Polyethylene-based laminate film

Abstract

To provide a polyethylene-based laminate film constituted from a mono-material, excellent in laminating properties, and excellent in sealability when being a packaged body.SOLUTION: A polyethylene-based laminate film having at least a base material film comprising a polyethylene-based resin, and a non-stretched sealant film comprising a polyethylene-based resin is such that: the base material film is a biaxial oriented film which has a tensile elasticity modulus of 1,000 MPa or more in a longitudinal direction (MD) and 2,000 MPa or more in a transverse direction (TD), and has a thermal shrinkage of 10% or less in the longitudinal direction (MD), and 10% or less in the transverse direction (TD) when being heated at 120°C for 15 minutes; the non-stretched sealant film has a dimensional change rate of 10% or less in the longitudinal direction (MD) when being heated at 80°C for 10 minutes under 100 N / m load; and the thickness of the base material film is smaller than the thickness of the non-stretched sealant film.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyethylene-based laminate film. [Background technology]

[0002] Plastic films such as polyester films are widely used as packaging materials due to their excellent mechanical properties, dimensional stability, transparency, chemical resistance, etc. Such plastic films are laminated films in which a base film and a sealant film are bonded together with an adhesive or the like (laminated). This type of laminated film has a structure in which films made of different materials, such as polyester film, nylon film, or polyolefin film, are laminated together.

[0003] On the other hand, with the recent increase in interest in environmental issues, there is a demand for recycling waste plastics. It is difficult to recycle laminated films made of different materials, as described above, by separating each resin. Therefore, there is a growing demand for laminated films made of a single material (monomaterial).

[0004] For example, with regard to polyethylene-based monomaterial laminate films, studies are being conducted on the use of a uniaxially or biaxially oriented film as the base film and a linear low-density polyethylene (LLDPE)-based film or the like as the sealant film. For example, Patent Document 1 discloses a laminate film manufactured by bonding, via a solventless adhesive, a first film made of linear low-density polyethylene and a second film made of high-density polyethylene or linear low-density polyethylene with a higher stretch ratio than the first film. Patent Document 2 discloses a biaxially oriented polyethylene film made of multiple layers made of polyethylene-based resin. [Prior art documents] [Patent documents]

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2023-016903 Patent Document 2: Japanese Patent Application Laid-Open No. 2023-143609 Summary of the Invention [Problem to be solved by the invention]

[0006] On the other hand, the above-mentioned polyethylene monomaterial laminate film has problems such as low mechanical properties such as rigidity and low heat resistance. From the viewpoint of reducing the environmental impact, it is desirable to have a monomaterial structure and also to make the laminate film thinner. When the thickness of the sealant portion is reduced and the rigidity is increased, the laminate film has excellent lamination properties when produced, but when the laminate film is used as a package, there is also the problem of poor sealing properties.

[0007] In view of the above problems, an object of the present invention is to provide a polyethylene-based laminated film that is made of a monomaterial, has excellent lamination properties, and exhibits excellent sealing properties when used in packaging. [Means for solving the problem]

[0008] As a result of extensive research, the present inventors have found that the above-mentioned problem can be solved by a polyethylene-based laminate film that has at least a base film having a specific tensile modulus and a specific thermal shrinkage rate, and a sealant film having a specific dimensional change rate, and in which the base film and the sealant film have a specific thickness ratio. That is, the present invention provides the following.

[0009] [1] A polyethylene-based laminate film comprising at least a substrate film made of a polyethylene-based resin and a non-stretch sealant film made of a polyethylene-based resin, wherein the substrate film is a biaxially oriented film having a tensile modulus of 1,000 MPa or more in the machine direction (MD) and 2,000 MPa or more in the transverse direction (TD), and a heat shrinkage rate of 10% or less in the machine direction (MD) and 10% or less in the transverse direction (TD) when heated at 120°C for 15 minutes, and the non-stretch sealant film has a dimensional change rate of 10% or less in the machine direction (MD) when heated at 80°C for 10 minutes under a load of 100 N / m, and the thickness of the substrate is less than the thickness of the non-stretch sealant film. [2] The polyethylene-based laminate film according to the above item [1], wherein the ratio of the thickness of the base film to the thickness of the non-stretch sealant film is 1:1.5 or more (base film:non-stretch sealant film). [3] A polyethylene-based laminate film according to item [1] or [2] above, having a tensile modulus in the machine direction (MD) of 700 MPa or more, a tensile modulus in the transverse direction (TD) of 1,000 MPa or more, a 1% modulus in the machine direction (MD) of 5 N / 10 mm or more, and a 1% modulus in the transverse direction (TD) of 7 N / 10 mm or more. [4] A packaging material comprising the polyethylene laminate film according to any one of the above items [1] to [3]. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a polyethylene-based laminate film that has excellent lamination properties and excellent sealing properties when used in a package. The package made of the polyethylene-based laminate film has excellent sealing properties. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention (hereinafter sometimes referred to as the present embodiment) will be described in detail, but the following description is an example of an embodiment, and the present invention is not limited to these in any way.

[0012] The polyethylene-based laminate film of this embodiment has at least a substrate film made of a polyethylene-based resin and a non-stretched sealant film made of a polyethylene-based resin. The substrate film is a biaxially stretched film stretched in two axial directions, the machine direction (MD) and the transverse direction (TD). The polyethylene-based laminate film of this embodiment has the substrate film and the sealant film made of a polyethylene-based resin, is basically composed of a single material (monomaterial), and is suitable for recycling.

[0013] The resin raw material used in the polyethylene-based laminate film of this embodiment is appropriately selected from polyethylene-based resins derived from petroleum, biomass, material recycling, chemical recycling, etc. Biomass-derived polyolefin resins are commercially available from Braskem, Dow Chemical, Lyondell Basell, SABIC, Borealis, Mitsui Chemicals, etc. By appropriately using biomass-derived polyethylene resins or recycled polyethylene resins while taking into consideration the balance of film properties, it is possible to further contribute to reducing the environmental load.

[0014] <Base film> In this embodiment, the substrate film is a biaxially stretched film having a tensile modulus of 1,000 MPa or more in the machine direction (MD) and 2,000 MPa or more in the transverse direction (TD), and a heat shrinkage of 10% or less in the machine direction (MD) and 10% or less in the transverse direction (TD) when heated at 120°C for 15 minutes. Because the polyethylene-based laminate film of this embodiment has the biaxially stretched substrate film, it has a high tensile modulus, low heat shrinkage, and excellent impact resistance, and also has excellent lamination properties due to small distortion when laminated. Because the substrate film has the above properties, the polyethylene-based laminate film of this embodiment also has excellent sealability when used as a package.

[0015] The polyethylene-based resin may be any resin having crystallinity that allows it to achieve a tensile modulus of 1,000 MPa or more in the machine direction (MD) and 2,000 MPa or more in the transverse direction (TD) by a biaxial stretching method described below. For example, high-density polyethylene resin (HDPE) or medium-density polyethylene resin (MDPE) can be used. Other polyethylene-based resins that can be used include copolymers of ethylene and other monomers. Among these, biaxially stretched high-density polyethylene resin (HDPE) is preferred as the polyethylene-based resin in the substrate film because of its excellent mechanical properties, such as tensile modulus and heat shrinkage, described below.

[0016] For example, HDPE has a density of 0.942 g / cm 3 or more, preferably 0.950 g / cm 3 More preferably, 0.960 g / cm 3 The above polyethylene resins can be used, and the medium density polyethylene resins are those with a density of 0.925 g / cm 3 More than 0.942g / cm 3 Polyethylene resins of less than 100% can be used.

[0017] (tensile modulus) The base film has a tensile modulus of 1,000 MPa or more in the machine direction (MD) and 2,000 MPa or more in the transverse direction (TD). If the tensile modulus is below the above range, the rigidity of the base film decreases, and the rigidity of the resulting polyethylene-based laminate film also decreases. The tensile modulus of elasticity in the machine direction (MD) of the substrate film is preferably 1,300 MPa or more, more preferably 1,500 MPa or more, even more preferably 1,800 MPa or more, and even more preferably 1,840 MPa or more. There is no particular upper limit, but it is 2,000 MPa or less. The tensile modulus of elasticity in the transverse direction (TD) of the substrate film is preferably 2,300 MPa or more, more preferably 2,500 MPa or more, even more preferably 2,700 MPa or more, and even more preferably 2,800 MPa or more. There is no upper limit, but it is preferably less than 4,000 MPa. When the substrate film has the above-mentioned tensile modulus, a polyethylene-based laminate film having superior rigidity can be obtained. In this specification, the tensile modulus can be measured by the method described in the examples.

[0018] (Thermal shrinkage rate) The base film has a heat shrinkage of 10% or less in the machine direction (MD) and 10% or less in the transverse direction (TD). The heat shrinkage here refers to the heat shrinkage when heated at 120°C for 15 minutes. If the heat shrinkage of the base film exceeds the above range, the heat resistance will be poor, resulting in poor heat resistance when processed at high temperatures, such as by heat sealing, to form a polyethylene laminate film. This can lead to wrinkles and a narrow heat seal width, resulting in poor film appearance and physical properties. The narrow heat seal width also reduces work efficiency.

[0019] The heat shrinkage rate of the base film in the machine direction (MD) is preferably 9% or less, more preferably 8.5% or less, and even more preferably 8% or less. The lower limit is not particularly limited, but is about 1%. The thermal shrinkage rate of the base film in the transverse direction (TD) is preferably 9% or less, more preferably 8.5% or less, and even more preferably 8% or less. The lower limit is not particularly limited, but is about 1%. When the base film has the above-mentioned heat shrinkage rate, the occurrence of wrinkles can be suppressed and the heat seal width can be increased, resulting in excellent lamination characteristics, and the polyethylene-based laminate film has excellent appearance and physical properties.In addition, the polyethylene-based laminate film can be produced efficiently. In this specification, the heat shrinkage rate can be measured by the method described in the examples.

[0020] Biaxially stretched substrate films can be obtained by known film forming methods such as the T-die method and inflation method. For example, film forming by the T-die method is preferred because it can achieve the high thickness precision required for substrate films. Biaxially stretched films are biaxially stretched in two directions, the machine direction (MD) and the transverse direction (TD) of the film. Either sequential biaxial stretching or simultaneous biaxial stretching can be used for biaxial stretching.

[0021] A more specific method for producing biaxially stretched film will be explained using the T-die method as an example. The raw resin is heated to 170°C or higher in an extruder, melted, and extruded into a sheet from a T-die. The extruded resin is cooled on a chill roll at a temperature of 10°C to 90°C, and then stretched 3 to 8 times in the machine direction (MD) on a stretching roll at a temperature of 60°C to 150°C. It is then stretched 3 to 14 times in the transverse direction (TD) at a temperature of 100 to 170°C, and then moderately relaxed by about 1 to 15% in the width direction, and if necessary, corona discharge treated before being wound up to obtain a biaxially stretched film.

[0022] <Non-stretch sealant film> In this embodiment, the unstretched sealant film is an unstretched film whose dimensional change rate in the machine direction (MD) is 10% or less when heated at 80°C for 10 minutes under a load of 100 N / m. Here, "unstretched" means that the film is produced by a method that does not substantially involve stretching during the production process. "Substantially without stretching" means that the film is produced without an explicit stretching step. Therefore, when an extrusion process performed under normal conditions is employed, slight orientation in the extrusion direction is acceptable. Furthermore, when lamination conditions used in producing polyethylene-based laminate films are employed, slight orientation is also acceptable. If the dimensional change rate of the unstretched sealant film is outside the above range, it will be more likely to distort and wrinkle when laminated to a substrate while applying a certain tension, resulting in poor lamination properties.

[0023] The dimensional change rate in the machine direction (MD) of the unstretched sealant film is preferably 7.5% or less, more preferably 7.0% or less, and even more preferably 6.5% or less. When the unstretched sealant film has a dimensional change rate within the above range, distortion and wrinkles can be suppressed, resulting in excellent lamination properties. The dimensional change rate is the value when heated at 80°C for 10 minutes under a load of 100 N / m, which is suitable for the conditions used in industrially producing laminated films. In this specification, the dimensional change rate can be measured by the method described in the examples.

[0024] The dimensional change rate of the unstretched sealant film can be adjusted by the type and ratio of the polyethylene resin that constitutes the film. Examples of the polyethylene resin that can be used include high density polyethylene resin (HDPE), medium density polyethylene resin (MDPE), low density polyethylene (LDPE), and linear low density polyethylene (LLDPE). Linear low-density polyethylene (LLDPE) is an ethylene-α-olefin copolymer, and the α-olefin preferably has 3 to 12 carbon atoms, more preferably 4 to 8 carbon atoms. The α-olefin is preferably an α-olefin such as propylene, butene-1, hexene-1, octene-1, or 4-methyl-1-pentene. Among the above-mentioned ethylene-α-olefin copolymers, ethylene-butene-1 copolymer, ethylene-hexene-1 copolymer, ethylene-octene-1 copolymer, etc. are preferred.

[0025] Among these, a combination of high-density polyethylene resin (HDPE) and low-density polyethylene (LDPE) or linear low-density polyethylene (LLDPE) is preferred. The ratio of high-density polyethylene resin (HDPE) to low-density polyethylene (LDPE) or linear low-density polyethylene (LLDPE) is preferably 1:1, more preferably 1:1 to 2:1, and even more preferably 2:1.

[0026] [Polyethylene laminated film] The polyethylene-based laminate film of the present embodiment has at least the above-described base film and a non-stretch sealant film. An intermediate layer may be provided to enhance the flexibility and adhesiveness of the laminated film. In this case, it is preferable to use an intermediate layer made of a polyethylene resin and to construct the laminated film from a monomaterial in order to achieve excellent recyclability. In order to reduce the environmental load, including by reducing the thickness, an embodiment that does not include any other layers such as an intermediate layer is also preferable.

[0027] The polyethylene-based laminate film of this embodiment must have a thickness that is less than that of the base film and more than that of the non-stretch sealant film. If the thickness of the base film is greater than that of the non-stretch sealant film, the sealing performance of a package made of the polyethylene-based laminate film will be insufficient. The thickness ratio of the base film to the non-stretch sealant film, base film:non-stretch sealant film, is preferably 1:1.5 or more, and more preferably 1:2 or more. The thickness of the base film is not particularly limited as long as it satisfies the above conditions, but from the viewpoint of ensuring a certain level of mechanical strength of the laminated film while suppressing film tearing and reducing the thickness, the thickness is preferably 9.0 μm or more, more preferably 10 μm or more, even more preferably 15 μm or more, and is preferably 50 μm or less, more preferably 45 μm or less, even more preferably 40 μm or less. The thickness of the unstretched sealant film is not particularly limited as long as it satisfies the above conditions, but from the viewpoint of suppressing film tearing while reducing the thickness and environmental impact, it is preferably 20 μm or more, more preferably 30 μm or more, even more preferably 45 μm or more, and preferably 110 μm or less, more preferably 70 μm or less, even more preferably 65 μm or less, and even more preferably 60 μm or less. Although there is an overlap between the thickness range of the base film and the thickness range of the non-stretch sealant film, the thickness is selected so as to satisfy the requirements of the base film thickness<the non-stretch sealant film.

[0028] (additives) The polyethylene-based laminate film of the present embodiment may contain, as an additive, an additive that functions as an antifogging agent and an antistatic agent. The additive may be contained in all layers of the polyethylene-based laminate film, but is preferably contained in at least the base film. The content of the additives that function as antifogging agents and antistatic agents in the layer containing the additives is preferably 0.4 to 1.0% by mass, and more preferably 0.6 to 0.8% by mass.

[0029] The type of additive that functions as an antifogging agent and an antistatic agent is not particularly limited as long as it is one that is commonly used in polyethylene-based films, and examples thereof include esters of polyhydric alcohols such as glycerin, polyethylene glycol, pentaerythritol, sorbitol, and polypropylene glycol with higher fatty acids such as lauric acid, stearic acid, and oleic acid, ethylene oxide adducts of higher aliphatic amines, higher aliphatic alkanolamides, higher alcohol phosphate ester salts, and mixtures thereof.

[0030] The polyethylene-based laminate film of this embodiment may contain additives other than the additives that function as the antifogging agent and antistatic agent described above. Examples of the additives include crystallization nucleating agents, antioxidants, lubricants, antiblocking agents, chlorine scavengers, cellulose nanofibers, inorganic fine particles, and starch. Examples of the inorganic fine particles include calcium carbonate, adsorbents, and antibacterial agents. The additives may be contained in the substrate film, the non-stretch sealant film, or both the substrate film and the non-stretch sealant film.

[0031] The method for producing a polyethylene-based laminate film having a base film and a non-stretch sealant film is not particularly limited, and examples thereof include dry lamination, extrusion lamination, and thermal lamination. When laminating the two by dry lamination, the non-stretch sealant film can be laminated on one side of the base film of the polyethylene-based laminate film via an adhesive. Examples of the adhesive include solvent-free adhesives such as polyurethane adhesives, polyester adhesives, polyether adhesives, acrylic adhesives, vinyl acetate adhesives, and water-based acrylic urethane adhesives. The thickness of the adhesive is not particularly limited, but is usually about 0.1 to 5 μm, and preferably about 0.5 to 2 μm.

[0032] The polyethylene-based laminated film of this embodiment has excellent mechanical properties, such as a high tensile modulus and a high 1% modulus.

[0033] (tensile modulus) The tensile modulus of elasticity in the machine direction (MD) of the polyethylene-based laminate film of this embodiment is preferably 700 MPa or more, more preferably 850 MPa or more, and even more preferably 1,000 MPa or more, and the tensile modulus of elasticity in the transverse direction (TD) is preferably 1,000 MPa or more, more preferably 1,200 MPa or more, and even more preferably 1,400 MPa or more. There are no particular upper limits, but the tensile modulus of elasticity in the machine direction (MD) is 2,000 MPa or less, and the tensile modulus of elasticity in the transverse direction (TD) is 3,000 MPa or less. The tensile modulus of elasticity can be measured by the method described in the Examples. The polyethylene-based laminate film of this embodiment has a high tensile modulus and is therefore excellent in rigidity.

[0034] (1% modulus) The 1% modulus in the machine direction (MD) of the polyethylene-based laminate film of this embodiment is preferably 5 N / 10 mm or more, more preferably 7 N / 10 mm or more, and even more preferably 10 N / 10 mm or more, and the 1% modulus in the transverse direction (TD) is preferably 7 N / 10 mm or more, more preferably 10 N / 10 mm or more, and even more preferably 15 N / 10 mm or more. There are no particular upper limits, but the 1% modulus in the machine direction is 20 N / 10 mm or less, and the 1% modulus in the transverse direction is 30 N / 10 mm or less. The polyethylene laminated film of this embodiment has a high 1% modulus, and therefore has high shape retention and can be made thin. In this specification, "1% modulus" refers to the load (N / 10 mm) when a 10 mm wide laminated film is stretched by 1%. The "1% modulus" can be measured by the method described in the examples.

[0035] As described above, the polyethylene laminate film of this embodiment has a high tensile modulus and a high 1% modulus, and therefore can be suitably used as a packaging material. Therefore, in another aspect of the present invention, a package made of the above polyethylene-based laminate film can be provided.

[0036] [Packaging] The polyethylene laminate film can be heat-sealed or fusion-cut sealed to form a package, which is suitable for use as a packaging material for various items such as food, daily necessities, and parts. A heat-sealed package can be obtained by processing the polyethylene laminate film of this embodiment into a bag shape having an opening, with the non-stretch sealant film facing inward. Specifically, the package can be obtained by folding the polyethylene laminate film to an appropriate size with the non-stretch sealant film on the inside and heat-sealing the edges to form a bag. Alternatively, the package can be obtained by preparing two polyethylene laminate films and heat-sealing the edges to form a bag. The heat sealing temperature is preferably a temperature at which the unstretched sealant films can be thermocompression bonded to each other, and can be, for example, 120 to 150° C. The heat sealing pressure can be, for example, about 0.1 to 0.5 MPa, and the heat sealing time can be, for example, 0.1 to 2 seconds. After the contents are placed in the resulting package, the opening can be heat-sealed to seal it. Alternatively, the package can be sealed by placing the object to be packaged on the laminated film and then heat-sealing the edges.

[0037] The polyethylene-based laminate film of this embodiment has the above-mentioned base film and non-stretch sealant film, and can be processed over a wide temperature range due to the high dimensional stability of the base film, so it can be suitably used as a packaging material that has excellent production efficiency during bag manufacturing and excellent appearance after bag manufacturing. Furthermore, the high tensile modulus of elasticity of the base film, the high dimensional stability of the non-stretched sealant film, and the specific thickness ratio between the base film and the non-stretched sealant film enable the film to have high sealing properties. The polyethylene laminated film itself has a high tensile modulus and a high 1% modulus, making it possible to create a packaging body that is thin, reduces environmental impact, and has high self-standing properties.

[0038] The packaging body of this embodiment can be used for a wide range of purposes, such as containers for liquids such as shampoo and cosmetics, bags for food, etc. It can be used as an environmentally friendly alternative to conventional containers made from laminated films made by laminating films of different materials such as polyester film, nylon film, and polyolefin film. [Example]

[0039] The present invention will be described in more detail by the following examples, but the present invention is not limited thereto.

[0040] [evaluation] (1) Tensile modulus In accordance with JIS K7127, the tensile modulus of elasticity in the machine direction (MD) and transverse direction (TD) was measured using a type 2 test piece at a tension speed of 50 mm / min using a tensile testing machine (AG-Xplus manufactured by Shimadzu Corporation).

[0041] (2) Dimensional change rate A rectangular specimen measuring 300 mm in length (MD) and 100 mm in width (TD) was cut from the film to prepare a test specimen. A reference line was drawn parallel to the long side, dividing the short side in half. A line segment was drawn on this reference line, extending 100 mm from the center of the reference line toward each end, for a total length of 200 mm. Two reference lines were then drawn at both ends of the line segment. A hanging clip was attached to the top of the specimen, and a 1,000 g load was attached to the bottom. The specimen was then hung in an oven at 80°C and allowed to stand for 10 minutes. After 10 minutes, the specimen was removed from the oven and allowed to cool naturally at room temperature for 2 minutes with the load still attached. After cooling, the clip and load were removed, and the distance between the previously marked lines was measured to calculate the dimensional change. The dimensional change rate was calculated by the following formula. S = {(L2-L1) / L1} × 100 S: Dimensional change rate (%) L1: Gauge distance before heating (mm) L2: Gauge distance after heating (mm)

[0042] (3) Heat shrinkage rate After cutting the film into a width of 15 mm and a length of 600 mm, a mark was made at a length of 500 mm on the film, and the film was left in an oven at 120°C for 15 minutes without a load. After that, it was allowed to cool at room temperature for 15 minutes, and the length of the mark was measured. The thermal shrinkage rate was calculated as follows: Heat shrinkage rate (%) = (500 - length between marks after shrinkage (mm)) x 100 / 500

[0043] (4) Thickness measurement The thickness of each target film was measured in accordance with JIS K 7130.

[0044] (5) 1% modulus The load (N / 10 mm) when a 10 mm wide test piece is stretched by 1% is defined as the 1% modulus. The film was previously left to stand in an environment of 23°C ± 2°C and 50 ± 10% relative humidity for at least 4 hours before use. The film was cut into a 10 mm wide and 200 mm long test piece and stretched using a tensile testing machine (Shimadzu Corporation AG-Xplus) at a tension speed of 50 mm / min with a chuck distance of 100 mm in the MD and 50 mm in the TD. The load at which the test piece was stretched by 1% was recorded and used as the 1% modulus.

[0045] (6) Sealing performance (bag-making processability) A benchtop heat seal tester (TP-701-S, Tester Sangyo Co., Ltd.) was used to prepare samples for evaluating sealability. The laminated film was cut into test pieces measuring 50 mm in length (MD) and 100 mm in width (TD). The test pieces were folded in half lengthwise with the seal layer facing inward and sealed parallel to the MD at a pressure of 0.2 MPa, a sealing time of 1.0 sec, and a width of 10 mm (preparing the MD seal). The cylindrical section formed by the seal and test piece was then pushed open and sealed parallel to the TD at a pressure of 0.2 MPa, a sealing time of 1.0 sec, and a width of 10 mm (preparing the TD seal). This simulated a vertical pillow bag cut in half horizontally. Next, a dye penetrant for flaw detection testing (Color Check FP-S, Taseto Co., Ltd.) was sprayed from the inside of the bag at the intersection of the MD seal (back seal) and the TD seal (bottom seal). The sealability was assessed based on the penetration of the dye penetrant. The sealability was judged by changing the temperature of the seal bar. Specifically, the temperature of the seal bar during sealing was changed in 1°C increments starting from 120°C. The bag was deemed to have sealability when the flaw detection liquid remained inside the bag, and the temperature range from the temperature at which sealability was exhibited until the seal ruptured was used to judge the sealability (bag-making processability). A temperature range of 7°C or higher was rated as good sealability, and a temperature range of 6°C or lower was rated as poor sealability. A rating of good sealability means that the temperature range from the appearance of sealability to the seal rupture was wide and the bag-making process was excellent, while a rating of poor sealability means that the temperature range from the appearance of sealability to the seal rupture was narrow and the bag-making process was not suitable.

[0046] (7) Independence A desktop heat seal tester (TP-701-S manufactured by Tester Sangyo Co., Ltd.) was used to prepare samples for evaluating self-supporting ability. The laminated film was cut into a length (MD direction) of 600 mm and a width (TD direction) of 200 mm, and then stand-up pouches were prepared using the desktop heat seal tester. When the bottom of the prepared stand-up pouch was opened and placed on a horizontal surface, pouches that could stand on their own without bending were evaluated as having a self-supporting ability of ∘, and pouches that bent and could not stand on their own were evaluated as having a self-supporting ability of ∘.

[0047] (8) Appearance When evaluating the sealing property, the appearance of the sealed portion was visually inspected. A seal with no roughness or shrinkage on the substrate surface was evaluated as ◯, and a seal with significant surface roughness or shrinkage was evaluated as ×.

[0048] (Base film) <Resin used> HDPE1: High-density polyethylene (Hanwha Total, F410A, density 0.952 g / cm 3 , melting point 130℃, MFR 1.0g / 10min) LLDPE1: Linear low-density polyethylene (Dow Chemical, TF80, density 0.926 g / cm 3 , melting point 126℃, MFR 1.7g / 10min) LLDPE2: Ethylene-1-hexene copolymer (EMB21 manufactured by Sumitomo Chemical Co., Ltd., melting point 101-113°C) LLDPE3: Ethylene-1-hexene copolymer (EMB10 manufactured by Sumitomo Chemical Co., Ltd., melting point 101-113°C)

[0049] (Non-stretch sealant film) <Resin used> HDPE2: High-density polyethylene (Dow Chemical ELITE AT6900, density 0.969 g / cm 3 , melting point 136℃, MFR 1.2g / 10min) HDPE3: High-density polyethylene (Japan Polyethylene Co., Ltd. HS471, density 0.956 g / cm 3Melting point 132℃, MFR 4.0g / 10min) LLDPE2: Ethylene-1-hexene copolymer (EMB21 manufactured by Sumitomo Chemical Co., Ltd., melting point 101-113°C) LLDPE3: Ethylene-1-hexene copolymer (EMB10 manufactured by Sumitomo Chemical Co., Ltd., melting point 101-113°C) LLDPE4: Ethylene-1-octene copolymer (Dow Chemical Affinity PL1850G, density 0.902 g / cm 3 , melting point 85℃, MFR 3.0g / 10min) LLDPE5: Ethylene-1-hexene copolymer (Ube Maruzen Polyethylene Co., Ltd., 057FA, density 0.902 g / cm 3 , melting point 111℃, MFR 5.5g / 10min) LLDPE6: Ethylene-α-olefin random copolymer elastomer (Mitsui Chemicals, Inc., A4085S, density 0.885 g / cm 3 , melting point 66℃, MFR 3.6g / 10min) LLDPE7: Ethylene-1-hexene copolymer (EMB11 manufactured by Sumitomo Chemical Co., Ltd., melting point 101-113°C)

[0050] Examples 1 to 5 HDPE1 was introduced into an extruder and melt-kneaded at 255°C. After that, it was stretched 4.6 times in MD and 8.6 times in TD at 120°C in MD and 165°C in TD, to form a biaxially stretched film with a relaxation rate of 9%. One side of the film was corona discharge treated and wound up to obtain a substrate film with the thickness shown in Table 1. Next, resin raw materials mixed with the compositions S1 to S3 shown in Table 2 were introduced into separate extruders and melt-kneaded at 250°C. The extruded films were then subjected to corona discharge treatment on one side and wound up to obtain unstretched films with the thicknesses shown in Table 1. The obtained unstretched film was cut to the size of A4 paper, and then a polyether urethane laminating adhesive (TM320:CAT-13B:ethyl acetate mixed at a weight ratio of 4:3:19, manufactured by Toyo-Morton Co., Ltd.) was applied to the corona discharge treated surface at a rate of 3 g / m using a bar coater. 2The film was coated so that the thickness was approximately 1 μm after drying, and then dried in an oven at 80°C for 30 seconds. After drying, the unstretched sealant film was removed from the oven, and a substrate film similarly cut to A4 size was attached to the adhesive-coated surface with the corona discharge-treated side facing the adhesive-coated side, and pressed together with a roller. After pressing, the film was aged at 40°C for 24 hours to obtain a laminated film. The evaluation results of the resulting laminated film are shown in Table 1.

[0051] Comparative Examples 1-2, 5-7 HDPE1 was introduced into an extruder and melt-kneaded at 255°C. After that, it was stretched 4.6 times in the MD and 8.6 times in the TD at 120°C in the MD and 165°C in the TD, with a relaxation rate of 9%. The biaxially stretched film was subjected to a corona discharge treatment on one side and wound up to obtain a substrate film with the thickness shown in Table 1. Next, resin raw materials mixed with the compositions S1 to S3 shown in Table 2 were introduced into separate extruders and melt-kneaded at 250°C. The extruded films were then subjected to corona discharge treatment on one side and wound up to obtain unstretched films with the thicknesses shown in Table 1. The obtained unstretched film was cut to the size of A4 paper, and then a polyether urethane laminating adhesive (TM320:CAT-13B:ethyl acetate mixed at a weight ratio of 4:3:19, manufactured by Toyo-Morton Co., Ltd.) was applied to the corona discharge treated surface at a rate of 3 g / m using a bar coater. 2 The film was coated so that the thickness was approximately 1 μm after drying, and then dried in an oven at 80°C for 30 seconds. After drying, the unstretched sealant film was removed from the oven, and a substrate film similarly cut to A4 size was attached to the adhesive-coated surface with the corona discharge-treated side facing the adhesive-coated side, and pressed together with a roller. After pressing, the film was aged at 40°C for 24 hours to obtain a laminated film. The evaluation results of the resulting laminated film are shown in Table 1.

[0052] Comparative Examples 3 and 4 A laminate film was obtained in the same manner as in Comparative Example 1, except that LLDPE1 was introduced into an extruder and melt-kneaded at 255°C, then stretched 4.6 times in MD and 8.6 times in TD at 120°C in MD and 165°C in TD to form a biaxially stretched film with a relaxation rate of 9%, which was then subjected to a corona discharge treatment on one side and wound up to form a base film having the thickness shown in Table 1. The evaluation results of the obtained laminate film are shown in Table 1.

[0053] [Table 1]

[0054] [Table 2]

[0055] It has been confirmed that the laminated film of this embodiment is thin, yet has excellent dimensional stability, excellent mechanical strength such as tensile modulus, excellent sealing properties when used as a package, and a wide sealing temperature range during bag manufacturing, making it suitable for bag manufacturing and self-supporting. It also has an excellent appearance after sealing, making it suitable for practical use. On the other hand, the laminated film of the comparative example was unable to achieve both dimensional stability and mechanical strength, and sealability and self-standing property when used as a package.

Claims

1. The film has at least a substrate film made of a polyethylene resin and a non-stretched sealant film made of a polyethylene resin, The base film is A tensile modulus of 1,000 MPa or more in the machine direction (MD) and 2,000 MPa or more in the transverse direction (TD), and Heat shrinkage of 10% or less in the machine direction (MD) and 10% or less in the transverse direction (TD) when heated at 120°C for 15 minutes A biaxially stretched film having The non-stretchable sealant film is The dimensional change rate when heated at 80°C for 10 minutes under a load of 100 N / m is 10% or less in the machine direction (MD), The thickness of the base film is less than the thickness of the non-stretched sealant film. Polyethylene laminated film.

2. 2. The polyethylene-based laminate film according to claim 1, wherein the ratio of the thickness of the base film to the thickness of the non-stretch sealant film is 1:1.5 or more (base film:non-stretch sealant film).

3. The tensile modulus in the machine direction (MD) is 700 MPa or more, and the tensile modulus in the transverse direction (TD) is 1,000 MPa or more; and 3. The polyethylene-based laminate film according to claim 1, wherein the 1% modulus in the machine direction (MD) is 5 N / 10 mm or more and the 1% modulus in the transverse direction (TD) is 7 N / 10 mm or more.

4. A packaging material comprising the polyethylene-based laminate film according to claim 1 or 2.

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