JP6736976B2 - Polyester film and packaging bag using the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyester film having excellent suitability for fusing and sealing, and a packaging bag using the same.

BACKGROUND OF THE INVENTION Films are used as materials for bags for packaging various products such as foods, pharmaceuticals, and industrial products. The packaging bag is generally manufactured by fusing and sealing. Therefore, when selecting the packaging material, not only the mechanical strength and transparency but also the strength and appearance of the fusion-sealed portion are considered. A film made of a polyolefin-based resin has a high fusing seal strength and is therefore widely used as a packaging material. However, for example, a film made of a polypropylene resin as described in Patent Document 1 does not have sufficient deodorant property (fragrance retaining property). Therefore, when the content has strong odor, odorous components may pass through the film. It will leak.

On the other hand, a film made of a polyester-based resin as described in Patent Document 2 is difficult to adsorb organic compounds contained in chemical products, pharmaceuticals, foods, etc., and it is also difficult for odorous components to pass therethrough, so that it has an aroma retaining property. Are better.

Japanese Patent No. 4867857 International publication 2014/175313 pamphlet

However, since a film made of a polyester resin has a high heat shrinkage rate, there is a problem that when the fusing and sealing is performed, the film is shrunk due to heat from the fusing blade and the sealing portion is wavy. Further, if such a film is fused and sealed to form a bag, and then left in a high temperature environment such as in a car in midsummer (about 80° C.), the film shrinks and cannot retain its original shape. There is also.

Further, when the polyolefin film disclosed in Patent Document 1 or the polyester film disclosed in Patent Document 2 is fused and sealed to form a bag, there is a problem in that the fused seal strength varies depending on the site. In this way, when the contents are put in a bag having a large variation in the fusing seal strength, if the bag is dropped, the bag will be broken from a weaker portion. Under such circumstances, there has been a demand for a material that has high fragrance-retaining property for contents and high fusion-cut seal strength, and also has little variation in the fusion-cut seal strength and less waviness in the fusion-sealed portion.

The present invention has been made by paying attention to the circumstances as described above, and its object is to have an aroma retaining property for various organic compounds, a high fusing seal strength, and a small variation in the fusing seal strength. In addition, it is to provide a polyester film which has less waviness in the fused and sealed portion and less shrinkage even in a high temperature environment. Moreover, this invention also makes it a subject to provide the laminated body which contains the said polyester film as at least one layer, and the packaging bag using the same.

The present inventors have conducted extensive studies to solve the above-mentioned problems, and are composed of a polyester-based resin containing a specific amount of an amorphous component, and the thermal shrinkage and the maximum shrinkage stress in the film width direction are specified. The present invention has been completed based on the finding that the polyester film in the range of 1) has excellent fusing sealing performance and can maintain a beautiful appearance even after being used for fusing sealing and in a high temperature environment. The present invention has the following configurations.
1. A polyester film for a sealant, which is composed of a polyester resin containing ethylene terephthalate as a main constituent and which satisfies the following requirements (1) to (7).
(1) The total of one or more monomer components that can be amorphous components in all the monomer components is 12 mol% or more and 30 mol% or less (2) The average value of the seal strength when the film is melt-sealed in the width direction. Is 10 N/15 mm or more and 18 N/15 mm, and the standard deviation of seal strength is 0.3 or more and 2.5 or less (3) The maximum shrinkage stress in the film width direction when the temperature is raised from room temperature to 160° C. is 2 MPa or less. (4) Thermal contraction rate when immersed in hot water at 80°C for 10 seconds is 10% or more and 10% or less in both the longitudinal direction and the width direction. (5) Tensile fracture strength in the longitudinal direction and the width direction is 80 MPa or more and 300 MPa. (6) Folding retention angle is 20 degrees or more and 70 degrees or less (7) Haze is 0% or more and 10% or less. 2. The polyester film as described in 1 above, wherein the thickness unevenness in both the longitudinal direction and the width direction is 18% or less.
3. A laminate having at least one layer of the polyester film as described in 1 or 2 above.
4. A packaging bag comprising at least a part of the polyester film according to 1 or 2 or the laminate according to 3 above.

In the present specification, the film longitudinal direction means the film flow direction during production, and the width direction means the direction orthogonal to the film flow direction.
In a film formed by general sequential biaxial stretching, the molecular orientation in the width direction tends to be larger than that in the longitudinal direction. This is because the stretching in the longitudinal direction in the sequential biaxial stretching is due to the speed difference between the rolls, and the magnification is usually (preferably) 1.5 times or more and less than 4 times, whereas in the width direction, This is because the tenter can (preferably) stretch 3 times or more. Therefore, in the case of stretching in the width direction in which a stretching ratio higher than that in the longitudinal direction is often set, the stress applied to the film tends to be larger than that in the stretching in the longitudinal direction, and the refractive index tends to be larger. ..
Therefore, when the longitudinal direction and the width direction of the film cannot be immediately specified because the area of the film is small, it is assumed that the smaller refractive index by the refractive index measurement described later is the longitudinal direction and the larger one is the width direction. be able to. Not all polyester films are applicable to this tendency, but it is possible to assume the length and width directions of the film in the above-mentioned way of distinguishing.

The polyester film of the present invention is excellent in aroma retaining property, has a high fusing seal strength, and has excellent fusing seal performance with little variation in the fusing seal strength. Further, since the polyester film of the present invention has a low shrinkage property, the seal portion is less wavy even if it is melt-sealed, and the deformation is small even in a high temperature environment. Therefore, according to the polyester film of the present invention, it is possible to provide a packaging bag which is excellent in aroma retaining property, has a high fusing sealing strength, and has a beautiful appearance.

The polyester film of the present invention is composed of a polyester resin containing ethylene terephthalate as a main constituent and satisfies the following requirements (1) to (7);
(1) The total of one or more monomer components that can be amorphous components in all the monomer components is 12 mol% or more and 30 mol% or less (2) The average value of the seal strength when the film is melt-sealed in the width direction. Is 10 N/15 mm or more and 18 N/15 mm, and the standard deviation of seal strength is 0.3 or more and 2.5 or less (3) The maximum shrinkage stress in the film width direction when the temperature is raised from room temperature to 160° C. is 2 MPa or less. (4) Thermal contraction rate when immersed in hot water at 80°C for 10 seconds is 10% or more and 10% or less in both the longitudinal direction and the width direction. (5) Tensile fracture strength in the longitudinal direction and the width direction is 80 MPa or more and 300 MPa. (6) Folding retention angle is 20 degrees or more and 70 degrees or less (7) Haze is 0% or more and 10% or less.

The polyester film of the present invention satisfying the above-mentioned requirements is suitable for a packaging bag because it hardly adsorbs various organic compounds and has excellent fusing sealing property. Further, since the polyester film of the present invention has little shrinkage when the film is heated, its shape can be maintained even when left in a high temperature environment. Furthermore, since the polyester film of the present invention has high tensile strength, it has good processability.

In particular, the above-mentioned fusing sealability and low shrinkability, and the fusing sealability and tensile strength are antinomic properties, respectively, and there has been no polyester-based film capable of satisfying all of these properties at the same time. Hereinafter, the polyester film of the present invention will be described.

1. Constituent material of polyester film 1.1. Type of Polyester Raw Material The polyester resin used in the present invention has an ethylene terephthalate unit as a main constituent component.

Further, the polyester resin used in the present invention contains, as a component other than the ethylene terephthalate unit, one or more kinds of monomer components capable of becoming an amorphous component (hereinafter, may be simply referred to as an amorphous component). This is because the presence of the amorphous component improves the fusing seal strength of the film.
Examples of the carboxylic acid component monomer that can be an amorphous component include isophthalic acid, 1,4-cyclohexanedicarboxylic acid, and 2,6-naphthalenedicarboxylic acid.

Examples of the diol component monomer that can be an amorphous component include neopentyl glycol, 1,4-cyclohexanedimethanol, 2,2-diethyl-1,3-propanediol, and 2-n-butyl-2-ethyl-. Examples thereof include 1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol and hexanediol.

Among the above-mentioned amorphous components, isophthalic acid, neopentyl glycol, and 1,4-cyclohexanedimethanol are preferable, and by using at least one of them, the amorphous property of the film is enhanced and the fusing seal strength is 10N. /15 mm or more easily. As the amorphous component, it is more preferable to use neopentyl glycol and/or 1,4-cyclohexanedimethanol, and it is particularly preferable to use neopentyl glycol.

The polyester raw material may contain a component (other component) other than ethylene terephthalate and an amorphous component. Examples of the other dicarboxylic acid components constituting the polyester include aromatic dicarboxylic acids such as orthophthalic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, and alicyclic dicarboxylic acids. You can However, trivalent or higher polyvalent carboxylic acids (eg, trimellitic acid, pyromellitic acid and their anhydrides) are preferably not used as a polyester raw material.

Examples of other diol components constituting the polyester resin include long-chain diols such as diethylene glycol and 1,4-butanediol, aliphatic diols such as hexanediol, and aromatic diols such as bisphenol A. it can. However, diols having 8 or more carbon atoms (eg, octane diol, etc.) or polyhydric alcohols having 3 or more valences (eg, trimethylolpropane, trimethylolethane, glycerin, diglycerin, etc.) are not used as a polyester raw material. It is preferable.

Furthermore, a polyester elastomer containing ε-caprolactone or tetramethylene glycol may be used as a component constituting the polyester resin. The polyester elastomer has the effect of lowering the melting point of the film, and thus can be preferably used.

1.2. Content of Each Component The polyester resin used in the present invention has an amorphous component amount of 12 mol% or more. It is preferably 13 mol% or more, more preferably 14 mol% or more. Moreover, the upper limit of the amount of the amorphous component is 30 mol %. It is preferably 29 mol% or less, more preferably 28 mol% or less. The amount of the amorphous component here means the total amount of the carboxylic acid or diol monomer components that can become the amorphous component. For one unit of ester component (one unit in which a carboxylic acid monomer and a diol monomer are connected by an ester bond), if either one of the acid component or the diol component can be an amorphous component, the ester unit is amorphous. This is because it can be considered that there is.

If the amount of the amorphous component is less than 12 mol%, even if the molten resin is extruded from the die and then rapidly solidified, the film is crystallized in the subsequent stretching and final heat treatment steps, which makes it difficult to melt the film during fusion cutting. It becomes difficult to set the fusing seal strength to 10 N/15 mm or more.

When the total amount of the amorphous components is more than 30 mol %, the film can be easily fused and sealed, but the shrinkage ratio of the film exceeds 10% even if the final heat treatment temperature described later is increased. Further, if the total amount of the amorphous components is more than 30 mol %, the thickness accuracy of the film is extremely deteriorated, which causes problems such as uneven thickness and slack in the roll wound as a product, resulting in poor processability. Will end up. When the amount of the amorphous component is within the above range, good fusing seal strength and heat shrinkability can be secured.

The ethylene terephthalate unit contained in the polyester resin used in the present invention is preferably 50 mol% or more and 85 mol% or less in 100 mol% of the polyester resin constituting unit. It is more preferably 55 mol% or more and 80 mol% or less. When the ethylene terephthalate unit content is less than 50 mol %, the mechanical strength and heat resistance of the film may be insufficient. On the other hand, when the ethylene terephthalate unit is more than 85 mol %, the amount of the amorphous component becomes relatively small, which makes it difficult to perform an appropriate fusing seal.

1.3. Other components Among the resins constituting the polyester film of the present invention, various additives such as waxes, antioxidants, antistatic agents, crystal nucleating agents, viscosity reducing agents, and heat stabilizers are added as necessary. Agents, coloring pigments, anti-coloring agents, ultraviolet absorbers and the like can be added. Further, fine particles may be added as a lubricant for improving the slip property of the film. Any fine particles can be used. For example, examples of the inorganic fine particles include silica, alumina, titanium dioxide, calcium carbonate, kaolin, barium sulfate, and the like, and organic fine particles include acrylic resin particles, melamine resin particles, silicone resin particles, crosslinked polystyrene. Examples thereof include particles. The average particle size of the fine particles is within a range of 0.05 μm to 3.0 μm (when measured by a Coulter counter) and can be appropriately selected as necessary.

The method of blending the fine particles with the resin constituting the polyester film is not particularly limited, and examples thereof include a method of adding the fine particles at an arbitrary stage of producing the polyester resin. As the step of adding the fine particles, for example, in the step of esterification, or after the completion of the transesterification reaction, and before the start of the polycondensation reaction, the fine particles are added as a slurry in which ethylene glycol or the like is dispersed to advance the polycondensation reaction. preferable. Further, using a kneading extruder with a vent, a method of blending a slurry of fine particles dispersed in ethylene glycol, water, or another solvent with a polyester resin raw material, or kneading dried fine particles with a polyester resin raw material A method of blending using an extruder is also included.

2. Properties of Polyester Film Next, the properties required for using the polyester film of the present invention as a sealant will be described.

2.1. Fusing Breaking Strength First, when the polyester films of the present invention are laminated and subjected to fusing sealing, the average value of the sealing strength is 10 N/15 mm or more and 18 N/15 mm. If the fusing seal strength is less than 10 N/15 mm, the fusing seal portion is easily peeled off when the contents are put in a packaging bag, and the bag is easily broken, so that it cannot be used. The fusing seal strength is preferably 11 N/15 mm or more, more preferably 12 N/15 mm or more. The larger the fusing seal strength, the more preferable, but the currently obtained upper limit is about 18 N/15 mm. The method of fusing and sealing will be described in Examples below.

2.2. Variation in fusing seal strength The standard deviation of the fusing seal strength when the polyester films of the present invention are laminated and fused and sealed is 0.3 or more and 2.5 or less. The method for obtaining the standard deviation of the fusing seal strength will be described in the examples below. When the standard deviation of the fusing seal strength is higher than 2.5, the fusing seal strength varies greatly. If the fusing seal strength varies widely, even if the average value of the fusing seal strength exceeds 10 N/15 mm for the entire bag, there are many locations where the fusing seal strength falls below 10 N/15 mm when viewed partially. Therefore, the bag is likely to be torn from the part, which makes it difficult to use as a packaging bag. The smaller the standard deviation of the fusing seal strength is, the less the variation of the fusing seal strength is, which is preferable, but 0.3 is the lower limit at the present technical level. The standard deviation of the fusing seal strength is preferably 2 or less, more preferably 1.5 or less, and further preferably 1 or less. Further, even if the lower limit of the standard deviation of the fusing seal strength is about 0.4 or about 0.5, it can be used as a packaging bag without any problem.

2.3. Maximum shrinkage stress in the width direction The polyester film of the present invention has a maximum shrinkage stress in the film width direction of 2 MPa or less when heated from room temperature to 160°C. At the time of fusing and sealing, the contraction force of the film due to the heat of the fusing blade and the drag force (friction between the film and the fusing blade) act on the contact part between the film and the fusing blade. .. Particularly, when the shrinkage force of the film in the direction parallel to the fusing seal direction is large, the corrugation phenomenon tends to occur at the fusing seal portion. In the process of processing a film that uses a fusing seal, a blade is often inserted along the width direction of the film from the viewpoint of productivity and the optimization of the processing process. It greatly affects the wavy phenomenon of the seal part. Therefore, if the maximum shrinkage stress in the width direction of the film is 2 MPa or less, the frictional force between the film and the fusing blade becomes predominant (shrinkage of the film is stopped by the fusing blade), and therefore heat shrinkage (waviness) of the fusing seal portion. Is unlikely to occur. On the other hand, if the maximum shrinkage stress in the width direction of the film is more than 2 MPa, the film shrinks against the frictional force with the fusing blade, causing waviness in the fusing part. The upper limit of the maximum shrinkage stress in the width direction of the film is preferably 1.5 MPa, more preferably the upper limit is 1 MPa.

2.4. Shrinkage rate The polyester-based film of the present invention has a hot water heat shrinkage rate of -10% or more and 10% or less in both the longitudinal direction and the width direction when immersed in hot water of 80°C for 10 seconds.
When the hot water heat shrinkage ratio exceeds 10% in both the longitudinal direction and the width direction, the shrinkage of the film in a high temperature environment becomes large, and it becomes difficult to maintain the original shape. In particular, when the hot water heat shrinkage ratio in the width direction is large, the variation in the fusing seal strength becomes large. When the film is melt-fused, the film is melted by the heat from the fusing blade and immediately cooled and solidified to form a resin lump (so-called seal ball). When the film has heat-shrinkability in the width direction, the film shrinks due to the heat from the fusing blade, which causes variations in the size of the seal balls formed after fusing, resulting in variations in the fusing seal strength. Will occur.

The hot water heat shrinkage rate in both the longitudinal direction and the width direction is preferably 9% or less, more preferably 8% or less, and further preferably 7% or less. On the other hand, when the hot water heat shrinkage rate is less than 0%, it means that the film stretches, and when the film stretches large, it becomes difficult to maintain the original shape of the film as in the case where the shrinkage rate is high. Tend. Therefore, the hot water shrinkage in the longitudinal direction and the width direction is preferably -9% or more, more preferably -8% or more, and further preferably -7% or more. The hot water heat shrinkage ratios in the longitudinal direction and the width direction do not have to be the same, and the hot water heat shrinkage ratios in the longitudinal direction and the width direction may be different as long as they are included in the range of the hot water heat shrinkage ratio.

2.5. Tensile breaking strength (tensile breaking strength)
The polyester film of the present invention has a tensile breaking strength in the longitudinal direction or the width direction of 80 MPa or more and 300 MPa or less. When the tensile strength at break is less than 80 MPa, the bag may be broken even when the bag is dropped with the contents put therein, even at a portion other than the fusing seal. In addition, if the tensile breaking strength is less than 80 MPa, the film may be broken by the tension applied to the film when it is unwound from the film roll and subjected to the fusion-sealing process. The tensile strength at break is preferably 90 MPa or more, more preferably 100 MPa or more. The higher the tensile fracture strength, the better the strength when formed into a bag and the elimination of breakage during bag making, which is preferable, but it is difficult for the film of the molecular design of the present invention to exceed 300 MPa, so the upper limit is 300 MPa. .. The tensile fracture strength may be within the above range in either the longitudinal direction or the width direction, but the tensile fracture strength is preferably within the above range in both the longitudinal direction and the width direction. The method for measuring the tensile fracture strength will be described in Examples.

2.6. Folding Retention Angle The polyester film of the present invention has a folding retention angle of 20 degrees or more and 70 degrees or less as measured by the method described below. When the folding holding angle is more than 70 degrees, the bottom of the bag is less likely to be folded and the bag is inflated. The upper limit of the preferable folding holding angle is 65 degrees, and the upper limit is more preferably 60 degrees. Further, the smaller the folding holding angle is, the more preferable it is, but the lower limit of the range that can be covered by the present invention is 20 degrees, and it can be said that the folding holding angle is 25 degrees or more in practical use.

2.7. Haze The polyester film of the present invention has a haze of 0% or more and 10% or less. If the haze exceeds 10%, the transparency of the film deteriorates, so that the visibility of the contents becomes poor when the bag is used. The upper limit of haze is more preferably 9% or less, and particularly preferably 8% or less. The lower the haze, the higher the transparency, which is preferable, but at the current state of the art, the lower limit is 1%, and even if it is 2% or more, it can be said to be practically sufficient.

2.8. Thickness unevenness in the longitudinal direction The polyester film of the present invention preferably has a thickness unevenness of 18% or less when the measurement length is 10 m in the longitudinal direction. If the thickness unevenness in the longitudinal direction exceeds 18%, printing defects are likely to occur when printing the film, which is not preferable. The thickness unevenness in the longitudinal direction is more preferably 16% or less, and particularly preferably 14% or less. Further, the smaller the thickness unevenness in the longitudinal direction is, the more preferable, but the lower limit is considered to be about 1% from the performance of the film forming apparatus.

2.9. Thickness unevenness in the width direction In the width direction, the thickness unevenness is preferably 18% or less when the measurement length is 1 m. If the thickness unevenness in the width direction exceeds 18%, printing defects may easily occur when printing the film. The thickness unevenness in the width direction is preferably 16% or less, more preferably 14% or less. The thickness unevenness in the width direction is preferably closer to 0%, but the lower limit is considered to be 1% from the viewpoint of the performance of the film forming apparatus and the ease of production.

2.10. Thickness The thickness of the polyester film of the present invention is not particularly limited, but is preferably 3 μm or more and 200 μm or less. If the thickness of the film is less than 3 μm, the strength may be insufficient and processing such as printing may be difficult. Further, the film thickness may be thicker than 200 μm, but since a large amount of heat is required for the fusing and sealing, the fusing and sealing property is deteriorated. In addition, if the thickness is more than 200 μm, the weight of the film used increases and the manufacturing cost increases, which is not preferable. The thickness of the film is more preferably 5 μm or more and 160 μm or less, and further preferably 7 μm or more and 120 μm or less.

3. Film-forming conditions for polyester film 3.1. Melt Extrusion The polyester film of the present invention is obtained by melt-extruding the polyester raw material described in “1. Constituent material of polyester film” by an extruder to form an unstretched film, which is subjected to a predetermined method shown below. Can be obtained by The film may be unstretched, and when stretched, any stretching method such as uniaxial stretching and biaxial stretching may be adopted, but from the viewpoint of film strength and productivity, the film obtained by biaxial stretching Is preferred. The polyester resin can be obtained by polycondensing by selecting the types and amounts of the dicarboxylic acid component and the diol component so that an appropriate amount of a monomer that can be an amorphous component is contained, as described above. The polyester resin in the form of chips obtained by polycondensation in advance may be used alone or in combination of two or more as a raw material for the film.

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

Then, an unstretched film can be obtained by rapidly cooling the film melted by extrusion. As a method of 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 solidifying it can be suitably adopted. The film is preferably stretched in at least one of the longitudinal (longitudinal) direction and the lateral (width) direction (uniaxially stretched film, biaxially stretched film). In the following, a transverse biaxial stretching method in which transverse stretching is first performed and then transverse stretching-longitudinal stretching is performed will be described. However, even in longitudinal stretching-horizontal stretching in which the order is reversed, the main orientation direction is It doesn't matter because it only changes. A simultaneous biaxial stretching method may also be used.

3.2. Transverse Stretching An unstretched film obtained by rapid cooling after melt extrusion is stretched in the transverse direction in a tenter (first tenter) while holding both ends of the film in the width direction by clips. The transverse stretching conditions are preferably 65° C. to 100° C. and a draw ratio of about 3 to 5 times. If the stretching temperature is lower than 65° C., the oriented crystallization of the film by the lateral stretching is promoted, which may cause breakage not only in the lateral stretching but also in the longitudinal stretching in the subsequent step. On the other hand, if the transverse stretching temperature is higher than 100°C, the thickness unevenness in the width direction may exceed 18%. Prior to transverse stretching, preheating is preferably performed, and preheating may be performed until the film surface temperature reaches 60°C to 100°C.

Further, if the transverse stretching ratio is lower than 3 times, not only the thickness unevenness in the width direction tends to exceed 18%, but also breakage may occur in the final heat treatment step described later. When the transverse stretching ratio is lower than 3 times, stretching propagation is difficult to reach the edge portion (during clipping) of the film, and there is a possibility that the unstretched portion (so-called stretching residue) is increased in the film edge portion. Since the molecules in the edge portion of the film where the stretching residual is generated are not oriented as compared with the central portion of the film and the elastic modulus is extremely low, the heat shrinkage stress in the width direction generated in the final heat treatment step is concentrated near the stretching residual portion. As a result, the thickness (resin volume) in the vicinity of the unstretched portion moves to the center side in the film width direction, and as a result, the thickness at the end portion in the film width direction sharply decreases and the strength becomes weak and the film breaks.

After transverse stretching, it is preferable to pass the film through an intermediate zone where no positive heating operation is performed. When there is a temperature difference between the transverse stretching zone of the first tenter and the intermediate heat treatment zone, the heat of the intermediate heat treatment zone (hot air itself or radiant heat) flows into the transverse stretching process, the temperature of the transverse stretching zone becomes unstable and the film quality is stable. It may not be done. Therefore, it is preferable that the film after the transverse stretching and before the intermediate heat treatment is passed through the intermediate zone for a predetermined time and then supplied to the intermediate heat treatment zone. In this intermediate zone, when a strip-shaped paper piece is hung in a state where the film is not passed, so that the paper piece hangs almost completely in the vertical direction, when the hot air from the lateral stretching zone or the intermediate heat treatment zone is cut off, A stable quality film can be obtained. A transit time of about 1 to 5 seconds is sufficient for passing through the intermediate zone. If it is shorter than 1 second, the length of the intermediate zone becomes insufficient and the hot air blocking effect becomes insufficient. Further, it is preferable that the transit time in the intermediate zone is long, but if it is too long, the equipment becomes large, so about 5 seconds is sufficient.

After passing through the intermediate zone, intermediate heat treatment before longitudinal stretching is performed. By this intermediate heat treatment, the shrinkage ratio in the width direction can be reduced. The temperature of the intermediate heat treatment is preferably the same as the temperature of the transverse stretching to +30°C. When the temperature of the intermediate heat treatment zone is lower than the transverse stretching temperature, the effect of reducing the shrinkage ratio in the transverse direction becomes difficult to be exhibited. On the other hand, if the transverse stretching temperature is higher than +30° C., the shrinkage ratio in the width direction becomes lower, but the film may be excessively crystallized, and it may be difficult to perform subsequent stretching in the longitudinal direction. The passing time through the intermediate heat treatment zone is preferably 2 seconds to 20 seconds. If it is shorter than 2 seconds, the length of the intermediate heat treatment zone is insufficient and it may be difficult to adjust the heat shrinkage ratio in the width direction. A longer passage time through the intermediate heat treatment zone is preferable, but about 20 seconds is sufficient. This gives a horizontally uniaxially stretched film.

At the time of the intermediate heat treatment, the relaxation treatment can be performed by reducing the distance between the clips of the first tenter by an arbitrary ratio. By the relaxation treatment, the molecules oriented in the lateral direction are relaxed without being crystallized, and the shrinkage ratio in the width direction can be reduced. The relaxation rate after transverse stretching can be arbitrarily set in the range of 0% (relaxation rate of 0% means no relaxation) to 20%. If the relaxation rate is higher than 20%, the orientation of the end portion (the edge portion of the film) is excessively relaxed, the elastic modulus is lowered, and as described above, the final heat treatment step may be broken.

3.3. Longitudinal stretching Subsequently, longitudinal stretching is performed. In the longitudinal stretching step, first, the lateral uniaxially stretched film is introduced into a longitudinal stretching machine in which a plurality of roll groups are continuously arranged. In longitudinal stretching, it is preferable to preheat by a preheating roll until the film temperature reaches 65°C to 110°C. When the film temperature is lower than 65° C., it tends to be difficult to stretch in the machine direction (that is, breakage easily occurs). On the other hand, when the temperature is higher than 110° C., the film is likely to stick to the roll, and there is a possibility that roll contamination may occur early in continuous production.

When the film temperature falls within the above range, longitudinal stretching is performed. The longitudinal stretching is performed by the difference in speed between the rolls. The stretching ratio is preferably 1.5 times to 5 times. At this time, not only the single-stage stretching in which the rolls used for stretching are low speed/high speed, but also the two-stage stretching in which low speed/medium speed/high speed is three, low speed/medium low speed/medium high speed/high speed 4 rolls are used. It is also possible to increase the number of three-stage stretching and the number of stretching stages.

By relaxing the film in the longitudinal direction after the longitudinal stretching (relaxing in the longitudinal direction), it is possible to reduce the shrinkage ratio in the longitudinal direction of the film caused by the longitudinal stretching. The relaxation rate in the longitudinal direction is preferably 0% or more and 70% or less (a relaxation rate of 0% indicates that relaxation is not performed). The upper limit of the relaxation rate in the longitudinal direction depends on the raw material used and the longitudinal stretching conditions, and the relaxation cannot be carried out beyond this. The upper limit of the relaxation rate in the longitudinal direction of the polyester film of the present invention is 70%. The relaxation in the longitudinal direction can be carried out by heating the film after longitudinal stretching to 65° C. to 100° C. and adjusting the roll speed difference. As the heating means, any of rolls, near infrared rays, far infrared rays, hot air heaters and the like can be used. Further, the relaxation in the longitudinal direction can be performed not only immediately after the longitudinal stretching but also by narrowing the clip interval in the longitudinal direction by the final heat treatment as described later. Conditions such as temperature and relaxation rate will be described later.

After relaxing in the longitudinal direction (longitudinal stretching when not relaxing), the film is preferably cooled once, and preferably cooled by a cooling roll having a surface temperature of 20°C to 40°C.

Next, the film after longitudinal stretching and cooling is introduced into the second tenter, and the final heat treatment and the relaxation treatment are simultaneously performed. It is a preferred embodiment to carry out the final heat treatment step after stretching the film, since the longitudinal and lateral shrinkage rates can be adjusted in the final heat treatment. Relaxation in the second tenter can be performed at any magnification in both the vertical and horizontal directions. The relaxation rate in both the vertical and horizontal directions is preferably 0% to 50%. The lower limit of the relaxation rate is 0%. If the relaxation rate is too high, there is a demerit that the production rate of the film and the product width are reduced. Therefore, the upper limit of the relaxation rate is preferably about 50%.

The heat treatment (relaxation) temperature is preferably 120°C to 160°C. When the heat treatment temperature is lower than 120°C, it becomes difficult to reduce the shrinkage rate of the film to 10% or less. On the other hand, the higher the heat treatment temperature is, the more the shrinkage rate of the film can be reduced, but the heat treatment temperature higher than 160° C. may cause breakage due to the decrease in the thickness of the film width direction end portion as described above. Further, if the final heat treatment temperature is higher than 160° C., the film may stick when it comes into contact with the tenter.
After the final heat treatment, a polyester film roll can be obtained by winding the film while cutting off both ends of the film.

The polyester film obtained as described above may be subjected to a surface treatment step of imparting various characteristics to the film surface before being wound on a film roll or after being once wound on a film roll. Examples of such surface treatment include corona treatment for improving the adhesiveness of the film surface, flame treatment, coating treatment for imparting antistatic performance, and the like. These treatments can improve the adhesiveness and antistatic property.

4. Laminate Using Polyester Film and Packaging Bag The polyester film of the present invention may be used alone, or may be laminated by laminating other materials. It is sufficient for the laminate to have at least one layer of the polyester film of the present invention, whereby the laminate has the above-mentioned properties such as the fusion-cut seal strength.

As the other layer constituting the laminate, for example, a non-stretched film containing polyethylene terephthalate as a constituent component, a non-stretched film containing another amorphous polyester as a constituent component, a uniaxially stretched or biaxially stretched film, a constituent component of nylon. Examples of the non-stretched film include a non-stretched film, a uniaxially stretched film or a biaxially stretched film, a non-stretched film containing polypropylene as a constituent component, a uniaxially stretched film or a biaxially stretched film, and the like, but are not limited thereto.

The position where the polyester film is present in the laminate is not particularly limited, but the polyester film of the present invention is preferably present in the outermost layer of the laminate. As a result, excellent fusing sealing performance can be exhibited.
The method for producing the laminate is not particularly limited, and a conventionally known method for producing a laminate such as a coating forming method, a co-extrusion method, a laminating method, and a heat sealing method can be used.

The polyester film and the laminate having the above characteristics can be suitably used as a packaging bag. All of the packaging bags may be composed of the polyester film or laminate according to the present invention, but it is sufficient that the above-mentioned polyester film or laminate is present in at least a part of the packaging bag. For example, by providing the above-mentioned polyester film on the fusing seal portion of the packaging bag, the packaging bag has excellent fusing sealability, and it is possible to prevent the occurrence of waviness at the fusing seal portion. When the packaging bag is made of the above polyester film or laminate, the packaging bag has excellent fusing sealing performance in addition to excellent fusing sealing performance, and further changes in shape even in a high temperature environment. It will be difficult.

The method for providing a polyester film or a laminate in a part of the packaging bag is not particularly limited, and a method similar to the method for producing a laminate such as a coating forming method, a laminating method, or a heat sealing method can be adopted. ..

The packaging bag is generally manufactured by fusing and sealing, but is not limited to this, and conventionally known such as heat sealing using a heat bar (heat jaw), adhesion using hot melt, and center sealing using a solvent. The manufacturing method of can also be used. Since the polyester film of the present invention has excellent fusing sealing performance, a packaging bag having a beautiful appearance can be obtained even if a bag is made by fusing sealing.

The packaging bag of the present invention can be suitably used as a packaging material for various articles such as foods, pharmaceuticals, and industrial products.

Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited to the following Examples, and may be appropriately modified within a range compatible with the gist of the preceding and the following. Of course, it is possible to carry out, and all of them are included in the technical scope of the present invention.
The evaluation method of the film is as follows. If the longitudinal direction and the width direction cannot be immediately specified because the area of the film is small, etc., it is possible to assume that the smaller refractive index is the longitudinal direction and the larger refractive index is the width direction by the refractive index measurement described later. ..

<Film evaluation method>
[Average and variation of fusing seal strength]
The film is folded in half so that the creases are along the flow direction of the film, and the film is set in a fusing and sealing machine (PP500 type side welder manufactured by Kyoei Printing Machinery Co., Ltd.). The film was fused and sealed under the condition of the number of shots of 140 bags/min to prepare a side seal bag. The size of the bag is 310 mm in a direction along the fusing seal line (width direction of the film roll)×220 mm in a direction orthogonal to the fusing seal line (flow direction of the film roll) (hereinafter, unless otherwise specified, fusing The direction along the seal line is called the "width direction", and the direction orthogonal to it is called the "flow direction."
A total of 40 samples (20 pieces on each side) with a size of 15 mm in the width direction and 100 mm in the flow direction are drawn from the fused and sealed portion (310 mm x 2 on each side = 620 mm on both sides) that was randomly drawn from the bag that was made. Sampled. According to JIS Z1707, the sample is opened 180 degrees and both ends are set in the universal tensile tester “DSS-100” (manufactured by Shimadzu Corporation) (distance between chucks: 50 mm), in the longitudinal direction (flow direction) of the sample. A tensile test was performed at a speed of 200 mm/min to measure the peel strength when the fused seal portion broke. The maximum value of the peel strength was recorded as the fusing seal strength as the strength per 15 mm (N/15 mm), and the average value of 40 samples was taken as the average value of the fusing seal strength.
Further, the standard deviation calculated using the following formula 1 was used as the variation in the fusing seal strength.
Standard deviation _{= [{(X 1 -X 0} ) 2 + (X 2 -X 0) 2 + ··· + (X n -X 0) 2} / n] 1/2 Equation 1
X _n : fusing seal strength of n-th sample X ₀ : average value of fusing seal strength n: number of samples (40)

[Maximum shrinkage stress in width direction]
A sample having a size of 25 mm in width direction×2 mm in flow direction was cut out from the film roll, and the maximum shrinkage stress was measured using a thermomechanical analyzer (TMA, manufactured by Seiko Instruments Inc.). The distance between chucks was 15 mm, and the sample was attached to the probe using a dedicated chuck. After setting the sample, the shrinkage stress was recorded when the temperature in the furnace was raised from room temperature to 160°C at 10°C/min, and the peak stress was taken as the maximum shrinkage stress in the width direction.

[Hot water heat shrinkage rate]
The film was cut into a square of 10 cm×10 cm, dipped in warm water of 80° C.±0.5° C. for 10 seconds under no load condition to shrink, and then dipped in water of 25° C.±0.5° C. for 10 seconds. , Taken out of the water. After that, the dimensions of the film in the width direction and the flow direction were measured, and the shrinkage ratio in each direction was calculated according to the following formula 2. In addition, the measurement was performed twice and the average value was calculated.
Shrinkage rate (%)={(length before shrinkage-length after shrinkage)/length before shrinkage}×100 Equation 2

[Refractive index]
According to JIS K0062, the Abbe refractometer NAR-1T (manufactured by Atago Co., Ltd.) was used to determine the refractive indices in the longitudinal direction and the width direction, respectively. A sodium D ray was used as a light source, a test piece having a refractive index of 1.74 was used, and methylene iodide was used as an intermediate liquid.

[Folding retention angle]
The film piece was left for 24 hours in a thermostatic chamber at 28° C. and 50% RH environment. Immediately thereafter, each film was cut into a 10 cm×10 cm square in a 20° C. 65% RH environment and folded in four (5 cm×5 cm square). When folding the film, the short side of the first two-fold rectangle was oriented in the flow direction. Then, the four-folded film was sandwiched between two pieces of glass having a size of 10 cm×15 cm and a thickness of 2 mm, and a 5 kg weight was placed on the glass and pressed for 20 seconds. After removing the weight from the four-folded film and leaving it for 10 seconds, the angle at which the film was opened was measured with the last crease formed as a reference point. It should be noted that the state in which the film is completely folded is 0 degree, and the angle in which the film is completely opened is 180 degrees.

[Tensile breaking strength]
According to JIS K7113, a strip-shaped film sample having a measuring direction (film longitudinal direction, width direction) of 140 mm and a direction orthogonal to the measuring direction of 20 mm was produced. Using a universal tensile tester "DSS-100" (manufactured by Shimadzu Corp.), hold both ends of the test piece with chucks by 20 mm on each side (distance between chucks: 100 mm), conditions of atmospheric temperature 23°C, pulling speed 200 mm/min The tensile test was carried out at, and the strength (stress) at the time of tensile fracture was defined as the tensile fracture strength (MPa). The measurement was performed twice and the average value was calculated.

[Haze]
It was measured using a haze meter (300D, manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K7136. In addition, the measurement was performed twice and the average value was calculated.

[Thickness variation in the longitudinal direction]
The film was sampled into a long roll of 11 m in the longitudinal direction and 40 mm in the width direction, and continuously sampled along the longitudinal direction of the film at a measuring speed of 5 m/min using a continuous contact type thickness meter manufactured by Micron Measuring Instruments Co., Ltd. The thickness was measured (measurement length was 10 m). At the time of measurement, the maximum thickness was Tmax., the minimum thickness was Tmin., and the average thickness was Tave.
Thickness unevenness (%)={(Tmax.-Tmin.)/Tave.}×100 Formula 3

[Width unevenness]
A wide strip-shaped sample having a length of 40 mm in the longitudinal direction and a width of 1.2 m in the width direction is sampled from the film roll, and a continuous contact type thickness meter manufactured by Micron Measuring Instruments Co., Ltd. is used at a measuring speed of 5 m/min. The thickness was continuously measured along the width direction of the film sample (measurement length was 1 m). At the time of measurement, the maximum thickness was Tmax., the minimum thickness was Tmin., and the average thickness was Tave.

[Aroma retention]
Two films cut into a 10 cm×10 cm square were overlapped, and three sides were heat-sealed at 160° C. to produce a three-sided sealed bag having only one side open. 20 g of limonene (manufactured by Nacalai Tesque, Inc.) and menthol (manufactured by Nacalai Tesque, Inc.) were placed in the bag, and the open side was also heat-sealed to seal the bag. The menthol used was dissolved in ethanol and adjusted to a concentration of 1 g/mL. This bag was put in a glass container having a capacity of 1000 mL and the lid was closed. One week later, people (age 4 in their 20s, 4 in their 30s, 4 in their 40s, 4 in their 50s, a total of 16; the ratio of males and females was 50 and 50 in each age) were covered by the glass container. Was opened so that the air in the container could be smelled, the air in the glass container was sniffed, and the judgment was made as follows.
Judgment ○ The number of people who smelled 0 to 1 judgment △ The number of people who smelled 2-3 people Judgment × The number of people who felt smell 4 to 16 people

[Adsorption]
The film was cut into a 10 cm×10 cm square, and the weight of the film was measured. Next, the film is immersed in a container containing 500 mL of a solution prepared by adding limonene (manufactured by Nacalai Tesque Co., Ltd.) and menthol (manufactured by Nacalai Tesque Co., Ltd.) to a concentration of 30% each for 1 week. I took it out later.
The film taken out was pressed with a long-fiber non-woven fabric made of cellulose (“Bencot (registered trademark)” of Asahi Kasei Fibers Corporation) to wipe off the solution, and dried in a room at a temperature of 23° C. and a humidity of 60% RH for 1 day. After drying, the weight of the film was measured, and the difference in the film weight obtained from the following equation 4 was used as the adsorption amount.
Adsorption amount (mg) = film weight after immersion-film weight before immersion Equation 4
The amount of adsorption was determined as follows.
Judgment ○ 0 mg or more, 5 mg or less Judgment △ Higher than 5 mg, 10 mg or less Judgment × Higher than 10 mg

[Rippling of fusing seal part]
Fold the film in half so that the folds are in the flow direction of the film roll, and set it in the fusing and sealing machine (PP500 type side welder made by Kyoei Printing Machinery Co., Ltd.), fusing blade angle 90 degrees, blade edge setting temperature 410°C. The film was fused and sealed under the condition of the number of shots of 140 bags/min to prepare a side seal bag of 310 mm in width direction×220 mm in flow direction.
One piece was randomly drawn from the prepared bag and the corrugation of the fusing part was evaluated. The length of the sealed portion after fusing was measured and applied to the following formula 5, and the ratio of shrinkage of the film in the width direction due to fusing was determined. In Formula 5, the length (width direction) of the film before fusing is 310 mm.
Shrinkage (%)={(length before fusing-length after fusing)/length before fusing}×100 Equation 5
This shrinkage rate was evaluated as follows as the corrugation of the fusion-cut seal portion.
Judgment ○ The rate of contraction due to fusing is less than 1% Judgment △ The rate of contraction due to fusing is 1% or more and 2% or less Judgment × The rate of contraction due to fusing is more than 2%

[Appearance after leaving in high temperature environment]
An adhesive for dry lamination (Mitsui Chemicals, Inc.) was prepared by cutting a film cut into a 10 cm×10 cm square and another biaxially stretched polyester film (E5100, 12 μm manufactured by Toyobo Co., Ltd.) that was also cut into a 10 cm×10 cm square. Manufactured by Takelac (registered trademark), A-950). The adhesive was applied to the entire surface of the film. This laminated body was placed in a thermo-hygrostat (IG400 manufactured by Yamato Scientific Co., Ltd.) in which the temperature was set to 80° C. and the humidity was set to 65% RH, and left for 24 hours. After 24 hours, the laminate was taken out, and the shrinkage rate obtained from the above equation 2 was calculated. The measurement was performed twice and the average value was calculated. When the shrinkage rate differs depending on the direction of the film, the shrinkage rate in the more shrinked direction was adopted.
The shrinkage rate was evaluated as follows as the appearance after being left in a high temperature environment.
Judgment ○ Shrinkage from original shape is less than 2% Judgment △ Shrinkage from original shape is 2% to 5% Judge × Shrinkage from original shape is more than 5%

[Drop bag evaluation]
Fold the film in half so that the creases are in the flow direction of the film, and set it on the fusing and sealing machine (Kyoei Printing Machinery Co., Ltd., PP500 type side welder), fusing blade angle 90 degrees, blade edge setting temperature 410°C. The side seal bag having a width direction of 310 mm and a flow direction of 220 mm was manufactured by fusing and sealing under the condition of the number of shots of 140 bags/min.

Five pieces were randomly drawn from the prepared bags and evaluated for drop bags. Five Kim towels (registered trademark, made by Nippon Paper Crecia, size 380 mm x 330 mm) that have been made to absorb water by adjusting the weight to 300 g are rolled into a bag, and the mouth of the bag is turned five times to twist and drop a sample for bag evaluation. Was produced. The bottom surface (opposite opening side) of this sample was dropped 5 times from a position of 80 cm in height toward the floor, and the number of times until the bag was broken was determined as a drop bag score as shown below. The drop bag score was calculated as the sum after 5 trials (maximum 4 points×5 times=maximum 20 points).
1st time broke bag 0 points 2nd time broke bag 1 point 3rd time broke bag 2 points 4th time broke bag 3 points 5th time broke bag 4 points Dropping bag score of 10 or above was passed (○), 9 points The following was regarded as a failure (x).

<Preparation of polyester raw material>
[Synthesis Example 1]
In a stainless steel autoclave equipped with a stirrer, a thermometer and a partial reflux condenser, dimethyl terephthalate (DMT) 100 mol% as a dicarboxylic acid component, and ethylene glycol (EG) 100 mol% as a polyhydric alcohol component, Ethylene glycol was added in a molar ratio of 2.2 times that of dimethyl terephthalate, and 0.05 mol% of zinc acetate (based on the acid component) was used as a transesterification catalyst to distill off the produced methanol out of the system. While carrying out the transesterification reaction. Then, 0.225 mol% of antimony trioxide (based on the acid component) was added as a polycondensation catalyst, and the polycondensation reaction was carried out under a reduced pressure condition of 26.7 Pa at 280° C. to obtain an intrinsic viscosity of 0.75 dl/g. Polyester (A) was obtained. This polyester (A) is polyethylene terephthalate.

[Synthesis example 2]
Polyesters (B) to (E) in which the monomers were changed were obtained in the same procedure as in Synthesis Example 1. The composition of each polyester is shown in Table 1. In Table 1, TPA is terephthalic acid, BD is 1,4-butanediol, NPG is neopentyl glycol, CHDM is 1,4-cyclohexanedimethanol, and DEG is diethylene glycol. During the production of the polyester (E), SiO ₂ (Silysia 266 manufactured by Fuji Silysia Chemical Ltd.) was added as a lubricant at a ratio of 7,000 ppm to the polyester. Each polyester was chipped appropriately. The intrinsic viscosity of each polyester was B: 0.73 dl/g, C: 0.73 dl/g, D: 0.80 dl/g, E: 0.75 dl/g, respectively.

[Example 1]
Polyester A, polyester B, polyester D, and polyester E were mixed in a mass ratio of 25:60:10:5, charged into a twin-screw extruder, melt-mixed at 270° C., and extruded from a T-die, then surface temperature An unstretched film was obtained by cooling on a chill roll set at 30°C.

The unstretched film was led to a tenter (first tenter) in which a transverse stretching zone, an intermediate zone and an intermediate heat treatment zone were continuously provided. In the intermediate zone, when a strip-shaped paper piece is hung in a state where the film is not passed, so that the paper piece hangs almost completely in the vertical direction, hot air from the lateral stretching zone and the intermediate heat treatment zone Hot air is shut off.
The unstretched film led to the first tenter was horizontally stretched in the transverse stretching zone at 82° C. under a condition of 3.8 times, and passed through the intermediate zone (passing time=about 1.2 seconds), and then to the intermediate heat treatment zone. A transversely uniaxially stretched film was obtained by conducting the heat treatment at a temperature of 97° C. for 8 seconds and reducing the clip width of the first tenter to perform 6% relaxation.

The transversely stretched film is guided to a longitudinal stretching machine in which rolls including low speed and high speed rolls are continuously arranged, preheated on a preheating roll until the film temperature reaches 90°C, and then stretched on low speed and high speed rolls. It was stretched so that the magnification was 2.8 times. Then, the longitudinally stretched film was forcibly cooled by a cooling roll set to a surface temperature of 25°C.

Then, after the cooled film is guided to a tenter (second tenter) and heat-treated in the second tenter for 10 seconds under an atmosphere of 140° C., the film is relaxed in the lateral direction (film width direction) by 17%. By cooling and cutting off both edges in the width direction, a polyester film having a thickness of about 13 μm was obtained.
The production conditions and characteristics of the obtained film are shown in Tables 2 and 3.

[Examples 2 to 9]
A polyester film was prepared by variously changing the mixing ratio of raw materials, resin extrusion conditions, transverse stretching, intermediate heat treatment, longitudinal stretching, and final heat treatment conditions, and evaluated. The passing time of the intermediate zone in Examples 2 to 9 was set to about 1.2 seconds. The film manufacturing conditions and characteristics of each example are shown in Tables 2 and 3.

[Comparative Example 1]
Polyester raw materials having the same compounding ratio as in Example 1 are mixed, charged into a twin-screw extruder, melt-mixed at 270° C. and extruded from a T die, and then cooled on a chill roll whose surface temperature is set to 30° C. Thus, an unstretched film was obtained.
By cutting and removing both widthwise edges of the obtained unstretched film, a polyester film having a thickness of about 20 μm was obtained.
The production conditions and characteristics of the obtained film are shown in Tables 2 and 3.

[Comparative Example 2]
A raw material containing 100% of polyester C is charged into a twin-screw extruder, melted at 270° C. and extruded from a T die, and then cooled on a chill roll whose surface temperature is set to 30° C. to form an unstretched film. Obtained.

This unstretched film was led to a tenter (first tenter) in which a transverse stretching zone, an intermediate zone and an intermediate heat treatment zone were continuously provided. In the intermediate zone, when a strip-shaped paper piece is hung in a state where the film is not passed, so that the paper piece hangs almost completely in the vertical direction, hot air from the lateral stretching zone and the intermediate heat treatment zone Hot air is shut off.
Then, the unstretched film led to the tenter was laterally stretched in the lateral stretching zone under conditions of 82° C. and 3.8 times, and allowed to pass through the intermediate zone (passing time=about 1.2 seconds), and then to the intermediate heat treatment zone. It was guided and heat-treated at a temperature of 83° C. for 8 seconds to obtain a laterally uniaxially stretched film. In the intermediate heat treatment, relaxation in the width direction was not performed.

Both edges of the obtained laterally uniaxially stretched film were cut and removed to obtain a polyester film having a thickness of about 13 μm.
The production conditions and characteristics of the obtained film are shown in Tables 2 and 3.

[Comparative Example 3]
Polyester A and polyester E were mixed at a mass ratio of 95:5, charged into a twin-screw extruder, melt-mixed at 270° C., extruded from a T die, and then cooled on a chill roll set to a surface temperature of 30° C. By doing so, an unstretched film was obtained.

This unstretched film was led to a tenter (first tenter) in which a transverse stretching zone, an intermediate zone and an intermediate heat treatment zone were continuously provided. In the intermediate zone, when a strip-shaped paper piece is hung in a state where the film is not passed, so that the paper piece hangs almost completely in the vertical direction, hot air from the lateral stretching zone and the intermediate heat treatment zone Hot air is shut off.
Then, the unstretched film led to the first tenter was laterally stretched in the transverse stretching zone at 90° C. under a condition of 3.8 times, and passed through the intermediate zone (passing time=about 1.2 seconds), then the intermediate heat treatment. It was introduced into the zone and heat-treated at a temperature of 97° C. for 8 seconds to obtain a laterally uniaxially stretched film. In the intermediate heat treatment, relaxation in the width direction was not performed.

Further, the transversely stretched film is guided to a longitudinal stretching machine in which rolls including low-speed rolls and high-speed rolls are continuously arranged, and preheated on a preheating roll until the film temperature reaches 100° C. The above drawing was performed so that the draw ratio was 2.8 times. Then, the longitudinally stretched film was forcibly cooled by a cooling roll set to a surface temperature of 25°C.

Then, the cooled film is guided to a tenter (second tenter), and heat-treated (relative rate in the film width direction is 0%) for 10 seconds in an atmosphere of 230° C. in the second tenter and then cooled, By cutting off both edges, a polyester film having a thickness of about 13 μm was obtained.
The production conditions and characteristics of the obtained film are shown in Tables 2 and 3.

[Comparative Example 4]
Evaluation was performed according to the method described above using a commercially available biaxially oriented polypropylene film having a thickness of 20 μm. The evaluation results are shown in Table 3.

As shown in Table 3, the films of Examples 1 to 9 were all excellent in aroma retention, mechanical properties, fusing sealing performance, and the like.
On the other hand, the film of Comparative Example 1 had a low tensile breaking strength and a dropping bag score of 6 points. From these results, it can be seen that the bag formed from the film of Comparative Example 1 is apt to break when dropped and is not preferable as a packaging bag.
The film of Comparative Example 2 had a high hot water shrinkage in the width direction, and the corrugation of the fusing and sealing portion was large. As a result, the variation in the fusing seal strength becomes large, and the suitability as a packaging bag is lacking. Further, due to the fact that the bag was not firmly sealed due to the corrugation of the fusing and sealing portion, the result was that the aroma retaining property was inferior to that of Examples 1 to 9. Further, the shape after being left in a high temperature environment is largely changed from the original shape, which is not preferable as a packaging bag.
Since the film of Comparative Example 3 could not be processed into a bag by fusing seal, the fusing seal strength could not be measured. The film of Comparative Example 3 could not be used as a bag.
The film of Comparative Example 4 had a high folding holding angle of 180 degrees, and the film opened even after being folded. Therefore, when the bag was made, the bottom crease was not cleanly formed, and the appearance was inferior to the bags using the films of Examples 1 to 9. The bag using the film of Comparative Example 4 was inferior in aroma retention.

Claims (4)

A polyester film for a sealant, which is composed of a polyester resin containing ethylene terephthalate as a main constituent and which satisfies the following requirements (1) to (7).
(1) The total of one or more monomer components that can be amorphous components in all the monomer components is 12 mol% or more and 30 mol% or less (2) The average value of the seal strength when the film is melt-sealed in the width direction. Is 10 N/15 mm or more and 18 N/15 mm or less , and the standard deviation of seal strength is 0.3 or more and 2.5 or less (3) The maximum shrinkage stress in the film width direction when the temperature is raised from room temperature to 160° C. is 2 MPa. (4) The thermal shrinkage when immersed in hot water at 80°C for 10 seconds is -10% or more and 10% or less in both the longitudinal direction and the width direction. (5) Tensile fracture strength in either the longitudinal direction or the width direction is 80 MPa or more. 300 MPa or less (6) Folding retention angle is 20 degrees or more and 70 degrees or less (7) Haze is 0% or more and 10% or less The polyester film according to claim 1, wherein the thickness unevenness in both the longitudinal direction and the width direction is 18% or less. A laminate comprising at least one layer of the polyester film according to claim 1 or 2. A packaging bag comprising at least a part of the polyester film according to claim 1 or 2 or the laminate according to claim 3.