Stretched multilayer film and packaging bag composed of the same

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 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, 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 layer of the PBT layer and the PET layer are laminated without using an adhesive.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a stretched multilayer film having excellent 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 which has a layer made of polybutylene terephthalate having excellent toughness and a layer made of polyethylene terephthalate having excellent heat resistance, and which can be stably obtained by stretching using a tenter method, and a packaging bag made of this stretched multilayer film. [Background technology]

[0002] Packaging bags for food and beverages and other contents are made from multilayer films (laminates) made by laminating layers of various materials to meet required performance requirements, such as heat resistance for heat sterilization such as boiling or retort sterilization, or heat cooking such as heating in a hot water bath or in a microwave oven, impact resistance to withstand the impact of being dropped, and barrier properties. For example, Patent Document 1 below proposes a packaging bag made of a laminate consisting of, from the outside, a biaxially oriented polyethylene terephthalate (hereinafter sometimes referred to as "PET") film, a polybutylene terephthalate (hereinafter sometimes referred to as "PBT") film, and a heat-adhesive resin layer in order to prevent holes from being formed when heated in a microwave oven.

[0003] Furthermore, Patent Document 2 listed below describes a laminate material in which a base layer, a barrier layer, and a sealant layer are laminated in that order, characterized in that the base layer is composed of a biaxially oriented multilayer film in which layers containing at least two types of polyester-based resin layers are directly laminated, and the laminate material described includes at least one PET layer and at least one PBT layer, with the PET layer and the PBT layer being laminated adjacent to each other. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2006-143223 A [Patent Document 2] JP 2018-187819 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the invention described in the above Patent Document 1, a laminate having excellent heat resistance and toughness mainly composed of PET film and PBT film is used, but since the biaxially oriented film is laminated via an adhesive layer, two lamination steps are required to form a three-layer laminate including a heat-adhesive resin layer, which is inferior in productivity and economic efficiency. In addition, as the number of adhesive layers increases, the amount of adhesive used also increases, which not only causes problems in productivity and economy but also raises concerns about the effect on the flavor of the contents.

[0006] Furthermore, the above-mentioned Patent Document 2 describes that a biaxially oriented multilayer film can be produced by laminating PET and PBT by coextrusion using a T-die method or an inflation method, and then biaxially stretching the laminate using a tubular method, a tenter method, or the like. However, in co-extruded films in which a PBT layer and a PET layer are adjacent, the difference in crystallinity between PBT and PET causes the film to curl when stretched using the tenter method, making it impossible to obtain a flat film all the way to the edges. In addition, commercially available PBT and PET generally contain copolymer components to obtain desired physical properties, but depending on the content of these copolymer components, the heat resistance and toughness expected of a stretched multilayer film in which a PBT layer and a PET layer are adjacent may be impaired.

[0007] Therefore, an object of the present invention is to provide a stretched multilayer film which has at least one PET layer and one PBT layer and can effectively exhibit both the excellent heat resistance and toughness that PET and PBT have. Another object of the present invention is to provide a method for efficiently producing a stretched multilayer film having at least one PET layer and one PBT layer and having mechanical strength and toughness such as impact resistance with a small number of lamination steps, and for producing the stretched film by stretching using a tenter system without curling. [Means for solving the problem]

[0008] According to the present invention, there is provided a stretched multilayer film having one or more PBT layers made of polybutylene terephthalate and one or more PET layers made of polyethylene terephthalate, wherein the total content of copolymerization components of the polybutylene terephthalate is 8 mol% or less, the total content of copolymerization components of the polyethylene terephthalate is 5 mol% or less, and the PBT layers and PET layers are laminated without an adhesive.

[0009] In the stretched multilayer film of the present invention, 1. The polybutylene terephthalate is a homopolybutylene terephthalate; 2. The polyethylene terephthalate is a homopolyethylene terephthalate; 3. The laminated order of the PBT layer and the PET layer is symmetrical in the thickness direction of the film. 4. The multilayer structure is a PBT layer / PET layer / PBT layer or a PET layer / PBT layer / PET layer, and is a coextruded film; 5. Having at least one functional resin layer; 6. The PET layer and / or the PBT layer contains a functional resin; 7. The functional resin is made of a resin or a resin composition having one or more functions selected from the group consisting of gas barrier properties, easy tearing properties, oxygen absorption properties, UV barrier properties, visible light barrier properties, and rigidity; 8. The PET layer and / or the PBT layer contains at least one of a reproduced resin, a recycled polyester resin, and a biomass polyester resin; 9. The total thickness of the PBT layers is in the range of 40 to 60% of the total thickness of all layers of the stretched multilayer film; 10. The puncture strength per unit thickness is 600N / mm or more. is preferred.

[0010] The present invention also provides a laminate comprising the above-mentioned stretched multi-layer film and a sealant layer laminated thereon. In the laminate of the present invention, 1. The sealant layer is laminated without the use of an adhesive; 2. The sealant layer is made of a polytetramethylene glycol-modified polyester resin or an acid-modified olefin resin; is preferred. The present invention further provides a packaging bag comprising the above laminate.

[0011] The present invention still further provides a method for producing a stretched multilayer film, comprising laminating by coextrusion a PBT layer made of polybutylene terephthalate having a total content of copolymerization components of 8 mol% or less and a PET layer made of polyethylene terephthalate having a total content of copolymerization components of 5 mol% or less to form a multilayer film, and then stretching the multilayer film by simultaneous biaxial stretching or sequential biaxial stretching using a tenter method. Effect of the Invention

[0012] In the stretched multilayer film of the present invention, by stretching a multilayer film coextruded using PBT and PET having copolymerization components of the above-mentioned value or less, mechanical strengths such as puncture resistance and impact resistance based on the PBT layer and heat resistance and barrier properties based on the PET layer are significantly improved. This is also evident from the results of the examples described later, and the stretched multilayer film of the present invention has superior puncture resistance and heat resistance compared to a stretched multilayer film formed by bonding a stretched film made of PBT and a stretched film made of PET. Furthermore, as is clear from the results of Examples 1 and 2 described below, by using PET with a reduced amount of copolymerization components, it is possible to obtain a synergistic effect of further improving not only heat resistance but also puncture resistance. Furthermore, since the PBT and PET are laminated by coextrusion, the amount of adhesive used is reduced and the product also has excellent flavor resistance. In the stretched multilayer film of the present invention, by adopting a multilayer structure in which the lamination order is symmetrical in the thickness direction of the film, it is possible to provide a stretched multilayer film in which curling is effectively prevented even when stretched by a tenter system.

[0013] Furthermore, in the method for producing a stretched multilayer film of the present invention, it is possible to improve economy and productivity by reducing the number of laminations and the amount of adhesive used, and it also becomes possible to stretch a stretched multilayer film having at least one PBT layer and one PET layer, which has conventionally been produced by coextrusion using an inflation method and stretching using a tubular method, using a tenter method, thereby providing it as a flat membrane. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] (Stretched multi-layer film) The stretched multilayer film of the present invention has an important feature in that a PBT layer made of PBT with a total content of copolymerization components of 8 mol% or less and a PET layer made of PET with a total content of copolymerization components of 5 mol% or less are laminated without an adhesive layer. This allows the film to have mechanical strength (toughness) such as puncture resistance and impact resistance based on the PBT layer and heat resistance based on the PET layer, and has excellent mechanical strength, particularly a puncture strength per unit thickness of 600 N / mm or more, particularly 650 N / mm or more. The method for measuring the puncture strength per unit thickness will be described later. In other words, when the amount of the copolymerization components of PBT and PET is greater than the above-mentioned value, the oriented crystallinity of PBT and PET decreases, so that not only are physical properties such as puncture strength and heat resistance, which improve with stretching, not improved sufficiently, but the stability of stretching also decreases. As is clear from the results of the examples described later, in the stretched multilayer film of the present invention, in dynamic viscoelasticity measurement (also called DMS or DMA), the tan δ peak value is 0.27 or less, and the tan δ peak temperature at said peak value is in the range of 115°C or more. Tan δ is a parameter called loss tangent, and is expressed as the ratio of loss modulus / storage modulus, where the loss modulus is the loss due to the amorphous part, and the storage modulus is the modulus due to the crystalline part. The smaller the peak value of tan δ, the more crystalline parts are present, and the higher the peak temperature showing this peak value, the higher the glass transition point. In the stretched multilayer film of the present invention, the peak value of tan δ is small and the peak temperature is high, and the film has excellent heat resistance.

[0015] In addition, since the multilayer film in which the PBT layer and the PET layer are laminated by co-extrusion lamination without an adhesive layer is stretched, the interfacial adhesion strength between the PBT layer and the PET layer is strong, and as a result, it is possible to exhibit superior puncture resistance and heat resistance than a stretched multilayer film laminated with a stretched PBT film and a stretched PET film.

[0016] Furthermore, as described below, by adopting a layer structure that is symmetrical in the thickness direction, such as PET layer / PBT layer / PET layer, it is possible to adjust the stretching balance by offsetting the stress that occurs due to the difference in crystallinity between PBT and PET during stretching, and to produce a flat stretched multilayer film. Furthermore, by having a PET layer and a resin layer that can be laminated by coextrusion other than the PET layer, in particular by having a functional resin layer described later, it becomes possible to impart various functions to the stretched multilayer film.

[0017] [PBT layer and PET layer] In the present invention, both the PBT layer and the PET layer are layers that can serve as base materials for a 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 contains as little copolymerization component as possible, and is preferably a homopolybutylene terephthalate containing 8 mol % or less of copolymerization component, and more preferably 0 mol % of copolymerization component. It is important that PBT is composed mainly of terephthalic acid as a dicarboxylic acid component and 1,4-butanediol as an alcohol component, and that the copolymerization component is 8 mol % or less (in this specification, the term polybutylene terephthalate (PBT) also includes butylene terephthalate copolymers containing copolymerization components).

[0018] In addition, the polyethylene terephthalate constituting the PET layer also preferably contains as little copolymerization component as possible, and it is important that the content is 5 mol % or less (in this specification, ethylene terephthalate copolymers containing copolymerization components are also referred to as polyethylene terephthalate (PET)). Note that, in PET, diethylene glycol is inevitably produced and contained as a side reaction during the synthesis of PET due to the dimerization of ethylene glycol, so that a homopolyethylene terephthalate is defined as a material containing zero copolymerization components excluding the unavoidably contained copolymerization components. Furthermore, the PBT and / or PET may be a blend of two or more of the above homopolyesters and copolymer polyesters, so long as the amount of copolymerization component is equal to or less than the above value.

[0019] Examples of carboxylic acid components (copolymer components) 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, and pyromellitic acid. On the other hand, examples of alcohol components (copolymer components) other than ethylene glycol and 1,4-butanediol include alcohol components such as propylene glycol, neopentyl glycol, 1,6-hexylene glycol, diethylene glycol, triethylene glycol, cyclohexane dimethanol, bisphenol A ethylene oxide adduct, glycerol, trimethylolpropane, pentaerythritol, dipentaerythritol, and sorbitan.

[0020] PBT and PET should have a molecular weight that allows them to be formed into a film, and from the viewpoint of mechanical strength, it is preferable that the intrinsic viscosity measured using a phenol / tetrachloroethane mixed solvent as the solvent is 0.5 dL / g or more, particularly in the range of 0.55 to 1.20 dL / g. The PBT layer and the PET layer may contain other resins, such as the functional resins described below, within the scope of not impairing the above-mentioned functions of the PBT layer and the PET layer. Although not limited thereto, the resins may be contained in an amount of 50% by mass or less of the PBT layer or the PET layer. Furthermore, the PBT layer and the PET layer may contain conventionally known resin compounding agents such as lubricants, antiblocking agents, fillers, antioxidants, colorants, and antistatic agents in known formulations.

[0021] From the viewpoint of impact resistance, etc., the thickness of the PBT layer before stretching is preferably in the range of 25 to 500 μm, particularly 50 to 200 μm, and when a plurality of PBT layers are provided, it is desirable that the total thickness is in the above range. If the thickness of the PBT layer is thinner than the above range, the impact resistance, puncture resistance, crack resistance, etc. will be inferior compared to when it is in the above range, while if it is thicker than the above range, the tear resistance and economy will be inferior compared to when it is in the above range. From the viewpoints of heat resistance, barrier properties, etc., the thickness of the PET layer before stretching is preferably in the range of 25 to 500 μm, particularly 50 to 200 μm, and when a plurality of PET layers are provided, it is desirable that the total thickness is in 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 to those in the above range, while if the thickness is thicker than the above range, the tearability and economy will be inferior to those in the above range.

[0022] [Multilayer structure] In the stretched multilayer film of the present invention, the PBT layer and the PET layer are laminated without an adhesive layer between them, and this multilayer structure is made such that the lamination order of the PBT layer and the PET layer is symmetrical in the thickness direction of the film. As described above, this makes it possible to offset the stress caused by the difference in the ultimate crystallization density of the PBT and the PET, thereby adjusting the stretching balance, and effectively prevents curling of the stretched multilayer film.

[0023] In the stretched multilayer film of the present invention, the multilayer structure in which the lamination order of the PBT layer and the PET layer is symmetrical in the thickness direction of the film is not limited to the following, and specific examples include PBT layer / PET layer / PBT layer, PET layer / PBT layer / PET layer, PBT layer / PET layer / functional resin layer / PET layer / PBT layer, PET layer / PBT layer / functional resin layer / PBT layer / PET layer, PBT layer / functional resin layer A / PET layer / functional resin layer B / PET layer / functional resin layer A / PBT layer, PET layer / PBT layer / functional resin layer A / functional resin layer B / PBT layer / PET layer, and the like, and it is important that the PBT layer and the PET layer are each symmetrical with respect to the center in the thickness direction of the film.

[0024] In the stretched multilayer film of the present invention, the multilayer structure in which the stacking order of the PBT layer and the PET layer is symmetrical in the thickness direction of the film is preferably a multilayer structure in which not only the above-mentioned layer arrangement but also the thicknesses of the opposing layers in the symmetrical positions are similar. Specifically, when there is a difference in thickness between the opposing layers, it is desirable that the difference in thickness between the two layers is 50% or less, preferably 30% or less, more preferably 15% or less of the thickness of the thick layer. The total thickness of the PBT layers is preferably in the range of 40 to 60% of the thickness of the multilayer stretched film. If the total thickness of the PBT layers is thinner than the above range, the mechanical strength such as puncture resistance and impact resistance provided by the PBT layers is insufficient, while if the PBT layers are thicker than the above range, the thickness of the PET layers becomes thin, which may result in a decrease in heat resistance.

[0025] [Functional resin layer] The functional resin layer can be a layer made of various functional resins as long as it can be co-extruded with the PBT layer and the PET layer, and examples include, but are not limited to, a gas barrier resin layer, an easy-tear resin layer, an oxygen-absorbing resin layer, a UV barrier resin layer, a visible light barrier resin layer, a rigid resin layer, an impact-resistant resin layer, a chemical-resistant layer, a puncture-resistant layer, and a heat-resistant layer. In the present invention, it is preferable that the functional resin layer be at least one layer of a gas barrier resin layer, an easy-tear resin layer, an oxygen-absorbing resin layer, a UV barrier resin layer, a visible light barrier resin layer, and a rigid resin layer. The functional resin layer is preferably made of a functional resin having as its base resin the polyester resin described for the PBT layer and the PET layer, and recycled polyester or biomass polyester can also be used as described later. The polyester resin that is the base of the functional resin should also have a molecular weight that allows film formation, similar to the above-mentioned PBT and PET, and preferably has an intrinsic viscosity in the above-mentioned range.

[0026] <Gas barrier resin layer> Examples of the resin constituting the gas barrier resin layer include, but are not limited to, polymetaxylylene adipamide (nylon MXD6) obtained by polycondensation reaction of metaxylylene diamine and adipic acid, polyvinyl alcohol (PVOH), ethylene-vinyl alcohol copolymer (EVOH), vinylidene chloride copolymer (PVDC), acrylonitrile copolymer (PAN), polyglycolic acid (PGA), etc. 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, 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 the thickness is within the above range, while if the thickness is thicker than the above range, the functions of the PBT layer and PET layer may be impaired and the economic efficiency will be poor.

[0027] <Easily tearable resin layer> The resin constituting the easy-tear resin layer is not limited to the above, but polyester-based resin compositions having linear tearability, such as a blend of polybutylene terephthalate containing polytetramethylene glycol units and polyethylene terephthalate, or a blend of polyethylene terephthalate and a polyester elastomer in which the polyester elastomer is dispersed in the polyethylene terephthalate, can be suitably used. The thickness of the easy-tear resin layer before stretching is preferably in the range of 5 to 500 μm, particularly 10 to 100 μm. If the thickness of the easy-tear resin layer is thinner than the above range, sufficient tearability cannot be obtained compared to the case of the above range, while if the thickness is thicker than the above range, there is a risk that the tearability may decrease.

[0028] <Oxygen-absorbing resin layer> The resin composition constituting the oxygen-absorbing resin layer may be a conventionally known oxygen-absorbing resin composition that uses a polyester resin that can be used in PBT layers and PET layers or the above-mentioned gas barrier resin as a matrix resin, and contains an oxidizable organic component and a transition metal catalyst. The oxidizing organic component may be, but is not limited to, an ethylenically unsaturated group-containing polymer, and in particular may be derived from a polyene monomer, such as a homopolymer of a polyene, or a random copolymer or block copolymer obtained by combining two or more types of polyene or by combining them with other monomers. The polyene polymer is preferably an acid-modified polyene polymer having a carboxylic acid group, a carboxylic anhydride group, or a hydroxyl group introduced therein.

[0029] The oxidizing organic component is preferably contained in the oxygen-absorbing resin composition in a proportion of 0.01 to 10% by weight. As the transition metal-based catalyst, Group VIII metals of the periodic table such as iron, cobalt, and nickel are preferable, but other Group I metals such as copper and silver, Group IV metals such as tin, titanium, and zirconium, Group V metals such as vanadium, Group VI metals such as chromium, Group VII metals such as manganese, etc. may also be used. The transition metal-based catalyst is generally used in the form of an inorganic salt, organic salt, or complex salt of the above transition metal with a lower valence number. The transition metal-based catalyst is preferably in the range of 100 to 3000 ppm as the concentration of transition metal atoms (based on weight concentration) 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 will be inferior.

[0030] <UV barrier resin layer> As the resin constituting the UV barrier resin layer, in the above-mentioned polyester resin, polyethylene naphthalate, polybutylene naphthalate, etc. containing 2,6-naphthalenedicarboxylic acid as the dicarboxylic acid can be used. The thickness of the UV barrier resin layer before stretching is preferably in the range of 5 to 500 μm, particularly 10 to 100 μm.

[0031] <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 oxide is added to the above-mentioned polyester resin can be used. The thickness of the visible light barrier resin layer before stretching is preferably in the range of 5 to 500 μm, particularly 10 to 100 μm.

[0032] <Rigid resin layer> The stretched multilayer film of the present invention has excellent rigidity by itself since it has layers made of PBT and PET, but it can also be provided 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 above-mentioned polyester resin can be used. Examples of inorganic fillers include layered silicate minerals such as the kaolinite group (kaolinite), the pyrophyllite group (pyrophyllite), the talc group (talc), the smectite group (montmorillonite, beidellite, hectorite, saponite, sauconite, stevensite), and the mica group (muscovite, sericite). In particular, mica mainly composed of talc, muscovite, and sericite can be preferably used. In addition, it is particularly preferable that the resin composition is a nanocomposite in which the inorganic filler is dispersed in the continuous phase at a nano-order level, which allows strain hardening to occur densely due to local overstretching during stretching, making it possible to obtain an excellent stretching balance. The thickness of the rigid resin layer before stretching is preferably in the range of 5 to 500 μm, particularly 10 to 100 μm.

[0033] <Other layers> In addition to the above, reproduced resins, recycled polyester resins, or biomass polyesters can also be used as the functional resin layers, and by having these layers, the stretched multilayer film can have the function of being excellent in environmental compatibility. The reproduced resin is a resin obtained by pulverizing and reducing the resin or film discharged in the process of producing the stretched multilayer film of the present invention, and is a resin mainly composed of PBT or PET. The reproduced resin may also contain virgin polyester. An example of a recycled polyester resin is polyester recycled by mechanical recycling. In general, the polyester is recycled by crushing and cleaning collected polyester bottles. This polyester generally 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 in addition to recycled polyester.

[0034] Examples of biomass polyesters include polyesters that use ethylene glycol derived from biomass ethanol produced from raw materials such as sugar cane or corn as a diol component and the above-mentioned dicarboxylic acids derived from fossil fuels as a dicarboxylic acid component. The biomass polyester may contain virgin polyester in addition to the biomass polyester.

[0035] (Method of manufacturing stretched multilayer film) The stretched multi-layer film of the present invention is produced in advance by coextrusion lamination using PBT and PET in which the contents of the above-mentioned copolymerization components are reduced as much as possible, and, if necessary, the above-mentioned functional resin. The production of a multilayer film by coextrusion can be carried out by a conventionally known method, in which melts of each resin are superimposed in a multilayer die using an extruder corresponding to the type of each resin layer, and the melts are extruded from the die orifice. This film material is previously formed into a multilayer cast film by a T-die method, an inflation method, or the like. When a coextruded film is produced by the T-die method, the film is stretched by the tenter method. That is, the multilayer film coextruded from a T-shaped multilayer die is taken up by a cast roll, and then stretched in the machine direction (MD) by a tenter or a stretching roll, and if necessary, stretched in the transverse direction (TD) by using a tenter, and further heat-set if necessary. The stretching may be either uniaxial or biaxial, but biaxial stretching is preferable. In the case of biaxial stretching, in addition to sequential biaxial stretching in which stretching is performed in the MD and TD directions in sequence, biaxial stretching in which stretching is performed in the MD and TD directions simultaneously by a tenter may also be used. On the other hand, when a coextruded film is produced by the inflation method, the film is stretched by the tubular method. That is, the multi-layer parison coextruded from a circular multi-layer die is cooled, and then the parison is heated to a stretching temperature and then blown, and if necessary, heat-set. The obtained tubular film can be folded as necessary to make a flat film, or slit and then wound into a roll.

[0036] In the present invention, since the occurrence of curling of the film is suppressed even when stretched by the tenter method, it is preferable to produce a stretched multilayer film by the T-die method and the tenter method. By producing a stretched multilayer film by the T-die method and the tenter method, it is possible to stably produce a wide, thin film with little thickness unevenness and no curling by high-speed film production. The stretching ratio is preferably 2 to 10 times, particularly preferably 2 to 5 times, in the case of uniaxial stretching, and is preferably 2 to 10 times, particularly preferably 2 to 5 times, in the case of biaxial stretching, in both MD and TD.

[0037] (Laminate) In the present invention, the stretched multi-layer film obtained through the above-mentioned co-extrusion and stretching steps may be further laminated with other layers to form a laminate. Examples of such other layers that may be laminated as necessary include a layer made of a resin that cannot be laminated by coextrusion with PBT and PET and has poor adhesion to them, a vapor deposition layer or coating layer, a gas barrier film that is provided with these layers separately, a printed layer or a topcoat layer for protecting the printed layer, a sealant layer, etc. Examples of lamination methods for such layers include the conventionally known dry lamination method, extrusion coating method, fusion bonding method, etc., and can be appropriately selected depending on the type of layer to be laminated. In the present invention, it is particularly preferable to laminate the sealant layer by extrusion coating. That is, if the sealant layer is laminated on one surface of the multilayer film simultaneously with the PBT layer and the PET layer by coextrusion lamination, the symmetry of the multilayer film in the thickness direction is lost and the heat sealability is reduced by stretching, so it is preferable to further laminate the sealant layer on the stretched laminate film.

[0038] As the resin constituting the sealant layer, a conventionally known heat-sealable resin can be used, and examples thereof include olefin-based resins such as polyethylene and polypropylene, as well as heat-sealable polyester resins. In the present invention, since lamination is preferably performed by extrusion lamination without using an adhesive, for example, amorphous polyesters such as PETG, low-melting point polyester resins such as ethylene terephthalate / isophthalate copolymers, polyester resins obtained by blending polyester resins with high glass transition temperatures (Tg) and polyester resins with low glass transition temperatures (Tg), heat-sealable polyester resins such as polyester-based thermoplastic elastomers such as polytetramethylene glycol-modified polybutylene terephthalate (PBT-PTMG), and acid-modified olefin-based resins can be suitably used. The thickness of the sealant layer is preferably in the range of 15 to 150 μm, particularly preferably 40 to 80 μm.

[0039] (packaging bag) The packaging bag of the present invention is produced by overlapping and sealing the laminate in which the sealant layer is formed on the above-mentioned stretched multilayer film so that the sealant layers face each other. The shape of the packaging bag is not limited as long as it is made of the above-mentioned laminate, and various shapes such as a pillow-type pouch, a gusset-type pouch, a standing pouch, etc. can be adopted. In the packaging bag of the present invention, when a printing layer and a topcoat layer are formed on the outer surface side of the laminate (the surface opposite the sealant resin layer), it is preferable to form the printing layer and the topcoat layer in the laminate state; however, a packaging bag may be first prepared by stacking and sealing a laminate having the necessary layers except for the printing layer and topcoat layer so that the sealant layers face each other, and then forming the printing layer and the topcoat layer on the outer surface of this packaging bag. EXAMPLES

[0040] (Method of Producing Stretched Film) 1.Material The base layer is made of three types of polyethylene terephthalate resin (PET1, 2, 3). 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, isophthalic acid 7.5 mol%) PBT3 (IV=1.00, isophthalic acid 30mol%) Each resin was dried before molding.

[0041] 2. Molding (1) Cast film molding A multilayer coextrusion cast film was produced using a Labo Plastomill (manufactured by Toyo Seiki Seisakusho Co., Ltd.) equipped with a multilayer T-die. In this equipment, the resins extruded from the first, second, and third extruders are joined in a feed block type T-die, and a three-type three-layer film laminated in the order of first / second / third can be produced. Multilayer films of other configurations were also produced by the following method. <Single Layer> When the three-kind three-layer film was produced, the same type of resin was supplied to the first, second and third extruders to produce the single layer film. <Two kinds, three layers> When the three kinds, three layers film was produced, the same kind of resin was supplied to the first and third extruders to produce the two kinds, three layers film. The temperature of the T-die was set to 280°C, and the temperature of the extruder was changed depending on the resin supplied. The thickness of the entire layer and each layer was adjusted by changing the rotation speed of the extruder and the take-up speed of the attached film take-up machine.

[0042] (2) Forming of stretched film The cast film was used as a raw sheet before stretching and biaxially stretched in a biaxial stretching tester (x6H-S: Toyo Seiki Seisakusho, Ltd.) to form a stretched film.

[0043] (Film evaluation method) (1) Film thickness measurement The thickness of the film was measured by a dial gauge conforming to JIS B 7503 (1997). The number of measurements (n=5) was averaged and the measured value was taken as the average value. (2) Layer ratio measurement of cast film A thin section was cut from the cross section of the cast film using a microtome and observed under a transmission polarizing microscope to measure the thickness of each layer. (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 50 mm / min. The number of measurements was 5 (n=5), and the average value was taken as the measured value. The measured puncture strength was divided by the total layer thickness of the stretched film to calculate the puncture strength per unit thickness (puncture strength / total layer thickness). The measured puncture strength was also divided by the total thickness of the PBT layers in the stretched multilayer film to calculate the puncture strength per unit thickness of the PBT layers (puncture strength / PBT layer thickness). (4) Dynamic viscoelasticity (tan δ) measurement of stretched film A test piece measuring 10 mm×30 mm was cut out from the stretched film and measured using a viscoelasticity spectrometer (EXSTAR6000DMS: Seiko Instruments Inc.) under the following measurement conditions. Measurement mode: Pulled sine wave mode Test piece gauge length: 5mm Frequency: 1Hz Minimum tension: 50mN Temperature profile: 25℃ to 200℃ at 2℃ / min From the obtained tan δ curve, the temperature at which tan δ is maximum (tan δ maximum temperature) was calculated.

[0044] Example 1 According to the molding method of the two-kind three-layer cast film, PET1 was fed to the first and third extruders (set temperature 280°C), and PBT1 was fed to the second extruder (set temperature 250°C), and a cast film with a three-layer symmetrical structure of PET1 / PBT1 / PET1 was molded. The total layer thickness of this film was 200μm, and the ratio of each layer thickness was PET1 / PBT1 / PET1=50 / 100 / 50. This cast film was used as a pre-stretched raw material and a stretched film was formed according to the above-mentioned stretched film forming method. The stretching conditions were a pre-stretch heating temperature of 90°C, a stretch ratio of 3.0 times in the vertical axis and 3.0 times in the horizontal axis, and an axial speed of 10 m / min, and a simultaneous biaxial stretching method. After the stretching was completed, a heat setting treatment was performed at 190°C for 120 seconds. The total layer thickness of this film was 25 μm. Various evaluation results are shown in Tables 1 and 2.

[0045] Example 2 A cast film having a three-layer symmetrical structure of PET2 / PBT1 / PET2 was molded in the same manner as in Example 1, except that PET2 was used instead of PET1. Using this cast film as a raw sheet before stretching, a stretched film was produced in the same manner as in Example 1. The total layer thickness of this film was 19 μm. Various evaluation results are shown in Tables 1 and 2.

[0046] Example 3 A cast film having a three-layer symmetrical structure of PET2 / PBT2 / PET2 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 a raw sheet before stretching, a stretched film was produced in the same manner as in Example 1. The total layer thickness of this film was 22 μm. Various evaluation results are shown in Tables 1 and 2.

[0047] Comparative Example 1 A cast film having a three-layer symmetrical structure of PET2 / PBT3 / PET2 was molded in the same manner as in Example 1, except that PET2 was used instead of PET1 and PBT3 was used instead of PBT1. Using this cast film as a raw sheet before stretching, a stretched film was produced in the same manner as in Example 1. The total layer thickness of this film was 24 μm. Various evaluation results are shown in Tables 1 and 2.

[0048] Comparative Example 2 A cast film having a three-layer symmetrical structure of PET3 / PBT1 / PET3 was molded in the same manner as in Example 1, except that PET3 was used instead of PET1. Using this cast film as a raw sheet before stretching, a stretched film was produced in the same manner as in Example 1. The total layer thickness of this film was 23 μm. Various evaluation results are shown in Tables 1 and 2.

[0049] Comparative Example 3 According to the above-mentioned method for forming a monolayer cast film, PBT1 was supplied to the first, second, and third extruders (set temperature 280° C.) to form a PBT monolayer cast film. The total layer thickness of this film was 127 μm. Using this cast film as a raw sheet before stretching, a stretched film was produced in the same manner as in Example 1. This film had a thickness of 12 μm. Various evaluation results are shown in Tables 1 and 2.

[0050] Comparative Example 4 According to the above-mentioned method for forming a monolayer cast film, PET1 was supplied to the first, second, and third extruders (set temperature 280° C.) to form a monolayer cast PET film. The total thickness of this film was 200 μm. Using this cast film as a raw sheet before stretching, a stretched film was produced in the same manner as in Example 1. This film had a thickness of 29 μm. Various evaluation results are shown in Tables 1 and 2.

[0051] Comparative Example 5 The PBT single-layer stretched film obtained in Comparative Example 3 and the PET single-layer stretched film obtained in Comparative Example 4 were dry laminated using a urethane adhesive (3 μm) to produce a multilayer stretched film. The multilayer stretched film had a thickness of 43 μm. The various evaluation results are shown in Tables 1 and 2.

[0052] [Table 1]

[0053] [Table 2] [Industrial Applicability]

[0054] The stretched multilayer film of the present invention has excellent mechanical strength such as impact resistance, heat resistance, barrier properties, etc., and is a flat-membrane stretched multilayer film with a small number of laminations and a reduced amount of adhesive used, so it is excellent in productivity and economy and can be used for various content applications. In particular, since it has excellent flavor properties, it can be preferably used for food applications.

Claims

1. A stretched multi-layer film having at least one PBT layer made of polybutylene terephthalate and at least one PET layer made of polyethylene terephthalate, The total content of the copolymerization components of the polybutylene terephthalate is 8 mol% or less, and the total content of the copolymerization components of the polyethylene terephthalate is 5 mol% or less, The PBT layer and the PET layer are laminated together without any adhesive, The laminate has a multilayer structure in which the lamination order of the PBT layer and the PET layer is symmetrical in the thickness direction of the film, Both of the layers at both ends of the multilayer structure are PET layers (excluding the case where the multilayer structure is a PET layer consisting of only polyethylene terephthalate / PBT layer consisting of only polybutylene terephthalate / PET layer consisting of only polyethylene terephthalate). the multilayer structure is a coextruded film; A stretched multilayer film, characterized in that the total thickness of the PBT layers is in the range of 40 to 60% of the total thickness of all layers of the stretched multilayer film, and the puncture strength per unit thickness in the total layer thickness of the stretched multilayer film is 600 N / mm or more.

2. A stretched multilayer film as described in claim 1 having at least one functional resin layer made of a functional resin.

3. A stretched multilayer film as described in claim 1 or 2, wherein the PET layer and / or the PBT layer contains a functional resin.

4. A stretched multilayer film described in any of claims 1 to 3, wherein the PET layer and / or the PBT layer contains at least one of reproduced resin, recycled polyester resin, and biomass polyester resin.

5. The stretched multilayer film as described in claim 1, wherein the multilayer structure is a PET layer / PBT layer / functional resin layer using reproduced resin / PBT layer / PET layer.

6. The stretched multilayer film as described in claim 1, wherein the multilayer structure is a PET layer / PBT layer containing reproduced resin / PET layer.

7. An oriented multilayer film as described in claim 1, wherein the multilayer structure is a PET layer containing a blend of virgin polyester resin and recycled polyester resin / PBT layer / PET layer containing a blend of virgin polyester resin and recycled polyester resin.

8. The stretched multilayer film as described in claim 1, wherein the multilayer structure is a functional resin layer consisting of a PET layer / PBT layer / functional resin / PBT layer / PET layer.

9. The stretched multilayer film as described in claim 1, wherein the multilayer structure is a PET layer containing a functional resin / PBT layer / PET layer containing a functional resin.

10. An oriented multilayer film as described in claim 1, wherein the multilayer structure is a PET layer blended with virgin polyester resin / a PET layer blended with recycled polyester resin / a PBT layer / a PET layer blended with recycled polyester resin / a PET layer blended with virgin polyester resin.

11. The functional resin is made of a resin or a resin composition having one or more of the following functions: gas barrier properties, easy tearing properties, oxygen absorption properties, UV barrier properties, visible light barrier properties, and rigidity.

11. The stretched multilayer film according to claim 2, 3, 9 or 10.

12. The stretched multilayer film of claim 1, wherein the polybutylene terephthalate is a homopolybutylene terephthalate.

13. A stretched multilayer film described in any one of claims 1 to 12, wherein the polyethylene terephthalate is homopolyethylene terephthalate.

14. A laminate comprising the stretched multi-layer film according to any one of claims 1 to 13 and a sealant layer laminated thereon.

15. 15. The laminate according to claim 14, wherein the sealant layer is laminated without the use of an adhesive.

16. 16. The laminate according to claim 14, wherein the sealant layer is made of a polytetramethylene glycol-modified polyester resin or an acid-modified olefin resin.

17. A packaging bag comprising the laminate according to any one of claims 14 to 16.

18. A method for producing a stretched multilayer film, comprising laminating a PBT layer made of polybutylene terephthalate and a PET layer made of polyethylene terephthalate by coextrusion to form a multilayer film, and then stretching the multilayer film by simultaneous biaxial stretching or successive biaxial stretching using a tenter method, comprising the steps of: The total content of the copolymerization components of the polybutylene terephthalate is 8 mol% or less, and the total content of the copolymerization components of the polyethylene terephthalate is 5 mol% or less, The laminate has a multilayer structure in which the lamination order of the PBT layer and the PET layer is symmetrical in the thickness direction of the film, Both of the layers at both ends of the multilayer structure are PET layers (excluding the case where the multilayer structure is a PET layer consisting of only polyethylene terephthalate / PBT layer consisting of only polybutylene terephthalate / PET layer consisting of only polyethylene terephthalate). A method for producing a stretched multilayer film, characterized in that a total thickness of the PBT layers is in the range of 40 to 60% of a total thickness of all layers of the stretched multilayer film, and a puncture strength per unit thickness in the total layer thickness of the stretched multilayer film is 600 N / mm or more.

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