Polyester-based sealant film and package using same

Abstract

The present disclosure addresses the problem of providing a polyester-based sealant film not only having sufficient fusion-cut seal strength and heat seal strength, but also preventing the occurrence of poor appearance during fusion-cut sealing while having excellent aroma retention.　A polyester-based sealant film according to the present disclosure is composed of a polyester-based resin having ethylene terephthalate as a main constituent component, and includes at least a heat seal layer A and a heat-resistant layer B, wherein the heat seal layer A is laminated on one side or both sides of the heat-resistant layer B, and the following requirements (1) to (3) are satisfied. (1) The fusion-cut seal strength is 5.0-18 N / 15 mm when the heat seal layers A are joined together and fusion-cut and sealed in the width direction of the film. (2) When the heat seal layers A are heat-sealed at 160°C and 0.2 MPa for 2 seconds, the heat seal strength is 5-15 N / 15 mm. (3) The thermal shrinkage at 120°C of the film is 0.01-10.0% in the longitudinal direction and the width direction.

Description

Polyester-based sealant film and packaging using the same

[0001] This disclosure relates to a polyester-based sealant film with excellent suitability for heat sealing and cutting, and to a packaging bag using the same.

[0002] Film is used as the material for bags that package a variety of items, including food, pharmaceuticals, daily necessities, and industrial products. Packaging bags can be manufactured by heat sealing (also called side sealing) or by heat sealing. Therefore, when selecting packaging materials, it is desirable that the material can be processed by heat sealing or heat sealing, or even both, and the strength and appearance of the sealed portion should be considered as characteristics of the film. For example, for bags that are heat-sealed, films made of polyolefin resins with relatively low melting points are widely used due to their versatility and the aforementioned characteristics. For example, Patent Document 1 proposes a polypropylene film that can be used for both heat sealing and heat sealing. Patent Document 2 also describes a heat-sealable film made of polyethylene. However, the films in Patent Documents 1 and 2 do not have sufficient deodorizing or fragrance-retaining properties, so if the contents have a strong odor, the odor components may pass through the film and leak out, or the active ingredients of the contents may dissolve into the film that makes up the bag or even pass through the film, resulting in a reduction in the amount of active ingredients. Furthermore, the polyolefin film described in Patent Document 1 does not have sufficient heat seal strength and requires further improvement.

[0003] On the other hand, packaging bags using films made of polylactic acid resin described in Patent Documents 3 and 4 have excellent fragrance retention properties because they do not easily adsorb organic compounds contained in chemical products, pharmaceuticals, foods, fragrances, etc., and do not easily allow odor components to pass through. Recently, with the growing concern for environmental issues, bio-based plastics have attracted attention, and biodegradable polylactic acid resin is favored as a sustainable material with little environmental impact. However, in processing at higher temperatures to improve the efficiency of bag manufacturing, there is an upper limit to the processing temperature, and it is thought that the appearance may not be satisfactory when melted and cut at high temperatures.

[0004] For these reasons, polyester resins are widely used as sealant films due to their excellent fragrance retention and deodorizing properties, as well as their high melting point. For example, as described in Patent Document 5, a film made of polyester resin is a blend of crystalline polyester resin and amorphous polyester resin, and sufficient heat sealing strength is obtained. However, in bag making processes at higher temperatures to improve production efficiency, the thermal shrinkage rate increases, causing shrinkage due to heat from the cutting blade during heat sealing, resulting in the problem of the sealed portion becoming wavy. On the other hand, a configuration in which a heat-seal layer, which is a blend of crystalline polyester resin and amorphous polyester resin, and a heat-resistant layer are laminated (Patent Document 6) is suitable for heat sealing. However, there was no mention of heat sealing and heat sealing strength.

[0005] Japanese Patent Publication No. 4867857, Japanese Unexamined Patent Publication No. 2007-262280, Japanese Patent Publication No. 5343484, Japanese Unexamined Patent Publication No. 2007-136770, Japanese Patent Publication No. 6736976, Japanese Patent Publication No. 6384324

[0006] This disclosure aims to resolve the problems of the prior art described above. Specifically, the objective of this disclosure is to provide a polyester-based sealant film that not only has sufficient heat-seal and thermal sealing strength, but also suppresses appearance defects during heat sealing and has excellent aroma retention. Furthermore, this disclosure also aims to provide a packaging body using the above-mentioned polyester-based sealant film.

[0007] This disclosure comprises the following components: 1. A polyester sealant film characterized by being composed of a polyester resin mainly composed of ethylene terephthalate, comprising at least a heat seal layer A and a heat-resistant layer B, wherein the heat seal layer A is laminated on one or both sides of the heat-resistant layer B, and satisfying the following requirements (1) to (3): (1) When the heat seal layers are joined together and heat-sealed in the width direction of the film, the heat seal strength is 5.0 N / 15 mm or more and 18 N / 15 mm or less. (2) When the heat seal layers are heat-sealed at 160°C at 0.2 MPa for 2 seconds, the heat seal strength is 5 N / 15 mm or more and 15 N / 15 mm or less. (3) The thermal shrinkage rate at 120°C in the longitudinal and width directions of the film is 0.01% or more and 10.0% or less. 2. The polyester sealant film according to 1. above, wherein the amount of ethylene terephthalate constituting the heat-resistant layer B is greater than the amount of ethylene terephthalate constituting the heat seal layer A. 3. 1. or 2. above, wherein the amount of components other than ethylene terephthalate constituting the heat seal layer A is 10 mol% or more and 45 mol% or less of the components constituting the heat seal layer A. 4. A polyester sealant film according to any one of 1. to 3. above, wherein the amount of components other than ethylene terephthalate constituting the heat-resistant layer B is 7 mol% or more and 20 mol% or less of the components constituting the heat-resistant layer B. 5. A polyester sealant film according to any one of 1. to 4. above, wherein the difference between the amount of components other than ethylene terephthalate constituting the heat seal layer A and the amount of components other than ethylene terephthalate constituting the heat-resistant layer B is 19.0 mol% or more and 28.0 mol% or less. 6. A polyester sealant film according to any one of the above 1 to 5, wherein, as a component other than ethylene terephthalate constituting the heat seal layer A and the heat-resistant layer B, the diol component comprises one or more selected from the group consisting of neopentyl glycol, 1,4-cyclohexanedimethanol, diethylene glycol, 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, 1,4-butanediol, and hexanediol.7. A polyester sealant film according to any one of 1 to 6 above, wherein the diol component constituting the heat seal layer A comprises 54 to 66 mol% ethylene glycol, 0 to 21 mol% neopentyl glycol, 10 to 25 mol% 1,4-butanediol, 0 to 6 mol% diethylene glycol, and 0 to 8 mol% 1,4-cyclohexanedimethanol, per 100 mol% of the diol component. 8. A polyester sealant film according to any one of 1 to 7 above, wherein the diol component constituting the heat-resistant layer B comprises 70 to 87 mol% ethylene glycol, 0 to 12 mol% neopentyl glycol, 5 to 13 mol% 1,4-butanediol, 0 to 4 mol% diethylene glycol, and 0 to 5 mol% 1,4-cyclohexanedimethanol, per 100 mol% of the diol component. 9. A polyester sealant film according to any one of 1 to 8, wherein one or both of the heat seal layer A and the heat-resistant layer B further contain fine particles, and the amount of fine particles is 100 to 2000 ppm relative to the entire heat seal layer A or the entire heat-resistant layer B. 10. A polyester sealant film according to any one of 1 to 9, wherein the film is biaxially oriented. 11. A polyester sealant film according to any one of 1 to 10, wherein the total thickness of the film is 5 μm or more and 19 μm or less. 12. The crystalline heat of fusion ΔHm of the polyester film is 30 mJ / cm. 2 The polyester sealant film according to any one of the following 1. to 11.: 13. The polyester sealant film according to any one of the following 1. to 12., wherein the degree of surface orientation ΔP of the surface of the heat seal layer A is 0.010 or more and 0.065 or less. 14. The polyester sealant film according to any one of the following 1. to 13., wherein the folding holding angle is 20 degrees or more and 70 degrees or less. 15. A packaging body characterized in that at least a portion of the polyester sealant film according to any one of the following 1. to 14. is used.

[0008] The polyester-based sealant film of this disclosure exhibits excellent heat-seal strength and thermal sealing strength, suppresses appearance defects during thermal sealing, and provides excellent fragrance retention.

[0009] The polyester sealant film of this disclosure will be described below. The polyester sealant film of this disclosure is composed of a polyester resin mainly composed of ethylene terephthalate, and includes at least a heat seal layer A and a heat-resistant layer B, wherein the heat seal layer A is laminated on one or both sides of the heat-resistant layer B, and the heat seal strength, heat seal strength, and thermal shrinkage rate are within a predetermined range. In addition, the polyester sealant film of the present invention preferably satisfies a predetermined crystalline heat melt capacity, plane orientation degree ΔP, and folding holding angle, as will be described later. Note that the polyester sealant film may also be referred to as polyester film, sealant film, sealant, or film. The polyester sealant film of this disclosure may be a uniaxially oriented film or a biaxially oriented film, and is preferably a biaxially oriented film. Note that in this disclosure, the numerical notation "〇〇 or more and □□ or less" is synonymous with the notation "〇〇 to □□", and both have the same meaning.

[0010] 1. Film Characteristics 1.1. Heat-Seal Strength First, for the polyester sealant film of this disclosure, when heat-seal layers A are joined together and heat-sealed in the width direction of the film, the heat-seal strength (average value of heat-seal strength) is 5.0 N / 15 mm or more and 18 N / 15 mm or less, preferably 6 N / 15 mm or more and 17 N / 15 mm or less, more preferably 7 N / 15 mm or more and 16 N / 15 mm or less, and even more preferably 8 N / 15 mm or more and 15 N / 15 mm or less. If the heat-seal strength is less than 5.0 N / 15 mm, the heat-sealed portion will easily peel off, and the bag will be prone to tearing, making it unusable. A higher heat-seal strength is preferable, but the upper limit that can be obtained at present is about 18 N / 15 mm, and even 15 N / 15 mm is practically preferable. The method for measuring the heat-seal strength may be as described in the examples below.

[0011] 1.2. Heat Seal Strength In the polyester sealant film of this disclosure, when heat-seal layers A are heat-sealed at a temperature of 160°C, a seal bar pressure of 0.2 MPa, and a sealing time of 2 seconds, the heat seal strength is 5 N / 15 mm or more and 15 N / 15 mm or less, preferably 6 N / 15 mm or more and 15 N / 15 mm or less, more preferably 7 N / 15 mm or more and 15 N / 15 mm or less, and even more preferably 8 N / 15 mm or more and 15 N / 15 mm or less. If the heat seal strength is less than 5 N / 15 mm, the sealed portion will easily peel off and cannot be used as a packaging bag. A high heat seal strength is preferable, but the upper limit that can be obtained at present is about 15 N / 15 mm. The heat seal strength can be measured as described in the examples below.

[0012] 1.3. Heat Shrinkage Rate When the polyester sealant film of this disclosure is treated in a dry oven at 120°C for 5 minutes, the heat shrinkage rate at 120°C in both the width direction and the longitudinal direction of the film is 0.01% to 10.0%, preferably 0.01% to 9.0%, more preferably 0.01% to 8.0%, even more preferably 0.01% to 7.0%, even more preferably 0.01% to 6.0%, and particularly preferably 0.1% to 5.0%. If the shrinkage rate exceeds 10.0%, the shrinkage will be large when the film is heat-sealed or cut, and the flatness after sealing will deteriorate. On the other hand, a heat shrinkage rate close to 0% is ideal, but in reality, it is desirable to have a rate of around 0.01%. Also, if the heat shrinkage rate is below zero, it means that the film will stretch, and as with a high shrinkage rate, the film will have difficulty maintaining its original shape.

[0013] 1.4. Heat Capacity of Crystallization The polyester sealant film disclosed herein has a heat capacity of crystallization ΔHm of 30 mJ / cm² measured by DSC. 2 The following is preferable: 10 mJ / cm 2 30mJ / cm or more 2 More preferably, the following is true: 12 mJ / cm 2 30mJ / cm or more 2 It is even more preferable that the following conditions are met: 14 mJ / cm 228 mJ / cm or less is even more preferable. The heat of fusion capacity ΔHmmeasured by DSC serves as an indication of the crystalline amount in the film. When the heat of fusion capacity ΔHm of the crystal is less than 10 mJ / cm 2 the film contains a large amount of an amorphous component, resulting in insufficient mechanical strength and inferior film processability. In addition, the heat resistance is insufficient, and wrinkles may occur during bag making, leading to poor appearance. Furthermore, the periphery of the heat load part blocks during bag making (a phenomenon where sealing occurs in a wider range than intended due to heat conduction from the heating member), making appropriate heat sealing difficult. On the other hand, when the heat of fusion capacity ΔHm of the crystal exceeds 30 mJ / cm 2 the crystallinity becomes too high, and in particular, the heat of the melting blade during melt cutting seal is difficult to transfer to the seal interface, so it cannot be fully melted and the bag-making property is inferior. The heat of fusion capacity ΔHm of the crystal can be measured as described in the examples below, and is defined as the value obtained by multiplying the heat of fusion capacity of the crystal measured by DSC by the film density and the film thickness. The heat of fusion capacity ΔHm per 1 cm 2 (mJ / cm 2 ) = the heat of fusion capacity ΔHm´ (J / g) of the crystal measured by DSC × film density (g / cm 2 ) × film thickness (cm). 3) × film thickness (μm) The heat capacity for crystalline fusion ΔHm' is measured, for example, using a DSC (DSC220, manufactured by Seiko Electronics Industries, Ltd.). Weigh 10 mg of film sample into an aluminum pan, increase the temperature from 20°C to approximately 250°C at 10°C / min, and the area enclosed by the appearing endothermic peak and baseline (melting peak area) can be taken as the heat capacity for crystalline fusion ΔHm'. The density of the film is measured by the density gradient method of JIS K 7112 D method, using calcium nitrate tetrahydrate as the gradient solution, a temperature in the gradient tube of 30°C, a sample size of 5 mm × 5 mm, and an immersion time of 16 hours. The sample is taken from 10 mm from the left and right ends in the film width direction toward the center, and the highest measured value is adopted. The film thickness is measured in accordance with JIS K7130-1999 A method, using a dial gauge, with 10 arbitrary points as measurement positions and the average value used. Generally, the heat capacity for crystalline fusion ΔHm is expressed in units per unit weight, such as J / g or mJ / mg. However, this does not take into account the thickness of the film itself and is therefore not considered an appropriate indicator of the melting of the film itself due to changes in film thickness. A more appropriate indicator of the film itself is the heat capacity for crystalline fusion per unit area, i.e., mJ / cm². 2 It is considered necessary to express this in units such as [specific units].

[0014] 1.5. Degree of Planar Orientation ΔP The degree of planar orientation ΔP of the surface of the heat seal layer A of the polyester sealant film of this disclosure is preferably 0.010 or more and 0.065 or less, more preferably 0.011 or more and 0.064 or less, and even more preferably 0.012 or more and 0.063 or less. The degree of planar orientation ΔP is measured as described in the examples below. The degree of planar orientation ΔP is a value calculated from the refractive index nx in the longitudinal direction, the refractive index ny in the width direction, and the refractive index nz in the thickness direction measured by an Abbe refractometer in the heat seal layer A of the polyester sealant film using the following equation (2): Degree of planar orientation ΔP = (nx + ny) / 2 - nz ... (2)

[0015] If ΔP is less than 0.010, problems arise with insufficient heat seal strength and thermal sealing strength. The reason for this is explained below. First, ΔP indicates the degree of orientation of the polymer chains that constitute the heat seal layer of the sealant. The larger ΔP, the more regularly aligned the polymer main chains are. Therefore, if ΔP is less than 0.010, the orientation of the polymer becomes more random, which is thought to reduce the mechanical strength in the planar direction of the film, and thus the heat seal strength and thermal sealing strength. On the other hand, if the planar orientation degree ΔP is greater than 0.065, the molecular chains are extremely aligned, the shrinkage rate increases, and curling and warping of the bag product may occur, resulting in poor appearance. In addition, because the mobility of the molecular chains during sealing is suppressed, the interlocking and entanglement of the polymers on the heat seal surface becomes insufficient, which is thought to reduce the seal strength.

[0016] 1.6. Folding and Holding Angle In the polyester sealant film of this disclosure, the folding and holding angle measured by the method described later is preferably 20 degrees or more and 70 degrees or less, more preferably 25 degrees or more and 65 degrees or less, and even more preferably 30 degrees or more and 60 degrees or less. When a bag is made using a film with a folding and holding angle of 70 degrees or less, the folds are easily formed along the semi-folded plate, especially in the heat-sealing process, so when the bags are stacked, bulging inside the bag is suppressed and they can be stacked neatly. Furthermore, when the opening is twisted, the twist is retained and the bag can be sealed without tying the opening. If the folding and holding angle exceeds 70 degrees, it becomes difficult to form folds at the bottom of the bag and the bag bulges, so the edges do not align well when the bags are stacked. Also, the smaller the folding and holding angle, the better, but in this disclosure 20 degrees is the practical lower limit, and even if the folding and holding angle is 25 degrees or more, it can be said to be practically preferable.

[0017] 2. Layer structure and layer ratio of polyester sealant film The polyester sealant film of this disclosure includes at least a heat seal layer A and a heat-resistant layer B, and each of the heat seal layer A and the heat-resistant layer B must be at least one layer. The heat seal layer A and the heat-resistant layer B each preferably consist of 1 to 8 layers, more preferably 1 to 6 layers, even more preferably 1 to 4 layers, and even more preferably 1 to 3 layers. The heat seal layer A and the heat-resistant layer B may have the same number of layers or different numbers of layers, but it is preferable that they have the same number of layers. When heat sealing, considering that contact is made using a heated cutting blade, etc., the polyester sealant film of this disclosure preferably has a two-layer structure with one layer each of the heat seal layer A and the heat-resistant layer B in order to achieve both heat sealability and heat resistance. As shown in Patent Document 5, if the heat-resistant layer B is not laminated and the heat seal layer A alone is a single layer structure, the thermal shrinkage rate will be large and the heat resistance will be insufficient. Heat treatments that can reduce thermal shrinkage will be discussed later.

[0018] The constituent requirements for each layer will be described later, but both the heat seal layer A and the heat-resistant layer B are made of a polyester resin whose main component is ethylene terephthalate. The layer with the highest ethylene terephthalate content becomes the heat-resistant layer, and the layer with the lowest ethylene terephthalate content becomes the heat seal layer. Furthermore, the layer configuration of the sealant may include a third layer other than the heat seal layer A and the heat-resistant layer B, as long as it does not impair the properties of the polyester sealant film according to this disclosure, but the heat seal layer A must be located on at least one of the outermost layers. In other words, in the polyester sealant film according to this disclosure, it is preferable that the heat seal layer A is laminated on one or both sides of the heat-resistant layer B, and that the heat seal layer A is laminated on one side of the heat-resistant layer B.

[0019] Examples of layers different from the heat-seal layer A and the heat-resistant layer B include adhesive layers, barrier layers, and base layer layers (preferably layers made of resins other than polyethylene terephthalate). In the polyester sealant film according to this disclosure, it is preferable that the heat-seal layer A and the heat-resistant layer B are laminated without any other layer (preferably an adhesive layer) in between.

[0020] The ratio of the heat seal layer A to the total thickness of the polyester sealant film is preferably 20% to 80%, more preferably 25% to 75%, even more preferably 30% to 70%, and even more preferably 35% to 65%. If the ratio of the heat seal layer A is less than 20%, the heat seal strength will decrease. If the heat seal layer A is located on both sides of the film, the ratio should be that of the heat seal layer A on only one side. If the ratio of the heat seal layer A exceeds 80%, the heat seal strength will improve, but the heat resistance and mechanical strength will decrease.

[0021] Furthermore, the outermost layer (including the heat-seal layer A) of the polyester sealant film disclosed herein can be subjected to corona treatment, coating treatment, flame treatment, etc., in order to improve the printability, slipperiness, and antistatic properties of the film surface. It is also possible to provide additional layers having these functions, and these can be provided arbitrarily within the scope that does not deviate from the requirements of this disclosure.

[0022] There are no restrictions on the overall thickness of the polyester sealant film as long as its physical properties are not impaired, but the heat capacity of crystalline fusion per unit area must be 30 mJ / cm². 2To achieve the following, a thickness of 4 μm to 25 μm is preferred, 5 μm to 23 μm is more preferred, and 5 μm to 19 μm is even more preferred. If the thickness is less than 4 μm, the heat resistance of the film will be insufficient, and wrinkles may occur during bag making, resulting in a poor appearance. Also, during bag making, the area around the heat load may block (a phenomenon in which a wider area than intended is sealed due to heat conduction from the heating element), making proper heat sealing difficult. On the other hand, if the thickness is greater than 25 μm, the heat capacity for crystal fusion becomes large, the degree of crystallinity becomes too high, and in particular, the heat from the cutting blade during heat sealing does not easily reach the sealing interface, so it does not melt completely and the bag making performance is poor.

[0023] 3. Constituent raw materials of polyester-based sealant film Below, a preferred embodiment of the present disclosure, consisting of a heat-seal layer A and a heat-resistant layer B, will be described.

[0024] 3.1. Polyester Raw Materials The polyester raw materials constituting the polyester-based sealant film disclosed herein have ethylene terephthalate as the main component in each layer described later. Here, "main component" means that it contains 50 mol% or more when the total amount of all components (total constituent units) is set to 100 mol%.

[0025] The polyester raw material preferably comprises a polycarboxylic acid monomer and a polyhydric alcohol monomer, and more preferably a dicarboxylic acid monomer and a diol monomer. The polycarboxylic acid monomer preferably comprises at least terephthalic acid or its lower dialkyl ester (preferably a C1-C6 dialkyl ester of terephthalic acid, more preferably dimethyl terephthalate, diethyl terephthalate, and even more preferably dimethyl terephthalate), and the polyhydric alcohol monomer preferably comprises at least ethylene glycol. Ethylene terephthalate is preferably a reaction product of terephthalic acid or its lower dialkyl ester as a dicarboxylic acid monomer and ethylene glycol as a diol monomer. In the polyester sealant film according to this disclosure, it is preferable that the amount of ethylene terephthalate constituting the heat-resistant layer B is greater than the amount of ethylene terephthalate constituting the heat-seal layer A. When the amount of ethylene terephthalate in the heat-resistant layer B is greater than that in the heat-seal layer A, the heat resistance of the heat-resistant layer B tends to increase, and the heat-sealability of the heat-seal layer A tends to increase.

[0026] Furthermore, it is preferable that the polyester used in the polyester resin layer of this disclosure contains one or more components other than ethylene terephthalate. This is because the presence of components other than ethylene terephthalate improves the heat seal strength of heat seal layer A. In heat-resistant layer B, it is preferable to have fewer components other than ethylene terephthalate, but including components other than ethylene terephthalate can reduce the difference in shrinkage rate with the heat seal layer, and has the effect of reducing curling of the laminate. The content of each component differs between heat seal layer A and heat-resistant layer B, and will be described later.

[0027] Examples of dicarboxylic acid monomers that can be components of ethylene terephthalate other than terephthalic acid or its lower dialkyl esters include aromatic dicarboxylic acids such as isophthalic acid, 1,4-cyclohexanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and orthophthalic acid, as well as aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid, and alicyclic dicarboxylic acids.

[0028] Furthermore, examples of diol monomers other than ethylene glycol that constitute ethylene terephthalate include neopentyl glycol, 1,4-cyclohexanedimethanol, diethylene glycol, 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, hexanediol, 1,4-butanediol, and other aliphatic diols, as well as aromatic diols such as bisphenol A. However, it is preferable that the polyester does not contain linear diols with 8 or more carbon atoms (e.g., octanediol) or polyhydric alcohols with a valency of 3 or higher (e.g., trimethylolpropane, trimethylolethane, glycerin, diglycerin).

[0029] Among these, the diol monomer preferably contains an aliphatic diol, more preferably contains one or more of neopentyl glycol, 1,4-cyclohexanedimethanol, 1,4-butanediol, and diethylene glycol, even more preferably contains one or more of 1,4-butanediol, neopentyl glycol, and 1,4-cyclohexanedimethanol, and particularly preferably contains 1,4-butanediol and neopentyl glycol. The use of an aliphatic diol is preferable because it makes it easier to achieve a seal strength of 5 N / 15 mm or more between heat seal layers A.

[0030] Furthermore, the polyester may also contain a polyester elastomer containing ε-caprolactone or tetramethylene glycol as a component of the polyester. Since the polyester elastomer has the effect of lowering the melting point of the polyester resin, it can be used particularly suitably in the heat seal layer A.

[0031] The polyester resin constituting the polyester sealant film of this disclosure may contain various additives as needed, such as waxes, antioxidants, antistatic agents, nucleating agents, viscosity reducers, heat stabilizers, coloring pigments, color inhibitors, and UV absorbers. Furthermore, it is preferable to add fine particles as lubricants to improve the slipperiness of the sealant, at least to the outermost layer of the film. The polyester resin further contains fine particles, preferably in an amount of 100 to 2000 ppm relative to the total polyester resin. Any fine particles can be selected. For example, inorganic fine particles include silica, alumina, titanium dioxide, calcium carbonate, kaolin, and barium sulfate, while organic fine particles include acrylic resin particles, melamine resin particles, silicone resin particles, and cross-linked polystyrene particles. The average particle size of the fine particles can be appropriately selected as needed within the range of 0.05 μm to 3.0 μm when measured with a Coulter counter. Among these, silica is particularly preferred for the fine particles. The amount of fine particles is more preferably 150 to 1800 ppm, even more preferably 200 to 1500 ppm, and even more preferably 250 to 1200 ppm relative to the total polyester resin. When the amount of fine particles is within the above range, the slipperiness of the polyester sealant film is good.

[0032] As a method for incorporating fine particles into the polyester resin constituting the polyester sealant film of this disclosure, for example, they can be added at any stage in the production of the polyester resin. However, it is preferable to add them as a slurry dispersed in ethylene glycol or the like at the esterification stage, or after the completion of the transesterification reaction but before the start of the polycondensation reaction, in order to proceed with the polycondensation reaction. Other methods include blending a slurry of particles dispersed in ethylene glycol, water, or other solvents with the polyester resin raw material using a vented kneading extruder, or blending dried particles with the polyester resin raw material using a kneading extruder.

[0033] In this specification, the amount of ethylene terephthalate refers to the content of ethylene terephthalate constituent units in the polyester resin constituting each layer, and the amount of components other than ethylene terephthalate refers to the total content of constituent units other than ethylene terephthalate constituting each layer. Both are expressed in mole percent when the total amount of all constituent units in each layer is set to 100 mol%. The mole percent of each constituent unit is: 1 The ratio may also be calculated from the decomposition residue ratio determined by H-NMR. If the calculation is based on the amount of raw material used, this should be clearly stated, and in case of any inconsistencies, the measured values ​​mentioned above should take precedence. Furthermore, if a lower dialkyl ester (e.g., dimethyl terephthalate) is used as the raw material for the polycarboxylic acid, the calculation in the polyester resin should be based on the terephthalic acid constituent units.

[0034] 3.2. Component Amounts of Polyester Raw Materials Contained in Heat - Seal Layer A The content of ethylene terephthalate constituting the heat - seal layer A (based on 100 mol% of all the constituent units of the heat - seal layer A) is preferably 55 mol% or more and 90 mol% or less, more preferably 55 mol% or more and 88 mol% or less, still more preferably 56 mol% or more and 86 mol% or less, even more preferably 56 mol% or more and 80 mol% or less, and particularly preferably 56 mol% or more and 75 mol% or less. When the content of ethylene terephthalate constituting the heat - seal layer is within the above range, the heat - sealability can be enhanced. The amount of components other than ethylene terephthalate (content of constituent units) constituting the heat - seal layer A, in 100 mol% of the components constituting the heat - seal layer A (100 mol% of all the constituent units of the heat - seal layer A), is preferably 10 mol% or more and 45 mol% or less, more preferably 12 mol% or more and 45 mol%, still more preferably 14 mol% or more and 44 mol% or less, and even more preferably 14 mol% or more and 43 mol% or less. When the content of the constituent units other than ethylene terephthalate constituting the heat - seal layer A is within the above range, it becomes possible to adjust the surface orientation ΔP and the crystal melting heat capacity to a predetermined range. When the content of the constituent units other than the ethylene terephthalate contained in the heat - seal layer A is less than 10 mol%, even if the molten resin is extruded from the die and then rapidly cooled and solidified, it will crystallize in the subsequent stretching and heat - setting processes. As a result, when sealing, the heat quantity cannot be sufficiently transmitted to the seal interface, and it becomes difficult to achieve a heat - seal strength of 5 N / 15 mm or more.

[0035] On the other hand, when the content of the constituent units other than the ethylene terephthalate contained in the heat - seal layer A is more than 45 mol%, due to the high non - crystallinity, the heat resistance of the heat - seal layer A becomes extremely low. Therefore, when heat - sealing, the surrounding of the heat - seal part will be blocked (a phenomenon in which sealing occurs in a wider range than intended due to heat conduction from the heating member), making it difficult to achieve proper heat - sealing.

[0036] The content of terephthalic acid structural units is preferably 70 mol% or more and 100 mol% or less, more preferably 80 mol% or more and 100 mol% or less, still more preferably 90 mol% or more and 100 mol% or less, and even more preferably 100 mol% in 100 mol% of all dicarboxylic acid monomer structural units of the heat-sealing layer A. When the content of terephthalic acid structural units is within the above range, it exhibits appropriate crystallinity and can maintain heat resistance.

[0037] The content of ethylene glycol structural units is preferably 54 mol% or more and 66 mol% or less, more preferably 55 mol% or more and 65 mol% or less, still more preferably 56 mol% or more and 64 mol% or less, and even more preferably 57 mol% or more and 63 mol% or less in 100 mol% of all diol monomer structural units of the heat-sealing layer A. When the content of ethylene glycol structural units is within the above range, it is possible to prevent a decrease in heat-sealing property while maintaining appropriate crystallinity.

[0038] The content of diol monomer structural units other than ethylene glycol is preferably 34 mol% or more and 46 mol% or less, more preferably 35 mol% or more and 45 mol% or less, still more preferably 36 mol% or more and 44 mol% or less, and even more preferably 37 mol% or more and 43 mol% or less in 100 mol% of all diol monomer structural units of the heat-sealing layer A. When the content of diol monomer structural units other than ethylene glycol is within the above numerical range, the amount of amorphous components increases and the heat-sealing property is improved.

[0039] 3.3. Amount of polyester raw materials contained in heat-resistant layer B The content of ethylene terephthalate constituting the heat-resistant layer B is preferably 70 mol% to 93 mol%, more preferably 72 mol% to 93 mol%, even more preferably 75 mol% to 92 mol%, even more preferably 78 mol% to 92 mol%, and particularly preferably 80 mol% to 91 mol%, based on 100 mol% of all constituent units of the heat-resistant layer B. When the content of ethylene terephthalate constituting the heat-resistant layer is within the above range, the heat resistance can be improved. The amount of components other than ethylene terephthalate constituting the heat-resistant layer B (content of constituent units) is preferably 7 mol% to 20 mol%, more preferably 8 mol% to 20 mol%, even more preferably 9 mol% to 20 mol%, even more preferably 9 mol% to 19 mol%, and particularly preferably 9 mol% to 18 mol%. If the content of constituent units other than ethylene terephthalate that make up the heat-resistant layer is within the above range, the degree of crystallinity will increase, and the heat resistance can be improved.

[0040] On the other hand, if the content of constituent units other than ethylene terephthalate in the heat-resistant layer B is greater than 20 mol%, the heat resistance of the sealant may decrease, such as causing holes to form due to the heat applied during heat sealing.

[0041] If the content of constituent units other than ethylene terephthalate in the heat-resistant layer B is less than 7 mol%, the difference in thermal shrinkage rate between it and the heat-seal layer A will increase, which may cause the sealant to curl more. Even if cooling after heat setting is strengthened, shrinkage toward the seal layer may increase, which may cause the curl to become more pronounced.

[0042] The difference between the amount of components other than ethylene terephthalate constituting the heat seal layer A and the amount of components other than ethylene terephthalate constituting the heat-resistant layer B (both based on 100 mol% of the total constituent units of each layer) is preferably 19.0 mol% or more and 28.0 mol% or less, more preferably 19.2 mol% or more and 27.0 mol% or less, even more preferably 19.4 mol% or more and 27.0 mol% or less, and even more preferably 19.6 mol% or more and 26.0 mol% or less. When the difference between the amount of components other than ethylene terephthalate constituting the heat seal layer A and the amount of components other than ethylene terephthalate constituting the heat-resistant layer B is within the above range, defects in appearance during heat sealing tend to be suppressed and the seal strength tends to be increased.

[0043] The content of terephthalic acid constituent units is preferably 70 mol% to 100 mol%, more preferably 80 mol% to 100 mol%, even more preferably 90 mol% to 100 mol%, and even more preferably 100 mol%, based on 100 mol% of the dicarboxylic acid monomer constituent units constituting the heat-resistant layer B. When the content of terephthalic acid constituent units is within the above numerical range, the crystallinity increases and the heat resistance improves.

[0044] The content of ethylene glycol constituent units is preferably 70 mol% to 96 mol%, more preferably 75 mol% to 95 mol%, even more preferably 80 mol% to 93 mol%, and even more preferably 80 mol% to 90 mol%, based on 100 mol% of the diol monomer constituent units constituting the heat-resistant layer B, and may also be 70 mol% to 87 mol%. When the content of ethylene glycol constituent units is within the above numerical range, crystallinity is increased and heat resistance is improved. The content of diol monomer constituent units other than ethylene glycol is preferably 4 mol% to 30 mol%, more preferably 5 mol% to 25 mol%, even more preferably 7 mol% to 20 mol%, and even more preferably 10 mol% to 20 mol%, based on 100 mol% of the diol monomer constituent units constituting the heat-resistant layer B. When the content of diol monomer constituent units other than ethylene glycol is within the above numerical range, crystallinity is adjusted and processability is improved without impairing heat resistance.

[0045] The components other than ethylene terephthalate that constitute the heat seal layer A and the heat-resistant layer B preferably include one or more diol components selected from the group consisting of neopentyl glycol, 1,4-cyclohexanedimethanol, diethylene glycol, 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, 1,4-butanediol, and hexanediol; more preferably include one or more selected from the group consisting of neopentyl glycol, 1,4-cyclohexanedimethanol, diethylene glycol, 1,4-butanediol, and hexanediol; and even more preferably include one or more selected from the group consisting of neopentyl glycol, 1,4-cyclohexanedimethanol, diethylene glycol, and 1,4-butanediol. It is even more preferable to include neopentyl glycol, 1,4-cyclohexanedimethanol, diethylene glycol, and 1,4-butanediol, and even more preferable to include 1,4-cyclohexanedimethanol, diethylene glycol, and 1,4-butanediol. It is also even more preferable to include neopentyl glycol, diethylene glycol, and 1,4-butanediol.

[0046] The diol component constituting the heat seal layer A preferably contains 54 to 66 mol% ethylene glycol, 0 to 21 mol% neopentyl glycol, 10 to 25 mol% 1,4-butanediol, 0 to 6 mol% diethylene glycol, and 0 to 8 mol% 1,4-cyclohexanedimethanol, per 100 mol% of the diol component, and more preferably contains 54 to 66 mol% ethylene glycol, 1 to 21 mol% neopentyl glycol, 10 to 25 mol% 1,4-butanediol, 1 to 6 mol% diethylene glycol, and 1 to 8 mol% 1,4-cyclohexanedimethanol, per 100 mol% of the diol component. It is even more preferable that the diol component constituting the heat seal layer A contains 54 to 66 mol% ethylene glycol, 4 to 21 mol% neopentyl glycol, 10 to 25 mol% 1,4-butanediol, 2 to 6 mol% diethylene glycol, and 1 to 8 mol% 1,4-cyclohexanedimethanol, per 100 mol% of the diol component. By setting the diol component constituting the heat seal layer A within the above range, it is possible to ensure crystallinity and heat resistance with ethylene glycol while mitigating crystallinity and imparting heat sealability by introducing neopentyl glycol, 1,4-butanediol, diethylene glycol, and 1,4-cyclohexanedimethanol. In this way, by using a composition that satisfies the above range, a heat seal layer A with a good balance of heat resistance and sealing properties can be obtained.

[0047] The diol component constituting the heat-resistant layer B preferably contains 70-87 mol% ethylene glycol, 0-12 mol% neopentyl glycol, 5-13 mol% 1,4-butanediol, 0-4 mol% diethylene glycol, and 0-5 mol% 1,4-cyclohexanedimethanol, per 100 mol% of the diol component. More preferably, the diol component constituting the heat-resistant layer B contains 70-87 mol% ethylene glycol, 1-12 mol% neopentyl glycol, 5-13 mol% 1,4-butanediol, 1-4 mol% diethylene glycol, and 1-5 mol% 1,4-cyclohexanedimethanol, per 100 mol% of the diol component. It is even more preferable that the diol component constituting the heat-resistant layer B contains 70 to 87 mol% ethylene glycol, 3 to 12 mol% neopentyl glycol, 5 to 13 mol% 1,4-butanediol, 1 to 4 mol% diethylene glycol, and 1 to 5 mol% 1,4-cyclohexanedimethanol, per 100 mol% of the diol component. By setting the diol component constituting the heat-resistant layer B within the above range, the crystallinity can be appropriately adjusted by introducing neopentyl glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, and diethylene glycol while ensuring crystallinity and heat resistance with ethylene glycol. In this way, by achieving a composition that satisfies the above range, a heat-resistant layer B can be obtained that has a good balance of sufficient heat resistance and seal strength even at high temperatures. The content of the above diol component is considered to be the content of the diol component constituent units constituting each layer.

[0048] The heat seal layer A and the heat-resistant layer B, or both, further contain fine particles, preferably in an amount of 100 to 2000 ppm relative to the entire heat seal layer A or the entire heat-resistant layer B, more preferably 150 to 1800 ppm, even more preferably 200 to 1600 ppm, and even more preferably 250 to 1400 ppm. By setting the amount of fine particles contained in the heat seal layer A and the heat-resistant layer B within the above range, it is possible to exhibit an anti-blocking effect while maintaining transparency and sealing performance.

[0049] 4. Manufacturing of Polyester-Based Sealant Film 4.1. Melt Extrusion The polyester-based sealant film of this disclosure can be obtained by melt-extruding the polyester raw material described in 3.1. "Raw Material Types for Polyester Resin Layers" using an extruder to form an unstretched film, and then stretching it by the following predetermined method. If the polyester-based sealant film includes a heat-seal layer A and a heat-resistant layer B, or other layers, the timing of lamination of each layer may be before or after stretching. When lamination is performed before stretching, it is preferable to melt-extrude the resins that will be the raw materials for each layer using separate extruders and join them using a feed block or the like in the middle of the resin flow path. When lamination is performed after stretching, it is preferable to use lamination, in which separately formed films are bonded together with an adhesive, or extrusion lamination, in which molten polyester resin is poured onto the surface of the individual or laminated films to laminate them. Among these, the method of laminating each layer before stretching is preferred.

[0050] As described above, polyester resin can be obtained by polycondensing dicarboxylic acid and diol components, selecting the type and amount of these components so that they contain appropriate amounts of monomers other than ethylene terephthalate. Alternatively, two or more types of chip-shaped polyester can be mixed and used as raw materials for a polyester resin layer.

[0051] When melt-extruding the raw resin, it is preferable to dry the polyester raw material of each layer using a dryer such as a hopper dryer or paddle dryer, or a vacuum dryer. After drying the polyester raw material of each layer in this way, it is melted using an extruder and extruded as a laminated film.

[0052] In the extruder, the polyester resin undergoes transesterification while being melted and mixed, resulting in a random copolymer polyester. This increases its amorphous properties, which are related to the sluice and heat seal strength. The degree of resin mixing, temperature, and residence time in the extruder can be set to any conditions within the characteristic range of this disclosure.

[0053] Extrusion can be carried out using any existing method, such as the T-die method or the tubular method.

[0054] Subsequently, an unstretched film can be obtained by rapidly cooling the film melted by extrusion. As a method for rapidly cooling the molten resin, a method of casting the molten resin from a die onto a rotating drum and rapidly cooling and solidifying it to obtain a substantially unoriented resin sheet can be suitably employed.

[0055] The film may be manufactured using any of the following methods: unstretched, uniaxial stretching (stretching in at least one direction, either longitudinal or transverse), or biaxial stretching. From the viewpoint of mechanical strength and productivity of the laminate of this disclosure, uniaxial stretching or biaxial stretching is preferred, and biaxial stretching is more preferred. The following description will focus on the sequential biaxial stretching method by longitudinal stretching followed by transverse stretching, but transverse stretching followed by longitudinal stretching is also acceptable, as only the main orientation direction changes. Furthermore, simultaneous biaxial stretching, where the longitudinal and transverse directions are stretched simultaneously, or diagonal stretching, where the speeds of the left and right clips differ during transverse stretching, may also be used as long as the physical properties are not impaired.

[0056] 4.2. First (Longitudinal) Stretching For stretching in the first direction (longitudinal or longitudinal direction), the unstretched film is preferably introduced into a longitudinal stretcher having multiple roll groups arranged in a continuous manner. For longitudinal stretching, it is preferable to preheat the film with a preheating roll until the film temperature reaches 65°C to 90°C (preferably 68°C to 89°C). If the film temperature during stretching is lower than 65°C, it becomes difficult to stretch in the longitudinal direction and breakage is more likely to occur, which is undesirable. Also, if it is higher than 90°C, the film tends to stick to the rolls, which is undesirable as it can lead to the film wrapping around the rolls and the rolls becoming easily soiled during continuous production. It is preferable to perform longitudinal stretching when the film temperature reaches 65°C to 90°C. The longitudinal stretching ratio is preferably 1x to 5x, more preferably 2x to 4.8x, and even more preferably 2.5x to 4.5x. Since no longitudinal stretching occurs at a ratio of 1, a transversely uniaxially oriented film is obtained when the longitudinal stretching ratio is 1, and a biaxially oriented film is obtained when the longitudinal stretching ratio is greater than 1.1. By setting the longitudinal stretching ratio to 1.1 or higher, molecular orientation can be given to the longitudinal direction of the film, increasing its mechanical strength, which makes it easier to keep the heat deformation rate when tension is applied below 10%. Furthermore, by setting the longitudinal stretching ratio to 1.1 or higher and giving molecular orientation to the longitudinal direction of the film, it becomes easier to bring the cooling deformity rate when tension is applied close to 0%. In addition, there is no upper limit to the longitudinal stretching ratio, but if the longitudinal stretching ratio is too high, transverse stretching becomes difficult and stretch fracture is more likely to occur, so it is preferable to keep it below 5.

[0057] 4.3. Intermediate Heat Treatment After the first (longitudinal) stretching, it is preferable to have a step (intermediate heat treatment) in which the film is heated in order to reduce the shrinkage rate of the film caused by stretching. In this intermediate heat treatment, constant length heating, in which the film is heated while keeping the length constant, or a relaxation treatment, in which the film is heated while relaxing in the longitudinal direction, can be employed. Among these, a relaxation treatment is a preferred embodiment in order to reduce the shrinkage rate of the film in the longitudinal direction caused by longitudinal stretching.

[0058] Relaxing the film in the longitudinal direction not only reduces the shrinkage rate in the longitudinal direction of the film, but also reduces the bowing phenomenon (strain) that occurs in the tenter. This is because in subsequent processes such as the second (transverse) stretching and final heat treatment, both ends of the film in the width direction are held while heating, so only the central part of the film shrinks in the longitudinal direction. The relaxation rate in the longitudinal direction is preferably 0% to 70% (a relaxation rate of 0% means no relaxation is performed), more preferably 2% to 60%, even more preferably 5% to 50%, and even more preferably 8% to 40%. The upper limit of the relaxation rate in the longitudinal direction is determined by the raw materials used and the longitudinal stretching conditions, so relaxation cannot be performed beyond this limit. Relaxation in the longitudinal direction can be performed by heating the film after longitudinal stretching at a temperature of 65°C to 100°C or lower, adjusting the speed difference of the rolls (slowing down the roll speed on the downstream side), or shortening the distance between clips (slowing down the movement speed on the downstream side). Any heating method can be used, such as a roll, near-infrared, far-infrared, or hot air heater. Furthermore, longitudinal relaxation can be performed not only immediately after longitudinal stretching, but also, for example, during transverse stretching (including the preheating zone) or the final heat treatment by narrowing the longitudinal clip spacing (in this case, both ends in the film width direction are also relaxed longitudinally, thus reducing bowing distortion), and can be performed at any time. After longitudinal relaxation (or longitudinal stretching if relaxation is not performed), it is preferable to cool the film once, preferably with a cooling roll with a surface temperature of 20 to 40°C. The final stretching ratio in the first stretching is preferably 1.5 times or more and 4.8 times or less, more preferably 1.8 times or more and 4.5 times or less, and even more preferably 2.1 times or more and 4.2 times or less.

[0059] 4.4. Second (Transverse) Stretching After the first (longitudinal) stretching, it is preferable to stretch the film transversely at a stretching ratio of 3 to 5 times (preferably 3.3 to 4.8 times, more preferably 3.5 to 4.5 times) at 65°C to 130°C (preferably 85°C to 120°C) while holding both ends of the film in the width direction (direction perpendicular to the longitudinal direction) with clips inside the tenter. It is preferable to preheat the film before stretching in the transverse direction, and preheating should be carried out until the film surface temperature reaches 75°C to 120°C (preferably 90°C to 120°C).

[0060] After transverse stretching, it is preferable to pass the film through an intermediate zone where no active heating operation is performed. Because the temperature in the final heat treatment zone is higher than in the transverse stretching zone of the tenter, if an intermediate zone is not provided, the heat from the final heat treatment zone (hot air itself and radiant heat) will flow into the transverse stretching process. In this case, the temperature in the transverse stretching zone will not be stable, which will not only worsen the accuracy of the film thickness but also cause variations in heat seal strength. Therefore, it is preferable to pass the transversely stretched film through an intermediate zone for a predetermined time before performing the final heat treatment. In this intermediate zone, it is important to block the accompanying flow associated with the movement of the film and the hot air from the transverse stretching zone and the final heat treatment zone so that when a strip of paper is hung down without the film passing through it, the strip hangs almost completely vertically. A passage time of 1 to 5 seconds (preferably 1 to 4 seconds) in the intermediate zone is sufficient. If it is shorter than 1 second, the length of the intermediate zone will be insufficient, and the heat blocking effect will be inadequate. On the other hand, a longer intermediate zone is preferable, but if it's too long, the equipment will become too large, so about 5 seconds is sufficient.

[0061] 4.5. Final Heat Treatment After passing through the intermediate zone, it is preferable to perform heat treatment in the final heat treatment zone to melt the heat seal layer and develop heat seal strength. A temperature of 190°C to 240°C is preferred, 195°C to 230°C is more preferred, and 200°C to 220°C is particularly preferred. By setting the heat treatment temperature within this particularly preferred temperature range, curling and warping of the manufactured bags can be suppressed, resulting in a good appearance and good alignment of the edges when the manufactured bags are stacked. Curling occurs when the difference in shrinkage rates between the layers of the film is large, causing the film to deform into a curve so that the layer with the larger shrinkage rate is on the inside. Warping is a wrinkle that occurs in an uneven manner when the absolute value of the shrinkage rate is large, even if the difference in shrinkage rates between the layers of the film is small.

[0062] To achieve sufficient heat seal strength and fused seal strength, it is important to have an appropriate crystal orientation, i.e., a plane orientation within a predetermined range. If the final heat treatment temperature is below 190°C, the plane orientation ΔP is large, resulting in a large thermal shrinkage rate, which is undesirable because it leads to significant curling and warping during bag making, and poor processability. Also, insufficient melting of the heat seal layer increases the heat capacity for crystal melting, which reduces heat seal strength and fused seal strength, and is undesirable. If the final heat treatment temperature exceeds 240°C, the plane orientation ΔP decreases and the shrinkage rate can be suppressed, but the heat seal layer is excessively melted, and the film may melt and fall into the tenter during the heat treatment process, which is undesirable.

[0063] During the final heat treatment, the shrinkage rate in the width direction can be reduced by shortening the distance between tenter clips by an arbitrary factor (relaxation in the width direction). Therefore, in the final heat treatment, it is preferable to perform relaxation in the width direction within the range of 0% to 10% (preferably 0.5% to 8%, more preferably 1% to 5%) (a relaxation rate of 0% means no relaxation is performed). Although the shrinkage rate in the width direction decreases as the relaxation rate in the width direction increases, the upper limit of the relaxation rate (the shrinkage rate in the width direction of the film immediately after transverse stretching) is determined by the raw materials used, the stretching conditions in the width direction, and the heat treatment temperature, so relaxation cannot be performed beyond this limit. In the polyester sealant film of this disclosure, the upper limit of the relaxation rate in the width direction is 20%. Furthermore, as mentioned above, during the final heat treatment, it is also possible to shorten the distance between tenter clips in the longitudinal direction by an arbitrary factor (relaxation in the longitudinal direction).

[0064] The longer the time spent in the final heat treatment zone, the more effective the heat treatment becomes. Therefore, a time of 2 to 20 seconds is preferable, 3 to 18 seconds is more preferable, and 5 to 15 seconds is even preferable. If the time spent is 2 seconds or less, the film will pass through the heat treatment zone before its surface temperature reaches the set temperature, rendering the heat treatment meaningless. However, increasing the time spent would require larger equipment, so for practical purposes, 20 seconds or less is sufficient.

[0065] 4.6. Cooling After passing through the final heat treatment zone, it is preferable to cool the film in the cooling zone with cooling air at 10°C to 30°C for 2 to 15 seconds (preferably 2 to 10 seconds). At this time, it is preferable to improve the cooling efficiency by lowering the temperature of the cooling air or increasing the airflow speed so that the actual temperature of the film at the tenter exit is lower than the glass transition temperature of either the seal layer or the heat-resistant layer, whichever is lower. The actual temperature refers to the film surface temperature measured with a non-contact radiation thermometer. If the actual temperature of the film at the tenter exit exceeds the glass transition temperature, the film will shrink due to heat when the ends of the film that were held by the clips are released. At this time, the film will curl towards the seal layer, which has a high thermal shrinkage rate, which is undesirable. After that, a film roll can be obtained by winding up the film while cutting off the ends of the film.

[0066] 5. Packaging Structure and Bag Manufacturing Method A polyester-based sealant film having the above characteristics can be suitably used as a packaging structure. The polyester-based sealant film of this disclosure can be made into a bag on its own, or other materials may be laminated with it. Examples of other layers constituting the polyester-based sealant film include, but are not limited to, an unoriented film containing polyethylene terephthalate as a component, an unoriented, uniaxially oriented, or biaxially oriented film containing other amorphous polyesters as a component, an unoriented, uniaxially oriented, or biaxially oriented film containing nylon as a component, or an unoriented, uniaxially oriented, or biaxially oriented film containing polypropylene as a component. The method of using the polyester-based sealant film in a packaging structure is not particularly limited, and conventionally known manufacturing methods such as coating, lamination, and heat sealing can be employed.

[0067] The packaging body may be composed of at least a portion of the polyester sealant film according to the present disclosure. Furthermore, the polyester sealant film of the present invention may be in any layer of the packaging body, but in order to fully obtain the effects of the present disclosure, considering the heat seal strength and heat seal strength when making the bag, it is preferable that the heat seal layer A of the polyester sealant film according to the present disclosure be the innermost layer of the bag. The method for making a packaging body having the polyester sealant film according to the present disclosure is not particularly limited, and conventionally known manufacturing methods such as heat sealing using a cutting blade, heat sealing using a heat bar (heat jaw), bonding using hot melt, and center sealing with a solvent can be employed. The packaging body having the polyester sealant film according to the present disclosure can be suitably used as a packaging material for various articles such as food, pharmaceuticals, daily necessities, and industrial products.

[0068] This application claims the benefit of priority based on Japanese Patent Application No. 2024-162475, filed on September 19, 2024. The entire specification of Japanese Patent Application No. 2024-162475, filed on September 19, 2024, is incorporated herein by reference.

[0069] Next, the present invention will be specifically described using examples and comparative examples, but this disclosure is not limited in any way to the embodiments of such examples, and can be modified as appropriate without departing from the spirit of this disclosure.

[0070] <Preparation of Polyester Raw Materials> [Synthesis Example 1] In a stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser, 100 mol% dimethyl terephthalate (DMT) as the dicarboxylic acid component and 100 mol% ethylene glycol (EG) as the polyhydric alcohol component were charged so that the molar ratio of ethylene glycol was 2.2 times that of dimethyl terephthalate. Using 0.05 mol% zinc acetate (relative to the acid component) as a transesterification catalyst, the transesterification reaction was carried out while distilling off the resulting methanol. Subsequently, 0.225 mol% antimony trioxide (relative to the acid component) was added as a polycondensation catalyst, and the polycondensation reaction was carried out at 280°C under reduced pressure of 26.7 Pa to obtain polyester A with an intrinsic viscosity of 0.75 dl / g. This polyester A is polyethylene terephthalate. The composition of polyester A is shown in Table 1.

[0071] [Synthesis Example 2] Polyesters B to F were obtained by changing the monomer using 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, IPA is isophthalic acid, BD is 1,4-butanediol, NPG is neopentyl glycol, CHDM is 1,4-cyclohexanedimethanol, and DEG is diethylene glycol. When producing polyester F, SiO2 (Silysia 266, manufactured by Fuji Silysia Co., Ltd.) was added as a lubricant at a ratio of 7,000 ppm relative to the polyester. Each polyester was made into chips as appropriate. The composition of polyesters B to F is shown in Table 1.

[0072]

[0073] <Method for manufacturing polyester-based sealant film>

[0074] [Example 1] Polyester A, polyester B, polyester E, and polyester F were mixed in a mass ratio of 9:62:22:7 as the raw material for heat seal layer A (also called layer A), and polyester A, polyester B, polyester E, and polyester F were mixed in a mass ratio of 50:37:6:7 as the raw material for heat-resistant layer B (also called layer B).

[0075] The mixed raw materials for each layer were fed into separate screw extruders and melted at 280°C. The molten resins were joined together by a feed block midway through the flow path and extruded from a T-die, where they were cooled on a chill roll set to a surface temperature of 30°C to obtain an unstretched laminated film. The flow path of the molten resin was set so that one side of the laminated film was layer A and the other side was layer B (a two-layer structure of two types, layer A / layer B), and the extrusion rate was adjusted so that the thickness ratio of layer A to layer B was 44 / 56.

[0076] The unstretched laminated film obtained by cooling and solidifying was guided as the first step to a longitudinal stretcher with multiple rolls arranged in a continuous pattern. After preheating on a preheating roll until the film temperature reached 87°C, it was stretched to 3.8 times its original length. Immediately after longitudinal stretching, the film was passed through a heating furnace set to 90°C with a hot air heater, and a 20% relaxation treatment was performed in the longitudinal direction using the speed difference between the rolls at the inlet and outlet of the heating furnace. Subsequently, the longitudinally stretched film was forcibly cooled by a cooling roll set to a surface temperature of 25°C.

[0077] After the relaxation treatment, the film was led to a tenter (transverse stretching machine) as the second step, where it was preheated for 5 seconds until the surface temperature reached 115°C, and then stretched 4.4 times in the width direction (transverse direction). The transversely stretched film was then led directly to the intermediate zone and passed through for 1.0 second. In the intermediate zone of the tenter, the hot air from the final heat treatment zone and the hot air from the transverse stretching zone were blocked so that when a strip of paper was hung down without the film passing through, the strip of paper would hang almost completely vertically.

[0078] Subsequently, the film that had passed through the intermediate zone was guided to the final heat treatment zone and heat-treated at 210°C for 5 seconds. At the same time as the heat treatment, the clip spacing in the width direction of the film was narrowed, thereby performing a 3% relaxation treatment in the width direction. After passing through the final heat treatment zone, the film was cooled for 5 seconds with 30°C cooling air. At this time, the actual film temperature at the tenter exit was 40°C. By cutting off both edges and winding the film into a roll with a width of 600 mm, a biaxially stretched film with a thickness of 13 μm was continuously produced over a predetermined length. The properties of the obtained film were evaluated by the method described above. The manufacturing conditions and evaluation results are shown in Tables 2A and 2B.

[0079] [Examples 2-8] In Examples 2-8, polyester sealant films were continuously produced by arbitrarily changing the raw material mixing ratio, layer structure, raw material resin extrusion ratio, stretching ratio and relaxation rate in the first step, final heat treatment conditions, and film thickness compared to Example 1. The manufacturing conditions and evaluation results for each film are shown in Tables 2A and 2B.

[0080] [Comparative Examples 1-3] Each polyester-based sealant film was obtained using the manufacturing method shown in Table 2. The evaluation results are shown in Tables 2A and 2B.

[0081] [Comparative Example 4] Polyester A, polyester B, polyester E, and polyester F were mixed in a mass ratio of 23:60:10:7. The mixed raw materials were fed into a screw extruder and melted at 280°C. The molten resin was extruded from a T-die and cooled on a chill roll set to a surface temperature of 30°C to obtain an unstretched film. The unstretched laminated film obtained by cooling and solidifying was led to a transverse stretcher (tenter) as the first step, where it was preheated for 5 seconds until the surface temperature reached 90°C, and then stretched 3.8 times in the width direction (transverse direction). The uniaxially stretched film was led to a longitudinal stretcher with multiple roll groups arranged in a series as the second step, where it was preheated on a preheating roll until the film temperature reached 86°C, and then stretched 2.4 times. After that, the longitudinally stretched film was forcibly cooled by a cooling roll set to a surface temperature of 25°C. The cooled film was then led to a final heat treatment machine as the third step. While heat-treating it in a 140°C atmosphere for 10 seconds, it was relaxed by 15% in the transverse direction (film width direction), then cooled, and the ends in the width direction were cut off to obtain a polyester sealant film with a thickness of 13 μm. The manufacturing conditions and physical properties of the obtained film are shown in Tables 2A and 2B.

[0082] [Comparative Examples 5 and 6] Each polyester-based sealant film was obtained using the manufacturing methods shown in Tables 2A and 2B. The evaluation results are shown in Tables 2A and 2B.

[0083]

[0084]

[0085] <Evaluation Method for Polyester-Based Sealant Films> The evaluation method for polyester-based sealant films is as follows.

[0086] [Heat-sealed strength] The film was folded in half so that the fold line aligned with the film's flow direction, and the heat-sealed layers A were aligned and set in a heat-sealed machine (PP500 type side welder, manufactured by Kyoei Printing Machinery Materials Co., Ltd.). The film was heat-sealed under the conditions of a heat-sealing blade angle of 90 degrees, a blade tip setting temperature of 410°C, and a shot rate of 140 bags / minute to produce side-sealed bags. The size of the bag was 310 mm in the direction along the heat-sealed line (width direction of the film roll) x 220 mm in the direction perpendicular to the heat-sealed line (flow direction of the film roll) (hereinafter, unless otherwise specified, the direction along the heat-sealed line will be called the "width direction," and the direction perpendicular to it will be called the "flow direction"). One bag was randomly selected from the produced bags, and a total of 10 samples (5 from each side) with a size of 15 mm in the width direction x 100 mm in the flow direction were sampled from the heat-sealed portion (310 mm on each side x 2 = 620 mm on both sides). In accordance with JIS Z1707, the sample was opened to 180 degrees and both ends were set in a universal tensile testing machine "DSS-100" (manufactured by Shimadzu Corporation) (chuck distance: 50 mm). A tensile test was performed in the longitudinal direction (flow direction) of the sample at a speed of 200 mm / min, and the peel strength at which the fused seal portion broke was measured. The maximum value of the peel strength was recorded as the fused seal strength as the strength per 15 mm (N / 15 mm), and the average value of 10 samples was taken as the average fused seal strength.

[0087] [Heat Seal Strength] Heat seal strength was measured in accordance with JIS Z1707. The specific procedure is as follows: Using a heat sealer, the heat seal layers A sides of the sample were joined together and bonded. The heat sealing conditions were an upper bar temperature of 160°C, a pressure of 0.2 MPa, and a time of 2 seconds. The heat-sealed sample was cut to a seal width of 15 mm. The peel strength was measured using a universal tensile testing machine "DSS-100" (manufactured by Shimadzu Corporation) at a tensile speed of 200 mm / min. The peel strength is expressed as strength per 15 mm (N / 15 mm).

[0088] [Heat Shrinkage Rate] The heat shrinkage rate of the film in the longitudinal and width directions at 120°C was measured in accordance with JIS Z1712 using the following method. The film was cut so that the measurement direction was 200 mm and the direction perpendicular to it was 20 mm, and then suspended in a 120°C hot air oven and heated for 5 minutes. The length after heating was measured, and the heat shrinkage rate at 120°C was determined as the ratio of the length shrunk to the original length.

[0089] [Degree of Planar Orientation ΔP] The refractive index was measured in accordance with JIS K7105. A sample was prepared by cutting a polyester sealant film to a width of 2 cm and a length of 3 cm. At this time, the sample was prepared so that the longitudinal direction of the sample was parallel to the longitudinal direction of the film. The surface of the heat seal layer A was measured using an Abbe refractometer 4T manufactured by Atago Optical Co., Ltd., and the degree of planar orientation ΔP was calculated from the refractive index nx in the longitudinal direction, the refractive index ny in the width direction, and the refractive index nz in the thickness direction using the following equation (2). Degree of planar orientation ΔP = (nx + ny) / 2 - nz ... (2) The solvent used for measurement was diiodomethane, and a test piece with a refractive index of 1.74 was used, and the measurement conditions were 23℃ and 60% R.H. or less. The number of measurements was n = 3. For the refractive index of the heat seal layer A, the lower values ​​of nx and ny were read from the three measurements, and the higher value of nz was adopted from the three measurements.

[0090] [Heat Capacity for Melting Crystals (ΔHm)] The heat capacity for fusion was measured using a DSC (DSC220, manufactured by Seiko Electronics Industries, Ltd.). Specifically, 10 mg of a film sample was weighed into an aluminum pan, and the temperature was increased from 20°C to approximately 250°C at a rate of 10°C / min. The heat quantity ΔHm' indicated by the area enclosed by the endothermic peak and the baseline (melting peak area) was determined. The measured value was then calculated using the following formula, and the result was obtained for 1 cm². 2 The heat capacity ΔHm of crystal fusion per 1 cm was calculated. 2 Heat of melting per unit area ΔHm (mJ / cm) 2 ) = ΔHm' (J / g) × film density (g / cm³) 3) × film thickness (μm) The density of the film was measured using the density gradient method of JIS K 7112 D, with calcium nitrate tetrahydrate as the gradient solution, the temperature inside the gradient tube at 30°C, the sample size 5 mm × 5 mm, and the immersion time 16 hours. Samples were taken from 10 mm from the left and right edges in the film width direction toward the center, and the highest measured value was adopted. The film thickness was measured in accordance with JIS K7130-1999 A, using a dial gauge, with 10 arbitrary points as measurement positions and the average value used.

[0091] [Folded Holding Angle] Film pieces were left in a constant temperature chamber at 28°C and 50% RH for 24 hours. Immediately thereafter, each film was cut into 10cm x 10cm squares at 20°C and 65% RH and folded into quarters (5cm x 5cm squares). When folding the film, the shorter side of the rectangle formed by the first two folds was aligned with the direction of the flow. Then, the four-folded film was placed between two pieces of glass measuring 10cm x 15cm and 2mm thick, and a 5kg weight was placed on top of the glass and pressed for 20 seconds. After removing the weight from the four-folded film and letting it stand for 10 seconds, the angle at which the film opened was measured using the last fold as the starting point. Note that a fully folded film is 0 degrees, and a fully open film is 180 degrees.

[0092] [Fragrance Retention] Two films were layered together, and three sides were heat-sealed at 160°C to create a three-sided sealed bag with an inner dimension of 10 cm, leaving only one side open. 20 g each of limonene (manufactured by Nacalai Tesque Co., Ltd.) and menthol (manufactured by Nacalai Tesque Co., Ltd.) were placed in the bag, and the open side was also heat-sealed to seal the bag. The menthol used was prepared by dissolving it in ethanol to a concentration of 1 g / mL. This bag was placed in a 1000 mL glass container and the lid was closed. After one week, 16 people (4 in their 20s, 4 in their 30s, 4 in their 40s, and 4 in their 50s; the gender ratio was 50 / 50 for each age group) opened the lid of the glass container, smelled the air inside, and made judgments as follows: Judgment 1: Number of people who smelled the odor: 0-1 Judgment 2: Number of people who smelled the odor: 2-3 Judgment 3: Number of people who smelled the odor: 4-16

[0093] [Waviness of the heat-sealed portion] The film was folded in half so that the fold was in the direction of the film roll's flow, and the heat-sealed layers A were aligned and set in a heat-sealing machine (PP500 type side welder, manufactured by Kyoei Printing Machinery Materials Co., Ltd.). The film was heat-sealed under the conditions of a heat-sealing blade angle of 90 degrees, a blade tip setting temperature of 410°C, and a shot rate of 140 bags / minute to produce a side-sealed bag measuring 310 mm in width and 220 mm in flow direction. One bag was randomly selected from the produced bags, and the wavyness of the heat-sealed portion was evaluated. The length of the sealed portion after heat-sealing was measured and applied to the following equation 5 to determine the percentage of shrinkage of the film in the width direction due to heat-sealing. In the following equation 5, the length of the film (width direction) before heat-sealing is 310 mm. Shrinkage rate (%) = {(Length before heat-sealing - Length after heat-sealing) / Length before heat-sealing} × 100 Equation 5 This shrinkage rate was evaluated as the wavyness of the heat-sealed portion as follows. Judgment 1: The percentage of shrinkage due to cutting is less than 1%. Judgment 2: The percentage of shrinkage due to cutting is 1% or more and 2% or less. Judgment 3: The percentage of shrinkage due to cutting is more than 2%.

[0094] [Film Evaluation Results] As shown in Tables 2A and 2B, all sealants from Example 1 to Example 8 satisfied the requirements for thermal seal strength, heat seal strength, thermal shrinkage rate, plane orientation degree ΔP, crystalline heat fusion heat capacity, fold retention angle, and aroma retention, demonstrating excellent performance as polyester-based sealant films. On the other hand, Comparative Examples 1 to 6 all yielded undesirable results for the following reasons. The film of Comparative Example 1 had a high plane orientation ΔP, resulting in low thermal seal strength and heat seal strength. From this result, it can be seen that bags formed from the film of Comparative Example 1 are prone to tearing after filling with contents and are therefore undesirable as bags. The film of Comparative Example 2 had a high plane orientation ΔP, a large crystalline heat fusion heat capacity, and low heat seal strength. Similar to Comparative Example 1, it was prone to tearing and was therefore undesirable as a packaging bag. In the film of Comparative Example 3, there was a large difference between the heat seal layer A and the heat-resistant layer B, which were components other than ethylene terephthalate, resulting in curling. Furthermore, due to its high thermal shrinkage rate, the sealed portion became significantly wavy during the sealing process, resulting in a bag appearance inferior to that of bags using the films of Examples 1 to 8. The film of Comparative Example 4 had a high surface orientation ΔP and a high thermal shrinkage rate, causing wrinkles in the sealed portion during bag making and resulting in an inferior appearance. The film of Comparative Example 5 had a high heat capacity for crystalline fusion and poor heat-seal strength. For this reason, it was unsuitable as a packaging bag for heat-seal applications. The film of Comparative Example 6 had a high heat capacity for crystalline fusion, resulting in packaging bags where the film did not completely melt during heat-sealing, making processing impossible.

[0095] The polyester sealant film of this disclosure exhibits low thermal shrinkage and has excellent sealing strength in heat-sealing and heat-cutting processes, and is therefore suitable for use in applications such as packaging bags manufactured in processes that include heat-sealing.

Claims

1. A polyester sealant film characterized by being composed of a polyester resin mainly composed of ethylene terephthalate, comprising at least a heat seal layer A and a heat-resistant layer B, wherein the heat seal layer A is laminated on one or both sides of the heat-resistant layer B, and satisfying the following requirements (1) to (3): (1) When heat seal layers A are joined together and heat-sealed in the width direction of the film, the heat seal strength is 5.0 N / 15 mm or more and 18 N / 15 mm or less. (2) When heat seal layers A are heat-sealed at 160°C at 0.2 MPa for 2 seconds, the heat seal strength is 5 N / 15 mm or more and 15 N / 15 mm or less. (3) The heat shrinkage rate at 120°C in both the longitudinal and width directions of the film is 0.01% or more and 10.0% or less.

2. The polyester sealant film according to claim 1, wherein the amount of ethylene terephthalate constituting the heat-resistant layer B is greater than the amount of ethylene terephthalate constituting the heat-seal layer A.

3. The polyester sealant film according to claim 1, wherein the amount of components other than ethylene terephthalate constituting the heat seal layer A is 10 mol% or more and 45 mol% or less of 100 mol% of the components constituting the heat seal layer A.

4. The polyester sealant film according to claim 1, wherein the amount of components other than ethylene terephthalate constituting the heat-resistant layer B is 7 mol% or more and 20 mol% or less of 100 mol% of the components constituting the heat-resistant layer B.

5. The polyester sealant film according to claim 1, wherein the difference between the amount of components other than ethylene terephthalate constituting the heat seal layer A and the amount of components other than ethylene terephthalate constituting the heat-resistant layer B is 19.0 mol% or more and 28.0 mol% or less.

6. The polyester sealant film according to claim 1, wherein, as components other than ethylene terephthalate constituting the heat seal layer A and the heat-resistant layer B, the diol component comprises one or more selected from the group consisting of neopentyl glycol, 1,4-cyclohexanedimethanol, diethylene glycol, 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, 1,4-butanediol, and hexanediol.

7. The polyester sealant film according to claim 1, wherein the diol component constituting the heat seal layer A comprises 54 to 66 mol% ethylene glycol, 0 to 21 mol% neopentyl glycol, 10 to 25 mol% 1,4-butanediol, 0 to 6 mol% diethylene glycol, and 0 to 8 mol% 1,4-cyclohexanedimethanol, based on 100 mol% of the diol component.

8. The polyester sealant film according to claim 1, wherein the diol component constituting the heat-resistant layer B comprises 70 to 87 mol% ethylene glycol, 0 to 12 mol% neopentyl glycol, 5 to 13 mol% 1,4-butanediol, 0 to 4 mol% diethylene glycol, and 0 to 5 mol% 1,4-cyclohexanedimethanol, based on 100 mol% of the diol component.

9. The polyester sealant film according to claim 1, wherein one or both of the heat seal layer A and the heat-resistant layer B further contain fine particles, and the amount of fine particles is 100 to 2000 ppm relative to the entire heat seal layer A or the entire heat-resistant layer B.

10. The polyester-based sealant film according to claim 1, which is a biaxially oriented film.

11. The polyester sealant film according to claim 1, wherein the overall thickness of the film is 5 μm or more and 19 μm or less.

12. The heat capacity ΔHm for crystalline fusion is 30 mJ / cm². 2 The polyester sealant film according to claim 1, which is as follows:

13. The polyester sealant film according to claim 1, wherein the degree of surface orientation ΔP of the surface of the heat seal layer A is 0.010 or more and 0.065 or less.

14. The polyester sealant film according to claim 1, wherein the folding and holding angle is 20 degrees or more and 70 degrees or less.

15. A packaging body characterized in that at least a portion of it is made of the polyester sealant film described in any one of claims 1 to 14.

Images