JP7427995B2 - Heat-shrinkable polyester film - Google Patents

Description

The present invention relates to a heat-shrinkable film, and more specifically, a heat-shrinkable polyester film suitable for bundling and covering containers and labeling, and a label using the heat-shrinkable polyester film and a cover covered by the heat-shrinkable polyester film. This relates to a package made of

In recent years, it has become common to see packaging in which the outside of plastic bottles and lunch containers is covered with a heat-shrinkable plastic film label for the purpose of protecting the contents, improving their appearance, and displaying the contents. ing. As heat-shrinkable plastic films for such labels, stretched films of polyester, polystyrene, polyolefin, polyvinyl chloride, and other resins are used.

Among such heat-shrinkable films, polyvinyl chloride films have low heat resistance and also have problems such as generating hydrogen chloride gas and causing dioxins when incinerated. In addition, polystyrene film has poor solvent resistance, requires the use of ink with a special composition when printing, and must be incinerated at high temperatures, producing a large amount of black smoke with an unpleasant odor when incinerated. There is a problem with doing so. Therefore, polyester heat-shrinkable films, which have high heat resistance, are easy to incinerate, and have excellent solvent resistance, are becoming widely used as shrink labels, and the amount used is increasing. be.

As ordinary heat-shrinkable films, those that shrink significantly in the width direction are widely used. In this way, heat-shrinkable plastic films whose main shrinkage direction is the width direction are stretched at a high ratio in the width direction, but are stretched at a low ratio in the longitudinal direction orthogonal to the main shrinkage direction. In many cases, the paper is simply stretched, and some are not stretched.
As such, films that have been stretched only at a low magnification in the longitudinal direction or films that have been stretched only in the width direction have the disadvantage of poor mechanical strength in the longitudinal direction. In addition, films with low stretching ratios tend to suffer from a decrease in mechanical strength after long-term storage, and have the disadvantage that the labels tend to crack due to vibrations and impacts during transportation.

Labels for bottles and food containers must be made into an annular shape and placed over the object and then heat-shrinked in the circumferential direction. Therefore, when attaching a heat-shrinkable film that heat-shrinks in the width direction as a label, After forming an annular body so that the width direction is the circumferential direction, the annular body must be cut into predetermined lengths and attached to a bottle or food container. For this reason, it is difficult to quickly attach a label made of a heat-shrinkable film that heat-shrinks in the width direction to a bottle or lunch container.

Furthermore, in recent years, due to the aging of the population and the increase in the number of dual-income households, the sale of bento boxes and noodles at convenience stores has increased. Therefore, by using a film that shrinks in the longitudinal direction, the film can be unwound from a roll and then wrapped directly around bottles, food containers, etc., making it possible to quickly attach the film. A mounting method has been developed that can automate the process of mounting annular labels. In addition, some of these packaging methods require the film to have heat sealability.

When processing by heat sealing, for example, shrink films unwound from two film rolls are partially heat-sealed and pasted together, and the packaged item (plastic such as noodle containers or lunch containers) is placed between the two films. A container) is inserted, and the film on the opposite side of the heat-sealed part is partially heat-sealed and pasted together to form an annular film, and the annular film is heated with hot air to shrink it. A band label can be attached to the container and the lid to ensure close contact with the package.

In addition, when attaching by heat shrinking with a hot air tunnel, unlike the steam tunnel that is generally used for attaching beverage bottles, hot air has less heat transfer than steam, so heat shrink film requires low temperature. Excellent shrinkage properties are required.

In order to improve the heat seal strength of a polyester film, it is necessary to increase the amount of amorphous crystals in the film without crystallizing the polyester in the film forming process.

Furthermore, there are two types of molecular chain conformation of polyester: trans conformation and gauche conformation. The trans conformation represents a state in which molecules are oriented, and the heat sealing strength can be improved as the trans conformation has a relatively low molecular mobility.

On the other hand, in order to increase the mechanical strength in the longitudinal direction and to suppress natural shrinkage after long-term storage, it is effective to increase the stretching ratio to further orient the molecules. However, when the stretching ratio is increased, the ratio of trans conformation increases and there is a problem in that the heat sealing strength decreases.

In order to eliminate the above-mentioned mechanical strength problems in the longitudinal direction and to develop the function of shrinking in the longitudinal direction, an unstretched sheet made of a polyester mixture containing butanediol as a monomer component was stretched in the longitudinal direction. Thereafter, an invention was made to obtain a film that exhibits shrinkage characteristics in the longitudinal direction and can be heat-sealed by performing a treatment to relax the orientation using a speed difference between stretching rolls and a heat treatment (for example, see Patent Document 1). ).

However, in this invention, the molecular orientation of the film by stretching is not sufficient, so the strength in the longitudinal direction is not sufficient, and natural shrinkage is likely to occur over time. Especially if the film is thin, cracks may occur during transportation after being attached as a label. Another disadvantage is that during storage in the form of a film roll or after being attached as a label, wrinkles tend to occur due to the tightness of the roll due to natural shrinkage over time.

In addition, Patent Document 2 describes a polyester heat-shrinkable film that uses a monomer as an amorphous component and shrinks in the longitudinal direction of the roll. The stress during stretching in the main shrinkage direction) becomes high, and as a result, the shrinkage stress during shrinkage becomes high. Furthermore, there is a problem that biaxial stretching advances orientation in the plane direction of the film, resulting in poor heat sealability. Furthermore, large-scale equipment for biaxial stretching is required, which increases the cost.

Japanese Patent Application Publication No. 2019-107854 Patent No. 4411556

The present invention has been made against the background of such problems of the prior art. That is, an object of the present invention is to solve the above-mentioned problems of the conventional heat-shrinkable film, to provide sufficient shrinkage in the longitudinal direction, which is the main shrinkage direction, to achieve a shrink finish with a good appearance, and to improve heat-sealability. It is an object of the present invention to provide a heat-shrinkable polyester film having excellent mechanical strength in the longitudinal direction and low natural shrinkage.

As described above, in the conventional technology, it has been difficult to achieve both improvement in strength in the longitudinal direction, suppression of natural shrinkage rate, and heat seal strength. As a result of intensive studies, the present inventors have found that the above-mentioned problems can be solved by the means shown below, and have arrived at the present invention.
That is, the present invention consists of the following configuration.
1. A heat-shrinkable polyester film that satisfies the following requirements (1) to (6).
(1) The shrinkage rate of the film in the longitudinal direction when treated in hot air at 80°C for 30 seconds is 30% or more and 70% or less (2) When the films are heat-sealed together at 130°C and a pressure of 0.2 MPa Seal peel strength of 4 N/15 mm or more and 15 N/15 mm or less (3) Planar orientation degree of the film 0.050 or more and 0.080 or less (4) Heat shrinkage measured by polarized ATR-FTIR method on at least one surface of the film The ratio A1/A2 of absorbance A1 at 1340 cm ^-1 and absorbance A2 at 1410 cm ^-1 of the film is 0.50 or more and 1.20 or less in the longitudinal direction of the film (5) Tensile strength at break in the longitudinal direction is 150 MPa or more 320 MPa or less (6) The natural shrinkage rate of the film in the longitudinal direction after aging at 30°C and 85% RH for 672 hours is 1.0% or less2. Furthermore, 1. satisfies the following requirements (7) to (8). The heat-shrinkable polyester film described in .
(7) The maximum shrinkage stress in the longitudinal direction of the film in hot air at 90°C is 2 MPa or more and 15 MPa or less (8) The direction perpendicular to the longitudinal direction (width) of the film when treated in hot air at 80°C for 30 seconds 3. Shrinkage rate in direction) is -5% or more and 10% or less. Furthermore, 1. satisfies the following requirements (9) to (10). or the heat-shrinkable polyester film described in 2.
(9) The thickness of the film is 6 μm or more and 25 μm or less (10) The IV value of the film is 0.60 or more and 4. Furthermore, 1. satisfies the following requirements (11) to (12). ~3. The heat-shrinkable polyester film according to any one of the above.
(11) The polyester constituting the film contains a glycol component that can become an amorphous component from 10 mol% to 23 mol% (12) The polyester constituting the film contains an ethylene glycol component from 50 mol% to 77 mol% Below 5. 1. Characterized by being a uniaxially stretched film. ~4. The heat-shrinkable polyester film according to any one of 6. 1. It is characterized by being used for band label packaging of plastic containers. ~5. The heat-shrinkable polyester film according to any one of the above.
7. Said 1. ~6. A package covered with a band label formed by heat-sealing the heat-shrinkable polyester film according to any one of the above and bonding the heat-shrinkable polyester film in an annular shape.

The heat-shrinkable polyester film of the present invention has high shrinkability in the longitudinal direction, which is the main shrinkage direction, and almost does not shrink in the direction perpendicular to the main shrinkage direction, so it can be quickly wrapped into bottles and lunch containers. It can be mounted efficiently, and when heat-shrinked after mounting, a good finish with very few wrinkles due to heat shrinkage in the width direction or insufficient shrinkage in the longitudinal direction can be achieved. Furthermore, since it has excellent heat sealability and can be processed by heat sealing, it can be applied to mounting methods that require heat sealability. Furthermore, it has high strength in the longitudinal direction and has low natural shrinkage even after long-term storage.

Diagram showing how a noodle container is covered with an annular label (band label) before shrinking

The heat-shrinkable polyester film of the present invention is a film suitable for packaging use, which is obtained by stretching an unstretched sheet obtained by extruding a thermoplastic polyester resin composition through a die, at least in the longitudinal direction, and is suitable for packaging purposes. Examples of objects include plastic bottles for beverages, various bottles, cans, plastic containers for confectionery and lunch boxes, paper boxes, etc. (hereinafter, these are collectively referred to as packaging objects). Normally, when covering such packaging items with a heat-shrinkable polyester film, the label made from the film is heat-shrinked by approximately 2 to 20% and adheres tightly to the packaging item. let

In addition, when covering the packaging object with a label, a method is adopted in which a ring-shaped body is formed in advance so that the main shrinkage direction is in the circumferential direction, and then the ring-shaped body is placed over the packaging object and heat-shrinked. However, when forming an annular body in this way, in addition to bonding heat-shrinkable films using various adhesives, it is also possible to melt heat-shrinkable polyester films using a high-temperature heating element. It is also possible to use methods such as bonding (fusion sealing, heat sealing), etc.

When forming an annular body by heat-sealing a heat-shrinkable polyester film, prepare two film rolls, use a specified automatic sealing machine, and adjust the temperature of the seal bar to a specified condition (for example, After adjusting the temperature of the sealing bar to 130℃, the film is unrolled at regular intervals from two rolls and sealed at a predetermined speed (for example, 30 pieces/min). Can be adopted. As mentioned above, the shrink films unwound from two film rolls are partially heat-sealed and pasted together, and an object to be packaged (a plastic container such as a noodle container or a bento container) is inserted between the two films. , the film on the opposite side of the heat-sealed part is partially heat-sealed and pasted together to form an annular film, and the annular film is heated in a hot air tunnel etc. to shrink it and tightly adhere to the packaged object. A band label can be attached to fasten the container and lid. The heat-shrinkable polyester film of the present invention is preferably used in this processing method.
When attaching the annular body to the object to be packaged, in addition to manually placing the annular object prepared in advance over the object to be packaged, the label can be wrapped around the object, heat-sealed, and then cut. It is also possible to obtain a packaged object covered with a label. Furthermore, the attached label is heat-shrinked in a hot air tunnel or the like to complete attachment to the packaged object.

The dicarboxylic acid component constituting the polyester used in the heat-shrinkable polyester film of the present invention includes aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, orthophthalic acid, adipic acid, azelaic acid, sebacic acid, Examples include aliphatic dicarboxylic acids such as decane dicarboxylic acid, and alicyclic dicarboxylic acids. Among these, it is preferable that terephthalic acid accounts for 50 mol % or more in 100 mol % of the dicarboxylic acid component in order to ensure the strength and heat resistance of the film. The content of terephthalic acid is more preferably 60 mol% or more, even more preferably 70 mol% or more, and particularly preferably 80 mol% or more.

When containing an aliphatic dicarboxylic acid (for example, adipic acid, sebacic acid, decanedicarboxylic acid, etc.), the content is preferably less than 3 mol %. Heat-shrinkable polyester films obtained using polyesters containing 3 mol % or more of these aliphatic dicarboxylic acids have insufficient film stiffness during high-speed installation.

Further, it is preferable not to contain polycarboxylic acids having a valence of 3 or more (for example, trimellitic acid, pyromellitic acid, anhydrides thereof, etc.). With heat-shrinkable polyester films obtained using polyesters containing these polyhydric carboxylic acids, it becomes difficult to achieve the required high shrinkage rate.

Diol components constituting the polyester used in the heat-shrinkable polyester film of the present invention include aliphatic compounds such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, hexanediol, and diethylene glycol. Examples include diols, alicyclic diols such as 1,4-cyclohexanedimethanol, aromatic diols such as bisphenol A, and the like.

The polyester used in the heat-shrinkable polyester film of the present invention is a diol or lactone having a linear chain of 3 to 6 carbon atoms (for example, 1,3-propanediol, 1,4-butanediol, ε-caprolactone, etc.). Polyester containing one or more of diols (diethylene glycol, triethylene glycol, etc.) having an ether bond with 3 to 6 carbon atoms and whose glass transition point (Tg) is adjusted to 55 to 70°C is preferable. .

In addition, the polyester used for the heat-shrinkable polyester film preferably has a total ethylene glycol component of 50 mol% or more, preferably 55 mol% or more, based on 100 mol% of the polyhydric alcohol component in the total polyester resin. is more preferable, and particularly preferably 58 mol% or more. If the total amount of ethylene glycol components is less than 50 mol%, it is not preferable because the strength of the film and heat resistance will decrease. On the other hand, if the ethylene glycol component exceeds 77 mol%, it is not preferable because the heat shrinkage rate decreases, the shrink finish deteriorates, and the heat sealing strength decreases.

In addition, monomers that can be the amorphous component of polyester used in heat-shrinkable polyester films include neopentyl glycol, 1,4-cyclohexanedimethanol, isophthalic acid, 1,4-cyclohexanedicarboxylic acid, and 2,6-naphthalene dicarboxylic acid. acid, 2,2-diethyl 1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di- Examples include n-butyl-1,3-propanediol and hexanediol. Among these, it is preferable to use neopentyl glycol, 1,4-cyclohexanedimethanol or isophthalic acid. More preferred are neopentyl glycol or 1,4-cyclohexanedimethanol, and even more preferred is neopentyl glycol.
The total amount of monomer components that can become amorphous components in 100 mol% of the polyhydric alcohol component in the total polyester resin is preferably 10 mol% or more, more preferably 12 mol% or more, particularly 14 mol%. It is preferable that it is above. If the total amount of monomer components that can become amorphous components is less than 10 mol %, it is not preferable because the heat shrinkage rate decreases, the shrink finish deteriorates, and the heat sealing strength decreases. On the other hand, if the total amount of monomer components that can become amorphous components exceeds 23 mol%, the heat resistance will decrease and the film may wrinkle during heat sealing or may be fused to the seal bar, so it is preferable. do not have.

The polyester used in the heat-shrinkable polyester film includes diols having 8 or more carbon atoms (e.g. octanediol, etc.) or polyhydric alcohols having 3 or more valences (e.g. trimethylolpropane, trimethylolethane, glycerin, diglycerin). etc.) is preferably not contained. With heat-shrinkable polyester films obtained using polyesters containing these diols or polyhydric alcohols, it becomes difficult to achieve the required high shrinkage rate.

It is preferable to add fine particles as a lubricant to the resin forming the heat-shrinkable polyester film of the present invention to improve the workability (slip properties) of the film. Any fine particles can be selected. For example, inorganic fine particles include silica, alumina, titanium dioxide, calcium carbonate, kaolin, barium sulfate, etc.; organic fine particles include acrylic resin, etc. Examples include particles, melamine resin particles, silicone resin particles, and crosslinked polystyrene particles. The average particle diameter of the fine particles can be appropriately selected as necessary within the range of 0.05 to 3.0 μm (when measured with a Coulter counter).

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

In addition, when a heat-shrinkable polyester film is treated in hot air at 80°C for 30 seconds under no load, the heat shrinkage in the longitudinal direction of the film is calculated from the length before and after shrinkage using formula 1 below. It is necessary that the thermal shrinkage rate (that is, the thermal shrinkage rate of hot air at 80° C.) is at least 30%.
Thermal shrinkage rate = {(length before shrinkage - length after shrinkage)/length before shrinkage x 100 (%)...Formula 1
Note that the above-mentioned "longitudinal direction" refers to the film forming direction during film forming (that is, the winding direction of the film wound into a roll).

If the hot air thermal shrinkage rate in the longitudinal direction at 80° C. is 30% or less, the amount of shrinkage is small and wrinkles or shrinkage spots will occur on the label after heat shrinking, which is not preferable. In addition, the lower limit of the hot air thermal shrinkage rate in the longitudinal direction at 80° C. is preferably 32% or more, particularly preferably 34% or more. On the other hand, if the hot air shrinkage rate is 70% or more, distortion tends to occur during shrinkage, which is not preferable. The upper limit of the hot air thermal shrinkage rate in the longitudinal direction at 80° C. is preferably 68% or less, and particularly preferably 65% or less.

In addition, when a heat-shrinkable polyester film is processed in hot air at 80°C for 30 seconds under no load, the film width direction (longitudinal The thermal shrinkage rate of hot air in the direction perpendicular to the direction perpendicular to the direction perpendicular to the direction perpendicular to the direction perpendicular to the direction perpendicular to the direction perpendicular to the direction perpendicular to the direction perpendicular to the direction shown in FIG.

If the hot air shrinkage rate in the width direction at 80° C. is less than -5%, the label will expand and become distorted when used as a label, making it impossible to obtain a good contracted appearance, which is not preferable. On the other hand, if the hot air thermal shrinkage rate in the width direction at 80° C. exceeds 10%, wrinkles tend to occur in the width direction during heat shrinkage when used as a label, which is not preferable. The lower limit of the hot air thermal shrinkage rate in the width direction at 80° C. is preferably -3% or more, more preferably -1% or more, and particularly preferably 0% or more. Further, the upper limit of the hot air thermal shrinkage rate in the width direction at 80° C. is preferably 7% or less, more preferably 5% or less, and particularly preferably 3% or less.

On the other hand, in the present invention, the maximum thermal shrinkage stress value in the longitudinal direction of the film is preferably 2 MPa or more and 15 MPa or less. If the maximum heat shrinkage stress value in the longitudinal direction of the film is less than 2 MPa, when it is attached as a label to a container such as a lunch box and heat-shrinked, the attachment will become loose and the label may fall off the container. I don't like it because it gets wet. On the other hand, if the maximum thermal shrinkage stress value in the longitudinal direction of the film exceeds 15 MPa, it is not preferable because there is a risk that the seal portion may peel off during shrinkage or that the packaged object may be deformed by the force of shrinkage. The lower limit of the maximum thermal shrinkage stress value in the longitudinal direction of the film is more preferably 3 MPa or more, particularly preferably 4 MPa or more. Further, the upper limit of the maximum heat shrinkage stress value in the longitudinal direction of the film is more preferably 13 MPa or less, particularly preferably 11 MPa or less.

When the heat-shrinkable polyester films of the present invention are heat-sealed together at a sealing bar temperature of 130° C., a sealing bar pressure of 0.2 MPa, and a sealing time of 2 seconds, the heat sealing strength is preferably 4 N/15 mm or more.
If the heat seal strength is less than 4 N/15 mm, it is not preferable because the seal portion will peel off due to the shrinking force when the label is heat-shrinked and attached to the packaged object as a label. The higher the heat-sealing strength of the film, the more preferable it is, but if it is greater than 15 N/15 mm, the film may be fused to the seal bar during heat-sealing, which is undesirable since productivity during processing will decrease. From the above, the heat sealing strength is preferably 5N/15mm or more, more preferably 8N/15mm or more, but if the sealing strength is high, fusion to the seal bar will occur during heat sealing, reducing productivity during processing. Therefore, the upper limit value needs to be 15N/15mm or less.

The natural shrinkage rate of the heat-shrinkable polyester film of the present invention in the longitudinal direction is required to be 1% or less after aging at 30° C. and 85% RH for 672 hours. If the natural shrinkage rate exceeds 1%, the film roll will be exposed to high temperatures of about 30 to 40 degrees Celsius in the summer for a long time, for example, during long-term storage or during transportation after being attached as a packaging label. If this happens, the film may shrink and become tightly wound, causing wrinkles and resulting in poor appearance, which is undesirable.

It is preferable that the degree of planar orientation ΔP of the heat-shrinkable polyester film of the present invention is 0.050 or more. The plane orientation degree ΔP indicates the orientation strength of the entire film plane. By setting the plane orientation degree ΔP of the film within this range, the mechanical strength of the film is less likely to decrease after being stored for a long period of time. On the other hand, if the plane orientation degree ΔP exceeds 0.080, it is not preferable because the heat sealing strength decreases.

The heat-shrinkable polyester film of ^the present invention has a ratio A1/A2 ( ^hereinafter simply referred to as (absorbance ratio) must be 0.50 or more and 1.20 or less in the longitudinal direction of the film.

The above absorbance ratio represents the trans conformation ratio of the polyester molecule. The present inventors focused on the molecular orientation (trans conformation ratio) in a film stretched in the longitudinal direction, and investigated what kind of molecular orientation exhibits suitable heat sealing strength. The present invention was arrived at by studying the formation ratio.
That is, the present inventors have obtained experimental results that, by changing the stretching ratio, conditions, raw material composition, etc., there is a relationship between changes in the trans conformation ratio and heat seal strength. The trans conformation is considered to represent the molecular chain orientation state of the glycol component in the polyester, and when the trans conformation ratio is high, the molecular chain orientation state is strong and the molecular chains are highly constrained. It is thought that in order to develop heat seal strength, it is necessary to once loosen the restraint of the molecular chains and allow the entanglement of the molecular chains between the sealing surfaces that are in contact to proceed. Therefore, it is thought that if the orientation of the molecular chains in the amorphous state is small (that is, the trans conformation ratio is small), the amount of heat required to disentangle can be reduced and the heat seal strength can be improved. It will be done.

In the longitudinal direction of the film, the absorbance ratio should be between 0.50 and 1.20. When the absorbance ratio in the longitudinal direction of the film is less than 0.50, the molecular orientation is low, so that the tensile fracture strength in the longitudinal direction becomes small. In addition, the natural shrinkage rate increases because the molecular chain is less constrained. The absorbance ratio in the longitudinal direction of the film is more preferably 0.55 or more, and even more preferably 0.60 or more. Furthermore, if the absorbance ratio in the longitudinal direction of the film is higher than 1.20, the molecular orientation becomes high and the tensile strength at break in the longitudinal direction also increases, which is preferable in this respect, but in addition to lowering the heat sealing strength, the 80°C The hot air shrinkage rate may also be too high, and as a result, wrinkles and distortions are likely to occur in the label after shrinkage. The absorbance ratio in the longitudinal direction of the film is more preferably 1.15 or less, and even more preferably 1.10 or less.

The heat-shrinkable polyester film of the present invention preferably has a tensile breaking strength in the longitudinal direction of the film of 150 MPa or more and 320 MPa or less. If the tensile strength is less than the above-mentioned tensile strength, the film becomes stiff and tends to wrinkle when attached to a food container or the like as a label, and cracks tend to occur when unrolling, which is not preferable. The tensile breaking strength is more preferably 170 MPa or more, and even more preferably 190 MPa or more. The tensile strength at break is preferably as high as possible, but the upper limit is 320 MPa in the design of the present invention.

In addition, the heat-shrinkable polyester film of the present invention preferably has thickness unevenness in the longitudinal direction of 20% or less. If the thickness unevenness in the longitudinal direction exceeds 20%, printing unevenness is likely to occur during printing during label creation, and shrinkage unevenness after heat shrinkage is likely to occur, which is not preferable. The thickness unevenness in the longitudinal direction is more preferably 18% or less, particularly preferably 15% or less.

The heat shrinkage rate, maximum heat shrinkage stress value, heat seal strength, uneven thickness in the longitudinal direction of the film, and degree of plane orientation of the heat-shrinkable polyester film described above are determined by the preferred manufacturing method described below using the preferred film composition described above. This can be achieved by combining.

The thickness of the heat-shrinkable polyester film of the present invention is preferably 6 to 25 μm. If the thickness is less than 6 μm, the film will not have enough stiffness and will wrinkle easily when attached to the packaged object, but will also lack mechanical strength, causing cracks to occur during transportation or tearing during unwinding. Undesirable. If the thickness is 25 μm or more, the force applied during shrinkage when attached as a label becomes large, and the packaging object, such as a lunch container, may be deformed due to shrinkage of the label, which is not preferable. Note that the thickness of the film is the thickness before shrinking.

Furthermore, a heat-shrinkable polyester film can be obtained by melt-extruding the polyester raw material described above using an extruder to form an unstretched film, and then stretching the unstretched film in the longitudinal direction by the method shown below. can.

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

Then, an unstretched film can be obtained by rapidly cooling the sheet-like molten resin after extrusion. In addition, as a method for rapidly cooling the molten resin, a method of obtaining a substantially unoriented resin sheet by casting the molten resin from a die onto a rotating drum and rapidly cooling and solidifying it can be suitably employed.

Furthermore, the unstretched sheet may be made into a multilayer structure by using two or more types of raw material resins and laminating them in a feed block using a plurality of extruders, or by coextruding them using a multi-manifold die.

Stretching treatment in the longitudinal direction (film forming direction) can be carried out by a roll method, a tenter method, etc., but a method of stretching in the longitudinal direction using a difference in circumferential speed between rolls is more preferable because the apparatus is inexpensive. . More specifically, for example, it is produced by stretching in the longitudinal direction 3.5 to 6.0 times, more preferably 4.0 to 5.5 times, at a glass transition temperature in the range of +10 to 50°C. . If the stretching ratio is less than 3.5 times, the degree of plane orientation will be insufficient, and mechanical strength will tend to decrease after long-term storage, which is not preferable. If the stretching ratio is greater than 6.0 times, it is not preferable because the film tends to break during film formation and productivity decreases, and the shrinkage stress increases and the heat sealing strength of the obtained film decreases.

If the stretching temperature in the longitudinal direction is lower than Tg+5°C, breakage tends to occur during stretching, which is not preferable. Moreover, if it is higher than Tg+40°C, thermal crystallization of the film will proceed and the shrinkage rate will decrease, which is not preferable. More preferably Tg+8°C or more and Tg+37°C or less, and even more preferably Tg+10°C or more and Tg+34°C or less.

The film after stretching is preferably cooled immediately after stretching, and the film temperature is preferably Tg-30°C or less at a cooling rate of 40°C/sec or more. By rapidly cooling the film after stretching, it is possible to suppress the transition of the molecular chains to the trans conformation.

As a means of achieving the above cooling rate, it is desirable that the cooling roll temperature after heating and stretching be 15° C. or less. Furthermore, by applying cold air using a cooling blower or the like to the surface that does not come into contact with the cooling roll during film cooling, and rapidly cooling both sides at the same time, it is possible not only to improve the rapid cooling ability but also to suppress the occurrence of curling of the film after winding. . Further, in order to prevent dew condensation on the cooling roll, the dew point in the room where the stretching process is performed is preferably controlled to 5° C. or lower.

The intrinsic viscosity (IV) of the polyester film of the present invention is preferably 0.60 dl/g or more, more preferably 0.65 dl/g or more. If the intrinsic viscosity is less than 0.60 dl/g, mechanical strength tends to decrease, which is not preferable.

Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the embodiments of the Examples, and can be modified as appropriate without departing from the spirit of the present invention. be. Table 1 shows the properties of the raw materials used in the Examples and Comparative Examples, and Table 2 shows the composition and film manufacturing conditions (stretching, heat treatment conditions, etc.) in the Examples and Comparative Examples.
The evaluation method for the film is as follows.

[Heat shrinkage rate (hot air heat shrinkage rate)]
The film was cut into squares of 10 cm x 10 cm, heat-shrinked in a hot air oven at 80 ± 1.0 °C for 30 seconds under no load, and then the dimensions of the film in the longitudinal and width directions were measured. , the thermal shrinkage rates were determined according to the following formula 1.
Heat shrinkage rate = {(length before shrinkage - length after shrinkage)/length before shrinkage x 100 (%)...Formula 1

[Longitudinal thickness unevenness]
The film was sampled in the form of a long roll with a length of 30 m and a width of 40 mm, and was measured at a speed of 5 (m/min) using a continuous contact thickness meter manufactured by Micron Keikiki Co., Ltd. In addition, in the sampling of the roll-shaped film sample described above, the length direction of the film sample was taken as the main shrinkage direction of the film. The maximum thickness at the time of measurement was Tmax., the minimum thickness was Tmin., and the average thickness was Tave., and the thickness unevenness in the longitudinal direction of the film was calculated from the following formula 2.
Thickness unevenness = {(Tmax. - Tmin.)/Tave.} × 100(%)...Formula 2

[Heat seal strength]
Heat seal strength was measured in accordance with JIS Z1707. Briefly show specific steps. The sealing conditions of the heat sealer were an upper bar temperature of 160°C, a lower bar temperature of 100°C, a pressure of 0.2 MPa, and a time of 2 seconds. The adhesive sample was cut out so that the seal width was 15 mm. The peel strength was measured using a universal tensile tester "DSS-100" (manufactured by Shimadzu Corporation) at a tensile speed of 200 mm/min. Peel strength is expressed as strength per 15 mm (N/15 mm). Then, the average value of the peel strengths determined for the 10 sample pieces was defined as the heat seal strength.

[Seal bar fusion properties]
When heat sealing was performed to measure the seal strength, the film was visually evaluated as ○ if it did not stick to the upper bar on the high temperature side at all, and × as if the film partially stuck to the bar.

[Maximum heat shrinkage stress value]
The film was cut into a size of main shrinkage direction x direction perpendicular to the main shrinkage direction = 200 mm x 20 mm. Thereafter, the temperature was adjusted to 90° C. in a universal tensile tester STM-50 manufactured by Baldwin Co., Ltd., and the cut film was set therein, and the maximum stress value when held for 30 seconds was measured.

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

[Plane orientation degree]
The plane orientation degree ΔP was calculated using the following equation 3.
ΔP=(nx+ny)/2 - nz...Formula 3
Here, nx, ny, and nz represent the refractive index in the longitudinal direction, the refractive index in the width direction, and the refractive index in the thickness direction, respectively.

[Tensile breaking strength]
The obtained film was cut into 5 sheets of length x width direction = 180 mm x 0 mm, and after being left in an atmosphere of 23°C and 65% RH for more than 2 hours, they were tested using a universal tensile tester "DSS-100" (manufactured by Shimadzu Corporation). A stretching test was conducted in the longitudinal direction at a tensile speed of 200 mm/min, the distance between the chucks was 100 mm, and the average value of the strength at break obtained in 5 measurements was taken as the tensile strength at break.

[Intrinsic viscosity (IV)]
1.2 g of a sample (polyester or film) was dissolved in 100 ml of orthochlorophenol, and the intrinsic viscosity was calculated from the solution viscosity measured at a temperature of 25° C. based on the following formula 4.
ηsp/C=[η]+K[η] ² ×C...Formula 4
Here, ηsp = (solution viscosity/solvent viscosity) - ¹ , C is the weight of the dissolved polymer per 100 ml of solvent (g/100 ml, usually taken as 1.2), and K is the Huggins constant (0.343 and ). In addition, solution viscosity and solvent viscosity were measured using an Ostwald viscometer.

[Tg (glass transition point)]
Using a differential scanning calorimeter (model: DSC 220) manufactured by Seiko Electronics Co., Ltd., 5 mg of unstretched film was heated from -40°C to 10°C at a heating rate of 10°C/min. It was determined from the endothermic curve. Tangent lines were drawn before and after the inflection point of the endothermic curve, and the intersection was defined as Tg (glass transition point).

[Absorbance ratio (trans conformation ratio)]
Infrared absorption spectra were measured using an FT-IR device "FTS 60A/896" (manufactured by Varian) in a measurement wave number range of 650 to 4000 cm ^-1 and with 128 integrations, applying polarization using the ATR method. The ratio A1/A2 of the absorbance A1 at 1340 cm ^-1 and the absorbance A2 at 1410 cm ^-1 was defined as the absorbance ratio.

[Natural shrinkage rate]
The obtained film was cut into samples of length x width direction = 150 mm x 20 mm, and the cut samples were left in an atmosphere of 30 ± 2 ° C x 85% RH for 672 hours or more. The shrinkage rate after time was determined in the direction.
Shrinkage rate after time = {(Length before shrinkage - Length after time) / Length before shrinkage x 100 (%) ... Formula 5

[Shrink finish]
A small slit roll was created by slitting the film roll obtained by the method described below to a width of about 80 mm, and then dividing it into predetermined lengths and winding them up. The film was unwound from the created roll to create two cut films each having a length of 240 mm. The ends of the two cut films were heat-sealed at 140°C and adhered to create a ring-shaped label, and a bowl-shaped noodle container with a lid (bottom diameter 110 mm, top lid diameter 180 mm, height from bottom to lid) was made. The noodle container (80 mm in length) was covered with a label prepared so as to be wound from the lid to the bottom of the noodle container as shown in Figure 1. Thereafter, the noodle container coated with the label was passed through a hot air tunnel under conditions of a passing time of 3 seconds and a zone temperature of 120° C. to shrink the label and attach it to the noodle container. When installing, the seal was adjusted so that it was on the side of the noodle container.
The finished state of the label attached around the noodle container was visually evaluated according to the following criteria.
○: No wrinkles or insufficient shrinkage, and no color spots are observed △: No insufficient shrinkage occurs, but some shrinkage spots or wrinkles are observed ×: Wrinkles or insufficient shrinkage occur

[Label adhesion]
Sensory evaluation was performed on the degree of misalignment between the attached label and the noodle container when the label was slightly twisted. If the label did not move, it was marked as ○, and if it slipped through or the label and the lunch container were misaligned, it was marked as ×.

[Deformation of packaging object]
After the label was attached to the noodle container, the presence or absence of deformation of the noodle container was visually evaluated. If the container was deformed by 5 mm or more due to bending, etc., it was evaluated as ×, if the deformation was less than 5 mm to 1 mm, it was evaluated as △, and if the deformation was less than 1 mm, it was evaluated as ○.

[Aging evaluation after completion of installation]
After attaching the label to the noodle container as described above, store the container with the label attached in an atmosphere of approximately 40°C x 85% RH for 144 hours, and visually check if there are no wrinkles or distortions. If so, it was marked as ×.

Further, the polyesters used in Examples and Comparative Examples are as follows.

<Preparation of polyester raw material>
[Synthesis example 1]
In a stainless steel autoclave equipped with a stirrer, a thermometer, and a partial reflux condenser, 100 mol% of dimethyl terephthalate (DMT) as a dicarboxylic acid component and 100 mol% of ethylene glycol (EG) as a polyhydric alcohol component were added. Ethylene glycol was charged at a molar ratio of 2.2 times that of dimethyl terephthalate, and the methanol produced was distilled out of the system using zinc acetate at 0.05 mol% (based on the acid component) as a transesterification catalyst. At the same time, transesterification reaction was carried out. Thereafter, 0.225 mol% of antimony trioxide (based on the acid component) was added as a polycondensation catalyst, and the polycondensation reaction was carried out at 280°C and under a reduced pressure of 26.7 Pa. Polyester (A) was obtained. This polyester (A) is polyethylene terephthalate. The composition of polyester (A) is shown in Table 1.
[Synthesis examples 2 to 5]
Polyesters (B) to (E) with different monomers were obtained in the same manner as in Synthesis Example 1. Table 1 shows the composition of each polyester. In Table 1, TPA is terephthalic acid, BD is 1,4-butanediol, NPG is neopentyl glycol, ε-CL is caprolactam, and DEG is diethylene glycol. In the production of polyester (E), SiO 2 (Silysia 266 manufactured by Fuji Silysia Co., Ltd.) was added as a lubricant at a ratio of 7,000 ppm to the polyester. Each polyester was appropriately made into chips. The compositions of polyesters (B) to (E) are shown in Table 1.

<Example 1>
10 parts of polyester A, 60 parts of polyester B, 25 parts of polyester D, and 5 parts of polyester F were mixed and charged 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 rapidly cooled to obtain an unstretched film with a thickness of 48 μm. The take-up speed of the unstretched film (rotational speed of the metal roll) at this time was about 20 m/min. Further, the Tg of the unstretched film was 65°C.

Thereafter, this unstretched film was introduced into a longitudinal stretching machine in which a plurality of roll groups were continuously arranged in a room whose dew point was controlled to 0°C, and the film was preheated on a preheating roll until the film temperature reached 70°C. Thereafter, the film was stretched 4.0 times between stretching rolls whose surface temperature was set to 95°C. Thereafter, both sides of the longitudinally stretched film were simultaneously rapidly cooled using a cooling roll whose surface temperature was set to 10°C and a cold air blower whose surface temperature was set to 10°C. Note that the surface temperature of the film before cooling was about 85°C, and the surface temperature of the film after cooling was about 25°C. Further, the time required to cool the film from 80°C to 25°C was about 1.2 seconds, and the cooling rate of the film was 50°C/second.

Thereafter, by cutting and removing both edges, a stretched film of about 12 μm was continuously formed over a predetermined length to obtain a film roll made of a heat-shrinkable polyester film.
The properties of the heat-shrinkable film, label (before attachment), and package (noodle container with label attached) obtained as above were evaluated by the method described above. The evaluation results are shown in Table 3.

<Example 2>
A heat-shrinkable film was obtained in the same manner as in Example 1, except that the thickness of the unstretched sheet was changed to 54 μm and the stretching ratio in the longitudinal direction was 4.5 times. The evaluation results are shown in Table 3.

<Example 3>
A heat-shrinkable film was obtained in the same manner as in Example 1, except that the thickness of the unstretched sheet was changed to 60 μm and the stretching ratio in the longitudinal direction was 5.0 times. The evaluation results are shown in Table 3.

<Example 4>
Example 1 except that the raw materials used for forming the unstretched sheet of Example 1 were changed to 24 parts of polyester A, 52 parts of polyester B, 19 parts of polyester D, and 5 parts of polyester F. A heat-shrinkable film was obtained in the same manner as in Example 1. The evaluation results are shown in Table 3.

<Example 5>
A heat-shrinkable film was obtained in the same manner as in Example 4, except that the thickness of the unstretched sheet was changed to 54 μm and the stretching ratio in the longitudinal direction was 5 times. The evaluation results are shown in Table 3.

<Example 6>
Example 1 except that the raw materials used for forming the unstretched sheet of Example 1 were changed to 15 parts of polyester A, 70 parts of polyester B, 10 parts of polyester D, and 5 parts of polyester F. A heat-shrinkable film was obtained in the same manner as in Example 1. The evaluation results are shown in Table 3.

<Example 7>
A heat-shrinkable film was obtained in the same manner as in Example 6, except that the thickness of the unstretched sheet was changed to 54 μm and the stretching ratio in the longitudinal direction was set to 4.5 times. The evaluation results are shown in Table 3.

<Example 8>
Example 1 except that the raw materials used for forming the unstretched sheet in Example 1 were changed to 15 parts of polyester A, 60 parts of polyester B, 20 parts of polyester C, and 5 parts of polyester F. A heat-shrinkable film was obtained in the same manner as in Example 1. The evaluation results are shown in Table 3.

<Comparative example 1>
Example 1 except that the raw materials used for forming the unstretched sheet of Example 1 were changed to 50 parts of polyester A, 35 parts of polyester B, 10 parts of polyester D, and 5 parts of polyester F. A heat-shrinkable film was obtained in the same manner as in Example 1. The evaluation results are shown in Table 3.

<Comparative example 2>
The raw materials used for forming the unstretched sheet in Example 1 were heated in the same manner as in Example 1, except that 85 parts of polyester B, 10 parts of polyester D, and 5 parts of polyester F were used. A shrinkable film was obtained. The evaluation results are shown in Table 3.

<Comparative example 3>
The raw materials used for forming the unstretched sheet in Example 1 were the same as in Example 1, except that the temperature of the cooling roll after stretching in the longitudinal direction was changed to 25°C and the cooling blower was not used. A heat-shrinkable film was obtained by the method. Note that the surface temperature of the film before cooling was about 85°C, and the surface temperature of the film after cooling was about 50°C. Further, the time required to cool the film from 85°C to 50°C was about 1.2 seconds, and the cooling rate of the film was 20°C/second. The evaluation results are shown in Table 3.

<Comparative example 4>
A heat-shrinkable film was obtained in the same manner as in Example 1, except that the thickness of the unstretched sheet was 78 μm and the stretching ratio in the longitudinal direction was changed to 6.5 times. The evaluation results are shown in Table 3.

<Comparative example 5>
5 parts of polyester A, 66 parts of polyester B, 24 parts of polyester D, and 5 parts of polyester F were mixed and charged into an extruder. Thereafter, this mixed resin was melted at 280° C. and extruded from a T-die to obtain an unstretched film having a thickness of 80 μm in the same manner as in Example 1. Further, the Tg of the unstretched film was 65°C.
Thereafter, this unstretched film was guided to a longitudinal stretching machine in which a plurality of roll groups were successively arranged at room temperature, and the film was preheated on a preheating roll until the film temperature reached 70°C, and then the surface temperature was 95°C. The film was stretched 4.0 times between stretching rolls set at . Thereafter, the longitudinally stretched film was cooled using a cooling roll whose surface temperature was set to 25°C. Note that the surface temperature of the film before cooling was about 85°C, and the surface temperature of the film after cooling was about 50°C. Further, the time required to cool the film from 85°C to 50°C was about 1.2 seconds, and the cooling rate of the film was about 20°C/second. After cooling, the film was reheated from both sides using a ceramic heater, and by lowering the speed of subsequent rolls than the cooling roll, relaxation treatment was performed in the longitudinal direction at a relaxation rate of 5%. Thereafter, heat treatment was performed using a tenter until the film temperature reached 80°C. Next, both edges of the film were cut and removed, and then wound into a roll to obtain a heat-shrinkable film. The evaluation results are shown in Table 3.

As is clear from Table 3, the films obtained in Examples 1 to 8 all had high shrinkability in the longitudinal direction and very low shrinkability in the orthogonal width direction. Further, all of the films obtained in Examples 1 to 8 had high heat sealing strength, good label adhesion, no shrinkage spots, and good shrink finish. Furthermore, the heat-shrinkable polyester films of Examples 1 to 8 have sufficiently high strength in the longitudinal direction and have little natural shrinkage over time, so even after long-term storage, there are almost no cracks or wrinkles due to tight winding, and heat It can be used as a shrinkable film without any problems.

On the other hand, the heat-shrinkable film obtained in Comparative Example 1 had a high absorbance ratio and low heat-sealing strength, so the seal part peeled off during shrinkage, and the force of shrinkage caused some parts of the packaged object to peel off. Deformation was observed. In addition, the heat-shrinkable film obtained in Comparative Example 2 has a high shrinkage rate in the longitudinal direction, wrinkles occur during shrinkage, the packaged object deforms due to the force of shrinkage, and the heat-sealing strength is too high, making it difficult to seal. Fusion to the bar was observed. In addition, since the natural shrinkage rate is large and the wrapping tends to tighten, the wrapping tightens due to aging after installation, causing distortion of the label and bending of the packaged object. The heat-shrinkable film obtained in Comparative Example 3 had a high absorbance ratio because it was not rapidly cooled after stretching. That is, as the transition to the trans conformation progressed, the heat sealing strength decreased, and peeling was observed at the sealed portion during shrinkage. Because the film obtained in Comparative Example 4 had a large stretching ratio, the orientation progressed, resulting in a decrease in heat-sealing strength, and the shrinkage force was large when it was shrunk, resulting in deformation of the packaged object and peeling of the sealed part. It was done. Although the film obtained in Comparative Example 5 had no problems with shrinkage finish, the natural shrinkage rate was high due to weak molecular orientation, wrinkles were observed due to tightening due to aging after installation, and wrinkles were observed in the longitudinal direction. The tensile fracture strength in the direction was also insufficient. That is, the films obtained in Comparative Examples 1 to 5 had problems in practical use as heat-shrinkable films for hot air.

Since the heat-shrinkable polyester film of the present invention has excellent properties as described above, it can be suitably used for packaging various articles.

Claims (7)

A heat-shrinkable polyester film that satisfies the following requirements (1) to (6).
(1) The shrinkage rate of the film in the longitudinal direction when treated in hot air at 80°C for 30 seconds is 30% or more and 70% or less (2) When the films are heat-sealed together at 130°C and a pressure of 0.2 MPa Seal peel strength of 4 N/15 mm or more and 15 N/15 mm or less (3) Planar orientation degree of the film 0.050 or more and 0.080 or less (4) Heat shrinkage measured by polarized ATR-FTIR method on at least one surface of the film The ratio A1/A2 of absorbance A1 at 1340 cm ^-1 and absorbance A2 at 1410 cm ^-1 of the film is 0.50 or more and 1.20 or less in the longitudinal direction of the film (5) Tensile strength at break in the longitudinal direction is 150 MPa or more 320 MPa or less (6) Natural shrinkage in the longitudinal direction of the film after aging at 30°C, 85% RH for 672 hours is 1.0% or less The heat-shrinkable polyester film according to claim 1, further satisfying the following requirements (7) to (8).
(7) The maximum shrinkage stress in the longitudinal direction of the film in hot air at 90°C is 2 MPa or more and 15 MPa or less (8) The direction perpendicular to the longitudinal direction (width) of the film when treated in hot air at 80°C for 30 seconds direction) shrinkage rate is -5% or more and 10% or less The heat-shrinkable polyester film according to claim 1 or 2, which further satisfies the following requirements (9) to (10).
(9) Film thickness is 6 μm or more and 25 μm or less (10) Film IV value is 0.60 dl/g or more The heat-shrinkable polyester film according to any one of claims 1 to 3, which further satisfies the following requirements (11) to (12).
(11) The polyester constituting the film contains a glycol component that can become an amorphous component, from 10 mol% to 23 mol% (12) The polyester constituting the film contains an ethylene glycol component from 50 mol% to 77 mol% below The heat-shrinkable polyester film according to any one of claims 1 to 4, which is a uniaxially stretched film. The heat-shrinkable polyester film according to any one of claims 1 to 5, which is used for band label packaging of plastic containers. A package comprising a band label covered with the heat-shrinkable polyester film according to any one of claims 1 to 6, which is bonded in a circular shape by heat sealing.