Stretched film and method for producing same

Abstract

Provided is a stretched film (10) comprising at least a substrate layer (3) and a barrier layer (5), wherein the substrate layer (3) is mainly composed of polyethylene having a density of at least 0.950 g / cm3, the barrier layer (5) is mainly composed of an ethylene-vinyl alcohol copolymer and has a water vapor permeability of 3.5 g / m2･day or less, and the film has a heat shrinkage rate of 5% or less when heated at 100°C for 10 minutes in the film stretching direction.

Description

[Technical Field]

[0001] The present invention relates to a stretched film used for packaging films and the like, and a method for producing the same. [Background technology]

[0002] Conventionally, as packaging films used for pouches and the like, a laminate has been used in which, for example, a base film made of a resin material and a sealant film made of a material different from the resin material that makes up the base film are laminated together.

[0003] There is a demand for reducing the environmental impact of plastics in general, and packaging films are also required to be recyclable. However, in the case of laminates in which films made of the above-mentioned different materials are stacked, there is a problem in that it is difficult to separate the materials, making recycling difficult.

[0004] Therefore, in recent years, there has been an active movement toward mono-material packaging films, which are made from a single material. Examples of resins used in mono-material packaging films include polyethylene, polypropylene, and polyethylene terephthalate. Of these, polyethylene is the most widely used material in existing packaging films, and is a material for which mono-materialization is particularly sought after. However, polyethylene alone has poor gas barrier properties (oxygen barrier properties), making it impossible to set expiration dates like with conventional laminated films, and there are also problems with odor leakage when the contents are cosmetics such as detergent or shampoo.

[0005] Therefore, as a method for providing gas barrier properties, for example, a stretched film including a base layer primarily composed of a polyethylene resin and a barrier layer primarily composed of an ethylene-vinyl alcohol copolymer (EVOH) has been proposed. It is described that, with this configuration, a barrier layer primarily composed of an ethylene-vinyl alcohol copolymer can be provided by a T-die or inflation molding method, as with conventional laminated films, and therefore a stretched film with added oxygen barrier properties can be produced without increasing the number of manufacturing facilities or manufacturing steps. It is also described that by constructing other layers (base layer, sealant film layer) from polyethylene and reducing the ethylene-vinyl alcohol copolymer content, the entire laminate can be considered as a single material made of polyethylene, thereby improving recyclability (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2021-154656 Summary of the Invention [Problem to be solved by the invention]

[0007] Here, ethylene-vinyl alcohol copolymers have oxygen barrier properties but do not have water vapor barrier properties. It is also known that the oxygen barrier properties of ethylene-vinyl alcohol copolymers decrease in high humidity environments. In the stretched film described in Patent Document 1, the resin constituting the base layer is 0.925 g / cm 3 Although polyethylene having the above density has been disclosed, the base layer has the problem of insufficient water vapor barrier properties. Furthermore, the heat shrinkage rate at 100°C is large, and the base layer shrinks during heat sealing performed during bag production, causing wrinkles and poor appearance. As a result, it has been difficult to achieve both water vapor barrier properties and heat resistance.

[0008] The present invention has been made in view of the above problems, and has an object to provide a stretched film that has excellent water vapor barrier properties and heat resistance as well as excellent oxygen barrier properties. [Means for solving the problem]

[0009] In order to achieve the above object, the stretched film of the present invention comprises at least a first substrate layer and a barrier layer, and the first substrate layer has a density of 0.950 g / cm 3 The barrier layer is made of polyethylene with a water vapor permeability of 3.5 g / m or more, and the barrier layer is made of ethylene-vinyl alcohol copolymer with a water vapor permeability of 3.5 g / m or more. 2 ·days or less, and the heat shrinkage rate when heated at 100°C for 10 minutes in the stretching direction of the film is 5% or less.

[0010] In addition, the method for producing a stretched film of the present invention is for producing a stretched film having a density of 0.950 g / cm 3 The method comprises at least the steps of preparing a raw film having at least a base layer mainly composed of the above-mentioned polyethylene and a barrier layer mainly composed of an ethylene-vinyl alcohol copolymer, and performing a stretching process on the raw film, wherein the stretching temperature in the stretching process is 80°C or higher and lower than 130°C, and the stretching ratio is 5 times or higher and 10 times or lower. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a stretched film that has excellent water vapor barrier properties and heat resistance, as well as excellent oxygen barrier properties. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view illustrating a laminate using a stretched film according to a first embodiment of the present invention. [Figure 2] FIG. 1 is a plan view illustrating a laminate using a stretched film according to a first embodiment of the present invention. [Figure 3] FIG. 4 is a cross-sectional view illustrating a laminate using a stretched film according to a second embodiment of the present invention. [Figure 4] FIG. 4 is a plan view illustrating a laminate using a stretched film according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] The stretched film of the present invention will be specifically described below. Note that the present invention is not limited to the following embodiments, and can be appropriately modified and applied within the scope of the present invention.

[0014] (First embodiment) FIG. 1 is a cross-sectional view showing a laminate using a stretched film according to a first embodiment of the present invention.

[0015] The laminate 1 comprises a stretched film 10 composed of a base layer 3 whose main component is polyethylene and a barrier layer 5 whose main component is an ethylene-vinyl alcohol copolymer and which is laminated to the base layer 3 via an adhesive layer 4, and a sealant film 2 laminated on the barrier layer 5 of the stretched film 10.

[0016] <Sealant film> From the viewpoint of mono-materials, the sealant film 2 is preferably a polyethylene resin, more specifically, high density polyethylene (HDPE), medium density polyethylene (MDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), etc.

[0017] From the viewpoint of improving heat sealability, it is preferable to use low-density polyethylene (LDPE) or linear low-density polyethylene (LLDPE) having a melting point lower than that of the base layer 3 in order to provide a difference in melting point with the base layer 3.

[0018] The polyethylene content in the sealant film 2 is preferably 70% or more, more preferably 90% or more, even more preferably 95% or more, and most preferably 100%.

[0019] The thickness of the sealant film 2 is preferably 20 μm to 200 μm, and more preferably 30 μm to 150 μm.

[0020] Furthermore, the sealant film 2 may contain components other than the polyethylene resin described above, as long as the properties of the sealant film 2 are not impaired.

[0021] Other components include olefin resins, amide antiblocking agents (such as stearic acid amide), plasticizers, ultraviolet absorbers, antioxidants, weather stabilizers, antistatic agents, colorants, antifogging agents, metal soaps, waxes, mildew inhibitors, antibacterial agents, nucleating agents, flame retardants, and lubricants.

[0022] <Base layer (first base layer)> The base layer 3 provides the stretched film 10 with water vapor barrier properties and is mainly composed of high density polyethylene (HDPE). In the present invention, the density of high density polyethylene is 0.950 g / cm 3 The density is 0.950 g / cm or more. 3 In the above cases, the crystallinity of the polyethylene is improved, and therefore the water vapor barrier property can be improved.

[0023] From the viewpoint of further improving the water vapor barrier property, the density of high-density polyethylene is 0.955 g / cm 3 Preferably, it is greater than 0.962 g / cm 3 More preferably, it is 0.970 / cm or more. 3 More preferably, it is equal to or greater than this.

[0024] The melt mass flow rate (MFR) of the high-density polyethylene is preferably 0.01 to 3.00 g / 10 min, more preferably 0.02 to 2.50 g / 10 min, and even more preferably 0.1 to 2.00 g / 10 min. This is because a melt mass flow rate (MFR) of 0.01 g / 10 min or more allows molding using a general-purpose extruder without the need for special equipment, and a melt mass flow rate (MFR) of 3.00 g / 10 min or less allows sufficient film strength to be achieved.

[0025] The melt mass flow rate can be obtained by measuring in accordance with the standard of JIS K7210:1999.

[0026] Furthermore, from the viewpoint of obtaining excellent water vapor barrier properties, the content of high-density polyethylene in the entire base layer 3 is preferably 90% by mass or more, and more preferably 95% by mass or more, of 100% by mass of the base layer.

[0027] From the above, the resin forming the base layer 3 is selected to have a density of 0.950 g / cm 3 By using the above high density polyethylene, the water vapor permeability of the stretched film 10 is 3.5 g / m 2 ·days or less, it is possible to provide a stretched film 10 with excellent water vapor barrier properties.

[0028] From the viewpoint of improving the water vapor barrier property, the water vapor permeability of the stretched film 10 is set to 3.0 g / m 2 ·day or less is preferable, 2.5g / m 2 ·day or less is preferable.

[0029] The term "water vapor permeability" as used herein refers to a value measured using a water vapor permeability measuring device in accordance with JIS K 7129-1 under an atmosphere of a temperature of 40°C and a humidity of 90%.

[0030] Furthermore, the base layer 3 may contain components other than the above-mentioned high-density polyethylene, as long as the stretchability of the film is not impaired.

[0031] Other components include olefin resins, amide antiblocking agents (such as stearic acid amide), plasticizers, ultraviolet absorbers, antioxidants, weather stabilizers, antistatic agents, colorants, antifogging agents, metal soaps, waxes, mildew inhibitors, antibacterial agents, nucleating agents, flame retardants, and lubricants.

[0032] <Barrier layer> The barrier layer 5 provides the stretched film 10 with oxygen barrier properties, and is composed mainly of ethylene-vinyl alcohol copolymer (EVOH).

[0033] The ethylene-vinyl alcohol copolymer used in the barrier layer 5 is not particularly limited, but the ethylene content (ethylene unit content) in the ethylene-vinyl alcohol copolymer is preferably 30 to 40 mol %, and more preferably 32 to 38 mol %, relative to the total amount (100 mol %) of all monomer units constituting the ethylene-vinyl alcohol copolymer. This is because an ethylene content of less than 30 mol % may reduce the processability of the barrier film, and an ethylene content of more than 40 mol % may result in insufficient oxygen barrier properties.

[0034] Furthermore, from the viewpoint of obtaining excellent oxygen barrier properties, the content of the ethylene-vinyl alcohol copolymer in the entire barrier layer 5 is preferably 90% by mass or more, and more preferably 95% by mass or more, of 100% by mass of the barrier layer.

[0035] From the above, by using an ethylene-vinyl alcohol copolymer as the resin for forming the barrier layer 5, the oxygen permeability of the stretched film 10 can be reduced to 10 cc / m 2 ·days or less, it is possible to provide a stretched film 10 with excellent oxygen barrier properties.

[0036] From the viewpoint of improving the oxygen barrier property, the oxygen permeability of the stretched film 10 is set to 5.0 cc / m 2 ·day or less is preferable, 3.0cc / m2 ·day or less is preferable, 1.5cc / m 2 ·day or less is even more preferable.

[0037] The "oxygen permeability" referred to here is measured using an oxygen permeability measuring device in accordance with JIS K 7126-1 in an atmosphere at a temperature of 23°C and humidity of 0%.

[0038] Furthermore, similar to the above-described base layer 3, the barrier layer 5 may contain components other than the ethylene-vinyl alcohol copolymer (for example, other components in the above-described base layer 3) to the extent that the stretchability of the film is not impaired.

[0039] <Adhesive layer (first adhesive layer)> The adhesive layer 4 is used to bond the base layer 3 and the barrier layer 5 together, and is mainly composed of a material that has excellent adhesive properties to the base layer 3 and the barrier layer 5, such as modified polyolefin.

[0040] Examples of the modified polyolefin include modified polyethylene and modified polypropylene. More specifically, acid-modified polyethylene and acid-modified polypropylene are included. From the viewpoint of monomaterials, modified polyethylene is preferred.

[0041] <Method of manufacturing laminate> Next, a method for producing a laminate using the stretched film of this embodiment will be described in detail.

[0042] First, resin compositions to be used for the substrate layer, barrier layer, and adhesive layer are prepared.

[0043] Next, using an extruder equipped with a T-die, the resin compositions for each layer are co-extruded at a predetermined temperature to obtain a raw film before stretching, which has a base layer 3, an adhesive layer 4 provided on the surface of the base layer 3, and a barrier layer 5 provided on the surface of the adhesive layer 4.

[0044] The raw film is then subjected to uniaxial stretching or biaxial stretching to produce a stretched film 10 in which the base layer 3, adhesive layer 4, and barrier layer 5 are laminated in this order, as shown in Figures 1 and 2, with the adhesive layer 4 provided between the base layer 3 and the barrier layer 5. The stretching method is not particularly limited, and examples thereof include roll stretching and tenter stretching.

[0045] The uniaxial stretching treatment described above refers to a stretching treatment performed in either the machine axis (longitudinal) direction (hereinafter referred to as "MD") of the film or the direction perpendicular to the MD (hereinafter referred to as "TD"), as shown in Figure 2. Note that a biaxial stretching treatment may also be performed in which stretching is performed in both the MD and TD directions.

[0046] The stretching temperature in the uniaxial stretching treatment is 80°C or higher and lower than 130°C, and preferably 100°C or higher and 120°C or lower. This is because if the temperature is lower than 80°C, the film may become cloudy. If the stretching temperature is 130°C or higher, the film may melt and break.

[0047] The stretching ratio in the uniaxial stretching treatment is 5 to 10 times. This is because if the stretching ratio is less than 5 times, unstretched portions will remain, which may result in a decrease in tensile strength and transparency. If the stretching ratio is more than 10 times, the film may break. From the viewpoint of improving tensile strength and transparency and preventing film breakage, a stretching ratio of 6 to 8 times is preferred.

[0048] The stretched film 10 produced by the above-described stretching process has a haze of 20% or less, making it possible to obtain excellent transparency.

[0049] From the viewpoint of further improving transparency, the haze of the stretched film 10 is preferably 15% or less, more preferably 10% or less, and even more preferably 7% or less.

[0050] The term "haze" used herein refers to an index of cloudiness measured in accordance with JIS K 7361.

[0051] Furthermore, the stretched film 10 of this embodiment has a heat shrinkage of 5% or less in the stretching direction of the film when heated at 100°C for 10 minutes. If the heat shrinkage is 5% or less, the dimensional stability during heat treatment is high, and therefore a stretched film with excellent heat resistance can be provided.

[0052] In addition, when the density of the high-density polyethylene that is the main component of the base layer 3 increases, the melting point of the high-density polyethylene increases, making it possible to suppress an increase in the heat shrinkage rate.

[0053] From the viewpoint of improving heat resistance, the heat shrinkage rate of the stretched film 10 is preferably 3% or less, and more preferably 1% or less.

[0054] The above-mentioned "thermal shrinkage rate" can be determined by the method described in the examples below.

[0055] In addition, the stretched film 10 of this embodiment preferably has a tensile breaking stress of 100 MPa or more in at least one of the MD and TD directions. If the tensile breaking stress is 100 MPa or more, the stretched film 10 has sufficient strength, and therefore can be provided with stable dimensions during transport and excellent transportability in post-processing such as printing and lamination.

[0056] From the viewpoint of improving transparency by stretching, the tensile breaking stress of the stretched film 10 is preferably 200 MPa or more, and more preferably 240 MPa or more.

[0057] The "tensile breaking stress" mentioned above refers to the stress measured in accordance with JIS K 7127.

[0058] The thickness of the raw film before stretching is preferably 50 to 400 μm, more preferably 80 to 300 μm. If the thickness of the raw film is 50 μm or more, it can have strength that can withstand the stress during stretching. If the thickness of the raw film is 400 μm or less, it can have sufficient transparency after stretching.

[0059] The thickness of the base layer after stretching is preferably 10 to 40 μm, more preferably 15 to 30 μm. If the thickness of the base layer 3 after stretching is 10 μm or more, sufficient strength and water vapor barrier properties as a base film can be obtained. If the thickness of the base layer after stretching is 40 μm or less, sufficient transparency can be obtained.

[0060] The thickness of the barrier layer 5 after stretching is preferably 2 to 10 μm, more preferably 3 to 6 μm. If the thickness of the barrier layer 5 after stretching is 2 μm or more, sufficient strength and oxygen barrier properties as a barrier film can be obtained. If the thickness of the barrier layer 5 after stretching is 10 μm or less, a film with excellent recyclability can be obtained.

[0061] The thickness of the adhesive layer 4 after the stretching treatment is not particularly limited, but is preferably 0.3 to 2 μm, more preferably 0.5 to 1 μm.

[0062] From the viewpoint of improving recyclability, the content of polyethylene in the entire stretched film 10 is preferably 70% by mass or more, and more preferably 75% by mass or more, based on 100% by mass of the stretched film.

[0063] By the above method, in this embodiment, it is possible to obtain a stretched film 10 that has excellent water vapor barrier properties and heat resistance, as well as excellent oxygen barrier properties.

[0064] Next, a raw material containing a polyethylene resin such as the above-mentioned high density polyethylene (HDPE), medium density polyethylene (MDPE), low density polyethylene (LDPE), and linear low density polyethylene (LLDPE) is prepared, and is formed into a film by melt extrusion using an extruder equipped with a T-die to produce sealant film 2.

[0065] Then, for example, the barrier layer 5 of the stretched film 10 and the sealant film 2 are laminated together via an adhesive, thereby producing the laminate 1 shown in FIG.

[0066] According to the guidelines of the European consortium "CEFLEX (Circular Economy for Flexible Packaging)," a laminate is recognized as a mono-material if the polyethylene content of the entire laminate is 90% by mass or more, and if an ethylene-vinyl alcohol copolymer or adhesive is used, the content of each of these components in the entire laminate is less than 5% by mass. Therefore, by configuring the stretched film 10 as described above, it is possible to provide a laminate 1 that is recognized as a mono-material when the sealant film 2 is laminated on the stretched film 10.

[0067] (Second embodiment) Next, a second embodiment of the present invention will be described. Note that components similar to those in the first embodiment are given the same reference numerals and descriptions thereof will be omitted.

[0068] Fig. 3 is a cross-sectional view showing a stretched film according to a second embodiment of the present invention. As shown in Fig. 3, the stretched film 11 of this embodiment is characterized in that it includes a substrate layer 3 described in the first embodiment, a barrier layer 5 laminated on the substrate layer 3 via an adhesive layer 4, and a substrate layer 7 laminated on the barrier layer 5 via an adhesive layer 6, that is, a two-layer substrate layer.

[0069] As shown in FIG. 3, the laminate 20 includes the above-mentioned stretched film 11 and the sealant film 2 laminated on the base layer 7 of the stretched film 11.

[0070] <Base layer (second base layer)> The base layer 7, like the base layer 3, is mainly composed of high density polyethylene, and the density of high density polyethylene is 0.950 g / cm 3 As a result, the crystallinity of the polyethylene is improved, and similarly to the base layer 3, the water vapor barrier property can be improved.

[0071] From the viewpoint of further improving the water vapor barrier property, the density of the high-density polyethylene is set to 0.955 g / cm, similarly to the base layer 3. 3 Preferably, it is greater than 0.962 g / cm 3 More preferably, it is 0.970 / cm or more. 3 More preferably, it is equal to or greater than this.

[0072] Furthermore, from the viewpoint of enabling molding using a general-purpose extruder and providing sufficient film strength, the melt mass flow rate (MFR) of the high-density polyethylene is preferably 0.01 to 3.00 g / 10 min, more preferably 0.02 to 2.50 g / 10 min, and even more preferably 0.1 to 2.00 g / 10 min, similar to the base layer 3.

[0073] Furthermore, similarly to the base layer 3, from the viewpoint of obtaining excellent water vapor barrier properties, the content of high-density polyethylene in the entire base layer 7 is preferably 90% by mass or more, and more preferably 95% by mass or more, of 100% by mass of the base layer.

[0074] Similar to the stretched film 10 described above, the water vapor permeability of the stretched film 11 is 3.5 g / m 2 ·day or less, but from the viewpoint of improving the water vapor barrier property, the water vapor permeability of the stretched film 11 is set to 3.0 g / m 2 ·day or less is preferable, 2.5g / m 2 ·day or less is preferable.

[0075] As with the base layer 3, the base layer 7 may contain the above-mentioned other components in addition to the high-density polyethylene, as long as the stretchability of the film is not impaired.

[0076] <Adhesive layer (second adhesive layer)> The adhesive layer 6 may be made of a material containing modified polyolefin as the main component, similar to the adhesive layer 4 described above.

[0077] <Method of manufacturing laminate> Next, a method for producing a laminate using the stretched film of this embodiment will be described in detail.

[0078] As in the case of the first embodiment described above, the laminated film 20 of this embodiment is prepared by first preparing resin compositions to be used for the base layer, barrier layer, and adhesive layer, and then co-extruding the resin compositions for each layer at a predetermined temperature using an extruder equipped with a T-die to obtain a raw film before stretching having a base layer 3, an adhesive layer 4 provided on the surface of the base layer 3, a barrier layer 5 provided on the surface of the adhesive layer 4, an adhesive layer 6 provided on the surface of the barrier layer 5, and a base layer 7 provided on the surface of the adhesive layer 6.

[0079] The raw film is then subjected to uniaxial stretching treatment to produce a stretched film 11 in which the base material layer 3, adhesive layer 4, barrier layer 5, adhesive layer 6, and base material layer 7 are laminated in this order as shown in Figures 3 and 4, with the adhesive layer 4 provided between the base material layer 3 and the barrier layer 5 and the adhesive layer 6 provided between the barrier layer 5 and the base material layer 7. The stretching method is not particularly limited, and examples thereof include roll stretching and tenter stretching.

[0080] The uniaxial stretching treatment described above refers to a stretching treatment carried out in either the MD or TD direction of the film as shown in Fig. 4. Note that a biaxial stretching treatment in which stretching is carried out in both the MD and TD directions may also be carried out.

[0081] As in the first embodiment described above, the stretching temperature in the uniaxial stretching process is 80°C or higher and lower than 130°C, and preferably 100°C or higher and 120°C or lower, and the stretching ratio in the uniaxial stretching process is 5 times or higher and 10 times or lower, and preferably 6 times or higher and 8 times or lower.

[0082] The stretched film 11 produced by the above-described stretching process has a haze of 20% or less, similar to the above-described stretched film 10, and therefore can have excellent transparency.

[0083] From the viewpoint of further improving transparency, the haze of the stretched film 11 is preferably 15% or less, more preferably 10% or less, and even more preferably 7% or less.

[0084] Furthermore, in the stretched film 11 of this embodiment, similar to the above-described stretched film 10, the heat shrinkage rate in the stretching direction of the film when heated at 100°C for 10 minutes is 5% or less. If the heat shrinkage rate is 5% or less, the dimensional stability during heat treatment is high, and therefore a stretched film 11 with excellent heat resistance can be provided.

[0085] As with the above-mentioned base layer 3, when the density of the high-density polyethylene, which is the main component of the base layer 7, increases, the melting point of the high-density polyethylene also increases, making it possible to suppress an increase in the heat shrinkage rate.

[0086] From the viewpoint of improving heat resistance, the heat shrinkage rate of the stretched film 11 is preferably 3% or less, and more preferably 1% or less.

[0087] Furthermore, the stretched film 11 of this embodiment preferably has a tensile breaking stress of 100 MPa or more in at least one of the MD and TD directions, similar to the above-described stretched film 10. If the tensile breaking stress is 100 MPa or more, the stretched film 11 has sufficient strength, and therefore can be provided with stable dimensions during transport and excellent transportability in post-processing such as printing and lamination.

[0088] From the viewpoint of improving transparency, the tensile breaking stress of the stretched film 11 is preferably 200 MPa or more, and more preferably 240 MPa or more.

[0089] The thickness of the raw film before stretching, the thickness of the barrier layer 5 after stretching, and the thickness of the adhesive layers 4 and 6 after stretching are preferably the same as those in the above-described first embodiment. The thickness of each of the base layer 3 and the base layer 7 is preferably 5 to 20 μm, more preferably 7 to 15 μm.

[0090] From the viewpoint of improving recyclability, the content of polyethylene in the entire stretched film 11 is preferably 70% by mass or more, and more preferably 75% by mass or more, based on 100% by mass of the stretched film.

[0091] By the above method, in this embodiment, it is possible to obtain a stretched film 11 that has excellent water vapor barrier properties and heat resistance, as well as excellent oxygen barrier properties.

[0092] Next, a raw material containing a polyethylene resin such as the above-mentioned high density polyethylene (HDPE), medium density polyethylene (MDPE), low density polyethylene (LDPE), and linear low density polyethylene (LLDPE) is prepared, and is formed into a film by melt extrusion using an extruder equipped with a T-die to produce sealant film 2.

[0093] Then, for example, the base material layer 7 of the stretched film 11 and the sealant film 2 are laminated via an adhesive to produce the laminate 20 shown in Fig. 3. Furthermore, as in the first embodiment, by configuring the stretched film 11 as described above, it is possible to provide a laminate 20 that is recognized as a mono-material when the sealant film 2 is laminated on the stretched film 11. [Example]

[0094] The present invention will be described below based on examples. However, the present invention is not limited to these examples, and these examples can be modified or changed based on the spirit of the present invention, and such modifications are not excluded from the scope of the present invention.

[0095] The materials used to prepare the stretched film are listed below. (1) HDPE1: High-density polyethylene (density: 0.971 g / cm 3 Melting point: 134°C, MFR: 1.2g / 10min, manufactured by Dow Chemical, trade name: ELITE AT6900) (2) HDPE2: High-density polyethylene (density: 0.962 g / cm 3 Melting point: 133°C, MFR: 0.24g / 10min, manufactured by Prime Polymer Co., Ltd., product name: Hi-Zex 520MB) (3) HDPE3: High-density polyethylene (density: 0.958 g / cm 3 Melting point: 133°C, MFR: 0.98g / 10min, manufactured by Prime Polymer Co., Ltd., trade name: Hi-Zex 3600F) (4) HDPE4: High-density polyethylene (density: 0.950 g / cm 3 Melting point: 133°C, MFR: 0.3g / 10min, manufactured by Prime Polymer Co., Ltd., product name: Hi-Zex 6800S) (5) HDPE5: High-density polyethylene (density: 0.943 g / cm 3 Melting point: 126°C, MFR: 0.24g / 10min, manufactured by Prime Polymer Co., Ltd., trade name: Hi-Zex 5100E) (6) EVOH1: Ethylene-vinyl alcohol copolymer (density: 1.16 g / cm 3 Melting point: 183°C, MFR: 2.0g / 10min, ethylene content: 32mol%, Kuraray Co., Ltd., trade name: EVAL SP482B) (7) EVOH2: Ethylene-vinyl alcohol copolymer (density: 1.18 g / cm 3 Melting point: 183°C, MFR: 1.7g / 10min, ethylene content: 32mol%, Kuraray Co., Ltd., product name: EVAL J171B) (8) Adhesive: Modified polyethylene (density: 0.91 g / cm3 Melting point: 120°C, MFR: 2.3g / 10min, Mitsui Chemicals, Inc., Trade name: Admer NF587)

[0096] Example 1 <Preparation of stretched film> First, the high-density polyethylene, ethylene-vinyl alcohol copolymer, and modified polyethylene shown in Table 1 were prepared.

[0097] Next, the prepared resins were co-extruded at 200°C using an extruder (manufactured by LABTECH) equipped with a T-die to form a film having a first substrate layer, a first adhesive layer provided on the surface of the first substrate layer, a barrier layer provided on the surface of the first adhesive layer, a second adhesive layer provided on the surface of the barrier layer, and a second substrate layer provided on the surface of the second adhesive layer, and the film was taken up on a take-up roll to obtain a raw film before stretching having the thickness shown in Table 1.

[0098] Then, this raw film was stretched by uniaxial stretching in the MD under the conditions of the stretching temperature and stretch ratio shown in Table 1, thereby producing a stretched film having the thickness shown in Table 1.

[0099] <Calculation of polyethylene content> Next, the density of each of the above materials [g / cm 3 ] and the thickness [μm] of each layer shown in Table 1 to calculate the weight per unit area of ​​each layer [g / cm 2 The polyethylene content [mass %] relative to the total amount of the stretched film was calculated by determining the polyethylene content [mass %]. The results are shown in Table 1.

[0100] In this example, the sum of the weights per unit area of ​​the first and second base layers made of high-density polyethylene is 0.002709 [g / cm 2 ], and the weight per unit area of ​​the barrier layer formed by ethylene-vinyl alcohol copolymer is 0.000661 [g / cm 2], and the sum of the weights per unit area of ​​the first adhesive layer and the second adhesive layer formed of modified polyethylene is 0.000145 [g / cm 2 ], so the content [mass %] of polyethylene in the entire produced stretched film was 0.002709 / (0.002709+0.000661+0.000145)=77.1 mass %.

[0101] <Measurement of water vapor permeability> Next, the water vapor permeability [g / m 2 ·day] was measured in accordance with JIS K 7129-1 using a water vapor transmission rate meter (manufactured by SYSTEC Illinois, product name: Water Vapor Transmission Rate Meter Lyssy L80-6000) in an atmosphere at a temperature of 40°C and a humidity of 90%. The results are shown in Table 1.

[0102] <Oxygen permeability measurement> Next, the oxygen permeability [cc / m 2 ·day] was measured in accordance with JIS K 7126-1 using a gas permeability measuring device (manufactured by GTR Tech Co., Ltd., product name: GTR-10XACT) in an atmosphere at a temperature of 23°C and humidity of 0%. The results are shown in Table 1.

[0103] <Haze and total light transmittance measurement> Using a spectrophotometer (manufactured by Suga Test Instruments, product name: Haze Meter HZ-V3), the haze [%] in the visible light range (360-750 nm) of polyethylene was measured as an index of the haze of the produced stretched film in accordance with JIS K 7361. The total light transmittance [%] of the produced stretched film was also measured in accordance with JIS K 7361-1. The results are shown in Table 1.

[0104] <Measurement of tensile breaking stress> The tensile breaking stress [MPa] of the prepared stretched film was measured in accordance with JIS K 7127. More specifically, a test film having a test piece type 3 dumbbell was prepared, and a tensile test was performed using a tensile tester (Shimadzu Corporation, trade name: Autograph AG-5000A) at a temperature of 25°C and a pulling speed of 100 mm / min, and the tensile breaking stress [MPa] in MD and TD was measured. The results are shown in Table 1.

[0105] <Calculating the thermal shrinkage rate> A sample of a specified size (7 cm x 7 cm) was cut from the prepared stretched film, and 5 cm long, perpendicular benchmark lines parallel to each side were drawn 1 cm inward from each side of the sample. The sample was placed in a 100°C oven and heated for 10 minutes, then removed and cooled to room temperature. The distance between the benchmark lines in the stretching direction (i.e., MD) of the heat-treated sample was measured, and the heat shrinkage rate [%] was calculated from the change in the distance between the benchmark lines in the stretching direction before and after heating using the following formula (1), which was used as an index of heat resistance. The results are shown in Table 1.

[0106] Heat shrinkage rate in the stretching direction [%] = [(gauge line distance before heating - gauge line distance after heating) / gauge line distance before heating] × 100 (1)

[0107] (Examples 2 to 7, Comparative Examples 1 to 4) A raw film having a thickness shown in Table 1 was stretched to produce a stretched film in the same manner as in Example 1 above, except that the composition of the stretched film (i.e., high-density polyethylene, ethylene-vinyl alcohol copolymer, and modified polyethylene) and the conditions of the uniaxial stretching treatment were changed to those shown in Table 1.

[0108] Then, the polyethylene content was calculated, the water vapor permeability was measured, the oxygen permeability was measured, the haze and total light transmittance were measured, the tensile breaking stress was measured, and the heat shrinkage rate was calculated in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0109] In Comparative Example 4, the stretched film melted and broke because the stretching temperature during film formation in the uniaxial stretching treatment was 130°C or higher (130°C). Therefore, in Comparative Example 4, it was not possible to calculate the polyethylene content, measure the water vapor permeability, measure the oxygen permeability, measure the haze and total light transmittance, measure the tensile breaking stress, or calculate the heat shrinkage rate.

[0110] (Comparative Example 5) <Preparation of stretched film> First, the high-density polyethylene shown in Table 2 was prepared. Next, the prepared high-density polyethylene was formed into a film by melt extrusion (extrusion temperature: 200°C) using an extruder (manufactured by Nagata Seisakusho Co., Ltd.) equipped with a T-die, and the film was taken up on a take-up roll to obtain a raw film before stretching having the thickness shown in Table 2.

[0111] Then, this raw film was stretched by uniaxial stretching in the MD under the conditions of the stretching temperature and stretch ratio shown in Table 2, and a stretched film (polyethylene film) made of high-density polyethylene and having the thickness shown in Table 2 was produced.

[0112] Then, the polyethylene content was calculated, the water vapor permeability was measured, the oxygen permeability was measured, the haze and total light transmittance were measured, the tensile stress at break was measured, and the heat shrinkage rate was calculated in the same manner as in Example 1. The results are shown in Table 1.

[0113] [Table 1]

[0114] [Table 2]

[0115] As shown in Table 1, in the stretched films of Examples 1 to 7, the density of polyethylene was 0.950 g / cm 3 or more, and the water vapor permeability is 3.5 g / m2 ·day or less, and oxygen permeability is 10cc / m 2 ·days or less, which indicates that it has excellent water vapor barrier and oxygen barrier properties. Furthermore, the heat shrinkage rate in the film's stretching direction when heated at 100°C for 10 minutes is 5% or less, which indicates that it has high dimensional stability and excellent heat resistance due to heat treatment. Furthermore, the haze is 20% or less, which indicates that it has excellent transparency.

[0116] On the other hand, as shown in Table 2, in the stretched films of Comparative Examples 1 and 2, the density of polyethylene was 0.950 g / cm 3 Because it is less than 3.5g / m 2 The water vapor barrier properties are poor. 3 The melting point of polyethylene is low, and the heat shrinkage rate is greater than 5%, indicating poor heat resistance.

[0117] In the stretched film of Comparative Example 3, the stretching temperature was low and the heat setting effect was not obtained, so the heat shrinkage rate was greater than 5%, indicating poor heat resistance. Also, because the stretching temperature was less than 80°C, the film became cloudy and the haze was significantly greater than 20%, indicating poor transparency.

[0118] In addition, the stretched film of Comparative Example 5 does not have a barrier layer formed of an ethylene-vinyl alcohol copolymer, so the oxygen permeability is 20 cc / m 2 It is clear that the oxygen barrier properties are poor. [Industrial Applicability]

[0119] As described above, the present invention is suitable for a stretched film used, for example, as a packaging film, and a method for producing the same. [Explanation of symbols]

[0120] 1. Laminate 2. Sealant film 3. Base material layer (first base material layer) 4 Adhesive layer (first adhesive layer) 5 Barrier Layer 6 Adhesive layer (second adhesive layer) 7 Base layer (second base layer) 10 Stretched film 11 Stretched film 20 laminate

Claims

1. A stretched film comprising at least a first substrate layer and a barrier layer, The first substrate layer has a density of 0.950 g / cm ３ The main component is polyethylene having the above properties, the barrier layer is composed mainly of an ethylene-vinyl alcohol copolymer; Water vapor permeability is 3.5 g / m ２ ・day or less, The oxygen permeability is 10 cc / m 2 ·day or less, The heat shrinkage rate in the stretching direction of the film is 5% or less when heated at 100°C for 10 minutes. A stretched film characterized by:

2. 2. The stretched film according to claim 1, further comprising a first adhesive layer provided between the first substrate layer and the barrier layer.

3. Further comprising a second substrate layer; The second substrate layer has a density of 0.950 g / cm ３ The main component is polyethylene having the above properties, 3. The stretched film according to claim 2, further comprising a second adhesive layer provided between the barrier layer and the second substrate layer.

4. Density is 0.950 g / cm ３ a step of preparing a raw film having at least the above-mentioned base layer mainly composed of polyethylene and a barrier layer mainly composed of an ethylene-vinyl alcohol copolymer; a step of performing a stretching process on the raw film; A method for producing a stretched film comprising at least The method for producing a stretched film is characterized in that the stretched film has a water vapor permeability of 3.5 g / m 2 ·day or less, an oxygen permeability of 10 cc / m 2 ·day or less, and a heat shrinkage rate of 5% or less when heated in the stretching direction of the film at 100°C for 10 minutes.

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