Stretched multilayer film and packaging bag made therefrom

Abstract

To provide a stretched multilayer film that has at least one of a PET layer and a PBT layer, and has mechanical strength such as impact resistance and heat resistance, in which a heat-sealable resin layer is simultaneously laminated by co-extrusion, and both excellent heat resistance and toughness of the PET and the PBT are effectively exhibited.SOLUTION: A stretched multilayer film has one or more layers of a PBT layer and a PET layer, and has a heat-sealable resin layer on one outermost surface, in which the total content of a copolymerization component of the PBT is 8 mol% or less, the total content of a copolymerization component of the PET is 5 mol% or less, and each of the PBT layer, the PET layer and the heat-sealable resin layer are laminated without using an adhesive.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a stretched multilayer film excellent in mechanical strength and heat resistance, and a packaging bag made of this stretched multilayer film. More specifically, the present invention relates to a stretched multilayer film having a heat-sealing resin layer together with a layer made of polyethylene terephthalate and a layer made of polybutylene terephthalate, and a packaging bag made of this stretched multilayer film.

Background Art

[0002] Packaging bags containing food and drink products as contents are formed from multilayer films (laminates) formed by laminating layers made of various materials in order to satisfy necessary properties such as heat resistance capable of withstanding heat sterilization such as boiling sterilization and retort sterilization, or heat cooking such as simmering and microwave heating, impact resistance capable of withstanding dropping impacts, or barrier properties. For example, in Patent Document 1 below, in order to prevent perforation by microwave heating, a packaging bag made of a laminate composed of a biaxially stretched polyethylene terephthalate (hereinafter sometimes referred to as "PET") - based film, a polybutylene terephthalate (hereinafter sometimes referred to as "PBT") - based film, and a heat - adhesive resin layer in that order from the outer surface is proposed.

[0003] Further, in Patent Document 2 below, a laminate in which a base material layer, a barrier layer, and a sealant layer are sequentially laminated is described. The base material layer is composed of a biaxially stretched multilayer film in which a layer containing at least two types of polyester - based resin layers is directly laminated, and a laminate containing at least one PET layer, at least one PBT layer, and a sealant layer, and in which the PET layer and the PBT layer are laminated adjacent to each other is described.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] In the invention described in Patent Document 1 above, a laminate with excellent heat resistance and toughness, mainly composed of PET film and PBT film, is used. However, because the biaxially oriented film is laminated via an adhesive layer, two lamination processes are required to form a three-layer laminate including a heat-adhesive resin layer, resulting in poor productivity and economic efficiency. Furthermore, increasing the number of adhesive layers increases the amount of adhesive used, raising concerns not only about productivity and economic efficiency but also about the impact on the flavor of the contents.

[0006] Furthermore, the above-mentioned Patent Document 2 involves laminating PET and PBT by co-extrusion using a T-die method or inflation method, then creating a biaxially oriented multilayer film by biaxial stretching using a tubular method or tenter method, and finally bonding a sealant layer. Therefore, similar to the above-mentioned Patent Document 1, a lamination process using an adhesive is required, and thus it is not yet fully satisfactory in terms of productivity, economy, and the impact of flavor on the contents. Furthermore, commercially available PBT and PET generally contain copolymer components to obtain the desired physical properties. However, depending on the content of these copolymer components, the heat resistance and toughness expected of a stretched multilayer film in which the PBT and PET layers are adjacent may be impaired.

[0007] Accordingly, the object of the present invention is to provide a stretched multilayer film having mechanical strength such as impact resistance and heat resistance, comprising at least one PET layer and one PBT layer, wherein a heat-sealable resin layer is simultaneously laminated by co-extrusion, and both the excellent heat resistance and toughness of PET and PBT are effectively expressed. Another object of the present invention is to provide a method for efficiently producing a stretched multilayer film having mechanical strength and toughness, such as impact resistance, comprising at least one PET layer, at least one PBT layer, and a heat-sealable resin layer, with a small number of laminations. [Means for solving the problem]

[0008] According to the present invention, a stretched multilayer film having one or more PBT layers made of polybutylene terephthalate and one or more PET layers made of polyethylene terephthalate, and having a heat-sealable resin layer on one of the outermost surfaces, wherein the copolymer component of the polybutylene terephthalate isophthalic acid The total content is 8 mol% or less, and the polyethylene terephthalate Isophthalic acid and / or diethylene glycol are copolymer components of the same. A stretched multilayer film is provided, characterized in that the total content is 5 mol% or less, and each layer of the PBT layer, the PET layer, and the heat-sealable resin layer is laminated without the use of an adhesive.

[0009] In the stretched multilayer film of the present invention, 1. The polybutylene terephthalate is homopolybutylene terephthalate. 2. The polyethylene terephthalate is homopolyethylene terephthalate. 3. It has at least one functional resin layer. 4. The PET layer and / or the PBT layer contains a functional resin. 5. The functional resin consists of a resin or resin composition having one or more functions among gas barrier properties, easy tearing, oxygen absorption, UV barrier properties, visible light barrier properties, and rigidity. 6. The PET layer and / or the PBT layer contains at least one of the following: a reproductive resin, a recycled polyester resin, or a biomass polyester resin. 7. The heat-sealable resin is a polytetramethylene glycol-modified polyester resin or an acid-modified olefin resin. 8. The total thickness of the PBT layers is within the range of 25-45% of the total thickness of all layers of the stretched multilayer film. 9. The puncture strength per unit thickness must be greater than 400 N / mm. This is preferable.

[0010] The present invention also provides a packaging bag characterized by being made of the stretched multilayer film described above. The present invention further provides a method for manufacturing a stretched multilayer film, characterized by laminating a PBT layer made of polybutylene terephthalate, a PET layer made of polyethylene terephthalate, and a heat-sealable resin layer by co-extrusion to form a multilayer film, and then stretching the multilayer film by simultaneous biaxial stretching or sequential biaxial stretching using the tenter method. [Effects of the Invention]

[0011] The stretched multilayer film of the present invention has one or more PBT layers and one or more PET layers, and a heat-sealable resin layer on one of the outermost surfaces, thereby combining the toughness of PBT and the heat resistance and barrier properties of PET with heat-sealability. Furthermore, by co-extruding the heat-sealable resin layer simultaneously with the lamination of the PBT and PET layers, it becomes possible to incorporate the heat-sealable resin layer, which was conventionally laminated after the molding of the stretched film, without going through a lamination process, resulting in superior productivity and cost-effectiveness. In the stretched multilayer film of the present invention, by stretching a multilayer film co-extruded using PBT and PET in which the copolymer component is less than or equal to the above value, the mechanical strength, such as puncture resistance and impact resistance based on the PBT layer, and the heat resistance and barrier properties based on the PET layer are significantly improved compared to a stretched film using PBT and / or PET that contains more copolymer component than the above value. Furthermore, as is evident from the results of Examples 1 and 2 described later, by using PET with a reduced copolymer component, it is possible to obtain a synergistic effect that further improves not only heat resistance but also puncture resistance. Furthermore, because PBT, PET, and heat-sealable resins are laminated by co-extrusion, the amount of adhesive used is reduced, and it also has excellent flavor resistance.

[0012] Furthermore, in the method for manufacturing stretched multilayer films of the present invention, by laminating PBT and PET with a heat-sealable resin by co-extrusion, it is possible to improve economic efficiency and productivity by reducing the number of laminations and the amount of adhesive used. [Modes for carrying out the invention]

[0013] (Stretched multilayer film) A key feature of the stretched multilayer film of the present invention is that a PBT layer made of PBT with a total copolymer content of 8 mol% or less, a PET layer made of PET with a total copolymer content of 5 mol% or less, and a heat-sealable resin layer are laminated without an adhesive layer. As a result, a stretched multilayer film having a heat-sealable resin layer can be obtained without going through a lamination process, resulting in excellent productivity and cost-effectiveness. Furthermore, it can adequately possess mechanical strength (toughness) such as puncture resistance and impact resistance based on the PBT layer, and heat resistance and barrier properties based on the PET layer, and in particular, it has excellent mechanical strength with a puncture strength of 400 N / mm or more per unit thickness, especially 500 N / mm or more. In other words, if the copolymer components of PBT and PET are greater than the above values, the orientation crystallinity of PBT and PET decreases, so not only do physical properties such as puncture strength and heat resistance that improve with stretching not improve sufficiently, but the stretching stability also decreases. The method for measuring the puncture strength per unit thickness will be described later. Also, as is clear from the results of the embodiments described later, in the stretched multilayer film of the present invention, in dynamic viscoelasticity measurement (also called DMS or DMA), the tanδ peak value is 0.27 or less, and the peak temperature (maximum temperature) of tanδ at the peak value is in the range of 115°C or higher. Tanδ is a parameter called loss tangent, which is expressed as the ratio of loss elastic modulus / storage elastic modulus. The loss elastic modulus is the loss caused by the amorphous part, and the storage elastic modulus is the elastic modulus caused by the crystal part. The smaller the peak value of tanδ, the more crystal parts exist, and the higher the peak temperature indicating this peak value, the higher the glass transition point. In the stretched multilayer film of the present invention, the peak value of tanδ is small and its peak temperature is high, having excellent heat resistance.

[0014] In addition, since the multilayer film in which the PBT layer and the PET layer are laminated without an adhesive layer by coextrusion lamination is stretched, the interfacial adhesion strength between the PBT layer and the PET layer becomes strong. As a result, it becomes possible to exhibit excellent puncture resistance and heat resistance compared to the stretched multilayer film obtained by laminating the stretched PBT film and the stretched PET film. Furthermore, in addition to the heat-sealing resin layer, it is possible to have a PET layer and a resin layer that can be laminated by coextrusion with the PET layer. In particular, by having the functional resin layer described later, various functions can be imparted to the stretched multilayer film.

[0015] [PBT layer and PET layer] In the present invention, both the PBT layer and the PET layer can be layers serving as the base material of the stretched multilayer film. The PBT layer improves the impact resistance and puncture resistance of the film, and the PET layer improves the heat resistance and barrier properties of the film. The polybutylene terephthalate constituting the PBT layer preferably has as little copolymer component as possible, and is preferably 8 mol% or less, particularly preferably homopolybutylene terephthalate with a copolymer component of 0 mol%. PBT has terephthalic acid as the dicarboxylic acid component and 1,4-butanediol as the main alcohol component, and it is important that the copolymer component is 8 mol% or less (in this specification, including the butylene terephthalate copolymer containing the copolymer component, it is referred to as polybutylene terephthalate (PBT)).

[0016] Also, for polyethylene terephthalate constituting the PET layer, it is preferable that the copolymer component is as small as possible, and it is important that it is 5 mol% or less (in this specification, including the ethylene terephthalate copolymer containing the copolymer component, it is referred to as polyethylene terephthalate (PET)). In the case of PET, since diethylene glycol is inevitably generated and contained by dimerization of ethylene glycol as a side reaction during the synthesis of PET, when the copolymer component excluding the unavoidably contained copolymer component is zero, it is defined as homopolyethylene terephthalate. Also, PBT and / or PET may be a blend of two or more of the above homopolyesters and copolyester as long as the amount of the copolymer component is below the above value.

[0017] Examples of the dicarboxylic acid component (copolymer component) other than the terephthalic acid component of PBT and PET include isophthalic acid, naphthalenedicarboxylic acid, p-β-oxyethoxybenzoic acid, biphenyl-4,4'-dicarboxylic acid, diphenoxyethane-4,4'-dicarboxylic acid, 5-sodium sulfoisophthalic acid, hexahydroterephthalic acid, adipic acid, sebacic acid, trimellitic acid, pyromellitic acid, etc. On the other hand, examples of the alcohol component (copolymer component) other than ethylene glycol and 1,4-butanediol include propylene glycol, neopentyl glycol, 1,6-hexylene glycol, diethylene glycol, triethylene glycol, cyclohexanedimethanol, bisphenol A ethylene oxide adduct, glycerol, trimethylolpropane, pentaerythritol, dipentaerythritol, sorbitan and other alcohol components.

[0018] PBT and PET should have a molecular weight that allows for film formation, and from the viewpoint of mechanical strength, it is preferable that the intrinsic viscosity measured using a phenol / tetrachloroethane mixed solvent is 0.5 dL / g or higher, particularly in the range of 0.55 to 1.20 dL / g. Other resins, such as functional resins described later, may be blended into the PBT layer and PET layer, provided that they do not impair the functions of the PBT layer and PET layer as described above. However, they may be blended in an amount of 50% by mass or less of the PBT layer or PET layer. Furthermore, conventionally known resin compounding agents such as lubricants, antiblocking agents, fillers, antioxidants, colorants, and antistatic agents can be incorporated into the PBT layer and PET layer in known formulations.

[0019] The thickness of the PBT layer before stretching is preferably in the range of 25 to 500 μm, particularly 50 to 200 μm, from the viewpoint of impact resistance, etc., and when multiple PBT layers are provided, it is desirable that the total thickness be within the above range. If the thickness of the PBT layer is thinner than the above range, it will be inferior in terms of impact resistance, puncture resistance, crack resistance, etc., compared to when it is within the above range, while if it is thicker than the above range, it will be inferior in terms of tear resistance and cost-effectiveness compared to when it is within the above range. Furthermore, the thickness of the PET layer before stretching is preferably in the range of 25 to 500 μm, particularly 50 to 200 μm, from the viewpoint of heat resistance, barrier properties, etc., and when multiple PET layers are provided, it is desirable that the total thickness be within the above range. If the thickness of the PET layer is thinner than the above range, the heat resistance and barrier properties will be inferior compared to when it is within the above range, while if it is thicker than the above range, the tear resistance and cost-effectiveness will be inferior compared to when it is within the above range.

[0020] [Heat-sealable resin] The resin constituting the heat-sealable resin layer can be used without limitation as long as it is a heat-sealable resin that can co-extrude PBT and PET. For example, although not limited to these, suitable heat-sealable polyester resins and acid-modified olefin resins can be used, such as amorphous polyesters like PETG, low-melting-point polyester resins like ethylene terephthalate / isophthalate copolymers, polyester resins made by blending high-glass transition temperature (Tg) polyester resins and low-glass transition temperature (Tg) polyester resins, and polyester-based thermoplastic elastomers such as polytetramethylene glycol-modified polybutylene terephthalate (PBT-PTMG). Among these, PBT-PTMG or acid-modified olefin resins can be used because they do not significantly reduce heat sealability due to stretching. Furthermore, the thickness of the heat-sealable resin layer before stretching is preferably in the range of 25 to 1000 μm, particularly 50 to 500 μm, taking into account the thinning caused by stretching.

[0021] [Functional resin layer] The stretched multilayer film of the present invention may comprise layers made of various functional resins other than heat-sealable resins, as long as they are co-extrudeable with PBT and PET. Examples of such functional resin layers include, but are not limited to, gas barrier resin layers, easily tearable resin layers, oxygen-absorbing resin layers, UV barrier resin layers, visible light barrier resin layers, rigid resin layers, impact-resistant resin layers, chemical-resistant layers, puncture-resistant layers, and heat-resistant layers. However, in the present invention, it is preferable that the functional resin layer be at least one of the following: gas barrier resin layer, easily tearable resin layer, oxygen-absorbing resin layer, UV barrier resin layer, visible light barrier resin layer, or rigid resin layer. Furthermore, the functional resin layer is preferably made of a functional resin based on the polyester resin described for the PBT layer and PET layer, and recycled polyester and biomass polyester can also be used, as will be described later. The polyester resin that forms the base of the functional resin should, like the PBT and PET mentioned above, have a molecular weight that allows for film formation, and preferably has an intrinsic viscosity within the above range.

[0022] <Gas barrier resin layer> The resins constituting the gas barrier resin layer are not limited to those listed above, but examples include polymetaxylylene adipamide (nylon MXD6) obtained from the polycondensation reaction of metaxylylenediamine and adipic acid, polyvinyl alcohol (PVOH), ethylene-vinyl alcohol copolymer (EVOH), vinylidene chloride copolymer (PVDC), acrylonitrile copolymer (PAN), and polyglycolic acid (PGA). Furthermore, two or more of the above gas barrier resins may be blended. The thickness of the gas barrier resin layer before stretching is preferably in the range of 5 to 500 μm, and particularly 10 to 100 μm. If the thickness of the gas barrier resin layer is thinner than the above range, sufficient gas barrier properties cannot be obtained compared to when it is within the above range. On the other hand, if it is thicker than the above range, there is a risk of impairing the functions of the PBT layer and PET layer, and it will also be less economical.

[0023] <Easily tearable resin layer> The resin constituting the easily tearable resin layer is not limited to this, but any polyester resin composition having linear tearing properties can be suitably used, such as a blend of polybutylene terephthalate and polyethylene terephthalate containing polytetramethylene glycol units, or a blend of polyethylene terephthalate and polyester elastomer, in which the polyester elastomer is dispersed in the polyethylene terephthalate. The thickness of the easily tearable resin layer before stretching is preferably in the range of 5 to 500 μm, and particularly 10 to 100 μm. If the thickness of the easily tearable resin layer is thinner than the above range, sufficient tearability cannot be obtained compared to when it is within the above range, while if it is thicker than the above range, the tearability may actually decrease.

[0024] <Oxygen-absorbing resin layer> As the resin composition constituting the oxygen-absorbing resin layer, a conventionally known oxygen-absorbing resin composition containing an oxidizing organic component and a transition metal-based catalyst with a polyester resin that can be used in the PBT layer and the PET layer, the above gas barrier resin, etc. as a matrix resin can be used. Examples of the oxidizing organic component include, but are not limited to, polymers containing an ethylenically unsaturated group, and particularly, polymers derived from polyene monomers, such as homopolymers of polyene, random copolymers or block copolymers obtained by combining two or more polyenes or combining polyene with other monomers, can be used as the oxidizing organic component. The polyene-based polymer is preferably an acid-modified polyene polymer into which a carboxylic acid group, a carboxylic anhydride group, or a hydroxyl group is introduced.

[0025] The oxidizing organic component is preferably contained in the oxygen-absorbing resin composition at a ratio of 0.01 to 10% by mass. As the transition metal-based catalyst, metals of Group VIII of the periodic table such as iron, cobalt, and nickel are suitable, but other metals such as Group I metals like copper and silver, Group IV metals like tin, titanium, and zirconium, Group V metals like vanadium, Group VI metals like chromium, and Group VII metals like manganese may also be used. The transition metal-based catalyst is generally used in the form of inorganic salts, organic salts, or complex salts of the above transition metals with a lower valence. The transition metal-based catalyst is preferably in the range of 100 to 3000 ppm in terms of the concentration of transition metal atoms (weight concentration basis) in the oxygen-absorbing resin composition. The thickness of the oxygen-absorbing resin layer before stretching is preferably in the range of 5 to 500 μm, particularly 10 to 100 μm. If the thickness of the oxygen-absorbing resin layer is thinner than the above range, sufficient oxygen absorption cannot be obtained compared to the case within the above range, while if it is thicker than the above range, the economy deteriorates.

[0026] ]> {This line seems to be incomplete or incorrect in the original. The translation is left as is for now.}<UV Barrier Resin Layer> As the resin constituting the UV barrier resin layer, polyethylene naphthalate, polybutylene naphthalate, etc. containing 2,6-naphthalenedicarboxylic acid as the dicarboxylic acid in the above-mentioned polyester resin can be used. The thickness of the UV barrier resin layer before stretching is preferably in the range of 5 to 500 μm, and particularly 10 to 100 μm.

[0027] <Visible light barrier resin layer> As the resin composition constituting the visible light barrier resin layer, a resin composition in which a white pigment such as titanium dioxide is added to the polyester resin described above can be used. The thickness of the visible light barrier resin layer before stretching is preferably in the range of 5 to 500 μm, and particularly 10 to 100 μm.

[0028] <Rigid resin layer> The stretched multilayer film of the present invention has layers made of PBT and PET, and therefore has excellent rigidity on its own, but it can also be further equipped with a rigid resin layer. As the resin composition constituting such a rigid resin layer, a resin composition in which an inorganic filler is added to the polyester resin described above can be used. Examples of inorganic fillers include layered silicate minerals such as kaolinite, pyrophyllite, talc, smectite (montmorillonite, beiderite, hectorite, saponite, souconite, stivunsite), and mica (muscovite, sericite). In particular, mica mainly composed of talc, muscovite, and sericite can be suitably used. Furthermore, it is particularly preferable that this resin composition be a nanocomposite in which the above-mentioned inorganic filler is dispersed on the nano-order in a continuous phase. This allows for dense strain hardening due to localized overstretching during stretching, making it possible to obtain an excellent stretch balance. The thickness of the rigid resin layer before stretching is preferably in the range of 5 to 500 μm, and particularly 10 to 100 μm.

[0029] <Other layers> In addition to the above, functional resin layers can also be made from recycled resin, recycled polyester resin, or biomass polyester. By having these layers, the stretched multilayer film can be given the function of being highly environmentally friendly. The recycled resin is a resin obtained by pulverizing and reducing resins and films discharged in the process of creating the stretched multilayer film of the present invention, and is a resin mainly composed of PBT or PET. The recycled resin may also contain virgin polyester. Examples of recycled polyester resin include polyester recycled through mechanical recycling, which is generally polyester obtained by crushing and purifying collected polyester bottles. This polyester typically contains ethylene glycol as an alcohol component and terephthalic acid and isophthalic acid as carboxylic acid components. The recycled polyester resin may contain virgin polyester along with the recycled polyester.

[0030] Examples of biomass polyesters include those made using ethylene glycol derived from biomass ethanol produced from raw materials such as sugarcane and corn as the diol component, and the aforementioned fossil fuel-derived dicarboxylic acid as the dicarboxylic acid component. Biomass polyester may also contain virgin polyester along with the biomass polyester.

[0031] [Layer composition] The layer configuration of the stretched multilayer film of the present invention is not particularly limited, except that the heat-sealable resin layer is located on one surface of the film. However, if the functional resin layer described above is included, it is preferable that it be located as an intermediate layer. Specifically, examples include PET layer / PBT layer / heat-sealable resin layer, PBT layer / PET layer / heat-sealable resin layer, PET layer / functional resin layer / PBT layer / heat-sealable resin layer, PBT layer / functional resin layer / PET layer / heat-sealable resin layer, PET layer / PBT layer / functional resin layer / heat-sealable resin layer, PET layer / functional resin layer A / PBT layer / functional resin layer B / heat-sealable resin layer, etc.

[0032] (Manufacturing method for stretched multilayer film) The stretched multilayer film of the present invention is manufactured in advance by co-extrusion lamination using PBT and PET in which the content of the copolymer components described above is reduced as much as possible, a heat-sealable resin that can be co-extruded with PBT and PET, and, if necessary, the functional resin described above. The production of multilayer films by co-extrusion can be carried out by conventionally known methods, using extruders corresponding to the type of resin layer, layering the molten materials of each resin in a multilayer die, and extruding them through the die orifice. A multilayer cast film is prepared in advance using the T-die method, inflation method, etc. When co-extruded films are produced using the T-die method, stretching is performed using the tenter method. That is, the multilayer film co-extruded from a T-type multilayer die is taken up to a cast roll, then stretched in the longitudinal direction (MD) by a tenter or stretching roll, stretched in the transverse direction (TD) using a tenter as needed, and then heat-set as needed. Stretching may be uniaxial or biaxial, but biaxial stretching is preferred. In the case of biaxial stretching, in addition to sequential biaxial stretching in the MD and TD directions, biaxial stretching in the MD and TD directions may also be performed simultaneously using a tenter. On the other hand, when co-extruded films are produced by the inflation method, stretching is performed using the tubular method. That is, a multilayer parison co-extruded from a circular multilayer die is cooled, then the parison is heated to the stretching temperature and inflated, and then heat-set as needed. The resulting tubular film can be folded into a flat film as needed, or slit and wound into a roll.

[0033] In this invention, since the occurrence of film curling is suppressed even when stretched by the tenter method, it is preferable to manufacture stretched multilayer films using the T-die method and the tenter method. By creating stretched multilayer films using the T-die method and the tenter method, it becomes possible to stably manufacture films with less thickness variation, wide width, thinness, and no curling at high speed. The stretching ratio is preferably 2 to 10 times, particularly 2 to 5 times, in the case of uniaxial stretching, and preferably 2 to 10 times, particularly 2 to 5 times, in the case of biaxial stretching, in both the MD direction and the TD direction.

[0034] (Laminated structure) In the present invention, a stretched multilayer film obtained through the co-extrusion and stretching processes described above can be further laminated with other layers to form a laminate. Other layers that can be laminated as needed include layers made of resins that cannot be laminated with PBT and PET by co-extrusion and have poor adhesion to them, vapor-deposited layers or coating layers, gas barrier films separately equipped with these, printed layers or topcoat layers to protect printed layers. Examples of methods for laminating such layers include conventionally known dry lamination methods, extrusion coating methods, and fusion methods, which can be appropriately selected depending on the type of layer to be laminated.

[0035] (packaging bag) The packaging bag of the present invention is manufactured by overlapping the heat-sealable resin layers of the stretched multilayer film described above so that their inner surfaces are facing each other, and then heat-sealing them. The shape of the packaging bag is not restricted, and various shapes such as pillow-type pouches, gusset-type pouches, and standing pouches can be used. In the packaging bag of the present invention, when forming a printing layer and a topcoat layer on the outer surface of the stretched multilayer film (the surface opposite the heat-sealable resin layer), it is preferable to form the printing layer and topcoat layer on the stretched multilayer film; however, the packaging bag may be made first, and the printing layer and topcoat layer may be formed on the outer surface of this packaging bag. [Examples]

[0036] (Method for producing stretched film) 1.Material Three types of polyethylene terephthalate resins (PET1, PET2, PET3) are used as the constituent resins of the base layer. • PET1 (IV=0.84, isophthalic acid 1.7 mol%, diethylene glycol 2.2 mol%) • PET2 (IV=0.80, diethylene glycol 1.6 mol%) • PET3 (IV=0.90, isophthalic acid 15 mol%, diethylene glycol 3.6 mol%) and polybutylene terephthalate resin (PBT1,2,3) • PBT1 (IV=1.14, homozygous PBT) • PBT2 (PBT1:PBT3=3:1 blend, 7.5 mol% isophthalic acid) PBT3 (IV=1.00, isophthalic acid 30 mol%) These materials were used for various molding processes. Each resin was dried before molding.

[0037] The following resins were used as heat-sealable resins. PBT-PTMG (melting point 170°C, glass transition temperature -50°C, weight-average molecular weight 1.6 × 10⁻⁶) 5 )

[0038] 2. Molding (1) Forming of cast film A three-layer co-extruded cast film was produced using a laboplast mill (manufactured by Toyo Seiki Seisakusho Co., Ltd.) equipped with a multi-layer T-die. This equipment combined resins extruded from the first, second, and third extruders using a feed-block type T-die, producing three types of three-layer films laminated in the order of first / second / third. The T-die temperature was set to 280°C for all layers, and the extruder temperature was varied depending on the supplied resin. The thickness of the entire layer and each layer was adjusted by changing the extruder rotation speed and the take-up speed of the attached film take-up machine.

[0039] (2) Forming of stretched film The aforementioned cast film was used as the raw material before stretching, and was biaxially stretched and molded using a biaxial stretching test apparatus (x6H-S: Toyo Seiki Mfg. Co., Ltd.) to form a stretched film.

[0040] (Methods for evaluating film) (1) Measuring the thickness of the film The film thickness was measured using a dial gauge conforming to JIS B 7503 (1997). The average value was taken from a sample size of n=5. (2) Measurement of the layer ratio of the cast film Thin sections were cut from the cross-section of the cast film using a microtome, observed with a transmission polarized light microscope, and the thickness of each layer was measured. (3) Measurement of puncture strength of stretched film The puncture strength of the stretched film was measured in accordance with JIS Z1707 (1997). The puncture speed was set to 50 mm / min. The average value was taken from n=5 measurements. The puncture strength per unit thickness (puncture strength / total thickness) was calculated by dividing this measured puncture strength by the total thickness of the stretched film layers. Furthermore, the puncture strength per unit thickness of the PBT layer (puncture strength / PBT layer thickness) was calculated by dividing this measured puncture strength by the total thickness of the PBT layer in the stretched multilayer film. (4) Measurement of the dynamic viscoelasticity (tanδ) of stretched film A 10mm x 30mm test piece was cut from the stretched film, and measurements were taken using a viscoelastic spectrometer (EXSTAR6000DMS: Seiko Instruments Inc.). The measurement conditions are as follows. Measurement mode: Pulled sine wave mode specimen gauge length: 5 mm Frequency: 1Hz Minimum tension: 50mN Temperature rise profile: Temperature rises from 25°C to 200°C at a rate of 2°C / min. From the obtained tanδ curve, the temperature at which tanδ is maximized (tanδ maximum temperature) was calculated.

[0041] (Example 1) Following the molding method for the two types of three-layer cast film described above, PET1 was supplied to the first extruder (set temperature 280°C), PBT1 to the second extruder (set temperature 250°C), and a dry blend of PBT-PTMG / PBT1 = 8 / 2 (by weight ratio) was supplied to the third extruder (set temperature 250°C) to form a cast film with a three-layer structure of PET1 / PBT1 / PBT-PTMG. The total thickness of this film was 200 μm, and the ratio of the thicknesses of each layer was PET1 / PBT1 / PTMG-PBT = 70 / 70 / 50. Using this cast film as the raw material before stretching, a stretched film was formed according to the stretched film forming method described above. The stretching conditions were a pre-stretching heating temperature of 90°C, a stretching ratio of 3.0 times in both the longitudinal and transverse axes, and a simultaneous biaxial stretching method at an axial speed of 10 m / min. After stretching, a heat-setting treatment was performed at 190°C for 120 seconds. The total thickness of this film was 27 μm. The various evaluation results are shown in Tables 1 and 2.

[0042] (Example 2) In Example 1, a cast film with a three-layer structure of PET2 / PBT1 / PBT-PTMG was formed in the same manner as in Example 1, except that PET2 was used instead of PET1. Using this cast film as the raw material before stretching, a stretched film was prepared in the same manner as in Example 1. The total thickness of this film was 27 μm. The various evaluation results are shown in Tables 1 and 2.

[0043] (Example 3) In Example 1, a cast film consisting of three layers of PET2 / PBT2 / PBT-PTMG was molded in the same manner as in Example 1, except that PET2 was used instead of PET1 and PBT2 (a blend of PBT1:PBT2 = 3:1) was used instead of PBT1. Using this cast film as the raw material before stretching, a stretched film was prepared in the same manner as in Example 1. The total thickness of this film was 27 μm. The various evaluation results are shown in Tables 1 and 2.

[0044] (Comparative Example 1) In Example 1, a cast film with a three-layer structure of PET1 / PBT3 / PBT-PTMG was formed in the same manner as in Example 1, except that PBT3 was used instead of PBT1. Using this cast film as the raw material before stretching, a stretched film was prepared in the same manner as in Example 1. The total thickness of this film was 27 μm. The various evaluation results are shown in Tables 1 and 2.

[0045] (Comparative Example 2) In Example 1, a cast film with a three-layer structure of PET3 / PBT1 / PBT-PTMG was molded in the same manner as in Example 1, except that PET3 was used instead of PET1. Using this cast film as the raw material before stretching, a stretched film was prepared in the same manner as in Example 1. The total thickness of this film was 27 μm. The various evaluation results are shown in Tables 1 and 2.

[0046] [Table 1]

[0047] [Table 2] [Industrial applicability]

[0048] The stretched multilayer film of the present invention is excellent in mechanical strength such as impact resistance, as well as heat resistance and barrier properties. Furthermore, because it requires fewer laminations and less adhesive, it is highly productive and economical, and can be used for various contents applications. In particular, its excellent flavor makes it suitable for food applications.

Claims

1. A stretched multilayer film having one or more PBT layers made of polybutylene terephthalate and one or more PET layers made of polyethylene terephthalate, and having a heat-sealable resin layer on one of its outermost surfaces, The total content of isophthalic acid, which is a copolymer component of the polybutylene terephthalate, is 8 mol% or less, and the total content of isophthalic acid and / or diethylene glycol, which are copolymer components of the polyethylene terephthalate, is 5 mol% or less. The PBT layer, the PET layer, and the heat-sealable resin layer are laminated without the use of an adhesive. The other surface of the stretched multilayer film has a PET layer (except when the layer structure of the stretched multilayer film consists of a PET layer made only of polyethylene terephthalate / a PBT layer made only of polybutylene terephthalate / a heat-sealable resin layer). A stretched multilayer film characterized in that the total thickness of the PBT layers is in the range of 25 to 45% of the total thickness of all layers of the stretched multilayer film, and the puncture strength per unit thickness of the total thickness of all layers of the stretched multilayer film is greater than 400 N / mm.

2. The stretched multilayer film according to claim 1, having at least one functional resin layer made of a functional resin.

3. The stretched multilayer film according to claim 1 or 2, wherein the PET layer and / or the PBT layer contains a functional resin.

4. The stretched multilayer film according to any one of claims 1 to 3, wherein the PET layer and / or the PBT layer contains at least one of a reproduct resin, a recycled polyester resin, and a biomass polyester resin.

5. The stretched multilayer film according to claim 1, wherein the layer configuration of the stretched multilayer film is a PET layer / PBT layer / functional resin layer using a remanufactured resin / heat-sealable resin layer.

6. The stretched multilayer film according to claim 1, wherein the layer structure of the stretched multilayer film is a PET layer / a PBT layer containing a reproduction resin / a heat-sealable resin layer.

7. The stretched multilayer film according to claim 1, wherein the layer structure of the stretched multilayer film is a PET layer / PBT layer / heat-sealable resin layer blended with virgin polyester resin and recycled polyester resin.

8. The stretched multilayer film according to claim 1, wherein the layer structure of the stretched multilayer film is a PET layer / PBT layer / functional resin layer made of a functional resin / heat-sealable resin layer.

9. The stretched multilayer film according to claim 1, wherein the layer structure of the stretched multilayer film is a PET layer / PBT layer / heat-sealable resin layer containing a functional resin.

10. The stretched multilayer film according to claim 1, wherein the layer structure of the stretched multilayer film is a PET layer containing virgin polyester resin / a PET layer containing recycled polyester resin / a PBT layer / a heat-sealable resin layer.

11. The stretched multilayer film according to any one of claims 3, 4, 9, or 10, wherein the functional resin is a resin or resin composition having one or more functions among gas barrier properties, tear resistance, oxygen absorption, UV barrier properties, visible light barrier properties, and rigidity.

12. The stretched multilayer film according to any one of claims 1 to 11, wherein the polybutylene terephthalate is homopolybutylene terephthalate.

13. The stretched multilayer film according to any one of claims 1 to 12, wherein the polyethylene terephthalate is homopolyethylene terephthalate.

14. The stretched multilayer film according to any one of claims 1 to 13, wherein the heat-sealable resin forming the heat-sealable resin layer is a polytetramethylene glycol-modified polyester resin or an acid-modified olefin resin.

15. A packaging bag characterized by being made of a stretched multilayer film according to any one of claims 1 to 14.

16. A method for manufacturing a stretched multilayer film, comprising laminating a PBT layer made of polybutylene terephthalate, a PET layer made of polyethylene terephthalate, and a heat-sealable resin layer by co-extrusion to form a multilayer film, and then stretching the multilayer film by simultaneous biaxial stretching or sequential biaxial stretching using the tenter method, The total content of isophthalic acid, which is a copolymer component of the polybutylene terephthalate, is 8 mol% or less, and the total content of isophthalic acid and / or diethylene glycol, which are copolymer components of the polyethylene terephthalate, is 5 mol% or less. The stretched multilayer film has a heat-sealable resin layer on one of its outermost surfaces and a PET layer on the other (except when the layer structure of the stretched multilayer film consists of a PET layer made only of polyethylene terephthalate / a PBT layer made only of polybutylene terephthalate / a heat-sealable resin layer). A method for manufacturing a stretched multilayer film, characterized in that the total thickness of the PBT layers is in the range of 25 to 45% of the total thickness of all layers of the stretched multilayer film, and the puncture strength per unit thickness of the total thickness of all layers of the stretched multilayer film is greater than 400 N / mm.

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