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 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, it relates to a stretched multilayer film having a layer made of polybutylene terephthalate excellent in toughness and a layer made of polyethylene terephthalate excellent in heat resistance, and capable of being stably obtained by stretching by the tenter method, and a packaging bag made of this stretched multilayer film.

Background Art

[0002] Packaging bags containing food and drinks as contents are made of multilayer films (laminates) formed by laminating layers made of various materials in order to satisfy necessary properties such as heat resistance corresponding to 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 order from the outer surface has been proposed.

[0003] Also, 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, and 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. A laminate containing at least one PET layer and at least one PBT 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, Patent Document 2 describes that a biaxially oriented multilayer film can be produced by co-extruding PET and PBT using a T-die method or an inflation method, and then biaxially stretching them using a tubular method or a tenter method. However, in co-extruded films where the PBT layer and 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 that is flat all the way to the edges. 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] Therefore, an object of the present invention is to provide a stretched multilayer film comprising at least one PET layer and at least one PBT layer, which can effectively exhibit both the excellent heat resistance and toughness of PET and PBT. 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 and one PBT layer, with a small number of laminations, and for producing a stretched film by tenter stretching without causing curling. [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, wherein the copolymer component of the polybutylene terephthalate isophthalic acid The total content of the copolymer component of polyethylene terephthalate is 8 mol% or less. isophthalic acid and / or diethylene glycol A stretched multilayer film is provided, characterized in that the total content of the material is 5 mol% or less, and each of the PBT layer and PET 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. The film 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. 4. The multilayer structure is a PBT layer / PET layer / PBT layer or a PET layer / PBT layer / PET layer, and is a co-extruded film. 5. It shall have at least one functional resin layer. 6. The PET layer and / or the PBT layer contains a functional resin. 7. 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. 8. 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. 9. The total thickness of the PBT layers is within the range of 40-60% of the total thickness of all layers of the stretched multilayer film. 10. The puncture strength per unit thickness must be 600 N / mm or more. This is preferable.

[0010] The present invention also provides a laminate characterized in that a sealant layer is laminated onto the stretched multilayer film described above. In the laminate of the present invention, 1. The sealant layer is laminated without the use of an adhesive. 2. The sealant layer is a polytetramethylene glycol-modified polyester resin or an acid-modified olefin resin. This is preferable. The present invention further provides a packaging bag characterized by being made of the above-mentioned laminate.

[0011] According to the present invention, furthermore, copolymer components isophthalic acid PBT layer and copolymer components consisting of polybutylene terephthalate with a total content of 8 mol% or less isophthalic acid and / or diethylene glycol A method for producing a stretched multilayer film is provided, characterized by laminating a PET layer made of polyethylene terephthalate with a total content of 5 mol% or less 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]

[0012] In the stretched multilayer film of the present invention, by stretching a multilayer film co-extruded using PBT and PET in which the copolymerization component is below the above value, 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 clear from the results of the examples described later, and the stretched multilayer film of the present invention has excellent puncture resistance and heat resistance compared to a stretched multilayer film formed by adhering a stretched film made of PBT and a stretched film made of PET. Also, as is clear from the results of Examples 1 and 2 described later, by using PET with a further reduced copolymerization component, it is possible to obtain a synergistic effect of further improving not only heat resistance but also puncture resistance. Furthermore, since PBT and PET are laminated by co-extrusion, the amount of adhesive used is reduced, and it 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 symmetric in the film thickness direction, it is possible to provide a stretched multilayer film in which the occurrence of curl is effectively prevented even when stretched by the tenter method.

[0013] Also, in the method for producing a stretched multilayer film of the present invention, it is possible to improve the economy and productivity by reducing the number of laminations and the amount of adhesive used, and it is possible to stretch a stretched multilayer film having at least one layer each of a PBT layer and a PET layer, which has been conventionally produced by co-extrusion by the inflation method and stretching by the tubular method, by the tenter method, and provide it as a flat flat film.

Mode for Carrying Out the Invention

[0014] (Stretched Multilayer Film) The stretched multilayer film of the present invention is characterized in that a PBT layer made of PBT with a total copolymer component content of 8 mol% or less and a PET layer made of PET with a total copolymer component content of 5 mol% or less are laminated without an adhesive layer therebetween. Thereby, it is possible to have mechanical strengths (toughness) such as puncture resistance and impact resistance based on the PBT layer and heat resistance based on the PET layer, and particularly has excellent mechanical strength with a puncture strength of 600 N / mm or more, particularly 650 N / mm or more per unit film thickness. The method for measuring the puncture strength per unit film thickness will be described later. That is, when the copolymer components of PBT and PET are more than the above values, the orientation crystallinity of PBT and PET decreases, so that physical properties such as puncture strength and heat resistance that improve with stretching are not sufficiently improved, and the stretching stability also decreases. Also, 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 tanδ peak value is 0.27 or less, and the peak temperature of tanδ at this peak value is in the range of 115°C or more. Tanδ is a parameter called loss tangent, which is represented by the ratio of loss elastic modulus / storage elastic modulus. The loss elastic modulus is a loss caused by the amorphous part, and the storage elastic modulus is an elastic modulus caused by the crystalline part. The smaller the tanδ peak value, the more crystalline 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 tanδ peak value is small and its peak temperature is high, and it has excellent heat resistance.

[0015] 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 is possible to exhibit better puncture resistance and heat resistance than a stretched multilayer film obtained by laminating a stretched PBT film and a stretched PET film.

[0016] Furthermore, as will be described later, by adopting a layer configuration that is symmetrical in the thickness direction, such as a PET layer / PBT layer / PET layer, it becomes possible to adjust the stretching balance by canceling out the stress caused by the difference in crystallinity between PBT and PET during stretching, and thus create a flat stretched multilayer film. Furthermore, by having a PET layer and other resin layers that can be laminated by co-extrusion, and especially by having a functional resin layer as 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 substrates for stretched multilayer films. The PBT layer improves the film's impact resistance and puncture resistance, while the PET layer improves the film's heat resistance and barrier properties. The polybutylene terephthalate constituting the PBT layer preferably contains as little copolymer as possible, preferably 8 mol% or less, and particularly preferably homopolybutylene terephthalate with 0 mol% copolymer. PBT primarily consists of terephthalic acid as the dicarboxylic acid component and 1,4-butanediol as the alcohol component, and it is important that the copolymer component is 8 mol% or less (in this specification, butylene terephthalate copolymers containing the copolymer component are also referred to as polybutylene terephthalate (PBT)).

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

[0019] Examples of carboxylic acid components (copolymer components) other than terephthalic acid in PBT and PET include isophthalic acid, naphthalenedicarboxylic acid, p-β-oxyethoxybenzoic acid, biphenyl-4,4'-dicarboxylic acid, diphenoxyethane-4,4'-dicarboxylic acid, 5-sodium sulfisoisophthalic acid, hexahydroterephthalic acid, adipic acid, sebacic acid, trimellitic acid, pyromellitic acid, and the like. On the other hand, examples of alcohol components (copolymerization components) 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, and sorbitan.

[0020] 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.

[0021] 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.

[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 in between. By making this multilayer structure 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, it becomes possible to adjust the stretch balance by canceling out the stress caused by the difference in the crystallization density of PBT and PET, and thereby effectively prevent the occurrence of curl in 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 this, but 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, etc., and it is important that the PBT layer and the PET layer are in symmetrical positions with respect to the center in the thickness direction of the film.

[0024] Furthermore, 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 desirable not only in the arrangement of the layers as described above, but also in the multilayer structure in which the thicknesses of opposing layers in symmetrical positions are approximate. Specifically, if there is a difference in the thickness of opposing layers, it is desirable that the difference in thickness between the two is 50% or less, preferably 30% or less, and more preferably 15% or less, of the thickness of the thicker layer. Furthermore, the total thickness of the PBT layer is preferably in the range of 40-60% of the thickness of the multilayer stretched film. If the total thickness of the PBT layer is thinner than the above range, sufficient mechanical strength such as puncture resistance and impact resistance obtained from the PBT layer cannot be obtained. On the other hand, if the PBT layer is thicker than the above range, the thickness of the PET layer will be reduced, which may decrease the heat resistance.

[0025] [Functional resin layer] The functional resin layer can be made of various functional resins as long as it is co-extrudeable with the PBT layer and the PET layer, and is not limited thereto. Examples include 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.

[0026] <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.

[0027] <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.

[0028] <Oxygen-absorbing resin layer> As the resin composition constituting the oxygen-absorbing resin layer, conventionally known oxygen-absorbing resin compositions can be used, which include a polyester resin that can be used in PBT layers and PET layers, or the above-mentioned gas barrier resin, as the matrix resin, and which contain an oxidizing organic component and a transition metal-based catalyst. Examples of the oxidizable organic component include, but are not limited to, polymers containing ethylenically unsaturated groups, particularly those derived from polyene monomers. A homopolymer of polyene, a random copolymer or a block copolymer obtained by combining two or more polyenes or combining polyene with other monomers can be used as the oxidizable organic component. The polyene polymer is preferably an acid-modified polyene polymer into which a carboxylic acid group, a carboxylic anhydride group or a hydroxyl group is introduced.

[0029] The oxidizable organic component is preferably contained in the oxygen-absorbing resin composition at a ratio of 0.01 to 10% by weight. As the transition metal catalyst, Group VIII metals of the periodic table such as iron, cobalt and nickel are preferred, 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, and Group VII metals such as manganese may also be used. The transition metal catalyst is generally used in the form of an inorganic salt, an organic salt or a complex salt of the above transition metal with a lower valence number. The transition metal catalyst is preferably present in the oxygen-absorbing resin composition in a range of 100 to 3000 ppm in terms of the concentration of transition metal atoms (based on weight concentration). 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 absorbency 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 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.

[0032] <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.

[0033] <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.

[0034] 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.

[0035] (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, and the functional resin described above if necessary. 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.

[0036] 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.

[0037] (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, or sealant layers. Examples of methods for laminating such layers include conventionally known methods such as dry lamination, extrusion coating, and fusion bonding, which 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 an extrusion coating method. That is, if the sealant layer is laminated on one surface of a multilayer film simultaneously with the PBT layer and the PET layer by co-extrusion lamination, the symmetry in the thickness direction of the multilayer film is impaired, and the heat sealability decreases due to stretching. Therefore, it is desirable to further laminate it on a stretched laminated film.

[0038] Conventional heat-sealable resins can be used as the resin constituting the sealant layer, and examples include olefin 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 the use of adhesives, heat-sealable polyester resins such as amorphous polyesters like PETG, low-melting-point polyester resins such as 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), as well as acid-modified olefin resins, can be suitably used. The thickness of the sealant layer is preferably in the range of 15 to 150 μm, and particularly 40 to 80 μm.

[0039] (packaging bag) The packaging bag of the present invention is manufactured by overlapping and sealing laminates, each having a sealant layer formed on the stretched multilayer film described above, so that the sealant layers face each other on the inside. As long as the packaging bag consists of the laminated material described above, its shape is not limited, and various shapes such as pillow-type pouches, gusset-type pouches, and standing pouches can be adopted. In the packaging bag of the present invention, when forming a printed layer and a topcoat layer on the outer surface of the laminate (the surface opposite the sealant resin layer), it is preferable to form the printed layer and the topcoat layer in the laminate state. However, a packaging bag may be created first by stacking laminates with the necessary layers excluding the printed layer and topcoat layer, so that the sealant layers face each other, and sealing them. Then, the printed layer and topcoat layer may be formed on the outer surface of this packaging bag. [Examples]

[0040] (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.

[0041] 2. Molding (1) Forming of cast film Multilayer co-extruded cast films were manufactured using a laboplast mill (manufactured by Toyo Seiki Seisakusho Co., Ltd.) equipped with a multilayer T-die. This equipment can combine resins extruded from the first, second, and third extruders using a feed block type T-die, and produce three types of three-layer films laminated in the order of first / second / third. In addition, multilayer films with other configurations were manufactured using the method described below. <Single-layer> When manufacturing the three types of three-layer films described above, single-layer films were produced by supplying the same type of resin to the first, second, and third extruders. <2 types, 3 layers> When manufacturing the 3 types, 3 layer film, the same type of resin was supplied to the first and third extruders to produce the 2 types, 3 layer film. 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.

[0042] (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.

[0043] (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 performed 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.

[0044] (Example 1) Following the molding method for the two types of three-layer cast film described above, PET1 was supplied to the first and third extruders (set temperature 280°C), and PBT1 was supplied to the second extruder (set temperature 250°C), thereby forming a cast film with a symmetrical three-layer structure of PET1 / PBT1 / PET1. The total thickness of this film was 200 μm, and the ratio of the thicknesses of each layer was PET1 / PBT1 / PET1 = 50 / 100 / 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, stretching ratios of 3.0 times in both the longitudinal and transverse axes, and an axial speed of 10 m / min using a simultaneous biaxial stretching method. After stretching, a heat-setting treatment was performed at 190°C for 120 seconds. The total thickness of this film was 25 μm. The various evaluation results are shown in Tables 1 and 2.

[0045] (Example 2) In Example 1, a cast film with a symmetrical three-layer structure of PET2 / PBT1 / PET2 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 19 μm. The various evaluation results are shown in Tables 1 and 2.

[0046] (Example 3) In Example 1, a cast film with a symmetrical three-layer structure of PET2 / PBT2 / PET2 was formed 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 22 μm. The various evaluation results are shown in Tables 1 and 2.

[0047] (Comparative Example 1) In Example 1, a cast film with a symmetrical three-layer structure of PET2 / PBT3 / PET2 was formed 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 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 24 μm. The various evaluation results are shown in Tables 1 and 2.

[0048] (Comparative Example 2) In Example 1, a cast film with a symmetrical three-layer structure of PET3 / PBT1 / PET3 was formed 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 23 μm. The various evaluation results are shown in Tables 1 and 2.

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

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

[0051] (Comparative Example 5) A multilayer stretched film was prepared by dry lamination using a urethane adhesive (3 μm) on the stretched PBT single-layer film obtained in Comparative Example 3 and the stretched PET single-layer film obtained in Comparative Example 4. This 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 is excellent in mechanical strength such as impact resistance, as well as heat resistance and barrier properties. Furthermore, because it is a flat stretched multilayer film that requires fewer laminations and less adhesive, it is excellent in productivity and cost-effectiveness and can be used for various contents applications. In particular, its excellent flavor characteristics make 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, 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 and the PET layer are laminated without an adhesive in between. The film 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 layers at both ends of the aforementioned multilayer structure are PET layers (except in cases where the multilayer structure consists of a PET layer made solely of polyethylene terephthalate, a PBT layer made solely of polybutylene terephthalate, and a PET layer made solely of polyethylene terephthalate). The aforementioned multilayer structure is a co-extruded 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 of the total thickness of all layers of the stretched multilayer film is 600 N / mm or more.

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 multilayer structure is a PET layer / PBT layer / functional resin layer using a recycled resin / PBT layer / PET layer.

6. The stretched multilayer film according to claim 1, wherein the multilayer structure is a PET layer / PBT layer compounded with a reproductive resin / PET layer.

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

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

9. The stretched multilayer film according to claim 1, wherein the multilayer structure is a PET layer / PBT layer / PET layer blended with a functional resin.

10. The stretched multilayer film according to 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 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. A stretched multilayer film according to any one of claims 2, 3, 9, or 10.

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. A laminate characterized by comprising a stretched multilayer film according to any one of claims 1 to 13, with a sealant layer laminated on top.

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

16. The laminate according to claim 14 or 15, wherein the sealant layer is a polytetramethylene glycol-modified polyester resin or an acid-modified olefin resin.

17. A packaging bag characterized by being made of a laminate according to any one of claims 14 to 16.

18. A method for manufacturing a stretched multilayer film, comprising laminating a PBT layer made of polybutylene terephthalate and a PET layer made of polyethylene terephthalate 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 film 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 layers at both ends of the aforementioned multilayer structure are PET layers (except in cases where the multilayer structure consists of a PET layer made solely of polyethylene terephthalate, a PBT layer made solely of polybutylene terephthalate, and a PET layer made solely of polyethylene terephthalate). A method for manufacturing 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 of the total thickness of all layers of the stretched multilayer film is 600 N / mm or more.

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