Biaxially oriented polyethylene film and laminated film and package

Abstract

To provide a biaxially oriented polyethylene film and a laminated film that have improved lamination strength with sealant film by adjusting the rigidity of the film surface, and to provide a package.SOLUTION: There is provided a biaxially oriented film, which is a laminate of at least two or more layers that has been stretched in two axial directions: the longitudinal (MD) direction and the transverse (TD) direction. An elastic modulus (E1) measured by atomic force microscopy (AFM) of the cross-section of the first surface layer that is the surface layer on one side of the biaxially oriented film, is 1.6 GPa or less. It is preferable that an elastic modulus (E2) measured by the atomic force microscopy (AFM) of the cross-section of the second surface layer that is the surface layer on the other side of the biaxially oriented film, satisfies E1≤E2 in relation to the elastic modulus (E1).SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a biaxially oriented polyethylene film, and a laminate film and a package using the biaxially oriented polyethylene film, and in particular to a biaxially oriented polyethylene film, a laminate film, and a package having excellent laminate strength. [Background technology]

[0002] In recent years, with the growing awareness of environmental issues, environmentally conscious efforts are being made in various fields. For example, recycling, which involves collecting used products and processing them into new products for reuse, is known as one representative effort to address environmental issues.

[0003] In general, in the field of packaging food and the like, laminates in which a plurality of different types of synthetic resin films are laminated are used to achieve high quality requirements. From an environmentally conscious perspective, it is desirable to reduce the environmental impact of this type of laminate by recycling or the like. Normally, when recycling a discarded laminate, since different types of films are laminated, the resins constituting the laminate become a mixture of resins that are not compatible even when remelted, resulting in a significant decrease in the quality of the recycled resources, and therefore the laminate is unsuitable as a recycled material.

[0004] In order to solve such problems, a laminate has been proposed in which the base film of the laminate and the sealant film are made of a single material (mono-material). This type of laminate uses a polyethylene-based resin for both the base film and the sealant film to make them a single material, which allows for good compatibility upon remelting and makes it possible to use the laminate as a recycled material.

[0005] The above laminate is required to have excellent film properties such as rigidity, toughness, heat resistance, etc., while achieving mono-materialization of the base film and sealant film. In response to this, a stretched polyethylene film has been proposed that uses a heat-sealable polyethylene film as the sealant film to achieve mono-materialization of the laminate, while improving properties such as rigidity, toughness, and heat resistance (for example, see Patent Document 1).

[0006] In this type of laminate, in addition to performance such as rigidity, lamination strength (adhesive strength) when bonding the base film and the sealant film is also an important film performance. If the lamination strength between the base film and the sealant film is low, there is a risk that problems such as reduced heat seal strength and resistance to tearing when used as a packaging bag, or high tear strength making it difficult to tear, may occur.

[0007] Therefore, the inventors conducted extensive research into a substrate film and a sealant film compatible with mono-materials, using a biaxially oriented polyethylene film as the substrate film, in order to improve the laminate strength between the substrate film and the sealant film. As a result, they found that there is a correlation between the rigidity of the film surface layer and the laminate strength with the sealant film, regardless of the rigidity of the substrate film. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2023-19592 A Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made in consideration of the above-mentioned points, and provides a biaxially oriented polyethylene film, a laminate film, and a packaging body in which the rigidity of the film surface layer is adjusted to improve the laminate strength with a sealant film. [Means for solving the problem]

[0010] That is, the first invention relates to a biaxially oriented polyethylene film, which is a laminate of at least two layers stretched in two axial directions, that is, the machine direction (MD) and the transverse direction (TD), and which is characterized in that the elastic modulus (E1) of a cross section of a first surface layer, which is one surface layer of the biaxially oriented film, measured by atomic force microscope (AFM) is 1.6 GPa or less.

[0011] The second invention relates to the biaxially oriented polyethylene film of the first invention, wherein the elastic modulus (E2) of a cross section of a second surface layer, which is the other surface layer of the biaxially oriented film, measured by the atomic force microscope (AFM) satisfies E1≦E2 in relationship with the elastic modulus (E1).

[0012] A third invention relates to the biaxially oriented polyethylene film according to the first or second invention, wherein the first surface layer of the biaxially oriented film is subjected to a surface treatment.

[0013] A fourth invention relates to the biaxially oriented polyethylene film according to the first or second invention, wherein the biaxially oriented film is a laminate of three or more layers.

[0014] A fifth aspect of the present invention relates to the biaxially oriented polyethylene film according to the third aspect of the present invention, wherein the biaxially oriented film is a laminate of three or more layers.

[0015] The sixth invention relates to a laminate film using the biaxially oriented polyethylene film of the first or second invention, in which a sealant film made of at least a polyethylene resin is laminated on the first surface layer of the biaxially oriented polyethylene film.

[0016] The seventh invention relates to a laminate film using the biaxially oriented polyethylene film of the third invention, in which a sealant film made of at least a polyethylene resin is laminated on the first surface layer of the biaxially oriented polyethylene film.

[0017] The eighth invention relates to a laminate film using the biaxially oriented polyethylene film of the fourth invention, in which a sealant film made of at least a polyethylene resin is laminated on the first surface layer of the biaxially oriented polyethylene film.

[0018] The ninth invention relates to a package made of the laminate film of the sixth invention.

[0019] A tenth aspect of the present invention relates to a package made of the laminate film according to the seventh aspect of the present invention.

[0020] An eleventh aspect of the present invention relates to a package comprising the laminate film according to the eighth aspect of the present invention. Effect of the Invention

[0021] The biaxially oriented polyethylene film of the first invention is a biaxially oriented film which is a laminate of at least two layers stretched in two axial directions, namely, the machine direction (MD) and the transverse direction (TD), and the first surface layer, which is one surface layer of the biaxially oriented film, has an elastic modulus (E1) of 1.6 GPa or less as measured by atomic force microscope (AFM) of a cross section thereof. This results in good flexibility of the first surface layer, and when a sealant film is laminated on the first surface layer, good laminate strength with the sealant film is obtained.

[0022] According to the biaxially oriented polyethylene film of the second invention, in the first invention, the elastic modulus (E2) of a cross section of the second surface layer, which is the other surface layer of the biaxially oriented film, measured by the atomic force microscope (AFM) satisfies E1≦E2 in relationship to the elastic modulus (E1). Therefore, the second surface layer has a higher rigidity than the first surface layer, thereby improving the processability as a packaging material.

[0023] According to the biaxially oriented polyethylene film of the third invention, in the first or second invention, the first surface layer of the biaxially oriented film is subjected to a surface treatment, so that when a sealant film is bonded to the first surface layer, the adhesion between the first surface layer and the sealant film is good.

[0024] According to the biaxially oriented polyethylene film of the fourth invention, in the first or second invention, the biaxially oriented film is a laminate of three or more layers, so that the biaxially oriented polyethylene film consisting of a laminate of three or more layers can have excellent laminate strength.

[0025] According to the biaxially oriented polyethylene film of the fifth invention, in the third invention, the biaxially oriented film is a laminate of three or more layers, so that the biaxially oriented polyethylene film consisting of a laminate of three or more layers can have excellent laminate strength.

[0026] According to the laminate film of the sixth invention, a sealant film made of at least a polyethylene resin is laminated on the first surface layer of the biaxially oriented polyethylene film of the first or second invention, thereby achieving a single material (monomaterial) and facilitating recycling, while providing a laminate film with excellent laminate strength between the biaxially oriented polyethylene film and the sealant film.

[0027] According to the laminate film of the seventh invention, a sealant film made of at least polyethylene resin is laminated on the first surface layer of the biaxially oriented polyethylene film of the third invention, thereby achieving a single material (monomaterial) and facilitating recycling, while providing a laminate film with excellent laminate strength between the biaxially oriented polyethylene film and the sealant film.

[0028] According to the laminate film of the eighth invention, a sealant film made of at least polyethylene resin is laminated to the first surface layer of the biaxially oriented polyethylene film of the fourth invention, thereby achieving a single material (monomaterial) and facilitating recycling, while providing a laminate film with excellent laminate strength between the biaxially oriented polyethylene film and the sealant film.

[0029] According to the ninth aspect of the present invention, the package is made of the laminate film of the sixth aspect of the present invention, and therefore the package can be made recyclable by being made of an easily recyclable laminate film.

[0030] According to the tenth aspect of the present invention, the package is made of the laminate film of the seventh aspect of the present invention, and therefore the package can be made of an easily recyclable laminate film and can be made recyclable.

[0031] According to the eleventh aspect of the present invention, the package is made of the laminate film of the eighth aspect of the present invention, and therefore the package can be made of an easily recyclable laminate film and can be made recyclable. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] The biaxially oriented polyethylene film according to one embodiment of the present invention is a biaxially oriented film that is a laminate of at least two layers that are oriented in two axial directions, namely, the machine direction (MD) and the transverse direction (TD). The biaxially oriented polyethylene film of the present invention can be used as a base film of a laminate film to which printing, deposition, etc. are applied. This laminate film is suitably used as a package for various articles such as food, daily necessities, and parts.

[0033] The biaxially oriented polyethylene film of the present invention is composed of a single material (monomaterial) whose main raw material is a polyethylene-based resin. Therefore, it can be suitably used as a recycled material. The term "single material" as used here means that the main raw material of each layer is the same type of resin material, and it is acceptable for small amounts of various additives to be contained.

[0034] The polyethylene resin used as the resin raw material for the biaxially oriented polyethylene film is appropriately selected from polyethylene resins derived from petroleum, biomass, material recycling, chemical recycling, etc., and is a homopolymer of ethylene or a random copolymer of ethylene and an α-olefin having 3 or more carbon atoms, such as propylene, 1-butene, 1-heptene, 1-hexene, 1-octene, etc. The polyethylene resin may be a mixture of one or more of the above.

[0035] The melt flow rate (MFR) of the polyethylene resin is not particularly limited. For example, a polyethylene resin having an MFR of 0.1 to 30 g / 10 min, particularly 0.1 to 20 g / 10 min, measured according to JIS K 7210 at 190° C. and a load of 2.16 kg, is preferably used. If the MFR of the polyethylene resin used is too low, the pressure of the extruder tends to be excessively high, which tends to reduce productivity. If the MFR is too high, the melt viscosity of the resin is low, which tends to cause breakage during stretching, making it difficult to form a film.

[0036] The resin raw material used for the biaxially oriented polyethylene film may be appropriately blended with a polyolefin-based elastomer such as an ethylene-α-olefin random copolymer elastomer, within the scope of the present invention, and may also be appropriately blended with additives such as antioxidants, neutralizing agents, antistatic agents, antifogging agents, lubricants, nucleating agents, and colorants.

[0037] The biaxially oriented polyethylene film of the present invention can be obtained by a known film forming method such as the T-die method or the inflation method. In particular, it is preferable to stretch and form a sheet formed by the T-die method. Film forming by the T-die method is advantageous in that it can obtain high thickness and thinness precision required for a base film of a laminate film. The biaxially oriented polyethylene film is a biaxially oriented film stretched in two axial directions, the machine direction (MD) and the transverse direction (TD), of the film. For biaxial stretching, either sequential biaxial stretching or simultaneous biaxial stretching can be used successfully.

[0038] As an example, a method for producing a biaxially stretched film by sequential longitudinal (MD) stretching and transverse (TD) stretching will be described. A polyethylene resin is melted and kneaded in an extruder, extruded into a sheet from a T-die, and cooled with a chill roll at a temperature of 10 to 70°C. The sheet is stretched 3 to 8 times in the longitudinal (MD) direction by roll-to-roll stretching with a stretching roll at 70 to 130°C. Next, it is stretched 5 to 15 times in the transverse (TD) direction at a temperature of 100 to 160°C, at least one surface is subjected to a corona discharge treatment, and the biaxially stretched polyethylene film is wound up with a winder.

[0039] The lower limit of the longitudinal (MD) stretching ratio is about 3 times. If the longitudinal (MD) stretching ratio is too low, there is a risk of unevenness in the film thickness. The upper limit of the longitudinal (MD) stretching ratio is 8 times, preferably 7 times. If the longitudinal (MD) stretching ratio is too high, there is a risk of it being difficult to perform transverse (TD) stretching. The lower limit of the longitudinal (MD) stretching temperature is 70°C, preferably 80°C. If the longitudinal (MD) stretching temperature is too low, the film will not be stretched uniformly, and there is a risk of unevenness in the film thickness. The upper limit of the longitudinal (MD) stretching temperature is 130°C. If the longitudinal (MD) stretching temperature is too high, there is a risk of the sheet not being able to be stretched due to the increased adhesion between the sheet and the roll. The lower limit of the transverse (TD) stretching ratio is 5 times, preferably 6 times. If the transverse (TD) stretching ratio is too low, there is a risk of unevenness in the film thickness. The upper limit of the transverse (TD) stretching ratio is 15 times, preferably 14 times, and more preferably 13 times. If the transverse (TD) stretching ratio is too high, there is a risk of breakage during stretching. The lower limit of the transverse (TD) stretching temperature is 100°C. If the transverse (TD) stretching temperature is too low, there is a risk of unevenness in the film thickness. The upper limit of the transverse (TD) stretching temperature is 160°C. If the transverse (TD) stretching temperature is too high, there is a risk of breakage of the film during stretching.

[0040] The biaxially oriented polyethylene film of the present invention is a laminated film of two or more layers including a first surface layer and a second surface layer. The first surface layer is one surface layer of the biaxially oriented polyethylene film, and is particularly the surface layer on the side to which a sealant film is attached when a laminate film is produced. On the other hand, the second surface layer is the other surface layer of the biaxially oriented polyethylene film relative to the first surface layer. An antiblocking agent is appropriately added to the first and second surface layers as necessary. The biaxially oriented polyethylene film of the present invention may also be a laminated film of three or more layers. In a laminated film of three or more layers, in addition to the first surface layer and the second surface layer, for example, a base layer interposed between the first surface layer and the second surface layer to serve as a support for both layers is provided. A surfactant is appropriately added to the base layer as necessary. In the laminated film, appropriate layers such as an adhesive layer can be laminated depending on the desired function. In the biaxially oriented polyethylene film of the present invention, when an antiblocking agent is added to both surface layers, a three-layer laminated film is preferable from the viewpoint of transparency. In addition, a five-layer laminate film is preferred from the viewpoint that intermediate layers can be provided between the first surface layer and the base layer, and between the second surface layer and the base layer, to impart functionality such as barrier properties to the intermediate layers.

[0041] The antiblocking agent added to the surface layer of the biaxially oriented polyethylene film of the present invention is not particularly limited in type, and organic or inorganic particles, or a mixture thereof, are preferably used. The organic particles are obtained, for example, by emulsion polymerization or suspension polymerization. Examples of the organic particles include polymethyl methacrylate, polystyrene, polyamide, etc. Examples of the inorganic particles include silica, zeolite, talc, etc. These antiblocking agents may be used alone or in combination of two or more. From the viewpoint of the blocking resistance and see-through feeling of the film, polymethyl methacrylate is preferably used as the organic particles, and silica and zeolite are preferably used as the inorganic particles. The method of adding the antiblocking agent is not particularly limited, and it can be added by a known method, such as mixing a high concentration master batch with the resin raw material of the film or mixing by dry blending. The amount of the antiblocking agent added to the surface layer is not particularly limited and may be appropriately determined.

[0042] The surfactants added to the substrate layer of the biaxially oriented polyethylene film include aliphatic amine compounds such as lauryl diethanolamine, myristyl diethanolamine, palmityl diethanolamine, oleyl diethanolamine, and stearyl diethanolamine, and aliphatic amine ester compounds which are ester compounds of these compounds, aliphatic amide compounds such as lauryl diethanolamide, myristyl diethanolamide, palmityl diethanolamide, oleyl diethanolamide, and stearyl diethanolamide, and aliphatic amide ester compounds which are ester compounds of these compounds, polyhydric alcohols such as glycerin monooleate, glycerin monostearate, and glycerin distearate, sorbitan fatty acid esters such as sorbitan laurate, sorbitan palmitate, sorbitan oleate, and sorbitan stearate, sulfonic acids such as alkyl sulfonates and alkyl benzene sulfonates, sulfates such as alkyl sulfates and polyoxyethylene alkyl ether sulfates, and phosphates such as alkyl phosphates and polyoxyethylene alkyl ether phosphates, and are appropriately selected and used. The amount of surfactant added to the substrate layer is not particularly limited and can be appropriately selected.

[0043] The thickness of the biaxially oriented polyethylene film of the present invention is not particularly limited and is appropriately determined depending on the demand and application, for example, 5 to 100 μm, preferably 10 to 70 μm. Among these, the thickness of the first surface layer and the second surface layer of the biaxially oriented polyethylene film is preferably 0.3 to 5 μm, preferably 0.4 to 4 μm, more preferably 0.5 to 2 μm. If the surface layer is too thin, the antiblocking agent may fall off when the film passes through the rolls during processing, whereas if it is too thick, the amount of antiblocking agent added may increase, resulting in poor visibility of the film.

[0044] Conventionally, biaxially oriented polyethylene films used as base films of laminate films used in packaging materials, etc., are required to have film properties such as rigidity, toughness, and heat resistance, as well as adhesiveness (lamination strength) when a sealant film is attached. In the adhesion between films, various factors such as the compatibility of the resins of each film, adjustment of additives, and film flexibility are thought to affect the adhesiveness. Therefore, the inventors have focused on the flexibility (rigidity) of the film and have conducted extensive research. In general, the flexibility (rigidity) of a film is understood as the elastic modulus of the entire film (all layers). In this type of biaxially oriented polyethylene film, there is a tendency to increase the rigidity by improving the elastic modulus of the film. However, since the part of the biaxially oriented polyethylene film that is in close contact with the sealant film is the surface layer (first surface layer), the inventors have found that there is a correlation between the rigidity of the first surface layer and the laminate strength with the sealant film, regardless of the rigidity of the biaxially oriented polyethylene film. That is, the biaxially oriented polyethylene film of the present invention requires that the elastic modulus E1 of the cross section of the first surface layer measured by atomic force microscope (AFM) is 1.6 GPa or less, preferably 0.2 GPa to 1.5 GPa, and more preferably 0.2 GPa to 1.4 GPa.

[0045] Measurements using an atomic force microscope (AFM) detect the atomic force acting between a probe and a measurement target, and can measure the physical properties of one layer (first or second surface layer) of a laminated film. The elastic modulus E1 of the first surface layer is an index indicating the hardness of the first surface layer, and is measured from the surface side of the first surface layer by an atomic force microscope (AFM). In measurements using an atomic force microscope (AFM), a biaxially oriented polyethylene film, which is a laminated film cut to a predetermined size, is prepared, and the elastic modulus E1 of each position of the first surface layer in a cross section cut in the transverse (TD) direction of this biaxially oriented polyethylene film is measured. This elastic modulus E1 is obtained by contacting a probe (probe) with a known spring constant at the tip of a cantilever to each position of the first surface layer and measuring the amount of deflection of the probe due to a predetermined indentation load.

[0046] It is considered that when the elastic modulus E1 of the first surface layer measured in this manner is 1.6 GPa or less, good flexibility is obtained and the adhesion between the first surface layer and the sealant film is improved, based on the examples described later. If the elastic modulus E1 of the first surface layer is too large, the flexibility of the first surface layer becomes insufficient, the adhesion between the first surface layer and the sealant film decreases, and the sealant film may easily peel off from the first surface layer.

[0047] Furthermore, in the biaxially oriented polyethylene film of the present invention, the elastic modulus E2 of the cross section of the second surface layer, which is the other surface layer of the film, measured by the atomic force microscope (AFM) preferably satisfies E1≦E2 in relation to the elastic modulus E1. Since the elastic modulus E2 is an index showing the hardness of the second surface layer, when the elastic modulus E2 is equal to or greater than the elastic modulus E1, the second surface layer has a higher rigidity than the first surface layer. This improves the processability as a package. Furthermore, when the second surface layer has a higher rigidity than the first surface layer, the second surface layer is less likely to bend, so that the biaxially oriented polyethylene film is more likely to maintain a planar shape, and it is easier to adhere a sealant film to the first surface layer of the biaxially oriented polyethylene film. Furthermore, the biaxially oriented polyethylene film of the present invention is also easy to handle as a packaging material because the second surface layer is less likely to bend and is more likely to maintain a planar shape.

[0048] In the biaxially oriented polyethylene film of the present invention, in order to broaden the range of use as a base film for laminate films, it is preferable to subject the first surface layer to a surface treatment. Examples of surface treatments include atmospheric pressure plasma treatment, flame treatment, and corona discharge treatment. It is preferable that the surface treated has a wet tension of 36 mN / m or more as measured by a wet tension test method in accordance with JIS K 6768 (1999). If the wet tension is too low, this is not preferable because it may cause printing defects or lamination defects. Note that the second surface layer may also be surface treated in the same manner as necessary.

[0049] In the present invention, a biaxially oriented polyethylene film is used as a base film, and a laminate film can be provided in which a printing process, a gas barrier layer, a sealant film, etc. are appropriately laminated. The printing process is performed on the surface of the biaxially oriented polyethylene film, and a known method such as screen printing, flexographic printing, offset printing, gravure printing, etc. is used. When printing is performed on the biaxially oriented polyethylene film of the present invention, the film surface is subjected to the above-mentioned surface treatment such as corona discharge treatment prior to printing, thereby improving the ink compatibility and adhesion. In addition, when a sealant film is bonded to the first surface layer of the biaxially oriented polyethylene film, the adhesion between the first surface layer and the sealant film is improved by subjecting the first surface layer to a surface treatment.

[0050] The gas barrier layer is disposed on a surface layer directly or via an anchor coat layer for the purpose of imparting a barrier property against water vapor, oxygen, etc. When a gas barrier layer is disposed on the biaxially oriented polyethylene film of the present invention, the film surface is previously subjected to a surface treatment such as a corona discharge treatment, thereby improving the wettability and adhesion to the anchor coat layer and the gas barrier layer.

[0051] The anchor coat layer is not particularly limited, and examples thereof include polyurethane resins and polyester resins. The gas barrier layer is also not particularly limited, and examples thereof include metal thin film layers and inorganic oxide layers. The metal thin film layer is a thin film layer made of known metals such as aluminum, gold, silver, copper, and chromium, and may be a thin film layer of oxides, sulfides, and nitrides of these metals. The metal thin film layer may be a single layer or a plurality of layers of two or more different types or the same type. The inorganic oxide layer is made of known inorganic oxides such as aluminum oxide, silicon oxide, magnesium fluoride, and magnesium oxide, and is a thin film layer using one or more types of inorganic oxides.

[0052] The sealant film is a film made of polyethylene resin and has heat sealability. The polyethylene resin used in the sealant film is selected from, for example, linear low-density polyethylene resin (LLDPE), high-density polyethylene (HDPE), low-density polyethylene (LDPE), etc., either alone or in combination. By making the sealant layer from the same polyethylene resin as the biaxially oriented polyethylene film that serves as the base film, a laminate film can be obtained that is a single material (mono-material) and facilitates recycling, while improving the lamination strength of the base film and the sealant layer. Furthermore, the laminate film can also be used to make a package. This makes it promising as a substitute for existing laminate films and packages that can be easily recycled. EXAMPLES

[0053] The materials described below were blended, melted, kneaded, extruded into three layers (first surface layer, base layer, and second surface layer) by the T-die method, stretched 5 times in the machine direction (MD), and then stretched 8 times in the transverse direction (TD) to form a film with a thickness of 20 μm, the first surface layer and second surface layer with a thickness of 1 μm, and the base layer with a thickness of 18 μm. The first surface layer was then surface-treated by corona discharge treatment to obtain biaxially oriented polyethylene films of prototypes 1 to 6.

[0054] In each prototype, the resin was blended so that the blending ratio of each base layer or surface layer was 100% by weight. In addition, in the production of biaxially oriented polyethylene film, the temperature of the stretching roll when stretching the sheet extruded from the T-die in the machine direction (MD) was 115°C, the temperature at which the film made of the sheet stretched in the machine direction (MD) was raised to a temperature at which it could be stretched in the transverse direction (TD) was 143°C to 145°C, and the heating temperature of the film when stretching the film stretched in the machine direction (MD) in the transverse direction (TD) was 122°C to 125°C.

[0055] [Materials used] The following resins, antiblocking agents, and surfactants were used as materials for each layer. The melt flow rate (MFR) of each resin material was measured at a test temperature of 190°C in accordance with JIS K 7210 (2014).

[0056] [Resin material] PE1: Linear low-density polyethylene (Dow Chemical; TF80), density 0.926 g / cm 3 MFR(190℃ / 2.16Kg):1.7g / 10min PE2: Ethylene-α-olefin random copolymer elastomer (Mitsui Chemicals: A-4085S), density 0.885g / cm 3 , MFR(190℃ / 2.16Kg):3.6g / 10min, Comonomer carbon number:4 PE3: High density polyethylene (Japan Polyethylene Corporation; HY430), density 0.954g / cm 3 , MFR(190℃ / 2.16Kg):0.8g / 10min PE4: High density polyethylene (Japan Polyethylene Corporation; HF562), density 0.963g / cm 3 , MFR(190℃ / 2.16Kg):7.5g / 10min

[0057] [Anti-blocking agent (AB agent)] AB1: Fuji Silysia Chemical Ltd.; SYLYSIA430, average particle size 4.1μm

[0058] [Surfactants] · AS1: Glycerin monostearate · AS2: Stearyl diethanolamine

[0059] [Prototype 1] Prototype example 1 is a biaxially oriented polyethylene film having a first surface layer made of 99.7% by weight PE1 and 0.3% by weight AB1, a base layer made of 100% by weight PE1, and a second surface layer made of 99.7% by weight PE1 and 0.3% by weight AB1.

[0060] [Prototype 2] Prototype example 2 is a biaxially oriented polyethylene film whose first surface layer is made of 89.7% by weight PE1, 10% by weight PE2, and 0.3% by weight AB1; whose base layer is made of 99.7% by weight PE1, 0.2% by weight AS1, and 0.1% by weight AS2; and whose second surface layer is made of 99.7% by weight PE1 and 0.3% by weight AB1.

[0061] [Prototype 3] Prototype example 3 is a biaxially oriented polyethylene film having a first surface layer made of 39.7 wt% PE1, 60 wt% PE2, and 0.3 wt% AB1, a base layer made of 99.7 wt% PE1, 0.2 wt% AS1, and 0.1 wt% AS2, and a second surface layer made of 99.7 wt% PE1 and 0.3 wt% AB1.

[0062] [Prototype 4] Prototype example 4 is a biaxially oriented polyethylene film using 70 wt% PE1, 29.7 wt% PE3, and 0.3 wt% AB1 for the first surface layer, 79.7 wt% PE1, 20 wt% PE3, 0.2 wt% AS1, and 0.1 wt% AS2 for the base layer, and 70 wt% PE1, 29.7 wt% PE3, and 0.3 wt% AB1 for the second surface layer.

[0063] [Prototype 5] Prototype example 5 is a biaxially oriented polyethylene film having a first surface layer made of 69.7 wt% PE1, 20 wt% PE3, 10 wt% PE4, and 0.3 wt% AB1, a base layer made of 99.7 wt% PE1, 0.2 wt% AS1, and 0.1 wt% AS2, and a second surface layer made of 99.7 wt% PE1 and 0.3 wt% AB1.

[0064] [Prototype 6] Prototype example 6 is a biaxially oriented polyethylene film having a first surface layer made of 5.7 wt% PE1, 62.4 wt% PE3, 31.6 wt% PE4, and 0.3 wt% AB1, a base layer made of 99.7 wt% PE1, 0.2 wt% AS1, and 0.1 wt% AS2, and a second surface layer made of 99.7 wt% PE1 and 0.3 wt% AB1.

[0065] The tensile modulus, AFM modulus E1 of the first surface layer, and AFM modulus E2 of the second surface layer were measured for the biaxially oriented polyethylene films of Samples 1 to 6, and the laminate strength was measured for the laminate films using these biaxially oriented polyethylene films. Table 1 below shows the results of the measurements of the tensile modulus, AFM modulus E1 and E2 of the first and second surface layers, and laminate strength, along with the blending ratio of the resin materials used in each of Samples 1 to 6.

[0066] [Measurement of tensile modulus of biaxially oriented polyethylene film] The tensile modulus of elasticity of the biaxially stretched polyethylene films of Samples 1 to 6 was measured in accordance with JIS K 7127 (1999). The tensile modulus of elasticity is an index for grasping the rigidity of the entire film (all layers). In this measurement, a rectangular test piece of 15 mm x 200 mm (TD direction x MD direction) was cut out from the biaxially stretched polyethylene films of Samples 1 to 6, and the tensile modulus of elasticity of the biaxially stretched polyethylene films in the machine direction (MD) was measured at an atmospheric temperature of 23°C with a distance between the chucks holding the test piece of 100 mm and a pulling speed of the test piece of 200 mm / min.

[0067] [Measurement of AFM elastic modulus of the first and second surface layers] In the measurement of the AFM elastic modulus, the AFM elastic modulus E1 in the direction perpendicular to the cross section of the first surface layer of prototypes 1 to 6 and the AFM elastic modulus E2 in the direction perpendicular to the cross section of the second surface layer were measured by an atomic force microscope (AFM). When measuring the AFM elastic modulus E1 of the first surface layer and the AFM elastic modulus E2 of the second surface layer, the biaxially stretched polyethylene films of prototypes 1 to 6 were cut to 30 mm x 30 mm (MD direction x TD direction) to obtain measurement pieces. Next, the measurement pieces of each prototype were cut in the transverse (TD) direction by a known microtome method to cut out a cross section, and this cross section was fixed to an atomic force microscope "NANOSCOPE V / DIMENSION ICON (manufactured by Brugger Aex)" as a measurement surface. The indentation load applied to the probe (probe) with a known spring constant at the tip of the cantilever was kept constant, and the fixing table to which the measurement surface was fixed was moved up and down to bring the probe into contact with the measurement surface (measurement piece). A force curve was measured, which is a curve plotting the relationship between the amount of movement of the measuring piece and the force acting on the cantilever (the product of the amount of deflection of the probe and the spring constant). The measurement conditions were as follows: Measurement mode: AFM-MA mode (PeakForce-QNM) Probe tip curvature radius: 30 nm Probe spring constant: 40N / m Measurement temperature: 23℃ Scanning speed: 0.25Hz Number of measurement points: 256 x 256 Poisson's ratio: 0.3

[0068] Next, the contact area between the probe and the measurement surface was calculated using a theoretical calculation formula for a contact model that assumes the shape of the probe tip is a sphere, and the results (force curves) obtained from the above measurement were analyzed using this contact area with the analysis software "NanoScope Analysis". The average value of the elastic modulus of 512 points corresponding to the first surface layer obtained by the analysis was calculated as the AFM elastic modulus E1 of the first surface layer, and the average value of the elastic modulus of 512 points corresponding to the second surface layer was calculated as the AFM elastic modulus E2 of the second surface layer.

[0069] [Preparation of laminate film] A non-oriented polyethylene film (LL-XMTN#50, manufactured by Futamura Chemical Co., Ltd.) was dry laminated (adhesive layer) on the first surface layer of the biaxially oriented polyethylene film of Prototype Examples 1 to 6 to produce a laminate film. The adhesive layer was prepared by mixing a base agent (TM-329, manufactured by Toyo Morton Co., Ltd.), a hardener (CAT-8B, manufactured by Toyo Morton Co., Ltd.), and ethyl acetate, and was applied to the surface of the first surface layer at a concentration of 2 g / m. 2 and dried at 80° C. Thereafter, the above-mentioned non-oriented polyethylene film was attached to the surface of the first surface layer to prepare a laminate film.

[0070] [Laminate strength measurement] The laminate strength is one of the indices of adhesive suitability, and was measured in accordance with JIS K 6854-3 (1999). In this measurement, a rectangular test piece of 15 mm x 200 mm (TD direction x MD direction of the film) was cut out from the laminate film prepared using the biaxially oriented polyethylene film of prototypes 1 to 6, and the non-oriented polyethylene film and the biaxially oriented polyethylene film were stretched 180 degrees up and down and fixed to a tensile tester (Shimadzu Corporation, EZ-SX). Then, the non-oriented polyethylene film and the biaxially oriented polyethylene film were pulled in the up and down direction (MD direction) at a test speed of 50 mm / min, and the adhesive parts of both were peeled off to determine the laminate strength. A laminate strength of 0.7 N / 15 mm or more was considered good.

[0071] [Table 1]

[0072] [Results and Discussion] The biaxially oriented polyethylene films of Samples 1 to 6 and the laminate films in which a sealant film is laminated on the first surface layer of the biaxially oriented polyethylene films are examined. These biaxially oriented polyethylene films are different in the type of resin in the first and second surface layers, the type of resin in the base layer, and the content of surfactant in the base layer. As can be seen from Table 1, the laminate strength of Samples 1 to 4 was good, whereas the laminate strength of Samples 5 and 6 was insufficient.

[0073] Here, comparing the physical properties of Prototypes 1 to 4 with those of Prototypes 5 and 6, first, no difference was observed in the tendency of the measurement results of the tensile modulus between Prototypes 1 to 4, which have good laminate strength, and Prototypes 5 and 6, which have insufficient laminate strength. In addition, the tensile modulus of Prototype 1 and Prototype 4, which have the same laminate strength, was significantly different, and the laminate strength was significantly different between Prototypes 2 and 3, which have the same tensile modulus, and between Prototypes 1 and 6, which have similar tensile modulus. From these findings, a clear correlation could not be confirmed between the rigidity (tensile modulus) of the entire biaxially oriented polyethylene film and the laminate strength.

[0074] Next, comparing the AFM elastic modulus E1 of the first surface layer of prototypes 1 to 4 with the AFM elastic modulus E1 of the first surface layer of prototypes 5 and 6, the AFM elastic modulus E1 of the first surface layer of prototypes 1 to 4, which have good laminate strength, was lower than the AFM elastic modulus E1 of prototypes 5 and 6, which have insufficient laminate strength. Also, comparing the AFM elastic modulus E1 of the first surface layer of prototypes 1 to 4, when the elastic modulus E1 is 0.2 GPa, the laminate strength is 1.8 N / 15 mm, when the elastic modulus E1 is 0.8 GPa, the laminate strength is 1.4 N / 15 mm, and when the elastic modulus E1 is 1.3 GPa or 1.4 GPa, the laminate strength is 1.1 N / 15 mm. Thus, the lower the value of the elastic modulus E1, the higher the laminate strength tends to be. From this, it is considered that there is a correlation between the AFM elastic modulus E1 of the first surface layer and the laminate strength.

[0075] On the other hand, when comparing the AFM elastic modulus E2 of the second surface layer of prototypes 1 to 4 with the AFM elastic modulus E2 of the second surface layer of prototypes 5 and 6, the laminate strength was significantly different between prototypes 1 and 4 and prototypes 5 and 6, in which the AFM elastic modulus E2 of the second surface layer was similar. Furthermore, in prototypes 1 to 4, which had good laminate strength, no clear correlation was found between the value of the AFM elastic modulus E2 of the second surface layer and the value of the laminate strength. From these findings, it was not possible to confirm that there is a correlation between the AFM elastic modulus E2 of the second surface layer and the laminate strength.

[0076] As described above, when the relationship between the tensile modulus, the AFM modulus E1 of the first surface layer, the AFM modulus E2 of the second surface layer, and the laminate strength is examined, no correlation is confirmed between the tensile modulus or the AFM modulus E2 of the second surface layer and the laminate strength, whereas a correlation is confirmed between the AFM modulus E1 of the first surface layer in close contact with the sealant film and the laminate strength, so that the AFM modulus E1 of the first surface layer is considered to be effective as an index representing good laminate strength. Therefore, when the AFM modulus E1 of the first surface layer is examined from the measurement results, it was confirmed that the maximum value of the AFM modulus E1 of the first surface layer of prototypes 1 to 4, which have good laminate strength, is 1.4 GPa, and the minimum value of the AFM modulus E1 of the first surface layer of prototypes 5 and 6, which have insufficient laminate strength, is 1.7 GPa. From these facts, it is considered that the AFM modulus E1 of the first surface layer that provides good laminate strength is preferably about 1.6 GPa or less. Moreover, from the measurement results of Prototype Examples 1 to 4, it is considered that the lower the AFM elastic modulus E1 of the first surface layer, the higher the laminate strength tends to be. Therefore, in the case of a biaxially oriented polyethylene film, regardless of the rigidity (tensile elastic modulus) of the entire film, good laminate strength can be obtained by having the first surface layer that adheres to the sealant film be flexible (AFM elastic modulus E1 is 1.6 GPa or less).

[0077] In addition, as described above, it was not possible to confirm that there is a direct correlation between the AFM elastic modulus E2 of the second surface layer and the laminate strength. However, when comparing the relationship between the elastic moduli between the prototypes 1 to 4 and the prototypes 5 and 6, the relationship E1≦E2 was established between the AFM elastic modulus E1 of the first surface layer and the AFM elastic modulus E2 of the second surface layer in the prototypes 1 to 4, which had good laminate strength, whereas the relationship E1≦E2 was not established in the prototypes 5 and 6, which had insufficient laminate strength. From these findings, it is believed that although the second surface layer is not the surface to which the sealant film is bonded when preparing a laminate film, the AFM elastic modulus E2 of the second surface layer is involved in the quality of the laminate strength between the first surface layer and the sealant film. In other words, when the AFM elastic modulus E2 of the second surface layer is equal to or greater than the AFM elastic modulus E1 of the first surface layer, as in the prototypes 1 to 4, the rigidity of the second surface layer is higher than that of the first surface layer. As a result, the second surface layer is less likely to bend, so the biaxially oriented polyethylene film is more likely to maintain its planar shape, and the sealant film is more likely to be adhered to the first surface layer of the biaxially oriented polyethylene film. Therefore, when the AFM elastic modulus E2 of the second surface layer is equal to or greater than the AFM elastic modulus E1 of the first surface layer, it is believed that the laminate strength will be good, as in prototypes 1 to 4.

[0078] From the above, the biaxially oriented polyethylene film of the present invention is a biaxially oriented film which is a laminate of at least two layers stretched in two axial directions, that is, the machine direction (MD) and the transverse direction (TD), and when the elastic modulus (E1) of a cross section of a first surface layer, which is one surface layer of the biaxially oriented film, measured by atomic force microscope (AFM) is 1.6 GPa or less, the flexibility of the first surface layer is good, and when a sealant film is laminated on the first surface layer, for example, the adhesion between the first surface layer and the sealant film is improved, resulting in excellent laminate strength between the first surface layer and the sealant film.

[0079] Furthermore, in the biaxially oriented polyethylene film of the present invention, when the relationship between the AFM elastic modulus E1 of the first surface layer and the AFM elastic modulus E2 of the second surface layer is E1≦E2, the second surface layer has a higher rigidity than the first surface layer. This improves the processability of the biaxially oriented polyethylene film as a package. In addition, since the second surface layer has a higher rigidity than the first surface layer and is less likely to bend, it becomes easier to adhere a sealant film to the first surface layer of the biaxially oriented polyethylene film. Furthermore, the biaxially oriented polyethylene film of the present invention has a second surface layer that is less likely to bend and is easier to maintain its planar shape, making it easier to handle as a packaging material. [Industrial Applicability]

[0080] The biaxially oriented polyethylene film of the present invention has a good flexibility of the first surface layer, and when a sealant film is laminated on the first surface layer, the adhesion between the first surface layer and the sealant film is good, and the laminate strength between the first surface layer and the sealant film is excellent. Furthermore, by laminating a sealant film made of at least a polyethylene resin on the first surface layer of the biaxially oriented polyethylene film of the present invention, a laminate film having excellent laminate strength between the biaxially oriented polyethylene film and the sealant film can be obtained while achieving a single material (monomaterial) and facilitating recycling. In addition, a package using the laminate film can be obtained. Therefore, it is promising as a package that is easy to recycle.

Claims

1. A biaxially stretched film which is a laminate of at least two layers stretched in two axial directions, namely, the machine direction (MD) and the transverse direction (TD), A biaxially oriented polyethylene film, characterized in that the elastic modulus (E1) of a cross section of a first surface layer, which is one surface layer of the biaxially oriented film, measured by an atomic force microscope (AFM) is 1.6 GPa or less.

2. 2. The biaxially oriented polyethylene film according to claim 1, wherein an elastic modulus (E2) of a cross section of a second surface layer, which is the other surface layer of the biaxially oriented film, measured by the atomic force microscope (AFM) satisfies E1≦E2 in relationship to the elastic modulus (E1).

3. The biaxially oriented polyethylene film according to claim 1 or 2, wherein the first surface layer of the biaxially oriented film is subjected to a surface treatment.

4. 3. The biaxially oriented polyethylene film according to claim 1, wherein the biaxially oriented film is a laminate of three or more layers.

5. 4. The biaxially oriented polyethylene film according to claim 3, wherein the biaxially oriented film is a laminate of three or more layers.

6. 3. A laminate film comprising the biaxially oriented polyethylene film according to claim 1 or 2, and a sealant film made of at least a polyethylene resin laminated on the first surface layer of the biaxially oriented polyethylene film.

7. A laminate film comprising the biaxially oriented polyethylene film according to claim 3 and a sealant film made of at least a polyethylene resin laminated on the first surface layer of the biaxially oriented polyethylene film.

8. A laminate film comprising the biaxially oriented polyethylene film according to claim 4 and a sealant film made of at least a polyethylene resin laminated on the first surface layer of the biaxially oriented polyethylene film.

9. A packaging material comprising the laminate film according to claim 6.

10. A packaging material comprising the laminate film according to claim 7.

11. A packaging material comprising the laminate film according to claim 8.

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