JP6988440B2 - Heat-shrinkable polyester film with excellent heat-sealing properties - Google Patents

Description

The present invention relates to a heat-shrinkable polyester film having excellent heat-sealing properties and a package, and more specifically, is suitable for band label packaging applications such as noodle containers such as convenience stores, and shrinks in the longitudinal direction of the film roll. Since the shrinkage stress is small during heat shrinkage, the packaged container does not deform, and the peeling strength when heat-sealing at low temperature is high, so the seal part does not peel off and the shrinkage finish can be performed satisfactorily. It relates to a shrinkable polyester film.

In recent years, polyvinyl chloride resin and polystyrene resin have been used for label packaging that protects glass bottles and PET bottles and displays products, banding packaging and band label packaging that are used to fasten the container and lid of convenience store lunch boxes. , Stretched films made of polyester resins and the like (so-called heat-shrinkable films) have been widely used. Among such heat-shrinkable films, polyvinyl chloride-based films have problems such as low heat resistance, generation of hydrogen chloride gas during incineration, and dioxin. In addition, polystyrene film is inferior in solvent resistance, it is necessary to use ink with a special composition at the time of printing, and it is necessary to incinerate it at a high temperature, and a large amount of black smoke is generated with an offensive odor at the time of incineration. There is a problem of doing. Therefore, polyester-based heat-shrinkable films having high heat resistance, easy incineration, and excellent solvent resistance have been widely used as shrinkage labels, and the amount used tends to increase. be.

Further, as a normal heat-shrinkable polyester-based film, a film that shrinks significantly in the width direction is widely used. When used as a label film for bottles or as a band label for lunch boxes, a heat-shrinkable film that heat-shrinks in the width direction must be attached because the film must be annularly attached to the bottle or lunch container and then heat-shrinked in the circumferential direction. When doing so, after forming an annular body so that the width direction of the film is the circumferential direction, the annular body must be cut into predetermined lengths and attached to a bottle or a lunch container by hand. It doesn't become. Therefore, it is difficult to attach a label film or a band label made of a heat-shrinkable film that heat-shrinks in the width direction to a bottle or a lunch box container at high speed. Therefore, recently, there is a demand for a film that heat-shrinks in the longitudinal direction so that the film unwound from the film roll can be directly wound around a bottle or a bento container and attached. It eliminates the need for a center sealing process for forming and sealing a film annular body, cutting, and hand covering, and can be mounted at high speed.

In recent years, the number of cooked noodle products such as udon and ramen has been increasing at convenience stores, etc., so put the cooked noodles in a deep plastic container, cover it from above, and then use an annular shrink film to cover the container and lid. The packaging form is such that the noodles are fastened from above and below (so-called band label packaging). Also in band label packaging, automatic packaging that is used by wrapping the film roll directly around the container is required, and the shrink film wound from the two film rolls is heat-sealed in the width direction, and between the two films. An object to be packaged (noodle container) is inserted, and the film on the opposite side of the heat-sealed part is heat-sealed to form an annular film. It becomes a band label that fastens the container and the lid.
As a performance of the shrink film of the band label, it is of course necessary to fasten the container and the lid, but it is necessary that the container is not deformed by the stress due to the shrinkage. If the container is deformed, it is not preferable in terms of the appearance of the product, and the contents may be spilled or foreign matter may be mixed in, which is a problem. It is also necessary that the heat-sealed portion does not come off due to stress due to shrinkage. If the heat seal part is peeled off, the original purpose of fastening the container and the lid cannot be achieved. Further, the heat-sealed portion needs to have high strength even when heat-sealed at a low temperature. As mentioned above, of the two heat seals on the band label, one is sealed after inserting the packaged object (noodle container) between the two films, but from the viewpoint of material saving of the film used. Therefore, it is often sealed at a position close to the packaged object. Therefore, the heat of the seal bar may deform the plastic packaged body. In order to prevent the deformation, it is necessary to lower the temperature of the seal bar, and the film for band label use needs to have low temperature sealing property.
From the above, the performance required for the shrink film used for the band label is that it has a sufficient shrinkage rate in the longitudinal direction, the shrinkage stress is low, and the heat seal strength when sealed at a low temperature is high. ..

For example, Patent Document 1 describes a polyester-based heat-shrinkable film that shrinks in the longitudinal direction of a roll by using a monomer as an amorphous component. The stretching stress in the main contraction direction) increases, and as a result, the contraction stress during contraction increases. Further, there is a problem that the biaxial stretching promotes the orientation in the film surface direction and lowers the heat sealability. Further, a large-scale facility for biaxially extending is required, which causes a problem of high cost.

Japanese Patent No. 441156

An object of the present invention is to prevent deformation of the packaged object during shrinkage by having sufficient heat shrinkage characteristics in the longitudinal direction, low shrinkage stress in the longitudinal direction, and high low-temperature heat-sealing property between films. The present invention is to provide a heat-shrinkable polyester-based film in which the heat-sealed portion is less likely to peel off.

The present invention has the following configuration.
1. 1. A heat-shrinkable polyester-based film, which is a heat-shrinkable polyester-based film and is characterized by satisfying the following requirements (1) to (4) and has excellent heat-sealing properties.
(1) The difference in refractive index between the longitudinal direction and the width direction of the film is 0.04 or more and 0.12 or less. (2) The shrinkage rate in the longitudinal direction after being immersed in warm water at 90 ° C. for 10 seconds is 40% or more and 80%. (3) The maximum shrinkage stress in the longitudinal direction of the film measured with hot air at 90 ° C is 2 MPa or more and 5 MPa or less (the upper limit of stress was lowered to remove the Mitsubishi patent).
(4) The peel strength after heat-sealing the films at a temperature of 130 ° C. and a pressure of 2 kg / cm ² is 3.0 N / 15 mm or more and 20.0 N / 15 mm or less. The film thickness is 6 μm or more and 30 μm or less. A heat-shrinkable polyester-based film with excellent heat-sealing properties.
3. 3. 1. The total glycol component of the polyester constituting the film contains 15 mol% or more and 40 mol% or less of the butanediol component. ~ 2. A heat-shrinkable polyester-based film having excellent heat-sealing properties as described in any of the above.
4. 1. The plane orientation coefficient is 0.03 or more and 0.08 or less. ~ 3. A heat-shrinkable polyester-based film having excellent heat-sealing properties as described in any of the above.
5. 1. It is a uniaxially stretched film. ~ 4. A heat-shrinkable polyester-based film having excellent heat-sealing properties as described in any of the above.
6. 1. It is characterized by being used for band label packaging of plastic containers. ~ 5. A heat-shrinkable polyester-based film having excellent heat-sealing properties as described in any of the above.
7. The above 1. ~ 6. A package in which the heat-shrinkable polyester-based film according to any one of the above is coated with a band label to which the heat-shrinkable polyester film is bonded in a ring shape with a heat seal.

As a result of diligent studies by the present inventors, an unstretched sheet having a polyester composition having a specific composition is uniaxially stretched in the longitudinal direction and then subjected to a relaxation treatment in the longitudinal direction so as to have a sufficient shrinkage rate in the longitudinal direction. Instead, it was found that the heat-sealed portion is less likely to peel off due to the low shrinkage stress in the longitudinal direction, which prevents deformation of the packaged object during shrinkage, and the high low-temperature heat-sealing property between the films. The invention was completed.

The heat-shrinkable polyester film of the present invention can be suitably used for band labels of 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 mounting, insufficient shrinkage does not occur, the deformation of the container is extremely small due to the low shrinkage stress, and the heat-sealing part is less likely to peel off due to the high low-temperature heat-sealing property. , It was possible to obtain a good finish.

Side view showing an example of band label packaging Top view showing an example of band label packaging The illustration of the container deformation amount evaluation of shrinkage finish is shown.

Hereinafter, the configuration of the heat-shrinkable polyester film having excellent heat-sealing properties according to the present invention will be described in detail.

The heat-shrinkable polyester-based film having excellent heat-sealing properties of the present invention is characterized in that the main shrinkage direction is the longitudinal direction and the following requirements (1) to (4) are satisfied.
(1) The difference in the refractive index between the longitudinal direction and the width direction of the film is 0.04 or more and 0.12 or less. (2) The shrinkage rate in the longitudinal direction after being immersed in warm water at 90 ° C. for 10 seconds is 40% or more and 80%. (3) The maximum shrinkage stress in the longitudinal direction of the film measured with hot air at 90 ° C is 2 MPa or more and 5 MPa or less (4) Peeling after heat-sealing the ^{films at a temperature of 130 ° C and a pressure of 2 kg / cm 2.} The strength is 3N / 15mm or more and 20N / 15mm or less. The above-mentioned "longitudinal direction" refers to the film forming direction at the time of film forming (that is, the winding direction of the film wound in a roll shape).

The heat-shrinkable polyester-based film having excellent heat-sealing properties of the present invention has a sufficient heat-shrinkability in the longitudinal direction and has a low heat-shrinkage stress by satisfying all the above requirements (1) to (4). Therefore, it is possible to extremely reduce the deformation of the container, and since it has a high low-temperature heat-sealing property, the heat-sealing portion is less likely to peel off, and it can be particularly suitably used for plastic band labels.
The heat-shrinkable polyester-based film of the present invention that satisfies the above requirements can be produced by using a polyester raw material having a specific composition described later and adopting a specific production method.

[Characteristics of the heat-shrinkable polyester film having excellent heat-sealing properties of the present invention]
The heat-shrinkable polyester film of the present invention is heat in the longitudinal direction of the film calculated by the following formula 1 from the length before and after shrinkage when treated in warm water at 90 ° C. under no load for 10 seconds. The shrinkage rate (that is, the heat shrinkage rate of hot water at 90 ° C.) is 40% or more and 80% or less.
Thermal shrinkage = {(length before shrinkage-length after shrinkage) / length before shrinkage} x 100 (%) ... Equation 1

If the heat shrinkage rate of hot water in the longitudinal direction at 90 ° C. is less than 40%, wrinkles and tarmi will occur on the label after heat shrinkage due to the small shrinkage amount when used as a band label, which is not preferable. .. On the other hand, when the thermal shrinkage rate of hot water in the longitudinal direction at 90 ° C. is larger than 80%, the shrinkage stress also increases at the same time, which causes a problem of deformation of the container to be packaged. The thermal shrinkage of hot water in the longitudinal direction is more preferably 75% or less, further preferably 70% or less. The lower limit of the thermal shrinkage rate of hot water in the longitudinal direction at 90 ° C. is more preferably 45% or more, and further preferably 50% or more.

In the heat-shrinkable polyester-based film of the present invention, the maximum value of shrinkage stress in the longitudinal direction of the film measured with hot air at 90 ° C. is preferably 2 MPa or more and 5 MPa or less. If the shrinkage stress in the hot air at 90 ° C. is less than 2 MPa, the band label does not have a tight finish after shrinkage finishing, and the original purpose of fastening the container and the lid cannot be achieved, which is a problem. Further, if the shrinkage stress exceeds 5 MPa, the container is deformed by the force, which is not preferable in appearance, and causes a problem that the contents are spilled or foreign matter is mixed. Further, the product containing the cooked noodles may be reheated together with the band label in a microwave oven or the like, and at that time, the reheated band label tries to shrink again, and shrinkage stress is generated. If the shrinkage stress is 5 MPa or more, the container is deformed due to the shrinkage stress due to reheating, which is a problem.

The heat-shrinkable polyester film of the present invention has a peeling strength (heat-sealing peeling strength) of 3 N / 15 mm or more and 20 N / 15 mm or less after heat-sealing the films at a temperature of 130 ° C. and a pressure of 2 kg / cm ^2. Is preferable. If the heat seal peeling strength is less than 3N / 15 mm, the seal portion is peeled off due to the shrinkage stress of the label during shrinkage finishing as a band label, which is a problem. Further, it is preferable that the heat seal peeling strength is high, but the upper limit currently obtained is 20 N / 15 mm.

The thickness of the heat-shrinkable polyester film of the present invention is preferably 6 to 30 μm as a heat-shrinkable film for label applications and banding applications including band labels. Further, 8 to 28 μm is more preferable, and 10 μm to 26 μm is particularly preferable. If the thickness is too thick, the absolute value of the shrinkage stress becomes large, and the container may be deformed for banding use.

The heat-shrinkable polyester film of the present invention preferably has a difference in refractive index between the longitudinal direction and the width direction of 0.04 or more and 0.12 or less. If it is less than 0.04, that is, it is an unoriented film or a biaxially oriented film, but the unoriented film cannot obtain the required heat shrinkage, and the biaxially oriented film cannot be obtained. This film is not preferable because sufficient heat-sealing properties cannot be obtained due to the progress of crystallization. On the other hand, even when the difference in refractive index exceeds 0.12, crystallization has progressed and the required heat-sealing property cannot be obtained, which is not preferable. More preferably, the difference in refractive index between the longitudinal direction and the width direction is 0.05 or more and 0.11 or less, and particularly preferably 0.06 or more and 0.10 or less.

The heat-shrinkable polyester film of the present invention preferably has a coefficient represented by the formula 2 of 0.03 or more and 0.08 or less.
Surface orientation coefficient = {(refractive index in the longitudinal direction + refractive index in the width direction) / 2--refractive index in the thickness direction} ... Equation 2
If the plane orientation coefficient is less than 0.03, the mechanical strength of the label is significantly lowered, which causes a problem such as tearing of the band label packaged in the container during transportation. Further, if the plane orientation coefficient exceeds 0.080, the crystallinity of the film becomes high and the heat seal peeling strength decreases, which is not preferable.

[Polyester used in the heat-shrinkable polyester film of the present invention]
The polyester used in the heat-shrinkable polyester-based film of the present invention preferably contains terephthalic acid as a main component as a dicarboxylic acid component. The term "terephthalic acid as a main component" means that 50 mol% or more of the 100 mol% of the dicarboxylic acid components constituting the polyester is terephthalic acid. The amount of terephthalic acid is more preferably 60 mol% or more, further preferably 70 mol% or more.

Examples of the dicarboxylic acid component other than terephthalic acid contained in the polyester constituting the heat-shrinkable polyester film of the present invention include aromatic dicarboxylic acids such as isophthalic acid, naphthalenedicarboxylic acid and orthophthalic acid, adipic acid and azelaic acid. Examples thereof include aliphatic dicarboxylic acids such as sebacic acid and decandicarboxylic acid, and alicyclic dicarboxylic acids.

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

Further, it is preferable that the polyester does not contain a polyvalent carboxylic acid having a valence of 3 or more (for example, trimellitic acid, pyromellitic acid and their anhydrides). The heat-shrinkable polyester-based film obtained by using the polyester containing these multivalent carboxylic acids makes it difficult to achieve the required high shrinkage rate.

Examples of the polyhydric alcohol component constituting the polyester used in the heat-shrinkable polyester-based film of the present invention include aliphatic diols such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, and hexanediol. , 1,4-Cyclohexanedimethanol and the like alicyclic diols, bisphenol A and the like aromatic diols and the like can be mentioned. Of the above, it is preferable that ethylene glycol is contained in the largest amount as a polyhydric alcohol component. The preferable content of ethylene glycol is 40 mol% or more, more preferably 45 mol% or more, in 100 mol% of the polyhydric alcohol component.

The polyester used in the heat-shrinkable polyester-based film of the present invention preferably contains 1,4-butanediol. By containing 1,4-butanediol, the glass transition temperature (Tg) of the film can be lowered, but by lowering the glass transition temperature, the stretching force at the time of stretching can be lowered, and as a result, the film can be lowered. Shrinkage stress is reduced. Further, as the glass transition temperature decreases, the peel strength after heat sealing increases. It is considered that this is because the motility of the molecular chains became higher due to the decrease in the glass transition temperature, and the effect of the molecular chains being entangled with each other due to the heat and pressure during heat sealing became higher. The content of the 1,4-butanediol component is preferably 15 mol% or more and 40 mol% or less in 100 mol% of the polyhydric alcohol component. If the 1,4-butanediol component is less than 15 mol%, low shrinkage stress and high heat sealability cannot be obtained, which is not preferable. On the other hand, if it exceeds 40 mol%, the stretching stress becomes too low and the thickness accuracy of the stretched film deteriorates, which is not preferable. The content of 1,4-butanediol is preferably 15 mol% or more and 40% mol or less, more preferably 16 mol% or more and 39 mol% or less, and particularly preferably 17 mol% or more and 38 mol or less%. Is.

Further, the polyester is 10 mol% or more in total of one or more monomer components that can be an amorphous component in 100 mol% of the polyhydric alcohol component or 100 mol% of the polyvalent carboxylic acid component in the total polyester resin. Is preferable in that it has high shrinkage. If it is less than 10 mol%, the required shrinkage rate cannot be obtained, and shrinkage is insufficient at the time of shrinkage finishing. The amorphous monomer component is 10 mol% or more, preferably 11 mol% or more, more preferably 12 mol% or more, and particularly preferably 13 mol% or more. Further, the upper limit of the total of the monomer components to be the amorphous component is not particularly limited, but the upper limit is preferably 40 mol%.
Here, the interpretation of the above-mentioned term "which can be an amorphous component" will be described in detail.

In the present invention, the "amorphous polymer" specifically refers to a case where the measurement by the DSC differential scanning calorimetry device does not have an endothermic peak due to melting. Amorphous polymers have not substantially progressed in crystallization and cannot take a crystalline state, or even if they are crystallized, the degree of crystallinity is extremely low.

In general, for a polymer in which a large number of monomer units are bonded, the stereoregularity of the polymer is low, the targetness of the polymer is poor, the side chains of the polymer are large, the polymer has many branches, and the molecules between the polymers are intermolecular. When it has various conditions such as low cohesive force, it becomes an amorphous polymer. However, depending on the state of existence, crystallization may proceed sufficiently to form a crystalline polymer. For example, even if the polymer has a large side chain, if the polymer is composed of a single monomer unit, crystallization may proceed sufficiently and the polymer may become crystalline. Therefore, even if the same monomer unit is used, the polymer may be crystalline or amorphous. Therefore, in the present invention, the expression "monomer-derived unit that can be an amorphous component" is used. Using.

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

When the monomer unit consisting of terephthalic acid and ethylene glycol is the main monomer unit constituting the polymer, the monomer unit consisting of isophthalic acid and ethylene glycol, the monomer unit consisting of terephthalic acid and neopentyl glycol, the terephthalic acid and 1.4-cyclohexane. Examples thereof include a monomer unit made of dimethanol, a monomer unit made of isophthalic acid and butanediol, and the like as a monomer-derived unit that can be the above-mentioned amorphous component.

Examples of the monomers that can be an amorphous component include neopentyl glycol, 1,4-cyclohexanedimethanol, isophthalic acid, 1,4-cyclohexanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 2,2-diethyl1, 3-Propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propane Examples thereof include diol and hexanediol. Among these, neopentyl glycol, 1,4-cyclohexanedimethanol or isophthalic acid is preferably used. It is also preferable to use ε-caprolactone. More preferably, it is neopentyl glycol or 1,4-cyclohexanedimethanol, and even more preferably neopentyl glycol.

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

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

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

[Method for producing a heat-shrinkable polyester film having excellent heat-sealing properties according to the present invention]
The heat-shrinkable polyester-based film of the present invention is not limited in its manufacturing method. For example, the polyester raw material described above is melt-extruded by an extruder to form an unstretched film, and the unstretched film is formed. It can be obtained by manufacturing by the method shown below.

When the raw material resin is melt-extruded, it is preferable to dry the polyester raw material using a dryer such as a hopper dryer or a paddle dryer, or a vacuum dryer. After the polyester raw material is dried in this way, it is melted at a temperature of 200 to 300 ° C. and extruded into a film using an extruder. For such extrusion, any existing method such as the T-die method and the tubular method can be adopted.

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

Further, as will be described later, the obtained unstretched film can be stretched in the longitudinal direction under predetermined conditions to obtain the heat-shrinkable polyester-based film of the present invention.

A normal heat-shrinkable polyester-based film is produced by stretching an unstretched film in a direction in which it is desired to shrink. In the present invention, uniaxial stretching is performed in the longitudinal direction, which is the main contraction direction. In the case of uniaxial stretching in the longitudinal direction, the unstretched film is guided to a longitudinal stretching machine in which a plurality of roll groups are continuously arranged, the film is heated to a predetermined temperature on a preheating roll (low speed roll), and then downstream of the preheating roll. A roll (high-speed roll) having a speed higher than that of the preheating roll is provided in the film, and the film is stretched in the longitudinal direction by the speed difference between the low-speed roll and the high-speed roll. It should be noted that the manufacturing means by uniaxial stretching in the longitudinal direction has an advantage that it can be manufactured by simple equipment because it does not use the stretching equipment in the lateral direction.

The longitudinal stretching method at this time is not particularly specified, but multi-step stretching such as two-step stretching is preferable. The multi-stage stretching disperses the stress during stretching and reduces the stress remaining on the film. Further, since the increase in surface orientation is suppressed, the heat sealability is improved.

The draw ratio at this time is not particularly specified, but is preferably 2 times or more and 6 times or less. If the draw ratio is less than 2 times, it is difficult to obtain a high shrinkage ratio in terms of mass balance, and the thickness accuracy is deteriorated. Further, when the draw ratio exceeds 6 times, not only the surface orientation is promoted and the heat seal peeling strength is lowered, but also the shrinkage stress becomes high, which is not preferable. Further, in the film of the present invention, biaxial stretching is not preferable. For example, a method of stretching the unstretched film in the width direction using a tenter and then stretching it in the longitudinal direction in the main contraction direction is conceivable, but the stretching stress during stretching in the longitudinal direction becomes high and the shrinkage stress becomes high. In addition, biaxial stretching promotes crystallization of the film, making it impossible to obtain good heat-sealing properties.

The method of heating the film before and during stretching is not particularly specified, but in addition to the method of heating on the roll described above, an infrared heater or a condensing infrared heater is used between the low-speed roll and the high-speed roll. It may be heated.

Further, if the stretching temperature in the longitudinal direction is less than Tg + 5 ° C., breakage is likely to occur during stretching, which is not preferable. Further, when the temperature is higher than Tg + 40 ° C., thermal crystallization of the film proceeds and the shrinkage rate decreases, which is not preferable. It is more preferably Tg + 8 ° C. or higher and Tg + 37 ° C. or lower, and further preferably Tg + 11 ° C. or higher and Tg + 34 ° C. or lower.

Further, after the above-mentioned stretching in the longitudinal direction, it is preferable to perform a treatment for relaxing in the longitudinal direction and a heat treatment for the purpose of adjusting so that the shrinkage rate in the longitudinal direction does not become too high and for the purpose of reducing the shrinkage stress. The method of relaxing in the longitudinal direction is not particularly limited, but for example, after the longitudinal stretching step, a roll having a slower speed than the high-speed roll of the longitudinal stretching machine is provided, and a ceramic heater is used between the longitudinal stretching machine and the roll. There is a method of shrinking and relaxing the film in the longitudinal direction by reheating the film. As another example, the film after longitudinal stretching is guided to a tenter device capable of gripping both ends of the film with clips and heated, and while heat treatment is performed, both ends of the film are cut or clipped inside the tenter. By opening, both ends of the film are not gripped inside the tenter, and the speed of the roll after the tenter is made slower than the speed of the entrance of the tenter, so that the film that is not gripped at both ends is contracted and relaxed in the longitudinal direction. There is a way. The method of heat treatment is not particularly limited, but for example, there is a method of guiding the film to a tenter device capable of holding both ends of the film with clips and heating the film, and heat-treating with hot air. The relaxation rate in the above-mentioned longitudinal relaxation is preferably 2% or more and 10% or less. If the relaxation rate is less than 2%, the effects of adjusting (decreasing) the shrinkage rate in the longitudinal direction and suppressing the shrinkage stress are not sufficient, which is not preferable. Further, if the relaxation rate exceeds 10%, the decrease in shrinkage rate and the decrease in stress are too large and fall below the specified range, which is not preferable. The heat treatment temperature is preferably Tg or more and Tg + 40 ° C. or less of the film. If the heating temperature is less than Tg, the above effect cannot be obtained, and if it exceeds Tg + 40 ° C., the shrinkage rate is too low, which is not preferable. Further, the above relaxation treatment may be used alone or in combination with the heat treatment, but it is preferable to combine both.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the embodiments of the embodiments and can be appropriately modified without departing from the spirit of the present invention. be.

The film evaluation method is as follows.
[Tg (glass transition point)]
Using a differential scanning calorific value analyzer (DSC220, manufactured by Seiko Electronics Inc.), put 5 mg of unstretched film in a sample pan, cover the pan, and change from -40 ° C to 120 ° C at 10 ° C / in a nitrogen gas atmosphere. It was measured by raising the temperature at a heating rate of 1 minute. Tg (° C.) was determined 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 at 30 ° C. using an Ostwald viscometer. The unit is dl / g.

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

[Shrink stress]
A sample with a length of 200 mm and a width of 20 mm in the main shrinkage direction is cut out from the heat-shrinkable film, and a strong elongation measuring machine with a heating furnace manufactured by Toyo Baldwin (currently known as Orientec) (Tecilon (registered trademark of Orientec). ) Was measured. The heating furnace was preheated to 90 ° C., and the distance between the chucks was set to 100 mm. The ventilation of the heating furnace was temporarily stopped, the door of the heating furnace was opened, the sample was attached to the chuck, and then the door of the heating furnace was closed immediately, and the ventilation was restarted.
The shrinkage stress was measured for 30 seconds or longer, and the maximum value during measurement was defined as the maximum shrinkage stress (MPa).

[Peeling strength after heat sealing]
The heat seal strength was measured according to JIS Z1707. The specific procedure is briefly shown. The films of the present invention, which had not been subjected to sample coating treatment, corona treatment, etc., were adhered to each other with a heat sealer. The sealing conditions were an upper bar temperature of 130 ° C., a lower bar temperature of 100 ° C., a pressure of 2 kg / cm ² , 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 at a tensile speed of 200 mm / min using a universal tensile tester "DSS-100" (manufactured by Shimadzu Corporation). The peel strength is indicated by the strength per 15 mm (N / 15 mm).

[Surface orientation coefficient]
The refractive indexes in the longitudinal direction, width direction, and thickness direction of the film were measured using an "Abbeb refractometer 4T type" manufactured by Atago Co., Ltd. after each sample film was left in an atmosphere of 23 ° C. and 65% RH for 2 hours or more. .. The surface orientation coefficient was obtained from the measurement results using the following equation 2 = {(refractive index in the longitudinal direction + refractive index in the width direction) / 2--refractive index in the thickness direction} ... Equation 2

[Shrinkability]
Compared to a plastic noodle container (long side 220 mm x short side 150 mm x height 50 mm) commercially available at convenience stores, the width is 90 mm above and below the container so that the body and lid of the container are fastened with a film. Two films were placed, and the film edges (two places) were heat-sealed at 130 ° C. That is, at this time, the noodle container is covered with the film that has been heat-sealed and formed into an annular shape. At this time, the shrinkage direction (longitudinal direction) of the film is set to be the circumferential direction of the annular film, and the long sides of the noodle container are positioned so as to be fastened to each other by the annular film. Made the midpoints match. The amount of slack in the annular film with respect to the container was set to 25%. The noodle container and the annular film were heated and shrunk with hot air at a set temperature of 110 ° C. using a hot air shrink tunnel (TORNAD 2500 manufactured by Nippon Technology Solutions), and the shrinkage finish was evaluated. In the evaluation of shrinkage finish, two points were evaluated: deformation of the container and tearing of the heat-sealed portion.

(Deformation of container)
For the deformation of the container, the change in the distance A from the midpoint of one long side of the container to the midpoint of the other long side before and after shrinkage was defined as the deformation amount R (formula 3 below).
Deformation amount R = A (before contraction) ― A'(after contraction) ・ ・ ・ Equation 3
The one with a large amount of change was judged to have a large deformation of the container, and the standard was as follows. ○: 0 mm ≤ R <2 mm
Δ: 3 mm ≤ R <5 mm
×: 5 mm ≤ R

(Peeling of heat seal part)
The peeling of the heat seal was judged by observing the two heat seal portions after the shrinkage finish and judging by the following criteria.
○: No peeling △: Some peeling.
×: At least one heat seal part is peeled off

<Preparation of polyester raw material>
[Synthesis Example 1]
In a stainless steel autoclave equipped with a stirrer, thermometer and partial recirculation 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 added. Ethylene glycol was charged to be 2.2 times the molar ratio of dimethyl terephthalate, 0.05 mol% of zinc acetate (relative to the acid component) as a transesterification catalyst, and 0.225 mol of antimony trioxide as a polycondensation catalyst. % (With respect to the acid component) was added, and the transesterification reaction was carried out while distilling off the produced methanol to the outside of the system. Then, a polycondensation reaction was carried out at 280 ° C. under a reduced pressure condition 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 2-5]
Polyesters 2 to 5 shown in Table 1 were obtained by the same method as in Synthesis Example 1. During the production of the polyester 2, SiO2 (Fuji Silysia Chemical Ltd. Silicia 266; average particle size 1.5 μm) was added as a lubricant at a ratio of 7200 ppm to the polyester. In the table, TPA is terephthalic acid, IPA is isophthalic acid, NPG is neopentyl glycol, BD is 1,4-butanediol, and CHDM is cyclohexanedimethanol. The intrinsic viscosities of the polyester were 2: 0.75 dl / g, 3: 0.75 dl / g, 4: 1.20 dl / g, and 5: 0.75 dl / g, respectively. In addition, each polyester was appropriately formed into chips. The composition of each polyester is shown in Table 1.

[Example 1]
The above-mentioned polyester 1, polyester 2, polyester 3 and polyester 4 were mixed at a mass ratio of 4: 6: 66: 24 and charged into an extruder. After that, the mixed resin was melted at 280 ° C., extruded from the T die, wound around a rotating metal roll cooled to a surface temperature of 30 ° C., and rapidly cooled to obtain an unstretched film having a thickness of μm. The Tg of the unstretched film was 65 ° C. The unstretched film is guided to a longitudinal stretching machine in which a plurality of roll groups are continuously arranged, heated in a preheated roll shape until the film temperature reaches 85 ° C. (Tg + 20 ° C.), and then the stretching ratio in the longitudinal direction is determined by the roll stretching method. The film was vertically stretched 4.0 times so that the thickness of the film after stretching was 20 μm. After longitudinal stretching, the film is cooled with a cooling roll set to a surface temperature of 25 ° C., then reheated from both sides of the film using a ceramic heater, and the subsequent rolls are relaxed by lowering the speed than the above cooling rolls. The relaxation treatment was performed in the longitudinal direction at a rate of 5%. Then, using a tenter, heat treatment was performed until the film temperature reached 80 ° C. (Tg + 15 ° C.). Then, both edges of the film were cut and removed, and then wound into a roll. The characteristics of the obtained film were evaluated by the above method. The manufacturing conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[Example 2]
Same as Example 1 except that the stretching ratio in the longitudinal direction was set to 3.0 times and the amount of extrusion from the T-die of the mixed resin melted so that the thickness of the film after stretching in the longitudinal direction was 20 μm was adjusted. And said. The manufacturing conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[Example 3]
Same as Example 1 except that the stretching ratio in the longitudinal direction was set to 5.0 times and the amount of extrusion from the T-die of the mixed resin melted so that the thickness of the film after stretching in the longitudinal direction was 20 μm was adjusted. And said. The manufacturing conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[Example 4]
The mass ratio of the polyester described above is mixed with polyester 1, polyester 2, polyester 3 and polyester 4 at a ratio of 10: 6: 70: 16 and charged into an extruder, and the film temperature at the time of stretching in the longitudinal direction is 90 ° C. ( Tg + 20 ° C.), and the same as in Example 1 except that the heat treatment temperature after stretching was 85 ° C. (Tg + 15 ° C.). At this time, the Tg of the unstretched film was 70 ° C. The manufacturing conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[Example 5]
The mass ratio of the polyester described above was mixed with polyester 2, polyester 3 and polyester 4 at 6:56:38 and charged into an extruder to bring the film temperature during longitudinal stretching to 80 ° C (Tg + 15 ° C). The same as in Example 1 except that the temperature of the heat treatment after stretching was set to 75 ° C. (Tg + 10 ° C.). At this time, the Tg of the unstretched film was 65 ° C. The manufacturing conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[Example 6]
The same procedure as in Example 2 was carried out except that the film temperature during the heat treatment after stretching was set to 95 ° C. (Tg + 30 ° C.). The manufacturing conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[Example 7]
During heat treatment after stretching, the stretching ratio in the longitudinal direction is increased to 3.0 times, and the amount of extrusion is adjusted from the T-die of the mixed resin melted so that the thickness of the film after stretching in the longitudinal direction becomes 20 μm. The same as in Example 5 except that the film temperature of No. 5 was set to 95 ° C. (Tg + 30 ° C.). The manufacturing conditions are shown in Table 2 and the evaluation results are shown in Table 3.

[Comparative Example 1]
The above-mentioned mass ratio of polyester is mixed with polyester 1, polyester 2, polyester 3 and polyester 4 at 18: 6: 66: 10 and put into an extruder to carry out relaxation in the longitudinal direction after longitudinal stretching. The same as in Example 1 was carried out except that the film temperature during the heat treatment after stretching was set to 95 ° C. (Tg + 23 ° C.). The Tg of the unstretched film at this time was 72 ° C. The manufacturing conditions are shown in Table 2 and the evaluation results are shown in Table 3.

[Comparative Example 2]
The above-mentioned polyester 1, polyester 2, polyester 3 and polyester 4 were mixed at a mass ratio of 4:15:66: 15 and charged into an extruder. After that, the mixed resin was melted at 280 ° C., extruded from the T-die, wound around a rotating metal roll cooled to a surface temperature of 30 ° C., and rapidly cooled to obtain an unstretched film having a thickness of 240 μm. The Tg of the unstretched film was 70 ° C. The unstretched film was guided to a tenter, heated until the film temperature reached 100 ° C. (Tg + 30 ° C.), and stretched laterally at a draw ratio of 4.0 times. Then, the film after the corresponding transverse stretching is guided to a longitudinal stretching machine in which a plurality of roll groups are continuously arranged, heated in a preheated roll shape until the film temperature reaches 85 ° C. (Tg + 15 ° C.), and then in the longitudinal direction by the roll stretching method. The film was vertically stretched so that the stretch ratio of the film was 3.0 times and the thickness of the film after stretching was 20 μm. After the longitudinal stretching, the film was cooled by a cooling roll set to a surface temperature of 25 ° C., and then the film was led to the tenter again. In the tenter, the distance between the clips gripping the end of the film was constant (that is, the film was not stretched and relaxed), and heat treatment was performed until the film temperature reached 80 ° C. (Tg + 10 ° C.). Next, both edges of the heat-treated film were cut and removed, and then wound into a roll. The characteristics of the obtained film were evaluated by the above method. The manufacturing conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[Comparative Example 3]
T of the mixed resin melted so that the film temperature during stretching in the longitudinal direction is 90 ° C. (Tg + 25 ° C.), the stretching ratio is 8.0 times, and the thickness of the film after stretching in the longitudinal direction is 20 μm. The same procedure as in Example 1 was carried out except that the amount of extrusion from the die was adjusted and relaxation in the longitudinal direction after longitudinal stretching was not performed. The manufacturing conditions are shown in Table 2, and the evaluation results are shown in Table 3.
[Comparative Example 4]
The above-mentioned polyester 4 and polyester 5 were mixed at a mass ratio of 15:85 and charged into an extruder. After that, the mixed resin was melted at 280 ° C., extruded from the T-die, wound around a rotating metal roll cooled to a surface temperature of 30 ° C., and rapidly cooled to obtain an unstretched film having a thickness of 110 μm. The Tg of the unstretched film was 68 ° C. The unstretched film is guided to a longitudinal stretching machine in which a plurality of roll groups are continuously arranged, heated in a preheated roll shape until the film temperature reaches 75 ° C. (Tg + 7 ° C.), and then the stretching ratio in the longitudinal direction is determined by the roll stretching method. It was stretched 5.0 times. After that, the film was guided to a tenter, heated until the film temperature reached 90 ° C. (Tg + 22 ° C.), and stretched in the width direction at a draw ratio of 1.1 times so that the film thickness became 20 μm. Then, both edges of the film were cut and removed, and then wound into a roll. The characteristics of the obtained film were evaluated by the above method. The manufacturing conditions are shown in Table 2, and the evaluation results are shown in Table 3.

As a result of the evaluation, the films of Examples 1 to 7 have sufficient shrinkage, low shrinkage stress, and excellent heat sealability, so that the container is not deformed or the heat seal is peeled off during shrinkage finishing. It was a film with high quality in label applications and excellent in practical use.

On the other hand, since the film of Comparative Example 1 has a low heat-sealing property, peeling of the heat-sealing portion occurred at the time of shrinkage finishing. Further, in Comparative Example 2, since the shrinkage stress is high and the heat sealability is low, the container is deformed at the time of shrinkage finishing, and the heat seal portion is also peeled off. In Comparative Example 3, although the heat seal did not peel off, the container was deformed due to the high contraction stress. In the film of Comparative Example 4, the container was deformed due to the high shrinkage stress, and the heat-sealed portion was also peeled off. That is, Comparative Examples 1 to 4 were unsuitable as a film for band label use and had a problem in practical use.

Since the heat-shrinkable polyester film having excellent heat-sealing properties of the present invention has excellent properties as described above, it can be suitably used for band label applications such as lunch boxes and noodle containers.

Claims (7)

A heat-shrinkable polyester-based film, which is a heat-shrinkable polyester-based film and is characterized by satisfying the following requirements (1) to (4) and has excellent heat-sealing properties.
(1) The difference in refractive index between the longitudinal direction and the width direction of the film is 0.04 or more and 0.12 or less. (2) The shrinkage rate in the longitudinal direction after being immersed in warm water at 90 ° C. for 10 seconds is 40% or more and 80%. (3) The maximum shrinkage stress in the longitudinal direction of the film measured with hot air at 90 ° C is 2 MPa or more and 5 MPa or less (4) Peeling after heat-sealing the ^{films at a temperature of 130 ° C and a pressure of 2 kg / cm 2.} The strength is 3.0N / 15mm or more and 20.0N / 15mm or less. The heat-shrinkable polyester-based film having excellent heat-sealing properties according to claim 1, wherein the film thickness is 6 μm or more and 30 μm or less. The heat-sealing property according to any one of claims 1 to 2, wherein the total glycol component of the polyester constituting the film contains 15 mol% or more and 40 mol% or less of the butanediol component. Heat shrinkable polyester film. The heat-shrinkable polyester-based film having excellent heat-sealing properties according to any one of claims 1 to 3, wherein the plane orientation coefficient is 0.03 or more and 0.08 or less. The heat-shrinkable polyester-based film having excellent heat-sealing properties according to any one of claims 1 to 4, wherein the film is a uniaxially stretched film. The heat-shrinkable polyester-based film having excellent heat-sealing properties according to any one of claims 1 to 5, which is used for band label packaging of plastic containers. Packaging body strip label heat-shrinkable polyester film according is adhered to the ring-shaped to claim 1 is coated.

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