Unstretched polyolefin film and method for producing the same

Abstract

The objective is to provide an unoriented polyolefin film containing recycled materials that exhibits excellent optical properties such as transparency, gloss, and image clarity, as well as high impact strength and excellent high-speed film formation capabilities. [Solution] An unstretched polyolefin film in which an outermost layer (A), at least one intermediate layer (B), and an outermost layer (C) which is a sealing layer are laminated in this order, wherein the outermost layer (A) contains a polypropylene resin (a) polymerized with a homogeneous catalyst, the outermost layer (C) contains a polypropylene resin (c) polymerized with a homogeneous catalyst, the intermediate layer (B) contains an ethylene-α-olefin copolymer (b1) polymerized with a homogeneous catalyst, an ethylene-α-olefin copolymer (b2) polymerized with a heterogeneous catalyst, and recycled raw materials (b3), wherein the recycled raw materials (b3) each contain recycled polypropylene resin (a), polypropylene resin (c), ethylene-α-olefin copolymer (b1), and ethylene-α-olefin copolymer (b2).

Description

[Technical Field]

[0001] The present invention relates to an unoriented polyolefin film and a method for producing the same. [Background technology]

[0002] Polyolefin films are known as packaging materials for various products, including everyday goods such as textiles and clothing, food packaging, and industrial parts packaging. Furthermore, unoriented polyolefin films are widely used as such packaging materials due to their good transparency and excellent mechanical suitability for processes such as bag making.

[0003] Patent Document 1 discloses an invention relating to a multilayer film that is an unoriented polypropylene film with excellent optical properties, blocking resistance, and low-temperature heat sealability, having an outermost laminate layer, at least one intermediate layer, and another outermost heat seal layer, wherein the intermediate layer contains long-chain branched LLDPE with a molecular weight distribution (Mw / Mn) of 7.5 to 15.0 and a number of branches of 8 or more carbon atoms of 1.5 to 5.0 per 1000 carbon atoms. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 6457402 [Overview of the project] [Problems that the invention aims to solve]

[0005] In recent years, the use of plant-derived and recycled materials has been explored from the perspective of reducing fossil plastics. The inventors considered using recycled raw materials obtained by recycling the unoriented polypropylene film described in Patent Document 1. However, it was found that when this recycled raw material was used as part of the raw materials for forming the intermediate layer described in Patent Document 1 to manufacture an unoriented polypropylene film, a problem arose in which the optical properties of the film, such as image clarity, deteriorated.

[0006] Therefore, the object of the present invention is to provide an unoriented polyolefin film containing recycled materials that has excellent optical properties such as transparency, gloss, and image clarity, high impact strength, and excellent high-speed film formation properties. [Means for solving the problem]

[0007] The inventors of this invention have conducted extensive research to achieve the above objective, An unoriented polyolefin film in which the outermost layer (A), at least one intermediate layer (B), and an outermost layer (C) which is a sealing layer are laminated in this order, The outermost layer (A) contains a polypropylene resin (a) polymerized with a homogeneous catalyst, The outermost layer (C) contains a polypropylene resin (c) polymerized with a homogeneous catalyst, The intermediate layer (B) comprises an ethylene-α-olefin copolymer (b1) polymerized with a homogeneous catalyst, an ethylene-α-olefin copolymer (b2) polymerized with a heterogeneous catalyst, and recycled raw materials (b3). The present invention was completed by finding that the above problems can be solved by an unstretched polyolefin film in which the recycled raw material (b3) contains the recycled polypropylene resin (a), the polypropylene resin (c), the ethylene-α-olefin copolymer (b1), and the ethylene-α-olefin copolymer (b2), respectively.

[0008] The gist of this invention is as follows: [1] to [7]. [1] An unoriented polyolefin film in which an outermost layer (A), at least one intermediate layer (B), and an outermost layer (C) which is a sealing layer are laminated in this order, The outermost layer (A) contains a polypropylene resin (a) polymerized with a homogeneous catalyst, The outermost layer (C) contains a polypropylene resin (c) polymerized with a homogeneous catalyst, The intermediate layer (B) comprises an ethylene-α-olefin copolymer (b1) polymerized with a homogeneous catalyst, an ethylene-α-olefin copolymer (b2) polymerized with a heterogeneous catalyst, and recycled raw materials (b3). The recycled raw material (b3) is an unstretched polyolefin film containing the recycled polypropylene resin (a), the polypropylene resin (c), the ethylene-α-olefin copolymer (b1), and the ethylene-α-olefin copolymer (b2), respectively. [2] The unstretched polyolefin film according to [1] above, wherein the α-olefin in the ethylene-α-olefin copolymer (b1) and the ethylene-α-olefin copolymer (b2) is an α-olefin having 8 or fewer carbon atoms. [3] The unstretched polyolefin film according to [1] or [2] above, wherein one or both of the ethylene-α-olefin copolymer (b1) and the ethylene-α-olefin copolymer (b2) contain a plant-derived resin. [4] The unstretched polyolefin film according to any one of [1] to [3] above, wherein the recycled material (b3) is a post-industrial recycled material and / or a post-consumer recycled material. [5] A bag made by cutting and sealing or heat sealing an unstretched polyolefin film as described in any of [1] to [4] above. [6] A method for producing an unoriented polyolefin film in which an outermost layer (A), at least one intermediate layer (B), and an outermost layer (C) which is a sealing layer are laminated in this order, The outermost layer (A) contains a polypropylene resin (a) polymerized with a homogeneous catalyst, The outermost layer (C) contains a polypropylene resin (c) polymerized with a homogeneous catalyst, The intermediate layer (B) comprises an ethylene-α-olefin copolymer (b1) polymerized with a homogeneous catalyst, an ethylene-α-olefin copolymer (b2) polymerized with a heterogeneous catalyst, and recycled raw materials (b3). The recycled raw material (b3) contains, respectively, the recycled polypropylene resin (a), the polypropylene resin (c), the ethylene-α-olefin copolymer (b1), and the ethylene-α-olefin copolymer (b2). A method for producing an unstretched polyolefin film, comprising the step of melt-kneading the ethylene-α-olefin copolymer (b1), the ethylene-α-olefin copolymer (b2), and the recycled raw material (b3) to form the intermediate layer (B). [7] The manufacturing method according to [6] above, comprising the step of co-extruding the outermost layer (A), the intermediate layer (B), and the outermost layer (C) and laminating them by extrusion lamination or dry lamination. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an unoriented polyolefin film containing recycled materials that has excellent optical properties such as transparency, gloss, and image clarity, high impact strength, and excellent high-speed film formation properties. [Modes for carrying out the invention]

[0010] [Unstretched polyolefin film] The unoriented polyolefin film of the present invention is an unoriented polyolefin film in which the outermost layer (A), at least one intermediate layer (B), and an outermost sealing layer (C) are laminated in this order. Note that the unoriented polyolefin film may also be simply referred to as "film."

[0011] <Outermost layer (A), (C)> The unstretched polyolefin film of the present invention comprises an outermost layer (A) and an outermost layer (C). The outermost layer (A) and the outermost layer (C) are the layers that constitute both surfaces of the unstretched polyolefin film.

[0012] The outermost layer (A) contains a polypropylene-based resin (a) polymerized with a homogeneous catalyst. Thereby, the optical properties such as the transparency, glossiness, and image sharpness of the film are improved. Although the reason for this is not clear, the polypropylene-based resin (a) polymerized with the homogeneous catalyst contained in the outermost layer is excellent in compatibility with the ethylene-α-olefin copolymer (b1) polymerized with the homogeneous catalyst contained in the intermediate layer. Therefore, it is considered that the optical fluctuation at the interface between the outermost layer and the intermediate layer is unlikely to occur.

[0013] Here, the homogeneous catalyst is a catalyst with uniform active sites, also called a single-site catalyst, and typically means a metallocene catalyst. The metallocene catalyst is a catalyst containing a transition metal compound (metallocene compound) composed of a ligand having a cyclopentadienyl skeleton and a transition metal. Examples of the transition metal include titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, and tungsten. Preferably, they are titanium, zirconium, and hafnium, and particularly preferably zirconium. In addition to the metallocene compound, the metallocene catalyst may contain a cocatalyst and an organoaluminum compound. The cocatalyst has a function of reacting with the metallocene compound to activate it to a stable ionic state.

[0014] In this specification, the polypropylene-based resin is a polymer having a propylene monomer as the main monomer, preferably a polymer containing 50 mol% or more, more preferably 70 mol% or more of the propylene monomer. Examples of polypropylene resins (a) include propylene homopolymers and propylene copolymers which are copolymers of propylene and comonomers. Preferred comonomers include ethylene and α-olefins, specifically ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, and 4-methyl-1-pentene, and one or more selected from these can be used. As for the polypropylene resin (a), it is preferable to use a propylene copolymer because it has good transparency and makes it easy to process the film into a packaging body. In particular, at least one selected from the group consisting of propylene-ethylene copolymer and propylene-ethylene-butene-1 copolymer is preferred, with propylene-ethylene copolymer being preferred. The copolymer may be either a random copolymer or a block copolymer. For example, the propylene-ethylene copolymer may be either a propylene-ethylene random copolymer (random PP) or a propylene-ethylene block copolymer (block PP), but the propylene-ethylene random copolymer (random PP) is preferred.

[0015] In propylene copolymers, the amount of comonomer is not particularly limited, but from the viewpoint of achieving a good balance of transparency, heat resistance, and heat sealability, it is preferably 0.5 to 10% by mass, and more preferably 1.0 to 5.0% by mass. Here, the amount of comonomer refers to the amount of ethylene in the case of propylene-ethylene copolymer, and the total amount of ethylene and 1-butene in the case of propylene-ethylene-butene-1 copolymer. In this specification, the amount of comonomer in the copolymer is: 13 This can be determined by 13C-NMR measurement.

[0016] Since the polypropylene resin (a) is polymerized with a homogeneous catalyst, its molecular weight distribution (Mw / Mn) is relatively narrow. The molecular weight distribution (Mw / Mn) of the polypropylene resin (a) is, for example, 2.0 to 5.0, preferably 2.5 to 3.5. This range of molecular weight distribution improves the optical properties of the film, such as transparency and image sharpness. In this specification, the molecular weight distribution (Mw / Mn) is defined as the value measured by gel permeation chromatography (GPC). Specifically, the molecular weight distribution (Mw / Mn) is the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) measured by gel permeation chromatography (GPC). The number-average molecular weight (Mn) and weight-average molecular weight (Mw) are values ​​on a polystyrene basis.

[0017] The melting point of the polypropylene resin (a) is not particularly limited, but is preferably 115 to 155°C, and more preferably 120 to 140°C, from the viewpoint of achieving a good balance of transparency, heat resistance, and heat sealability. The melting point refers to the peak top temperature of the maximum endothermic peak in the differential scanning calorimeter (DSC) chart. Details of the method for measuring the melting point are described in the examples. Furthermore, the melt flow rate (MFR) of the polypropylene resin (a) is not particularly limited, but from the viewpoint of improving film-forming properties, it is preferably 1 to 15 g / 10 min, and more preferably 4 to 10 g / 10 min. The MFR of the polypropylene resin was measured at 230°C with a load of 2.16 kg in accordance with JIS K 7210.

[0018] Polypropylene resin (a) may be used alone or in combination of two or more types. The content of polypropylene resin (a) in the outermost layer (A) is, for example, 50% by mass or more, preferably 70% by mass or more, and more preferably 90% by mass or more.

[0019] The outermost layer (C) of the unoriented polyolefin film of the present invention is a sealing layer when the unoriented polyolefin film is made into a bag by heat sealing or other processes. The outermost layer (C) contains a polypropylene resin (c) polymerized with a homogeneous catalyst. This improves the optical properties of the film, such as transparency (haze) and image sharpness. The polypropylene resin (c) can be the same as the polypropylene resin (a) described above. In other words, the polypropylene resin (c) can be any type described above as polypropylene resin (a) without any particular limitations. The molecular weight distribution (Mw / Mn), melting point, and melt flow rate (MFR) of the polypropylene resin (c) are within the range described above as polypropylene resin (a), and the preferred range is also the same.

[0020] Polypropylene resin (c) may be used alone or in combination of two or more types. The content of polypropylene resin (c) in the outermost layer (C) is, for example, 50% by mass or more, preferably 70% by mass or more, and more preferably 90% by mass or more.

[0021] The outermost layer (A) and the outermost layer (C) mainly consist of the polypropylene resin (a) and polypropylene resin (c) described above, respectively, but may also contain other resins. Examples of other resins include polypropylene resin polymerized with a heterogeneous catalyst, polyethylene resin, polystyrene resin, ethylene-vinyl acetate copolymer, and petroleum resin. The content of other resins in each of the outermost layers (A) and (C) is preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 10% by mass or less.

[0022] The outermost layer (A) and the outermost layer (C) may contain additives, either one or both. Examples of additives include slip agents and antiblocking agents. While not particularly limited, examples of slip agents include higher fatty acid amides such as erucic acid amide, oleic acid amide, stearic acid amide, behenic acid amide, ethylenebisstearoamide, N-stearylerucic acid amide, and N,N'-ethylenebisoleic acid amide. The antiblocking agent is not particularly limited as long as it is used in general polyolefin films, but examples include inorganic fillers and organic fillers, and inorganic fillers are preferred because they are thermally and chemically stable. Among these inorganic fillers, talc, calcium carbonate, barium sulfate, silica, and aluminosilicates are preferably used.

[0023] In addition to the slip agents and antiblocking agents mentioned above, other additives such as antioxidants, antifogging agents, crystallization nucleating agents, chlorine scavengers, and antistatic agents may also be used.

[0024] The thickness of the outermost layer (A) and the outermost layer (C) is not particularly limited, but from the viewpoint of sealing properties, ease of opening, and heat resistance, it is preferably 1.5 to 20 μm, more preferably 2 to 15 μm, and even more preferably 4 to 12 μm. The thicknesses of the outermost layer (A) and the outermost layer (C) may be the same or different.

[0025] <Middle layer (B)> The intermediate layer (B) contains an ethylene-α-olefin copolymer (b1) polymerized with a homogeneous catalyst, an ethylene-α-olefin copolymer (b2) polymerized with a heterogeneous catalyst, and recycled raw materials (b3). The recycled raw materials (b3) contain recycled polypropylene resin (a), recycled polypropylene resin (c), recycled ethylene-α-olefin copolymer (b1), and recycled ethylene-α-olefin copolymer (b2).

[0026] The intermediate layer (B) contains both an ethylene-α-olefin copolymer (b1) polymerized with a homogeneous catalyst and an ethylene-α-olefin copolymer (b2) polymerized with a heterogeneous catalyst, resulting in an unoriented polyolefin film with excellent high-speed film formation during film manufacturing and high impact strength.

[0027] Furthermore, the intermediate layer (B) contains recycled material (b3). By including recycled material (b3), the amount of fossil plastic used can be reduced, and an unstretched polyolefin film with reduced environmental impact can be obtained. Furthermore, in the present invention, the intermediate layer (B) contains, together with the recycled raw material (b3), an ethylene-α-olefin copolymer (b1) polymerized with a homogeneous catalyst as described above, and an ethylene-α-olefin copolymer (b2) polymerized with a heterogeneous catalyst. The ethylene-α-olefin copolymer (b1) and the ethylene-α-olefin copolymer (b2) polymerized with a heterogeneous catalyst have better compatibility with polypropylene resins contained in the recycled raw material compared to low-density polyethylene (LDPE) and the like. Therefore, it is possible to obtain an unoriented polyolefin film with good optical properties such as transparency and image sharpness.

[0028] <Ethylene-α-olefin copolymer (b1)> Ethylene-α-olefin copolymer (b1) is a linear low-density polyethylene (LLDPE) obtained by polymerizing ethylene and α-olefin using a homogeneous catalyst. In the ethylene-α-olefin copolymer (b1), the α-olefin is preferably one having 8 or fewer carbon atoms, from the viewpoint of improving the optical properties of the film. Examples of α-olefins having 8 or fewer carbon atoms include propylene, butene-1, hexene-1, octen-1, and 4-methyl-1-pentene, with hexene-1 being the most preferred. The α-olefin content in the ethylene-α-olefin copolymer (b1) is not particularly limited, but is, for example, 1 to 15% by mass, and preferably 2 to 10% by mass.

[0029] The ethylene-α-olefin copolymer (b1) preferably does not have long-chain branching. Here, "not having long-chain branching" means that 13 This means that the number of branches with 8 or more carbon atoms, as measured by 13C-NMR, is less than 1.5 per 1000 carbon atoms. By using an ethylene-α-olefin copolymer (b1) that does not have long-chain branching, compatibility with polypropylene resins contained in recycled raw materials is improved, and the deterioration of optical properties can be suppressed. Whether or not a molecule has branches with eight or more carbon atoms can be determined by focusing on the second methylene carbon from the end of the branch and examining its chemical shift. For information on measuring the number of branches with eight or more carbon atoms, please refer to the details in Japanese Patent No. 6457402.

[0030] Since the ethylene-α-olefin copolymer (b1) is polymerized with a homogeneous catalyst, its molecular weight distribution (Mw / Mn) is relatively narrow, and the molecular weight distribution (Mw / Mn) of the ethylene-α-olefin copolymer (b1) is, for example, 2.0 to 6.0, preferably 4.0 to 5.5. This range of molecular weight distribution improves the optical properties of the film, such as transparency (haze) and image sharpness.

[0031] The density of the ethylene-α-olefin copolymer (b1) can be adjusted as appropriate from the viewpoint of the mechanical strength and flexibility of the film, preferably 0.890 g / cm³. 3 More than 0.960g / cm 3 The following, and more preferably 0.910 g / cm³ 3 More than 0.940g / cm 3 The following applies:

[0032] The MFR of the ethylene-α-olefin copolymer (b1) is preferably 1 g / 10 min to 10 g / 10 min, and more preferably 2 g / 10 min to 6 g / 10 min. When the MFR of the ethylene-α-olefin copolymer (b1) is within this range, film formation can be carried out stably. The MFR of the ethylene-α-olefin copolymer was measured at 190°C with a load of 2.16 kg in accordance with JIS K 7210.

[0033] <Ethylene-α-olefin copolymer (b2)> Ethylene-α-olefin copolymer (b2) is a linear low-density polyethylene (LLDPE) obtained by polymerizing ethylene and α-olefin using a heterogeneous catalyst. Here, a heterogeneous catalyst is a catalyst in which the properties of the active sites are heterogeneous, and the so-called Ziegler-Natta catalyst falls under the category of heterogeneous catalysts. The Ziegler-Natta catalyst is a commonly used catalyst in the production of polyolefin resins and generally contains titanium compounds and organoaluminum compounds that have titanium-halogen bonds.

[0034] In the ethylene-α-olefin copolymer (b2), the α-olefin is preferably one having 8 or fewer carbon atoms, from the viewpoint of improving the optical properties of the film. Examples of α-olefins having 8 or fewer carbon atoms include propylene, butene-1, hexene-1, octen-1, and 4-methyl-1-pentene, with hexene-1 being the most preferred. The α-olefin content in the ethylene-α-olefin copolymer (b2) is not particularly limited, but is, for example, 1 to 15% by mass, and preferably 2 to 10% by mass.

[0035] The ethylene-α-olefin copolymer (b2) preferably does not have long-chain branching. Here, "not having long-chain branching" means that 13 This means that the number of branches with 8 or more carbon atoms, as measured by 13C-NMR, is less than 1.5 per 1000 carbon atoms. By using an ethylene-α-olefin copolymer (b2) that does not have long-chain branching, the deterioration of optical properties can be suppressed.

[0036] The molecular weight distribution (Mw / Mn) of the ethylene-α-olefin copolymer (b2) is, for example, from 4.0 to 10.0, preferably from 6.0 to 8.0. Being within such a range of molecular weight distribution improves the high-speed film-forming property during film production.

[0037] The density of the ethylene-α-olefin copolymer (b2) may be appropriately adjusted from the viewpoints of the mechanical strength and flexibility of the film, and is preferably 0.890 g / cm 3 or more and 0.960 g / cm 3 or less, more preferably 0.900 g / cm 3 or more and 0.930 g / cm 3 or less.

[0038] The MFR of the ethylene-α-olefin copolymer (b2) is preferably 0.5 g / 10 min or more and 10 g / 10 min or less, more preferably 1 g / 10 min or more and 5 g / 10 min or less, and even more preferably 1 g / 10 min or more and 3 g / 10 min or less. When the MFR of the ethylene-α-olefin copolymer (b2) is within such a range, film formation of the film can be carried out stably.

[0039] The ethylene-α-olefin copolymer (b1) may be a petroleum-derived resin, a plant-derived resin, or may contain both a petroleum-derived resin and a plant-derived resin. The ethylene-α-olefin copolymer (b2) may be a petroleum-derived resin, a plant-derived resin, or may contain both a petroleum-derived resin and a plant-derived resin. One or both of the ethylene-α-olefin copolymer (b1) and the ethylene-α-olefin copolymer (b2) preferably contain a plant-derived resin. In other words, it is preferable that at least a part or all of the ethylene-α-olefin copolymer (b1) is a plant-derived resin (that is, a plant-derived polyethylene resin). Further, it is preferable that at least a part or all of the ethylene-α-olefin copolymer (b2) is a plant-derived resin (that is, a plant-derived polyethylene resin).

[0040] By using plant-derived resins, petroleum consumption and CO2 emissions can be reduced, thereby suppressing the environmental impact. As described above, the unoriented polyolefin film of the present invention contains recycled materials in the intermediate layer, so by using recycled materials and plant-derived resins, an unoriented polyolefin film with a highly reduced environmental impact can be obtained.

[0041] Plant-derived resins are polymers of monomer components that include plant-derived monomers. Examples of plant-derived monomers include plant-derived ethylene monomers. From the viewpoint of reducing environmental impact, the biomass content of plant-derived resins is preferably 60% or more, and more preferably 80% or more.

[0042] Plant-derived resins contain a certain concentration of C14 because C14 is present in the atmosphere at a constant concentration. However, petroleum trapped underground contains almost no C14. Therefore, by measuring the concentration of C14 using accelerator mass spectrometry, the proportion of plant-derived raw materials (biomass content) in the resin can be determined.

[0043] For example, the concentration of C14 in a resin can be measured as follows: The sample to be measured is burned to generate carbon dioxide, and the purified carbon dioxide is reduced with hydrogen using iron as a catalyst to purify graphite. This graphite is then mounted in a dedicated C14-AMS device (manufactured by NEC Corporation) based on a tandem accelerator to measure the count of C14, the concentration of C13 (C13 / C12), and the concentration of C14 (C14 / C12). From these measurements, the ratio of the C14 concentration of the sample carbon to the standard modern carbon is calculated. Oxalic acid (HOXII), provided by the National Institute of Standards and Technology (NIST), is used as the standard sample.

[0044] Plant-derived resins include polyolefin resins manufactured using a mass balance method certified by ISCC PLUS and other standards. While polyolefin resins allocated as biomass products using the mass balance method may not contain C14, they can contribute to reducing environmental impact when considering the entire process of manufacturing, using, and disposing of various products in the petrochemical industry.

[0045] Furthermore, when the intermediate layer contains a plant-derived resin, it is preferable to use a petroleum-derived resin in combination, preferably with an amorphous component content of 3.0% by mass or less, more preferably 1.5% by mass or less, as measured by the thermal elution fractionation method (TREF), from the viewpoint of reducing stickiness on the film surface. The petroleum-derived resin is preferably an ethylene-α-olefin copolymer polymerized with a homogeneous catalyst. In other words, in the intermediate layer, if the amount of amorphous components measured by the thermal elution fractionation method (TREF) of the ethylene-α-olefin copolymer (b1) polymerized with a homogeneous catalyst is preferably 3.0% by mass or less, more preferably 1.5% by mass or less, and the amount of amorphous components polymerized by the heterogeneous catalyst (b2) contains plant-derived polyethylene resin, then the resulting film has reduced environmental impact and suppressed surface stickiness, which is preferable. The method for measuring the amount of amorphous components by the thermal elution fractionation method (TREF) is as described in the examples.

[0046] <Recycled material (b3)> The recycled material (b3) contains recycled polypropylene resin (a), recycled polypropylene resin (c), recycled ethylene-α-olefin copolymer (b1), and recycled ethylene-α-olefin copolymer (b2). Recycled raw material (b3) is a raw material prepared by processing products molded into films, bottles, trays, etc., through recovery processes such as crushing and dissolution, and includes polypropylene resin (a), polypropylene resin (c), ethylene-α-olefin copolymer (b1), and ethylene-α-olefin copolymer (b2). In the recovery process, it is preferable to melt-knead and pelletize as needed. Therefore, recycled raw material (b3) can be said to be a raw material that has been subjected to more shear force and thermal history during processing compared to virgin raw material.

[0047] The recycled material (b3) is not particularly limited as long as it contains various recycled resins as described above [(a), (c), (b1), (b2)], but it is preferable to use (i) or (ii) below as the recycled material (b3). (i) In the unoriented polyolefin film of the present invention, a film is produced in which the intermediate layer (B) does not contain recycled raw materials (b3) (i.e., a film made only from virgin raw materials), and a portion of that film is recovered. (ii) A portion of the film recovered after manufacturing the unoriented polyolefin film of the present invention (i.e., one in which recycled materials are included in the intermediate layer (B)).

[0048] Furthermore, in the methods described in (i) and (ii) above, if the outermost layer (A) or (C) of the recovered unoriented polyolefin film contains the additives described above, the recycled raw material (b3) will also contain the additives. When an unoriented polyolefin film is manufactured using such recycled raw material (b3), the intermediate layer (B) will also contain the same type of additive as that used in the outermost layer (A) or (C).

[0049] Recycled materials (b3) may be post-industrial recycled materials, post-consumer recycled materials, or both. Post-industrial recycled materials are materials recovered from products generated during the manufacturing process before the product reaches the consumer, while post-consumer recycled materials are materials recovered from products after they have been used by the consumer.

[0050] Furthermore, when collecting used film to manufacture recycled raw materials (b3), if the film is a film that has undergone secondary processing, such as a film containing printing ink, adhesive, or a base film of a different material, or a film coated or vapor-deposited with a material that can impart functionality (e.g., barrier properties), it is preferable to deink it as appropriate before manufacturing the recycled raw materials. By deinking, substances that cause discoloration and fisheye in the film can be removed, and the unoriented polyolefin film of the present invention with good quality can be manufactured.

[0051] <Content of each component in the middle layer> The content of ethylene-α-olefin copolymer (b1) in the intermediate layer (B) is preferably 20 to 95 parts by mass, more preferably 40 to 90 parts by mass, and even more preferably 50 to 85 parts by mass, based on 100 parts by mass of the total of ethylene-α-olefin copolymer (b1) and ethylene-α-olefin copolymer (b2). The content of ethylene-α-olefin copolymer (b2) in the intermediate layer (B) is preferably 5 to 80 parts by mass, more preferably 10 to 60 parts by mass, and even more preferably 15 to 50 parts by mass, based on 100 parts by mass of the total of ethylene-α-olefin copolymer (b1) and ethylene-α-olefin copolymer (b2). By adjusting the content of ethylene-α-olefin copolymer (b1) and ethylene-α-olefin copolymer (b2) within the above range, it becomes easier to obtain an unoriented polyolefin film that exhibits excellent high-speed film formation during film manufacturing and high impact strength.

[0052] The content of recycled raw material (b3) in the intermediate layer (B) is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 50 parts by mass or more, and preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and even more preferably 120 parts by mass or less, based on 100 parts by mass of the total of ethylene-α-olefin copolymer (b1) and ethylene-α-olefin copolymer (b2). Setting the recycled material (b3) content above the lower limit makes it easier to obtain an unoriented polyolefin film with reduced environmental impact. Setting the recycled material (b3) content below the upper limit makes it easier to obtain an unoriented polyolefin film with good optical properties such as transparency and image clarity.

[0053] The total amount of ethylene-α-olefin copolymer (b1), ethylene-α-olefin copolymer (b2), and recycled raw material (b3) in the intermediate layer is preferably 90% by mass or more, and more preferably 95% by mass or more.

[0054] The intermediate layer (B) may contain other resins other than the ethylene-α-olefin copolymer (b1), ethylene-α-olefin copolymer (b2), and recycled material (b3) described above, as long as they do not impede the effects of the present invention. Examples of other resins include polystyrene resin, ethylene-vinyl acetate copolymer, and petroleum resin. The content of other resins in the intermediate layer is preferably 10% by mass or less, and more preferably 5% by mass or less.

[0055] The intermediate layer may contain additives, such as antioxidants, anti-fogging agents, crystallization nucleating agents, chlorine scavenging agents, antistatic agents, slip agents, and antiblocking agents.

[0056] The thickness of the intermediate layer (B) is not particularly limited, but from the viewpoint of increasing the flexibility of the film while ensuring appropriate mechanical strength when used as a packaging material, it is preferably 10 to 100 μm, more preferably 11 to 40 μm, and even more preferably 12 to 25 μm. Furthermore, from the viewpoint of making the film of the present invention easy to open when used as packaging, it is also preferable to reduce the thickness of the intermediate layer (B) to a certain extent to lower its tear strength. Lowering the tear strength makes the film easier to shred, thus making it easier to obtain recycled materials.

[0057] The unoriented polyolefin film of the present invention may have at least one intermediate layer (B) between the outermost layer (A) and the outermost layer (C). It may also have two or more intermediate layers (B) between the outermost layer (A) and the outermost layer (C), but from the viewpoint of ease of manufacture and cost, it is preferable to have one intermediate layer (B) between the outermost layer (A) and the outermost layer (C).

[0058] <Film properties> The unoriented polyolefin film of the present invention preferably has a haze of 4% or less. By reducing the haze to 4% or less, the transparency of the film is increased, and when the film is used as packaging, the visibility of the contents is improved. From this viewpoint, the haze of the film is preferably 3.5% or less. The lower limit of the haze is not particularly limited, but it is preferably 1.0% or more. When the haze is above the above lower limit, the film surface has a certain degree of unevenness, which makes it easier to suppress blocking of the film. Haze can be measured by the method described in the examples.

[0059] The unoriented polyolefin film of the present invention preferably has an image clarity of 70% or higher. An image clarity of 70% or higher allows for clear and distinct identification of the contents when the film is used as packaging. From this viewpoint, the image clarity of the film is preferably 80% or higher. While there is no particular upper limit to the image clarity, it is typically 95% or lower. Image clarity can be measured by the method described in the examples.

[0060] The unoriented polyolefin film of the present invention preferably has a surface gloss of 135% or higher. A gloss of 135% or higher enhances its aesthetic appeal. From this viewpoint, the surface gloss of the film is preferably 137% or higher. There is no particular upper limit to the gloss, but it is preferably 150% or lower. When the gloss is below the above upper limit, the film surface has a certain degree of unevenness, which makes it easier to suppress film blocking. It is preferable that the glossiness of at least one surface of the unoriented polyolefin film is within the above range, and it is more preferable that the glossiness of both surfaces is within the above range. The gloss level can be measured by the method described in the examples.

[0061] The unstretched polyolefin film of the present invention preferably has an impact strength of 0.4 J or higher. An impact strength of 0.4 J or higher increases the impact resistance of the film, making it easier to prevent the bags from tearing during transportation after processing. From this viewpoint, the impact strength of the film is preferably 0.5 J or higher, and more preferably 0.6 J or higher. There is no particular upper limit to the impact strength, but it is preferably 2.5 J or lower. An impact strength of 2.5 J or lower makes it easier to crush the film when obtaining recycled material. The impact strength can be measured by the method described in the examples.

[0062] The unoriented polyolefin film of the present invention preferably has a tear strength of 1.0 N or less. A tear strength of 1.0 N or less makes it easier to open bags after the film has been processed into bags and sealed. Furthermore, a low tear strength makes it easier to crush the film when obtaining recycled raw materials. From this viewpoint, the tear strength of the film is preferably 0.8 N or less, and more preferably 0.6 N or less. The lower limit of the tear strength is not particularly limited, but it is preferably 0.05 N or more from the viewpoint of ensuring a certain degree of airtightness. The tear strength is measured with respect to the MD direction of the film. The MD direction refers to the flow direction during film manufacturing. The tear strength can be measured by the method described in the examples.

[0063] <Method for manufacturing unoriented polyolefin film> The method for producing the unoriented polyolefin film of the present invention is not particularly limited. Here, "unoriented" means that the film is produced by a method that does not involve stretching in the manufacturing process, and "substantially without stretching" means that it is produced without going through an explicit stretching step. Therefore, it is permissible for some orientation to occur in the extrusion direction when an extrusion process under commonly used conditions is employed. As a method for producing the unoriented polyolefin film of the present invention, methods such as extrusion and casting can be appropriately employed, but production by extrusion is preferred. As the die in the extrusion method, T-dies, annular dies, etc., can be used, but from the viewpoint of precisely controlling the thickness of the layer and obtaining excellent optical properties, it is preferable to use a T-die.

[0064] The process for producing the unoriented polyolefin film of the present invention includes a step of molding an intermediate layer (B). The intermediate layer (B) is formed by melt-kneading an ethylene-α-olefin copolymer (b1), the ethylene-α-olefin copolymer (b2), and the recycled raw material (b3) using an extruder or the like.

[0065] As described above, it is preferable to use either (i) or (ii) below as the recycled raw material (b3) used in the production of the intermediate layer (B). (i) In the unoriented polyolefin film of the present invention, a film is produced in which the intermediate layer (B) does not contain recycled raw materials (b3) (i.e., a film made only from virgin raw materials), and a portion of that film is recovered. (ii) A portion of the film recovered after manufacturing the unoriented polyolefin film of the present invention (i.e., one in which recycled materials are included in the intermediate layer (B)).

[0066] Here, the recovery in (i) and (ii) above includes, for example, a step of crushing the film, and after crushing, it is preferably pelletized. The fact that the recycled raw material (b3) used in the production of the intermediate layer (B) is in pellet form improves handling and simplifies manufacturing.

[0067] The unoriented polyolefin film of the present invention has a multilayer structure consisting of at least three layers: an outermost layer (A), at least one intermediate layer (B), and an outermost layer (C) which is a sealing layer. When multilayering the film, it is preferable to include a step of laminating each layer by co-extrusion such as the multi-manifold method or feed-block method, extrusion lamination, or dry lamination.

[0068] Furthermore, in the co-extrusion method, each resin composition for forming the outermost layer (A), intermediate layer (B), and outermost layer (C) is melted, and the molten resin compositions are extruded from separate extruders to dies to form an unstretched polyolefin film precursor. Preferably, the film precursor is sequentially cooled by one or more cooling rolls to form an unstretched multilayer film.

[0069] <bag> A bag (packaging) made of unoriented polyolefin film can be obtained by molding the unoriented polyolefin film obtained as described above into a bag shape with an opening, with the outermost layer (C) facing inward. Specifically, the unoriented polyolefin film can be folded to an appropriate size with the outermost layer (C) facing inward, and the ends can be heat-sealed or cut and sealed to form a bag shape. In this case, a laminate can be prepared by laminating a base film such as a biaxially oriented polypropylene film or polyethylene terephthalate film (PET film) to the outermost layer (A) of an unoriented polyolefin film. The outermost layer (C) of the laminate can then be folded to an appropriate size with the outermost layer (C) facing inward, and the ends can be heat-sealed or cut to form a bag.

[0070] In the heat sealing process, the heat sealing temperature is preferably set to a temperature at which the outermost layers (C) can be heat-pressed together, for example, around 100 to 200°C. The heat sealing pressure can be, for example, around 0.1 to 1.0 MPa, and the heat sealing time can be, for example, around 0.1 to 5.0 seconds. The heat-sealing process can be carried out using a commercially available side welder (heat-sealing machine) by a known method. For the heat-sealing conditions, the temperature of the sealing blade should be, for example, 200 to 400°C, and the bag-making speed should be, for example, 60 to 400 shots / minute.

[0071] The bursting strength of a bag formed from an unstretched polyolefin film is preferably 16 kPa or higher, and more preferably 20 kPa or higher. The upper limit of the bursting strength is not particularly limited, but for example, it is 40 kPa or lower. The bursting strength can be measured by preparing a sealed package from an unstretched polyolefin film as described in the examples, and then measuring it using the method described in the examples.

[0072] As described above, the resulting bags can be used as packaging for contents such as food, daily necessities, and textiles. [Examples]

[0073] The present invention will be described in more detail below, but the present invention is not limited to these embodiments.

[0074] [evaluation] <Melting point> Approximately 4 mg of the sample was accurately weighed and sealed in an aluminum pan. This pan was then mounted on a differential scanning calorimeter (PerkinElmer, Inc., model "DSC8500AS") and heated to 230°C in a nitrogen stream of 20 mL / min. The sample was held at this temperature for 5 minutes, and then cooled to -10°C at a rate of 10°C / min. After cooling to -10°C, the melting point was defined as the peak temperature showing maximum endothermic reaction in the endothermic curve obtained when the sample was heated to 230°C at a rate of 10°C / min.

[0075] <Melt Flow Rate (MFR)> Measurements were taken in accordance with JIS K 7210 under a load of 2.16 kg. The measurement temperature was 230°C for polypropylene resins and 190°C for ethylene-α-olefin copolymers.

[0076] <Biomass content> The concentration of C14 was determined by the method described in the specification.

[0077] <Amount of amorphous component> The amount of amorphous components is the weight percentage of the fraction that elutes during the period when the column temperature is maintained at 0°C after the start of solvent supply, in a temperature-controlled elution fractionation method under the following conditions. Measuring device: Manufactured by Senshu Scientific Co., Ltd., model number "TREF device special type" Column: Inner diameter 10mm x 300mm Filler: Chromosolve P NAW (manufactured by GL Sciences Co., Ltd., 30 / 60 mesh) Sample solution concentration: 5 mg / mL Sample solution injection volume: 2 mL Solvent: Orthodichlorobenzene Flow rate: 1mL / min Sample injection temperature: 140℃ Cooling rate: 5℃ / h Cooling temperature reached: 0℃ Maintenance time at the target temperature: 30 minutes Heating rate: 5°C / h Detector: Infrared detector Measurement wavenumber: 3.42 μm

[0078] For each example and comparative example, the unoriented polyolefin film was measured for environmental suitability, high-speed film formation, haze, gloss, image clarity, impact strength, and tear strength as follows. In addition, sealed packaging was prepared using each example and comparative example's unoriented polyolefin film, and the burst strength of the bags was measured.

[0079] <Environmental suitability> Unoriented polyolefin films containing plant-derived resins were evaluated as "○" for reducing environmental impact, while unoriented polyolefin films not containing plant-derived resins were evaluated as "×" for not reducing environmental impact.

[0080] <High-speed film forming performance> In each example and comparative example, the thickness variation was observed when the film formation speed for producing unstretched polyolefin films was set to 200 m / min. ○...The film did not break, and the thickness and thinness accuracy was also good. △The film did not break, but a thickness variation of more than ±10% occurred relative to the standard thickness. ×...The film broke.

[0081] <Hayes> Haze was measured using a haze meter (model number: NDH5000) manufactured by Nippon Denshoku Industries Co., Ltd., in accordance with JIS K 7136.

[0082] <Glossiness> A gloss meter (model number: UGV-5D) manufactured by Suga Test Instruments Co., Ltd. was used to measure gloss (%) in accordance with JIS K 7105. This gloss evaluation was performed on both the outermost layer (A) and the outermost layer (B) of the multilayer film.

[0083] <Image sharpness (image quality)> Using a Suga Test Instruments Co., Ltd. image clarity measuring instrument (model number: ICM-1DP), the image clarity (%) was measured in accordance with JIS K 7105, with the slit width of the optical comb set to 0.125 mm.

[0084] <Impact strength> The impact strength was measured using a film impact tester manufactured by Toyo Seiki Seisakusho Co., Ltd. under the following conditions. Specimen dimensions: 120mm x 120mm Measurement temperature: 0°C ambient temperature

[0085] <Tear strength (Elmendorf method)> Measurements were performed at 23°C using an Elmendorf tear tester manufactured by Toyo Seiki Seisakusho Co., Ltd., in accordance with JIS K 7128-2. The measurement direction was the same as the flow direction during film processing.

[0086] <Bag burst strength> For the sealed packaging prepared as described below, 1.0 L / min of air was injected into the sealed packaging using a burst strength measuring instrument (305-BP) manufactured by Sun Science Co., Ltd., and the maximum pressure at which it burst was measured. (Preparation of sealed packaging) As a base film, the corona discharge treated surface of a biaxially oriented polypropylene film (product name "PA20", thickness 20 μm) manufactured by RM Tohcello Co., Ltd. and the corona discharge treated surface (outermost layer (A)) of the unoriented polyolefin film obtained in each example and comparative example were bonded together with a urethane adhesive to obtain a laminate. Next, using a vertical pillow packaging machine (manufactured by Tokyo Automatic Machinery Works Co., Ltd., model name "TWX1N"), the outermost layers (C) of the laminate were heat-sealed together under the conditions of a heat seal width of 15 mm, a heat seal temperature of 140°C, a time of 0.6 seconds, and a pressure of 0.5 MPa (bag making conditions: A), thereby obtaining a sealed package in pillow packaging with dimensions of 200 mm in length and 130 mm in width.

[0087] Table 1 shows the details of the resins used in each example and comparative example. In the table, PP represents "polypropylene resin", LLDPE represents "linear low-density polyethylene", LDPE represents "low-density polyethylene", C2 represents "ethylene", C3 represents "propylene", C4 represents "butene", and C6 represents "hexene".

[0088] [Example 1] (Production of recycled materials) Recycled raw materials were prepared using the following method. A T-die type film manufacturing apparatus with a three-layer configuration was used, consisting of a total of three extruders: one single-screw extruder with a screw diameter of 75 mm for the intermediate layer (B) and two single-screw extruders with a screw diameter of 50 mm for the outermost layers (outermost layer (A) and outermost layer (C)). Then, according to the composition shown in "Virgin Raw Material Blending Amount" in Table 2, 80 parts by mass of LLDPE polymerized with a homogeneous catalyst and 20 parts by mass of LLDPE polymerized with a heterogeneous catalyst were supplied to the extruder for the intermediate layer (B), PP polymerized with a homogeneous catalyst was supplied to the extruder for the outermost layer (A), and PP polymerized with a homogeneous catalyst was supplied to the extruder for the outermost layer (C). All were extruded from the T-die under conditions of a resin temperature of 250°C, a residence time of 1 minute, and a T-die temperature of 240°C, and passed through a cooling roll at 25°C to obtain a three-layer multilayer film. Next, corona discharge treatment was applied to the outermost layer (A) of this multilayer film so that the wetting tension of the surface was 42 mN / m, and then aged at 40°C for 24 hours to obtain an unoriented polyolefin film made only from virgin raw materials. The unoriented polyolefin film made only from virgin raw materials was crushed in a pulverizer and then formed into pellets using a single-screw extruder with a screw diameter of 50 mm to create recycled raw materials.

[0089] (Preparation of unstretched polyolefin film containing recycled materials in the intermediate layer) Unstretched polyolefin films were manufactured using the following method. A T-die type film manufacturing apparatus with a three-layer configuration was used, consisting of a total of three extruders: one single-screw extruder with a screw diameter of 75 mm for the intermediate layer (B) and two single-screw extruders with a screw diameter of 50 mm for the outer layers (outermost layer (A) and outermost layer (C)). The films were manufactured according to the composition shown in Table 2 for the virgin raw material content and the recycled raw material content for the intermediate layer, as follows. 80 parts by mass of LLDPE polymerized with a homogeneous catalyst, 20 parts by mass of LLDPE polymerized with a heterogeneous catalyst, and 40 parts by mass of recycled material were supplied to the extruder for the intermediate layer (B). Polypropylene resin polymerized with a homogeneous catalyst was supplied to the extruder for the outermost layer (A), and polypropylene resin polymerized with a homogeneous catalyst was supplied to the extruder for the outermost layer (C). Both were extruded from the T-die under conditions of a resin temperature of 250°C, a residence time of 1 minute, and a T-die temperature of 240°C, and passed through a cooling roll at 25°C to obtain a three-layer unoriented polyolefin film. The obtained unoriented polyolefin film was subjected to the evaluations described above.

[0090] [Examples 2-11, Comparative Examples 1-4] Except for changing the type and amount of resin according to the virgin raw material content and intermediate layer recycled raw material content shown in Table 2, an unstretched polyolefin film containing recycled raw materials in the intermediate layer was obtained, as described in Example 1.

[0091] [Table 1]

[0092] [Table 2] The recycled material content in the intermediate layer in Table 2 is shown as parts by mass relative to 100 parts by mass of virgin material in the intermediate layer.

[0093] Each of the examples of the present invention that satisfies the requirements of this invention contains recycled materials in the intermediate layer, thus effectively utilizing fossil plastics. Furthermore, the unoriented polyolefin films of each example, while containing recycled materials, exhibited excellent optical properties such as haze, gloss, and image clarity, as well as high impact strength and excellent high-speed film formation capabilities. In addition, the unoriented polyolefin films of each example contained plant-derived polyethylene resin, making them environmentally friendly.

[0094] On the other hand, each comparative example is an unstretched polyolefin film that contains recycled materials in the intermediate layer but does not satisfy the requirements of the present invention. Comparative Example 1 did not use an ethylene-α-olefin copolymer polymerized with a heterogeneous catalyst in the intermediate layer, and therefore had poor high-speed film formation. Comparative Example 2 was an example in which a homogeneous PP was not used in the outermost layer, and had poor gloss and image clarity. Comparative Example 3 did not contain an ethylene-α-olefin copolymer polymerized with a heterogeneous catalyst in the intermediate layer, but contained long-chain branched LLDPE, and had poor image clarity. Comparative Example 4 did not contain an ethylene-α-olefin copolymer polymerized with a heterogeneous catalyst in the intermediate layer, but contained LDPE, and had poor image clarity.

Claims

1. An unoriented polyolefin film in which an outermost layer (A), at least one intermediate layer (B), and an outermost layer (C) which is a sealing layer are laminated in this order, The outermost layer (A) contains a polypropylene resin (a) polymerized with a homogeneous catalyst, The outermost layer (C) contains a polypropylene resin (c) polymerized with a homogeneous catalyst, The intermediate layer (B) comprises an ethylene-α-olefin copolymer (b1) polymerized with a homogeneous catalyst, an ethylene-α-olefin copolymer (b2) polymerized with a heterogeneous catalyst, and recycled raw materials (b3). The recycled material (b3) is an unstretched polyolefin film containing the recycled polypropylene resin (a), the polypropylene resin (c), the ethylene-α-olefin copolymer (b1), and the ethylene-α-olefin copolymer (b2), respectively.

2. The unstretched polyolefin film according to claim 1, wherein the α-olefin in the ethylene-α-olefin copolymer (b1) and the ethylene-α-olefin copolymer (b2) is an α-olefin having 8 or fewer carbon atoms.

3. The unstretched polyolefin film according to claim 1, wherein one or both of the ethylene-α-olefin copolymer (b1) and the ethylene-α-olefin copolymer (b2) contain a plant-derived resin.

4. The unstretched polyolefin film according to claim 1, wherein the recycled material (b3) is a post-industrial recycled material and / or a post-consumer recycled material.

5. A bag made by heat-sealing or cutting a non-stretched polyolefin film according to any one of claims 1 to 4.

6. A method for manufacturing an unoriented polyolefin film in which an outermost layer (A), at least one intermediate layer (B), and an outermost layer (C) which is a sealing layer are laminated in this order, The outermost layer (A) contains a polypropylene resin (a) polymerized with a homogeneous catalyst, The outermost layer (C) contains a polypropylene resin (c) polymerized with a homogeneous catalyst, The intermediate layer (B) comprises an ethylene-α-olefin copolymer (b1) polymerized with a homogeneous catalyst, an ethylene-α-olefin copolymer (b2) polymerized with a heterogeneous catalyst, and recycled raw materials (b3). The recycled material (b3) contains, respectively, the recycled polypropylene resin (a), the polypropylene resin (c), the ethylene-α-olefin copolymer (b1), and the ethylene-α-olefin copolymer (b2). A method for producing an unstretched polyolefin film, comprising the step of melt-kneading the ethylene-α-olefin copolymer (b1), the ethylene-α-olefin copolymer (b2), and the recycled raw material (b3) to form the intermediate layer (B).

7. The manufacturing method according to claim 6, comprising the step of co-extruding the outermost layer (A), the intermediate layer (B), and the outermost layer (C) and laminating them by extrusion lamination or dry lamination.

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