Unstretched polyolefin film and method for producing the same

Abstract

The objective is to provide an unoriented polyolefin film in which an outermost layer (A), at least one intermediate layer (B), and an outermost sealing layer (C) are laminated in this order, and which exhibits excellent optical properties such as transparency and image clarity, and good high-speed film formation even when the unoriented polyolefin film is remanufactured using recycled raw materials obtained by recycling the said film. [Solution] An unstretched polyolefin film is provided, in which an outermost layer (A), at least one intermediate layer (B), and an outermost sealing layer (C) 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, and the intermediate layer (B) contains an ethylene-α-olefin copolymer (b1) polymerized with a homogeneous catalyst and a polymer polymerized by a high-pressure method with a density of 0.930~0.940 g / cm³ 3 An unstretched polyolefin film containing an ethylene polymer (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 present invention aims to provide an unoriented polyolefin film in which an outermost layer (A), at least one intermediate layer (B), and an outermost sealing layer (C) are laminated in this order, and which exhibits excellent optical properties such as transparency and image clarity, and good high-speed film formation even when the unoriented polyolefin film is remanufactured using recycled raw materials obtained by recycling the said film. [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) consists of an ethylene-α-olefin copolymer (b1) polymerized with a homogeneous catalyst and a polymer polymerized by a high-pressure method with a density of 0.930-0.940 g / cm³. 3 We discovered that the above problems can be solved by an unoriented polyolefin film containing an ethylene polymer (b2), and thus completed the present invention.

[0008] The gist of this invention is as follows: [1] to [8]. [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) consists of an ethylene-α-olefin copolymer (b1) polymerized with a homogeneous catalyst and a polymer polymerized by a high-pressure method with a density of 0.930-0.940 g / cm³. 3 An unstretched polyolefin film containing an ethylene polymer (b2). [2] The unstretched polyolefin film according to [1] above, wherein the intermediate layer (B) contains recycled material (b3), and the recycled material (b3) contains the recycled polypropylene resin (a), the polypropylene resin (c), the ethylene-α-olefin copolymer (b1), and the ethylene polymer (b2), respectively. [3] The unstretched polyolefin film according to [1] or [2] above, wherein the α-olefin in the ethylene-α-olefin copolymer (b1) is an α-olefin having 8 or fewer carbon atoms. [4] An unstretched polyolefin film according to any one of [1] to [3] above, wherein one or both of the ethylene-α-olefin copolymer (b1) and the ethylene polymer (b2) contain a plant-derived resin. [5] The unstretched polyolefin film according to any one of [2] to [4] above, wherein the recycled material (b3) is a post-industrial recycled material and / or a post-consumer recycled material. [6] A bag made by cutting and sealing or heat sealing an unstretched polyolefin film as described in any of [1] to [5] above. [7] 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) contains an ethylene-α-olefin copolymer (b1) polymerized with a homogeneous catalyst, an ethylene polymer (b2) having a density of 0.930 to 0.940 g / cm 3 polymerized by the high-pressure method, and a recycled raw material (b3). The recycled raw material (b3) contains the recycled polypropylene-based resin (a), the polypropylene-based resin (c), the ethylene-α-olefin copolymer (b1), and the ethylene polymer (b2), respectively. A method for producing a non-stretched polyolefin film, comprising a step of melt-kneading the ethylene-α-olefin copolymer (b1), the ethylene polymer (b2), and the recycled raw material (b3) to form the intermediate layer (B). [8] The production method according to [7] above, comprising a 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.

Effect of the Invention

[0009] According to the present invention, there is provided a non-stretched polyolefin film in which an outermost layer (A), at least one intermediate layer (B), and an outermost layer (C) as a seal layer are laminated in this order. Even when a non-stretched polyolefin film is reproduced using a recycled raw material obtained by recycling the film, a non-stretched polyolefin film excellent in optical properties such as transparency and image sharpness and having good high-speed film-forming properties can be provided.

Embodiments for Carrying Out the Invention

[0010] [Non-stretched Polyolefin Film] The non-stretched polyolefin film of the present invention is a non-stretched polyolefin film in which an outermost layer (A), at least one intermediate layer (B), and an outermost layer (C) as a seal layer are laminated in this order. Note that the non-stretched polyolefin film may be simply referred to as a film.

[0011] <Outermost Layers (A) and (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 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 propylene monomer as the main monomer, preferably a polymer containing 50 mol% or more, more preferably 70 mol% or more of 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) consists of an ethylene-α-olefin copolymer (b1) polymerized with a homogeneous catalyst and a polymer polymerized by high pressure with a density of 0.930-0.940 g / cm³. 3 It contains the ethylene polymer (b2).

[0026] The intermediate layer (B) contains both an ethylene-α-olefin copolymer (b1) and an ethylene polymer (b2) polymerized with a homogeneous catalyst, resulting in an unoriented polyolefin film with excellent high-speed film formation during film manufacturing. Furthermore, unoriented polyolefin films have a relatively low tear strength, making them easy to open after being processed into bags.

[0027] Furthermore, even when the intermediate layer (B) contains recycled material (b3), it can maintain good optical properties such as transparency and image sharpness. The recycled material (b3) is a recycled material obtained from the unoriented polyolefin film of the present invention, and the recycled material (b3) contains recycled polypropylene resin (a), recycled polypropylene resin (c), recycled ethylene-α-olefin copolymer (b1), and recycled ethylene polymer (b2).

[0028] Regarding the intermediate layer (B), the reason why good optical properties such as transparency and image clarity can be maintained even when recycled material (b3) is included is not clear, but it is thought that this is because the density of the ethylene polymer (b2) contained in the intermediate layer (B) is within a specific range, and therefore the compatibility between the ethylene polymer (b2) and the polypropylene resin contained in the recycled material (b3) is good. Furthermore, by including recycled materials (b3) in the intermediate layer (B), fossil plastics can be effectively utilized, reducing their usage and resulting in an unstretched polyolefin film with reduced environmental impact.

[0029] <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.

[0030] The ethylene-α-olefin copolymer (b1) preferably has no long-chain branches. Here, having no long-chain branches means that 13 the number of branches having 8 or more carbon atoms measured by C-NMR is less than 1.5 per 1000 carbon atoms. By using the ethylene-α-olefin copolymer (b1) having no long-chain branches, the compatibility with the polypropylene-based resin contained in the recycled raw material becomes good, and a decrease in optical properties can be suppressed. Whether or not it has a branch having 8 or more carbon atoms can be determined by paying attention to the second methylene carbon from the branch end and its chemical shift. Regarding the measurement of the number of branches having 8 or more carbon atoms, reference can be made to the matters described in Japanese Patent No. 6457402.

[0031] Since the ethylene-α-olefin copolymer (b1) is polymerized with a homogeneous catalyst, the 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. With such a range of molecular weight distribution, optical properties such as film transparency (haze) and image sharpness are improved.

[0032] The density of the ethylene-α-olefin copolymer (b1) 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 0.910 g / cm 3 or more and 0.940 g / cm 3 or less.

[0033] The MFR of the ethylene-α-olefin copolymer (b1) is preferably 1 g / 10 min or more and 10 g / 10 min or less, more preferably 2 g / 10 min or more and 6 g / 10 min or less. When the MFR of the ethylene-α-olefin copolymer (b1) is within such a range, film formation of the film can be stably performed. The MFR of the ethylene-α-olefin copolymer was measured at 190°C under a load of 2.16 kg in accordance with JIS K 7210.

[0034] <Ethylene polymer (b2)> Ethylene polymer (b2) is polymerized by high-pressure method and has a density of 0.930-0.940 g / cm³. 3 It is an ethylene polymer. The high-pressure method is a method of polymerizing ethylene under high temperature and high pressure to obtain ethylene polymers, resulting in low-density polyethylene (LDPE) with a structure that combines both long-chain and short-chain branching. In other words, the ethylene polymer (b2) has a density of 0.930-0.940 g / cm³. 3 It is low-density polyethylene (LDPE).

[0035] The density of ethylene polymer (b2) is 0.930-0.940 g / cm³. 3 That is the case. Because the density of the ethylene polymer (b2) is within the above range, the transparency and image clarity are excellent even when recycled material (b3) is included in the intermediate layer (B). Furthermore, because the ethylene polymer (b2) has a certain degree of long-chain branching, it also exhibits excellent high-speed film-forming properties during film manufacturing. The density of the ethylene polymer (b2) is preferably 0.932 to 0.938 g / cm³. 3 And more preferably 0.933~0.935 g / cm³. 3 That is the case.

[0036] The molecular weight distribution (Mw / Mn) of the ethylene polymer (b2) is, for example, 2.0 to 8.0, preferably 3.0 to 5.0. This molecular weight distribution range improves the high-speed film formation during film manufacturing.

[0037] The MFR of the ethylene polymer (b2) is preferably 0.5 g / 10 min to 10 g / 10 min, more preferably 1 g / 10 min to 8 g / 10 min, and even more preferably 3 g / 10 min to 7 g / 10 min. When the MFR of the ethylene polymer (b2) is within this range, film formation can be carried out stably.

[0038] Preferably, one or both of the ethylene-α-olefin copolymer (b1) and the ethylene polymer (b2) contain a plant-derived resin. In other words, it is preferable that the ethylene-α-olefin copolymer (b1) is at least part or all of a plant-derived resin (i.e., plant-derived polyethylene resin). It is also preferable that the ethylene polymer (b2) is at least part or all of a plant-derived resin (i.e., plant-derived polyethylene resin).

[0039] 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 can contain recycled materials in the intermediate layer, and in this case, by using recycled materials while using plant-derived resins, an unoriented polyolefin film with a highly suppressed environmental impact can be obtained.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] <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 polymer (b2). Recycled raw material (b3) is a raw material prepared by processing products that have been molded into films, bottles, trays, etc., into polypropylene resin (a), polypropylene resin (c), ethylene-α-olefin copolymer (b1), and ethylene polymer (b2), and then undergoing recovery processes such as crushing and dissolution. In the recovery process, it is preferable to melt-knead and pelletize the material 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.

[0045] The recycled material (b3) is preferably one of the following (i) or (ii). (i) A portion of the film recovered after manufacturing the unoriented polyolefin film of the present invention (a film made using only virgin raw materials). (ii) The unoriented polyolefin film of the present invention, in which the intermediate layer (B) contains recycled raw materials, and a portion of the film is recovered after production.

[0046] 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).

[0047] 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.

[0048] 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.

[0049] <Content of each component in the middle layer> The content of the ethylene-α-olefin copolymer (b1) in the intermediate layer (B) is preferably 20 to 95 parts by mass, more preferably 30 to 85 parts by mass, and even more preferably 50 to 70 parts by mass, based on 100 parts by mass of the total of the ethylene-α-olefin copolymer (b1) and the ethylene polymer (b2). The content of the ethylene polymer (b2) in the intermediate layer (B) is preferably 5 to 80 parts by mass, more preferably 15 to 70 parts by mass, and even more preferably 30 to 50 parts by mass, based on 100 parts by mass of the total of the ethylene-α-olefin copolymer (b1) and the ethylene polymer (b2). By adjusting the content of ethylene-α-olefin copolymer (b1) and ethylene polymer (b2) within the above range, it becomes easier to obtain an unstretched polyolefin film that exhibits excellent high-speed film formation during film manufacturing and has a tear strength below a certain level.

[0050] When the intermediate layer (B) contains recycled material (b3), the content of recycled material (b3) 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 polymer (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.

[0051] The total amount of ethylene-α-olefin copolymer (b1), ethylene polymer (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.

[0052] The intermediate layer (B) may contain other resins other than the ethylene-α-olefin copolymer (b1), ethylene polymer (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.

[0053] 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.

[0054] 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.

[0055] 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).

[0056] <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, and more preferably 3.0% 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.

[0057] 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.

[0058] 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.

[0059] <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.

[0060] The process of manufacturing an unoriented polyolefin film includes a step of forming an intermediate layer (B). When manufacturing an unoriented polyolefin film in which recycled materials are included in the intermediate layer, the intermediate layer (B) is formed by melt-kneading an ethylene-α-olefin copolymer (b1), the ethylene polymer (b2), and the recycled materials (b3) using an extruder or the like.

[0061] 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) A portion of the film recovered after manufacturing the unoriented polyolefin film of the present invention (a film made using only virgin raw materials). (ii) The unoriented polyolefin film of the present invention, in which the intermediate layer (B) contains recycled raw materials, and a portion of the film is recovered after production.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] <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.

[0066] 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.

[0067] 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.

[0068] As described above, the resulting bags can be used as packaging for contents such as food, daily necessities, and textiles. [Examples]

[0069] The present invention will be described in more detail below, but the present invention is not limited to these embodiments.

[0070] [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.

[0071] <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.

[0072] For each example and comparative example, the unoriented polyolefin film containing recycled materials in the intermediate layer was measured for high-speed film formation, haze, image clarity, and tear strength as follows. In addition, sealed packaging was prepared using the unoriented polyolefin film containing recycled materials in the intermediate layer of each example and comparative example, and the burst strength of the bags was measured.

[0073] <High-speed film formation> 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.

[0074] <Hayes> Haze was measured using a haze meter (model number: NDH5000) manufactured by Nippon Denshoku Industries Co., Ltd., in accordance with JIS K 7136.

[0075] <Image sharpness (image quality)> Using an image clarity measuring instrument (model number: ICM-1DP) manufactured by Suga Test Instruments Co., Ltd., the image clarity (%) was measured in accordance with JIS K 7105, with the slit width of the optical comb set to 0.125 mm.

[0076] <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.

[0077] <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.

[0078] 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".

[0079] [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, 50 parts by mass of LLDPE polymerized with a homogeneous catalyst and 50 parts by mass of LDPE polymerized by the high-pressure method 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.

[0080] (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. 50 parts by mass of LLDPE polymerized with a homogeneous catalyst, 50 parts by mass of LDPE polymerized by a high-pressure method, 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). In both cases, the materials 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 an unstretched polyolefin film with a three-layer structure.

[0081] [Examples 2-7, Comparative Examples 1-3] 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.

[0082] [Table 1]

[0083] [Table 2] The amount of recycled material in the intermediate layer shown in Table 2 represents the number of parts by mass relative to 100 parts by mass of virgin material in the intermediate layer.

[0084] When unoriented polyolefin films (virgin raw materials only) of each embodiment satisfying the requirements of the present invention were recycled to obtain recycled raw materials, and unoriented polyolefin films containing these recycled raw materials as an intermediate layer were produced, the optical properties such as haze and image clarity were good, and the film-forming properties were also excellent at high speed. On the other hand, Comparative Example 1 had an intermediate layer polymerized by a high-pressure method with a density of 0.930-0.940 g / cm³. 3 This example did not contain ethylene polymers and exhibited poor high-speed film-forming properties. Comparative Example 2 is an example in which the intermediate layer contains an ethylene polymer polymerized by high pressure with a density of less than 0.930 g / cm³, but the image clarity was inferior. Comparative Example 3 also contains an intermediate layer polymerized by high pressure with a density of 0.930 to 0.940 g / cm³. 3 It did not contain ethylene polymers and contained LLDPE with long-chain branching, resulting in inferior 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) consists of an ethylene-α-olefin copolymer (b1) polymerized with a homogeneous catalyst and a polymer polymerized by a high-pressure method with a density of 0.930 to 0.940 g / cm³. ３ An unstretched polyolefin film containing an ethylene polymer (b2).

2. The unstretched polyolefin film according to claim 1, wherein the intermediate layer (B) contains recycled material (b3), and the recycled material (b3) contains the recycled polypropylene resin (a), the polypropylene resin (c), the ethylene-α-olefin copolymer (b1), and the ethylene polymer (b2), respectively.

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

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

5. The unstretched polyolefin film according to claim 2, wherein the recycled material (b3) is a post-industrial recycled material and / or a post-consumer recycled material.

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

7. 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) consists of an ethylene-α-olefin copolymer (b1) polymerized with a homogeneous catalyst and a polymer polymerized by a high-pressure method with a density of 0.930 to 0.940 g / cm³. ３ It contains an ethylene polymer (b2) and recycled raw materials (b3), The recycled material (b3) contains the recycled polypropylene resin (a), the polypropylene resin (c), the ethylene-α-olefin copolymer (b1), and the ethylene polymer (b2), respectively. A method for producing an unstretched polyolefin film, comprising the step of melt-kneading the ethylene-α-olefin copolymer (b1), the ethylene polymer (b2), and the recycled raw material (b3) to form the intermediate layer (B).

8. The manufacturing method according to claim 7, 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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