Stretched film and method for manufacturing the same

Abstract

The objective is to provide a stretched film that has excellent water vapor barrier properties and heat resistance, as well as excellent oxygen barrier properties. [Solution] The stretched film 10 comprises at least a base layer 3 and a barrier layer 5, and the base layer 3 has a density of 0.950 g / cm³ 3 The main component is polyethylene, the thickness of the base layer 3 is 10 μm to 40 μm, and the barrier layer 5 is mainly composed of ethylene-vinyl alcohol copolymer with an oxygen permeability of 10 cc / m³. 2 The film is less than or equal to 5% in length, and its thermal shrinkage rate when heated at 100°C for 10 minutes in the stretching direction is 5% or less.

Description

[Technical Field]

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

[0002] Conventionally, packaging films used for pouches and the like have employed laminates, which consist of 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.

[0003] While there is a demand for reducing the environmental impact of plastics in general, and recyclability is also required for packaging films, the problem with laminates made of different materials is that separating the materials is difficult, making recycling challenging.

[0004] Therefore, in recent years, there has been a growing movement towards monomaterialization of packaging films, using a single material. Examples of resins used in monomaterial packaging films include polyethylene, polypropylene, and polyethylene terephthalate. Of these, polyethylene has the highest usage rate in existing packaging films and is a material for which monomaterialization is particularly desired. However, polyethylene alone has poor gas barrier properties (oxygen barrier properties), making it impossible to set an expiration date like conventional laminated films, and there is a problem of odor leakage when the contents are cosmetics such as detergents and shampoos.

[0005] Therefore, as a method for providing gas barrier properties, a stretched film comprising a base layer mainly composed of polyethylene resin and a barrier layer mainly composed of ethylene-vinyl alcohol copolymer (EVOH) has been proposed. It is stated that with this configuration, the barrier layer mainly composed of ethylene-vinyl alcohol copolymer can be provided by methods such as T-die or inflation molding, similar to conventional laminated films, and thus a stretched film with added oxygen barrier properties can be manufactured without increasing manufacturing equipment or processes. It is also stated that by making the other layers (base layer, sealant film layer) out of polyethylene and reducing the content of ethylene-vinyl alcohol copolymer, the entire laminate can be considered as a single material 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 [Overview of the project] [Problems that the invention aims to solve]

[0007] Here, the ethylene-vinyl alcohol copolymer has oxygen barrier properties but does not have water vapor barrier properties. Furthermore, it is known that the oxygen barrier properties of the ethylene-vinyl alcohol copolymer decrease under high humidity conditions. In the stretched film described in Patent Document 1, the resin constituting the base layer is 0.925 g / cm³. 3 Although polyethylene having the above density has been disclosed, the base layer in this material had the problem of insufficient water vapor barrier properties. In addition, the thermal shrinkage rate at 100°C was large, causing the base layer to shrink during heat sealing in bag making, resulting in wrinkles and poor appearance. As a result, it was difficult to achieve both water vapor barrier properties and heat resistance.

[0008] Therefore, the present invention has been made in view of the above problems, and an object thereof is to provide a stretched film having excellent water vapor barrier properties and heat resistance, and also excellent oxygen barrier properties.

Means for Solving the Problems

[0009] In order to achieve the above object, the stretched film of the present invention includes at least a base material layer and a barrier layer. The base material layer is mainly composed of polyethylene having a density of 0.950 g / cm 3 or more, the thickness of the base material layer is 10 μm or more and 40 μm or less, the barrier layer is mainly composed of an ethylene-vinyl alcohol copolymer, and the oxygen permeability is 10 cc / m 2 ·day or less, and in the stretching direction of the film, the heat shrinkage rate when heated at 100 ° C for 10 minutes is 5% or less.

[0010] Further, the method for producing the stretched film of the present invention includes at least a step of preparing a raw film including at least a base material layer mainly composed of polyethylene having a density of 0.950 g / cm 3 or more and a barrier layer mainly composed of an ethylene-vinyl alcohol copolymer, and a step of performing a stretching treatment on the raw film. The thickness of the base material layer of the stretched film is 10 μm or more and 40 μm or less, the oxygen permeability of the stretched film is 10 cc / m 2 ·day or less, and in the stretching direction of the film, the heat shrinkage rate when heated at 100 ° C for 10 minutes is 5% or less.

Effects of the Invention

[0011] According to the present invention, it is possible to provide a stretched film having excellent water vapor barrier properties and heat resistance, and also excellent oxygen barrier properties.

Brief Description of the Drawings

[0012] [Figure 1] It is a cross-sectional view for explaining a laminate using the stretched film according to the first embodiment of the present invention. [Figure 2] This is a plan view illustrating a laminate using a stretched film according to the first embodiment of the present invention. [Figure 3] This is a cross-sectional view illustrating a laminate using a stretched film according to a second embodiment of the present invention. [Figure 4] This is a plan view illustrating a laminate using a stretched film according to a second embodiment of the present invention. [Modes for carrying out the invention]

[0013] The stretched film of the present invention will be described in detail below. However, the present invention is not limited to the following embodiments, and can be modified and applied as appropriate without altering the essence of the invention.

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

[0015] The laminate 1 comprises a stretched film 10 composed of a base layer 3 mainly made of polyethylene and a barrier layer 5 mainly made of ethylene-vinyl alcohol copolymer, 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 a monomaterial standpoint, the sealant film 2 is preferably made of polyethylene resin. More specifically, examples include high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE).

[0017] Furthermore, from the viewpoint of improving heat sealability, low-density polyethylene (LDPE) or linear low-density polyethylene (LLDPE), which has a lower melting point than the base layer 3, is preferred in order to create a difference in melting points with the base layer 3.

[0018] In addition, the content of polyethylene in the sealant film 2 is preferably 70% or more, more preferably 90% or more, still more preferably 95% or more, and most preferably 100%.

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

[0020] In addition, the sealant film 2 may contain other components other than the above-mentioned polyethylene-based resin as long as the properties of the sealant film 2 are not impaired.

[0021] Examples of other components include olefin resins, amide-based antiblocking agents (such as stearic acid amide), plasticizers, ultraviolet absorbers, antioxidants, weather stabilizers, antistatic agents, colorants, antifogging agents, metal soaps, waxes, antifungal agents, antibacterial agents, nucleating agents, flame retardants, lubricants, etc.

[0022] <Base material layer (first base material layer)> The base material layer 3 imparts water vapor barrier properties to the stretched film 10 and is composed mainly of high-density polyethylene (HDPE). In the present invention, the density of the high-density polyethylene is 0.950 g / cm 3 or more. When the density is 0.950 g / cm 3 or more, the crystallinity of polyethylene is improved, so that the water vapor barrier property can be improved.

[0023] From the viewpoint of further improving the water vapor barrier property, the density of the high-density polyethylene is preferably more than 0.955 g / cm 3 and more preferably 0.962 g / cm 3 or more, and still more preferably 0.970 / cm 3 or more.

[0024] Furthermore, the melt mass flow rate (MFR) of 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 when the melt mass flow rate (MFR) is 0.01 g / 10 min or higher, it can be molded using a general-purpose extruder without the need for special equipment, and when it is 3.00 g / 10 min or lower, it is possible to achieve sufficient film strength.

[0025] The melt mass flow rate mentioned above is obtained by measurement in accordance with the provisions of JIS K7210:1999.

[0026] Furthermore, from the viewpoint of obtaining excellent water vapor barrier properties, the content of high-density polyethylene in the 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] Based on the above, the resin used to form the base layer 3 has a density of 0.950 g / cm³. 3 By using the high-density polyethylene described above, the water vapor permeability of the stretched film 10 is 3.5 g / m². 2 Since the water vapor barrier properties are less than or equal to 1 day, it becomes possible to provide a stretched film 10 with excellent water vapor barrier properties.

[0028] Furthermore, from the viewpoint of improving water vapor barrier properties, the water vapor permeability of the stretched film 10 is 3.0 g / m². 2 • Preferably less than 2.5 g / m² 2 • Days or less are preferable.

[0029] Furthermore, the term "water vapor transmission rate" as used herein refers to the rate measured using a water vapor transmission rate measuring instrument in accordance with JIS K 7129-1, under conditions of 40°C and 90% humidity.

[0030] Furthermore, the base layer 3 may contain other components besides the high-density polyethylene described above, as long as they do not impair the stretchability of the film.

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

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

[0033] Furthermore, 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 of all monomer units constituting the ethylene-vinyl alcohol copolymer (100 mol%). This is because if the ethylene content is less than 30 mol%, the processability of the barrier film may decrease, and if it is more than 40 mol%, the oxygen barrier properties may be insufficient.

[0034] Furthermore, from the viewpoint of obtaining excellent oxygen barrier properties, the content of ethylene-vinyl alcohol copolymer in the 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] Based on the above, by using an ethylene-vinyl alcohol copolymer as the resin forming the barrier layer 5, the oxygen permeability of the stretched film 10 becomes 10 cc / m². 2 Since the result is less than 1 day, it becomes possible to provide a stretched film 10 with excellent oxygen barrier properties.

[0036] Furthermore, from the perspective of improving oxygen barrier properties, the oxygen permeability of the stretched film 10 is set to 5.0 cc / m². 2 • Preferably less than 3.0 cc / m²2 • Less than 1.5 days is preferable, and 1.5 cc / m 2 • Days or less are even more preferable.

[0037] Furthermore, the term "oxygen permeability" as used herein refers to the value measured using an oxygen permeability measuring instrument in accordance with JIS K 7126-1, under conditions of 23°C and 0% humidity.

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

[0039] <Adhesive layer (first adhesive layer)> The adhesive layer 4 is for bonding the substrate layer 3 and the barrier layer 5, and is mainly composed of a material that has excellent adhesion to the substrate layer 3 and the barrier layer 5, such as a modified polyolefin.

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

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

[0042] First, prepare the resin compositions to be used for the base layer, barrier layer, and adhesive layer.

[0043] Next, using an extruder equipped with a T-die, the resin composition of each layer is co-extruded at a predetermined temperature 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, and a barrier layer 5 provided on the surface of the adhesive layer 4.

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

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

[0046] Furthermore, the stretching temperature in the uniaxial stretching process should be between 80°C and 130°C, preferably between 100°C and 120°C. This is because if the temperature is below 80°C, the film may become cloudy. Also, if the stretching temperature is above 130°C, the film may melt and break.

[0047] Furthermore, the stretching ratio in the uniaxial stretching process is between 5 and 10 times. This is because if the stretching ratio is less than 5 times, unstretched portions remain, which may reduce tensile strength and transparency. Also, if the stretching ratio is greater than 10 times, the film may break. Moreover, from the viewpoint of improving tensile strength and transparency and preventing film breakage, a stretching ratio of 6 to 8 times is preferable.

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

[0049] Furthermore, 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] Furthermore, the term "haze" used here refers to an index of cloudiness measured in accordance with JIS K 7361.

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

[0052] Furthermore, increasing the density of high-density polyethylene, which is the main component of the base layer 3, raises the melting point of the high-density polyethylene, making it possible to suppress the increase in the thermal shrinkage rate.

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

[0054] Furthermore, the aforementioned "thermal shrinkage rate" can be determined by the method described in the examples below.

[0055] Furthermore, in the stretched film 10 of this embodiment, it is preferable that the tensile breaking stress in at least one direction of MD and TD is 100 MPa or more. If the tensile breaking stress is 100 MPa or more, it has sufficient strength, and therefore, a stretched film 10 can be provided that maintains its dimensions stably during transport and has excellent transportability during post-processing such as printing and lamination.

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

[0057] Furthermore, the "tensile fracture stress" mentioned above refers to the stress measured in accordance with JIS K 7127.

[0058] Furthermore, the thickness of the raw film before stretching is preferably 50 to 400 μm, and more preferably 80 to 300 μm. If the thickness of the raw film is 50 μm or more, sufficient strength to withstand the stress during stretching can be obtained. Also, if the thickness of the raw film is 400 μm or less, sufficient transparency can be obtained after stretching.

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

[0060] Furthermore, the thickness of the barrier layer 5 after stretching is preferably 2 to 10 μm, and 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 can be obtained as a barrier film. If the thickness of the barrier layer 5 after stretching is 10 μm or less, a film with excellent recyclability can be obtained.

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

[0062] Furthermore, from the viewpoint of improving recyclability, the polyethylene content of the stretched film 10 is preferably 70% by mass or more, and more preferably 75% by mass or more, of 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, raw materials containing polyethylene-based resins such as high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE) are prepared and molded into a film by melt extrusion using an extruder equipped with a T-die to produce sealant film 2.

[0065] Then, for example, by laminating the barrier layer 5 of the stretched film 10 and the sealant film 2 via an adhesive, the laminate 1 shown in Figure 1 is manufactured.

[0066] According to the guidelines of the European consortium "CEFLEX (Circular Economy for Flexible Packaging)," a laminate is certified as a monomaterial if the polyethylene content in the entire laminate is 90% by mass or more, and if ethylene-vinyl alcohol copolymers or adhesives are used, their respective content in the entire laminate is less than 5% by mass. Therefore, by configuring the stretched film 10 as described above, it becomes possible to provide a laminate 1 that is certified as a monomaterial when the sealant film 2 is laminated onto 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 will be denoted by the same reference numerals, and their descriptions will be omitted.

[0068] Figure 3 is a cross-sectional view showing a stretched film according to a second embodiment of the present invention. As shown in Figure 3, the stretched film 11 of this embodiment is characterized in that, in addition to the base layer 3 described in the first embodiment above and a barrier layer 5 laminated on the base layer 3 via an adhesive layer 4, it also comprises a base layer 7 laminated on the barrier layer 5 via an adhesive layer 6, and thus has two base layers.

[0069] As shown in Figure 3, the laminate 20 comprises the stretched film 11 described above and a sealant film 2 laminated on the base layer 7 of the stretched film 11.

[0070] <Substrate layer (second substrate layer)> The base layer 7, like the base layer 3, is mainly composed of high-density polyethylene, and the density of the high-density polyethylene is 0.950 g / cm³. 3 That concludes the explanation. Therefore, since the degree of crystallinity of polyethylene is improved, the water vapor barrier properties can be improved, similar to the base layer 3.

[0071] Furthermore, from the viewpoint of further improving water vapor barrier properties, the density of the high-density polyethylene is 0.955 g / cm³, similar to the base layer 3. 3 It is preferable that it be greater than 0.962 g / cm³. 3 It is more preferable that the rate is 0.970 / cm² or higher. 3 It is even more preferable that the above conditions are met.

[0072] Furthermore, from the viewpoint of enabling molding with a general-purpose extruder and ensuring 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, similar to the base layer 3, from the viewpoint of obtaining excellent water vapor barrier properties, the content of high-density polyethylene in the 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 transmission rate of the stretched film 11 is 3.5 g / m². 2 Although it is less than 3 days, from the viewpoint of improving water vapor barrier properties, the water vapor transmission rate of the stretched film 11 is 3.0 g / m². 2 • Preferably less than 2.5 g / m² 2 • Days or less are preferable.

[0075] Furthermore, similar to the base layer 3, the base layer 7 may contain other components other than high-density polyethylene, as long as they do not impair the stretchability of the film.

[0076] <Adhesive layer (second adhesive layer)> The adhesive layer 6 can be made primarily of modified polyolefin, similar to the adhesive layer 4 described above.

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

[0078] In this embodiment, the laminated film 20 is produced in the same manner as in the first embodiment described above. First, resin compositions to be used for the base layer, barrier layer, and adhesive layer are prepared. 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, 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] Then, by performing a uniaxial stretching process on the raw film, the following layers are laminated in this order as shown in Figures 3-4: base layer 3, adhesive layer 4, barrier layer 5, adhesive layer 6, and base layer 7. An adhesive layer 4 is provided between the base layer 3 and the barrier layer 5, and an adhesive layer 6 is provided between the barrier layer 5 and the base layer 7. A stretched film 11 is produced. The stretching method is not particularly limited and examples include roll stretching and tenter stretching.

[0080] Furthermore, the uniaxial stretching process described above refers to a stretching process performed in either the MD or TD direction of the film, as shown in Figure 4. Alternatively, biaxial stretching, which stretches the film in both the MD and TD directions, may also be performed.

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

[0082] Furthermore, the stretched film 11 produced by the stretching process described above, like the stretched film 10 described above, has a haze of 20% or less, making it possible to obtain excellent transparency.

[0083] Furthermore, 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 stretched film 10 described above, the thermal shrinkage rate when heated at 100°C for 10 minutes in the stretching direction of the film is 5% or less. Since the thermal shrinkage rate is 5% or less, the dimensional stability due to heat treatment is high, and a stretched film 11 with excellent heat resistance can be provided.

[0085] Furthermore, similar to the base material layer 3 described above, increasing the density of the high-density polyethylene, which is the main component of the base material layer 7, raises the melting point of the high-density polyethylene, making it possible to suppress the increase in the thermal shrinkage rate.

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

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

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

[0089] Furthermore, 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 in the first embodiment described above. In addition, the thickness of the base layer 3 and the base layer 7 are preferably 5 to 20 μm, and more preferably 7 to 15 μm.

[0090] Furthermore, from the viewpoint of improving recyclability, the polyethylene content of the stretched film 11 is preferably 70% by mass or more, and more preferably 75% by mass or more, of 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, raw materials containing polyethylene-based resins such as high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE) are prepared and molded into a film by melt extrusion using an extruder equipped with a T-die to produce sealant film 2.

[0093] Then, for example, by laminating the base layer 7 of the stretched film 11 and the sealant film 2 via an adhesive, the laminate 20 shown in Figure 3 is manufactured. Also, 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 monomaterial when the sealant film 2 is laminated onto the stretched film 11. [Examples]

[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 and altered in accordance with the spirit of the invention; such modifications do not exclude them from the scope of the invention.

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

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

[0097] Next, using an extruder equipped with a T-die (manufactured by LABTECH), the prepared resin was co-extruded at 200°C to form a film having a first base layer, a first adhesive layer provided on the surface of the first base 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 base layer provided on the surface of the second adhesive layer. The film was then wound onto a winding roll to obtain a raw film roll before stretching with the thickness shown in Table 1.

[0098] Then, the raw film was stretched by uniaxial stretching using MD under the stretching temperature and stretching ratio conditions shown in Table 1, thereby producing stretched films with the thicknesses shown in Table 1.

[0099] <Calculation of polyethylene content> Next, the density of each of the above materials [g / cm³] 3 The product of [ ] and the thickness [μm] of each layer shown in Table 1 is calculated to determine the weight per unit area of ​​each layer [g / cm³]. 2 The polyethylene content [mass %] of the total stretched film was calculated by determining [ ]. The results are shown in Table 1.

[0100] In this embodiment, the sum of the weights per unit area of ​​the first and second base layers, which are made of high-density polyethylene, is 0.002709 [g / cm³]. 2 The weight per unit area of ​​the barrier layer formed by the ethylene-vinyl alcohol copolymer is 0.000661 [g / cm³]. 2The sum of the weights per unit area of ​​the first adhesive layer and the second adhesive layer formed by modified polyethylene is 0.000145 [g / cm³]. 2 Therefore, the polyethylene content [mass%] of the total stretched film produced was 0.002709 / (0.002709+0.000661+0.000145)=77.1% by mass.

[0101] <Measurement of water vapor transmission rate> Next, the water vapor transmission rate of the stretched film [g / m²] 2 The water vapor permeability [day] was measured using a water vapor permeability meter (SYSTEC illinois, product name: Water vapor permeability meter Lyssy L80-6000) in accordance with JIS K 7129-1, under conditions of 40°C and 90% humidity. The results are shown in Table 1.

[0102] <Measurement of oxygen permeability> Next, the oxygen permeability of the stretched film that was prepared [cc / m 2 The gas permeability of [day] was measured using a gas permeability measuring device (GTR Tech Co., Ltd., product name: GTR-10XACT) in accordance with JIS K 7126-1, under conditions of 23°C and 0% humidity. The results are shown in Table 1.

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

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

[0105] <Calculation of thermal shrinkage rate> A sample of a predetermined size (7cm x 7cm) was cut from the prepared stretched film. Five perpendicular gauge lines, each 5cm long and parallel to the edge, were marked 1cm inward from each side of the sample. The sample was then placed in a 100°C oven and heated for 10 minutes. After removal, it was allowed to cool to room temperature. The distance between the gauge lines in the stretching direction (i.e., MD) was measured in the heat-treated sample. The thermal shrinkage rate [%] was calculated from the change in the distance between the gauge lines before and after heating in the stretching direction using the following formula (1), and this was used as an indicator of heat resistance. The results are shown in Table 1.

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

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

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

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

[0110] (Comparative Example 5) <Preparation of stretched film> First, high-density polyethylene as 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 equipped with a T-die (manufactured by Nagata Seisakusho Co., Ltd.), and the film was wound onto a winding roll to obtain a raw film roll before stretching with the thickness shown in Table 2.

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

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

[0113] [Table 1]

[0114] [Table 2]

[0115] As shown in Table 1, the stretched films of Examples 1 to 7 had a polyethylene density of 0.950 g / cm³. 3 The above conditions are met, and the water vapor transmission rate is 3.5 g / m³.2 • Less than 10 days, and oxygen permeability of 10 cc / m³ 2 Since the saturation period is less than 1 day, it is clear that the film has excellent water vapor barrier and oxygen barrier properties. Furthermore, since the thermal shrinkage rate when heated at 100°C for 10 minutes in the stretching direction of the film is 5% or less, it is clear that the film has high dimensional stability after heat treatment and excellent heat resistance. In addition, since the haze is 20% or less, it is clear that the film has excellent transparency.

[0116] On the other hand, as shown in Table 2, the stretched films of Comparative Examples 1 and 2 had a polyethylene density of 0.950 g / cm³. 3 Since it is less than 3.5 g / m³, the water vapor transmission rate is 3.5 g / m³. 2 The density is larger than that of day, indicating poor water vapor barrier properties. Also, the density of polyethylene is 0.950 g / cm³. 3 Since it is less than 5%, the melting point of polyethylene is low, resulting in a thermal shrinkage rate greater than 5%, indicating poor heat resistance.

[0117] Furthermore, in the stretched film of Comparative Example 3, the stretching temperature was low, and the heat-fixing effect was not obtained, resulting in a thermal shrinkage rate greater than 5%, indicating poor heat resistance. In addition, because the stretching temperature was less than 80°C, the film became cloudy, and the haze was considerably greater than 20%, indicating poor transparency.

[0118] Furthermore, in the stretched film of Comparative Example 5, there is no barrier layer formed by the ethylene-vinyl alcohol copolymer, and therefore the oxygen permeability is 20 cc / m². 2 It is considerably larger than the day, indicating poor oxygen barrier properties. [Industrial applicability]

[0119] As described above, the present invention is suitable, for example, for stretched films used in packaging films and the like, and for methods of manufacturing the same. [Explanation of symbols]

[0120] 1. Laminate 2. Sealant film 3. Substrate layer (first substrate layer) 4. Adhesive layer (first adhesive layer) 5. Barrier layer 6. Adhesive layer (second adhesive layer) 7. Substrate layer (second substrate layer) 10 Stretched film 11 Stretched film 20 Laminate

Claims

1. A stretched film comprising at least a substrate layer and a barrier layer, The aforementioned substrate layer has a density of 0.950 g / cm³. ３ The above is mainly composed of polyethylene, The thickness of the substrate layer is 10 μm or more and 40 μm or less. The barrier layer mainly consists of an ethylene-vinyl alcohol copolymer, Oxygen permeability of 10 cc / m ２ - less than or equal to day, The thermal shrinkage rate of the film when heated at 100°C for 10 minutes in the stretching direction is 5% or less. A stretched film characterized by the following features.

2. Density is 0.950 g / cm³ ３ The process of preparing a raw film comprising at least a base layer mainly composed of polyethylene and a barrier layer mainly composed of ethylene-vinyl alcohol copolymer, A step of performing a stretching treatment on the aforementioned raw film roll A method for manufacturing a stretched film comprising at least the following: The thickness of the substrate layer of the stretched film is 10 μm or more and 40 μm or less. The oxygen permeability of the stretched film is 10 cc / m². ２ A method for manufacturing a stretched film, characterized in that the film is less than or equal to 5 days old, and the thermal shrinkage rate when heated at 100°C for 10 minutes in the stretching direction of the film is 5% or less.

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