Multilayer films, packaging materials and packaging bodies

Abstract

To provide a multilayer film that can be used as a sealant film and offers an excellent balance of opacity and cold impact resistance. [Solution] A multilayer film comprising a heat-sealable first outer layer, an inner layer, and a second outer layer in that order, wherein the first outer layer contains a propylene homopolymer (A) and a propylene copolymer resin (B), the inner layer contains a propylene-ethylene block copolymer resin (C) and an ethylene-propylene copolymer elastomer (D), and the second outer layer contains a propylene resin and titanium dioxide (E), with the mass fraction of titanium dioxide (E) being 2.8 to 7.0% by mass based on the total mass of the first outer layer, inner layer, and second outer layer.

Description

【Technical Field】 【0001】 The present disclosure relates to a multilayer film, a packaging material, and a package. 【Background Art】 【0002】 Polypropylene-based films are excellent in rigidity and heat resistance and inexpensive, and thus may be used as a sealant film in various packaging materials such as food packaging. 【0003】 Patent Document 1 proposes a three-layer polypropylene-based composite film including a heat-sealing layer, a shielding layer, and a laminate layer in this order, wherein the shielding layer contains titanium oxide. 【Prior Art Documents】 【Patent Documents】 【0004】 【Patent Document 1】 International Publication No. 2023 / 218968 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0005】 Although the polypropylene-based composite film described in Patent Document 1 is excellent in shielding properties, there is room for improvement from the viewpoint of cold impact resistance. 【0006】 The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a multilayer film that can be used as a sealant film and has an excellent balance between shielding properties and cold impact resistance. Another object of the present disclosure is to provide a packaging material including the above multilayer film and a package formed by bag-making from the packaging material. 【Means for Solving the Problems】 【0007】 The present disclosure provides the following [1] to [6]. [1] comprising a first outer layer having heat-sealing properties, an inner layer, and a second outer layer in this order, The first outer layer comprises a propylene homopolymer (A) and a propylene copolymer resin (B), The inner layer comprises a propylene-ethylene block copolymer resin (C) and an ethylene-propylene copolymer elastomer (D), The second outer layer comprises a propylene resin and titanium dioxide (E), A multilayer film in which the mass fraction of titanium oxide (E) is 2.8 to 7.0% by mass, based on the total mass of the first outer layer, the inner layer, and the second outer layer. [2] The multilayer film according to [1], wherein the first outer layer further comprises titanium oxide (E). [3] The multilayer film according to [1] or [2], wherein the melting point of the first outer layer is 132 to 160°C. [4] The multilayer film according to any one of [1] to [3], wherein the content of the elastomer (D) is 10 to 50% by mass, based on the total mass of the inner layer. [5] A packaging material comprising a multilayer film according to any one of [1] to [4] and a base material on the second outer layer side. [6] A package made from the packaging material described in [5]. [Effects of the Invention] 【0008】 According to this disclosure, a multilayer film is provided that can be used as a sealant film and has an excellent balance of opacity and cold impact resistance. Furthermore, this disclosure provides a packaging material comprising the above-mentioned multilayer film, and a package made from the packaging material. [Brief explanation of the drawing] 【0009】 [Figure 1] Figure 1 is a schematic cross-sectional view showing one embodiment of the multilayer film of the present disclosure. [Figure 2] Figure 2 is a schematic cross-sectional view showing one embodiment of the packaging material of this disclosure. [Figure 3]Figure 3 is a schematic cross-sectional view showing another embodiment of the packaging material of this disclosure. [Modes for carrying out the invention] 【0010】 In this specification, numerical ranges indicated using "~" represent a range that includes the numbers before and after "~" as the minimum and maximum values, respectively. Unless otherwise explicitly stated, the units of the numbers before and after "~" are the same. In numerical ranges described in stages within this specification, the upper or lower limit of one stage may be replaced with the upper or lower limit of another stage. Furthermore, in numerical ranges described within this specification, the upper or lower limit of a range may be replaced with the values ​​shown in the examples. Additionally, individually described upper and lower limits can be combined in any way. Furthermore, the sources of raw materials for the polymerization of the resins described herein (propylene homopolymer (A), propylene copolymer resin (B), propylene-ethylene block copolymer resin (C), and ethylene-propylene copolymer elastomer (D)) are not particularly limited, and any raw materials derived from any source can be used, such as components refined from conventional petroleum, components produced by chemical recycling methods, or plant-derived components. 【0011】 <Multilayer film> Figure 1 is a schematic cross-sectional view showing one embodiment of the multilayer film of the present disclosure. The multilayer film 10 comprises, in this order, a first outer layer 1 having heat-sealing properties, an inner layer 2, and a second outer layer 3. The first outer layer 1 contains a propylene homopolymer (A) and a propylene copolymer resin (B), the inner layer 2 contains a propylene-ethylene block copolymer resin (C) and an ethylene-propylene copolymer elastomer (D), and the second outer layer 3 contains a propylene resin and titanium dioxide (E). By including titanium dioxide (E) in the outer layer (especially the second outer layer 3) instead of the inner layer 2, a multilayer film with an excellent balance of opacity and cold impact resistance is obtained. 【0012】 Titanium oxide (E) is included in the second outer layer 3 as described above, but a part of it may be included in the first outer layer 1 from the viewpoint of making it easier to balance cold impact resistance and hiding property. The content of titanium oxide (E) in the second outer layer 3 may be 40% by mass or more, 80% by mass or more, or 100% by mass based on the total mass of titanium oxide (E) contained in the multilayer film from the viewpoint of excellent hiding property. The content of titanium oxide (E) in the first outer layer 1 may be 60% by mass or less, 20% by mass or less, or 0% by mass based on the total mass of titanium oxide (E) contained in the multilayer film from the viewpoint of preventing inhibition of heat seal performance. 【0013】 The mass fraction of titanium oxide (E) is 2.8 to 7.0% by mass based on the total mass of the first outer layer, the inner layer, and the second outer layer. By the mass fraction of titanium oxide (E) being 2.8% by mass or more, hiding property can be sufficiently ensured, and by being 7.0% by mass or less, it becomes easier to obtain good cold impact resistance. From these viewpoints, the mass fraction of titanium oxide (E) may be 2.8% by mass or more, 4.0% by mass or more, or 5.0% by mass or more, and may be 7.0% by mass or less, 6.5% by mass or less, or 5.6% by mass or less based on the total mass of the first outer layer, the inner layer, and the second outer layer. 【0014】 The mass fraction is calculated by the following calculation formula. Since titanium oxide is not contained in the inner layer in the present disclosure, (thickness of the inner layer) × (titanium oxide content rate in the inner layer) in the calculation formula is 0. Mass fraction (mass%) = { (thickness of the first outer layer) × (titanium oxide content rate in the first outer layer) + (thickness of the inner layer) × (titanium oxide content rate in the inner layer) + (thickness of the second outer layer) × (titanium oxide content rate in the second outer layer)} ÷ thickness of the entire layer 【0015】 The above multi-layer film 10 can be used as a sealant film (for example, a non-stretched polypropylene-based sealant film), and has an excellent balance between concealability and cold impact resistance. Therefore, the multi-layer film 10 is suitably used for packaging materials (for example, a packaging sealant film, or a packaging film including a packaging sealant film and a base material). The multi-layer film 10 may be used as a single film or may be used by laminating it with a base material. When the multi-layer film 10 is used as a packaging material, the method of using it as the packaging material is not particularly limited. 【0016】 The cold impact resistance of the multi-layer film 10 can be evaluated by the impact strength when the film is stored at a low temperature. Specifically, using a film impact tester, measure the impact strength of the film under the conditions of a temperature of -5°C, a weighing of 3.0 J, and a bullet size of 3 / 4 inch. The impact strength of the film measured under the above conditions is, for example, 13 J / mm or more (for example, 13 to 20 J / mm), and by adjusting the composition and thickness of each layer, it can also be 14 J / mm or more, 15 J / mm or more, 16 J / mm or more, 17 J / mm or more, or 18 J / mm or more. 【0017】 The concealability of the multi-layer film 10 can be evaluated by the transmission density. The transmission density is the common logarithm value of the reciprocal of the transmittance, and can be measured using a transmission densitometer (for example, a portable transmission densitometer manufactured by X-RITE). The transmission density of the multi-layer film 10 is, for example, 0.30 or more (for example, 0.30 to 0.50), and by adjusting the composition and thickness of each layer, it can also be 0.35 or more, 0.40 or more, or 0.45 or more. 【0018】 In the field of packaging materials for foods and the like, efforts are being made to "monomaterialize" the packaging material by using a single material. Since the above multi-layer film has sufficient concealability without containing non-polypropylene-based materials such as an aluminum base material that has been conventionally used to impart concealability to packaging materials, it is particularly suitably used for monomaterial packaging materials that require concealability. 【0019】 In monomaterialization efforts, since the sealant film and the substrate are made of the same material, the melting points of the sealant film and the substrate inevitably become close, making it easier for the substrate to melt together with the sealant film during the heat sealing process. Therefore, sealant films used in monomaterial packaging materials are sometimes required to have excellent heat sealability at low temperatures (hereinafter also referred to as "low-temperature sealability"). In this respect, the above multilayer film also has excellent low-temperature sealability by using a low-melting-point material (for example, a propylene copolymer resin (B) with a melting point of 150°C or less) as the material for the first outer layer. 【0020】 The following describes each layer of the multilayer film 10 in detail. In the following description, symbols are omitted. Note that each layer may contain components other than those explicitly stated below, to the extent that they do not inhibit the function of each layer. 【0021】 (First outer layer: heat seal layer) The first outer layer comprises a propylene homopolymer (A) and a propylene copolymer resin (B). 【0022】 [Propylene homopolymer (A)] Propylene homopolymer (A) is a propylene homopolymer that can be obtained by homopolymerizing propylene using, for example, a Ziegler-Natta type catalyst, a metallocene catalyst, or a half-metallocene catalyst. When the first outer layer contains propylene homopolymer (A), the multilayer film also exhibits excellent heat resistance (hereinafter simply referred to as "heat resistance"), enabling it to withstand retort processing, which involves sterilization and disinfection under high pressure at high temperatures of 120-135°C. Therefore, a multilayer film having a first outer layer containing propylene homopolymer (A) can be suitably used for packaging applications that undergo harsh processing such as boiling water treatment and retort processing. 【0023】 As the propylene homopolymer (A), for example, one having a melting onset temperature of 150°C or higher and a melting point (peak melting temperature) of 155°C or higher may be used. Those with both the melting onset temperature and melting point within this range have superior heat resistance, and for example, fusion is less likely to occur on the inner surface of the packaging bag after high-temperature retort processing. From the viewpoint of obtaining even better heat resistance, the melting onset temperature of the propylene homopolymer (A) may be 151°C or higher or 152°C or higher, and the melting point of the propylene homopolymer (A) may be 156°C or higher or 158°C or higher. The melting onset temperature of the propylene homopolymer (A) may be, for example, 160°C or lower, and from the viewpoint of obtaining superior low-temperature sealing properties, it may be 155°C or lower or 153°C or lower. The melting point of the propylene homopolymer (A) may be, for example, 170°C or lower, and from the viewpoint of obtaining superior low-temperature sealing properties, it may be 165°C or lower or 160°C or lower. From the above viewpoint, the melting onset temperature of propylene homopolymer (A) may be, for example, 150 to 160°C, and the melting point of propylene homopolymer (A) may be, for example, 155 to 170°C. In this specification, the melting onset temperature and melting point are values ​​obtained by differential scanning calorimetry in accordance with JIS K 7121. 【0024】 As the propylene homopolymer (A), a propylene homopolymer (A) with a melt flow rate (MFR) in the range of 2.0 to 7.0 g / 10 min may be used. A melt flow rate above the lower limit reduces the extruder load during molding, making it easier to maintain excellent productivity without a decrease in processing speed. Furthermore, a melt flow rate below the upper limit allows the first outer layer to have better cold shock resistance. From these viewpoints, the melt flow rate of the propylene homopolymer (A) may be 2.5 to 6.0 g / 10 min or 3.0 to 5.0 g / 10 min. In this specification, the melt flow rate is a value measured under conditions of 230°C and a load of 2.16 kg in accordance with ISO 1133. 【0025】 [Propylene copolymer resin (B)] Propylene copolymer resin (B) is a resin obtained by copolymerizing propylene with other copolymer monomers (comonomers). 【0026】 The propylene copolymer resin (B) may have a lower melting point than the propylene homopolymer (A). Preferably, the melting point of the propylene copolymer resin (B) is 150°C or lower. When the first outer layer contains a propylene copolymer resin having such a melting point, the multilayer film also exhibits excellent low-temperature sealing properties. Such a multilayer film is more preferably used as a sealant film for monomaterial packaging. From the viewpoint of superior heat resistance and cold shock resistance, the melting point of the propylene copolymer resin (B) may be 132°C or higher, 135°C or higher, 140°C or higher, or 145°C or higher. From the above viewpoint, the melting point of the propylene copolymer resin (B) may be, for example, 132-150°C, 135-150°C, 140-150°C, or 145-150°C. The melting start temperature of the propylene copolymer resin (B) may be 120-145°C, 125-145°C, or 135-145°C, from the viewpoint of achieving a better balance between heat resistance and low-temperature sealing properties. The melting point of the propylene copolymer resin (B) after the formation of the first outer layer can be determined by separating the first outer layer using a high-temperature LC method with graphite carbon as an adsorbent, for example, and measuring the melting point of each layer. 【0027】 The propylene copolymer resin (B) may be a resin obtained by copolymerizing propylene with a copolymer monomer containing ethylene (a resin containing a copolymer of propylene and ethylene). From the viewpoint of the multilayer film having superior low-temperature sealing properties, the propylene copolymer resin (B) may contain a propylene-ethylene random copolymer. The propylene-ethylene random copolymer can be obtained, for example, by adding ethylene as a comonomer to a main monomer consisting of propylene using a Ziegler-Natta type catalyst, a metallocene catalyst, or a half-metallocene catalyst and copolymerizing them. The copolymer constituting the propylene copolymer resin (B) may be one type or multiple types. If the propylene copolymer resin (B) is a mixture of multiple copolymers, the melting point of the mixture is taken as the melting point of the propylene copolymer resin (B). 【0028】 The ethylene content in the propylene copolymer resin (B) may be 6.0% by mass or less, based on the total mass of the propylene copolymer resin (B). An ethylene content of 6.0% by mass or less maintains low-temperature sealing properties without excessively reducing heat resistance, and suppresses fusion on the inner surface of the packaging bag after retort processing. From the viewpoint of obtaining this effect more significantly, the ethylene content may be 5.5% by mass or less, or 4.5% by mass or less. While there is no particular lower limit to the ethylene content, it can be 3.0% by mass from the viewpoint of low-temperature sealing properties. From these viewpoints, the ethylene content in the propylene copolymer resin (B) may be 3.0 to 6.0% by mass, 3.0 to 5.5% by mass, or 3.0 to 4.5% by mass, based on the total mass of the propylene copolymer resin (B). 【0029】 The ethylene content of propylene copolymer resin (B) can be measured according to the quantitative method for ethylene content (IR method) described on pages 412-413 of the Polymer Analysis Handbook (May 10, 2013, 3rd printing), edited by the Polymer Analysis Symposium of the Japan Society for Analytical Science. 【0030】 The melt flow rate (MFR: ISO 1133) of the propylene copolymer resin (B) (at a temperature of 230°C and a load of 2.16 kg) may be between 1.0 and 10.0 g / 10 min. A melt flow rate above the lower limit reduces the extruder load during molding, making it easier to maintain good productivity without a decrease in processing speed. A melt flow rate below the upper limit allows the first outer layer to exhibit excellent cold shock resistance. From these viewpoints, the melt flow rate of the propylene copolymer resin (B) may also be between 2.0 and 9.0 g / 10 min or between 3.0 and 8.0 g / 10 min. 【0031】 The first outer layer may consist substantially of only a propylene homopolymer (A) and a propylene copolymer resin (B), that is, the total amount of propylene homopolymer (A) and propylene copolymer resin (B) in the first outer layer may be substantially 100% by mass. In this case, instead of using the total amount standard (parts by mass) of the propylene homopolymer (A) and propylene copolymer resin (B) described later as the basis for calculating the preferred amounts, the total mass standard (mass%) of the first outer layer can be used. 【0032】 The first outer layer may contain components other than propylene homopolymer (A) and propylene copolymer resin (B). Titanium dioxide (E) is an example of such a component. In this case, the total amount of propylene homopolymer (A) and propylene copolymer resin (B) in the first outer layer may be at least 70% by mass, 80% by mass, or 85% by mass, from the viewpoint of using the multilayer film as a packaging material for monomaterials composed of the same polypropylene material, and from the viewpoint of imparting desired properties to the first outer layer. The propylene content in the first outer layer can be measured according to Raman spectroscopy. 【0033】 From the viewpoint of achieving a better balance between heat resistance and low-temperature sealing performance, it is preferable that, based on a total mass of 100 parts by mass of propylene homopolymer (A) and propylene copolymer resin (B), the content of propylene homopolymer (A) be 30 to 90 parts by mass and the content of propylene copolymer resin (B) be 10 to 70 parts by mass. 【0034】 The content of propylene homopolymer (A) in the first outer layer may be 30 parts by mass or more, 40 parts by mass or more, 50 parts by mass or more, 60 parts by mass or more, 70 parts by mass or more, or 75 parts by mass or more, based on 100 parts by mass of the total mass of propylene homopolymer (A) and propylene copolymer resin (B), from the viewpoint of superior heat resistance. The content of propylene homopolymer (A) in the first outer layer may be 90 parts by mass or less or 85 parts by mass or less, based on 100 parts by mass of the total mass of propylene homopolymer (A) and propylene copolymer resin (B), from the viewpoint of superior low-temperature sealing properties and cold shock resistance. 【0035】 The content of the propylene copolymer resin (B) in the first outer layer may be 10 parts by mass or more, or 15 parts by mass or more, based on 100 parts by mass of the total mass of the propylene homopolymer (A) and the propylene copolymer resin (B), from the viewpoint of superior low-temperature sealing properties and cold shock resistance. The content of the propylene copolymer resin (B) in the first outer layer may be 70 parts by mass or less, 60 parts by mass or less, 50 parts by mass or less, 40 parts by mass or less, 30 parts by mass or less, or 25 parts by mass or less, based on 100 parts by mass of the total mass of the propylene homopolymer (A) and the propylene copolymer resin (B), from the viewpoint of superior heat resistance. 【0036】 When a good balance is achieved between heat resistance and low-temperature sealing properties, and when concealment is also required in the first outer layer, titanium dioxide (E), as described below, can also be included in the first outer layer. In this case, it is preferable that the titanium dioxide (E) content be greater than 0% by mass and 30% by mass or less, based on the total mass of the first outer layer. The remainder may be a propylene-based resin containing a propylene homopolymer (A) and a propylene copolymer resin (B). 【0037】 The titanium(E) content in the first outer layer may be 3% by mass or 5% by mass or more, based on the total mass of the first outer layer, from the viewpoint of superior opacity. The titanium(E) content in the first outer layer may be 20% by mass or less or 15% by mass or less, based on the total mass of the first outer layer, from the viewpoint of superior cold shock resistance and heat sealability. 【0038】 The mass ratio [(B) / (A)] of the propylene copolymer resin (B) to the propylene homopolymer (A) in the first outer layer may be 0.1 to 1 from the viewpoint of superior heat resistance and cold shock resistance. The mass ratio [(B) / (A)] may be 0.15 or more, or 0.2 or more, and may be 0.75 or less, 0.5 or less, or 0.3 or less from the viewpoint of even superior heat resistance and cold shock resistance. 【0039】 The melting point of the first outer layer may be 132°C or higher, 135°C or higher, or 140°C or higher, from the viewpoint of excellent heat resistance. The melting point of the first outer layer may be 160°C or lower, or 155°C or lower, from the viewpoint of excellent low-temperature sealing performance. 【0040】 (Inner layer) The inner layer contains a propylene-ethylene block copolymer resin (C) and an ethylene-propylene copolymer elastomer (D). This enables excellent cold shock resistance. From this viewpoint, the inner layer does not contain titanium dioxide (E). 【0041】 [Propylene-ethylene block copolymer resin (C)] Propylene-ethylene block copolymer resin (C) is a resin obtained by block copolymerization of propylene and ethylene. 【0042】 A propylene-ethylene block copolymer resin (C) comprises, for example, a propylene homopolymer component (c1) and an ethylene-propylene copolymer component (c2), which is a copolymer of ethylene and propylene (e.g., a random copolymer). Such a propylene-ethylene block copolymer resin (C) can be obtained, for example, by producing a propylene homopolymer component (c1) in a first step, and then producing an ethylene-propylene copolymer component (c2) in a second step by gas-phase polymerization in the presence of the propylene homopolymer component (c1). For polymerization, for example, a Ziegler-Natta type catalyst, a metallocene catalyst, a half-metallocene catalyst, etc., can be used. It is generally understood that the propylene-ethylene block copolymer resin (C) obtained by this method is not a block copolymer formed by bonding the ends of a propylene homopolymer to the ends of an ethylene-propylene copolymer (a block copolymer composed of repeating blocks consisting of a propylene homopolymer component (c1) and blocks consisting of an ethylene-propylene copolymer component (c2)), but rather a mixture of a propylene homopolymer component (c1) and an ethylene-propylene copolymer component (c2). 【0043】 The propylene-ethylene block copolymer resin (C) may contain 60.0 to 90.0% by mass of the above-mentioned propylene homopolymer component (c1) and 10.0 to 40.0% by mass of the above-mentioned ethylene-propylene copolymer component (c2), based on the total mass of the propylene-ethylene block copolymer resin (C). By having the content of each component within the above range, it is easier to obtain better cold shock resistance. From the above viewpoint, the content of the propylene homopolymer component (c1) in the propylene-ethylene block copolymer resin (C) may be 65.0 to 87.5% by mass or 70.0 to 85.0% by mass, based on the total mass of the propylene-ethylene block copolymer resin (C). Similarly, the content of the ethylene-propylene copolymer component (c2) in the propylene-ethylene block copolymer resin (C) may be 12.5 to 35.0% by mass or 15.0 to 30.0% by mass, based on the total mass of the propylene-ethylene block copolymer resin (C). 【0044】 The ethylene content in the ethylene-propylene copolymer component (c2) may be 20.0 to 40.0% by mass, based on the total mass of the ethylene-propylene copolymer component (c2). A ethylene content below the upper limit suppresses the tackiness of the product, making it easier to maintain excellent productivity by reducing contamination from tackiness during manufacturing. A ethylene content above the lower limit makes it easier to obtain superior cold shock resistance. 【0045】 The ethylene content of the ethylene-propylene copolymer component (c2) can be measured according to the quantitative method for ethylene content (IR method) described on pages 412-413 of the Polymer Analysis Handbook (May 10, 2013, 3rd printing), edited by the Polymer Analysis Symposium of the Japan Society for Analytical Science. 【0046】 As the propylene-ethylene block copolymer resin (C), a material with a melt flow rate (MFR: ISO 1133) (temperature 230°C, load 2.16 kg) in the range of 0.5 to 2.5 g / 10 min can be used. A melt flow rate above the lower limit reduces the extruder load during molding, making it easier to maintain excellent productivity without a decrease in processing speed. A melt flow rate below the upper limit allows the inner layer to easily exhibit excellent cold shock resistance. From these viewpoints, the melt flow rate of the propylene-ethylene block copolymer resin (C) may be 1.0 to 2.2 g / 10 min or 1.5 to 2.0 g / 10 min. 【0047】 [Ethylene-propylene copolymer elastomer (D)] Ethylene-propylene copolymer elastomer (D) is an elastomer obtained by block copolymerization of propylene and ethylene. 【0048】 The ethylene-propylene copolymer elastomer (D) can be obtained by slurry polymerization in the presence of an inert hydrocarbon such as hexane, heptane, or kerosene, or a liquefied α-olefin solvent such as propylene, or by gas-phase polymerization without a solvent. Specifically, the ethylene-propylene copolymer elastomer (D) can be obtained using a known multi-stage polymerization method. That is, it may be a polymerizable high-rubber-containing polypropylene resin obtained by polymerization of propylene and / or a propylene-α-olefin polymer in a first-stage reactor, followed by copolymerization of propylene and α-olefin in a second-stage reactor. For polymerization, for example, a Ziegler-Natta type catalyst, a metallocene catalyst, or a half-metallocene catalyst can be used. 【0049】 The melt flow rate (MFR: ISO 1133) of the ethylene-propylene copolymer elastomer (D) (at a temperature of 230°C and a load of 2.16 kg) may be between 0.5 and 3.5 g / 10 min. A melt flow rate above the lower limit reduces the extruder load during molding, making it easier to maintain good productivity without a decrease in processing speed. A melt flow rate below the upper limit improves the compatibility between the propylene-ethylene block copolymer resin (C) and the ethylene-propylene copolymer elastomer (D), making it easier to obtain better cold shock resistance. 【0050】 In the ethylene-propylene copolymer elastomer (D), the mass ratio of propylene content to ethylene content [propylene content / ethylene content] may be 1.5 to 4.0, or 2.0 to 3.5 or 2.5 to 3.0, from the viewpoint of easily obtaining even better cold shock resistance. 【0051】 The propylene content of ethylene-propylene copolymer elastomer (D) can be measured according to Raman spectroscopy. Furthermore, the ethylene content of ethylene-propylene copolymer elastomer (D) can be measured according to the quantitative method for ethylene content (IR method) described on pages 412-413 of the Polymer Analysis Handbook (May 10, 2013, 3rd printing), edited by the Polymer Analysis Symposium of the Japan Society for Analytical Science. 【0052】 The inner layer may contain components other than propylene-ethylene block copolymer resin (C) and ethylene-propylene copolymer elastomer (D). However, from the perspective of use in packaging materials for monomaterials composed of the same polypropylene material, it is preferable that the propylene content in the inner layer be 70% by mass or more. The propylene content in the inner layer can be measured according to Raman spectroscopy. 【0053】 From the viewpoint of achieving a better balance between heat resistance and cold shock resistance, it is preferable that the content of propylene-ethylene block copolymer resin (C) be 50 to 90% by mass and the content of ethylene-propylene copolymer elastomer (D) be 10 to 50% by mass, based on the total mass of the inner layer. 【0054】 The content of propylene-ethylene block copolymer resin (C) in the inner layer may be 50% by mass or 60% by mass or more, based on the total mass of the inner layer, from the viewpoint of superior heat resistance. The content of propylene-ethylene block copolymer resin (C) in the inner layer may be 90% by mass or less, 80% by mass or less, or 70% by mass or less, based on the total mass of the inner layer, from the viewpoint of superior cold shock resistance. 【0055】 The content of ethylene-propylene copolymer elastomer (D) in the inner layer may be 10% by mass or more, 15% by mass or more, or 20% by mass or more, based on the total mass of the inner layer, from the viewpoint of superior cold shock resistance. The content of ethylene-propylene copolymer elastomer (D) in the inner layer may be 50% by mass or less, 40% by mass or less, or 30% by mass or less, based on the total mass of the inner layer, from the viewpoint of superior heat resistance. 【0056】 The mass ratio [(D) / (C)] of the ethylene-propylene copolymer elastomer (D) to the propylene-ethylene block copolymer resin (C) in the inner layer is preferably 0.1 to 1 from the viewpoint of superior heat resistance and cold shock resistance. The mass ratio [(D) / (C)] may be 0.2 or higher, 0.3 or higher, or 0.4 or higher from the viewpoint of even superior cold shock resistance. The mass ratio [(D) / (C)] may be 0.8 or lower, 0.6 or lower, or 0.5 or lower from the viewpoint of even superior heat resistance. 【0057】 (Second outer layer: laminate layer, concealing layer) The second outer layer is a layer that has laminating properties to the substrate and functions as an opacity layer. The second outer layer may contain substantially only propylene resin and titanium(E) oxide, that is, the total amount of propylene resin and titanium(E) oxide in the second outer layer may be substantially 100% by mass. Adding a second outer layer makes it easier to suppress distortion and curling of the multilayer film. 【0058】 [Titanium(E)] Titanium(E) dioxide is, for example, particulate and dispersed in a layer. The average particle size of titanium dioxide may be 15 to 800 nm, or it may be 30 to 500 nm or 50 to 300 nm. The average particle size of titanium dioxide is measured by laser diffraction / scattering. 【0059】 The amount of propylene resin in the second outer layer may be at least 30% by mass, from the viewpoint of using the multilayer film as a monomaterial packaging material composed of the same polypropylene material, and from the viewpoint of imparting desired properties to the second outer layer. On the other hand, the amount of propylene resin in the second outer layer may be 90% by mass or less, from the viewpoint of allowing the second outer layer to function as a concealing layer. The propylene content in the second outer layer can be measured according to Raman spectroscopy. 【0060】 From the viewpoint of achieving a good balance of heat resistance, cold shock resistance, and opacity, it is preferable that the titanium(E) content of the second outer layer be 10 to 70% by mass, based on the total mass. The remainder may be a propylene-based resin. 【0061】 The titanium(E) content in the second outer layer may be 15% by mass or more, 20% by mass or more, or 25% by mass or more, based on the total mass of the second outer layer, from the viewpoint of superior opacity. From the viewpoint of superior processability, the titanium(E) content in the second outer layer may be 65% by mass or less, 60% by mass or less, or 55% by mass or less, based on the total mass of the second outer layer. 【0062】 The propylene-based resin in the second outer layer may contain at least one of a propylene homopolymer (A) and a propylene copolymer resin (B). From the viewpoint of suppressing film curling after film molding, the second outer layer may have the same component composition ratio as the first outer layer. When the second outer layer contains a propylene homopolymer (A) and a propylene copolymer resin (B), the description of the first outer layer can be used to refer to the preferred ratios of each. 【0063】 (Thickness of the layer) The thickness of a multilayer film is not particularly limited, as long as it is within a range suitable for use as packaging material. However, if the film is too thick, it becomes a cost disadvantage. For this reason, the thickness of a multilayer film may be 100 μm or less (e.g., 50 to 100 μm) or 70 μm or less (e.g., 50 to 70 μm). 【0064】 The thickness of the first outer layer may be 8-30% of the thickness of the multilayer film. A ratio of the first outer layer thickness above the lower limit makes it easier to obtain superior cold shock resistance. Conversely, a ratio of the first outer layer thickness below the upper limit makes it easier to obtain superior low-temperature sealing performance. From these viewpoints, the thickness of the first outer layer may be 8-25%, 10-25%, 8-21%, or 10-21% of the thickness of the multilayer film. For example, the thickness of the first outer layer may be 5-20 μm. 【0065】 The thickness of the inner layer may be 20 μm or more, from the viewpoint of easily obtaining cold shock resistance. From this viewpoint, the thickness of the inner layer may be 25 μm or more, 30 μm or more, 35 μm or more, or 40 μm or more. There is no particular upper limit to the thickness of the inner layer, but since this would be a cost disadvantage, it may be 60 μm or less or 50 μm or less. 【0066】 The thickness of the inner layer may be 50-92% of the thickness of the multilayer film, from the viewpoint of easily obtaining cold shock resistance. The thickness of the inner layer may be 58% or more, 60% or more, 65% or more, 70% or more, 75% or more, or 79% or more, from the thickness of the multilayer film from the viewpoint of easily obtaining cold shock resistance. 【0067】 The total thickness of the first and second outer layers may be 16% or more, 20% or more, or 25% or more, and 42% or less, 40% or less, or 35% or less, based on the thickness of the multilayer film. A ratio of the total thickness of the first and second outer layers above the lower limit makes it easier to obtain superior cold shock resistance. Furthermore, a ratio of the total thickness of the first and second outer layers below the upper limit makes it easier to obtain superior low-temperature sealing performance. From these viewpoints, the total thickness of the first and second outer layers may be 16-42%, 20-40%, or 25-35%, based on the thickness of the multilayer film. For example, the total thickness of the first and second outer layers may be 10-40 μm. 【0068】 The method for manufacturing the above-mentioned multilayer film is not particularly limited, and known methods can be used. For example, thermoforming methods include melt-kneading methods using general mixers such as single-screw extruders, twin-screw extruders, and multi-screw extruders, and methods in which the solvent is removed by heating after dissolving or dispersing each component. When considering workability, a single-screw extruder or a twin-screw extruder can be used. When using a single-screw extruder, examples of screws include full-flight screws, screws with mixing elements, barrier-flight screws, and fluted screws, and these can be used without particular limitation. As for twin-screw mixers, co-rotating twin-screw extruders and opposite-rotating twin-screw extruders can be used, and the screw shape can be full-flight screws, kneading disc types, etc., without particular limitation. 【0069】 In the above method, it is possible to use a method in which a multilayer film is melted using a single-screw extruder or a twin-screw extruder, and then the film is formed using a T-die via a feed block or a multi-manifold. 【0070】 The resulting multilayer film may be subjected to surface modification treatments as needed to improve its suitability for subsequent processes. For example, surface modification treatments may be performed on the printing surface or the surface in contact with the substrate to improve printability when using a single film or to improve lamination suitability when using a laminate. Examples of surface modification treatments include treatments that generate functional groups by oxidizing the film surface, such as corona discharge treatment, plasma treatment, and flame treatment, as well as wet process modification treatments that form an easily adhesive layer by coating. 【0071】 Although the multilayer film of this disclosure has been described above, the multilayer film of this disclosure is not limited to the embodiments described above. For example, the multilayer film may have layers other than the first outer layer, inner layer, and second outer layer. However, from the viewpoint of using the multilayer film as a packaging material for monomaterials composed of the same polypropylene material and from the viewpoint of obtaining better low-temperature sealing properties, the propylene content in the multilayer film (based on the total mass of the multilayer film) is preferably 70% by mass or more. The propylene content in the multilayer film can be measured according to Raman spectroscopy. 【0072】 <Packaging material> The packaging material may consist solely of the multilayer film described above, or it may include the multilayer film described above and a substrate. 【0073】 A packaging material comprising a multilayer film and a substrate can be obtained, for example, by laminating at least one layer of a substrate such as biaxially oriented polyamide film (ONy), biaxially oriented polyester film (PET), biaxially oriented polypropylene film (OPP), printing paper, metal foil (AL foil), or transparent vapor-deposited film onto a multilayer film. The substrate is positioned on the second outer layer side of the multilayer film. From the viewpoint of making the packaging material a monomaterial packaging material (single-material packaging material), it is preferable to use biaxially oriented polypropylene film (OPP) as the substrate. In other words, the packaging material may be a single-material packaging material comprising a biaxially oriented polypropylene film and a multilayer film. Conventionally, aluminum substrates or the like are used to impart opacity to packaging materials. However, packaging materials equipped with the above-mentioned multilayer film have sufficient opacity without the need to use opaque substrates such as aluminum substrates. 【0074】 When the packaging material is a laminate, its layer structure is not particularly limited and can be adjusted as appropriate according to the required characteristics of the packaging, such as barrier properties to meet the shelf life of the packaged food, size and impact resistance to accommodate the weight of the contents, and visibility of the contents. 【0075】 Figure 2 is a schematic cross-sectional view showing one embodiment of the packaging material of the present disclosure. The packaging material may be, for example, a laminate as shown in the figure. The packaging material 100 comprises a multilayer film 10, an adhesive layer 4, and a transparent vapor-deposited film 5 in this order. The vapor-deposited layer of the transparent vapor-deposited film 5 is provided on the multilayer film 10 side. The multilayer film 10 comprises, from the outer layer side of the packaging material 100, a first outer layer 1 with heat-sealing properties, an inner layer 2, and a second outer layer 3 in this order. That is, the first outer layer 1 is located on the contents side. Figure 3 is a schematic cross-sectional view showing another embodiment of the packaging material of the present disclosure. The packaging material may be, for example, a laminate as shown in the figure. The packaging material 101 comprises, in this order, a packaging material 100, an adhesive layer 6, and a base material (base film) 7. 【0076】 The manufacturing method for the packaging material can preferably involve a conventional dry lamination method, in which the films constituting the packaging material are bonded together using an adhesive. However, if necessary, a method of directly extruding and laminating a multilayer film onto a substrate can also be employed. 【0077】 <Package> The packaging is made by forming a bag from the above-mentioned packaging material. There are no particular restrictions on the packaging method. The packaging may be, for example, a flat bag, a three-sided bag, a gusseted bag, a standing pouch, a spouted pouch, a beaked pouch, etc., using the above-mentioned multilayer film of packaging material as the sealing material. [Examples] 【0078】 The contents of this disclosure will be described in more detail below using examples and comparative examples, but this disclosure is not limited to the following examples. 【0079】 <Preparing the materials> The following materials were prepared: propylene homopolymer (A), propylene copolymer resin (B), propylene-ethylene block copolymer resin (C), ethylene-propylene copolymer elastomer (D), and titanium dioxide (E). The melting onset temperature and melting point of the materials listed below are values ​​obtained by differential scanning calorimetry in accordance with JIS K 7121. The melt flow rate is a value measured in accordance with ISO 1133 under conditions of 230°C and a load of 2.16 kg. The ethylene content was measured according to the quantitative method for ethylene content (IR method) described on pages 412-413 of the Polymer Analysis Handbook (May 10, 2013, 3rd printing), edited by the Polymer Analysis Symposium of the Japan Society for Analytical Science. The propylene content of the following materials was measured according to Raman spectroscopy. 【0080】 (Propylene homopolymer (A)) • Resin (A): A propylene homopolymer with a melting onset temperature of 153°C, a melting point (melting peak temperature) of 159°C, and a melt flow rate of 3.0 g / 10 min. 【0081】 (Propylene copolymer resin (B)) • Resin (B): A propylene-ethylene random copolymer with a melting onset temperature of 142°C, a melting point (melting peak temperature) of 147°C, a melt flow rate of 7.5 g / 10 min, and an ethylene content of 3.4% by mass. 【0082】 (Propylene-ethylene block copolymer resin (C)) • Resin (C): A propylene-ethylene block copolymer resin having a melt flow rate of 1.8 g / 10 min, containing 81.5% by mass of a propylene homopolymer component (c1) and 18.5% by mass of an ethylene-propylene copolymer component (c2), with the ethylene content in the ethylene-propylene copolymer component (c2) being 36.2% by mass. 【0083】 (Ethylene-propylene copolymer elastomer (D)) • Elastomer (D): An ethylene-propylene copolymer elastomer with a melt flow rate of 0.6 g / 10 min and a mass ratio of propylene content to ethylene content (propylene content / ethylene content) of 2.7. 【0084】 (Titanium(E) dioxide) Titanium(E) dioxide particles with an average particle size of 250 nm. 【0085】 <Fabrication of multilayer films> A twin-screw extruder was used to knead each component. For the formation of the first outer layer, pellets of propylene homopolymer (A) and pellets of propylene copolymer resin (B) were kneaded in the proportions shown in Table 1, and then titanium dioxide (E) was added and kneaded further in the proportions shown in Table 1 as needed to prepare a masterbatch (I). For inner layer formation, pellets of propylene-ethylene block copolymer resin (C) and pellets of ethylene-propylene copolymer elastomer (D) were kneaded in the proportions shown in Table 1, and then titanium dioxide (E) was added and kneaded further in the proportions shown in Table 1 as needed to prepare a masterbatch (II). For the formation of the second outer layer, pellets of propylene homopolymer (A) and pellets of propylene copolymer resin (B) were kneaded in the proportions shown in Table 1, and then titanium dioxide (E) was added and kneaded further in the proportions shown in Table 1 as needed to prepare a masterbatch (III). 【0086】 The masterbatches (I) to (III) described above were supplied to a T-die extruder with a feed block heated to 250°C and kneaded in a molten state. The molten masterbatches were then extruded and laminated so that each layer had the thickness shown in Table 1 to produce a multilayer film. The propylene content in each layer of the resulting multilayer film was 70% by mass or more. 【0087】 <Various evaluations> The following evaluations were performed on the multilayer films obtained in each example. The results are shown in Table 1. 【0088】 [Titanium dioxide mass fraction] Mass fraction (mass%) = {(thickness of the first outer layer) × (titanium oxide content in the first outer layer) + (thickness of the inner layer) × (titanium oxide content in the inner layer) + (thickness of the second outer layer) × (titanium oxide content in the second outer layer)} ÷ total thickness of the layers 【0089】 [Cold shock resistance evaluation] Using a film impact tester manufactured by Toyo Seiki Co., Ltd., the impact strength of multilayer films obtained in each example during low-temperature storage was measured under the conditions of -5°C, weighing capacity of 3.0 J, and bullet size of 3 / 4 inch. A film with an impact strength (film impact) of 13 J / mm or higher was considered to have excellent cold impact resistance. 【0090】 [Concealing properties] The opacity of the multilayer films obtained in each example was evaluated using an X-RITE portable transmission density meter (model 341C). Sufficient opacity was determined when the measured transmission density was 0.30 or higher. 【0091】 [Seal start temperature] The first outer layers of the multilayer films obtained in each example were placed facing each other, and heat-sealed using a heat sealer manufactured by Tester Industries Co., Ltd. under the conditions of a sealing pressure of 0.2 MPa, a sealing time of 1 second, and a sealing width of 5 mm, at sealing temperatures between 130°C and 150°C in 2°C increments. After heat sealing at each temperature, the sealed portion was cut out to a width of 15 mm x 80 mm, and the heat seal strength was measured using a tensile testing machine manufactured by Shimadzu Corporation at a tensile speed of 100 mm / min. The temperature at which the heat seal strength reached 10 N / 15 mm or more was determined to be the sealing start temperature. 【0092】 [Low temperature fusion properties] The first outer layers of the multilayer films obtained in each example were placed facing each other, and heat-sealed using a heat sealer manufactured by Tester Industries Co., Ltd. under the following conditions: sealing pressure of 0.05 MPa, sealing time of 30 seconds, sealing width of 10 mm, and sealing temperature of 128 °C. Afterward, the heat-sealed films were cut into 15 mm wide x 80 mm sections, and T-shaped peeling was performed using a tensile testing machine manufactured by Shimadzu Corporation at a tensile speed of 300 mm / min to measure the heat-sealing strength of the heat-sealed portion. A lower heat-sealing strength indicated better heat resistance. 【0093】 [Evaluation of thermal shrinkage rate] Measurements were performed in accordance with JIS K 7133. Two straight lines, each at least 100 mm long and parallel to the MD and TD directions, were drawn on 120 mm x 120 mm samples cut from the multilayer films obtained in each example, with a gap of 10 mm from the edges. A nonwoven cloth was placed in an oven heated to a predetermined temperature (130°C), and the sample was placed on top of the cloth and heated for 50 minutes. After heating, the sample was removed from the oven and left at room temperature for 30 minutes. The straight-line distance from the center of one straight line in the MD direction to the center of the opposite straight line was measured as the MD direction length before and after heating, and the MD direction thermal shrinkage rate was calculated using the following formula (1). MD direction thermal shrinkage rate (%) = (MD direction length after heating - MD direction length before heating) / MD direction length before heating × 100 …(1) Similarly, the thermal shrinkage rate in the TD direction was determined using the following equation (2). TD direction thermal shrinkage rate (%) = (TD direction length after heating - TD direction length before heating) / TD direction length before heating × 100 …(2) When the heat shrinkage rate of MD and TD exceeds 2%, distortion of the packaging material occurs during bag making. Therefore, a heat shrinkage rate of 2% or less was considered to be within the range of good physical properties. 【0094】 [Table 1] [Explanation of Symbols] 【0095】 1...First outer layer, 2...Inner layer, 3...Second outer layer, 4...Adhesive layer, 5...Transparent vapor-deposited film, 6...Adhesive layer, 7...Substrate, 10...Multilayer film, 100,101...Packaging material.

Claims

[Claim 1] It comprises a first outer layer with heat-sealing properties, an inner layer, and a second outer layer in this order. The first outer layer comprises a propylene homopolymer (A) and a propylene copolymer resin (B), The inner layer comprises a propylene-ethylene block copolymer resin (C) and an ethylene-propylene copolymer elastomer (D), The second outer layer comprises a propylene resin and titanium dioxide (E), A multilayer film in which the mass fraction of titanium oxide (E) is 2.8 to 7.0% by mass, based on the total mass of the first outer layer, the inner layer, and the second outer layer. [Claim 2] The multilayer film according to claim 1, wherein the first outer layer further comprises titanium oxide (E). [Claim 3] The multilayer film according to claim 1, wherein the melting point of the first outer layer is 132 to 160°C. [Claim 4] The multilayer film according to claim 1, wherein the content of the elastomer (D) is 10 to 50% by mass, based on the total mass of the inner layer. [Claim 5] A packaging material comprising a multilayer film according to any one of claims 1 to 4 and a base material on the second outer layer side. [Claim 6] A package made from the packaging material described in claim 5.

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