Stretched film and production method for same

Abstract

A stretched film (10) comprises at least a substrate layer (3) and a barrier layer (5), wherein: the substrate layer (3) has, as the main component thereof, a high-density polyethylene which has a density of not less than 0.950 g / cm3; the barrier layer (5) has, as the main component thereof, an ethylene-vinyl alcohol copolymer which has an ethylene content of 27-38 mol%; oxygen permeability in an atmosphere with a humidity of 90% and a temperature of 25°C is not more than 2.5 cc / m2･day; and thermal shrinkage in the stretching direction of the film upon heating for 10 minutes at 120°C is not more than 5%.

Description

Stretched film and method for manufacturing the same

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

[0002] Conventionally, packaging films used in pouches and the like have employed laminates in which 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] 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, where packaging films are made from 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 in demand.

[0005] However, when polyethylene is used as the material that makes up the base film, there is a problem that misalignment (printing misalignment) is likely to occur during printing because its mechanical strength is insufficient compared to conventional base films.

[0006] Furthermore, polyethylene alone has poor gas barrier properties (oxygen barrier properties), making it impossible to set an expiration date like conventional laminated films. In addition, when the contents are cosmetics such as detergents or shampoos, there is a problem of odor leakage.

[0007] Therefore, in order to improve strength and printability and enhance gas barrier properties, a laminate has been proposed comprising, for example, a polyolefin layer mainly containing medium-density polyethylene and a barrier resin layer mainly containing ethylene-vinyl alcohol copolymer (EVOH), which has been subjected to a stretching treatment, and a printed layer provided on one or both sides of the barrier substrate. It has been stated that with such a configuration, a laminate can be provided that has printability and strength, as well as improved gas barrier properties (oxygen barrier properties).

[0008] Japanese Patent Publication No. 2023-149087

[0009] However, in the laminate described in Patent Document 1 above, medium-density polyethylene is used for the polyolefin layer, which is the base film. As a result, the heat resistance is insufficient, and during heat sealing performed when making bags, the base film shrinks, causing wrinkles and resulting in a poor appearance.

[0010] Furthermore, when using an ethylene-vinyl alcohol copolymer with a high ethylene content, the content of the vinyl alcohol component that contributes to oxygen barrier properties becomes low, resulting in insufficient oxygen barrier properties. In addition, generally, the oxygen barrier properties of ethylene-vinyl alcohol copolymers decrease as humidity increases, so there was a problem in that sufficient oxygen barrier properties could not be obtained, especially under high humidity conditions (for example, in an atmosphere with 90% humidity).

[0011] Therefore, the present invention has been made in view of the above problems, and aims to provide a stretched film that has excellent oxygen barrier properties as well as excellent heat resistance.

[0012] To achieve the above objective, the stretched film of the present invention is a stretched film comprising at least a first substrate layer and a barrier layer, wherein the first substrate layer has a density of 0.950 g / cm³ ３ The main component is high-density polyethylene, and the barrier layer is mainly composed of an ethylene-vinyl alcohol copolymer with an ethylene content of 27 mol% to 38 mol%, and has an oxygen permeability of 2.5 cc / m³ in an atmosphere of 25°C and 90% humidity. ２- The film is characterized by being less than or equal to 5 days, and having a thermal shrinkage rate of 5% or less when heated at 120°C for 10 minutes in the stretching direction of the film.

[0013] According to the present invention, it is possible to provide a stretched film that has excellent oxygen barrier properties as well as excellent heat resistance.

[0014] This is a cross-sectional view illustrating a laminate using a stretched film according to the first embodiment of the present invention. This is a plan view illustrating a laminate using a stretched film according to the first embodiment of the present invention. This is a cross-sectional view illustrating a laminate using a stretched film according to the second embodiment of the present invention. This is a plan view illustrating a laminate using a stretched film according to the second embodiment of the present invention.

[0015] 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.

[0016] (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.

[0017] The laminate 1 comprises a stretched film (barrier base 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 on 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 (i.e., provided on the surface of the barrier layer 5 opposite to the adhesive layer 4 side).

[0018] <Sealant Film> From the viewpoint of monomaterials, polyethylene resin is preferred for sealant film 2. More specifically, examples include high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE).

[0019] Furthermore, from the viewpoint of improving heat sealability, low-density polyethylene (LDPE) or linear low-density polyethylene (LLPE), 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.

[0020] Furthermore, the polyethylene content in the sealant film 2 is preferably 70% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and most preferably 100% by mass.

[0021] Furthermore, the thickness of the sealant film 2 is preferably 20 μm to 200 μm, and more preferably 30 μm to 150 μm.

[0022] Furthermore, the sealant film 2 may contain other components besides the polyethylene resin described above, as long as they do not impair the properties of the sealant film 2.

[0023] 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.

[0024] <Base Layer (First Base Layer)> The base layer 3 provides heat resistance to the stretched film 10 and is mainly composed of high-density polyethylene (HDPE). In this invention, the density of the high-density polyethylene is 0.950 g / cm³. ３ That's all. The density is 0.950 g / cm³. ３ If the density is less than 0.950 g / cm³, the melting point of polyethylene becomes lower, making it difficult to stretch at high temperatures. This increases the thermal shrinkage rate, reduces heat resistance, and lowers film strength. In other words, the density of high-density polyethylene is 0.950 g / cm³. ３ In the above cases, stretching at high temperatures becomes possible, which increases the effect of heat fixation by high-temperature stretching, improving heat resistance and also improving film strength.

[0025] Furthermore, the density of high-density polyethylene is 0.971 g / cm³.３ It is preferable that it is as follows. This is because when the density is greater than 0.971 g / cm ３ it becomes hard and brittle, and it may be difficult to produce a stretched film.

[0026] Also, 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. When the melt mass flow rate (MFR) is 0.01 g / 10 min or more, it can be molded with a general-purpose extruder without using special equipment. When it is 3.00 g / 10 min or less, sufficient film strength can be obtained.

[0027] The above melt mass flow rate is obtained by measuring in accordance with the provisions of JIS K7210:1999.

[0028] Further, from the viewpoint of further improving the heat resistance, the content of the high-density polyethylene with respect to the whole (100% by mass) of the base material layer 3 is preferably 50% by mass or more (that is, it is the main component of the base material layer 3). From the viewpoint of further improving the recyclability, 70% by mass or more is more preferable, 90% by mass or more is even more preferable, and 95% by mass or more is particularly preferable.

[0029] From the above, as the resin forming the base material layer 3, by using high-density polyethylene with a density of 0.950 g / cm ３ or more, an increase in the heat shrinkage rate of the stretched film 10 can be suppressed, and thus it becomes possible to provide a stretched film 10 having excellent heat resistance.

[0030] In addition, the base material layer 3 may contain other components other than the above-mentioned high-density polyethylene within a range that does not impair the stretchability of the film.

[0031] 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, fungicides, antibacterial agents, nucleating agents, flame retardants, lubricants, etc.

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

[0033] Also, the ethylene content (content of ethylene units) in the ethylene-vinyl alcohol copolymer used for the barrier layer 5 is 27 to 38 mol%, preferably 27 to 32 mol%, based on the total amount (100 mol%) of all monomer units constituting the ethylene-vinyl alcohol copolymer. This is because when the ethylene content is less than 27 mol%, the processability of the barrier film may decrease, and when it is more than 38 mol%, the oxygen barrier property may become insufficient.

[0034] Further, 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, more preferably 95% by mass or more, out of 100% by mass of the barrier layer.

[0035] From the above, by using the above-mentioned ethylene-vinyl alcohol copolymer as the resin for forming the barrier layer 5, the oxygen permeability of the stretched film 10 becomes 2.5 cc / m ２ ·day or less, so it becomes possible to provide a stretched film 10 having excellent oxygen barrier properties.

[0036] Incidentally, from the viewpoint of improving the oxygen barrier property, the oxygen permeability of the stretched film 10 is preferably 2.0 cc / m ２ ·day or less, more preferably 1.5 cc / m ２ ·day or less, even more preferably 1.0 cc / m ２ ·day or less.

[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 7126-2, under conditions of 25°C and 0% humidity, or under conditions of 25°C and 90% 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 base material layer 3 and the barrier layer 5, and is mainly composed of a material that has excellent adhesion to the base material layer 3 and the barrier layer 5, such as 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 the Laminate> Next, the method for manufacturing the laminate using the stretched film of this embodiment will be described in detail.

[0042] 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, 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.

[0043] Then, by performing uniaxial or biaxial stretching on the raw film roll, the base layer 3, adhesive layer 4, and barrier layer 5 shown in Figures 1 and 2 are laminated in this order, 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.

[0044] 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.

[0045] Furthermore, by performing this uniaxial stretching, the resin becomes oriented, which improves the tensile strength and tensile modulus of the film, thus preventing printing misalignment and improving printability. In addition, the oxygen barrier properties of the barrier layer 5, which is mainly composed of ethylene-vinyl alcohol copolymer, are improved, and in particular, the oxygen barrier properties under high humidity conditions (at an atmosphere of 90% humidity) are dramatically improved.

[0046] Furthermore, from the viewpoint of increasing the effect of heat fixation and improving heat resistance, the stretching temperature in the uniaxial stretching process is 121°C or higher and less than 130°C, preferably 125°C or higher and 129°C or lower, and more preferably 128°C or higher and 129°C or lower. This is because if the stretching temperature is below 121°C, the heat resistance may not be sufficiently improved, and if the stretching temperature is 130°C or higher, the film may melt and break.

[0047] Furthermore, from the viewpoint of preventing misprinting and improving printability, as well as improving the oxygen barrier properties of the barrier layer 5 (especially improving oxygen barrier properties under high humidity conditions (at an atmosphere of 90% humidity)), the stretching ratio in the uniaxial stretching process is preferably 4 times or more and 8 times or less, and preferably 5 times or more and 7 times or less. This is because if the stretching ratio is less than 4 times, misprinting may occur and printability may decrease, and if the stretching ratio is greater than 8 times, the film may break.

[0048] Furthermore, in the stretched film 10 of this embodiment, the thermal shrinkage rate when heated at 120°C for 10 minutes in the stretching direction of the film is 5% or less. If the thermal shrinkage rate is 5% or less, it is possible to prevent the occurrence of wrinkles caused by the shrinkage of the base film during heat sealing performed during bag making, thereby providing a stretched film 10 with high dimensional stability due to heat treatment and excellent heat resistance.

[0049] 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.

[0050] 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 2% or less.

[0051] Furthermore, the aforementioned "thermal shrinkage rate" can be determined by the method described in the examples below.

[0052] Furthermore, in the stretched film 10 of the present invention, it is preferable that the tensile modulus of elasticity in the stretching direction of the film is 2000 MPa or more and less than 5000 MPa. This is because if the tensile modulus of elasticity is less than 2000 MPa, it may be difficult to suppress the occurrence of printing misalignment due to the stretching of the film when transporting the film in the printing process. Also, if the tensile modulus of elasticity is 5000 MPa or more, the flexibility of the film decreases, which may cause cracks or fissures to occur.

[0053] Furthermore, the tensile modulus is more preferably 2500 MPa or higher, and even more preferably 3000 MPa or higher.

[0054] Furthermore, the above-mentioned "tensile modulus" can be obtained by measurement in accordance with JIS K 7127.

[0055] Furthermore, from the viewpoint of improving recyclability, the polyethylene content in the entire laminate 1, which is composed of the stretched film 10 and the sealant film 2, is preferably 90% by mass or more of the total mass of the laminate. According to the guidelines of the European consortium "CEFLEX (Circular Economy for Flexible Packaging)", if the polyethylene content in the entire laminate is 90% by mass or more, and if ethylene-vinyl alcohol copolymer or adhesive is used, the laminate is certified as a monomaterial if the respective content in the entire laminate is less than 5% by mass. Therefore, by configuring the laminate 1 as described above, it is possible to provide a laminate 1 that is certified as a monomaterial when the sealant film 2 is laminated onto the stretched film 10.

[0056] Furthermore, the thickness of the base material layer 3 after stretching is 6 to 40 μm, preferably 10 to 40 μm, and more preferably 15 to 30 μm. If the thickness of the base material layer 3 after stretching is 6 μm or more, sufficient strength and heat resistance can be obtained as a base film. Also, if the thickness of the base material layer after stretching is 30 μm or less, costs can be reduced, sufficient transparency can be obtained, and the amount of plastic used can be reduced when used for flexible packaging, thus providing an environmentally friendly stretched film 10.

[0057] Furthermore, the thickness of the barrier layer 5 after stretching is 1 to 8 μm, preferably 2 to 6 μm, and more preferably 2 to 5 μm. If the thickness of the barrier layer 5 after stretching is 1 μm or more, sufficient strength and oxygen barrier properties can be obtained as a barrier film. Also, if the thickness of the barrier layer 5 after stretching is 8 μm or less, a film with excellent recyclability can be obtained.

[0058] 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.

[0059] Furthermore, by setting the thicknesses of the base material layer 3, barrier layer 5, and adhesive layer 4 after the stretching process to the respective ranges described above, it becomes possible to provide the laminate 1 with excellent recyclability when a sealant film 2 (for example, with a thickness of 50 to 150 μm) is laminated on the stretched film 10.

[0060] The thickness of the raw film before stretching is not particularly limited, as long as the thicknesses of the base layer 3, barrier layer 5, and adhesive layer 4 after stretching are within the ranges described above. For example, 50 to 300 μm is preferred, and 80 to 250 μm is more preferred.

[0061] By the above method, in this embodiment, it is possible to obtain a stretched film 10 that has excellent oxygen barrier properties as well as excellent heat resistance.

[0062] Next, raw materials containing polyethylene resins such as high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE) are prepared and formed into a film by melt extrusion using an extruder equipped with a T-die to produce a sealant film 2 (for example, with a thickness of 50 to 150 μm).

[0063] Then, for example, the laminate 1 shown in Figure 1 is manufactured by laminating the barrier layer 5 of the stretched film 10 and the sealant film 2 via an adhesive.

[0064] (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.

[0065] 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 has two base layers.

[0066] 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 (i.e., provided on the surface of the base layer 7 opposite to the adhesive layer 6 side).

[0067] <Base Layer (Second Base Layer)> Base layer 7, like base layer 3, is mainly composed of high-density polyethylene, and the density of high-density polyethylene is 0.950 g / cm³. ３ This concludes the explanation. Therefore, since stretching at high temperatures becomes possible, the effect of heat fixation by high-temperature stretching is increased, and, similar to the base material layer 3, heat resistance can be improved, as can film strength.

[0068] Furthermore, from the viewpoint of facilitating the production of stretched films, the density of the high-density polyethylene is 0.971 g / cm³, similar to the base layer 3. ３ The following is preferable:

[0069] Furthermore, from the viewpoint of enabling molding with a versatile 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.

[0070] Furthermore, similar to the base layer 3, from the viewpoint of further improving heat resistance, the content of high-density polyethylene in the base layer 7 is preferably 50% by mass or more of the total base layer 100% by mass, and from the viewpoint of further improving recyclability, it is more preferably 70% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more.

[0071] 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.

[0072] <Adhesive layer (second adhesive layer)> The adhesive layer 6 can be made primarily of modified polyolefin, similar to the adhesive layer 4 described above.

[0073] <Method for Manufacturing the Laminate> Next, the method for manufacturing the laminate using the stretched film of this embodiment will be described in detail.

[0074] 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.

[0075] 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.

[0076] Furthermore, the uniaxial stretching process described above refers to a stretching process performed in either the medium-distance (MD) or tangential (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.

[0077] Furthermore, similar to the first embodiment described above, the stretching temperature in the uniaxial stretching process is 121°C or higher and less than 130°C, preferably 125°C or higher and 129°C or lower, and more preferably 128°C or higher and 129°C or lower. Also, similar to the first embodiment described above, the stretching ratio in the uniaxial stretching process is 4 times or higher and 8 times or lower, preferably 5 times or higher and 7 times or lower.

[0078] Furthermore, similar to the stretched film 10 described above, the oxygen permeability of the stretched film 11 of this embodiment is 2.5 cc / m². ２ - Since it is less than or equal to 2.0 days, and from the viewpoint of improving oxygen barrier properties, the oxygen permeability of the stretched film 11 is 2.0 cc / m². ２ - Preferably less than 1.5 cc / m２ - More preferably 1.0 cc / m³ or less. ２ - Day or below is even more preferable.

[0079] Furthermore, in the stretched film 11 of this embodiment, similar to the stretched film 10 described above, the thermal shrinkage rate when heated at 120°C for 10 minutes in the stretching direction of the film is 5% or less. If the thermal shrinkage rate is 5% or less, it is possible to provide a stretched film 11 with high dimensional stability due to heat treatment and excellent heat resistance.

[0080] 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.

[0081] 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 2% or less.

[0082] Furthermore, in the stretched film 11 of this embodiment, similar to the stretched film 10 described above, from the viewpoint of suppressing the occurrence of printing misalignment due to film elongation and the occurrence of cracks and fissures, it is preferable that the tensile modulus of elasticity in the stretching direction of the film be 2000 MPa or more and less than 5000 MPa, more preferably 2500 MPa or more, and even more preferably 3000 MPa or more.

[0083] Furthermore, the thickness of the raw film before stretching, the thickness of the barrier layer 5 after stretching, and the thickness of the adhesive layer 4 after stretching are preferably the same as in the first embodiment described above, and the thickness of the adhesive layer 6 after stretching is preferably the same as the thickness of the adhesive layer 4 after stretching.

[0084] Furthermore, the thickness of the base material layer 3 and base material layer 7 after stretching is preferably 3 to 20 μm, more preferably 5 to 20 μm, and even more preferably 7 to 15 μm. If the thickness of the base material layer 3 and base material layer 7 after stretching is 3 μm or more, sufficient strength and heat resistance can be obtained as a base material film. Also, if the thickness of the base material layer 3 and base material layer 7 after stretching is 20 μm or less, costs can be reduced, sufficient transparency can be obtained, and the amount of plastic used can be reduced when used for flexible packaging, thus providing an environmentally friendly stretched film 11.

[0085] Furthermore, by setting the thicknesses of the base material layer 3 and base material layer 7, barrier layer 5, and adhesive layer 4 and adhesive layer 6 after the stretching process to the respective ranges described above, it becomes possible to provide the laminate 20 with excellent recyclability when a sealant film 2 (for example, with a thickness of 50 to 150 μm) is laminated on the stretched film 11.

[0086] Furthermore, similar to the first embodiment described above, from the viewpoint of improving recyclability, the polyethylene content in the entire laminate 20 composed of the stretched film 11 and the sealant film 2 is more preferably 90% by mass or more of 100% by mass of the laminate.

[0087] By the above method, in this embodiment, it is possible to obtain a stretched film 11 that has excellent oxygen barrier properties as well as excellent heat resistance.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] The materials used to produce the stretched film are as follows: (1) HDPE1: High-density polyethylene (density: 0.951 g / cm³) ３ (1) HDPE2: High-density polyethylene (density: 0.971 g / cm³) ３ (3) HDPE3: High-density polyethylene (density: 0.960 g / cm³) ３ (4) MDPE: Medium-density polyethylene (density: 0.943 g / cm³) ３ (5) EVOH1: Ethylene-vinyl alcohol copolymer (density: 1.19 g / cm³) ３ (6) EVOH2: Ethylene-vinyl alcohol copolymer (density: 1.21 g / cm³) ３(7) EVOH3: Ethylene-vinyl alcohol copolymer (density: 1.14 g / cm³) ３ (8) Adhesive: Acid-modified polyethylene (density: 0.91 g / cm³) ３ Melting point: 120°C, MFR (190°C): 2.3 g / 10 min, manufactured by Mitsui Chemicals, Inc., product name: Admer NF587)

[0092] (Example 1) <Preparation of stretched film> First, high-density polyethylene, ethylene-vinyl alcohol copolymer, and acid-modified polyethylene were prepared as shown in Table 1.

[0093] Next, using a multilayer extruder equipped with a T-die (Labtech, product name: LCR-350), the prepared resin was co-extruded at 230°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.

[0094] Then, using a longitudinal stretcher (Labtech, product name: LMDO-350), the raw film was subjected to uniaxial stretching in the medium-density direction under the stretching temperature and stretching ratio conditions shown in Table 1, thereby stretching the raw film and producing stretched films with the thicknesses shown in Table 1.

[0095] <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 ratio of polyethylene to polyethylene]. The results are shown in Table 1.

[0096] In this embodiment, the sum of the weights per unit area of ​​the first and second base material layers, which are made of high-density polyethylene, is 0.001446 [g / cm³]. ２ The weight per unit area of ​​the barrier layer formed by the ethylene-vinyl alcohol copolymer is 0.000286 [g / cm³]. ２ The sum of the weights per unit area of ​​the first adhesive layer and the second adhesive layer formed by acid-modified polyethylene is 0.000218 [g / cm³]. ２ Therefore, the polyethylene content [mass%] of the total stretched film produced was [0.001446 / (0.001446 + 0.000286 + 0.000218)] × 100 = 74.2 mass%.

[0097] <Measurement of Oxygen Permeability> Next, using an oxygen permeability measuring device (Labthink Corporation, product name: C203H), the oxygen permeability [cc / m²] of the stretched film prepared in accordance with JIS K 7126-2 was measured. ２ The values ​​for [day] were measured under conditions of 25°C and 0% humidity, and under conditions of 25°C and 90% humidity. The results are shown in Table 1.

[0098] <Measurement of Tensile Modulus> The tensile modulus [MPa] of the stretched film was measured in accordance with JIS K 7127. More specifically, strip-shaped test pieces measuring 200 mm in the MD direction and 10 mm in the TD direction were prepared from the stretched film. Using a tensile testing machine (Shimadzu Corporation, product name: Autograph AG-5000A), the test pieces were pulled in the stretching direction (MD) under conditions of a temperature of 25°C and a humidity of 65%, with a chuck distance of 80 mm and a tensile speed of 10 mm / min. The ratio of the tensile stress corresponding to the strain between two points of strain from 0 to 1% and the corresponding strain was calculated, and the calculated value was defined as the tensile modulus [MPa]. The results are shown in Table 1.

[0099] <Calculation of Heat Shrinkage Rate> A sample of a predetermined size (12 cm x 12 cm) was cut from the prepared stretched film. Orthogonal markings, each 10 cm long and parallel to the edge, were drawn 1 cm inward from each edge of the sample. The sample was placed in a 120°C oven and heated for 10 minutes, then removed and allowed to cool to room temperature. The distance between the markings in the stretching direction (i.e., MD) was measured in the heat-treated sample, and the heat shrinkage rate [%] was calculated from the change in the distance between the markings 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.

[0100] Thermal shrinkage rate in the stretching direction [%] = [(gauge distance before heating - gauge distance after heating) / gauge distance before heating] × 100 (1)

[0101] (Examples 2-11, Comparative Examples 1-6) Except for changing at least one of the composition of the stretched film (i.e., the combination of polyethylene, ethylene-vinyl alcohol copolymer, and adhesive) and the conditions of the uniaxial stretching treatment to the conditions shown in Table 1, a roll of film having the thickness shown in Tables 1 to 3 was stretched in the same manner as in Example 1 described above to produce a stretched film.

[0102] Then, in the same manner as in Example 1 described above, the polyethylene content was calculated, the oxygen permeability was measured, the tensile modulus was measured, and the thermal shrinkage rate was calculated. The results are shown in Tables 1 to 3.

[0103] In Comparative Example 1, the stretching ratio during film formation in the uniaxial stretching process was high (9 times), causing the stretched film to break. Therefore, in Comparative Example 1, it was not possible to measure oxygen permeability, measure tensile modulus, or calculate thermal shrinkage.

[0104] Furthermore, in Comparative Example 3, 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. Consequently, in Comparative Example 3, it was not possible to measure oxygen permeability, measure tensile modulus, or calculate thermal shrinkage.

[0105] Furthermore, in Comparative Example 6, the first and second base material layers were made of medium-density polyethylene. Because polyethylene has a low density (low melting point), the film melted and broke at a stretching temperature of 125°C. Therefore, in Comparative Example 6, it was not possible to measure oxygen permeability, measure tensile modulus, or calculate thermal shrinkage.

[0106] (Comparative Example 7) A raw film roll with the thickness shown in Table 1 was prepared in the same manner as in Example 1 described above. Then, in the same manner as in Example 1 described above, the polyethylene content, oxygen permeability, tensile modulus, and thermal shrinkage rate of this raw film roll were calculated. The results are shown in Table 3.

[0107]

[0108]

[0109]

[0110] As shown in Tables 1 and 2, the first and second substrate layers have a density of 0.950 g / cm³. ３ In the stretched films of Examples 1 to 11, which mainly consist of high-density polyethylene and whose barrier layer mainly consists of an ethylene-vinyl alcohol copolymer with an ethylene content of 27 mol% to 38 mol%, the oxygen permeability at a temperature of 25°C and 0% humidity, and at a temperature of 25°C and 90% humidity, was 2.5 cc / m². ２ Since the temperature is less than 1 day, it is clear that the oxygen barrier properties are excellent. Furthermore, since the thermal shrinkage rate when heated at 120°C for 10 minutes in the stretching direction of the film is 5% or less, it is clear that the dimensional stability after heat treatment is high and the heat resistance is excellent.

[0111] On the other hand, as shown in Table 3, in the stretched film of Comparative Example 2, the stretching temperature was less than 121°C (115°C), and the effect of heat fixation was not obtained, resulting in a thermal shrinkage rate greater than 5%, indicating poor heat resistance.

[0112] Furthermore, in the stretched film of Comparative Example 4, the barrier layer is mainly composed of an ethylene-vinyl alcohol copolymer with an ethylene content greater than 38 mol% (44 mol%), and the oxygen permeability at 25°C and 0% humidity, and at 25°C and 90% humidity, is 2.5 cc / m². ２ - It is larger than the day, indicating poor oxygen barrier properties.

[0113] Furthermore, in the stretched film of Comparative Example 5, the first and second base material layers are composed of medium-density polyethylene. Since polyethylene has a low density (low melting point), the stretching process must be performed at a low stretching temperature of less than 121°C (120°C). As a result, the thermal shrinkage rate is greater than 5%, indicating poor heat resistance. In addition, the tensile modulus is less than 2000 MPa, making it impossible to suppress the occurrence of printing misalignment due to film elongation when the film is transported during the printing process.

[0114] Furthermore, in Comparative Example 7, since the original film was not stretched, the oxygen permeability in an atmosphere of 25°C and 90% humidity was 2.5 cc / m². ２ - It is larger than day, indicating poor oxygen barrier properties. Furthermore, the tensile modulus is less than 2000 MPa, meaning that it cannot suppress the occurrence of printing misalignment due to film elongation when transporting the film during the printing process.

[0115] As described above, the present invention is suitable, for example, for stretched films used in packaging films and the like, and for manufacturing the same.

[0116] 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 first substrate layer and a barrier layer, wherein the first substrate layer has a density of 0.950 g / cm³. ３ The main component is high-density polyethylene, and the barrier layer is mainly composed of an ethylene-vinyl alcohol copolymer with an ethylene content of 27 mol% to 38 mol%, and the oxygen permeability in an atmosphere of 25°C and 90% humidity is 2.5 cc / m³. ２ A stretched film characterized by having a temperature of 5 days or less, and a thermal shrinkage rate of 5% or less when heated at 120°C for 10 minutes in the stretching direction of the film.

2. The stretched film according to claim 1, characterized in that a first adhesive layer is provided between the first substrate layer and the barrier layer.

3. Further comprising a second substrate layer, wherein the second substrate layer has a density of 0.950 g / cm³ ３ The stretched film according to claim 2, wherein the main component is high-density polyethylene as described above, and a second adhesive layer is provided between the barrier layer and the second base material layer.

4. The stretched film according to claim 2, characterized in that a sealant film is provided on the surface of the barrier layer opposite to the first adhesive layer side.

5. The stretched film according to claim 3, characterized in that a sealant film is provided on the surface of the second substrate layer opposite to the side of the second adhesive layer.

6. Density is 0.950 g / cm³ ３ A method for producing a stretched film, comprising at least the steps of: preparing a base film comprising a base layer mainly composed of polyethylene and a barrier layer mainly composed of an ethylene-vinyl alcohol copolymer having an ethylene content of 27 mol% or more and 38 mol% or less; and performing a stretching treatment on the base film, wherein the stretching temperature in the stretching treatment is 121°C or more and less than 130°C, and the stretching ratio is 4 times or more and 8 times or less.

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