Packaging film

Abstract

To provide a packaging film which has excellent stretchability, can be stretched with a weak force, and has excellent transparency after stretching.SOLUTION: A packaging film 1 is provided with an intermediate layer 2 containing a thermoplastic elastomer, and surface layers 3, 4 provided on both surfaces of the intermediate layer 2 and containing a propylene-based elastomer. The propylene-based elastomer is obtained by copolymerizing propylene with ethylene, the content of the propylene-based elastomer relative to the entire surface layer 3 (or surface layer 4) is 45 mass% or more and 95 mass% or less, and the total content of ethylene units in the propylene-based elastomer relative to the entire surface layer 3 (or surface layer 4) is 1 mass% or more and less than 7 mass%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a packaging film used when packaging articles. [Background technology]

[0002] Traditionally, when shipping goods in cardboard boxes or other packaging containers, cushioning materials such as styrofoam, bubble wrap, or newspaper were used to fill the gaps between the goods and the cardboard box, securing the goods during transport.

[0003] However, these cushioning materials were large in volume compared to the products themselves, making disposal after use cumbersome and time-consuming.

[0004] Therefore, as an alternative to these cushioning materials, packaging films for securing and transporting goods have been proposed. For example, a polyolefin film has been proposed having an inner layer, a first outer layer disposed on one side of the inner layer, and a second outer layer disposed on the other side of the inner layer, wherein the thickness of the inner layer is 1.5 times or more than the thickness of the first and second outer layers. It has been stated that with such a configuration, when packaging goods, the goods can be suitably supported by tension (see, for example, Patent Document 1).

[0005] Furthermore, a packaging film has been proposed comprising a thermoplastic elastomer-containing layer and a polyolefin resin-containing layer provided on one side of the thermoplastic elastomer-containing layer, wherein the polyolefin resin-containing layer contains a polarity imparting agent. It has been stated that this configuration makes it possible to provide a packaging film with excellent low-temperature adhesion to paper substrates such as corrugated cardboard sheets (see, for example, Patent Document 2). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2016-22958 [Patent Document 2] Japanese Patent Publication No. 2019-218092 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, in the packaging film described in Patent Document 1 above, there was a problem in that the tensile stress during stretching of the packaging film was large, making it difficult to stretch the packaging film with a weak force when packaging goods.

[0008] Furthermore, in the packaging film described in Patent Document 2 above, there was a problem that when the packaging film was stretched during packaging of goods, whitening occurred in the stretched portion after stretching.

[0009] Therefore, the present invention has been made in view of the above problems, and aims to provide a packaging film that is highly elastic, can be stretched with little force, and has excellent transparency after stretching. [Means for solving the problem]

[0010] To achieve the above objective, the packaging film of the present invention comprises an intermediate layer containing a thermoplastic elastomer and a surface layer provided on both sides of the intermediate layer and containing a propylene-based elastomer, wherein the propylene-based elastomer is a propylene-based elastomer obtained by copolymerizing propylene with ethylene, the content of the propylene-based elastomer relative to the entire surface layer is 45% by mass or more and 95% by mass or less, and the total content of ethylene units in the propylene-based elastomer relative to the entire surface layer is 1% by mass or more and less than 7% by mass. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a packaging film that is highly elastic, can be stretched with little force, and has excellent transparency after stretching. [Brief explanation of the drawing]

[0012] [Figure 1] This is a cross-sectional view for explaining the packaging film according to an embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, the packaging film of the present invention will be specifically described. Note that the present invention is not limited to the following embodiments, and can be appropriately changed and applied without changing the gist of the present invention.

[0014] 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 an intermediate layer 2, a first surface layer 3 provided on the first surface 2a of the intermediate layer 2 (hereinafter, may be simply referred to as "surface layer 3"), and a second surface layer 4 provided on the second surface 2b of the intermediate layer 2 (hereinafter, may be simply referred to as "surface layer 4").

[0015] (Intermediate layer) The intermediate layer 2 contains a thermoplastic elastomer having rubber elasticity at normal temperature, and is a layer for imparting stretchability to the packaging film 1.

[0016] <Thermoplastic elastomer> Examples of this thermoplastic elastomer include olefin-based thermoplastic elastomers, styrene-based thermoplastic elastomers, and polyester-based thermoplastic elastomers. The thermoplastic elastomer may be used alone or in combination of two or more.

[0017] Also, from the viewpoint of improving the adhesion to the surface layers 3 and 4, it is preferable to use an olefin-based thermoplastic elastomer among these thermoplastic elastomers.

[0018] Examples of olefin-based thermoplastic elastomers include copolymers or homopolymers mainly composed of olefins having 3 or more carbon atoms, and copolymers of ethylene and olefins having 3 or more carbon atoms.

[0019] More specifically, examples include (1) α-olefin homopolymers such as propylene homopolymers and 1-butene homopolymers with low stereoregularity, (2) α-olefin copolymers such as propylene-ethylene copolymer, propylene-ethylene-1-butene copolymer, 1-butene-ethylene copolymer, 1-butene-propylene copolymer, 4-methylpentene-1-propylene copolymer, 4-methylpentene-1-1-butene copolymer, 4-methylpentene-1-propylene-1-butene copolymer, propylene-1-butene copolymer, ethylene-propylene copolymer, ethylene-hexene copolymer, and ethylene-octene copolymer, and (3) ethylene-α-olefin-diene ternary copolymers such as ethylene-propylene-ethylidene norbornene copolymer, ethylene-propylene-butadiene copolymer, and ethylene-propylene-isoprene copolymer. Alternatively, an elastomer in which the above-mentioned elastomers are dispersed in a crystalline polyolefin matrix may be used. Furthermore, olefin-based thermoplastic elastomers may be used individually or in combination of two or more types.

[0020] Furthermore, olefin-based thermoplastic elastomers are generally composed of a hard segment that governs basic physical properties such as mechanical properties and a soft segment that governs rubber-like properties such as elasticity. When the hard segment of an olefin-based thermoplastic elastomer is made of polypropylene, it is called a propylene-based elastomer. When a propylene-based elastomer (propylene-ethylene copolymer) is used as the olefin-based thermoplastic elastomer constituting the intermediate layer, the content of ethylene units relative to the total units is preferably 3% to 20% by mass, and more preferably 10% to 20% by mass. If the content of ethylene units, which are the soft segment, is 3% to 20% by mass, excellent flexibility and excellent elasticity can be obtained in the packaging film.

[0021] Furthermore, the content of thermoplastic elastomer in the entire intermediate layer is preferably 70 to 100% by mass, more preferably 90 to 100% by mass, and even more preferably 95 to 100% by mass, of the total mass of the intermediate layer. If the thermoplastic elastomer content is 70% by mass or more, the elasticity of the packaging film is sufficiently improved, making it possible to improve the holding stability of articles when using the packaging film.

[0022] <Other ingredients> The intermediate layer 2 may contain other components as needed, as long as it does not impair the effects of the present invention. Examples of other components include olefin resins such as polyethylene and polypropylene, antioxidants, weather stabilizers, antistatic agents, antifogging agents, metal soaps, waxes, antifungal agents, antibacterial agents, nucleating agents, flame retardants, and slip agents.

[0023] (Surface layer) The surface layers 3 and 4 are layers that improve the transparency of the packaging film 1 after stretching, as well as improve the elasticity of the packaging film 1.

[0024] As shown in Figure 1, surface layers 3 and 4 are provided on both sides of the intermediate layer 2 (i.e., both the first surface 2a and the second surface 2b), with surface layer 3 provided on the first surface 2a of the intermediate layer 2 and surface layer 4 provided on the second surface 2b of the intermediate layer 2. Surface layers 3 and 4 may be of the same type (i.e., the same composition and thickness), or they may be of different types.

[0025] The surface layers 3 and 4 are layers containing at least one propylene-based elastomer (hereinafter sometimes simply referred to as "propylene-based elastomer") which is obtained by copolymerizing propylene with ethylene, as described in the intermediate layer 2 above.

[0026] <Propylene-based elastomer> In the propylene-based elastomer contained in surface layers 3 and 4, the content of ethylene units in the propylene-based elastomer (i.e., relative to the total weight (total units) of the propylene-based elastomer) is preferably 3% to 20% by mass. If the content of ethylene units, which constitute the soft segment, is 3% to 20% by mass, excellent flexibility and excellent stretchability can be obtained due to the elasticity of the soft segment. More preferably, the content of ethylene units in the propylene-based elastomer is 4% to 16% by mass.

[0027] Furthermore, in the packaging film of the present invention, the total content of ethylene units in the propylene-based elastomer relative to the entire surface layer 3 (or the entire surface layer 4) is preferably 1% by mass or more and less than 7% by mass, and more preferably 3% by mass or more and 6% by mass or less, of 100% by mass of the surface layer. This is because if it is less than 1% by mass, the proportion of soft segments contained in the elastomer will be small, resulting in poor flexibility and elasticity, and if it is 7% by mass or more, the proportion of soft segments contained in the elastomer will be too large, which may cause stickiness.

[0028] Furthermore, in the packaging film of the present invention, the content of propylene-based elastomer relative to the entire surface layer 3 (or the entire surface layer 4) is 45% by mass or more and 95% by mass or less of 100% by mass of the surface layer. If the content of propylene-based elastomer is within the above range, excellent flexibility and excellent stretchability are obtained due to the elasticity of the soft segments contained in the elastomer, so that the packaging film can be stretched with little force when packaging goods. In addition, in polyolefin resins that contain a large amount of crystalline components, when the film is stretched, the crystallization of the resin is promoted and whitening occurs in the stretched part, but since elastomers have fewer crystalline components, which are hard segments, than polyolefin resins, whitening of the stretched part can be suppressed even when the packaging film is stretched when packaging goods. Furthermore, if the content of propylene-based elastomer relative to the entire surface layer 3 (or the entire surface layer 4) is 95% by mass or less, the proportion of soft segments contained in the elastomer does not become too high, and stickiness can be prevented.

[0029] Furthermore, the density of the propylene-based elastomer is 0.900 g / cm³. 3 Preferably, it is 0.895 g / cm³. 3 It is more preferable that the following is the case: 0.890 g / cm³ 3 It is even more preferable that the density is 0.900 g / cm³. 3 In the following cases, the proportion of soft segments contained in the elastomer increases, resulting in superior flexibility and excellent elasticity.

[0030] Furthermore, 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 multilayering is possible when manufacturing the film.

[0031] The meltmass flow rate mentioned above is obtained by measurement in accordance with the provisions of ASTM D1238.

[0032] In addition, commercially available propylene elastomers may be used. Examples of commercially available propylene elastomers include Vistamaxx® 6102FL, Vistamaxx® 3020FL, and Vistamaxx® 3588FL from ExxonMobil.

[0033] <Olefin resin> Furthermore, the surface layers 3 and 4 may contain an olefin resin. The olefin resin is preferably one that is compatible with the propylene elastomer in the surface layers 3 and 4, such as polyethylene resin or polypropylene resin. Polyethylene resin is preferred from the viewpoint of suppressing a decrease in the elasticity of the surface layers 3 and 4. The olefin resin may be used alone or in combination of two or more types.

[0034] Examples of polyethylene resins include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE).

[0035] Furthermore, from the perspective of reducing environmental impact, low-density polyethylene derived from plants (biomass) may be used.

[0036] This plant-derived low-density polyethylene is a biomass polyethylene, which is a polymer of monomers containing ethylene derived from biomass. For example, sugarcane-derived low-density polyethylene can be cited.

[0037] Furthermore, the packaging film of the present invention can use low-density polyethylene having a biomass content of 95% or more.

[0038] In this context, "biomass content" specifically refers to the amount of radioactive carbon (CO2) measured by an accelerator mass spectrometer (AMS) in accordance with ASTM D6866. 14This refers to a value measured based on the principle of radiocarbon dating by determining the concentration of C).

[0039] Furthermore, the surface layer is made of an olefin-based resin with a density of 0.930 g / cm³, chosen from the perspective of suppressing a decrease in flexibility. 3 Preferably, it contains low-density polyethylene (LDPE) as follows:

[0040] Furthermore, from the viewpoint of preventing stickiness on the surface layer and preventing blocking when winding the packaging film, the density of the low-density polyethylene is set to 0.870 g / cm³. 3 Preferably, it should be 0.880 g / cm³ or more. 3 It is more preferable that the above conditions are met.

[0041] Furthermore, the melt mass flow rate (MFR) of 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 multilayering is possible when manufacturing the film.

[0042] The meltmass flow rate mentioned above is obtained by measurement in accordance with the provisions of ASTM D1238.

[0043] Furthermore, in the packaging film of the present invention, when the surface layers 3 and 4 contain an olefin resin, it is preferable that the content of the olefin resin relative to the entire surface layer 3 (or the entire surface layer 4) is greater than 0% by mass and 45% by mass or less of 100% by mass of the surface layer. If the content of the olefin resin is within the above range, the proportion of propylene elastomer contained in the surface layers 3 and 4 will not be too low, and if the olefin resin is low-density polyethylene, it has fewer crystalline components than olefin resins such as random polypropylene, so sufficient elasticity and transparency after stretching can be ensured.

[0044] <Polarity imparting agent> Furthermore, surface layers 3 and 4 may contain a polarity imparting agent. The polarity imparting agent is used to impart polarity to the olefin resin as described above. By imparting polarity to the olefin resin, the adhesion between the surface layer and the substrate such as a paper substrate is improved, thereby improving the peel strength of the packaging film of the present invention to the paper substrate or the like to which it is attached by heat welding or adhesive bonding.

[0045] Examples of polarity imparters include polyolefin resins having a carboxylic acid anhydride structure in the molecule, polyolefin resins having an epoxy structure in the molecule, and polyolefin resins having an acrylic acid structure in the molecule. Of these, from the viewpoint of excellent compatibility with polyolefin resins, it is preferable to use polyolefin resins having a carboxylic acid anhydride structure in the molecule, such as maleic anhydride, acetic anhydride, propionic anhydride, oxalic anhydride, succinic anhydride, phthalic anhydride, and benzoic anhydride. Examples include polypropylene having a carboxylic acid anhydride structure in the molecule and polyethylene having a carboxylic acid anhydride structure. Note that one polarity imparter may be used alone, or two or more may be used in combination.

[0046] Furthermore, the melting point of the polarity-imparting agent is preferably between 120°C and 150°C. If the melting point of the polarity-imparting agent is within the above range, the adhesive strength will be improved when heat welding or adhesive bonding is performed to the substrate.

[0047] Furthermore, the acid value of the polarity-imparting agent is preferably 1.0 to 60 mg KOH / g, and more preferably 11 to 52 mg KOH / g. If the acid value is 1.0 to 60 mg KOH / g, an excellent polarity-imparting effect can be obtained.

[0048] The above acid value is obtained by measurement in accordance with the provisions of JIS K 0070.

[0049] Furthermore, 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 relative to the entire surface layer 3 (or the entire surface layer 4) is preferably 1.0% by mass or more and 20% by mass or less, and more preferably 5.0% by mass or more and 15% by mass or less, of 100% by mass of the surface layer. If the content of the polarity imparting agent is 1.0% by mass or more and 20% by mass or less, the adhesion of the packaging film to paper substrates and the like can be improved.

[0050] <Lubricant> Furthermore, surface layers 3 and 4 may contain a lubricant. The lubricant is used to prevent blocking when winding the packaging film, and for example, an organic lubricant is preferred, and an amide lubricant is more preferred. Examples of amide lubricants include erucic acid amide lubricants and stearic acid amide lubricants, with erucic acid amide lubricants being preferred.

[0051] Furthermore, in the packaging film of the present invention, if the surface layers 3 and 4 contain a lubricant, it is preferable that the lubricant content relative to the entire surface layer 3 (or the entire surface layer 4) is greater than 0% by mass and less than or equal to 10% by mass of 100% by mass of the surface layer. Blocking of the packaging film can be prevented if the lubricant content is within the above range.

[0052] <Other ingredients> Furthermore, the surface layers 6 and 7 may contain other components as needed, as long as they do not impair the effects of the present invention.

[0053] Other ingredients include antioxidants, weather stabilizers, antistatic agents, colorants, antifogging agents, metallic soaps, waxes, antifungal agents, antibacterial agents, nucleating agents, and flame retardants.

[0054] As described above, in the packaging film 1 of the present invention, the content of propylene-based elastomer in the entire surface layer 3 (or the entire surface layer 4) is 45% by mass or more and 95% by mass or less, and the total content of ethylene units in the propylene-based elastomer in the entire surface layer is 1% by mass or more and less than 7% by mass. Therefore, it has excellent elasticity and flexibility, and the packaging film can be stretched with little force when packaging goods. Furthermore, since propylene-based elastomer has a small amount of crystalline components, crystallization of the resin is not easily promoted when the film is stretched. Therefore, even when the packaging film is stretched when packaging goods, whitening of the stretched portion after stretching can be suppressed.

[0055] <Method for manufacturing packaging film> Next, the method for manufacturing the packaging film of the present invention will be described in detail.

[0056] The packaging film of the present invention is first obtained by mixing a thermoplastic elastomer and, if necessary, other components such as the olefin resin mentioned above in a predetermined mixing ratio to obtain a resin mixture for forming an intermediate layer.

[0057] Similarly, a propylene-based elastomer and, if necessary, the aforementioned olefin-based resin, polarity imparter, lubricant, and other components are mixed in predetermined proportions to obtain a resin mixture for surface layer formation.

[0058] Next, using an extruder equipped with a T-die, the resin mixture for forming the intermediate layer and the resin mixture for forming the surface layer are extruded at a predetermined temperature to obtain a packaging film 1, as shown in Figure 1, having an intermediate layer 2, a first surface layer 3 provided on the first surface 2a of the intermediate layer 2, and a second surface layer 4 provided on the second surface 2b of the intermediate layer.

[0059] While the cast film process method described above is preferable from a productivity standpoint, the method for manufacturing the packaging film of the present invention is not particularly limited, and for example, the inflation method may also be used.

[0060] When using the inflation method, a resin mixture for forming the intermediate layer and a resin mixture for forming the surface layer are melted at a predetermined temperature in an extruder equipped with a circular die, formed into a film by co-extrusion, and the film is wound up on a winding roll to obtain the packaging film 1 shown in Figure 1.

[0061] Furthermore, from the viewpoint of improving slipperiness and further preventing the blocking of the packaging film, an uneven surface may be formed on the surface of the packaging film 1 (i.e., at least one of the outer surface 3a of the surface layer 3 and the outer surface 4a of the surface layer 4).

[0062] These irregularities can be formed by known methods such as embossing, for example, by pressing the circumferential surface of an embossed roll (such as a cast roll or heated pinch roll) that has been embossed (i.e., has an irregular shape on its circumferential surface) against the surface of a packaging film.

[0063] Furthermore, from the viewpoint of adjusting the mechanical properties of the film (especially shrinkage stress and permanent strain), the packaging film may be stretched in at least one direction: the mechanical axis (longitudinal direction) (hereinafter referred to as "MD") and the direction perpendicular to the MD (hereinafter referred to as "TD"). When stretching is performed on the packaging film, it may be a uniaxially oriented film or a biaxially oriented film.

[0064] Methods for stretching packaging film include, for example, gear stretching, which involves clamping the film between a pair of gears; roll stretching, which uses a roll to stretch the film; and clip stretching, which involves gripping the film with a clip. However, from the standpoint of productivity, gear stretching is preferred.

[0065] Furthermore, the packaging film manufactured using the method described above (i.e., the packaging film before stretching) will have a haze of 10% or less, making it possible to achieve excellent transparency.

[0066] Furthermore, after stretching the packaging film manufactured by the above method to 100%, the haze becomes 25% or less. Therefore, even when the packaging film is stretched during packaging, whitening of the stretched portion can be suppressed, making it possible to obtain excellent transparency.

[0067] Furthermore, from the viewpoint of further improving transparency, the haze of the packaging film before stretching is preferably 8% or less, and more preferably 6% or less. Similarly, the haze of the packaging film after 100% stretching is preferably 20% or less, and more preferably 15% or less.

[0068] Furthermore, the term "haze" used here refers to an index measured in accordance with JIS K 7136.

[0069] Furthermore, the packaging film manufactured by the above method exhibits a stress of 5.0 MPa or less when stretched to 50% in MD, and a stress of 6.0 MPa or less when stretched to 100% in MD. Therefore, when packaging goods, the packaging film can be stretched with little force, making it possible to easily package goods.

[0070] Furthermore, it is preferable that the stress at 50% elongation in MD is 4.5 MPa or less, and the stress at 100% elongation in MD is 5.0 MPa or less. From the viewpoint of stretching the packaging film with weak force and easily packaging goods, 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 4.0 MPa or less.

[0071] Similarly, packaging films manufactured by the method described above have a stress of 4.0 MPa or less when stretched to 50% in TD and a stress of 4.0 MPa or less when stretched to 100% in TD. Therefore, when packaging goods, the packaging film can be stretched with little force, making it possible to easily package goods.

[0072] Furthermore, from the viewpoint of stretching the packaging film with weak force and easily packaging goods, it is preferable that the stress at 50% stretch in TD is 3.5 MPa or less, and the stress at 100% stretch in TD is 3.5 MPa or less.

[0073] Furthermore, in the packaging film manufactured by the method described above, it is preferable that the absolute value of the difference between the stress (at 50% elongation) and the stress (at 100% elongation) in MD and TD is 0.5 MPa or less, and more preferably less than 0.3 MPa. If the absolute value of the difference between the stress (at 50% elongation) and the stress (at 100% elongation) is 0.5 MPa or less, the packaging film can be stretched with a constant, weak force when packaging goods, making it possible to easily package goods.

[0074] Furthermore, the packaging film manufactured by the above method preferably has an absolute difference of less than 2.0 MPa between the stress at TD (at 100% elongation) and the stress at MD (at 100% elongation), more preferably less than 1.0 MPa, and even more preferably less than 0.5 MPa. If the absolute difference between the stress at TD (at 100% elongation) and the stress at MD (at 100% elongation) is less than 2.0 MPa, the isotropy of the packaging film is excellent when packaging goods, making it possible to easily package the goods.

[0075] The above-mentioned "stress at 50% elongation in MD," "stress at 100% elongation in MD," "stress at 50% elongation in TD," and "stress at 100% elongation in TD" can be determined by the method described in the examples below.

[0076] Furthermore, since the packaging film manufactured by the above method has a permanent deformation of 25% or less, its elasticity is improved, making it possible to improve the holding power of the packaged goods.

[0077] Furthermore, from the viewpoint of further improving the retention of the packaged goods, it is preferable that the permanent deformation of the packaging film be 20% or less.

[0078] Furthermore, the term "permanent deformation" as used here refers to the amount calculated by the following method.

[0079] A strip of test material measuring 100 mm in one direction and 25 mm in the direction perpendicular to that direction is cut from the packaging film. This test material is fixed to the grips of a precision universal testing machine (Shimadzu Corporation, Autograph AG-5000A) with a grip distance of 25 mm. The test material is then stretched in the longitudinal direction at a speed of 254 mm / min until the elongation (stretching ratio) calculated by formula (1) below reaches 100%, and then immediately contracted at the same speed. The permanent strain [%] is then calculated from formula (2) below.

[0080] Elongation [%] = (L1 - L0) / L0 × 100 (1) Permanent deformation [%] = (L2 / L0) × 100 (2)

[0081] However, L0 is the distance between the grips before stretching (mm), L1 is the distance between the grips after stretching (mm), and L2 is the distance between the grips when the load on the test piece (N / 25mm) becomes 0 during contraction (mm).

[0082] Furthermore, from the viewpoint of improving the heat seal strength of the packaging film on the paper substrate, it is preferable that the peel strength of the packaging film on the paper substrate be 4N / 50mm or more, and more preferably 5N / 50mm or more.

[0083] The "peel strength of the packaging film on the paper substrate" can be determined by the method described in the examples below.

[0084] Furthermore, the thickness of the intermediate layer 2 is preferably 20 to 200 μm, and more preferably 30 to 180 μm. If the thickness of the intermediate layer 2 is 20 μm or more, the rubber elasticity effect of the thermoplastic elastomer contained in the intermediate layer can be fully utilized, improving the elasticity of the packaging film. Also, if the thickness of the intermediate layer is 200 μm or less, the film can be precisely slit to a specified width with a slitting blade, so the film ends can be neatly wound when the film is wound into a roll.

[0085] Furthermore, the thickness of the surface layers 3 and 4 is preferably 3 to 15 μm, and more preferably 5 to 10 μm. If the thickness of the surface layers 3 and 4 is 3 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 15 μm or less, it becomes possible to ensure sufficient thickness of the intermediate layer 2, thereby significantly improving the elasticity of the packaging film.

[0086] Furthermore, the thickness of the packaging film 1 is preferably 30 to 250 μm, and more preferably 40 to 200 μm. If the thickness of the packaging film 1 is 30 to 250 μm or less, the elasticity of the packaging film can be improved, and it can be precisely slit to a specified width with a slitting blade, so that the film ends can be neatly wound when the film is wound into a roll.

[0087] Furthermore, even in packaging film 1 where the thickness ratio of surface layers 3 and 4 to the total thickness of the packaging film is small, from the viewpoint of improving elasticity, it is preferable that the thickness ratio of surface layer 3 (or surface layer 4) to intermediate layer 2 be surface layer:intermediate layer = 1:3 to 1:20, and more preferably 1:5 to 1:18.

[0088] <Packaging materials> The packaging member of the present invention comprises the packaging film 1 of the present invention described above, 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.

[0089] The packaging component comprises an attachment section to which the surface layer and base material are attached, and an unattached section to which the surface layer and base material are not attached. The packaging is configured such that an article is inserted and contained between the base material and the packaging film in the unattached section, and the article is held between the base material and the packaging film to be packaged.

[0090] Examples of base materials include paper base materials, resin sheets, and nonwoven fabrics, with paper base materials being preferable. Furthermore, from the viewpoint of improving strength, corrugated cardboard or thick paper is more preferable, and corrugated cardboard is even more preferable.

[0091] Furthermore, while the base material can be rectangular, square, circular, or elliptical in shape, it is not limited to these shapes and can be appropriately selected according to the shape of the items to be packaged or the shape of the packaging container.

[0092] Another method for manufacturing packaging components is to laminate a base material and a surface layer of a packaging film in contact with each other, and then heat the peripheral edge of the packaging film to heat-seal the peripheral edge of the packaging film to the base material, thereby manufacturing a packaging component having an attachment portion where the surface layer and base material are attached, and an unattached portion where the surface layer and base material are not attached.

[0093] Furthermore, packaging materials are used when transporting goods, typically in a state where they are contained within packaging containers such as boxes or bags made of paper or resin (for example, cardboard boxes). [Examples]

[0094] The present invention will be described below based on examples. However, the present invention is not limited to these examples, and these examples can be modified and altered in accordance with the spirit of the invention; such modifications do not exclude them from the scope of the invention.

[0095] The materials used in the manufacture of the packaging film are listed below.

[0096] (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) LDPE: 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) (4) Lubricant: Elucic acid amide-containing masterbatch (manufactured by Riken Vitamin Co., Ltd., trade name: Lichemaster ELM080, density: 0.919 g / cm 3 ) (5) Polarity imparting agent 1: 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 ) (6) Polarity imparting agent 2: Polyolefin resin having an intramolecular carboxylic anhydride structure (manufactured by Sanyo Chemical Industries, Ltd., trade name: Yumex 5500, melting point: 123 °C, acid value: 17 mgKOH / g, density: 0.918 g / cm 3 ) (7) R-PP: Random polypropylene (manufactured by Prime Polymer Co., Ltd., trade name: Prime Polypro F227, melting point: 152 °C, density: 0.910 g / cm 3 , MFR: 8.0 g / 10 min) (8) Polyolefin-based elastomer (manufactured by Dow Chemical, trade name: Affinity PL 1880G, ethylene-octene copolymer, density: 0.902 g / cm 3 1], MFR: 1.0 g / 10 min) (9) Olefin block copolymer (manufactured by Dow Chemical, trade name: INFUSE9100, ethylene / octene block copolymer, density: 0.877 g / cm³) 3 (MFR: 1.0g / 10 minutes)

[0097] (Example 1) <Manufacturing of packaging film> First, the materials shown in Table 1 were mixed to prepare the intermediate layer forming material and the surface layer forming material (first surface layer and second surface layer) of Example 1 having the composition (parts by mass) shown in Table 1, thereby obtaining the intermediate layer forming resin mixture and the surface layer forming resin mixture.

[0098] Next, using an extruder equipped with a T-die (manufactured by Mitsubishi Heavy Industries), the resin mixture for forming the intermediate layer and the resin mixture for forming the surface layer were extruded at 200°C. A three-layer film having an intermediate layer, a first surface layer provided on the first surface of the intermediate layer, and a second surface layer provided on the second surface of the intermediate layer was formed by the cast film process method. The film was then cooled by being placed in close contact with a chill roll at 25°C to obtain a packaging film. The thickness of the manufactured packaging film, as well as the thicknesses of the intermediate layer and surface layer, are shown in Table 1.

[0099] Table 1 also shows the total amount of ethylene units in the propylene-based elastomer relative to the entire surface layer (first surface layer) (parts by mass) and the total amount of ethylene units in the propylene-based elastomer relative to the entire surface layer (second surface layer) (parts by mass).

[0100] In this embodiment, the first surface layer (or second surface layer) contains 87 parts by mass of propylene elastomer 1 (ethylene unit content: 4% by mass) per 100 parts by mass of the first surface layer (or second surface layer). Therefore, the total amount of ethylene units in the propylene elastomer relative to the entire surface layer (first surface layer or second surface layer) is 87 × 0.04 = 3.48 parts by mass (i.e., the total amount of ethylene units in the propylene elastomer relative to the entire first surface layer (or entire second surface layer) is 3.48% by mass of the 100% by mass of the surface layer).

[0101] <Evaluation of the stickiness of Chill Roll> Using the cast film process described above, a three-layer film was formed, comprising an intermediate layer, a first surface layer provided on the first surface of the intermediate layer, and a second surface layer provided on the second surface of the intermediate layer. The film was then placed in close contact with a chill roll at 25°C, and the stickiness of the chill roll was evaluated during cooling according to the following criteria. The results are shown in Table 1.

[0102] Film can be manufactured without sticking to the chill roll: no stickiness. The film adheres to the chill roll, making it impossible or difficult to manufacture: sticky.

[0103] <Measurement of permanent deformation> From the manufactured packaging film, strip-shaped test pieces measuring 100 mm in one direction and 25 mm in the direction perpendicular to that direction were cut. These test pieces were fixed to the grips of a precision universal testing machine (Shimadzu Corporation, Autograph AG-5000A) with a grip distance of 25 mm. The test pieces were then stretched in the longitudinal direction at a speed of 254 mm / min until the elongation (stretch ratio) calculated by formula (1) above reached 100%, and then immediately contracted at the same speed. The permanent strain [%] for MD and TD was then calculated from formula (2) above. The tests were conducted at room temperature (23℃ ± 2℃). The results are shown in Table 1.

[0104] <Haze Measurement> Using a turbidimeter (manufactured by Nippon Denshoku Co., Ltd., product name: Haze Meter NDH-5000), the haze [%] of the manufactured packaging film (packaging film before stretching) was measured in accordance with JIS K 7136. The haze was measured six times, and the average value of these six measurements was calculated as the haze [%] of the manufactured packaging film. The results are shown in Table 1.

[0105] Furthermore, strip-shaped test pieces measuring 50 mm in one direction and 100 mm in the direction perpendicular to that direction were cut from the manufactured packaging film. These test pieces were fixed to the grips of a precision universal testing machine (Shimadzu Corporation, Autograph AG-5000A) with a grip distance of 25 mm. Then, in the MD, the test pieces were stretched in the longitudinal direction at a speed of 254 mm / min until the elongation (stretching ratio) calculated by formula (1) above reached 100%, and then immediately contracted at the same speed.

[0106] Then, using a turbidimeter (manufactured by Nippon Denshoku Co., Ltd., product name: Haze Meter NDH-5000), the haze [%] of the packaging film after 100% stretching in MD was measured in accordance with JIS K 7136. The haze measurement was performed three times, and the average value of the three haze measurements was calculated and used as the haze [%] of the manufactured packaging film. The results are shown in Table 1.

[0107] <Measurement of stress at 50% elongation in the extension direction (MD)> In the hysteresis test in MD, test specimens were prepared by cutting the manufactured packaging film to 25 mm in the TD direction and 100 mm in the MD direction. Under conditions of a chuck distance of 25 mm and a test speed of 254 mm / min, the test specimens were stretched to MD until the chuck distance was 50 mm (100%), and then the chuck distance was returned to 25 mm without holding that state. The stress [MPa] in MD was then measured when the chuck distance was 37.5 mm (50% elongation) during the stretching process to 50 mm (100%) using a precision universal testing machine (Shimadzu Corporation, product name: Autograph AG-5000A). The results are shown in Table 1.

[0108] <Stress at 50% elongation in the direction perpendicular to the elongation direction (TD)> In the hysteresis test at TD, test specimens were prepared by cutting the manufactured packaging film to 25 mm in the MD direction and 100 mm in the TD direction. Under conditions of a chuck distance of 25 mm and a test speed of 254 mm / min, the test specimens were stretched to TD until the chuck distance was 50 mm (100%), and then the chuck distance was returned to 25 mm without holding that state. The stress [MPa] at TD when the chuck distance was 37.5 mm (50% elongation) during the stretching of the test specimen to TD was measured using a precision universal testing machine (Shimadzu Corporation, product name: Autograph AG-5000A). The results are shown in Table 1.

[0109] <Stress at 100% elongation in the stretching direction (MD)> In the hysteresis test in MD, test specimens were prepared by cutting the manufactured packaging film to 25 mm in the TD direction and 100 mm in the MD direction. Under conditions of a chuck distance of 25 mm and a test speed of 254 mm / min, the test specimens were stretched to MD until the chuck distance was 50 mm (100%), and then the chuck distance was returned to 25 mm without holding that state. The stress [MPa] in MD at a chuck distance of 50 mm (100% stretch) was then measured using a precision universal testing machine (Shimadzu Corporation, product name: Autograph AG-5000A). The results are shown in Table 1.

[0110] <Stress at 100% elongation in the direction perpendicular to the elongation direction (TD)> In the hysteresis test at TD, test specimens were prepared by cutting the manufactured packaging film to 25 mm in the MD direction and 100 mm in the TD direction. Under conditions of a chuck distance of 25 mm and a test speed of 254 mm / min, the test specimens were stretched to TD until the chuck distance was 50 mm (100%), and then the chuck distance was returned to 25 mm without holding that state. The stress [MPa] at TD when the chuck distance was 50 mm (100% elongation) was then measured using a precision universal testing machine (Shimadzu Corporation, product name: Autograph AG-5000A). The results are shown in Table 1.

[0111] <Measurement of peel strength> Packaging components were manufactured by heat sealing a packaged film onto a paper substrate under conditions of a temperature of 180°C and a pressure of 0.15 MPa.

[0112] Next, the heat seal strength of the packaging film on the paper substrate in the obtained packaging material was evaluated. More specifically, a test piece measuring 50 mm in width and 100 mm in length was cut from the packaging material, and a tensile testing machine (Shimadzu Corporation, product name: Autograph AG-5000A) was used to perform a 180° peel on the test piece under the conditions of a measurement temperature of 23°C and a tensile speed of 200 mm / min, and the peel strength [N / 50 mm] of the packaging film on the paper substrate was measured.

[0113] Furthermore, a peel strength of 4N / 50mm or higher was evaluated as indicating excellent heat-seal strength of the packaging film on the paper substrate. The results are shown in Table 1.

[0114] (Examples 2-10, Comparative Examples 1-3) Except for changing the composition (parts by mass) of the packaging film to the conditions shown in Tables 1 and 2, packaging films having the thicknesses shown in Tables 1 and 2 were manufactured in the same manner as in Example 1 described above.

[0115] Then, in the same manner as in Example 1 described above, the stickiness of the chill roll was evaluated, permanent strain was measured, haze was measured, stress was measured, and peel strength was measured. The results are shown in Tables 1 and 2.

[0116] In Comparative Examples 2 and 3, permanent strain, haze, stress, and peel strength measurements could not be performed due to stickiness of the chill roll (stickiness of the surface layer caused by the properties of the elastomer).

[0117] (Comparative Example 4) <Manufacturing of packaging film> Except for changing the composition (parts by mass) of the packaging film to the conditions shown in Table 2 and changing the extruder to one manufactured by Labtech, a packaging film having the thickness shown in Table 2 was manufactured in the same manner as in Example 1 described above.

[0118] Then, in the same manner as in Example 1 described above, the stickiness of the chill roll was evaluated, permanent strain was measured, haze was measured, stress was measured, and peel strength was measured. The results are shown in Table 2.

[0119] [Table 1]

[0120] [Table 2]

[0121] As shown in Table 1, in the packaging films of Examples 1 to 10, the content of propylene elastomer (propylene elastomer 1 to 3) in the surface layer is 45% to 95% by mass, and the total content of ethylene units in the propylene elastomer in the surface layer is 1% to less than 7% by mass. Therefore, the stress during elongation in MD and TD is small, and the packaging film can be stretched with little force when packaging goods. Furthermore, since the haze after stretching is 25% or less, even when the packaging film is stretched when packaging goods, whitening of the stretched portion after stretching can be suppressed, and it can be seen that it has excellent transparency. Furthermore, it can be seen that stickiness caused by the properties of the elastomer can be prevented. In addition, since the peel strength is 4N / 50mm or more, it can be seen that the heat seal strength of the packaging film on paper substrates is excellent.

[0122] On the other hand, as shown in Table 2, in the packaging film of Comparative Example 1, the surface layer (first surface layer) does not contain a propylene-based elastomer but contains random polypropylene, resulting in a very large haze (84.6%) after stretching. When the packaging film is stretched for packaging goods, whitening occurs in the stretched area, indicating poor transparency.

[0123] Furthermore, in the packaging film of Comparative Example 2, the content of propylene-based elastomer (propylene-based elastomer 3) relative to the entire surface layer is greater than 95% by mass, and the total content of ethylene units in the propylene-based elastomer relative to the entire surface layer is greater than 6% by mass. As described above, this indicates that stickiness of the chill roll (stickiness of the surface layer due to the properties of the elastomer) occurs.

[0124] Furthermore, in Comparative Example 3, since the total content of ethylene units in the propylene-based elastomer relative to the entire surface layer is greater than 6% by mass, it can be seen that stickiness of the chill roll (stickiness of the surface layer due to the properties of the elastomer) occurs, as described above.

[0125] Furthermore, in Comparative Example 4, the surface layer does not contain a propylene-based elastomer, and the surface layer (second surface layer) contains an ethylene-octene copolymer. As a result, the stress during elongation in MD and TD is large, making it difficult to stretch the packaging film with a weak force when packaging goods.

[0126] Furthermore, in Comparative Example 4, since it does not contain a polarity imparting agent, the peel strength is less than 4N / 50mm, indicating that the heat seal strength of the packaging film on the paper substrate is poor. [Industrial applicability]

[0127] As described above, the present invention is suitable for packaging films used when packaging articles. [Explanation of Symbols]

[0128] 1. Packaging film 2. Middle Class 3. Surface layer (first surface layer) 4. Surface layer (second surface layer)

Claims

1. The system comprises an intermediate layer containing a thermoplastic elastomer and surface layers provided on both sides of the intermediate layer, which contain a propylene-based elastomer. The propylene-based elastomer is a propylene-based elastomer obtained by copolymerizing propylene with ethylene, The content of the propylene-based elastomer in relation to the entire surface layer is 45% by mass or more and 95% by mass or less. The total content of ethylene units in the propylene-based elastomer relative to the entire surface layer is 1% by mass or more and less than 7% by mass. A packaging film characterized by the following features.

2. The thickness of the aforementioned surface layer is 3 to 15 μm. The packaging film according to claim 1, characterized in that the thickness ratio of the surface layer to the intermediate layer is surface layer:intermediate layer = 1:3 to 1:

20.

3. The packaging film according to claim 1 or 2, characterized in that the surface layer contains a polarity imparting agent.

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