Multilayer stretched film

Abstract

To provide a multilayer stretched film in which a pinhole due to piercing is unlikely to be produced and in which a pinhole due to friction is also unlikely to be produced.SOLUTION: Provided is a multilayer stretched film in which a layer A1 and a layer A2 containing functional resin selected from among polyamide resin, polyester resin, and ethylene-vinyl alcohol copolymer resin, a layer B containing adhesive resin, and a layer C containing sealant resin are arranged in an order of A1 / B / A2 / C, in which the film has a thickness of 25 to 70 μm, the layer A1 has a thickness of 10 to 90% of the sum of the layer A1 and the layer A2, and the multilayer stretched film has a G / T3 value of more than or equal to 50 N / mm2, the G / T3 value being obtained by dividing a flexural rigidity G found by Expressions (1) and (2): (in Expressions (1) and (2), Ei represents the Young's modulus of resin constituting a layer i, ti represents the thickness of the layer i, and n represents the total number of layers) by the cube of a thickness T of the multilayer stretched film.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a multilayer stretched film, and more specifically to a multilayer stretched film comprising a layer containing a polyamide resin, a polyester resin or an ethylene-vinyl alcohol copolymer and a layer containing a sealant resin. [Background technology]

[0002] Multilayer stretched films having layers containing polyamide resins, polyester resins, or ethylene-vinyl alcohol copolymers are less susceptible to pinholes and are used in many fields as packaging films.

[0003] In recent years, from the viewpoint of environmental issues, efforts are being made to reduce the weight of plastic products, and efforts are being made to make packaging films thinner. However, when films are made thinner, the strength of the film decreases, making them more susceptible to pinholes.

[0004] In view of this, Japanese Patent Laid-Open Publication No. 5-169603 (Patent Document 1) proposes a multilayer stretched film as a packaging film that is less likely to develop pinholes due to puncture or bending, which includes any one of polyamide resin layers (A) (A'), saponified ethylene-vinyl acetate copolymer resin layers (B), adhesive resin layers (C), (C'), or (C") and a seal layer (D), with the lamination order being (1) AC-A', (2) ACB-A', (3) ACB-C'-A', (4) AC-A'-C'-D, (5) ACB-A'-C'-D, or (6) ACB-C'-A'-C"-D.

[0005] In addition, JP 2020-82678 A (Patent Document 2) describes a multilayer stretched film that is less likely to develop pinholes due to puncture, and which comprises an outermost layer containing polyamide 610 or the like, a polyamide-based intermediate layer containing polyamide 6 or the like, an adhesive layer containing an adhesive resin, and an innermost layer containing a polyolefin-based resin. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 5-169603 [Patent Document 2] JP 2020-82678 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, the multilayer stretched films described in Patent Documents 1 and 2 have a problem in that pinholes are easily generated due to friction.

[0008] The present invention has been made in consideration of the problems associated with the above-mentioned conventional techniques, and has an object to provide a multilayer stretched film that is not only less susceptible to the occurrence of pinholes due to puncture, but also to the occurrence of pinholes due to friction. [Means for solving the problem]

[0009] As a result of intensive research by the inventors in order to achieve the above object, it has been found that, in a multilayer stretched film comprising a layer containing at least one functional resin selected from the group consisting of polyamide-based resins, polyester-based resins, and ethylene-vinyl alcohol copolymers, and a layer containing a sealant resin, at least two layers containing the functional resin are formed, and these two layers containing the functional resin (layer A1 and layer A2) are bonded together with a layer B containing an adhesive resin to form a layer structure (A1 / B / A2), and further, a bending stiffness G of the multilayer stretched film divided by the cube of the film thickness T is obtained by dividing the bending stiffness G of the multilayer stretched film by the cube of the film thickness T, thereby obtaining a film structure having a thickness of at least 100 mm. 3 The inventors discovered that by setting the value within a predetermined range, not only is it possible to reduce the occurrence of pinholes due to puncture, but it is also possible to reduce the occurrence of pinholes due to friction, and have thus completed the present invention.

[0010] That is, the present invention provides the following aspects.

[0011] [1] A multilayer stretched film comprising Layer A1 and Layer A2 each containing at least one functional resin selected from the group consisting of a polyamide resin, a polyester resin, and an ethylene-vinyl alcohol copolymer resin, Layer B containing an adhesive resin, and Layer C containing a sealant resin, arranged in the order of A1 / B / A2 / C from the outside, The thickness of the multilayer stretched film is 25 to 70 μm, the thickness of the layer A1 is 10 to 90% of the total thickness of the layer A1 and the layer A2, Regarding the multilayer stretched film, the following formulas (1) and (2):

[0012]

number

[0013] (In formulas (1) and (2), E i represents the Young's modulus of the resin constituting layer i, and t i represents the thickness of layer i, and n represents the total number of layers.) The bending stiffness G calculated by dividing the bending stiffness G by the cube of the thickness T of the multilayer stretched film, 3 Value is 50N / mm 2 This is the multilayer stretched film.

[0014] [2] The multilayer stretched film according to [1], wherein the coefficient of dynamic friction when the surfaces of layers A1 of two of the multilayer stretched films are brought into contact with each other and slid against each other is 0.25 or less.

[0015] [3] The multilayer stretched film according to [1] or [2], wherein the sum of the thicknesses of the layers A1 and A2 is 30 to 70% of the total thickness of the multilayer stretched film.

[0016] [4] The multilayer stretched film according to any one of [1] to [3], wherein the layer A1 is composed of two or more layers containing the functional resin.

[0017] [5] The multilayer stretched film according to [4], wherein the thickness of the outermost layer of the two or more layers containing the functional resin constituting the layer A1 is 2 to 30% of the total thickness of the layer A1.

[0018] [6] The multilayer stretched film according to any one of [1] to [5], wherein the Layer A1 and the Layer A2 are each independently a layer containing at least one polyamide resin selected from the group consisting of polyamide 6, polyamide 66, polyamide 6-66, and polyamide MXD6.

[0019] [7] The multilayer stretched film according to [6], wherein the layer A1 and the layer A2 are layers containing polyamide 6.

[0020] [8] The multilayer stretched film according to any one of [1] to [7], wherein at least one of the layers A1 and A2 is a layer containing an amorphous polyamide resin or a terpolymer polyamide, and a polyamide-based resin other than the amorphous polyamide resin and the terpolymer polyamide.

[0021] [9] The multilayer stretched film according to any one of [1] to [8], wherein Layer C is a layer containing a polyolefin-based resin. Effect of the Invention

[0022] According to the present invention, it is possible to obtain a multilayer stretched film which is not only less susceptible to pinholes caused by puncture but also less susceptible to pinholes caused by friction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The present invention will be described in detail below based on preferred embodiments thereof.

[0024] The multilayer stretched film of the present invention is a multilayer stretched film in which layers A1 and A2 containing specific functional resins, layer B containing an adhesive resin, and layer C containing a sealant resin are arranged in the order A1 / B / A2 / C from the outside.

[0025] [Layer A1 and Layer A2 Containing Functional Resin] In the multilayer stretched film of the present invention, at least one functional resin selected from the group consisting of polyamide resins, polyester resins, and ethylene-vinyl alcohol copolymer resins is used as the resin forming Layer A1 and Layer A2. A multilayer stretched film having a layer containing such a functional resin is less likely to develop pinholes due to piercing.

[0026] Examples of the polyamide resin include polyamide 4, polyamide 6, polyamide 7, polyamide 11, polyamide 12, polyamide 46, polyamide 66, polyamide 69, polyamide 610, polyamide 611, polyamide 612, polyamide 6T, polyamide 6I, polyamide 9T, polyamide M5T, polyamide MXD6, copolymer polyamide 6-66, copolymer polyamide 6-610, copolymer polyamide 6-611, copolymer polyamide 6-12, copolymer polyamide 6-612, copolymer polyamide 6-6T, copolymer polyamide 6-6I, copolymer polyamide 6-66-610, copolymer polyamide 6-66-12, copolymer polyamide 6-66-612, copolymer polyamide 66-6T, copolymer polyamide 66-6I, copolymer polyamide 6T-6I, and copolymer polyamide 66-6T-6I. These polyamide resins may be used alone or in combination of two or more. Among these polyamide resins, polyamide 6, polyamide 66, polyamide MXD6, and copolymer polyamide 6-66 are preferred, with polyamide 6 being more preferred, from the viewpoint of the tendency to be less susceptible to pinholes due to puncture and friction and from the viewpoint of moldability.

[0027] Examples of the polyester resin include aromatic polyester resins such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate. These polyester resins may be used alone or in combination of two or more. Among these polyester resins, polybutylene terephthalate or its copolymer is preferred from the viewpoint of the tendency to be less susceptible to pinholes due to puncture and friction and from the viewpoint of moldability.

[0028] The ethylene-vinyl alcohol copolymer resin may have an ethylene content of 32 to 44 mol %.

[0029] In the multilayer stretched film of the present invention, the layers A1 and A2 are layers containing at least one functional resin selected from the polyamide resin, the polyester resin, and the ethylene-vinyl alcohol copolymer resin, and from the viewpoint of the tendency of pinholes due to puncture and friction to be unlikely to occur, the layers are preferably layers containing the polyamide resin, more preferably layers containing at least one polyamide resin selected from polyamide 6, polyamide 66, polyamide MXD6, and copolymer polyamide 6-66, and particularly preferably layers containing polyamide 6. The resins constituting the layers A1 and A2 may be the same or different.

[0030] In the multilayer stretched film of the present invention, at least one of the layers A1 and A2 is preferably a layer containing an amorphous polyamide resin or a terpolymer polyamide resin (a copolymer resin of three types of polyamides) and a polyamide-based resin other than the amorphous polyamide resin and the terpolymer polyamide resin (hereinafter, also referred to as "other polyamide-based resin"). This tends to stabilize the stretch moldability. Examples of the amorphous polyamide resin include copolymer polyamide 6T-6I and copolymer polyamide 66-6T-6I. Examples of the terpolymer polyamide resin include copolymer polyamide 6-66-610, copolymer polyamide 6-66-12, copolymer polyamide 6-66-612, and copolymer polyamide 66-6T-6I. These amorphous polyamide resins and terpolymer polyamide resins may be used alone or in combination of two or more. Among these amorphous polyamide resins and terpolymer polyamide resins, copolymer polyamide 6T-6I and copolymer polyamide 6-66-12 are preferred, and copolymer polyamide 6T-6I is more preferred, from the viewpoint that stretch moldability tends to be stable.

[0031] Furthermore, in the multilayer stretched film of the present invention, the layer A1 may be composed of one layer containing the functional resin, or may be composed of two or more layers containing the functional resin, but from the viewpoint of a tendency to reduce the occurrence of pinholes due to friction, it is preferable that the layer A1 is composed of two or more layers containing the functional resin. Moreover, in such a layer A1 composed of two or more layers containing the functional resin, the resins constituting each layer may be the same or different.

[0032] In the multilayer stretched film of the present invention, it is preferable that at least one of an antiblocking agent and a slipping agent is contained in the outermost layer (when the layer A1 is one layer, the layer A1, when the layer A1 is two or more layers, the outermost layer of the layer A1). This reduces the friction on the surface of the multilayer stretched film, and pinholes due to friction tend to be less likely to occur. Examples of the antiblocking agent include inorganic particles such as silica and zeolite, and examples of the slipping agent include ethylene bis fatty acid amides such as ethylene bis stearic acid amide and ethylene bis behenic acid amide, and fatty acid metal salts such as sodium montanate. The content of such an antiblocking agent and a slipping agent is not particularly limited, but is preferably 0.1 to 2.0 parts by mass, more preferably 0.2 to 0.6 parts by mass, based on 100 parts by mass of the functional resin.

[0033] Furthermore, in the multilayer stretched film of the present invention, the Layer A1 and the Layer A2 may contain various additives, such as an antistatic agent, an antioxidant, and an agent for improving pinhole resistance against bending, if necessary.

[0034] [Layer B containing adhesive resin] Examples of the adhesive resin include polyolefin resins modified with unsaturated aliphatic carboxylic anhydrides, such as maleic anhydride-modified polyethylene resins; olefin copolymer elastomers modified with unsaturated aliphatic carboxylic anhydrides, such as maleic anhydride-modified ethylene-propylene copolymer elastomers; ethylene-vinyl acetate copolymers modified with unsaturated aliphatic carboxylic anhydrides, such as maleic anhydride-modified ethylene-vinyl acetate copolymers; and copolymers of ethylene and unsaturated aliphatic carboxylic acids, such as ethylene-(meth)acrylic acid copolymers.

[0035] [Layer C containing sealant resin] Examples of the sealant resin include polyethylene-based resins such as high density polyethylene (HDPE), medium density polyethylene (MDPE), low density polyethylene (LDPE), and linear low density polyethylene (LLDPE); ethylene-based copolymers such as ethylene-α-olefin copolymers consisting of ethylene and an α-olefin having 3 to 20 carbon atoms, ethylene-acrylic acid copolymers, ethylene-acrylic acid ester copolymers, ethylene-methacrylic acid copolymers, ethylene-methacrylic acid ester copolymers (EMMA), and ethylene-vinyl acetate copolymers (EVA); and polyolefin-based resins such as polypropylene-based resins such as polypropylene.

[0036] In the multilayer stretched film of the present invention, the layer C is a layer containing the sealant resin, and preferably further contains an adhesive resin from the viewpoint of improving adhesion to a layer (particularly, layer A2) adjacent to the layer C. When the layer C is a layer containing the sealant resin and the adhesive resin, the layer C may be a layer consisting of a mixture of the sealant resin and the adhesive resin, or a layer in which a layer consisting of the sealant resin and a layer consisting of the adhesive resin are laminated.

[0037] [Multilayer Stretched Film] The multilayer stretched film of the present invention is a multilayer stretched film in which layers A1 and A2 containing the functional resin, layer B containing the adhesive resin, and layer C containing the sealant resin are arranged in the order A1 / B / A2 / C from the outside.

[0038] The multilayer stretched film of the present invention has a layer structure [A1 / B / A2] in which the layer A1 containing the functional resin and the layer A2 are bonded by the layer B containing the adhesive resin. This makes it difficult for pinholes due to piercing to occur, and also makes it difficult for pinholes due to friction to occur. On the other hand, when the layer A1 and the layer A2 are not bonded by the layer B, that is, when the multilayer stretched film has a layer structure [A1 / A2], pinholes due to piercing are unlikely to occur, but pinholes due to friction are likely to occur. In addition, when the layer A2 is not formed, for example, when the layer A1 and the layer C containing the sealant resin are bonded by the layer B, that is, when the multilayer stretched film has a layer structure [A1 / B / C], pinholes due to friction are likely to occur.

[0039] In the multilayer stretched film of the present invention, the thickness of the film is 25 to 70 μm. A multilayer stretched film having such a thickness is thin and is unlikely to develop pinholes due to puncture. On the other hand, if the thickness of the film is less than the lower limit, pinholes due to puncture are likely to develop. On the other hand, if the thickness of the film is more than the upper limit, the film is not sufficiently thin. In addition, from the viewpoint of sufficiently thinning the film and making it less likely to develop pinholes due to puncture, the thickness of the multilayer stretched film is preferably 30 to 65 μm, more preferably 35 to 60 μm, and particularly preferably 40 to 55 μm.

[0040] In the multilayer stretched film of the present invention, the thickness of the layer A1 is 10 to 90% of the total thickness of the layer A1 and the layer A2. A multilayer stretched film in which the thickness ratio of the layer A1 is within the above range is less likely to have pinholes due to puncture and friction. On the other hand, when the thickness ratio of the layer A1 is less than the lower limit, pinholes due to puncture and friction are more likely to occur. On the other hand, when the thickness ratio of the layer A1 is more than the upper limit, pinholes due to friction are more likely to occur. In addition, from the viewpoint of less likely to have pinholes due to puncture and friction, the thickness ratio of the layer A1 is preferably 20 to 80%, more preferably 30 to 70%, and particularly preferably 40 to 60% of the total thickness of the layer A1 and the layer A2.

[0041] Furthermore, in the multilayer stretched film of the present invention, the following formulas (1) and (2):

[0042]

number

[0043] (In formulas (1) and (2), E i represents the Young's modulus of the resin constituting layer i, and t i represents the thickness of layer i, and n represents the total number of layers.) The bending stiffness G calculated by dividing the bending stiffness G by the cube of the thickness T of the multilayer stretched film, 3 Value is 50N / mm 2 That's all. 3 Multilayer stretched films with this value are less likely to wrinkle and are less likely to develop pinholes due to friction. 3 If the value is less than the lower limit, wrinkles are likely to occur in the film, and pinholes (pinholes due to friction) are likely to occur due to rubbing of these wrinkles. 3 The value is 55N / mm 2 More than 60N / mm is preferable. 2 More than 100% is preferable. On the other hand, G / T 3There is no particular upper limit for the value, but from the viewpoint of film manufacturing costs, it is set to 100N / mm 2 Less than 80N / mm is preferable. 2 The following is more preferred:

[0044] In addition, G / T 3 The Young's modulus of the resin can be increased by dividing the layer A1 containing the functional resin or increasing the stretch ratio, and can be decreased by integrating the layer A1 containing the functional resin or decreasing the stretch ratio. The Young's modulus of the resin can be measured by the method described later.

[0045] In the multilayer stretched film of the present invention, the coefficient of dynamic friction when the surfaces of two sheets of the multilayer stretched film (i.e., the surfaces of the layer A1) are brought into contact with each other and slid against each other is preferably 0.25 or less, more preferably 0.20 or less. A multilayer stretched film having such a coefficient of dynamic friction is less likely to develop pinholes due to friction.

[0046] Furthermore, in the multilayer stretched film of the present invention, it is preferable to use a resin having a dynamic friction coefficient within the above range (preferably a resin having a smaller dynamic friction coefficient) as the resin constituting the outermost layer (when layer A1 is a single layer, layer A1, or when layer A1 is two or more layers, the outermost layer of layer A1). An example of such a resin having a dynamic friction coefficient within the above range is polyamide 6.

[0047] In the multilayer stretched film of the present invention, the total thickness of the layer A1 and the layer A2 is preferably 30 to 70%, more preferably 40 to 60%, of the total thickness of the multilayer stretched film. A multilayer stretched film in which the ratio of the total thickness of the layer A1 and the layer A2 is within the above range is less likely to develop pinholes due to puncture and friction. On the other hand, if the ratio of the total thickness of the layer A1 and the layer A2 is less than the lower limit, pinholes due to puncture and friction tend to be more likely to be developed, and on the other hand, if the ratio of the total thickness of the layer A1 and the layer A2 exceeds the upper limit, the seal strength tends to be insufficient.

[0048] Furthermore, in the multilayer stretched film of the present invention, the layer A1 may be one layer containing the functional resin or two or more layers containing the functional resin. When the layer A1 is two or more layers containing the functional resin, the thickness of the outermost layer is preferably 2 to 30% of the total thickness of the layer A1, more preferably 5 to 20%, and particularly preferably 8 to 15%. A multilayer stretched film in which the thickness ratio of the outermost layer is within the above range is less likely to cause pinholes due to puncture and friction. On the other hand, if the thickness ratio of the outermost layer is less than the lower limit, pinholes due to puncture and friction tend to be more likely to occur, and on the other hand, if the thickness ratio of the outermost layer exceeds the upper limit, the amount of antiblocking agent added tends to increase, resulting in increased costs.

[0049] The multilayer stretched film of the present invention can be produced, for example, as follows. 3 The functional resin A1 forming the layer A1 (when the layer A1 is composed of two or more layers, the functional resins forming each layer) A1, the functional resin A2 forming the layer A2, the adhesive resin B forming the layer B, and the sealant resin C forming the layer C are selected so that the value falls within a predetermined range, and the thickness of each layer is set [Preparation step]. Then, the selected functional resin A1, the adhesive resin B, the functional resin A2, and the sealant resin C are co-extruded so that each layer has a predetermined thickness, to form a multilayer film having a layer structure [A1 / B / A2 / C] [Co-extrusion step]. Next, this multilayer film is biaxially stretched in the machine direction (MD) of the film and in the direction perpendicular thereto (TD) so that each layer has a set thickness [Stretching step]. Thereafter, the stretched multilayer film is heat-treated at a temperature near the melting point of the functional resin [Heat treatment step] to obtain a desired multilayer stretched film.

[0050] The co-extrusion method in the co-extrusion step is not particularly limited, but a method in which the resins (or compositions thereof) of each layer are co-extruded and laminated using multiple extruders and annular dies, and then molded into a tubular shape by a water-cooled inflation method to obtain a multilayer film (co-extrusion water-cooled inflation method) is preferred.

[0051] The stretching method in the stretching step is not particularly limited, but it is preferable to subject the tubular multilayer film to simultaneous longitudinal and transverse biaxial stretching by a tubular stretching method. By subjecting the multilayer film to biaxial stretching, the mechanical strength of the multilayer stretched film can be improved.

[0052] In the heat treatment step, the stretched multilayer film is heat-treated at a temperature near the melting point of the functional resin. This relieves residual stress caused by stretching, and a multilayer stretched film with excellent dimensional stability can be obtained. In addition, such heat treatment may be performed in a state where the stretched multilayer film is relaxed in MD and / or TD.

[0053] The method of the heat treatment in the heat treatment step is not particularly limited, but for example, a tenter can be used for the heat treatment. At this time, in order to prevent the innermost layers from fusing together, it is preferable to perform the heat treatment while supplying air into the inside of the tubular multilayer film to prevent the innermost layers from contacting each other, or to perform the heat treatment while slitting both ends of the tubular multilayer film and providing a gap between the films. In addition, coextrusion, stretching, and heat treatment may be performed in a state in which the layer C that will ultimately become the innermost layer is on the outside, and slits are made at both ends of the obtained tubular multilayer stretched film to produce the multilayer stretched film of the present invention. EXAMPLES

[0054] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples. The Young's modulus of each resin was measured according to the following method. The Young's modulus of the resins used in the examples and comparative examples is shown in Table 1.

[0055] [Young's Modulus] (How to prepare test specimens) For each resin, a film formed by the water-cooled inflation method was subjected to simultaneous longitudinal and transverse biaxial stretching by the tubular stretching method at a stretch ratio of 3 times in the machine direction (MD) of the film and 3 times in the direction perpendicular to this (TD), and then heat-treated at 220°C using a tenter. The heat-treated film was conditioned in accordance with JIS K7100 in an environment of a temperature of 23°C and a relative humidity of 50%, and a rectangular test piece (thickness: 0.05 mm) with one side of 10 mm and the other side extending in the direction perpendicular to the first side of 150 mm was prepared.

[0056] (Method of measuring Young's modulus) Young's modulus was measured using Shimadzu Corporation's Autograph AGS-X in accordance with JIS K7127. In an environment with a temperature of 23°C and a relative humidity of 50%, the test piece was moved from the initial state held between the gripping tools at a distance of 80 mm, and the Young's modulus was calculated from the stress at a stroke of 0.4 to 1.4 mm.

[0057] [Table 1]

[0058] Example 1 The layers were arranged in the order of Layer A1 / Layer B / Layer A2 / Layer C from the outside, and a multilayer stretched film was produced in which Layer A1 was made up of two layers. A 6NY composition obtained by adding silica (5400 ppm) as an antiblocking agent and ethylenebisfatty acid amide (2200 ppm) as a slip agent to 6NY as a functional resin for the outermost layer of the layer A1; The functional resin of the inner layer of the layer A1 is 6NY+ANY, AD as the adhesive resin of layer B; As the functional resin of layer A2, 6NY and Layer C sealant resin is mLL+LD+AD. Using these, five types of five layers were coextruded by the coextrusion water-cooling inflation method at an extrusion temperature of 250°C for the 6NY composition, 260°C for the 6NY+ANY, 220°C for the AD, and 230°C for the mLL+LD+AD, to produce a multilayer film consisting of 6NY layer (3) / 6NY+ANY layer (23) / AD layer (23) / 6NY layer (26) / mLL+LD+AD layer (25). The numbers in parentheses for each layer indicate the percentage of the thickness relative to the entire film (unit: %) (same below). This multilayer film was subjected to simultaneous longitudinal and transverse biaxial stretching by a tubular stretching method at a stretch ratio of 3 times in the machine direction (MD) of the film and 3 times in the direction perpendicular to the machine direction (TD), and then heat treatment was performed at 220°C using a tenter to obtain a multilayer stretched film (film thickness: 50 μm) consisting of 6NY layer (3) / 6NY+ANY layer (23) / AD layer (23) / 6NY layer (26) / mLL+LD+AD layer (25).

[0059] Example 2 A 6NY composition obtained by adding silica (5400 ppm) as an antiblocking agent and ethylenebisfatty acid amide (2200 ppm) as a slip agent to 6NY as a functional resin for the outermost layer of the layer A1; The functional resin of the inner layer of the layer A1 is 6NY, AD as the adhesive resin of layer B; The functional resin of layer A2 is 6NY+ANY, Layer C sealant resin is mLL+LD+AD. A multilayer stretched film (thickness: 50 μm) consisting of 6NY layer (3) / 6NY layer (23) / AD layer (23) / 6NY+ANY layer (26) / mLL+LD+AD layer (25) was obtained in the same manner as in Example 1, except that the above was used.

[0060] Example 3 The outermost layer of the layer A1 is made of a MXD6+6NY composition obtained by adding silica (1300 ppm) as an antiblocking agent and ethylenebisfatty acid amide (2400 ppm) as a slip agent to MXD6+6NY as a functional resin. The functional resin of the inner layer of the layer A1 is 6NY+ANY, AD as the adhesive resin of layer B; The functional resin of layer A2 is 6NY+ANY, Layer C sealant resin is mLL+LD+AD. A multilayer stretched film (film thickness: 50 μm) consisting of an MXD6+6NY layer (3) / 6NY+ANY layer (23) / AD layer (23) / 6NY+ANY layer (26) / mLL+LD+AD layer (25) was obtained in the same manner as in Example 1, except that the extrusion temperature of the MXD6+6NY composition was 260° C.

[0061] Example 4 A PBT composition obtained by adding silica (13,000 ppm) as an antiblocking agent and sodium montanate (6,800 ppm) as a slip agent to PBT as a functional resin for the outermost layer of the layer A1; The functional resin of the inner layer of the layer A1 is PBT, AD as the adhesive resin of layer B; The functional resin of layer A2 is 6NY+ANY, Layer C sealant resin is mLL+LD+AD. A multilayer stretched film (film thickness: 50 μm) consisting of PBT (3) / 6NY+ANY layer (10) / AD layer (23) / 6NY+ANY layer (39) / mLL+LD+AD layer (25) was obtained in the same manner as in Example 1, except that the extrusion temperature of the PBT composition was 250° C.

[0062] Comparative Example 1 A multilayer stretched film was produced in the order of Layer A1 / Layer B / Layer C from the outside, with Layer A1 being composed of two layers. A 610NY composition obtained by adding silica (5000 ppm) as an antiblocking agent and ethylenebisfatty acid amide (47 ppm) as a slip agent to 610NY as a functional resin for the outermost layer of the layer A1; The functional resin of the inner layer of the layer A1 is 6NY+ANY, AD as the adhesive resin of layer B; As the sealant resin for layer C, LL and A multilayer stretched film (film thickness: 50 μm) consisting of a 610NY layer (3) / 6NY+ANY layer (53) / AD layer (10) / LL layer (34) was obtained in the same manner as in Example 1, except that the extrusion temperatures of the 610NY composition and the LL composition were set to 250° C. and 220° C., respectively, and four types of four layers were co-extruded.

[0063] Comparative Example 2 The outermost layer of the layer A1 is made of a functional resin composition obtained by adding silica (6800 ppm) as an antiblocking agent and ethylenebisfatty acid amide (230 ppm) as a slip agent to 6NY, The functional resin of the inner layer of the layer A1 is 6NY+ANY, AD as the adhesive resin of layer B; As the functional resin of layer A2, 6-66NY and Layer C sealant resin is mLL+LD+AD. A multilayer stretched film (film thickness: 50 μm) consisting of 6NY layer (4) / 6NY+ANY layer (24) / AD layer (25) / 6-66NY layer (20) / mLL+LD+AD layer (27) was obtained in the same manner as in Example 1, except that the extrusion temperature of 6-66NY was set to 240° C.

[0064] Comparative Example 3 A 6NY composition obtained by adding silica (4900 ppm) as an antiblocking agent and ethylenebisfatty acid amide (420 ppm) as a slip agent to 6NY as a functional resin for the outermost layer of the layer A1; The functional resin of the inner layer of the layer A1 is 6NY, AD as the adhesive resin of layer B; As the sealant resin for layer C, LL and A multilayer stretched film (film thickness: 65 μm) consisting of a 6NY layer (3) / 6NY layer (36) / AD layer (10) / LL layer (51) was obtained in the same manner as in Comparative Example 1, except that the extrusion temperature of the 6NY composition and 6NY was 250° C.

[0065] Comparative Example 4 A multilayer film was prepared in which the layer A1 and the layer C were arranged in this order from the outside. Specifically, As layer A1, an ONY film; The sealant resin for layer C is PE and PE was extruded onto the ONY film at an extrusion temperature of 180° C. to obtain a multilayer stretched film (film thickness: 70 μm) consisting of an ONY layer (21) and a PE layer (79).

[0066] (Bending strength) The bending stiffness G of the obtained multilayer stretched film was calculated using the following formulas (1) and (2):

[0067]

number

[0068] (In formulas (1) and (2), E i represents the Young's modulus of the resin constituting layer i, and t i represents the thickness of layer i, and n represents the total number of layers.) The obtained G value is divided by the cube of the thickness T of the multilayer stretched film to obtain G / T 3 The values ​​were calculated and the results are shown in Table 2.

[0069] (Kinematic friction coefficient) The dynamic friction coefficient was measured when the surfaces of the outermost layers of the two obtained multilayer stretched films were brought into contact with each other and slid against each other according to the method described in JIS K7125: 1999. The results are shown in Table 2.

[0070] (Puncture strength) According to the method described in JIS Z0238:1998, the obtained multilayer stretched film was fixed to a film piercing strength test fixture and pierced with a semicircular needle having a diameter of 1.0 mm and a tip radius of 0.5 mm at a speed of 50±5 mm per minute, and the maximum stress until the needle penetrated was measured. The results are shown in Table 2.

[0071] (Transportation packaging test (number of pinholes caused by friction)) The obtained multilayer stretched film was made into a bag with a size of 200 mm x 300 mm, 500 g of cut pumpkin was put into the obtained bag, vacuum-packed, and then frozen at -20 ° C. 20 bags of this frozen product were prepared, and these were put into two cardboard boxes, 10 bags each, and a transportation packaging test (vibration test) was performed for each cardboard box under the condition of a transportation distance of 3000 km using a three-axis simultaneous vibration generation type transportation packaging tester ("BF-50UT" manufactured by IDEXX Co., Ltd.). This transportation packaging test was performed on 20 bags of the frozen product (two cardboard boxes), and the number of bags that broke out of the 20 bags was evaluated as the number of pinholes caused by friction. The results are shown in Table 2.

[0072] [Table 2]

[0073] As shown in Table 2, in a multilayer stretched film having a layer containing a functional resin such as a polyamide resin or a polyester resin and a layer containing a sealant resin, at least two layers containing the functional resin are formed, and the two layers containing the functional resin (layer A1 and layer A2) are bonded with layer B containing an adhesive resin to form a layer structure (A1 / B / A2). Furthermore, the bending stiffness G of the multilayer stretched film is divided by the cube of the film thickness T, giving a G / T 3 It was confirmed that by setting the value within a predetermined range, not only was pinholes caused by puncture less likely to occur, but pinholes caused by friction were also less likely to occur (Examples 1 to 4). In addition, by comparing the multilayer stretched films obtained in Examples 1 and 2 with the multilayer stretched film obtained in Example 3, it was also found that by reducing the surface kinetic friction coefficient, pinholes caused by friction were less likely to occur.

[0074] On the other hand, even if the multilayer stretched film has a layer containing the functional resin and a layer containing a sealant resin, the multilayer stretched film has a layer structure (A1 / B / C) in which the layer A1 containing the functional resin and the layer C containing the sealant resin are bonded with the layer B containing an adhesive resin, and the G / T of the multilayer stretched film is 3When the value was smaller than the predetermined range (Comparative Examples 1 and 3), pinholes due to puncture were unlikely to occur, but pinholes due to friction were likely to occur. In particular, it was found that as the surface kinetic friction coefficient increased, pinholes due to friction tended to occur more easily.

[0075] In addition, even if the multilayer stretched film has the layer structure (A1 / B / A2), the G / T of the multilayer stretched film is 3 It was found that when the value was smaller than the predetermined range (Comparative Example 2), pinholes due to friction were easily generated. Furthermore, even in the case of a multilayer stretched film having a layer containing a functional resin and a layer containing a sealant resin, the layer A1 containing the functional resin and the layer C containing the sealant resin were laminated without the layer B containing an adhesive resin in between (A1 / C), and the G / T of the multilayer stretched film was 3 It was found that when the value was smaller than the predetermined range (Comparative Example 4), pinholes due to friction were likely to occur, and pinholes due to puncture were also likely to occur. [Industrial Applicability]

[0076] As described above, according to the present invention, it is possible to obtain a multilayer stretched film that is not only less susceptible to pinholes caused by puncture but also less susceptible to pinholes caused by friction. Therefore, the multilayer stretched film of the present invention is useful as a lid material for various containers, a pillow packaging material, a pouch packaging material, etc. in various fields such as food, medicine, and daily necessities, and is particularly useful as a vacuum packaging material.

Claims

1. A multilayer stretched film comprising a layer A1 and a layer A2 each containing at least one functional resin selected from the group consisting of a polyamide-based resin, a polyester-based resin, and an ethylene-vinyl alcohol copolymer resin, a layer B containing an adhesive resin, and a layer C containing a sealant resin, which are arranged in this order from the outside in the order of A1 / B / A2 / C, The thickness of the multilayer stretched film is 25 to 70 μm, the thickness of the layer A1 is 10 to 90% of the total thickness of the layer A1 and the layer A2, Regarding the multilayer stretched film, the following formulas (1) and (2): [0010] (In formulas (1) and (2), E ｉ represents the Young's modulus of the resin constituting the layer i, and t ｉ represents the thickness of layer i, and n represents the total number of layers. The bending stiffness G obtained by dividing the bending stiffness G by the cube of the thickness T of the multilayer stretched film is G / T. ３ Value is 50N / mm ２ A multilayer stretched film characterized by the above.

2. 2. The multilayer stretched film according to claim 1, wherein the coefficient of dynamic friction when the surfaces of the layers A1 of two sheets of the multilayer stretched film are brought into contact with each other and slid against each other is 0.25 or less.

3. 2. The multilayer stretched film according to claim 1, wherein the sum of the thicknesses of the layers A1 and A2 is 30 to 70% of the total thickness of the multilayer stretched film.

4. 2. The multilayer stretched film according to claim 1, wherein the layer A1 comprises two or more layers containing the functional resin.

5. The multilayer stretched film according to claim 4, characterized in that the thickness of the outermost layer among the two or more layers containing the functional resin that constitute the layer A1 is 2 to 30% of the total thickness of the layer A1.

6. The multilayer stretched film according to claim 1, wherein the Layer A1 and the Layer A2 are each independently a layer containing at least one polyamide-based resin selected from the group consisting of polyamide 6, polyamide 66, polyamide 6-66, and polyamide MXD6.

7. 7. The multilayer stretched film according to claim 6, wherein the layer A1 and the layer A2 contain polyamide 6.

8. 2. The multilayer stretched film according to claim 1, wherein at least one of the layers A1 and A2 is a layer containing an amorphous polyamide resin or a terpolymer polyamide, and a polyamide-based resin other than the amorphous polyamide resin and the terpolymer polyamide.

9. 2. The multilayer stretched film according to claim 1, wherein the layer C is a layer containing a polyolefin resin.

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