinkage stress ratio expressed by the following formula is 0.6 or more and 1.0 or less.

(4) The refractive index in the main shrinkage direction of the film is 1.600 or more

2. The heat-shrinkable polyester film according to 1 above, characterized in that the maximum shrinkage stress in the main shrinkage direction of the film measured under hot wind at 90°C is 15 MPa or less.

3. Heat shrinkability according to 1 or 2 above, characterized in that ethylene terephthalate is a main component and contains 10 mol% or more of at least one monomer component that may be an amorphous component in the total polyester resin component. polyester film.

4. The heat-shrinkable polyester film according to any one of 1 to 3, characterized in that neopentyl glycol is used as at least one monomer component that may be an amorphous component.

5. A package obtained by coating at least a part of the outer periphery of the object to be packaged with the heat-shrinkable polyester film according to any one of 1 to 4, followed by heat-shrinkage.

As a result of intensive studies by the present inventors, in a single-layer film made of a single resin or a laminated film in which different types of resins are laminated, the shrinkage stress in the main shrinkage direction is not too high by using at least one layer of polyester resin of a specific composition, respectively, In addition, since the damping of the shrinkage stress is small, it has been found that the followability to the container, which is an object to be packaged, is high during shrinkage, and thus loosening is less likely to occur, and thus the present invention has been completed.

That is, according to the present invention, it has sufficient heat shrinkage characteristics in the main shrinkage direction, which is the longitudinal direction, and has a low rate of heat shrinkage in the width direction orthogonal to the main shrinkage direction, the shrinkage stress in the main shrinkage direction is not too high, and the shrinkage stress Since the attenuation of the film is small, it is possible to provide a heat-shrinkable polyester film that has a high followability to a container, which is an object to be packaged, during shrinkage, and is less likely to become loose. The heat-shrinkable polyester film of the present invention can be very suitably used as a film label for a bottle or a banding film for binding containers such as lunch boxes, and since the main shrinkage direction is the longitudinal direction, it can be mounted very efficiently within a short time. In addition, when heat-shrinked after installation, insufficient shrinkage, vertical sink marks, and deformation of the container are very small, and since the damping of the shrinkage stress is small, the followability to the container is good, and loosening is difficult to occur, making it possible to obtain a good finish. did.

1 is a view showing a plastic lunch box in which the wrinkles of the film after shrinkage were evaluated.
2 is a view showing a plastic lunch box in which the sink mark of the film is evaluated after shrinkage.
Explanation of symbols
1: Lunch box
2: film
3: Wrinkles
4: Lunch box
5: Film

Hereinafter, the configuration of the heat-shrinkable polyester film of the present invention will be described in detail.

The heat-shrinkable polyester film of the present invention has at least one layer or more of a layer containing 50 mol% or more of ethylene terephthalate units among 100 mol% of polyester constituent units. The details will be described later, but as a result of research by the present inventors, a film having at least one layer containing 50 mol% or more of an ethylene terephthalate unit among 100 mol% of the constituent units of polyester, if the draw ratio is higher than 3 times, As crystallization proceeded, it was found that the decay rate of the shrinkage stress was small and the shrinkage stress increased 30 seconds after the start of the shrinkage.

[In the case of a single-layer film]

In the case of a single-layer film, from the above reasons, the polyester used for the heat-shrinkable polyester film has an ethylene terephthalate unit as a main component, and the ethylene terephthalate unit is 50 mol% out of 100 mol% of the constituent units of the polyester. More than that. In order to promote crystallization during longitudinal stretching, which will be described later, the ethylene terephthalate unit is more preferably 55 mol% or more, and still more preferably 60 mol% or more, out of 100 mol% of the constituent units of the polyester. However, when the ratio of the ethylene terephthalate unit is too high, the shrinkage property is inhibited by crystallization and it becomes difficult to obtain a required high shrinkage. Therefore, the upper limit of the ethylene terephthalate unit is preferably 70% or less.

As other dicarboxylic acid components constituting the polyester of the present invention, aromatic dicarboxylic acids such as isophthalic acid, naphthalenedicarboxylic acid and orthophthalic acid, adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, etc. of aliphatic dicarboxylic acid and alicyclic dicarboxylic acid.

When an aliphatic dicarboxylic acid (for example, adipic acid, sebacic acid, decanedicarboxylic acid, etc.) is contained in the polyester, the content must be less than 3 mol% (in 100 mol% of the dicarboxylic acid component). desirable.

Moreover, it is preferable not to contain the polyhydric carboxylic acid (for example, trimellitic acid, pyromellitic acid, these anhydrides, etc.) in polyester. With a heat-shrinkable polyester film obtained by using these polyhydric carboxylic acid-containing polyesters, it becomes difficult to achieve the required high shrinkage.

Examples of the diol component constituting the polyester include aliphatic diols such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol and hexanediol, alicyclic diols such as 1,4-cyclohexanedimethanol, and bisphenol Aromatic diols, such as A, etc. are mentioned.

In addition, the total of one or more monomer components which may be an amorphous component in 100 mol% of polyhydric alcohol component or 100 mol% of polyhydric carboxylic acid component in polyester resin is 2% or more, Preferably polyester is 3 % or more, more preferably 4% or more, particularly preferably 5% or more. In addition, if the amount of the monomer component that can be an amorphous component increases, crystallization during stretching in the longitudinal direction does not proceed sufficiently, so that the upper limit is preferably 20 mol%.

Examples of the monomer that can be an amorphous component include neopentyl glycol, 1,4-cyclohexanedimethanol, isophthalic acid, 1,4-cyclohexanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2 ,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di- n-butyl-1,3-propanediol and hexanediol are mentioned. Among these, it is preferable to use neopentyl glycol, 1, 4- cyclohexane dimethanol or isophthalic acid. It is also preferable to use ?-caprolactone.

In the resin for forming the heat-shrinkable polyester film of the present invention, if necessary, various additives, for example, waxes, antioxidants, antistatic agents, crystal nucleating agents, viscosity reducing agents, heat stabilizers, coloring pigments, coloring inhibitors, ultraviolet absorbers etc. can be added.

It is preferable to add microparticles|fine-particles as a lubricant which improves workability|operativity (slip property) of a film to the resin which forms the heat-shrinkable polyester film of this invention. Any fine particles can be selected. For example, as inorganic fine particles, silica, alumina, titanium dioxide, calcium carbonate, kaolin, barium sulfate, etc., organic fine particles, for example, acrylic resin particles, melamine resin particles, silicone resin particles, crosslinking. Polystyrene particle etc. are mentioned. The average particle diameter of the fine particles can be appropriately selected as needed within the range of 0.05 to 3.0 µm (measured with a Coulter counter).

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

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

[In the case of laminated film]

In the case of a laminated film in which resin layers having different resin compositions are laminated, it is necessary to use at least one layer of a polyester layer having 50 mol% or more of ethylene terephthalate units in 100 mol% of the polyester constituent units in the laminated structure of the film. For the same reason as in the case of a single-layer film, that is, by having at least one layer containing at least 50 mol% of an ethylene terephthalate unit in the film composition of the laminated film, if the draw ratio is higher than 3 times, crystallization proceeds. It has the characteristics that the damping rate is small and the shrinkage stress 30 seconds after the start of shrinkage becomes high.

When setting it as three-layer structure in this invention, it is preferable to make the outermost layer (skin layer) into a layer containing 50 mol% or more of ethylene terephthalate units. The reason for doing this is to promote the crystallization of the outermost layer by stretching to reduce the damping rate of the shrinkage stress.

The composition of the resin forming the core layer is not particularly limited, but from the viewpoint of mechanical strength, etc., it is preferable that the ethylene terephthalate unit is the main constituent, and the ethylene terephthalate unit is 85 moles out of 100 mole% of the constituent units of the polyester. % or less. When there are too many ethylene terephthalate units, since crystallization is accelerated|stimulated too much, high shrinkage cannot be obtained.

Examples of the diol component constituting the polyester of the core layer include aliphatic diols such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol and hexanediol, and alicyclic such as 1,4-cyclohexanedimethanol. Aromatic diols, such as diol and bisphenol A, etc. are mentioned.

In addition, the total of one or more monomer components which may be an amorphous component in 100 mol% of polyhydric alcohol component or 100 mol% of polyhydric carboxylic acid component in polyester resin is 2% or more, Preferably polyester is 3 % or more, more preferably 4% or more, particularly preferably 5% or more.

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

In the present invention, the term "amorphous polymer" specifically refers to the case where it does not have an endothermic peak due to melting in the measurement by a DSC differential scanning calorimetry apparatus. The amorphous polymer does not substantially crystallize and thus does not take a crystalline state, or has a very low degree of crystallinity even if it is crystallized.

In addition, in this invention, "crystalline polymer" refers to the case which is not the said "amorphous polymer", ie, the case where it has an endothermic peak by melting in the measurement by a DSC differential scanning calorimetry apparatus. A crystalline polymer is one that can be crystallized when the temperature of the polymer is raised, has crystallizable properties, or is already crystallized.

In general, with respect to a polymer in which a large number of monomer units are bonded, the polymer has low stereoregularity, poor polymer compatibility, large polymer side chains, many polymer branches, and low intermolecular cohesion between polymers. When it has, it becomes an amorphous polymer. However, depending on the state of existence, crystallization may proceed sufficiently to form a crystalline polymer. For example, even for a polymer having a large side chain, when the polymer is composed of a single monomer unit, crystallization may proceed sufficiently to become crystalline. For this reason, even with the same monomer unit, the polymer may become crystalline or non-crystalline in some cases. Therefore, in the present invention, the expression "unit derived from a monomer capable of becoming an amorphous component" is used.

Here, in the present invention, the monomer unit refers to a repeating unit constituting a polymer derived from one polyhydric alcohol molecule and one polyhydric carboxylic acid molecule, and in the case of ε-caprolactone, ring opening of the lactone ring. ) represents a structural unit obtained by

When the monomer unit composed of terephthalic acid and ethylene glycol is the main monomer unit constituting the polymer, a monomer unit composed of isophthalic acid and ethylene glycol, a monomer unit composed of terephthalic acid and neopentyl glycol, terephthalic acid and 1,4-cyclohexanedimethanol The monomer unit which consists of a monomer unit, the monomer unit which consists of isophthalic acid and butanediol, etc. are mentioned as a unit derived from the monomer which can become the said amorphous component.

Examples of the monomer that can be an amorphous component of the resin forming the core layer include neopentyl glycol, 1,4-cyclohexanedimethanol, isophthalic acid, 1,4-cyclohexanedicarboxylic acid, and 2,6- Naphthalenedicarboxylic acid, 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol , 2,2-di-n-butyl-1,3-propanediol, and hexanediol. Among these, it is preferable to use neopentyl glycol, 1, 4- cyclohexane dimethanol or isophthalic acid.

It is preferable that the value which divided the sum total of skin layer thickness by the thickness of a core layer is 0.1-0.5. When the value obtained by dividing the total thickness of the skin layer by the thickness of the core layer is less than 0.1, the amount of the layer containing 50 mol% or more of the polyethylene terephthalate unit in the film configuration of the laminated film is decreased, and the damping rate of the shrinkage stress is reduced It is not preferable because the effect of making it is not sufficiently obtained. On the other hand, when the value obtained by dividing the total thickness of the skin layer by the thickness of the core layer exceeds 0.5, the core layer, which mainly exhibits thermal shrinkage behavior, becomes relatively too small, which is not preferable because the required thermal contraction rate cannot be achieved.

In the heat-shrinkable polyester film of the present invention, the core layer and the skin layer preferably each have a thickness of at least 1 µm or more. When the thickness of the core layer or the skin layer is less than 1 m, the required heat shrinkability is not obtained, so it is not preferable.

In the case of any layer of the skin layer and the core layer, in the resin forming the layer, various additives, for example, waxes, antioxidants, antistatic agents, crystal nucleating agents, viscosity reducing agents, heat stabilizers, coloring pigments, color inhibitors, A UV absorber or the like may be added.

When setting it as a laminated|multilayer film, it can manufacture by the well-known method used when manufacturing a laminated|multilayer film, Methods, such as a feedblock system and a multi-manifold system, are mentioned. For example, in the case of the co-extrusion method, the various resin mixtures forming the layer are individually melted with an extruder, merged in a T-die mold equipped with a multi-manifold system, and extruded, and then stretched with a stretching device to make a laminated film. can get

Although the form of the laminated film is not particularly limited, for example, a laminated form of A/B 2-type 2-layer configuration, B/A/B 2-type 3-layer configuration, and C/A/B 3-type 3-layer configuration can be heard

[Characteristics of the heat-shrinkable polyester film of the present invention]

When the heat-shrinkable polyester film of the present invention is treated for 10 seconds under no load in 98°C hot water, the heat shrinkage rate in the longitudinal direction, which is the main shrinkage direction of the film, calculated by Equation 1 below from the length before and after shrinkage ( That is, the thermal contraction rate of hot water at 98°C) is 40% or more and 80% or less.

When the thermal contraction rate of hot water in the longitudinal direction at 98°C is less than 40%, the amount of shrinkage is small when used as a banding film, and wrinkles or slack are generated in the label after thermal contraction, which is not preferable. On the other hand, when the thermal contraction rate of hot water in the longitudinal direction at 98°C is greater than 80%, a problem occurs in that the container is deformed when packaged in a thin and soft beverage bottle or lunch box. In addition, there is a problem in that the adhesive portion of the tubular label or the banding film is peeled off due to high shrinkage stress. As for the thermal contraction rate of hot water in the longitudinal direction, it is more preferable that it is 75 % or less, and it is still more preferable that it is 70 % or less. Moreover, in 90 degreeC, it is more preferable that it is 45 % or more, and, as for the lower limit of the thermal contraction rate of the longitudinal direction, it is still more preferable in it being 50 % or more.

In addition, when the heat-shrinkable polyester film of the present invention is treated for 10 seconds in a non-load state in 98°C warm water, the direction orthogonal to the main shrinkage direction of the film calculated by Equation 1 from the length before and after shrinkage The hot water thermal contraction rate in the phosphor width direction is -5% or more and 15% or less. When the thermal contraction rate of hot water in the width direction exceeds 15% at 98°C, when used as a bending film, the length of the film in the direction orthogonal to the contraction direction during thermal contraction becomes short (sink mark), resulting in a decrease in binding force, resulting in a lunch box It is not preferable because the contents overflow and problems such as mixing of foreign substances occur. On the other hand, when it is less than -5%, the label length in the direction orthogonal to the main shrinkage direction becomes longer during heat shrinkage, causing slack and wrinkling, which is not preferable. Moreover, in 98 degreeC, it is preferable that it is -4 % or more and 9 % or less of hot water thermal contraction rate in the width direction, it is more preferable if it is -3 % or more and 8 % or less, It is still more preferable if it is -2 % or more and 7 % or less.

The heat-shrinkable polyester film of the present invention has a shrinkage stress ratio of 0.6 or more and 1.0 or less with respect to the shrinkage stress in the main shrinkage direction of the film measured under hot wind at 90°C.

That is, the heat-shrinkable polyester film of the present invention exhibits a unique heat-shrinkage characteristic that shows a shrinkage stress of the same degree as the maximum heat-shrinkage stress even after 30 seconds after the start of heat shrinkage. If the shrinkage stress/maximum shrinkage stress (hereafter, the stress ratio) after 30 seconds is less than 0.6, in the case of a label for a beverage bottle, it cannot follow the shape and becomes a label without tension, and the consumer holds the body of the bottle and opens the cap of the bottle. In this case, it is not preferable because a problem arises that the label rotates and is difficult to open. In addition, in the case of the bending use of the lunch box container, the finish of the shrink film is not tight, so that the contents of the lunch box overflow, and problems such as mixing of foreign substances occur.

The stress ratio is more preferably 0.75 or more, and still more preferably 0.8 or more. The larger the stress ratio, the better the followability. However, since the shrinkage stress after 30 seconds cannot exceed the maximum shrinkage stress, the maximum value of the stress ratio is 1.

The heat-shrinkable polyester film of the present invention has a refractive index of 1.600 or more in the longitudinal direction, which is the main shrinkage direction of the film. If the refractive index in the longitudinal direction is less than 1.600, the film does not have rigidity (hard feeling) and wrinkles are likely to occur when used as a label, which is not preferable. The lower limit of the refractive index in the longitudinal direction is preferably 1.625 or more, and particularly preferably 1.650 or more. On the other hand, when the refractive index in the longitudinal direction exceeds 1.700, it is not preferable because the adhesiveness to a solvent when used as a label deteriorates.

In the case of the heat-shrinkable polyester film of the present invention, the heat-shrinkable stress value in the longitudinal direction, which is the main shrinkage direction of the film, was measured in hot air at a temperature of 90 ° C. When measured in, it is preferable that the maximum thermal contraction stress value is 15 MPa or less. If the maximum heat shrinkage stress value is 15 MPa or less, the shrinkage stress is not too high, and there is no problem such as deformation of the container when packaged in a thin and soft beverage bottle or lunch box. In addition, it is preferable because problems such as peeling of the adhesive portion of the cylindrical label or the banding film due to high shrinkage stress do not occur. The maximum thermal shrinkage stress value is more preferably 14 MPa or less, more preferably 12 MPa or less. On the other hand, if the shrinkage stress is too small, the tension after finishing shrinkage is insufficient when packaged in a beverage bottle or lunch box, and when the consumer holds the bottle body and opens the bottle cap, the label rotates and is difficult to open. Problems occur, and also, in the case of the banding use of the lunch box, the contents of the lunch box overflow, and problems such as mixing of foreign substances occur. Accordingly, the maximum thermal contraction stress value measured by the above method is preferably 5 MPa or more, more preferably 6 MPa or more.

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

In addition, the heat-shrinkable polyester film of the present invention is not limited at all with respect to its manufacturing method, for example, the above-described polyester raw material is melt-extruded by an extruder to form an unstretched film, and the unstretched film is It can obtain by extending|stretching by the method shown below.

When melt-extruding the raw material resin, it is preferable to dry the polyester raw material using a dryer such as a hopper dryer or a paddle dryer, or a vacuum dryer. After drying the polyester raw material in this way, it is melted at a temperature of 200 to 300° C. using an extruder and extruded into a film shape. At the time of such extrusion, conventional methods such as the T-die method and the tubular method may be employed.

And an unstretched film can be obtained by quenching the sheet-like molten resin after extrusion. Moreover, as a method of rapidly cooling molten resin, the method of obtaining a substantially unoriented resin sheet by casting a molten resin on a rotary drum from a nozzle|cap|die and quenching and solidifying can be employ|adopted suitably.

Further, as will be described later, the obtained unstretched film can be stretched in the longitudinal direction under predetermined conditions to obtain the heat-shrinkable polyester film of the present invention. Below, the preferable stretching for obtaining the heat-shrinkable polyester film of the present invention will be described in detail while considering the difference from the conventional stretching method of the heat-shrinkable polyester film.

[Preferred method of stretching heat-shrinkable polyester film]

A conventional heat-shrinkable polyester film is prepared by stretching an unstretched film in a direction to be contracted. Conventionally, there has been a high demand for a heat-shrinkable polyester film that follows the shape of the object during shrinkage and shrinks in the longitudinal direction with a feeling of tightness after shrinkage, but the unstretched film is simply stretched in the longitudinal direction It is impossible to obtain a polyester film having a small rate of attenuation of the shrinkage stress and a high shrinkage stress 30 seconds after the start of shrinkage by only doing it.

Accordingly, a preferred method of stretching the heat-shrinkable film of the present invention will be described.

As a result of the study, the present inventors found that a film having at least one layer containing at least 50 mol% of an ethylene terephthalate unit among 100 mol% of the constituent units of polyester proceeds with crystallization when the draw ratio is higher than 3 times, so the shrinkage stress It was found that the damping rate of is small, and the shrinkage stress after 30 seconds from the start of the shrinkage is high.

In the conventional heat-shrinkable polyester film containing a large amount of amorphous components, when stretching only uniaxially, the shrinkage stress attenuation rate is large, and the shrinkage stress after 30 seconds from the start of the shrinkage is low. On the other hand, in the present invention, by having at least one layer containing 50 mol% or more of ethylene terephthalate units and stretching at a high magnification of 3 times or more, the damping rate of the shrinkage stress is reduced. The attenuation of this shrinkage stress is thought to be related to crystallization by stretching. In the case of a polyester film having at least one layer containing at least one layer containing 50 mol% or more of the ethylene terephthalate unit of the present invention and stretched at a high magnification of 3 times or more, molecular crystallization tends to occur. It is thought that the crystallization of this molecule has lower mobility when heat is applied than the amorphous molecule, and when the film is heat-shrinked, it suppresses the rapid relaxation of the molecular orientation, and a gradual relaxation of the molecular orientation occurs. That is, since orientation relaxation occurs over a long period of time, it is considered that the damping rate of the shrinkage stress is lowered and the shrinkage stress after 30 seconds is increased. When a large amount of amorphous component is included or when the draw ratio in the longitudinal direction is less than 3 times, crystallization does not proceed relatively, so it is considered that the attenuation rate of the shrinkage stress in the longitudinal direction is large, and the shrinkage stress after 30 seconds is considered to be small. .

From the above study results, it is preferable that the draw ratio in the longitudinal direction is 3 times or more and 7 times or less. If the draw ratio in the longitudinal direction is less than 3 times, crystallization of the film is insufficient, and the shrinkage stress does not persist, so it cannot sufficiently follow the shape of the object to be packaged. It is undesirable because Moreover, the thickness variation in the longitudinal direction of the film becomes large, which is undesirable. The upper limit of the longitudinal draw ratio is not particularly defined, but when it is higher than 7 times, it is not preferable because it becomes difficult to extend in the longitudinal direction (so-called breakage tends to occur). More preferably, they are 3.2 times or more and 6.5 times or less, More preferably, they are 3.5 times or more and 6 times or less.

The package of the present invention is formed by coating a banding film (and a label) obtained from the heat-shrinkable polyester film of the present invention on at least a part of the outer periphery of an object to be packaged and heat-shrinking. Examples of the packaging object include plastic containers such as lunch boxes (including PET bottles for beverages, various bottles, cans, and confectionery), paper boxes, and the like. In addition, when the packaging object is usually coated with a label obtained from a heat-shrinkable polyester film by heat-shrinking, the banding film (and label) is heat-shrinked by about 5 to 70% to bring it into close contact with the package. In addition, printing may be performed to the banding film (and a label) coat|covered to a packaging object, and printing does not need to be performed.

As a method for producing a banding film (and label), a rectangular film is rolled in the longitudinal direction and the ends are overlapped to form a label, or a film wound in a roll is rolled in the longitudinal direction of a roll and the ends are overlapped and adhered to the film. The tube-shaped body is cut to form a label shape. The film bonding method can be performed using a known method, such as fusion sealing, solvent bonding, bonding by a hot melt adhesive, and bonding by an energy ray-curable adhesive.

Example

The present invention will be described in more detail below by way of Examples, but the present invention is not limited in any way to the aspects of these Examples, and appropriate changes can be made without departing from the spirit of the present invention. The composition of the raw materials used in 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, and the film production conditions and evaluation results in Examples and Comparative Examples are shown in Tables 3 and 4.

In addition, the evaluation method of a film is as follows.

[Tg (glass transition point)]

Using a differential scanning calorimetry device (manufactured by Seiko Electronics Co., Ltd., DSC220), 5 mg of unstretched film was placed in a sample pan, the pan was covered, and the temperature was 10°C/min from -40°C to 120°C in a nitrogen gas atmosphere. It was measured by raising the temperature at a temperature increase rate. Tg (degreeC) was calculated|required based on JIS-K7121-1987.

[Intrinsic Viscosity (IV)]

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

[Heat shrinkage (hot water heat shrinkage)]

The film was cut into a square of 10 cm × 10 cm, immersed in hot water at a predetermined temperature ± 0.5 ° C for 10 seconds under no-load condition to heat shrink, then immersed in water at 25 ° C ± 0.5 ° C for 10 seconds, and then removed from the water and the film was measured in the longitudinal and transverse directions, and the thermal contraction rate was obtained according to the following equation (1). The direction with a large thermal contraction rate was made into the main contraction direction.

[Shrinkage Stress]

A rectangular film sample of 150 mm in length and 20 mm in width in the main shrinkage direction was cut from the heat-shrinkable film, and a heating furnace attached elongation tester, Tensilon Universal Tester PTM-250 (Orientec) manufactured by Toyo Baldwin Co., Ltd. (current company name: Orientec) Shrinkage stress was measured using a registered trademark of the Company. In the heating furnace of the elongation measuring instrument, the inside of the furnace was previously heated to 90°C, and the distance between chucks for holding the film sample was set to 100 mm. When attaching the sample to the chuck of the elongation measuring instrument, stop the blowing of the heating furnace and open the door of the heating furnace, insert 25 mm each of both ends of the 150 mm sample in the longitudinal direction between the chucks, and set the distance between the chucks to 100 mm. The lengthwise direction was coincident and the sample was fixed without loosening so that it was horizontal. After the sample was mounted on the chuck, the furnace door was quickly closed and blowing was resumed. The time when the door of the heating furnace was closed and ventilation was resumed was taken as the measurement start time of the shrinkage stress, and the shrinkage stress (MPa) after 30 seconds was calculated. In addition, the maximum value of the measurement value of the shrinkage stress between the measurement start time of the shrinkage stress and 30 seconds after the start of the measurement was set as the maximum value of the shrinkage stress (maximum shrinkage stress (MPa)). In addition, when measuring the shrinkage stress, the distance between the chucks was fixed to 100 mm, and the transition of the shrinkage stress from the start of the measurement to 30 seconds after the start of the measurement was measured. Then, the ratio of the shrinkage stress value 30 seconds after the start of the measurement to the maximum value of the shrinkage stress was defined as the shrinkage stress ratio (expressed by the formula below).

[Refractive Index]

It measured, after leaving each sample film to stand in 23 degreeC and 65 %RH atmosphere for 2 hours or more using "Abe refractometer 4T type" by the Atago company.

[Shrinkable finish (wrap around)]

For a plastic lunch container (150 × 150 mm in side, 100 mm in height), wind a film of 50 mm in width with the circumferential direction of the container as the shrinking direction of the film so that the film binds the body and the cap of the container, and then at 220°C. After melting and sealing, it was heat-shrinked in a plastic lunch box in a shrinkage tunnel with a set temperature of 90°C. In the evaluation of shrinkage finish, 4 points were evaluated: wrinkles, sink marks, insufficient shrinkage, and looseness. About the wrinkle evaluation, it was judged by the number of wrinkles 5 cm or more in length entering the side direction of the lunch box in FIG. 1, and the standard was set as follows.

○: 0-4

△: 5 to 14 pieces

×: 15 or more

Regarding the sink mark, FIG. 2 is a view from above of the bending film and the lunch box after shrinkage. Let L be the length from the film end of one side to the film end of the other side, and the length L is 5 mm pitch in the circumferential direction of the lunch box. The difference between the maximum value Lmax and the minimum value Lmin when measured with R was defined as R. A large R was judged as a large sink mark, and the criteria were as follows.

○: 0 mm ≤ R < 10 mm

Δ: 10 mm ≤ R < 15 mm

×: 15 mm ≤ R

About the lack of shrinkage, it was judged by whether or not the lack of shrinkage occurred after the completion of the shrinkage, and the criteria were as follows.

○: No lack of shrinkage

×: Insufficient shrinkage

Regarding the loosening, the bending film after shrinking was not completely in close contact with the lunch box, and there was no tension when touched by hand, and it was judged as loosening that the film had floated, and the standards were as follows.

○: There is no lifting because the film is tight.

×: The finish of the film is loose and there is a float.

<Preparation of polyester raw material>

Synthesis Example 1

In a stainless steel autoclave equipped with a stirrer, a thermometer and a partial reflux type cooler, 100 mol% of dimethyl terephthalate (DMT) as a dicarboxylic acid component and 100 mol% of ethylene glycol (EG) as a polyhydric alcohol component were mixed with ethylene glycol. Methanol produced by adding 0.05 mol% of zinc acetate (relative to the acid component) as a transesterification catalyst and 0.225 mol% of antimony trioxide (relative to the acid component) as a polycondensation catalyst is added in a molar ratio of 2.2 times that of dimethyl terephthalate The transesterification reaction was performed while distilling off the system. Thereafter, a polycondensation reaction was performed at 280°C under reduced pressure of 26.7 Pa to obtain Polyester 1 having an intrinsic viscosity of 0.75 dl/g. The composition is shown in Table 1.

Synthesis Examples 2-7

Polyesters 2-4 shown in Table 1 were obtained by the method similar to Synthesis Example 1. In the production of polyester 2, SiO2 (Silicia 266 manufactured by Fuji Silicia Corporation; average particle diameter of 1.5 μm) was added as a lubricant at a ratio of 7,200 ppm with respect to the polyester. In the table, NPG is neopentyl glycol, BD is 1,4-butanediol, and DEG is diethylene glycol as a by-product. The intrinsic viscosity of each polyester was 2:0.75 dl/g, 3:1.20 dl/g, and 4:1.20 dl/g, respectively, respectively. In addition, each polyester was made into chip shape suitably.

[Example 1]

The polyester 1, the polyester 2, and the polyester 3 were mixed at a mass ratio of 45:5:50 and put into an extruder. Thereafter, 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 quenched to obtain an unstretched film having a thickness of 42 µm. Tg of the unstretched film was 75 degreeC. The unstretched film was guided to a longitudinal stretching machine in which a plurality of roll groups were continuously arranged and heated on a preheating roll until the film temperature reached 80 ° C. was longitudinally stretched to a thickness of 12 μm. After longitudinal stretching, it cooled with the cooling roll set to the surface temperature of 25 degreeC, and then wound up in roll shape. The properties of the obtained film were evaluated by the above method. Table 3 shows the evaluation results. As a result of the evaluation, it was a film having sufficient shrinkability and good shrinkage finish.

[Example 2]

It was the same as Example 1 except that the draw ratio in the longitudinal direction was set to 4.5, and the extrusion amount was adjusted from the T-die of the molten mixed resin so that the thickness of the film after stretching in the longitudinal direction was 12 µm. As a result of the evaluation, it was a film having sufficient shrinkability and good shrinkage finish.

[Example 3]

It was the same as in Example 1 except that the draw ratio in the longitudinal direction was increased to 5.5, and the extrusion amount was adjusted from the T-die of the melted mixed resin so that the thickness of the film after stretching in the longitudinal direction was 12 µm. As a result of the evaluation, it was a film having sufficient shrinkability and good shrinkage finish.

[Example 4]

It was the same as in Example 1 except that the stretching ratio in the longitudinal direction was increased to 6, and the extrusion amount was adjusted from the T-die of the mixed resin melted so that the thickness of the film after stretching in the longitudinal direction was 12 µm. As a result of the evaluation, it was a film having sufficient shrinkability and good shrinkage finish.

[Example 5]

The above polyester 1, polyester 2, and polyester 3 were mixed in a mass ratio of 45:5:50 to obtain a resin mixture for a skin layer. The above polyester 1, polyester 2, polyester 3 and polyester 4 were mixed at a mass ratio of 25:5:60:10 to obtain a resin mixture for the core layer. The resin mixture for each layer of the skin layer and the core layer was co-extruded at a temperature of 280° C. using a T-die mold equipped with a two-layer manifold using two twin screw extruders, and rapidly cooled with a cooling roll to make the skin layer / A sheet of two core layers was produced. At this time, it co-extruded so that the thickness ratio of a skin layer and a core layer might become skin layer:core layer=2:8. Then, the sheet was heated to 80° C. and longitudinally stretched by a roll stretching method so that the stretch ratio in the longitudinal direction was increased to 3.5 and the total thickness of the film after stretching was 12 μm. After longitudinal stretching, it cooled with a cooling roll, and then wound up in roll shape. The properties of the obtained film were evaluated by the above method. Table 3 shows the evaluation results. As a result of the evaluation, it was a film having sufficient shrinkability and good shrinkage finish.

[Example 6]

It was the same as in Example 5 except that the stretching ratio in the longitudinal direction was 4.5 times, and the extrusion amount was adjusted from the T-die of the molten mixed resin so that the thickness of the film after stretching in the longitudinal direction was 12 µm. As a result of the evaluation, it was a film having sufficient shrinkability and good shrinkage finish.

[Example 7]

It was the same as Example 5 except that the draw ratio in the longitudinal direction was increased to 5.5, and the extrusion amount was adjusted from the T-die of the melted mixed resin so that the thickness of the film after stretching in the longitudinal direction was 12 µm. As a result of the evaluation, it was a film having sufficient shrinkability and good shrinkage finish.

[Example 8]

It was the same as in Example 5 except that the stretching ratio in the longitudinal direction was 6 times, and the extrusion amount was adjusted from the T-die of the mixed resin melted so that the thickness of the film after stretching in the longitudinal direction was 12 µm. As a result of the evaluation, it was a film having sufficient shrinkability and good shrinkage finish.

[Example 9]

It carried out similarly to Example 5 except having mixed the above-mentioned polyester 1, polyester 2, and polyester 3 at a mass ratio of 70:5:25 and having set it as the resin mixture for skin layers. As a result of the evaluation, it was a film having sufficient shrinkability and good shrinkage finish.

[Example 10]

It was the same as Example 9 except that the draw ratio in the longitudinal direction was set to 4.5, and the extrusion amount was adjusted from the T-die of the melted mixed resin so that the thickness of the film after stretching in the longitudinal direction was 12 µm. As a result of the evaluation, it was a film having sufficient shrinkability and good shrinkage finish.

[Example 11]

It was the same as Example 9 except that the draw ratio in the longitudinal direction was increased to 5.5, and the extrusion amount was adjusted from the T-die of the mixed resin melted so that the thickness of the film after stretching in the longitudinal direction was 12 µm. As a result of the evaluation, it was a film having sufficient shrinkability and good shrinkage finish.

[Example 12]

It was the same as Example 9 except that the stretching ratio in the longitudinal direction was increased to 6, and the extrusion amount was adjusted from the T-die of the molten mixed resin so that the thickness of the film after stretching in the longitudinal direction was 12 µm. As a result of the evaluation, it was a film having sufficient shrinkability and good shrinkage finish.

[Example 13]

It carried out similarly to Example 9 except having mixed the above-mentioned polyester 1, polyester 2, polyester 3, and polyester 4 in mass ratio 5:5:66:24 and set it as the resin mixture for core layers. As a result of the evaluation, it was a film having sufficient shrinkability and good shrinkage finish. Table 4 shows the evaluation results.

[Example 14]

It was the same as Example 13 except that the draw ratio in the longitudinal direction was set to 4.5, and the extrusion amount was adjusted from the T-die of the melted mixed resin so that the thickness of the film after stretching in the longitudinal direction was 12 µm. As a result of the evaluation, it was a film having sufficient shrinkability and good shrinkage finish.

[Example 15]

It was the same as Example 13 except that the draw ratio in the longitudinal direction was increased to 5.5, and the extrusion amount was adjusted from the T-die of the molten mixed resin so that the thickness of the film after stretching in the longitudinal direction was 12 µm. As a result of the evaluation, it was a film having sufficient shrinkability and good shrinkage finish.

[Example 16]

It was the same as Example 13 except that the stretching ratio in the longitudinal direction was increased to 6, and the extrusion amount was adjusted from the T-die of the melted mixed resin so that the thickness of the film after stretching in the longitudinal direction was 12 µm. As a result of the evaluation, it was a film having sufficient shrinkability and good shrinkage finish.

[Example 17]

The above polyester 1, polyester 2, and polyester 3 were mixed in a mass ratio of 45:5:50 to obtain a resin mixture for a skin layer. The above polyester 1, polyester 2, polyester 3 and polyester 4 were mixed at a mass ratio of 25:5:60:10 to obtain a resin mixture for the core layer. The resin mixture for each layer of the skin layer and the core layer was co-extruded at a temperature of 280° C. using a T-die mold equipped with a three-layer manifold using two twin screw extruders, and rapidly cooled with a cooling roll to make the skin layer / A sheet of three layers of core layer/skin layer was produced. At this time, it co-extruded so that the thickness ratio of a skin layer and a core layer might become skin layer:core layer:skin layer=1:8:1. Then, the sheet was heated to 80° C. and longitudinally stretched by a roll stretching method so that the stretch ratio in the longitudinal direction was increased to 4.5 and the total thickness of the film after stretching was 12 μm. After longitudinal stretching, it extended|stretched with a cooling roll, and then wound up in roll shape. The properties of the obtained film were evaluated by the above method. Table 4 shows the evaluation results. As a result of the evaluation, it was a film having sufficient shrinkability and good shrinkage finish.

[Example 18]

It carried out similarly to Example 17 except having mixed the above-mentioned polyester 1, polyester 2, and polyester 3 at a mass ratio of 70:5:25 and having set it as the resin mixture for skin layers. As a result of the evaluation, it was a film having sufficient shrinkability and good shrinkage finish.

[Example 19]

It carried out similarly to Example 18 except having mixed the above-mentioned polyester 1, polyester 2, polyester 3, and polyester 4 at a mass ratio of 5:5:66:24 and set it as the resin mixture for core layers. As a result of the evaluation, it was a film having sufficient shrinkability and good shrinkage finish.

[Comparative Example 1]

It was the same as Example 1 except that the draw ratio in the longitudinal direction was doubled, and the extrusion amount was adjusted from the T-die of the melted mixed resin so that the thickness of the film after stretching in the longitudinal direction was 12 µm. As a result of the evaluation, slack occurred in the banding film after shrinkage, and it was a film having poor shrinkage finish.

[Comparative Example 2]

The above-mentioned polyester 1, polyester 2 and polyester 3 are mixed in a mass ratio of 70:5:25 and put into an extruder, the draw ratio in the longitudinal direction is 2.5 times, and the thickness of the film after stretching in the longitudinal direction is 12 μm It was carried out similarly to Example 1 except having adjusted the extrusion amount from the T-die of the mixed resin melted so that it might become. As a result of the evaluation, the bending film after shrinkage was a film having poor shrinkage finish due to insufficient shrinkage.

[Comparative Example 3]

It carried out similarly to Example 2 except having mixed the above-mentioned polyester 1, polyester 2, polyester 3, and polyester 4 at a mass ratio of 25:5:60:10 and injecting|throwing-in to the extruder. As a result of the evaluation, slack occurred in the label after shrinkage and the film was poor in shrink finish properties.

[Comparative Example 4]

It carried out similarly to Example 2 except having mixed said polyester 1, polyester 2, polyester 3, and polyester 4 in mass ratio 5:5:66:24 and injecting|throwing-in to the extruder. As a result of the evaluation, slack occurred in the banding film after shrinkage, and it was a film having poor shrinkage finish.

[Comparative Example 5]

It was the same as in Comparative Example 4 except that the stretching ratio in the longitudinal direction was tripled and the extrusion amount was adjusted from the T-die of the melted mixed resin so that the thickness of the film after stretching in the longitudinal direction was 12 µm. As a result of the evaluation, slack occurred in the banding film after shrinkage, and it was a film having poor shrinkage finish.

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

Claims (5)

A heat-shrinkable polyester film whose main shrinkage direction is in the longitudinal direction, characterized in that it satisfies the following requirements (1) to (4).
(1) In the case of treatment in 98°C hot water for 10 seconds, the shrinkage rate of hot water in the main shrinkage direction of the film is 40% or more and 80% or less.
(2) When treated in 98°C hot water for 10 seconds, the shrinkage rate of hot water in the direction orthogonal to the main shrinkage direction of the film is -5% or more and 15% or less
(3) With respect to the shrinkage stress in the main shrinkage direction of the film measured under hot wind at 90°C, the shrinkage stress ratio expressed by the following formula is 0.6 or more and 1.0 or less.

(4) The refractive index in the main shrinkage direction of the film is 1.600 or more The method of claim 1,
A heat-shrinkable polyester film, characterized in that the maximum shrinkage stress in the main shrinkage direction of the film measured under hot air at 90°C is 15 MPa or less. 3. The method of claim 1 or 2,
A heat-shrinkable polyester film comprising ethylene terephthalate as a main component and containing 2 mol% or more of at least one monomer component that may be an amorphous component in the total polyester resin. 3. The method of claim 1 or 2,
A heat-shrinkable polyester film, characterized in that neopentyl glycol is used as at least one monomer component that can be an amorphous component. A package obtained by coating at least a part of the outer periphery of an object to be packaged with the heat-shrinkable polyester film according to claim 1 or 2, followed by heat-shrinkage.

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