Packaging film

Abstract

To provide a packaging film which exhibits superior stretchability and is extendable under a weak force.SOLUTION: A packaging film 1 comprises a core layer 2 containing an olefin-based elastomer, and surface layers 3 and 4 provided on both sides of the core layer 2. The surface layers 3 and 4 contain an olefin-based elastomer and low-density polyethylene. The low-density polyethylene is characterized in that: as determined from an integrated molecular weight distribution curve obtained by measurement using gel permeation chromatography (GPC), the content of components with a molecular weight of 1,000-10,000 is 6.5% or more, and the content of components with a molecular weight of 1,000,000 or less is 90% or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a packaging film used when packing an article.

Background Art

[0002] Conventionally, when packing an article in a packing container such as a cardboard box and delivering it, a cushioning material such as styrofoam, an air cap, or newspaper is packed into a gap generated between the article and the cardboard to fix the article and transport it.

[0003] However, these cushioning materials have a problem in that they are larger in volume than the product, the disposal after use is complicated, and the clean-up is troublesome.

[0004] Therefore, instead of these cushioning materials, a packaging film for fixing and transporting an article has been proposed. For example, a polyolefin film having an inner layer, a first outer layer disposed on one surface side of the inner layer, and a second outer layer disposed on the other surface side of the inner layer, wherein the thickness of the inner layer is 1.5 times or more the thickness of each of the first outer layer and the second outer layer has been proposed. And it is described that an article can be suitably supported using tension when packing the article (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the packaging film described in Patent Document 1 above, when the packaging film is stretched, a large tensile stress is generated during stretching, so a strong force is required when packing an article. Therefore, since it is difficult to stretch the packaging film with a weak force, there is a problem that it is not suitable for long-time packaging work.

[0007] Therefore, the present invention has been made in view of the above problems, and an object thereof is to provide a packaging film that is excellent in stretchability and can be stretched with a weak force.

Means for Solving the Problems

[0008] In order to achieve the above object, the packaging film of the present invention includes a core layer containing an olefin-based elastomer and surface layers provided on both sides of the core layer. The surface layer contains an olefin-based elastomer and low-density polyethylene. The low-density polyethylene has a proportion of components having a molecular weight of 1,000 to 10,000 obtained from an integrated molecular weight distribution curve measured by gel permeation chromatography (GPC) method of 6.5% or more, and a proportion of components having a molecular weight of 1 million or less of 90% or more.

Effects of the Invention

[0009] According to the present invention, it becomes possible to provide a packaging film that is excellent in stretchability and can be stretched with a weak force.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0011] Hereinafter, the packaging film of the present invention will be specifically described. It should be noted that the present invention is not limited to the following embodiments, and can be appropriately modified and applied without changing the gist of the present invention.

[0012] FIG. 1 is a cross-sectional view showing the packaging film of the present invention. As shown in FIG. 1, the packaging film 1 of the present invention includes a core layer 2, a first intermediate layer 5 provided on the first surface 2a of the core layer 2 (hereinafter, may be simply referred to as "intermediate layer 5"), and a second intermediate layer 6 provided on the second surface 2b of the core layer 2 (hereinafter, may be simply referred to as "intermediate layer 6").

[0013] Further, the packaging film 1 of the present invention includes a first surface layer 3 provided on the surface 5a of the intermediate layer 5 (hereinafter, may be simply referred to as "surface layer 3"), and a second surface layer 4 provided on the surface 6a of the intermediate layer 6 (hereinafter, may be simply referred to as "surface layer 4"). Surface layers 3 and 4 are provided on both sides of the core layer 2, the intermediate layer 5 is provided between the core layer 2 and the surface layer 3, and the intermediate layer 6 is provided between the core layer 2 and the surface layer 4.

[0014] (Core layer) The core layer 2 contains an olefin-based elastomer having rubber elasticity at normal temperature, and is a layer for imparting stretchability to the packaging film 1.

[0015] <Olefin-based elastomer> Examples of this olefin-based elastomer include copolymers or homopolymers mainly composed of olefins having 3 or more carbon atoms, and copolymers of olefins having 3 or more carbon atoms mainly composed of ethylene. The olefin-based elastomer may be used alone or in combination of two or more.

[0016] More specifically, for example, (1) α-olefin homopolymers such as polypropylene homopolymers and 1-butene homopolymers with low stereoregularity, (2) α-olefin copolymers such as propylene-ethylene copolymers, propylene-ethylene-1-butene copolymers, 1-butene-ethylene copolymers, 1-butene-propylene copolymers, 4-methylpentene-1-propylene copolymers, 4-methylpentene-1-1-butene copolymers, 4-methylpentene-1-propylene-1-butene copolymers, propylene-1-butene copolymers, ethylene-propylene copolymers, ethylene-hexene copolymers, and ethylene-octene copolymers, (3) ethylene-α-olefin-diene terpolymers such as ethylene-propylene-ethylidene norbornene copolymers, ethylene-propylene-butadiene copolymers, and ethylene-propylene-isoprene copolymers, etc. may be mentioned. Further, an elastomer in which the above-mentioned elastomer is dispersed in a matrix of crystalline polyolefin may also be used. Note that the olefin-based thermoplastic elastomer may be used alone or in combination of two or more.

[0017] In addition, olefin-based elastomers are generally composed of a hard segment that controls basic physical properties such as mechanical properties and a soft segment that controls elasticity, which is a rubbery property. An olefin-based elastomer in which the hard segment is made of polypropylene is called a propylene-based elastomer. When using a propylene-based elastomer obtained by copolymerizing ethylene with propylene as the olefin-based elastomer constituting the core layer, the content of ethylene units in the propylene-based elastomer (that is, with respect to the total weight (all units) of the propylene-based elastomer) is preferably 3% by mass to 20% by mass, and more preferably 10% by mass to 20% by mass. If the content of ethylene units, which is the soft segment, is 3% by mass to 20% by mass, excellent flexibility and excellent stretchability can be obtained in the packaging film due to the elasticity of the soft segment.

[0018] In addition, the density of the propylene-based elastomer is 0.900 g / cm 3It is preferably as follows, 0.895 g / cm 3 More preferably, it is as follows, 0.890 g / cm 3 Even more preferably, it is as follows. When the density is 0.900 g / cm 3 In the following case, the proportion of the soft segment contained in the elastomer increases, and excellent flexibility and excellent stretchability can be obtained.

[0019] Also, the content of the propylene-based elastomer with respect to the whole of the core layer 2 is preferably 50 to 100% by mass, more preferably 75% by mass or more, and even more preferably 90% by mass or more out of 100% by mass of the core layer. When the content of the propylene-based elastomer is 50% by mass or more, the stretchability of the packaging film is sufficiently improved, and it becomes possible to improve the holding stability of the article when using the packaging film.

[0020] Also, commercially available products may be used as the propylene-based elastomer. Examples of commercially available products of the propylene-based elastomer include Vistamaxx (registered trademark) 6102FL manufactured by ExxonMobil, Vistamaxx (registered trademark) 3020FL manufactured by ExxonMobil, Vistamaxx (registered trademark) 3588FL manufactured by ExxonMobil, etc.

[0021] <Recycled material> The core layer 2 may contain a recycled material of the packaging film of the present invention. Here, the "recycled material" refers to the end material generated in the production process of the packaging film, for example, the end material generated when cutting the end before the winding process after film formation of the packaging film.

[0022] And by using such a recycled material, waste can be reduced and the cost can be reduced.

[0023] As this recycled material, for example, those containing a propylene-based elastomer, low-density polyethylene, a polarity-imparting agent, and a lubricant in the examples described later can be used.

[0024] Also, the content of the recycled material with respect to the entire core layer 2 is preferably 50% by mass or less out of 100% by mass of the core layer. This is because when the content of the recycled material is more than 50% by mass, permanent strain and stress increase, resulting in a decrease in stretchability and difficulty in stretching the packaging film with a weak force.

[0025] <Other components> The core layer 2 may contain other components as necessary within a range that does not impair the effects of the present invention. Examples of other components include olefin-based resins such as polyethylene and polypropylene, antioxidants, weather stabilizers, antistatic agents, antifogging agents, metal soaps, waxes, fungicides, antibacterial agents, nucleating agents, flame retardants, and slip agents.

[0026] (Intermediate layer) As the intermediate layers 5 and 6, those containing the above-described olefin-based elastomer can be used in the same manner as the core layer 2. Also, similar to the core layer 2, the above-described recycled material and other components may be included. Note that the intermediate layers 5 and 6 may be intermediate layers of the same type (i.e., having the same composition and thickness), or may be intermediate layers of different types. Also, the intermediate layers 5 and 6 may have the same composition as the core layer 2.

[0027] Also, the content of the propylene-based elastomer with respect to the entire intermediate layer 5 (or intermediate layer 6) is preferably 50 to 100% by mass, more preferably 75% by mass or more, and even more preferably 90% by mass or more out of 100% by mass of the intermediate layer 5 (or intermediate layer 6). If the content of the propylene-based elastomer is 50% by mass or more, the stretchability of the packaging film is sufficiently improved, so that it becomes possible to improve the holding stability of the article when using the packaging film.

[0028] Also, from the same perspective as in the case of the above-mentioned core layer 2, the content of the recycled material with respect to the entire intermediate layer 5 (or intermediate layer 6) is preferably 50% by mass or less out of 100% by mass of the intermediate layer.

[0029] (Surface layer) The surface layers 3 and 4 are layers for improving the transparency after stretching in the packaging film 1 and for improving the stretchability of the packaging film 1. Note that the surface layers 3 and 4 may be the same type (i.e., having the same composition and thickness) of surface layers or different types of surface layers.

[0030] As the surface layers 3 and 4, those containing the above-mentioned olefin-based elastomer can be used. When using the above-mentioned propylene-based elastomer as the olefin-based elastomer, from the same perspective as in the case of the core layer 2, the content rate of the ethylene unit with respect to the total unit is preferably 3% by mass to 20% by mass, and more preferably 10% by mass to 20% by mass.

[0031] Also, from the same perspective as in the case of the core layer 2, the density of the propylene-based elastomer is preferably 3 0.900 g / cm or less, more preferably 3 0.895 g / cm or less, and even more preferably 3 0.890 g / cm or less.

[0032] Also, the content of the propylene-based elastomer with respect to the entire surface layer 3 (or surface layer 4) is preferably 35 to 90% by mass, more preferably 40% by mass or more, and even more preferably 45% by mass or more out of 100% by mass of the surface layer 3 (or surface layer 4). If the content of the propylene-based elastomer is within the above range, excellent flexibility and excellent stretchability can be obtained due to the elasticity of the soft segments contained in the elastomer. Therefore, when packing an article, the packing film can be stretched with a weak force. Further, if the content of the propylene-based elastomer with respect to the entire surface layer 3 (or surface layer 4) is 90% by mass or less, the proportion of the soft segments contained in the elastomer does not become too large, stickiness can be prevented, and a decrease in the heat seal strength of the packing film with respect to the paper substrate can be prevented.

[0033] Further, in the packing film of the present invention, the total content of ethylene units in the propylene-based elastomer with respect to the entire surface layer 3 (or surface layer 4) is 1% by mass or more and less than 7% by mass, preferably 3% by mass or more and 6% by mass or less out of 100% by mass of the surface layer 3 (or surface layer 4). This is because when it is less than 1% by mass, the proportion of the soft segments contained in the elastomer decreases, resulting in poor flexibility and stretchability. When it is 7% by mass or more, the proportion of the soft segments contained in the elastomer becomes too large, stickiness occurs, and blocking may occur when winding the packing film.

[0034] Also, the melt mass flow rate (MFR) of the propylene-based elastomer is preferably 0.5 to 20 g / 10 min, more preferably 1 to 15 g / 10 min, and even more preferably 1 to 10 g / 10 min. When the melt mass flow rate (MFR) is 0.5 to 20 g / 10 min, the compatibility with the intermediate layer is improved, and multi-layer formation can be achieved when manufacturing the film.

[0035] Note that the above melt mass flow rate is obtained by measuring in accordance with the provisions of ASTM D1238.

[0036] <Olefin resin> Further, the surface layers 3 and 4 contain an olefin resin. As the olefin resin, those having compatibility with the propylene-based elastomer in the surface layers 3 and 4 are preferable. For example, a polyethylene resin or a polypropylene resin is preferable. In addition, from the viewpoint of suppressing a decrease in the stretchability of the surface layers 3 and 4, a polyethylene resin is preferable. Further, the olefin resin may be used alone or in combination of two or more.

[0037] Examples of the polyethylene resin include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE).

[0038] Further, from the viewpoint of imparting flexibility to the packaging film and suppressing a decrease in stress, the surface layers 3 and 4 preferably contain low-density polyethylene (LDPE) having a density of 0.930 g / cm 3 or less.

[0039] This low-density polyethylene has a large number of long-chain branches and a low crystallinity, and thus is compatible with the propylene-based elastomer, thereby imparting flexibility to the packaging film and contributing to a decrease in stress.

[0040] In addition, from the viewpoint of preventing stickiness on the surface of the surface layer and preventing blocking during winding of the packaging film, the density of the low-density polyethylene is preferably 0.890 g / cm 3 or more, and more preferably 0.900 g / cm 3 or more.

[0041] In the packaging film of the present invention, the proportion (weight fraction) of components having a molecular weight of 1,000 to 10,000 determined from the integral molecular weight distribution curve obtained by measurement by gel permeation chromatography (GPC) is 6.5% or more, and the proportion of components having a molecular weight of 1 million or less determined from the above integral molecular weight distribution curve is 90% or more, and low-density polyethylene is used.

[0042] Such low-density polyethylene has a large proportion of low-molecular-weight components (components having a molecular weight of 1,000 to 10,000) and a small proportion of high-molecular-weight components (components having a molecular weight greater than 1 million), so the flexibility of the resin is improved, and the permanent strain and stress are reduced. Therefore, the stretchability of the packaging film is improved, and it becomes possible to stretch the packaging film with a weak force.

[0043] The proportion of components having a molecular weight of 1,000 to 10,000 and the proportion of components having a molecular weight of 1 million or less can be calculated by the method described in the following examples using the integral molecular weight distribution curve obtained using data processing software.

[0044] Further, the melt mass flow rate (MFR) of the low-density polyethylene is preferably 0.5 to 20 g / 10 min, more preferably 1.0 to 15 g / 10 min, and even more preferably 1.0 to 10 g / 10 min. When the melt mass flow rate (MFR) is 0.5 to 20 g / 10 min, the compatibility with the intermediate layer is improved, and multilayer formation can be achieved when producing the film.

[0045] In addition, in the packaging film of the present invention, when the surface layers 3 and 4 contain an olefin resin, the content of the olefin resin with respect to the entire surface layer 3 (or surface layer 4) is preferably more than 0% by mass and 45% by mass or less out of 100% by mass of the surface layer 3 (or surface layer 4). If the content of the olefin resin is within the above range, the proportion of the propylene-based elastomer contained in the surface layers 3 and 4 does not become too small. When the olefin resin is low-density polyethylene, since the crystal component is less than that of olefin resins such as random polypropylene, sufficient stretchability and transparency after stretching can be ensured.

[0046] From the viewpoint of reducing the environmental load, as the above-mentioned low-density polyethylene, plant-derived (biomass-derived) low-density polyethylene may be used.

[0047] This plant-derived low-density polyethylene is biomass polyethylene which is a polymer of a monomer containing biomass-derived ethylene, and examples thereof include low-density polyethylene derived from sugarcane.

[0048] In addition, in the packaging film of the present invention, low-density polyethylene having a biomass degree of 95% or more can be used.

[0049] Here, the "biomass degree" specifically refers to a value measured based on the principle of radiocarbon dating by determining the concentration of radiocarbon ( 14 C) in accordance with ASTM D6866 using an accelerator mass spectrometer (AMS).

[0050] <Polarity-imparting agent> In addition, the surface layers 3 and 4 may contain a polarity-imparting agent. The polarity-imparting agent is for imparting polarity to the above-mentioned olefin resin. By imparting polarity to the olefin resin, the adhesiveness between the surface layer and a base material such as a paper base material is enhanced, so that the peel strength of the packaging film of the present invention with respect to a paper base material or the like attached by heat welding or adhesive bonding can be improved.

[0051] Examples of the polarity-imparting agent include polyolefin resins having an intramolecular carboxylic anhydride structure, polyolefin resins having an intramolecular maleic anhydride structure, polyolefin resins having an intramolecular epoxy structure, and polyolefin resins having an intramolecular acrylic acid structure. Among these, from the viewpoint of excellent compatibility with polyolefin resins, it is preferable to use polyolefin resins having a structure of carboxylic anhydrides such as maleic anhydride, acetic anhydride, propionic anhydride, oxalic anhydride, succinic anhydride, phthalic anhydride, and benzoic anhydride in the molecule. For example, polypropylene having an intramolecular carboxylic anhydride structure and polyethylene having an intramolecular carboxylic anhydride structure can be mentioned. The polarity-imparting agent may be used alone or in combination of two or more.

[0052] In addition, the melting point of the polarity-imparting agent is preferably 120°C or higher and 150°C or lower. When the melting point of the polarity-imparting agent is within the above range, the adhesive strength is improved when heat welding or adhesive bonding to the base material is performed.

[0053] In addition, the acid value of the polarity-imparting agent is preferably 1.0 to 60 mgKOH / g, more preferably 11 to 52 mgKOH / g. When the acid value is 1.0 to 60 mgKOH / g, an excellent polarity-imparting effect can be obtained.

[0054] The above acid value is obtained by measuring in accordance with the provisions of JIS K 0070.

[0055] In the packaging film of the present invention, when the surface layers 3 and 4 contain a polarity-imparting agent, the content of the polarity-imparting agent with respect to the entire surface layer 3 (or surface layer 4) is preferably 1.0% by mass or more and 20% by mass or less, more preferably 5.0% by mass or more and 15% by mass or less out of 100% by mass of the surface layer 3 (or surface layer 4). When the content of the polarity-imparting agent is 1.0% by mass or more and 20% by mass or less, the adhesiveness to a paper base material or the like of the packaging film can be improved.

[0056] <Lubricant> In addition, the surface layers 3 and 4 may contain a lubricant. The lubricant is for preventing blocking when winding the packaging film, and for example, an organic lubricant is preferable, and an amide lubricant is more preferable. Further, examples of the amide lubricant include erucic acid amide lubricants, stearic acid amide lubricants, etc., and erucic acid amide lubricants are preferable.

[0057] In addition, in the packaging film of the present invention, when the surface layers 3 and 4 contain a lubricant, the content of the lubricant with respect to the entire surface layer 3 (or surface layer 4) is preferably more than 0% by mass and 10% by mass or less out of 100% by mass of the surface layer 3 (or surface layer 4). If the content of the lubricant is within the above range, blocking of the packaging film can be prevented.

[0058] <Other components> In addition, the surface layers 6 and 7 may contain other components as necessary within a range that does not impair the effects of the present invention.

[0059] Examples of other components include antioxidants, weather stabilizers, antistatic agents, colorants, antifogging agents, metal soaps, waxes, fungicides, antibacterial agents, nucleating agents, flame retardants, etc.

[0060] From the above, in the packaging film 1 of the present invention, the surface layers 3 and 4 contain an olefin-based elastomer and low-density polyethylene, and the low-density polyethylene has a proportion of components with a molecular weight of 1,000 to 10,000 obtained from the integrated molecular weight distribution curve measured by gel permeation chromatography (GPC) method of 6.5% or more, and a proportion of components with a molecular weight of 1 million or less of 90% or more. Therefore, it has excellent stretchability and can be stretched with a weak force when packaging an article.

[0061] <Method for manufacturing the packaging film> Next, the method for manufacturing the packaging film of the present invention will be described in detail.

[0062] The packaging film of the present invention first mixes an olefin-based elastomer and, if necessary, other components such as the above-mentioned recycling materials and olefin-based resins at a predetermined blending ratio to obtain a resin mixture for forming a core layer and a resin mixture for forming an intermediate layer.

[0063] Similarly, a propylene-based elastomer, an olefin-based resin, and, if necessary, the above-mentioned polarity imparting agent, lubricant, and other components are mixed at a predetermined blending ratio to obtain a resin mixture for forming a surface layer.

[0064] Next, using an extruder equipped with a T-die, the resin mixture for forming the core layer, the resin mixture for forming the intermediate layer, and the resin mixture for forming the surface layer are extruded and molded at a predetermined temperature, and by the cast film process method, as shown in FIG. 1, a core layer 2, an intermediate layer 5 provided on the first surface 2a of the core layer 2, an intermediate layer 6 provided on the second surface 2b of the core layer 2, a surface layer 3 provided on the surface 5a of the intermediate layer 5, and a surface layer 4 provided on the surface 6a of the intermediate layer 6 are obtained.

[0065] From the viewpoint of productivity, it is preferable to use the above-mentioned cast film process method, but the manufacturing method of the packaging film of the present invention is not particularly limited, and for example, an inflation method may be used.

[0066] When using the inflation method, the resin mixture for forming the core layer, the resin mixture for forming the intermediate layer, and the resin mixture for forming the surface layer are melted at a predetermined temperature in an extruder equipped with a circular die, and are formed into a film shape by coextrusion, and the film is wound up by a winding roll to obtain the packaging film 1 shown in FIG. 1.

[0067] Further, from the viewpoint of improving the slipperiness and further preventing the blocking of the packaging film, an uneven shape may be formed on the surface of the packaging film 1 (that is, at least one of the outer surface 3a of the surface layer 3 and the outer surface 4a of the surface layer 4).

[0068] This unevenness can be formed by a known method such as embossing. For example, it can be formed by bringing the peripheral surface of an embossing roll (a casting roll or a heated pinch roll) having an embossing treatment (that is, having an uneven shape on the peripheral surface) into close contact with the surface of the packaging film.

[0069] Also, from the viewpoint of adjusting the mechanical properties of the film (especially shrinkage stress and permanent strain), a stretching treatment may be performed in at least one direction of the machine axis (longitudinal) direction (hereinafter referred to as "MD") of the packaging film and the direction orthogonal to MD (hereinafter referred to as "TD"). When performing a stretching treatment on the packaging film, it may be a uniaxially stretched film or a biaxially stretched film.

[0070] Examples of the method for stretching the packaging film include gear stretching in which the film is sandwiched between a pair of gears and stretched, roll stretching in which the film is stretched using rolls, clip stretching in which the film is grasped by clips and stretched, etc. From the viewpoint of productivity, gear stretching is preferable.

[0071] And the packaging film manufactured by the above method has a stress at 50% elongation in MD of 5.0 MPa or less and a stress at 100% elongation in MD of 6.0 MPa or less. Therefore, when packaging an article, the packaging film can be stretched with a weak force, and it becomes possible to easily package the article.

[0072] From the viewpoint of stretching the packaging film with a weak force and more easily packaging the article, it is more preferable that the stress at 50% elongation in MD is 4.0 MPa or less and the stress at 100% elongation in MD is 5.0 MPa or less.

[0073] Also, similarly, the packaging film manufactured by the above-described method has a stress at 50% elongation in the TD direction of 5.0 MPa or less and a stress at 100% elongation in the TD direction of 5.0 MPa or less. Therefore, when packaging an article, the packaging film can be stretched with a weak force, and it becomes possible to easily package the article.

[0074] In addition, from the viewpoint of stretching the packaging film with a weak force and easily packaging the article, it is preferable that the stress at 50% elongation in the TD direction is 4.0 MPa or less and the stress at 100% elongation in the TD direction is 4.0 MPa or less.

[0075] Also, the packaging film manufactured by the above-described method preferably has an absolute value of the difference between the stress (at 50% elongation) and the stress (at 100% elongation) in the MD and TD directions of 0.8 MPa or less, more preferably less than 0.6 MPa, and even more preferably 0.5 MPa or less. If the absolute value of the difference between the stress (at 50% elongation) and the stress (at 100% elongation) is 0.8 MPa or less, when packaging an article, the packaging film can be stretched with a certain weak force, and it becomes possible to easily package the article.

[0076] The “stress at 50% elongation in the MD direction”, “stress at 100% elongation in the MD direction”, “stress at 50% elongation in the TD direction”, and “stress at 100% elongation in the TD direction” can be obtained by the method described in the examples below.

[0077] Also, the packaging film manufactured by the above-described method has a permanent strain of 20% or less, so the stretchability is improved, and it becomes possible to improve the holding property of the article to be packaged.

[0078] In addition, from the viewpoint of further improving the holding property of the article to be packaged, the permanent strain of the packaging film is more preferably 19% or less.

[0079] Moreover, the “permanent strain” referred to here means the one calculated by the following method.

[0080] Cut a strip-shaped test piece measuring 100 mm in one direction of the film and 25 mm in the direction perpendicular to the one direction from the packaging film, and fix this test piece to the grips of a precision universal testing machine (manufactured by Shimadzu Corporation, Autograph AG-5000A) so that the grip distance is 25 mm. Then, the test piece is extended in the longitudinal direction under the condition of a speed of 254 mm / min so that the elongation (elongation magnification) calculated by the following formula (1) becomes 100%, and immediately after that, the test piece is contracted at the same speed. Then, the permanent strain [%] is calculated from the following formula (2).

[0081] Elongation [%] = (L1 - L0) / L0 × 100 (1) Permanent strain [%] = (L2 / L0) × 100 (2)

[0082] However, L0 is the grip distance (mm) before elongation, L1 is the grip distance (mm) after elongation, and L2 is the grip distance (mm) when the load (N / 25 mm) of the test piece becomes 0 during contraction.

[0083] Also, from the viewpoint of improving the heat seal strength of the packaging film with respect to the paper substrate, the peel strength of the packaging film with respect to the paper substrate is preferably 4 N / 50 mm or more, more preferably 5 N / 50 mm or more, and even more preferably 6 N / 50 mm or more.

[0084] The "peel strength of the packaging film with respect to the paper substrate" can be determined by the method described in the examples below.

[0085] In addition, the packaging film manufactured by the above method (that is, the packaging film before elongation) has a haze of 15% or less, so it is possible to obtain excellent transparency.

[0086] From the viewpoint of further improving the transparency, the haze of the packaging film before elongation is preferably 12% or less, and more preferably 9% or less.

[0087] Here, the "haze" refers to the index measured in accordance with JIS K 7136.

[0088] Also, the thickness of the core layer 2 is preferably 10 to 50 μm, more preferably the lower limit is 15 μm or more and the upper limit is 40 μm or less. If the thickness of the core layer 2 is 10 μm or more, the rubber elasticity effect of the olefin-based elastomer contained in the core layer can be sufficiently exerted, and the stretchability of the packaging film can be improved. Also, if the thickness of the core layer is 50 μm or less, it can be accurately slit to a specified width with a slit blade, so that the film end can be neatly wound when the film is wound into a roll.

[0089] Also, the thickness of the intermediate layers 5 and 6 is preferably 10 μm or less, more preferably the lower limit is 2 μm or more and the upper limit is 8 μm or less. If the thickness of the intermediate layers 5 and 6 is 2 μm or more, the use of recycled materials becomes possible in the intermediate layers 5 and 6, so that waste can be reduced and costs can be reduced. Also, if the thickness of the intermediate layers 5 and 6 is 10 μm or less, it can be accurately slit to a specified width with a slit blade, so that the film end can be neatly wound when the film is wound into a roll.

[0090] Also, the thickness of the surface layers 3 and 4 is preferably 1 to 10 μm, more preferably the lower limit is 2 μm or more and the upper limit is 6 μm or less. If the thickness of the surface layers 3 and 4 is 1 μm or more, it becomes possible to suppress blocking when winding the packaging film. Also, if the thickness of the surface layers 3 and 4 is 10 μm or less, it becomes possible to sufficiently ensure the thickness of the core layer 2, so that the stretchability of the packaging film can be sufficiently improved.

[0091] Also, the thickness of the packaging film 1 is preferably 30 to 70 μm, more preferably the lower limit value is 35 μm or more and the upper limit value is 50 μm or less. If the thickness of the packaging film 1 is 30 to 70 μm or less, the stretchability of the packaging film can be improved, and it can be accurately slit to a specified width with a slit blade. Therefore, when the film is wound into a roll, the film end can be neatly wound.

[0092] Also, from the viewpoint of improving flexibility, the density of the packaging film 1 is preferably 3 0.910 g / cm or less, more preferably 3 0.900 g / cm or less, and even more preferably 3 0.890 g / cm or less.

[0093] <Packaging member> The packaging member of the present invention includes the above-described packaging film 1 of the present invention and a base material to which the surface layer 3 (or surface layer 4) of the packaging film is attached, for example, by heat welding or adhesive bonding.

[0094] The packaging member includes an attachment portion where the surface layer and the base material are attached and an unattachment portion where the surface layer and the base material are not attached. An article is inserted and accommodated between the base material and the packaging film in the unattachment portion, and the article is sandwiched between the base material and the packaging film, thereby forming a configuration for packaging the article.

[0095] Examples of the base material include a paper base material, a resin sheet, and a non-woven fabric, and it is preferable to use a paper base material. Also, from the viewpoint of improving strength, a corrugated board or cardboard is more preferable, and a corrugated board is even more preferable.

[0096] Examples of the shape of the base material include a rectangular shape, a square shape, a circular shape, and an elliptical shape, but it is not limited to these shapes and can be appropriately selected according to the shape of the article to be packaged and the shape of the packaging container.

[0097] In addition, as a method for manufacturing the packaging member, for example, a method of manufacturing a packaging member including an attachment portion where a surface layer of a packaging film and a base material are attached and a non-attachment portion where the surface layer and the base material are not attached is provided. The method includes laminating a base material and a surface layer of a packaging film in a contacting state, and heat-sealing a peripheral portion of the packaging film to the base material by heating the peripheral portion of the packaging film.

[0098] In addition, the packaging member is used in a state of being housed in a packaging container such as a box or a bag (for example, a cardboard box) formed of paper or resin when transporting an article.

[0099] <Other forms> In the above-described embodiment, an intermediate layer 5 is provided between the core layer 2 and the surface layer 3, and an intermediate layer 6 is provided between the core layer 2 and the surface layer 4, and a five-layer structure laminated in the order of surface layer 4 / intermediate layer 6 / core layer 2 / intermediate layer 5 / surface layer 3 has been described as an example. However, a packaging film having a three-layer structure in which the intermediate layers 5 and 6 are not provided and only the core layer 2 and the surface layers 3 and 4 are provided and laminated in the order of surface layer 4 / core layer 2 / surface layer 3 may be used.

[0100] In this case, after obtaining the resin mixture for forming the core layer and the resin mixture for forming the surface layer as described above, an extruder equipped with a T-die is used to extrude the resin mixture for forming the core layer and the resin mixture for forming the surface layer at a predetermined temperature, and a packaging film having a core layer 2, a surface layer 3 provided on a first surface 2a of the core layer 2, and a surface layer 4 provided on a second surface 2b of the core layer 2 is obtained by a cast film process method.

[0101] Also in this case, similar to the case of the above-described embodiment, it is possible to provide a packaging film that is excellent in stretchability and can be stretched with a weak force when packaging an article.

Example

[0102] The present invention will be described below based on examples. Note that the present invention is not limited to these examples, and these examples can be modified and changed based on the spirit of the present invention, and they are not excluded from the scope of the present invention.

[0103] The materials used in the production of the packaging film are shown below.

[0104] (1) Propylene-based elastomer 1 (manufactured by ExxonMobil, trade name: Vistamaxx® 3588FL, propylene-ethylene copolymer, ethylene unit content: 4% by mass, density: 0.889 g / cm 3 , MFR (230 °C): 8.0 g / 10 min) (2) Propylene-based elastomer 2 (manufactured by ExxonMobil, trade name: Vistamaxx® 6102FL, propylene-ethylene copolymer, ethylene unit content: 16% by mass, density: 0.862 g / cm 3 , MFR (230 °C): 3.0 g / 10 min) (3) LDPE1: Low-density polyethylene (manufactured by Ube Maruzen Polyethylene, trade name: F522N, density: 0.922 g / cm 3 , MFR (190 °C): 5.0 g / 10 min) (4) LDPE2: Low-density polyethylene (manufactured by Braskem, trade name: SBC818, biomass content: 95%, density: 0.918 g / cm 3 , MFR (190 °C): 8.3 g / 10 min) (5) LDPE3: Low-density polyethylene (manufactured by Lotte Chemical Titan, trade name: LDF200YZ, density: 0.922 g / cm 3 , MFR (190 °C): 2.1 g / 10 min) (6) LDPE4: Low-density polyethylene (manufactured by Japan Polyethylene, trade name: Novatech LC604, density: 0.918 g / cm 3 , MFR (190 °C): 8.0 g / 10 min) (7) Polarity imparting agent: Polypropylene having an intramolecular carboxylic anhydride structure (manufactured by Sanyo Chemical Industries, Ltd., trade name: Yumex 1001, melting point: 142 °C, acid value: 26 mgKOH / g, density: 0.95 g / cm 3 ) (8) Lubricant: Elucic acid amide-containing masterbatch (manufactured by Riken Vitamin Co., Ltd., trade name: Rikemaster ELM080, density: 0.919 g / cm 3 ) (9) Polyolefin-based elastomer (manufactured by Dow Chemical Company, trade name: Affinity PL 1880G, ethylene-octene copolymer, density: 0.902 g / cm 3 , MFR: 1.0 g / 10 min) (10) Olefin block copolymer (manufactured by Dow Chemical Company, trade name: INFUSE9100, ethylene / octene block copolymer, density: 0.877 g / cm 3 , MFR: 1.0 g / 10 min) (11) Recycled material (in Example 2, the end material generated when cutting and molding the end of the packaging film was used, containing propylene-based elastomer 1 ([thickness of surface layer / total thickness] × compounding amount (parts by mass) = [10 / 40] × 30 = 7.5 parts by mass), propylene-based elastomer 2 ([thickness of surface layer / total thickness] × compounding amount (parts by mass) + [thickness of core layer / total thickness] × compounding amount (parts by mass) = [10 / 40] × 15 + [30 / 40] × 100 = 78.75 parts by mass), LDPE2 ([thickness of surface layer / total thickness] × compounding amount (parts by mass) = [10 / 40] × 45 = 11.25 parts by mass), polarity imparting agent ([thickness of surface layer / total thickness] × compounding amount (parts by mass) = [10 / 40] × 7 = 1.75 parts by mass), and lubricant ([thickness of surface layer / total thickness] × compounding amount (parts by mass) = [10 / 40] × 3 = 0.75 parts by mass), density: 0.872 g / cm 3 )

[0105] Note that the composition of the recycled material was calculated from the compounding ratio and thickness of each layer in Example 2.

[0106] <Calculation of the ratio (weight fraction) of components having a molecular weight of 1,000 to 10,000 and the ratio of components having a molecular weight of 1 million or less in low-density polyethylene>

[0107] For LDPE1 to 4, using a GPC device, chromatograms were measured under the following conditions, and the number average molecular weight (Mn), weight average molecular weight (Mw), the ratio (weight fraction) of components having a molecular weight of 1,000 to 10,000, and the ratio of components having a molecular weight of 1 million or less were calculated.

[0108] <Measurement conditions> GPC device: Manufactured by Tosoh Corporation, product name: HLC-8321GPC / HT Detector: RI detector Column: TSKgel GMHHR-H HT (7.8 mm I.D. × 30 cm) × 2 columns Eluent: Orthodichlorobenzene + BHT (0.05 wt%) Flow rate of eluent: 1.0 ml / min Sample concentration: 2.0 mg / ml Sample injection volume: 300 μl Column temperature: 145°C Sample preparation: The weighed sample was wrapped with a stainless steel mesh (50 mm × 50 mm, mesh opening: 26 μm), placed in a sample cup, eluent was added, and then set in a sample dissolution and filtration device (manufactured by Tosoh Corporation, product name: DF-8321H (145°C, shaking at 60 times / min, 180 min)) for dissolution. Calibration curve: Prepared using standard sample solutions in which standard polystyrene resins (manufactured by Tosoh Corporation, product names: F-850, F-40, F-4, A-5000, A-500) were dissolved in the eluent.

[0109] In addition, in accordance with JIS K 7252-1, the baseline was determined, and for the number average molecular weight (Mn) and weight average molecular weight (Mw) of each low-density polyethylene (LDPE1 to 4), the molecular weights in terms of standard polystyrene were adopted.

[0110] Further, using the obtained calibration curve and the data processing software (8321GPC-WS) for the measuring device, the integral value of the molecular weight (logarithmic value) on the horizontal axis and the weight fraction [%] on the vertical axis was plotted to obtain the integral molecular weight distribution curves of each low-density polyethylene (LDPE1 to LDPE4).

[0111] The integral molecular weight distribution curves of each low-density polyethylene (LDPE1 to LDPE4) obtained using the data processing software are shown in Figure 2, and a partially enlarged view of the integral molecular weight distribution curve shown in Figure 2 (a view in which the portion with a molecular weight of 1,000 to 10,000 is enlarged) is shown in Figure 3.

[0112] In addition, the ratios of the molecular weights in each low-density polyethylene (LDPE1 to LDPE4) calculated using the integral molecular weight distribution curve (the ratio of the component with a molecular weight of 1,000 to 10,000 and the ratio of the component with a molecular weight of 1 million or less) are shown below.

[0113] LDPE1 (the ratio of the component with a molecular weight of 1,000 to 10,000 is 7.1%, and the ratio of the component with a molecular weight of 1 million or less is 99.3%) LDPE2 (the ratio of the component with a molecular weight of 1,000 to 10,000 is 6.8%, and the ratio of the component with a molecular weight of 1 million or less is 93.0%) LDPE3 (the ratio of the component with a molecular weight of 1,000 to 10,000 is 5.2%, and the ratio of the component with a molecular weight of 1 million or less is 98.0%) LDPE4 (the ratio of the component with a molecular weight of 1,000 to 10,000 is 6.4%, and the ratio of the component with a molecular weight of 1 million or less is 89.8%)

[0114] (Example 1) <Manufacture of Packaging Film> First, each material shown in Table 1 was mixed to prepare a material for forming the core layer of Example 1 having the composition (parts by mass) shown in Table 1, a material for forming the intermediate layer (the first surface layer and the second surface layer), and a material for forming the surface layer (the first surface layer and the second surface layer), and a resin mixture for forming the core layer, a resin mixture for forming the intermediate layer, and a resin mixture for forming the surface layer were obtained.

[0115] Next, using an extruder equipped with a T-die (manufactured by Labtech), the resin mixture for core layer formation, the resin mixture for intermediate layer formation, and the resin mixture for surface layer formation were extrusion-molded at 200 °C. By the cast film process method, a film having a five-layer structure including a core layer, a first intermediate layer provided on the first surface of the core layer, a second intermediate layer 6 provided on the second surface of the core layer, a first surface layer provided on the surface of the first intermediate layer 5, and a second surface layer provided on the surface of the second intermediate layer was formed. The film was brought into close contact with a chill roll at 25 °C and cooled to obtain a packaging film. The thickness of the manufactured packaging film and the thicknesses of the core layer, intermediate layer, and surface layer are shown in Table 1.

[0116] Also, the density of the packaging film [g / cm 3 is shown in Table 1. In this example, with respect to 100 parts by mass of the first surface layer and 100 parts by mass of the second surface layer, 30 parts by mass of propylene-based elastomer 1 (density: 0.889 g / cm 3 ), 15 parts by mass of propylene-based elastomer 2 (density: 0.862 g / cm 3 ), 43 parts by mass of low-density polyethylene 1 (density: 0.922 g / cm 3 ), 7 parts by mass of a polarity-imparting agent (density: 0.95 g / cm 3 ), and 5 parts by mass of a lubricant (density: 0.919 g / cm 3 ) were contained. With respect to 100 parts by mass of the first intermediate layer and 100 parts by mass of the second intermediate layer, 57 parts by mass of propylene-based elastomer 2 (density: 0.862 g / cm 3 ) and 43 parts by mass of a recycled material (density: 0.872 g / cm 3 ) were contained. With respect to 100 parts by mass of the core layer, propylene-based elastomer 2 (density: 0.862 g / cm 3It contains 100 parts by mass of [[ID=]], and with respect to the total thickness (40 μm) of the packaging film, the total thickness of the first surface layer and the second surface layer is 10 μm, the total thickness of the first intermediate layer and the second intermediate layer is 14 μm, and the thickness of the core layer is 16 μm. Therefore, the density of the packaging film is {(0.889×0.3)+(0.862×0.15)+(0.922×0.43)+(0.95×0.07)+(0.919×0.05)}×10 / 40+{(0.862×0.57)+(0.872×0.43)}×14 / 40+(0.862×16 / 40)=0.874 g / cm 3 becomes

[0117] In addition, Table 1 shows the total content (parts by mass) of ethylene units in the propylene-based elastomer with respect to the entire surface layer (the first surface layer) and the total content (parts by mass) of ethylene units in the propylene-based elastomer with respect to the entire surface layer (the second surface layer).

[0118] In the first surface layer (or the second surface layer) of this example, 30 parts by mass of propylene-based elastomer 1 (ethylene unit content rate: 4% by mass) and 15 parts by mass of propylene-based elastomer 2 (ethylene unit content rate: 16% by mass) are contained with respect to 100 parts by mass of the first surface layer (or the second surface layer). Therefore, the total content (parts by mass) of ethylene units in the propylene-based elastomer with respect to the entire surface layer (the first surface layer or the second surface layer) is (30×0.04)+(15×0.16)=3.6 parts by mass (that is, the total content of ethylene units in the propylene-based elastomer with respect to the entire first surface layer (or the entire second surface layer) is 3.6% by mass out of 100% by mass of the surface layer).

[0119] <Measurement of permanent strain> From the manufactured packaging film, a strip-shaped test piece with a length of 100 mm in one direction of the film and a width of 25 mm in the direction perpendicular to the one direction was cut out. This test piece was fixed to the grips of a precision universal testing machine (manufactured by Shimadzu Corporation, Autograph AG-5000A) so that the distance between the grips was 25 mm. Then, the test piece was stretched in the longitudinal direction at a speed of 254 mm / min until the elongation (elongation ratio) calculated by the above formula (1) reached 100%, and immediately after that, the test piece was contracted at the same speed. Then, the permanent strain [%] in MD and TD was calculated from the above formula (2). The test was conducted at room temperature (23°C ± 2°C). The above results are shown in Table 1.

[0120] <Measurement of haze> Using a turbidimeter (manufactured by Nippon Denshoku Industries Co., Ltd., product name: Haze Meter NDH-5000), in accordance with JIS K 7136, the haze [%] of the manufactured packaging film (the packaging film before stretching) was measured. The haze was measured 6 times, and the average value of the haze for the 6 measurements was calculated and taken as the haze [%] of the manufactured packaging film. The above results are shown in Table 1.

[0121] <Measurement of stress at 50% elongation in the machine direction (MD)> In the hysteresis test in MD, a test piece cut out from the manufactured packaging film with a size of 25 mm in TD and 100 mm in MD was prepared. Under the conditions that the distance between the chucks was 25 mm and the test speed was 254 mm / min, the test piece was stretched in MD until the distance between the chucks reached 50 mm (100%), and then without holding that state, the distance between the chucks was returned to 25 mm. Then, the stress [MPa] in MD when the distance between the chucks was 37.5 mm (at 50% elongation) during the process of stretching the test piece in MD to 50 mm (100%) between the chucks was measured using a precision universal testing machine (manufactured by Shimadzu Corporation, product name: Autograph AG-5000A). The above results are shown in Table 1.

[0122] <Stress at 50% elongation in the direction perpendicular to the stretching direction (TD)> In the TD hysteresis test, a test piece was prepared by cutting the manufactured packaging film to 25 mm in the MD and 100 mm in the TD. Under the conditions that the distance between the chucks was 25 mm and the test speed was 254 mm / min, the test piece was stretched in the TD to 50 mm (100%) between the chucks, and then the distance between the chucks was returned to 25 mm without maintaining that state. Then, the stress [MPa] in the TD when the distance between the chucks was 37.5 mm (at 50% elongation) during the stretching of the test piece to 50 mm (100%) in the TD was measured using a precision universal testing machine (manufactured by Shimadzu Corporation, product name: Autograph AG-5000A). The above results are shown in Table 1.

[0123] <Stress at 100% elongation in the stretching direction (MD)> In the MD hysteresis test, a test piece was prepared by cutting the manufactured packaging film to 25 mm in the TD and 100 mm in the MD. Under the conditions that the distance between the chucks was 25 mm and the test speed was 254 mm / min, the test piece was stretched in the MD to 50 mm (100%) between the chucks, and then the distance between the chucks was returned to 25 mm without maintaining that state. Then, the stress [MPa] in the MD when the distance between the chucks was 50 mm (at 100% elongation) was measured using a precision universal testing machine (manufactured by Shimadzu Corporation, product name: Autograph AG-5000A). The above results are shown in Table 1.

[0124] <Stress at 100% elongation in the direction perpendicular to the stretching direction (TD)> In the TD hysteresis test, a test piece was prepared by cutting the manufactured packaging film to 25 mm in the MD and 100 mm in the TD. Under the conditions that the distance between the chucks was 25 mm and the test speed was 254 mm / min, the test piece was stretched in the TD to 50 mm (100%) between the chucks, and then the distance between the chucks was returned to 25 mm without maintaining that state. Then, the stress [MPa] in the TD when the distance between the chucks was 50 mm (at 100% elongation) was measured using a precision universal testing machine (manufactured by Shimadzu Corporation, product name: Autograph AG-5000A). The above results are shown in Table 1.

[0125] <Measurement of peel strength> Under the conditions of a temperature of 180°C and a pressure of 0.15 MPa, the packaging film produced by heat sealing was heat - welded to a paper substrate to manufacture a packaging member.

[0126] Next, the heat - seal strength of the packaging film with respect to the paper substrate in the obtained packaging member was evaluated. More specifically, a test piece with a width of 50 mm and a length of 100 mm was cut out from the packaging member, and using a tensile testing machine (manufactured by Shimadzu Corporation, product name: Autograph AG - 5000A), under the conditions of a measurement temperature of 23°C and a tensile speed of 200 mm / min, 180° peeling was performed on the test piece, and the peel strength [N / 50 mm] of the packaging film with respect to the paper substrate was measured.

[0127] And when the peel strength was 4 N / 50 mm or more, it was evaluated that the heat - seal strength of the packaging film with respect to the paper substrate was excellent. The above results are shown in Table 1.

[0128] (Example 2) First, each material shown in Table 1 was mixed to prepare a material for forming the core layer and a material for forming the surface layer (the first surface layer and the second surface layer) of Example 2 having the composition (parts by mass) shown in Table 1, and a resin mixture for forming the core layer and a resin mixture for forming the surface layer were obtained.

[0129] Next, using an extruder equipped with a T - die (manufactured by Mitsubishi Heavy Industries, Ltd.), the resin mixture for forming the core layer and the resin mixture for forming the surface layer were extruded at 200°C, and by the cast - film process method, a film having a three - layer structure including a core layer, a first surface layer provided on the first surface of the core layer, and a second surface layer provided on the second surface of the core layer was formed. The film was brought into close contact with a chill roll at 25°C and cooled to obtain a packaging film. The thickness of the manufactured packaging film and the thicknesses of the core layer and the surface layer are shown in Table 1.

[0130] And in the same manner as in Example 1 described above, measurement of permanent strain, measurement of haze, measurement of stress, and measurement of peel strength were performed. The above results are shown in Table 1.

[0131] (Examples 3 - 4, Comparative Examples 1 - 2) A packaging film having the thickness shown in Table 1 was produced in the same manner as in Example 1 above, except that the composition (parts by mass) of the packaging film was changed to the conditions shown in Table 1.

[0132] Then, in the same manner as in Example 1 above, measurements of permanent strain, haze, stress, and peel strength were performed. The above results are shown in Table 1.

[0133] (Comparative Example 3) (Manufacture of Packaging Film) A packaging film having the thickness shown in Table 1 was produced in the same manner as in Example 1 above, except that the composition (parts by mass) of the packaging film was changed to the conditions shown in Table 1 and the extruder was changed to one manufactured by Labtech.

[0134] Then, in the same manner as in Example 1 above, measurements of permanent strain, haze, stress, and peel strength were performed. The above results are shown in Table 1.

[0135] [Table 1]

[0136] As shown in Table 1, in the packaging films of Examples 1 to 4, the surface layer contains a propylene-based elastomer and low-density polyethylene. The low-density polyethylene has a proportion of components with a molecular weight of 1,000 to 10,000 determined from the integrated molecular weight distribution curve obtained by measurement using gel permeation chromatography (GPC) of 6.5% or more (7.1%, 6.8%), and a proportion of components with a molecular weight of 1 million or less of 90% or more (99.3%, 93.0%). Therefore, it can be seen that the permanent strain in MD and TD is small and the stretchability is excellent. Also, it can be seen that the stress during elongation in MD and TD is small, and when packaging an article, the packaging film can be stretched with a weak force. Further, since the haze after elongation is 15% or less, it can be seen that the transparency is excellent. Also, since the peel strength is 4 N / 50 mm or more, it can be seen that the heat seal strength of the packaging film to the paper substrate is excellent.

[0137] On the other hand, as shown in Table 1, in the packaging film of Comparative Example 1, the surface layer has a proportion of components with a molecular weight of 1,000 to 10,000 determined from the integrated molecular weight distribution curve obtained by measurement using gel permeation chromatography (GPC) of less than 6.5% (5.2%). Therefore, it can be seen that the permanent strain in MD and TD is large and the stretchability is poor. Also, it can be seen that the stress during elongation in MD is large, and when packaging an article, it is difficult to stretch the packaging film with a weak force. Further, it can be seen that the haze after elongation is greater than 15% and the transparency is poor.

[0138] Also, in the packaging film of Comparative Example 2, the proportion of components with a molecular weight of 1,000 to 10,000 obtained from the integral molecular weight distribution curve measured by gel permeation chromatography (GPC) in the surface layer is less than 6.5% (6.4%), and the proportion of components with a molecular weight of 1 million or less is less than 90% (89.8%). Therefore, it can be seen that the permanent strain in the MD is large and the stretchability is poor. Also, the stress during elongation in the MD is large, and it can be seen that it is difficult to stretch the packaging film with a weak force when packaging an article. Further, the haze after elongation is greater than 15%, indicating poor transparency.

[0139] Also, in Comparative Example 3, since the surface layer does not contain a propylene-based elastomer and low-density polyethylene and contains only an ethylene-octene copolymer, it can be seen that the permanent strain in the TD is large and the stretchability is poor. Also, the stress during elongation in the MD is large, and it can be seen that it is difficult to stretch the packaging film with a weak force when packaging an article.

[0140] Also, in Comparative Example 3, since it does not contain a polarity-imparting agent, the peel strength is less than 4 N / 50 mm, indicating poor heat seal strength of the packaging film to the paper substrate.

Industrial Applicability

[0141] As described above, the present invention is suitable for a packaging film used when packaging an article.

Explanation of Symbols

[0142] 1 Packaging film 2 Core layer 3 Surface layer (first surface layer) 4 Surface layer (second surface layer) 5 Intermediate layer (first intermediate layer) 6 Intermediate layer (second intermediate layer)

Claims

1. A core layer containing an olefin-based elastomer and surface layers provided on both sides of the core layer, wherein the surface layer contains the olefin-based elastomer and low-density polyethylene, and the low-density polyethylene has a proportion of components having a molecular weight of 1,000 to 10,000, determined from an integrated molecular weight distribution curve obtained by measurement by gel permeation chromatography (GPC), of 6.5% or more, and a proportion of components having a molecular weight of 1 million or less of 90% or more. A packaging film characterized by this.

2. An intermediate layer is provided between the core layer and the surface layer, The packaging film according to claim 1, wherein the intermediate layer contains the olefin-based elastomer.

3. The packaging film according to claim 1 or claim 2, wherein the olefin-based elastomer is a propylene-based elastomer obtained by copolymerizing ethylene with propylene.

4. The packaging film according to claim 3, wherein the surface layer contains a polarity-imparting agent.

5. The packaging film according to claim 4, wherein the polarity-imparting agent is a polyolefin-based resin having an intramolecular carboxylic anhydride structure.

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