Laminated film and process for producing the same

Abstract

To provide a laminated film excellent in low-temperature sealability and resistance to bag opening at a low temperature.SOLUTION: The laminated film includes a base material layer and a heat seal layer. The base material layer is an oriented polypropylene film, the heat-sealing layer contains a propylene-based polymer (A) satisfying a1-a4 and a propylene-based thermoplastic elastomer (B) satisfying b1-b4, and the ratio of (A) (B) to the total of (A) and (B) is 51-90 wt.% and 10-49 wt.%, respectively. (a1) MFR is 1 to 50g / 10 minutes (a2) Flexural modulus is more than 100 to 1,000 MPa (a3) Content of unit derived from propylene is more than 88.0 to 99.9% by weight (a4) Content of unit derived from ethylene or the like is 0.1 to less than 12.0% by weight (b1) MFR is 1 to 30g / 10 minutes (b2) Flexural modulus is 5 to 35 MPa (b3) Content of unit derived from propylene is 60.0 to 80.0% by weight (b4) Content of unit derived from ethylene or the like is 12.0 to 40.0% by weight SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a laminated film having excellent seal strength and resistance to bag drop at low temperatures, and a method for producing the same. [Background technology]

[0002] Polypropylene film has a variety of excellent properties, including transparency, rigidity, and heat resistance, and is therefore widely used as packaging film for food, clothing, medical care, pharmaceuticals, stationery, miscellaneous goods, industrial materials, and other industrial applications. In particular, films dry-laminated with polyethylene and biaxially oriented polyamide film, biaxially oriented polyester film, or biaxially oriented polypropylene film are the mainstream on the market, and are used for food packaging and as exterior packaging for lithium-ion batteries. Meanwhile, with the recent rise in environmental awareness, interest has been growing in so-called monomaterial packaging, which uses the same material to create packaging materials and is recyclable. While polypropylene film has the characteristics of having a higher melting point and rigidity than polyethylene film, its applications are limited due to its inferior heat seal strength, low-temperature heat sealability, impact resistance, puncture resistance, and tear strength, as well as its poor resistance to bag drop at low temperatures.

[0003] To overcome these drawbacks, a propylene-ethylene random copolymer (Patent Document 1) has been proposed, in which ethylene is copolymerized with the main component propylene, with the aim of improving the impact resistance of crystalline propylene-based resins. Also proposed is a propylene-based resin film (Patent Document 2) that is made from a resin composition with specified MFR and melting properties, and has excellent impact resistance. Furthermore, a highly transparent film (Patent Document 3) has been proposed in which a nucleating agent is blended into a specific propylene-based block copolymer, improving transparency, impact resistance, and the like.

[0004] Meanwhile, sealant films made of polypropylene-based resins have also been studied. For example, Patent Document 4 discloses a retort sealant film that is composed of a core layer made of 100 parts by weight of polypropylene-based elastomer and 0 to 150 parts by weight of polypropylene-based resin, and a heat-seal layer laminated on at least one side of the core layer and made of a mixture of 30 to 70 parts by weight of polypropylene-based resin and 70 to 30 parts by weight of polypropylene-based elastomer, and is shown to have excellent impact resistance and low-temperature sealability.

[0005] Patent Documents 5 and 6 disclose packaging materials that include at least a biaxially oriented polypropylene film and a polypropylene-based unoriented film, in which the polypropylene-based unoriented film contains a propylene homopolymer and a propylene-ethylene random copolymer, and show that the balance between heat resistance and low-temperature sealability can be improved. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 58-138721 [Patent Document 2] Japanese Patent Application Publication No. 11-269226 [Patent Document 3] Japanese Patent Application Publication No. 11-92619 [Patent Document 4] Japanese Patent Application Publication No. 9-150491 [Patent Document 5] Japanese Patent Application Publication No. 2023-161216 [Patent Document 6] Japanese Patent Application Publication No. 2023-161210 Summary of the Invention [Problem to be solved by the invention]

[0007] Although the propylene-based resin films obtained in Patent Documents 1 to 3 show a certain degree of improvement in impact resistance, their impact resistance in low-temperature environments is insufficient, and they could not be used for food packaging applications such as vegetable packaging, which are used at relatively low temperatures and require impact resistance. The sealant film of Patent Document 4 and the packaging materials disclosed in Patent Documents 5 and 6 also have insufficient impact resistance in low-temperature environments, and no consideration is given to bag drop resistance at low temperatures.

[0008] An object of the present invention is to provide a laminated film that is excellent in heat seal strength, low-temperature sealability, and resistance to bag drop at low temperatures. [Means for solving the problem]

[0009] As a result of extensive research aimed at solving the above problems, the present inventors have found that a film obtained by laminating a heat seal layer containing a specific propylene-based polymer and a specific propylene-based thermoplastic elastomer in specific ratios with a stretched polypropylene film has excellent heat seal strength, low-temperature sealability, and bag drop resistance at low temperatures, and have completed the present invention. The present invention relates to the following [1] to

[13] .

[0010] [1] A laminated film comprising a base layer and a heat-sealing layer, wherein the base layer is a stretched polypropylene film; the heat-sealing layer comprises a propylene polymer (A) that satisfies the following requirements (a1) to (a4), and a propylene thermoplastic elastomer (B) that satisfies the following requirements (b1) to (b4); and the proportions of the components (A) and (B) relative to 100% by weight of the total of the components (A) and (B) are 51 to 90% by weight and 10 to 49% by weight, respectively. (a1) The MFR measured in accordance with JIS K 7210-1:2014 (230°C, 2.16 kg load) is 1 to 50 g / 10 min. (a2) The flexural modulus measured in accordance with JIS K 7171:2022 at a test speed of 2 mm / min is greater than 100 MPa and less than 1,000 MPa. (a3) The content of units derived from propylene is more than 88.0% by weight and not more than 99.9% by weight. (a4) The content of units derived from ethylene and α-olefins having 4 to 20 carbon atoms is 0.1% by weight or more and less than 12.0% by weight. (b1) The MFR measured in accordance with JIS K 7210-1:2014 (230°C, 2.16 kg load) is 1 to 30 g / 10 min. (b2) The flexural modulus measured in accordance with JIS K 7171:2022 at a test speed of 2 mm / min is 5 to 35 MPa. (b3) The content of units derived from propylene is 60.0 to 88.0% by weight. (b4) The content of units derived from ethylene and α-olefins having 4 to 20 carbon atoms is 12.0 to 40.0% by weight. [2] The laminated film according to [1], wherein the component (A) is a propylene-ethylene copolymer or a propylene-ethylene-1-butene copolymer that satisfies the following requirement (a5): (a5) The melting point is 110 to 155°C. [3] The laminated film according to [1] or [2], wherein the ratios of the thickness of the base material layer and the heat seal layer to the total thickness of the base material layer and the heat seal layer are 5 to 90% and 10 to 95%, respectively. [4] The laminated film according to any one of [1] to [3], wherein the sealing temperature at which the heat seal strength reaches 10 N / 15 mm as measured under the following conditions is less than 120°C. <Measurement of the sealing temperature at which the heat seal strength reaches 10N / 15mm> After storing the laminated film at an ambient temperature of 23°C for 7 days, it was cut into strips measuring 180 mm (MD) x 80 mm (TD), folded in half in the MD so that the heat-sealable layers were in contact with each other, and heat-sealed at a width of 10 mm at a position 20-30 mm from the fold under the following sealing conditions. The resulting partially heat-sealed sample was cut into strips with a width of 15 mm in the TD to obtain test pieces. The resulting test pieces were pulled at both ends in a 180° peel direction using a Schopper-type tensile tester at a rate of 500 mm / min, and the maximum force required to peel the heat-sealed portions was measured and used as the heat-seal strength. Sealing conditions: Sealing pressure: 2.0 kg / cm 2 (0.196 MPa), sealing time: 1.0 second, sealing temperature: 90°C to 170°C in 10°C increments. In the seal curve obtained from the seal temperature and heat seal strength, the data between any two points measured at 10°C intervals is approximated with a linear function to determine the seal temperature at which the heat seal strength reaches 10N / 15mm. [5] The laminated film according to any one of [1] to [4], which has a haze of less than 10% as measured in accordance with JIS K 7136:2000. [6] The laminated film according to any one of [1] to [5], which has a puncture strength of 10 N or more as measured in accordance with JIS Z 1707:2019. [7] The laminated film according to any one of [1] to [6], wherein the average number of times the bag breaks after being dropped is 6 or more times in a bag drop impact test measured under the following conditions: <Dropped bag impact test> Two 120mm x 150mm sheets are cut from the laminated film, and the heat-sealed layers of each sheet are overlapped. Then, three sides are sealed using an impulse sealer under the following sealing conditions to create a 120mm x 150mm sample bag. 100ml of water is poured into the sample bag, and the open side is sealed using an impulse sealer under the following sealing conditions to create a water seal test piece. After storing the water seal test piece in a 0°C atmosphere for one day, it is dropped 50 times consecutively from a height of 1.5m onto a metal plate. The maximum number of times the bag does not break is recorded as the number of bag breakage drops. The test is repeated five times, and the average number of bag breakage drops is calculated. The sealing conditions are as follows: a Fuji Impulse poly sealer (product name: PC-300), seal width: 2 mm, scale: 10 (sealing time: 1.6 seconds). [8] A food packaging film comprising the laminate film according to any one of [1] to [7]. [9] A film for packaging heavy goods, comprising the laminate film according to any one of [1] to [7].

[10] A liquid packaging film comprising the laminate film according to any one of [1] to [7].

[11] A method for producing a laminated film according to any one of [1] to [7], comprising a step of bonding the substrate layer and the heat seal layer by dry lamination.

[12] An unstretched sealant film comprising a propylene polymer (A) satisfying the following requirements (a1) to (a4) and a propylene thermoplastic elastomer (B) satisfying the following requirements (b1) to (b4), wherein the proportions of the components (A) and (B) relative to 100% by weight of the total of the components (A) and (B) are 51 to 90% by weight and 10 to 49% by weight, respectively. (a1) The MFR measured in accordance with JIS K 7210-1:2014 (230°C, 2.16 kg load) is 1 to 50 g / 10 min. (a2) The flexural modulus measured in accordance with JIS K 7171:2022 at a test speed of 2 mm / min is greater than 100 MPa and less than 1,000 MPa. (a3) The content of units derived from propylene is more than 88.0% by weight and not more than 99.9% by weight. (a4) The content of units derived from ethylene and α-olefins having 4 to 20 carbon atoms is 0.1% by weight or more and less than 12.0% by weight. (b1) The MFR measured in accordance with JIS K 7210-1:2014 (230°C, 2.16 kg load) is 1 to 30 g / 10 min. (b2) The flexural modulus measured in accordance with JIS K 7171:2022 at a test speed of 2 mm / min is 5 to 35 MPa. (b3) The content of units derived from propylene is 60.0 to 88.0% by weight. (b4) The content of units derived from ethylene and α-olefins having 4 to 20 carbon atoms is 12.0 to 40.0% by weight.

[13] The unstretched sealant film according to

[12] , which is to be laminated to at least one surface of a stretched polypropylene film. [Effects of the Invention]

[0011] The present invention provides a laminated film that is excellent in heat seal strength, low-temperature sealability, and bag drop resistance at low temperatures. DETAILED DESCRIPTION OF THE INVENTION

[0012] The laminated film comprises a base layer and a heat-sealing layer, the base layer being a stretched polypropylene film; the heat-sealing layer comprising a propylene polymer (A) satisfying the following requirements (a1) to (a4), and a propylene thermoplastic elastomer (B) satisfying the following requirements (b1) to (b4); the proportions of the components (A) and (B) relative to 100% by weight of the total of the components (A) and (B) are 51 to 90% by weight and 10 to 49% by weight, respectively. (a1) The MFR measured in accordance with JIS K 7210-1:2014 (230°C, 2.16 kg load) is 1 to 50 g / 10 min. (a2) The flexural modulus measured in accordance with JIS K 7171:2022 at a test speed of 2 mm / min is greater than 100 MPa and less than 1,000 MPa. (a3) The content of units derived from propylene is more than 88.0% by weight and not more than 99.9% by weight. (a4) The content of units derived from ethylene and α-olefins having 4 to 20 carbon atoms is 0.1% by weight or more and less than 12.0% by weight. (b1) The MFR measured in accordance with JIS K 7210-1:2014 (230°C, 2.16 kg load) is 1 to 30 g / 10 min. (b2) The flexural modulus measured in accordance with JIS K 7171:2022 at a test speed of 2 mm / min is 5 to 35 MPa. (b3) The content of units derived from propylene is 60.0 to 88.0% by weight. (b4) The content of units derived from ethylene and α-olefins having 4 to 20 carbon atoms is 12.0 to 40.0% by weight. By laminating the base layer and heat seal layer of the present invention, a laminate film with excellent low-temperature sealing properties and low-temperature bag drop resistance can be obtained. Furthermore, because the laminate film has high heat seal strength, it can be used in heavy-duty packaging applications that conventional polypropylene laminate films could not handle. Furthermore, in light of recent market environmental concerns, there is a need in the film industry to reduce the amount of resin used. Since the laminate film maintains high heat seal strength even when the heat seal layer is thin, the thickness of the heat seal layer can be made thinner than before, thereby reducing the amount of resin used. Furthermore, because the heat seal initiation temperature can be lowered, the set temperature of the sealing mold can be lowered, thereby saving energy.

[0013] In this specification, the propylene polymer (A), the propylene thermoplastic elastomer (B), and the stretched polypropylene film are each polymers containing 50% by weight or more of polymerization units derived from propylene. Each component, production method, and application will be described below.

[0014] <Heat seal layer> The heat seal layer contains a propylene polymer (A) and a propylene thermoplastic elastomer (B).

[0015] [Propylene polymer (A)] The propylene polymer (A) is a copolymer of propylene and ethylene or an α-olefin having 4 to 20 carbon atoms in a content of 0.1% by weight or more, and satisfies the following requirements (a1) to (a4). The ethylene and the α-olefin having 4 to 20 carbon atoms, which are copolymerization components with propylene, may be one type or a combination of two or more types. The copolymerization component is preferably ethylene or an α-olefin having 4 to 10 carbon atoms. Specific examples of the copolymerization component include ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 3-methyl-1-butene, 4-methyl-1-pentene, 2-methyl-1-pentene, and 2-methyl-1-hexene, with ethylene or 1-butene being particularly preferred. The propylene polymer (A) may be a blend of two or more of a propylene homopolymer and a random copolymer of propylene with ethylene or an α-olefin having 4 to 20 carbon atoms. The blend may be either a melt blend obtained by melt-kneading these polymers produced separately, or a polymer blend obtained as a multistage polymer produced by the multistage polymerization method described below. The propylene polymer (A) may be used alone or in combination of two or more kinds.

[0016] In this specification, the content of units derived from ethylene in a propylene-ethylene copolymer is a value calculated based on the following formula. Content of ethylene-derived units (%) = Weight of ethylene-derived units / (Weight of units derived from propylene + Weight of units derived from ethylene) x 100 The content of units derived from each monomer in other copolymers such as propylene-ethylene-1-butene copolymer can also be calculated in the same manner as above.

[0017] (a1) The MFR measured in accordance with JIS K 7210-1:2014 (230°C, 2.16 kg load) is 1 to 50 g / 10 min. The propylene polymer (A) has a melt flow rate (MFR) of 1 to 50 g / 10 min, measured in accordance with JIS K 7210-1:2014 (230°C, 2.16 kg load). The MFR is preferably 2 to 40 g / 10 min, more preferably 3 to 30 g / 10 min. When the propylene polymer (A) has an MFR in the range of 1 to 50 g / 10 min, it has good compatibility with the propylene thermoplastic elastomer (B) and therefore good film processability. Methods for controlling the MFR value are well known, and the MFR value can be easily adjusted by adjusting the temperature and pressure, which are polymerization conditions for the propylene polymer (A), or by controlling the amount of a chain transfer agent such as hydrogen added during polymerization.

[0018] (a2) The flexural modulus measured in accordance with JIS K 7171:2022 at a test speed of 2 mm / min is greater than 100 MPa and less than 1,000 MPa. The propylene polymer (A) has a flexural modulus of more than 100 MPa and not more than 1,000 MPa, as measured at a test speed of 2 mm / min in accordance with JIS K 7171:2022. The flexural modulus is preferably more than 100 MPa and not more than 900 MPa, and more preferably more than 100 MPa and not more than 800 MPa. If the flexural modulus is 100 MPa or less, the formability of the heat-sealable layer deteriorates, while if it exceeds 1,000 MPa, the flexibility of the heat-sealable layer is impaired, resulting in deterioration of the heat-seal strength, low-temperature heat-sealability, transparency, impact resistance, puncture strength, tear strength, and low-temperature bag drop resistance. The method for controlling the flexural modulus is well known, and it can be easily adjusted by controlling the content ratio of ethylene and / or α-olefin having 4 to 20 carbon atoms to be copolymerized.

[0019] (a3) The content of units derived from propylene is more than 88.0% by weight and not more than 99.9% by weight. The content of the propylene-derived units in the propylene polymer (A) is more than 88.0 wt% and not more than 99.9 wt%. By setting the content of the propylene-derived units within the above range, the flexibility of the heat seal layer can be maintained. The content of the propylene-derived units is preferably more than 88.5 wt% to 98.0 wt%, more preferably more than 89.0 wt% to 97.0 wt%.

[0020] (a4) The content of units derived from ethylene and α-olefins having 4 to 20 carbon atoms is 0.1% by weight or more and less than 12.0% by weight. The content of units derived from ethylene and an α-olefin having 4 to 20 carbon atoms in the propylene polymer (A) is 0.1% by weight or more and less than 12.0% by weight. By setting the content of units derived from ethylene and an α-olefin having 4 to 20 carbon atoms within the above range, the flexibility of the heat seal layer can be maintained. The content of units derived from ethylene and an α-olefin having 4 to 20 carbon atoms is preferably 2.0% by weight to less than 11.5% by weight, and more preferably 3.0% by weight to less than 11.0% by weight. The content of units derived from ethylene in the propylene polymer (A) is preferably from 0.1 to 7.0% by weight, more preferably from 1.0 to 5.0% by weight. The content of units derived from 1-butene in the propylene polymer (A) is preferably from 0 to 11.0% by weight, more preferably from 0 to 10.0% by weight. The total content of units derived from ethylene and 1-butene in the propylene polymer (A) is preferably 0.1% by weight or more and less than 12.0% by weight, more preferably 2.0 to less than 11.5% by weight, and even more preferably 3.0 to less than 11.0% by weight.

[0021] The propylene polymer (A) preferably further satisfies the following requirement (a5).

[0022] (a5) The melting point is 110 to 155°C. The melting point of the propylene polymer (A) is preferably 110 to 155° C., more preferably 115 to 145° C., and even more preferably 120 to 140° C. By adjusting the melting point to within the range of 110 to 155° C., good low-temperature heat sealability can be achieved. Methods for controlling the melting point are well known, and the melting point can be easily adjusted by controlling the content ratio of ethylene and / or α-olefin having 4 to 20 carbon atoms to be copolymerized.

[0023] In this specification, the melting point is measured as follows: Using a differential scanning calorimeter (DSC), a 5.0 mg sample is heated to 200°C, held at 200°C for 5 minutes, and then cooled to 40°C at a rate of 10°C / min. The sample is then heated at a rate of 10°C / min, and the top temperature of the endothermic peak is taken as the melting peak temperature (melting point / Tm).

[0024] From the viewpoint of imparting flexibility and low-temperature heat sealability to the heat seal layer, the propylene-based polymer (A) is preferably a propylene-ethylene copolymer or a propylene-ethylene-1-butene copolymer satisfying the above requirements (a1) to (a5), and more preferably a propylene-ethylene-1-butene copolymer.

[0025] The polymerization catalyst for producing the propylene polymer (A) may be a Ziegler-Natta catalyst and / or a metallocene catalyst, but may also be other catalysts. Ziegler-Natta catalysts are described in Section 2.3.1 (pp. 20-57) of "Polypropylene Handbook," edited by Edward P. Moore Jr., translated and supervised by Tetsuo Yasuda and Nobu Sakuma, published by the Industrial Research Institute (1998). Ziegler-Natta catalysts include (1) titanium trichloride catalysts consisting of titanium trichloride and organoaluminum halide, combined with magnesium chloride and titanium halide, (2) magnesium-supported catalysts consisting of a solid catalyst component containing an electron-donating compound and an organoaluminum and organosilicon compound, and (3) catalysts combining an organoaluminum compound component with an organosilicon-treated solid catalyst component formed by contacting a solid catalyst component with an organoaluminum and organosilicon compound.

[0026] The metallocene catalyst is a catalyst comprising (i) a transition metal compound of Group 4 of the periodic table containing a ligand having a cyclopentadienyl skeleton (a so-called metallocene compound), (ii) a co-catalyst capable of activating the metallocene compound to a stable ionic state by reacting with the metallocene compound, and, if necessary, (iii) an organoaluminum compound, and any known catalyst can be used. The metallocene compound is preferably a bridged metallocene compound capable of stereoregular polymerization of propylene, and more preferably a bridged metallocene compound capable of isoregular polymerization of propylene.

[0027] (i) As the metallocene compound, for example, those disclosed in JP-A-60-35007, JP-A-61-130314, JP-A-63-295607, JP-A-1-275609, JP-A-2-41303, JP-A-2-131488, JP-A-2-76887, JP-A-3-163088, JP-A-4-300887, JP-A-4-211694, JP-A-5-43616, JP-A-5-209013, JP-A-6-239914, JP-T-7-504934, and JP-A-8-85708 can be preferably used.

[0028] Specifically, methylenebis(2-methylindenyl)zirconium dichloride, ethylenebis(2-methylindenyl)zirconium dichloride, ethylene 1,2-(4-phenylindenyl)(2-methyl-4-phenyl-4H-azulenyl)zirconium dichloride, isopropylidene(cyclopentadienyl)(fluorenyl)zirconium dichloride, isopropylidene(4-methylcyclopentadienyl)(3-t-butylindenyl)zirconium dichloride, dimethylsilylene(2-methyl-4-t-butyl-cyclopentadienyl)(3'-t-butyl-5'-methyl-cyclopentadienyl)zirconium dichloride, dimethylsilylenebis(indenyl) methylsilylenebis(4,5,6,7-tetrahydroindenyl)zirconium dichloride, dimethylsilylenebis[1-(2-methyl-4-phenylindenyl)]zirconium dichloride, dimethylsilylenebis[1-(2-ethyl-4-phenylindenyl)]zirconium dichloride, dimethylsilylenebis[4-(1-phenyl-3-methylindenyl)]zirconium dichloride, dimethylsilylene(fluorenyl)t-butylamido zirconium dichloride, methylphenylsilylenebis[1-(2-methyl-4,(1-naphthyl)-indenyl)]zirconium dichloride, dimethylsilylenebis[1-(2-methyl-4,5-benzoindenyl)] zirconium dichloride, dimethylsilylenebis[1-(2-methyl-4-phenyl-4H-azulenyl)] zirconium dichloride, dimethylsilylenebis[1-(2-ethyl-4-(4-chlorophenyl)-4H-azulenyl)] zirconium dichloride, dimethylsilylenebis[1-(2-ethyl-4-naphthyl-4H-azulenyl)] zirconium dichloride, diphenylsilylenebis[1-(2-methyl-4-(4-chlorophenyl)-4H-azulenyl)] zirconium dichloride Examples of zirconium compounds include dimethylsilylenebis[1-(2-ethyl-4-(3-fluorobiphenyl)-4H-azulenyl)]zirconium dichloride, dimethylsilylenebis[1-(2-ethyl-4-(3-fluorobiphenyl)-4H-azulenyl)]zirconium dichloride, dimethylgermylenebis[1-(2-ethyl-4-(4-chlorophenyl)-4H-azulenyl)]zirconium dichloride, and dimethylgermylenebis[1-(2-ethyl-4-phenylindenyl)]zirconium dichloride.

[0029] In the above, compounds in which zirconium is replaced with titanium, hafnium, etc. can also be used. It is also preferable to use a mixture of a zirconium compound and a hafnium compound. Chloride can also be replaced with other halogen compounds, hydrocarbon groups such as methyl, isobutyl, and benzyl, amide groups such as dimethylamide and diethylamide, alkoxide groups such as methoxy and phenoxy, and hydride groups. Among these, metallocene compounds in which an indenyl group or an azulenyl group is bridged with a silicon or germyl group are particularly preferred.

[0030] The metallocene compound may be supported on an inorganic or organic carrier. The carrier is preferably a porous inorganic or organic compound, and specific examples include inorganic compounds such as ion-exchangeable layered silicates, zeolites, SiO, AlO, silica alumina, MgO, ZrO, TiO, BO, CaO, ZnO, BaO, and ThO; organic compounds such as porous polyolefins, styrene-divinylbenzene copolymers, and olefin-acrylic acid copolymers; and mixtures thereof.

[0031] (ii) Preferred examples of the co-catalyst capable of reacting with a metallocene compound to activate it to a stable ionic state include organoaluminum oxy-compounds (e.g., aluminoxane compounds), ion-exchangeable layered silicates, Lewis acids, boron-containing compounds, ionic compounds, and fluorine-containing organic compounds.

[0032] (iii) Preferred examples of organoaluminum compounds include trialkylaluminums such as triethylaluminum, triisopropylaluminum, and triisobutylaluminum, dialkylaluminum halides, alkylaluminum sesquihalides, alkylaluminum dihalides, alkylaluminum hydrides, and organoaluminum alkoxides.

[0033] The method for producing the propylene polymer (A) is not particularly limited, and the propylene polymer (A) can be produced by any of conventionally known methods such as slurry polymerization, bulk polymerization, and gas phase polymerization. Furthermore, the propylene polymer (A) can also be produced by a multistage polymerization method within the range.

[0034] [Propylene-based thermoplastic elastomer (B)] The propylene-based thermoplastic elastomer (B) is a copolymer of propylene and ethylene or an α-olefin having 4 to 20 carbon atoms, and satisfies the following requirements (b1) to (b4). The ethylene and α-olefin having 4 to 20 carbon atoms, which are copolymerization components with propylene, may be one type or a combination of two or more types. The copolymerization component is preferably ethylene or an α-olefin having 4 to 10 carbon atoms. Specific examples of the copolymerization component include ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 3-methyl-1-butene, 4-methyl-1-pentene, 2-methyl-1-pentene, and 2-methyl-1-hexene, with ethylene or 1-butene being particularly preferred. Examples of the propylene-based thermoplastic elastomer (B) include random copolymer rubbers of propylene with ethylene or an α-olefin having 4 to 20 carbon atoms, and specific examples include propylene-ethylene copolymers and propylene-ethylene-1-butene copolymers. The propylene-based thermoplastic elastomer (B) may be used alone or in combination of two or more kinds.

[0035] (b1) The MFR measured in accordance with JIS K 7210-1:2014 (230°C, 2.16 kg load) is 1 to 30 g / 10 min. The propylene-based thermoplastic elastomer (B) has an MFR of 1 to 30 g / 10 min, measured in accordance with JIS K 7210-1:2014 (230°C, 2.16 kg load). The MFR is preferably 2 to 20 g / 10 min, more preferably 2 to 10 g / 10 min. When the propylene-based thermoplastic elastomer (B) has an MFR within the range of 1 to 30 g / 10 min, a film with good appearance can be obtained. Methods for controlling the MFR value are well known, and the MFR value can be easily adjusted by adjusting the temperature and pressure, which are polymerization conditions for the propylene-based thermoplastic elastomer (B), or by controlling the amount of a chain transfer agent such as hydrogen added during polymerization.

[0036] (b2) The flexural modulus measured in accordance with JIS K 7171:2022 at a test speed of 2 mm / min is 5 to 35 MPa. The propylene-based thermoplastic elastomer (B) has a flexural modulus of 5 to 35 MPa as measured at a test speed of 2 mm / min in accordance with JIS K 7171:2022. The flexural modulus is preferably 8 to 33 MPa, and more preferably 10 to 30 MPa. A flexural modulus of 5 MPa or more suppresses surface stickiness during molding of the heat-sealable layer, while a flexural modulus of 35 MPa or less improves the flexibility of the heat-sealable layer and improves the heat-seal strength, low-temperature heat-sealability, transparency, impact resistance, puncture strength, tear strength, and low-temperature bag drop resistance. The method for controlling the flexural modulus is well known, and it can be easily adjusted by controlling the content ratio of ethylene and / or α-olefin having 4 to 20 carbon atoms to be copolymerized.

[0037] (b3) The content of units derived from propylene is 60.0 to 88.0% by weight. The content of propylene-derived units in the propylene-based thermoplastic elastomer (B) is 60.0 to 88.0% by weight. By setting the content of propylene-derived units within this range, the flexibility of the heat seal layer can be improved, and the heat seal strength, low-temperature heat sealability, transparency, impact resistance, puncture strength, tear strength, and low-temperature bag drop resistance can be improved. The content of propylene-derived units is preferably 60.0 to 87.0% by weight, more preferably 64.0 to 85.0% by weight.

[0038] (b4) The content of units derived from ethylene and α-olefins having 4 to 20 carbon atoms is 12.0 to 40.0% by weight. The content of units derived from ethylene and an α-olefin having 4 to 20 carbon atoms in the propylene-based thermoplastic elastomer (B) is 12.0 to 40.0% by weight. By setting the content of units derived from ethylene and an α-olefin having 4 to 20 carbon atoms within the above range, the flexibility of the heat seal layer is improved, and the heat seal strength, low-temperature heat sealability, transparency, impact resistance, puncture strength, tear strength, and low-temperature bag drop resistance can be improved. The content of units derived from ethylene and an α-olefin having 4 to 20 carbon atoms is preferably 13.0 to 40.0% by weight, more preferably 15.0 to 36.0% by weight. The content of units derived from ethylene in the propylene-based thermoplastic elastomer (B) is preferably 6.0 to 20.0% by weight, more preferably 8.0 to 18.0% by weight. The content of units derived from 1-butene in the propylene-based thermoplastic elastomer (B) is preferably 0 to 23.0% by weight, more preferably 0 to 18.0% by weight. The total content of units derived from ethylene and 1-butene in the propylene-based thermoplastic elastomer (B) is preferably 12.0 to 40.0% by weight, more preferably 13.0 to 40.0% by weight, and even more preferably 15.0 to 36.0% by weight.

[0039] Examples of the propylene-based thermoplastic elastomer (B) that can be used include the propylene-1-butene copolymers described in JP 2004-099909 A; the propylene-ethylene-1-butene copolymers described in JP 2004-315830 A, JP 2007-169666 A, and JP 2010-163626 A; and the propylene-α-olefin copolymers described in JP 2022-152305 A and JP 2022-152304 A.

[0040] (Method for calculating the content of units derived from ethylene and α-olefins having 4 to 20 carbon atoms) The content ratio of units derived from ethylene and an α-olefin having 4 to 20 carbon atoms in the propylene polymer (A) and the propylene thermoplastic elastomer (B) is 13 It can be calculated from the integrated intensity of the spectrum obtained by C-NMR measurement. For example, in the case of a propylene-ethylene-1-butene copolymer, the ethylene and 1-butene contents (wt%) can be calculated from the following (Equation 1) and (Equation 2), respectively. Ethylene content (mol%) = IE × 100 / (IE + IP + IB) Ethylene content (wt%) = [Ethylene content (mol%) × Molecular weight of ethylene] / [Ethylene content (mol%) × Molecular weight of ethylene + Propylene content (mol%) × Molecular weight of propylene + 1-butene content (mol%) × Molecular weight of 1-butene] (Equation 1) 1-Butene content (mol%) = IB × 100 / (IE + IP + IB) 1-butene content (wt%) = [1-butene content (mol%) × molecular weight of 1-butene] / [ethylene content (mol%) × molecular weight of ethylene + propylene content (mol%) × molecular weight of propylene + 1-butene content (mol%) × molecular weight of 1-butene] (Equation 2) where IE, IP, and IB are the integrated intensities of carbon derived from ethylene, propylene, and 1-butene, respectively.

[0041] [Other ingredients] The heat seal layer may contain other components within the range that does not impair the effects of the present invention. Such optional components include resins other than components (A) and (B), and antioxidants, ultraviolet absorbers, crystal nucleating agents, clarifying agents, lubricants, antiblocking agents, antistatic agents, antifogging agents, neutralizing agents, light stabilizers, metal deactivators, colorants, dispersants, peroxides, fillers, and fluorescent brighteners that are commonly used in polyolefin resin materials.

[0042] [Composition ratio of each ingredient] In the heat seal layer, the proportions of the components (A) and (B) relative to the total of the components (A) and (B) being 100% by weight are in the following ranges. The content of the propylene polymer (A) is 51 to 90% by weight, preferably 51 to 80% by weight, more preferably 51 to 70% by weight, and even more preferably 51 to 60% by weight. When the content of component (A) is 51% by weight or more, stickiness of the heat seal layer is suppressed and good moldability is achieved. On the other hand, when the content of component (A) is 90% by weight or less, the heat seal layer has flexibility, and the obtained laminate film has improved heat seal strength, low-temperature heat sealability, transparency, impact resistance, puncture strength, tear strength, and low-temperature bag drop resistance. The content of the propylene-based thermoplastic elastomer (B) is 10 to 49% by weight, preferably 20 to 49% by weight, more preferably 30 to 49% by weight, and even more preferably 40 to 49% by weight. When the content of component (B) is within the above range, the resulting laminated film has excellent heat seal strength, low-temperature heat sealability, transparency, impact resistance, puncture strength, tear strength, and low-temperature bag drop resistance.

[0043] The proportion of other components relative to the total of components (A) and (B) (100% by weight) is preferably 10% by weight or less, more preferably 0.1 to 9% by weight, and even more preferably 0.5 to 8% by weight.

[0044] [Method for producing heat seal layer] The heat-seal layer can be produced by a conventionally known method. For example, the raw resin is heated, melted, and kneaded in an extruder, and then extruded through a T-die into a film or sheet to obtain the heat-seal layer. The melt-kneaded raw resin may be processed into pellets or the like, and these may be extruded through a T-die into a film or sheet to obtain the heat-seal layer. The heat-seal layer may be subjected to corona treatment or the like.

[0045] <Base material layer> The substrate layer functions as a layer that provides the laminate film with a predetermined strength. The substrate layer is a stretched polypropylene film. By using a stretched polypropylene film for the substrate layer, the strength of the laminate film is improved, and in combination with the heat seal layer, it can be suitably used as a mono-material packaging material, and the laminate film can be made recyclable. The substrate layer may be a uniaxially stretched polypropylene film or a biaxially stretched polypropylene film, but from the viewpoint of versatility, a biaxially stretched polypropylene film is preferred.

[0046] Examples of polypropylene constituting the stretched polypropylene film include propylene homopolymer, random copolymer of propylene and ethylene or an α-olefin having 4 to 20 carbon atoms, and block copolymer of propylene and ethylene or an α-olefin having 4 to 20 carbon atoms. The stretched polypropylene film may be composed of one type of polypropylene, or may be composed of two or more types of polypropylene. From the viewpoint of the strength and secondary processability of the laminated film, the stretched polypropylene film preferably contains 80% by weight or more, more preferably 90% by weight or more, and even more preferably 95% by weight or more of units derived from propylene. The stretched polypropylene film is particularly preferably a propylene homopolymer.

[0047] The base layer may contain other components as long as the effects of the present invention are not impaired. Examples of such optional components include those exemplified as other components in the heat seal layer.

[0048] The unstretched polypropylene film can be produced by a conventionally known method, for example, by heating, melting, and kneading a raw material resin in an extruder, and then extruding the raw material resin into a film or sheet shape through a T-die to obtain the unstretched polypropylene film.

[0049] As the stretching method, a known method can be used, for example, a tubular method, a tenter type stretching method, a pantograph type batch stretching method, etc.

[0050] The stretching direction is not particularly limited, but is usually the longitudinal direction and / or the transverse direction. In the case of uniaxial stretching, either longitudinal uniaxial stretching or transverse uniaxial stretching may be used, and examples thereof include a method utilizing the difference in roll peripheral speed. The stretching temperature is preferably 90 to 140°C, more preferably 100 to 130°C. The stretching ratio is preferably 3 to 12 times, more preferably 4 to 12 times.

[0051] In the case of biaxial stretching, either sequential biaxial stretching or simultaneous biaxial stretching may be used. An example of the stretching method is a method in which a sheet obtained by a T-die method is roll-stretched 3.0 to 6.0 times in the machine direction (MD) and then stretched 8.0 to 12.0 times in the transverse direction (TD) by a tenter method. Another example of the stretching method is the so-called tubular stretching method, in which a tubular unstretched sheet obtained by air-cooling or water-cooling from a circular die is heated to below the melting temperature, and then stretched in a bubble shape with air to 3.0 to 7.0 times in the machine direction (MD) and 3.0 to 7.0 times in the transverse direction (TD). In the case of biaxial stretching, the stretching temperature is preferably 100 to 170°C, more preferably 110 to 160°C.

[0052] The stretched polypropylene film can be subjected to a surface treatment to improve printability, lamination properties, etc. Examples of the surface treatment method include corona discharge treatment, plasma treatment, flame treatment, acid treatment, etc., and there are no particular limitations. Corona discharge treatment, plasma treatment, or flame treatment is preferred because it allows continuous treatment and can be easily carried out before the winding step in the film production process.

[0053] <Laminated film> The laminated film includes a base layer and a heat seal layer. From the viewpoint of improving heat seal strength, low-temperature sealability, and resistance to bag drop at low temperatures, the ratios of the thickness of the base layer and the heat seal layer to the total thickness of the base layer and the heat seal layer are preferably 5 to 90% and 10 to 95%, respectively. The ratio of the thickness of the base layer to the total thickness of the base layer and the heat seal layer is more preferably 5 to 80%, and even more preferably 10 to 70%.The ratio of the thickness of the heat seal layer to the total thickness of the base layer and the heat seal layer is more preferably 20 to 95%, and even more preferably 30 to 90%.

[0054] The total thickness of the laminated film is preferably from 17 to 500 μm, more preferably from 35 to 200 μm, and even more preferably from 50 to 150 μm. The thickness of the heat seal layer is preferably 8 to 400 μm, more preferably 20 to 150 μm, and even more preferably 30 to 100 μm. The thickness of the substrate layer is preferably 9 to 475 μm, more preferably 15 to 80 μm, and even more preferably 20 to 70 μm.

[0055] [Physical properties of laminated film] The sealing temperature at which the laminated film reaches a heat seal strength of 10 N / 15 mm, measured under the following conditions, is preferably less than 120°C, more preferably 80°C to 119°C, and even more preferably 90°C to 118°C. Setting the sealing temperature below 120°C improves low-temperature sealability. As a result, it is possible to increase production speed by shortening the sealing time and lower the temperature setting of the seal bar, which makes it less likely for the laminated film to shrink during bonding and improves secondary processability. The sealing temperature can be achieved by changing the type and blending ratio of the resins constituting the heat seal layer, changing the type of resin in the base layer, or adjusting the thickness ratio of the base layer and the heat seal layer. <Measurement of the sealing temperature at which the heat seal strength reaches 10N / 15mm> After storing the laminated film at an ambient temperature of 23°C for 7 days, it was cut into strips measuring 180 mm (MD) x 80 mm (TD), folded in half in the MD so that the heat-sealable layers were in contact with each other, and heat-sealed at a width of 10 mm at a position 20-30 mm from the fold under the following sealing conditions. The resulting partially heat-sealed sample was cut into strips with a width of 15 mm in the TD to obtain test pieces. The resulting test pieces were pulled at both ends in a 180° peel direction using a Schopper-type tensile tester at a rate of 500 mm / min, and the maximum force required to peel the heat-sealed portions was measured and used as the heat-seal strength. Sealing conditions: Sealing pressure: 2.0 kg / cm 2 (0.196 MPa), sealing time: 1.0 second, sealing temperature: 90°C to 170°C in 10°C increments. In the seal curve obtained from the seal temperature and heat seal strength, the data between any two points measured at 10°C intervals is approximated with a linear function to determine the seal temperature at which the heat seal strength reaches 10N / 15mm.

[0056] The laminate film preferably has a haze of less than 10% as measured in accordance with JIS K 7136:2000. By making the haze less than 10%, the transparency of the laminate film can be improved. The haze is more preferably 0.5 to 9%, and even more preferably 1 to 8%. If the haze is less than 0.5%, the unevenness of the laminate film surface will be small, which may cause excessive adhesion between films (blocking), resulting in poor secondary processability.

[0057] The laminated film preferably has a puncture strength measured in accordance with JIS Z 1707:2019 of 10 N or more, more preferably 11 N or more, and even more preferably 12 N or more. The upper limit of the puncture strength is not particularly limited, but is usually 20 N or less. If the puncture strength is less than 10 N, cracks may occur in the laminated film and the bag may break during secondary processing or distribution in the market.

[0058] In a bag drop impact test measured under the following conditions, the average number of times the laminate film breaks after being dropped is preferably 6 or more, more preferably 10 or more, and even more preferably 20 or more. The average number of times the bag breaks after being dropped is rounded down to an integer. <Dropped bag impact test> Two 120mm x 150mm sheets are cut from the laminated film, and the heat-sealed layers of each sheet are overlapped. Then, three sides are sealed using an impulse sealer under the following sealing conditions to create a 120mm x 150mm sample bag. 100ml of water is poured into the sample bag, and the open side is sealed using an impulse sealer under the following sealing conditions to create a water seal test piece. After storing the water seal test piece in a 0°C atmosphere for one day, it is dropped 50 times consecutively from a height of 1.5m onto a metal plate. The maximum number of times the bag does not break is recorded as the number of bag breakage drops. The test is repeated five times, and the average number of bag breakage drops is calculated. The sealing conditions are as follows: a Fuji Impulse poly sealer (product name: PC-300), seal width: 2 mm, scale: 10 (sealing time: 1.6 seconds).

[0059] As shown in the examples, in a laminated film, it is preferable that the maximum heat seal strength (a) (unit: N / 15 mm), the impact strength of the heat seal layer (b) (unit: kJ / m), and the sealing temperature at which the heat seal strength reaches 10 N / 15 mm (hereinafter also referred to as the heat seal initiation temperature (c)) (unit: °C) satisfy the following (Equation 3): a × b / c ≧7 (Formula-3) The present inventors have found that by satisfying formula 3, the laminated film can achieve excellent bag drop resistance at low temperatures. That is, the bag drop resistance at low temperatures is correlated with the product of the maximum heat seal strength (a) and the impact strength (b) of the heat seal layer, which in turn has a certain relationship with the heat seal initiation temperature (c).

[0060] <Laminated film manufacturing method> The method for bonding the substrate layer and the heat-sealing layer is not particularly limited, and a conventionally known method can be used. For example, the substrate layer and the heat-sealing layer can be bonded by providing an adhesive layer by an extrusion method, a dry lamination method, or the like. Among these, the dry lamination method is preferred from the viewpoints of obtaining high adhesive strength, fast processing speed, and high productivity. That is, another aspect of the present invention is a method for producing a laminated film, which includes a step of bonding the substrate layer and the heat-sealing layer by a dry lamination method.

[0061] In the dry lamination method, an adhesive may be applied to a substrate layer and then a heat seal layer may be laminated thereto, or an adhesive may be applied to a heat seal layer and then a substrate layer may be laminated thereto. The adhesive may be produced from an adhesive composition prepared by mixing a first composition containing a base agent and a solvent with a second composition containing a curing agent and a solvent. Specifically, the adhesive includes a cured product produced by reaction of the base agent and the curing agent in the adhesive composition.

[0062] An example of an adhesive is polyurethane. Polyurethane is a cured product of a polyol and an isocyanate compound produced by reacting a polyol as a base material with an isocyanate compound as a curing agent. Examples of polyurethane include polyether polyurethane and polyester polyurethane. Polyether polyurethane is a cured product produced by reacting a polyether polyol as a base material with an isocyanate compound as a curing agent. Polyester polyurethane is a cured product produced by reacting a polyester polyol as a base material with an isocyanate compound as a curing agent. Examples of isocyanate compounds that can be used include aromatic isocyanate compounds such as tolylene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), and xylylene diisocyanate (XDI); aliphatic isocyanate compounds such as hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI); and adducts or polymers of the above-mentioned various isocyanate compounds.

[0063] The thickness of the adhesive layer is not particularly limited, but is preferably in the range of 0.01 to 5 μm, more preferably in the range of 0.03 to 3 μm, and particularly preferably in the range of 0.05 to 2 μm. When the thickness of the adhesive layer is equal to or greater than the above lower limit, more sufficient interlayer adhesive strength can be obtained.

[0064] <Applications of laminated film> The laminated film has excellent sealing strength and resistance to bag drop at low temperatures, making it suitable for use as a food packaging film, a heavy-duty packaging film, and a liquid packaging film, particularly as a rice bag or for individual packaging of frozen foods.

[0065] <Sealant film> Another aspect of the present invention is an unstretched sealant film comprising a propylene polymer (A) satisfying the above requirements (a1) to (a4) and a propylene thermoplastic elastomer (B) satisfying the above requirements (b1) to (b4), wherein the proportions of components (A) and (B) relative to 100% by weight of the total of components (A) and (B) are 51 to 90% by weight and 10 to 49% by weight, respectively. Yet another aspect of the present invention is the unstretched sealant film for laminating to at least one surface of a stretched polypropylene film. The requirements (a1) to (a4), the requirements (b1) to (b4), and the blending ratios of each component, including preferred ranges, are as described above. The unstretched sealant film can be suitably used as a heat seal layer of a laminated film.

[0066] From the viewpoint of resistance to bag drop, the thickness of the sealant film is preferably 8 to 400 μm, more preferably 20 to 150 μm, and even more preferably 30 to 100 μm.

[0067] [Sealant film properties] The sealant film preferably has a haze of less than 10% as measured in accordance with JIS K 7136:2000. By setting the haze to less than 10%, the transparency of the sealant film can be improved. The haze is more preferably 0.5 to 9%, and even more preferably 1 to 8%. If the haze is less than 0.5%, the unevenness of the sealant film surface will be small, which may cause excessive adhesion between films (blocking), resulting in poor secondary processability.

[0068] The impact strength of the sealant film measured under the following conditions is preferably 35 kJ / m or more, more preferably 40 kJ / m or more, and even more preferably 45 kJ / m or more. The upper limit of the impact strength is not particularly limited, but is usually 100 kJ / m or less. <Impact resistance> After storing the sealant film at an ambient temperature of 23°C for 24 hours, the film is fixed to a circular holder with a diameter of 50 mm and struck with a hemispherical metal penetrator with a diameter of 25.4 mm in a device conforming to JIS P 8134:1998 under the same atmosphere to measure the work (J) required for penetration and destruction. The work obtained is divided by the film thickness to obtain the impact strength.

[0069] [How to make sealant film] The sealant film can be produced by a conventionally known method. For example, a raw resin is heated, melted, and kneaded in an extruder, and then extruded through a T-die into a film or sheet to obtain a sealant film. The melt-kneaded raw resin may be processed into pellets or the like, and these may be extruded through a T-die into a film or sheet to obtain a sealant film. One or both sides of the sealant film may be subjected to a corona treatment or the like. [Example]

[0070] The present invention will be described in detail below using examples, but the present invention is not limited to these examples. The raw materials used in the examples and the evaluation methods of the obtained films are as follows.

[0071] 1. Evaluation Method (1) MFR The MFR of components (A) and (B) was measured in accordance with JIS K 7210-1:2014 (230°C, 2.16 kg load).

[0072] (2) Melting point (Tm) For component (A), a differential scanning calorimeter (DSC) was used. A 5.0 mg sample was heated to 200°C, held at 200°C for 5 minutes, and then cooled to 40°C at a rate of 10°C / min. The sample was then heated at a rate of 10°C / min, and the top temperature of the endothermic peak was taken as the melting point (Tm).

[0073] (3) Flexural modulus For components (A) and (B), injection-molded test specimens measuring 4.0 mm thick, 10.0 mm wide, and 80 mm long were prepared. Dumbbell-shaped tensile test specimens (Type A) were molded using a Toshiba Machine IS80G injection molding machine at a molding temperature of 200°C and a mold temperature of 40°C. The flexural modulus of the test specimens thus obtained was measured in accordance with JIS K 7171:2022 (ISO178) at a test speed of 2 mm / min.

[0074] (4) Ethylene and 1-butene content The ethylene and 1-butene contents in components (A) and (B) are 13 The sample preparation and NMR measurement conditions were as follows: 200 mg of component (A) or (B) was dissolved in an NMR sample tube with an inner diameter of 10 mm together with 2.4 ml of o-dichlorobenzene / deuterated bromide benzene (C6D5Br) = 4 / 1 (volume ratio) and hexamethyldisiloxane as a chemical shift reference substance. NMR measurements were performed using a Bruker Biospin AV400 NMR instrument equipped with a 10 mm diameter cryoprobe. 13 The C-NMR measurement was performed at a sample temperature of 120°C, a pulse angle of 90°, a pulse interval of 15 seconds, and an accumulation count of 512. The ethylene content (wt%) and 1-butene content (wt%) of components (A) and (B) are 13 The integrated intensities of the spectra obtained by C-NMR measurement were used to calculate the values ​​using the following (Equation 1) and (Equation 2), respectively. Ethylene content (mol%) = IE × 100 / (IE + IP + IB) Ethylene content (wt%) = [Ethylene content (mol%) × Molecular weight of ethylene] / [Ethylene content (mol%) × Molecular weight of ethylene + Propylene content (mol%) × Molecular weight of propylene + 1-butene content (mol%) × Molecular weight of 1-butene] (Equation 1) 1-Butene content (mol%) = IB × 100 / (IE + IP + IB) 1-butene content (wt%) = [1-butene content (mol%) × molecular weight of 1-butene] / [ethylene content (mol%) × molecular weight of ethylene + propylene content (mol%) × molecular weight of propylene + 1-butene content (mol%) × molecular weight of 1-butene] (Equation 2) where IE, IP, and IB are the integrated intensities of carbon derived from ethylene, propylene, and 1-butene, respectively.

[0075] (5) Transparency (unit: %) The haze of the unstretched sealant films and laminate films obtained in the examples and comparative examples was measured in accordance with JIS K 7136: 2000. A haze of less than 10% was determined to be excellent in transparency.

[0076] (6) Tensile modulus (unit: MPa) The tensile modulus (Young's modulus) of the unstretched sealant films obtained in the Examples and Comparative Examples was measured in the machine direction (MD) and transverse direction (TD) according to JIS K 7127:1999 under the following conditions. Sample shape: Strip Sample length: 150mm Sample width: 15mm Chuck distance: 100mm Crosshead speed: 1mm / min

[0077] (7) Impact resistance (unit: kJ / m) The unstretched sealant films obtained in the examples and comparative examples were stored for 24 hours at an ambient temperature of 23°C. Then, under the same ambient conditions, the film was fixed to a circular holder with a diameter of 50 mm using an apparatus conforming to JIS P 8134:1998, and struck with a hemispherical metal penetrator with a diameter of 25.4 mm to measure the work (J) required for penetration and destruction. This was divided by the film thickness to determine the impact strength. An impact strength of 40 kJ / m or more was considered to be excellent in impact resistance.

[0078] (8) Tear strength (unit: N / mm) The tear strength in the transverse direction (TD) of the unstretched sealant films obtained in the Examples and Comparative Examples was measured using an Elmendorf tear strength meter manufactured by Toyo Seiki Seisakusho Co., Ltd. in accordance with JIS K 7128-2:1998.

[0079] (9) Piercing strength (unit: N) For the laminated films obtained in the examples and comparative examples, a test specimen was fixed and pierced with a semicircular needle having a diameter of 1.0 mm and a tip radius of 0.5 mm at a rate of 50±5 mm per minute in accordance with JIS Z 1707:2019, and the maximum stress until the needle penetrated was measured and recorded as the puncture strength (N). A puncture strength of 10 N or more was determined to be excellent.

[0080] (10) Maximum heat seal strength (unit: N / 15 mm) The laminated films obtained in the Examples and Comparative Examples were stored at an ambient temperature of 23°C for 7 days, then cut into strips measuring 180 mm (MD) x 80 mm (TD). The strips were folded in half along the MD so that the sealant film sides were in contact with each other, and heat-sealed at a position 20-30 mm from the fold line over a 10 mm width under the following sealing conditions. The resulting partially heat-sealed samples were cut into strips with a TD width of 15 mm to obtain test pieces. The resulting test pieces were pulled at both ends in a 180° peel direction at a rate of 500 mm / min using a Shopper-type tensile tester (manufactured by Tester Sangyo Co., Ltd.), and the maximum force required to peel the heat-sealed portions was measured and recorded as the heat seal strength. The sealing conditions are: sealing pressure: 2.0 kg / cm 2 (0.196 MPa), sealing time: 1.0 second, sealing temperature: in the range of 90°C to 170°C in 10°C increments. After obtaining a seal curve from the sealing temperature and heat seal strength, the average value of the heat seal strength between 140°C and 170°C was taken as the maximum heat seal strength. A maximum heat seal strength of 25N / 15mm or more was determined to be excellent in heat seal strength.

[0081] (11) Heat seal initiation temperature (unit: °C) In the seal curve obtained by the method for obtaining the maximum heat seal strength in the range of 90°C to 170°C, the data between any two points measured at 10°C intervals was approximated by a linear function, and the seal temperature at which the heat seal strength reached 10 N / 15 mm was determined to be the heat seal initiation temperature. The lower this temperature, the faster the heat seal strength rises, and the better the low-temperature heat sealability of the film can be said to be. A heat seal initiation temperature of less than 120°C was determined to have excellent low-temperature heat sealability.

[0082] (12) Drop-bag impact test (drop-bag resistance at low temperatures) Two 120mm x 150mm sheets were cut from the laminated film obtained in the examples and comparative examples. The sealant film sides of each sheet were then overlapped, and three sides were sealed using an impulse sealer under the following sealing conditions to create a 120mm x 150mm sample bag with a 116mm opening. 100mL of water was poured into the opening of the sample bag, and one side of the opening was sealed using an impulse sealer under the following sealing conditions to create a water seal test piece. After storing the water seal test piece in an atmosphere at 0°C for one day, it was dropped 50 times consecutively onto a metal plate from a height of 1.5m. The maximum number of times the bag did not break was recorded as the bag breakage drop count. The test was repeated five times, and the average number of bag breakage drop counts was calculated. The average number of bag breakage drop counts was rounded down to an integer, and this was used as an index of bag drop resistance at low temperatures. The sealing conditions were a Fuji Impulse poly sealer (product name: PC-300) with a seal width of 2 mm and a scale of 10 (sealing time: 1.6 seconds). Bags that broke and fell 20 times or more on average were judged to have excellent resistance to bag breakage.

[0083] 2.Raw materials [Propylene polymer (A)] A-1: Novatec (registered trademark) FX4GF (propylene-ethylene-1-butene copolymer produced by Ziegler-Natta catalyst), manufactured by Japan Polypropylene Corporation MFR=5.0 g / 10 min, Tm=126°C, flexural modulus=650 MPa, propylene content=89.2 wt%, ethylene content=2.8 wt%, 1-butene content=8.0 wt% A-2: Wintec (registered trademark) WFX4M (propylene-ethylene copolymer produced by metallocene catalyst), manufactured by Japan Polypropylene Corporation MFR=7.0 g / 10 min, Tm=125°C, flexural modulus=750 MPa, propylene content=96.9 wt%, ethylene content=3.1 wt%

[0084] [Propylene-based thermoplastic elastomer (B)] B-1: Vistamaxx (registered trademark) VM6102 (propylene-ethylene copolymer), manufactured by ExxonMobil Corporation MFR = 3 g / 10 min, flexural modulus = 14 MPa, propylene content = 84 wt%, ethylene content = 16 wt% B-2: Mitsui Chemicals, Inc., trade name: Tafmer (registered trademark) PN2070 [propylene-ethylene-1-butene copolymer] MFR=7 g / 10 min, flexural modulus=14 MPa, propylene content=74.1 wt%, ethylene content=9.4 wt%, 1-butene content=16.5 wt% B-3: ExxonMobil Corporation, trade name: Vistamaxx (registered trademark) VM3000 [propylene-ethylene copolymer] MFR=8g / 10min, flexural modulus=40MPa, propylene content=89% by weight, ethylene content=11% by weight

[0085] [Base material layer] Biaxially oriented polypropylene film (Futamura Chemical Co., Ltd., product type: FOR, thickness 20 μm, one side corona treated)

[0086] [Example 1] 90% by weight of the propylene polymer (A-1) and 10% by weight of the propylene thermoplastic elastomer (B-1) were thoroughly mixed in a blender, and then melt-extruded at 230°C to form pellets. The resulting pellets were melt-extruded through a T-die attached to an extruder with a 35 mm diameter at a resin temperature of 240°C and a width of 320 mm to form a film, which was then corona-treated on one side to produce an unstretched sealant film with a thickness of 50 μm. Next, a solution of a 1:1 mixture of a urethane adhesive (Unoflex (registered trademark) J-24, manufactured by Sanyo Chemical Industries, Ltd.) and a diluent (NC401 solvent C, manufactured by Toyo Ink Co., Ltd.) was applied to the corona-treated surface of the biaxially oriented polypropylene film using the dry lamination method, and dried to form an adhesive layer. This was then bonded to the corona-treated surface of the sealant film to obtain a laminated film. The sealant film was measured for haze, tensile modulus, impact strength, and tear strength. The laminated film was also evaluated for haze, puncture strength, maximum heat seal strength, heat seal initiation temperature, and low-temperature bag drop resistance. The composition and evaluation results of the sealant film in Example 1 and the evaluation results of the laminated film are shown in Table 1.

[0087] [Example 2] Except for using 80% by weight of the propylene polymer (A-1) and 20% by weight of the propylene thermoplastic elastomer (B-1), an unstretched sealant film and a laminate film were obtained in the same manner as in Example 1. The composition and evaluation results of the sealant film of Example 2 and the evaluation results of the laminate film are shown in Table 1.

[0088] [Example 3] Except for using 60% by weight of the propylene polymer (A-1) and 40% by weight of the propylene thermoplastic elastomer (B-1), an unstretched sealant film and a laminate film were obtained in the same manner as in Example 1. The composition and evaluation results of the sealant film of Example 3 and the evaluation results of the laminate film are shown in Table 1.

[0089] [Example 4] An unstretched sealant film and a laminate film were obtained in the same manner as in Example 1, except that the propylene polymer (A-1) was 60% by weight and the propylene thermoplastic elastomer (B-2) was 40% by weight. The composition and evaluation results of the sealant film of Example 4 and the evaluation results of the laminate film are shown in Table 1.

[0090] [Example 5] An unstretched sealant film and a laminate film were obtained in the same manner as in Example 1, except that the propylene polymer (A-2) was 60% by weight and the propylene thermoplastic elastomer (B-1) was 40% by weight. The composition and evaluation results of the sealant film of Example 5 and the evaluation results of the laminate film are shown in Table 1.

[0091] [Comparative Example 1] Except for using 100% by weight of the propylene polymer (A-1), an unstretched sealant film and a laminate film were obtained in the same manner as in Example 1. The composition and evaluation results of the sealant film of Comparative Example 1 and the evaluation results of the laminate film are shown in Table 1.

[0092] Comparative Example 2 Except for using 95% by weight of the propylene polymer (A-1) and 5% by weight of the propylene thermoplastic elastomer (B-1), an unstretched sealant film and a laminate film were obtained in the same manner as in Example 1. The composition and evaluation results of the sealant film of Comparative Example 2 and the evaluation results of the laminate film are shown in Table 1.

[0093] Comparative Example 3 Except for using 60% by weight of the propylene polymer (A-1) and 40% by weight of the propylene thermoplastic elastomer (B-3), an unstretched sealant film and a laminate film were obtained in the same manner as in Example 1. The composition and evaluation results of the sealant film of Comparative Example 3 and the evaluation results of the laminate film are shown in Table 1.

[0094] [Table 1]

[0095] As is clear from Table 1, the laminated films of Examples 1 to 5 had a heat seal initiation temperature of less than 120°C, and were excellent in low-temperature heat sealability. They also had excellent bag drop resistance at low temperatures while maintaining maximum heat seal strength, transparency, and puncture strength. On the other hand, Comparative Example 1, in which the sealant film did not contain the propylene-based thermoplastic elastomer (B), and Comparative Example 2, in which the sealant film contained 5% by weight of the propylene-based thermoplastic elastomer (B), had insufficient flexibility in the heat seal layer and were inferior in low-temperature heat sealability, maximum heat seal strength, and drop resistance at low temperatures. Furthermore, Comparative Example 3, in which the flexural modulus of the propylene-based thermoplastic elastomer in the sealant film exceeded 35 MPa, was inferior in drop resistance at low temperatures.

[0096] The laminated films of the examples have maximum heat seal strength (a) (unit: N / 15 mm), impact strength of the sealant film (b) (unit: kJ / m), and heat seal initiation temperature (c) (unit: °C) that satisfy the following (Equation-3). a × b / c ≧ 7 (Formula-3) The laminated films of the examples have excellent resistance to bag drop at low temperatures. As a result, it is clear that in order to improve resistance to bag drop, it is important for the laminated film to satisfy the above formula (3). [Industrial Applicability]

[0097] The laminated film can be suitably used as a packaging film for general foods, frozen foods, heavy goods, and liquids.

Claims

1. A laminated film comprising a substrate layer and a heat seal layer, The substrate layer is a stretched polypropylene film, The heat seal layer comprises a propylene polymer (A) that satisfies the following requirements (a1) to (a4), and a propylene thermoplastic elastomer (B) that satisfies the following requirements (b1) to (b4); the proportions of the components (A) and (B) relative to 100% by weight of the total of the components (A) and (B) are 51 to 90% by weight and 10 to 49% by weight, respectively. (a1) The MFR measured in accordance with JIS K 7210-1:2014 (230°C, 2.16 kg load) is 1 to 50 g / 10 min. (a2) The flexural modulus measured in accordance with JIS K 7171:2022 at a test speed of 2 mm / min is greater than 100 MPa and not greater than 1,000 MPa. (a3) The content of units derived from propylene is more than 88.0% by weight and not more than 99.9% by weight. (a4) The content of units derived from ethylene and α-olefins having 4 to 20 carbon atoms is 0.1% by weight or more and less than 12.0% by weight. (b1) The MFR measured in accordance with JIS K 7210-1:2014 (230°C, 2.16 kg load) is 1 to 30 g / 10 min. (b2) The flexural modulus measured in accordance with JIS K 7171:2022 at a test speed of 2 mm / min is 5 to 35 MPa. (b3) The content of units derived from propylene is 60.0 to 88.0% by weight. (b4) The content of units derived from ethylene and an α-olefin having 4 to 20 carbon atoms is 12.0 to 40.0% by weight.

2. 2. The laminated film according to claim 1, wherein the component (A) is a propylene-ethylene copolymer or a propylene-ethylene-1-butene copolymer that satisfies the following requirement (a5): (a5) The melting point is 110 to 155°C.

3. 2. The laminated film according to claim 1, wherein the ratios of the thickness of the substrate layer and the thickness of the heat seal layer to the total thickness of the substrate layer and the heat seal layer are 5 to 90% and 10 to 95%, respectively.

4. 2. The laminated film according to claim 1, wherein the sealing temperature at which the heat seal strength reaches 10 N / 15 mm as measured under the following conditions is less than 120°C. <Measurement of the sealing temperature at which the heat seal strength reaches 10 N / 15 mm> After storing the laminated film at an ambient temperature of 23°C for 7 days, it was cut into strips measuring 180 mm (MD) x 80 mm (TD), folded in half in the MD so that the heat-sealable layers were in contact with each other, and heat-sealed at a position 20-30 mm from the fold, over a 10 mm width, under the following sealing conditions. The resulting partially heat-sealed sample was cut into strips with a 15 mm width in the TD to obtain test pieces. The resulting test pieces were pulled at both ends in a 180° peel direction using a Schopper-type tensile tester at a rate of 500 mm / min, and the maximum force required to peel the heat-sealed portions was measured and used as the heat-seal strength. The sealing conditions were: sealing pressure: 2.0 kg / cm ２ (0.196 MPa), sealing time: 1.0 second, sealing temperature: in the range of 90°C to 170°C in 10°C increments. In the seal curve obtained from the seal temperature and heat seal strength, the data between any two points measured at 10°C intervals is approximated by a linear function to determine the seal temperature at which the heat seal strength reaches 10 N / 15 mm.

5. 2. The laminated film according to claim 1, which has a haze of less than 10% as measured in accordance with JIS K 7136:2000.

6. The laminate film according to claim 1, having a puncture strength of 10 N or more measured in accordance with JIS Z 1707:2019.

7. 2. The laminated film according to claim 1, wherein the average number of times the bag breaks when dropped is six or more times in a bag drop impact test measured under the following conditions. <Dropped bag impact test> Two 120 mm x 150 mm sheets were cut from the laminated film, and the heat-sealed layers of each sheet were then overlapped. Three sides were sealed using an impulse sealer under the following sealing conditions to prepare a 120 mm x 150 mm sample bag. 100 ml of water was poured into the sample bag, and the open side was sealed using an impulse sealer under the following sealing conditions to prepare a water-sealing test piece. After storing the water-sealing test piece in an atmosphere at 0°C for one day, it was dropped 50 times consecutively onto a metal plate from a height of 1.5 m. The maximum number of times the bag did not break was recorded as the number of bag-breaking drops. The test was repeated five times, and the average number of bag-breaking drops was calculated. The sealing conditions were as follows: a poly sealer (trade name: PC-300) manufactured by Fuji Impulse Co., Ltd., seal width: 2 mm, scale: 10 (sealing time: 1.6 seconds).

8. A food packaging film comprising the laminate film according to any one of claims 1 to 7.

9. A film for packaging heavy goods, comprising the laminate film according to any one of claims 1 to 7.

10. A liquid packaging film comprising the laminated film according to any one of claims 1 to 7.

11. The method for producing the laminated film according to any one of claims 1 to 7, comprising a step of bonding the substrate layer and the heat seal layer by dry lamination.

12. An unstretched sealant film comprising a propylene polymer (A) that satisfies the following requirements (a1) to (a4), and a propylene thermoplastic elastomer (B) that satisfies the following requirements (b1) to (b4), A sealant film, wherein the proportions of components (A) and (B) relative to the total of components (A) and (B) (100% by weight) are 51 to 90% by weight and 10 to 49% by weight, respectively. (a1) The MFR measured in accordance with JIS K 7210-1:2014 (230°C, 2.16 kg load) is 1 to 50 g / 10 min. (a2) The flexural modulus measured in accordance with JIS K 7171:2022 at a test speed of 2 mm / min is greater than 100 MPa and not greater than 1,000 MPa. (a3) The content of units derived from propylene is more than 88.0% by weight and not more than 99.9% by weight. (a4) The content of units derived from ethylene and α-olefins having 4 to 20 carbon atoms is 0.1% by weight or more and less than 12.0% by weight. (b1) The MFR measured in accordance with JIS K 7210-1:2014 (230°C, 2.16 kg load) is 1 to 30 g / 10 min. (b2) The flexural modulus measured in accordance with JIS K 7171:2022 at a test speed of 2 mm / min is 5 to 35 MPa. (b3) The content of units derived from propylene is 60.0 to 88.0% by weight. (b4) The content of units derived from ethylene and an α-olefin having 4 to 20 carbon atoms is 12.0 to 40.0% by weight.

13. 13. The unstretched sealant film of claim 12 for laminating to at least one surface of an oriented polypropylene film.

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