Polyethylene resin composition for monomaterial sealant film and sealant film made thereof

Abstract

To provide a polyethylene resin composition which is suitable as a heat seal layer in a polyethylene mono-material packaging material, a sealant film using the same, and a resin laminate and a packaging material using the same.SOLUTION: A polyethylene resin composition for a mono-material sealant film satisfies the conditions of: (a-1) a melt flow rate (MFR) at a temperature of 190°C and a load of 2.16 kg of 0.5-20 g / 10 min; (a-2) a density of 0.870-0.920 g / cm3: (a-3) a ratio (Mw / Mn) of a weight average molecular weight (Mw) to a number average molecular weight (Mn) determined by GPC of 3.3 or less; and (a-4) an SCB index obtained by calculating the number of short chain branches per 1,000 pieces of carbon determined by GPC by using Expression (1): (number of short chain branches at log of 5.2) / (number of short chain branches at log of 4.2) of 1.02 or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyethylene resin composition having excellent low-temperature heat-sealing properties as a polyethylene monomaterial packaging material, a sealant film made from the composition, a resin laminate containing the sealant film, and a packaging material made from the laminate. [Background technology]

[0002] Conventionally, one of the basic structures of packaging materials is one in which a heat seal layer and a base layer are bonded together with an adhesive. Of these, a film made of a polyethylene resin composition, which has moderate flexibility, transparency, and excellent heat sealability, is widely used for the heat seal layer. On the other hand, a stretched film made of a polyester resin composition or a polyamide resin composition is used for the base layer in terms of rigidity, impact resistance, and heat resistance (see Patent Document 1).

[0003] In recent years, along with the growing demand for the creation of a recycling-oriented society, there has been a demand for packaging materials with high recyclability. However, as described above, conventional packaging materials are composed of different types of resin materials, and because it is difficult to separate the resin materials, they are not currently recycled.

[0004] One way to achieve high recyclability is to create packaging materials made entirely of the same resin material (mono-material packaging materials).Since polyethylene resin compositions are widely used as raw materials for packaging materials, mono-material packaging materials in which both the heat seal layer and the base layer are made of films made of polyethylene resin compositions are expected to be highly recyclable packaging materials that will help realize a recycling-oriented society.

[0005] Polyethylene monomaterial packaging materials are generally composed of a polyethylene resin base material and a polyethylene resin heat-seal layer. Examples of heat-seal layers for polyethylene monomaterial packaging materials include polyethylene monomaterial packaging materials that use a film made of linear low-density polyethylene that is available on the market as the heat-seal layer (Patent Document 2), and polyethylene monomaterial packaging materials that use a polyethylene resin composition with specific resin properties as the heat-seal layer to improve processability during sealing (Patent Document 3). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-202519 [Patent Document 2] Japanese Patent Application Publication No. 2019-166810 [Patent Document 3] Special Publication No. 2020-526412 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the above-mentioned polyethylene monomaterial packaging materials, the difference in melting point between the substrate and the heat seal layer is small, and therefore there is a problem that the substrate melts onto the seal bar during processing involving heat sealing, such as bag making, and this problem has not yet been solved by the above-mentioned Patent Documents 2 and 3. For these reasons, there has been a demand for the development of a polyethylene resin composition that has good low-temperature heat sealability for polyethylene monomaterial packaging materials. An object of the present invention is to provide a polyethylene resin composition suitable as a heat seal layer in a polyethylene monomaterial packaging material, a sealant film using the same, and a resin laminate and packaging material using the same. [Means for solving the problem]

[0008] As a result of intensive research into solving the above problems, the present inventors have found that the use of a polyethylene resin composition that satisfies specific conditions as a heat seal layer exhibits properties that can solve the above problems, and have completed the present invention based on these findings.

[0009] That is, according to the present invention [1], there is provided a polyethylene resin composition for a monomaterial sealant film, which is used for a polyethylene monomaterial resin laminate having at least a polyethylene base material and a polyethylene sealant film, and which is characterized by satisfying the following (a-1) to (a-4): (a-1) Melt flow rate (MFR) at a temperature of 190°C and a load of 2.16 kg is 0.5 to 20 g / 10 min (a-2) Density: 0.870~0.920g / cm 3 (a-3) The ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) determined by GPC (Gel Permeation Chromatography) is 3.3 or less. (a-4) The number of short chain branches per 1,000 carbon atoms determined by GPC is calculated using the SCB index of 1.02 or more using formula (1). Equation (1) SCB index = (number of short chain branches at log5.2) / (number of short chain branches at log4.2)

[0010] According to the present invention [2], there is also provided the polyethylene resin composition for a monomaterial sealant film according to the above [1], characterized in that the polyethylene resin composition is high-pressure ionically polymerized polyethylene.

[0011] Furthermore, according to the present invention [3], there is provided a polyethylene sealant film for use in a polyethylene monomaterial resin laminate having at least a polyethylene base material and a polyethylene sealant film, characterized in that the polyethylene resin composition for a monomaterial sealant film described in [1] or [2] above is contained in at least one of the outermost surface layers.

[0012] The present invention [4] also provides the monomaterial sealant film described in [3] above, characterized in that in a heat seal measurement between outermost layers containing the polyethylene resin composition described in [1] or [2] above, the heat seal temperature at which the heat seal strength is 15 N / 15 mm or more is 120°C or less.

[0013] According to the present invention [5], there is provided a polyethylene monomaterial resin laminate comprising at least a polyethylene substrate and the monomaterial sealant film described in [3] or [4] above.

[0014] Furthermore, according to the present invention [6], there is provided the polyethylene monomaterial resin laminate according to the above [5], characterized in that the polyethylene substrate is a stretched substrate film made of a polyethylene resin composition.

[0015] Furthermore, according to the present invention [7], there is provided the resin laminate according to the above [5] or [6], characterized in that all of the layers constituting the polyethylene monomaterial resin laminate are monomaterial resin laminates composed of a polyethylene resin composition.

[0016] According to the present invention [8], there is provided a packaging material using the resin laminate according to any one of the above [5] to [7]. [Effects of the Invention]

[0017] The polyethylene resin composition of the present invention can provide a sealant film suitable as a heat-sealable layer in a polyethylene monomaterial packaging material. Furthermore, by using a stretched PE film as a packaging material substrate and laminating it with the sealant film of the present invention, it is possible to provide a highly recyclable packaging material, particularly a monomaterial laminate and packaging material made of a single material. [Brief explanation of the drawings]

[0018] [Figure 1] The results of GPC measurement of Example 1-1 and Comparative Example 1-1 are shown below. [Figure 2] The results of heat seal strength measurement for Example 2-1 and Comparative Example 2-1 are shown below. DETAILED DESCRIPTION OF THE INVENTION

[0019] 1. Polyethylene resin composition The polyethylene resin composition in the present invention is a resin composition used as a raw material for the sealant film, and means either a polyethylene resin alone or a polyethylene resin mixture, to which necessary additives may be added.

[0020] Polymerization catalyst and polymerization method for polyethylene resin composition The polyethylene resin for constituting the polyethylene resin composition is produced using either or both of ethylene derived from petroleum feedstocks and ethylene derived from biomass feedstocks as raw materials, using a conventionally known catalyst such as a polymerization catalyst, such as a Ziegler-Natta catalyst, a Phillips catalyst, or a metallocene catalyst. A Ziegler-Natta catalyst or a metallocene catalyst is preferred. Generally, these catalysts are in the form of a complex composed of an organometallic compound supported on a carrier such as silica or a magnesium compound.

[0021] Polymerization methods include high-pressure, solution, slurry, and gas-phase polymerization. High-pressure polymerization uses a radical-generating source such as oxygen or peroxide, or a catalyst composed of a metal complex, as an initiator. Ethylene, comonomer, and initiator are introduced into a reactor under high-temperature and high-pressure conditions. Depending on the reactor shape, this can be further divided into tubular and autoclave processes. Solution polymerization is carried out in a state where the polymer is dissolved in a hydrocarbon solvent at a temperature above the melting point of the polymer. Slurry polymerization uses a hydrocarbon compound such as hexane or isobutane as the solvent, and the resulting polyethylene exists in the solvent as a slurry. Depending on the reactor shape, it can be broadly divided into autoclave and loop-pipe processes. Gas-phase polymerization is a polymerization method in which ethylene, an α-olefin as a comonomer, and hydrogen as a chain transfer agent are fed in gaseous form into the bottom of a vertical reactor, followed by the addition of a polymerization catalyst (edited by Kazuo Matsuura and Hisataka Mikami, Polyethylene Technology Reader). High-pressure and autoclave processes are preferred for producing the polyethylene resin composition of the present invention.

[0022] The polyethylene resin compositions obtained by these production methods have a wide range of combinations of density, melt flow rate (MFR), and other resin physical properties in order to meet the various applications known so far, but the present invention is characterized by selecting and using a polyethylene resin composition for sealant films that satisfies the requirements of the present invention.

[0023] Comonomer composition of polyethylene resin composition The polyethylene resin composition according to the present invention is an ethylene homopolymer or a copolymer of ethylene and one or more α-olefins selected from α-olefins having 3 to 18 carbon atoms. The α-olefins having 3 to 18 carbon atoms are preferably those having 3 to 12 carbon atoms, and specific examples thereof include propylene, 1-butene, 1-hexene, 1-octene, and 4-methyl-1-pentene. The total content of these α-olefins is preferably selected within a range of usually 30 mol% or less, and preferably 20 mol% or less. Within this range, films and the like can have good flexibility and heat resistance. Here, the content of α-olefin is determined under the following conditions: 13 This is a value measured by the C-NMR method. Equipment: JEOL-GSX270 manufactured by JEOL Concentration: 300mg / 2mL Solvent: orthodichlorobenzene

[0024] ·density The polyethylene resin composition according to the present invention has a density of 0.870 to 0.920 g / cm 3 The preferred density is 0.870 to 0.915 g / cm 3 Here, the density is a value measured in accordance with JIS K6922-1 and 2. Density is 0.870g / cm 3 If the density is less than 0.920 g / cm, the formability and processability of the sealant film will be deteriorated, which is undesirable. 3 If it exceeds this value, the low-temperature heat sealability of the sealant film will deteriorate, which is not preferable.

[0025] Melt flow rate (MFR) The polyethylene resin composition according to the present invention must have an MFR in the range of 0.5 to 20 g / 10 min. A preferred MFR is in the range of 0.5 to 10 g / 10 min. An MFR of less than 0.5 g / 10 min may result in the formation of gels, while an MFR of more than 20 g / 10 min is undesirable because it deteriorates the moldability of the sealant film. The MFR is the extrusion rate measured in accordance with JIS K6922-2 by extruding a molten polymer through a die (length 8 mm, outer diameter 9.5 mm, inner diameter 2.095 mm) at 190°C and a load of 2.16 kg.

[0026] ·Molecular weight distribution The polyethylene resin composition according to the present invention must have a molecular weight distribution [ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) (Mw / Mn)] of 3.3 or less. A preferred Mw / Mn ratio is 3.25 or less. An Mw / Mn ratio of more than 3.3 is undesirable because it increases the amount of high-melting-point components and deteriorates low-temperature heat sealability. Use of a polyethylene resin composition having an Mw / Mn of 3.3 or less is preferred because it makes it possible to obtain a low-temperature sealant film suitable for polyethylene monomaterial packaging materials.

[0027] ·SCB index The polyethylene resin composition according to the present invention must have an SCB index of 1.02 or more, preferably 1.03 or more. The SCB index is a value calculated using the following formula (1) for the number of short chain branches per 1,000 carbon atoms determined by GPC (gel permeation chromatography). That is, the SCB index is the quotient of the number of short chain branches at logM=5.2 (Mw=158,000) and the number of short chain branches at logM=4.2 (Mw=15,800). Equation (1) SCB index = (number of short chain branches at log5.2) / (number of short chain branches at log4.2)

[0028] Resin Blend The polyethylene resin composition according to the present invention may be a single composition, or two or more compositions may be blended to produce a polyethylene resin that satisfies the requirements of the present invention, and the resulting polyethylene resin may be used. Examples of polyethylene resin compositions to be blended include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE). From the viewpoint of film formability, blending with LDPE is preferred.

[0029] Additives The polyethylene resin or resin composition according to the present invention may be blended with additives generally used for resin compositions, such as antioxidants, heat stabilizers, neutralizing agents, antiblocking agents, tackifiers, antistatic agents, slip agents, nucleating agents, foaming agents, crosslinking agents, biomass resources, and biodegradation accelerators, within the scope of the present invention.

[0030] 2. Stretched base film The stretched substrate film refers to a film obtained by stretching a film obtained by inflation molding or T-die molding of a polyethylene resin composition, and is used as a substrate for a resin laminate.

[0031] Polyethylene resin composition used The polyethylene resin composition used for the stretched substrate film is not particularly limited, but examples include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE), and a polyethylene resin composition containing a mixture of these may also be used.

[0032] · Raw material manufacturing method and manufacturing conditions The stretched substrate film is obtained by stretching a raw sheet. Examples of methods for producing the raw sheet include inflation molding, T-die molding, and calender molding, with inflation molding and T-die molding being preferred from the viewpoints of production speed, ease of production, and the like. The film may be a single-layer film using a single polyethylene resin composition, or a multi-layer film using multiple polyethylene resin compositions. Although the manufacturing conditions for the raw film are not particularly limited, the thickness of the raw film is preferably 20 μm to 200 μm, more preferably 30 μm to 200 μm, and even more preferably 50 μm to 200 μm.

[0033] ·Stretching method The stretched substrate film may be a uniaxially stretched film or a biaxially stretched film. The stretching method may be any of longitudinal uniaxial stretching, transverse uniaxial stretching, sequential biaxial stretching, and simultaneous biaxial stretching.

[0034] Longitudinal stretching ratio The stretching ratio in the machine direction (MD) of the stretched substrate film is preferably 2 times or more and 15 times or less, more preferably 5 times or more and 10 times or less, and more preferably 7 times or more. Increasing the stretching ratio in the machine direction (MD) of the stretched substrate film can improve the strength and heat resistance of the laminate of the present invention. Furthermore, the printability of the substrate can be improved. Furthermore, the transparency of the substrate can be improved, thereby improving the visibility of an image formed on the surface of the substrate facing the heat seal layer. Meanwhile, the upper limit of the stretching ratio in the machine direction (MD) of the stretched substrate film is not particularly limited, but is preferably 15 times or less, more preferably 10 times or less, from the viewpoint of the breaking limit of the stretched film.

[0035] ·Horizontal stretch ratio The TD stretching ratio of the stretched substrate film is preferably 1.5 times or more, and more preferably 2 times or more. By setting the TD stretching ratio of the stretched substrate film to 1.5 times or more, the strength and heat resistance of the laminate of the present invention can be improved. Furthermore, the printability of the substrate can be improved. Furthermore, since the transparency of the substrate can be improved, when an image is formed on the surface of the substrate on the heat seal layer side, the visibility of the image can be improved. On the other hand, the upper limit of the TD stretching ratio of the stretched substrate film is not particularly limited, but it is preferably 10 times or less from the viewpoint of the breaking limit of the stretched film.

[0036] ·Biaxial stretching ratio When the stretched substrate film is stretched in both MD and TD, the stretching is preferably 1.5 times or more, more preferably 2 times or more, in each direction. Increasing the MD and TD stretching ratios of the stretched substrate film can improve the strength and heat resistance of the laminate of the present invention. Furthermore, the printability of the substrate can be improved. Furthermore, the transparency of the substrate can be improved, thereby improving the visibility of an image formed on the heat-sealable layer side surface of the substrate. While the upper limits of the MD and TD stretching ratios of the stretched substrate film are not particularly limited, it is preferable that the lower limits of the MD and TD stretching ratios are 1.5 times, preferably 2 times, and that the product of the MD stretching ratio and the TD stretching ratio is 50 or less, from the viewpoint of the breaking point limit of the stretched substrate film.

[0037] Multilayer stretched film The film may be a laminate of a substrate made of a stretched substrate film made of a polyethylene resin composition, and a layer made of a film obtained by further stretching a film made of at least one or more polyethylene resin compositions and obtained by inflation molding or T-die molding. Usable resins include high density polyethylene (HDPE), medium density polyethylene (MDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), and ultra low density polyethylene (ULDPE). The lamination method may involve further stretching a co-extruded film obtained by co-extrusion molding, or bonding films together using an adhesive.

[0038] 3. Sealant film Polyethylene resin composition used A sealant film is a film that contains at least one layer made of a polyethylene resin composition and can be sealed by fusing these layers. Usable polyethylene resin compositions are not particularly limited other than the polyethylene resin composition of the present invention, but examples include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE).

[0039] ·Sealant film manufacturing method and manufacturing conditions The sealant film can be produced by known techniques. Specific examples include inflation molding, T-die molding, and calendar molding, with inflation molding and T-die molding being preferred. The thickness of the sealant film is not particularly limited, but is preferably 10 to 200 μm, and more preferably 30 to 180 μm.

[0040] ·Sealant film structure The sealant may have a single-layer structure or a multi-layer structure. In the case of a single-layer structure, the polyethylene resin composition of the present invention may be used alone or in combination with other polyethylene resin compositions as long as the effects of the present invention are not impaired. In the case of a multi-layer structure, it is preferable to use the above-mentioned known techniques and form the sealant by co-extrusion molding. Furthermore, it is preferable that the polyethylene resin composition of the present invention is contained in at least one outermost surface of the multi-layer structure.

[0041] 4.Other The resin laminate may be a resin laminate in which all layers constituting the resin laminate are composed of polyethylene-based resins. This resin laminate can be treated as a monomaterial resin laminate. The proportion of the main component in the monomaterial resin laminate is not particularly limited, but is preferably 80% by weight, more preferably 90% by weight.

[0042] Surface treatment The stretched substrate film and the sealant are preferably subjected to a surface treatment, which can improve adhesion between adjacent layers. The surface treatment method is not particularly limited, and examples thereof include physical treatments such as corona discharge treatment, ozone treatment, low-temperature plasma treatment using oxygen gas and / or nitrogen gas, and glow discharge treatment, as well as chemical treatments such as oxidation treatment using chemicals. Alternatively, an anchor coating layer may be formed on the surface of the substrate using a conventionally known anchor coating agent.

[0043] ·printing An image such as a letter, a pattern, a symbol, etc. may be formed on at least one surface of the stretched base film or the sealant. In order to prevent deterioration of the image over time, it is preferable that the image be formed on the surface where the stretched base film and the sealant face each other. The method for forming the image is not particularly limited, and examples thereof include conventionally known printing methods such as gravure printing, offset printing, flexographic printing, etc. Among these, flexographic printing is preferred from the viewpoint of environmental load.

[0044] Vapor deposition film At least one surface of the stretched substrate film or sealant may be provided with a vapor-deposited film, such as a vapor-deposited film made of a metal such as aluminum, or an inorganic oxide such as aluminum oxide, silicon oxide, magnesium oxide, calcium oxide, zirconium oxide, titanium oxide, boron oxide, hafnium oxide, or barium oxide.

[0045] The thickness of the vapor-deposited film is preferably 1 nm or more and 150 nm or less, more preferably 5 nm or more and 60 nm or less, and even more preferably 10 nm or more and 40 nm or less. By making the thickness of the vapor-deposited film 1 nm or more, the oxygen barrier property and water vapor barrier property of the laminate of the present invention can be further improved, and by making the thickness of the vapor-deposited film 150 nm or less, the occurrence of cracks in the vapor-deposited film can be prevented and the recyclability of the laminate of the present invention can be improved.

[0046] When the vapor-deposited film is an aluminum vapor-deposited film, the OD value thereof is preferably 2 or more and 3.5 or less. This makes it possible to improve the oxygen barrier property and water vapor barrier property while maintaining the productivity of the laminate of the present invention. In the present invention, the OD value can be measured in accordance with JIS-K-7361.

[0047] The vapor-deposited film can be formed by a conventionally known method, for example, physical vapor deposition methods (PVD methods) such as vacuum deposition, sputtering, and ion plating, and chemical vapor deposition methods (CVD methods) such as plasma chemical vapor deposition, thermal chemical vapor deposition, and photochemical vapor deposition.

[0048] Also, for example, a composite film consisting of two or more layers of vapor-deposited films of different inorganic oxides can be formed and used by combining physical vapor deposition and chemical vapor deposition. The degree of vacuum in the deposition chamber is 10 -2 ~10 -8 After oxygen is introduced, the pressure is preferably about 10 -1 ~10 -6 A pressure of about mbar is preferred. The amount of oxygen introduced varies depending on the size of the deposition machine. An inert gas such as argon gas, helium gas, or nitrogen gas may be used as a carrier gas for the oxygen introduced, provided that this does not cause any problems. The film transport speed can be about 10 to 800 m / min.

[0049] The surface of the deposited film is preferably subjected to the above-mentioned surface treatment, which can improve adhesion to adjacent layers.

[0050] Coat At least one surface of the stretched substrate film or sealant may be provided with a heat-resistant coating layer or a barrier coating layer, which contains at least one resin material, such as polyester, polyolefin, cellulose resin, (meth)acrylic resin, urethane resin, or vinyl resin.

[0051] The proportion of the resin material contained in the coating layer to the total weight of the laminate is preferably 3% by mass or less, more preferably 1% by mass or less, which allows the heat resistance and barrier properties of the laminate of the present invention to be improved while maintaining the recyclability.

[0052] The thickness of the coating layer is preferably 0.1 μm or more and 5 μm or less, and more preferably 0.5 μm or more and 3 μm or less, which can improve the heat resistance and barrier properties while maintaining the recyclability of the laminate obtained using the stretched substrate film of the present invention.

[0053] ·glue An adhesive can be used to laminate the resin laminate. The adhesive used contains at least one resin composition, but there are no particular limitations. Examples of adhesives that can be used include epoxy, acrylic, and urethane adhesives. The adhesive containing any of the above resin compositions is not particularly limited, and one-component, two-component, or hot melt type may be used as needed. In addition, using an adhesive with barrier properties, such as PASLIM (manufactured by DIC Corporation) or Maxive (manufactured by Mitsubishi Gas Chemical Company, Inc.), is preferable because it reduces the amount of other barrier materials used and increases the proportion of polyethylene in the resin laminate.

[0054] 4. Packaging material The laminate of the present invention can be particularly suitably used for packaging material applications. The shape of the packaging material is not particularly limited and may be a packaging bag or a stand-up pouch. In the stand-up pouch, only the body may be formed of the resin laminate, only the bottom may be formed of the resin laminate, or both the body and the bottom may be formed of the resin laminate.

[0055] ·Packaging bag The bag-shaped packaging material can be produced by folding the laminate in half, overlapping it so that the sealant layer (heat seal layer) of the laminate is on the inside, and heat sealing the ends. Alternatively, a bag-shaped packaging material can be produced by overlapping two laminates with their heat-sealable layers facing each other, and then heat-sealing the ends of the laminate.

[0056] Stand-up pouch A stand-up pouch-shaped packaging material can be produced by heat-sealing the laminate into a cylindrical shape with the heat-seal layer facing inward to form a body, then folding the laminate into a V-shape with the heat-seal layer facing inward, sandwiching one end of the body, and heat-sealing to form a bottom.

[0057] The heat sealing method is not particularly limited, and can be performed by any known method such as bar sealing, rotary roll sealing, belt sealing, impulse sealing, high frequency sealing, or ultrasonic sealing.

[0058] The contents filled in the packaging material are not particularly limited, and may be liquid, powder, or gel. The contents may also be food or non-food. After filling the contents, the opening can be heat-sealed to form a package. [Example]

[0059] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The evaluations and resins used in the examples and comparative examples are as follows.

[0060] <Evaluation method> (1) Density Measurements were carried out in accordance with JIS K6922-1 and 2.

[0061] (2) MFR Measurement was carried out in accordance with JIS K6922-2 at 190°C under a load of 2.16 kg.

[0062] (3)Molecular weight distribution Measurement was carried out by GPC (Gel Permeation Chromatography) under the following conditions. [Measurement conditions] Model used: Polymer Char HT GPC-IR System Detector: IR-6 Measurement temperature: 145℃ Solvent: Orthodichlorobenzene (ODCB) (trimethylphenol 3.6g / 18L added as antioxidant) Column: Showa Denko Shodex HT-806M x 2 Flow rate: 1.0mL / min Injection volume: 20μL

[0063] Sample preparation 5-8 mg of sample was placed in a vial and set in the autosampler. 8 mL of solvent (room temperature) was injected into the autosampler, and the autosampler was programmed to dissolve the sample at 150 °C for 2 hours. Heptane was used as a flow marker to correct the pump flow rate.

[0064] -Creating a calibration curve A calibration curve was prepared using standard polystyrenes, including the Showdex Standard SM-105 sample set, n-eicosane, and n-tetracontane, and the values ​​were converted to polyethylene.

[0065] Molecular weight calculation Measurements were performed under the above conditions, and chromatograms were recorded at sampling intervals of 1 s. Chromatogram recording (data acquisition) and average molecular weight calculation were performed using dedicated software (GPC One, manufactured by Polymer Char) on a PC with Microsoft Windows 10 installed.

[0066] (4) SCB index The number of short chain branches was calculated using an IR-6 manufactured by Polymer Char Co., Ltd. Specifically, the concentrations of CH2 (methylene) and CH3 (methyl) were measured by IR, and the number of short chain branches was determined from a calibration curve of a standard sample with a known number of short chain branches. The number of short chain branches thus determined was calculated using the following formula (1) to determine the SCB index, which is the quotient of the SCB index, the number of short chain branches at logM=5.2 (Mw=158000), and the number of short chain branches at logM=4.2 (Mw=15800). Equation (1) SCB index = (number of short chain branches at log5.2) / (number of short chain branches at log4.2)

[0067] (5) Heat seal strength -Creating sheet sticker samples Measurements were made with reference to JIS Z1713. A sample measuring 200mm x 150mm (MD x TD) was prepared, folded in half along the TD, covered with a 12µm PET film, and heat-sealed along the TD. The sealing conditions were a pressure of 0.2MPa and a sealing time of 1.0s. The minimum sealing temperature was changed as appropriate depending on the sample, and eight samples were prepared at 10°C intervals, including the minimum value.

[0068] Heat seal strength measurement The heat seal samples prepared above were cut into 15mm widths in the MD and measured using an Orientech Tensilon universal testing machine. The measurement conditions were a chuck distance of 50mm and a pulling speed of 500mm / min. Five measurements were taken, and the weighted average of the five measurements was used to determine the heat seal strength. The temperature at which the heat seal strength reached 15N / 15mm or more was taken as the heat seal rise temperature.

[0069] [Example 1-1] A linear low-density polyethylene (product name: Kernel (registered trademark)) with a grade of KF270 manufactured by Japan Polyethylene Co., Ltd. was prepared and subjected to MFR, density, and GPC measurements. Other physical properties of the resin and the results of each item are shown in Table 1, and the results of the GPC measurement are shown in Figure 1.

[0070] [Example 1-2] A linear low-density polyethylene (product name: Kernel (registered trademark)) with a grade of KF272 manufactured by Japan Polyethylene Co., Ltd. was prepared and subjected to MFR, density, and GPC measurements. Other physical properties of the resin and the results of each item are shown in Table 1.

[0071] [Examples 1-3] A linear low-density polyethylene (product name: Kernel (registered trademark)) with a grade of KS340T manufactured by Japan Polyethylene Co., Ltd. was prepared and subjected to MFR, density, and GPC measurements. Other physical properties of the resin and the results of each item are shown in Table 1.

[0072] [Examples 1-4] A linear low-density polyethylene (product name: Kernel (registered trademark)) with a grade of KF360T manufactured by Japan Polyethylene Co., Ltd. was prepared and subjected to MFR, density, and GPC measurements. Other physical properties of the resin and the results of each item are shown in Table 1.

[0073] [Examples 1-5] A linear low-density polyethylene (product name: Kernel (registered trademark)) with a grade of KF370 manufactured by Japan Polyethylene Co., Ltd. was prepared and subjected to MFR, density, and GPC measurements. Other physical properties of the resin and the results of each item are shown in Table 1.

[0074] [Comparative Example 1-1] A linear low-density polyethylene (product name: Harmolex (registered trademark)) with a grade of NF366A manufactured by Japan Polyethylene Co., Ltd. was prepared and subjected to MFR, density, and GPC measurements. Other physical properties of the resin and the results of each item are shown in Table 1, and the results of the GPC measurement are shown in Figure 1.

[0075] [Comparative Example 1-2] A linear low-density polyethylene (product name: Harmolex (registered trademark)) with a grade of NF464N manufactured by Japan Polyethylene Co., Ltd. was prepared and subjected to MFR, density, and GPC measurements. Other physical properties of the resin and the results of each item are shown in Table 1.

[0076] [Comparative Example 1-3] A linear low-density polyethylene (product name: Novatec (registered trademark) LL, grade UF320) manufactured by Japan Polyethylene Co., Ltd. was prepared and subjected to MFR, density, and GPC measurements. Other physical properties of the resin and the results of each item are shown in Table 1.

[0077] [Example 2-1] Using the formulations in Table 2, a multi-layer inflation molding machine (die diameter: 200 mmφ, die lip: 3 mm, die temperature: 190°C) was used to mold a three-layer tubular film with a total thickness of 120 μm. The thicknesses of the outermost layer, middle layer, and innermost layer were 30 μm, 60 μm, and 30 μm, respectively. A heat-sealing test was conducted on the resulting film. The results are shown in Table 2, and the results of the heat-sealing strength measurement are shown in Figure 2.

[0078] [Comparative Example 2-1] A film was formed in the same manner as in Example 2-1 according to the formulation in Table 2. The results are shown in Table 2, and the results of the heat seal strength measurement are shown in FIG.

[0079] [Table 1]

[0080] [Table 2] [Industrial Applicability]

[0081] According to the present invention, it is possible to provide a polyethylene resin composition having excellent low-temperature sealing properties and a sealant film using the same. Therefore, the polyethylene resin composition of the present invention is suitable for use as a packaging material requiring low-temperature sealing property, and can be particularly suitably used for applications such as polyethylene monomaterial packaging materials in which both the base material and the sealant are composed of the polyethylene resin composition.

Claims

1. The monomaterial sealant film is used for a polyethylene monomaterial resin laminate having at least a stretched polyethylene base film and a polyethylene sealant film, the monomaterial sealant film having a polyethylene resin ratio of 80% by weight or more, the monomaterial sealant film comprising at least one layer made of a polyethylene resin composition, and characterized in that at least one outermost layer contains a polyethylene resin composition that satisfies the following (a-1) to (a-4): (a-1) A melt flow rate (MFR) of 0.5 to 20 g / 10 min at a temperature of 190°C and a load of 2.16 kg. (a-2) Density: 0.870~0.920 g / cm³ ３ (a-3) The ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) determined by GPC (Gel Permeation Chromatography) is 3.3 or less. (a-4) The SCB index, calculated by using the number of short chain branches per 1,000 carbon atoms determined by GPC and formula (1), is 1.02 or more. SCB index = (number of short chain branches at log 5.2) / (number of short chain branches at log 4.2)

2. 2. The monomaterial sealant film according to claim 1, wherein the polyethylene resin in the polyethylene resin composition is high-pressure ion-polymerized polyethylene.

3. 3. The monomaterial sealant film according to claim 2, wherein in a heat seal measurement between outermost layers containing the polyethylene resin composition according to claim 1, the heat seal temperature at which the heat seal strength is 15 N / 15 mm or more is 120°C or less.

4. A polyethylene monomaterial resin laminate comprising at least a stretched polyethylene substrate film and the monomaterial sealant film according to any one of claims 1 to 3.

5. A packaging material using the resin laminate according to claim 4.

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