Easy-to-open film and package

Abstract

To provide an easy-to-open film having both sufficient sealability and easy openability (easy peelability) even when heat seal is performed at a high temperature and further having heat resistance which can withstand high temperature treatment such as high temperature sterilization, and a package.SOLUTION: An easy-to-open film has at least a seal layer, wherein the seal layer includes a polypropylene resin (a) having a melting point of 145°C or higher, and a polyethylene resin (b) having a melting point of 105°C or higher, and the polypropylene resin (a) is a main component of the seal layer.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an easy-open film having a predetermined sealing layer and suitable for use in packaging food and the like, and to a package. [Background technology]

[0002] Deep-drawn packages in which a deep-drawn base material is sealed with a lid material have been known as packages for packaging contents such as food. In addition, such deep-drawn packages may be subjected to high-temperature treatment such as high-temperature sterilization after packaging the contents.

[0003] As a film for the base material, Patent Document 1 describes a co-extruded film having a polyamide resin layer / adhesive resin layer / adhesive resin layer etc. / polypropylene resin layer. Patent Document 1 also describes that the co-extruded film has good pinhole resistance and can suppress curling of the flange portion (the surface seal portion around the housing portion) after high-temperature sterilization. Furthermore, Patent Document 2 describes a co-extruded film having a polyamide resin layer / polyethylene resin layer / (sealing layer) as a film for the base material of deep-drawn packaging that does not undergo delamination (peeling) during retort.

[0004] On the other hand, laminated films of a polypropylene layer (outer layer) / adhesive resin layer / polypropylene layer (sealing layer) are often used as lid materials for high-temperature treatment, so a sealing layer whose main component is polypropylene resin is used for the film used as the base material for deep-draw packaging that is resistant to high-temperature treatment and has easy-open properties. However, if the melting point of the polypropylene resin in the sealing layer is lower than 140°C, the lid material and base material at the opening trigger part of the package will fuse together during high-temperature treatment, making it difficult to open. On the other hand, if the melting point of the polypropylene resin in the sealing layer is 140°C or higher, the heat-sealing temperature must be set to 160°C or higher, which can cause the polypropylene resin used in the outer layer of the lid material to fuse to the sealing hot plate.

[0005] Furthermore, in order to increase the heat sealing temperature, the polypropylene layer used in the outer layer of the lid material can be changed to a resin with a higher melting point. However, polypropylene resins with high melting points generally have poor impact resistance, such as pinhole resistance, at low temperatures, and therefore tend to lack the properties required for packaging materials. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 10-76616 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-128884 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide an easy-open film and a package that have both sufficient sealability and easy-openability (easy-peel property) even when heat-sealed at high temperatures, and further have heat resistance that enables them to withstand high-temperature treatments such as high-temperature sterilization. [Means for solving the problem]

[0008] As a result of intensive research to solve the above-mentioned problems, the inventors discovered that the above-mentioned problems can be solved by using a polypropylene-based resin and a polyethylene-based resin having a specific melting point as the sealing layer of an easy-open film, and further by making the polypropylene-based resin having the specific melting point the main component of the sealing layer, and thus completed the present invention.

[0009] That is, the gist of the present invention is the following [1] to [9]. [1] An easy-to-open film having at least a seal layer, wherein the seal layer contains a polypropylene-based resin (a) having a melting point of 145°C or higher and a polyethylene-based resin (b) having a melting point of 105°C or higher, and the polypropylene-based resin (a) is the main component of the seal layer. [2] The easy-open film according to [1], wherein the polypropylene-based resin (a) is homopolypropylene. [3] The easy-open film according to [1] or [2], wherein the polyethylene resin (b) is a linear low-density polyethylene resin. [4] The easy-open film according to any one of [1] to [3], wherein the surface softening temperature of the seal layer measured by nano thermal analysis is 125°C or lower. [5] The storage modulus of the sealing layer at 120°C measured according to JIS K7244-4 (1999) is 8.0 × 10 7 The easy-open film according to any one of [1] to [4], wherein the film has a resistance to deformation of 100 Pa or more. [6] The easy-open film according to any one of [1] to [5], wherein the monomers constituting the polypropylene-based resin (a) and / or the polyethylene-based resin (b) are plant-derived biomass raw materials. [7] The easy-open film according to any one of [1] to [6], which has a thermoplastic resin layer adjacent to the seal layer. [8] The easy-open film according to any one of [1] to [7], further comprising a barrier resin layer. [9] A package obtained by heat-sealing the easy-open film according to any one of [1] to [8] and a film or container made of a thermoplastic resin. [Effects of the Invention]

[0010] The easy-open film of the present invention has both sufficient sealability and easy-openability (easy peelability) even when heat-sealed at high temperatures, and can also withstand high-temperature treatments such as high-temperature sterilization. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to the embodiments described below.

[0012] In this specification, the term "major component" refers to a component that accounts for the largest percentage by mass when the total of the target substance is 100% by mass, and is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more.

[0013] Furthermore, when it is written as "X to Y" (X and Y are any numbers), unless otherwise specified, it means "X or more and Y or less," as well as "preferably greater than X" and "preferably smaller than Y." When expressed as "X or more" (X is any number) or "Y or less" (Y is any number), it also means that "it is preferably greater than X" or "it is preferably less than Y." In this specification, "X and / or Y (X and Y are any configurations)" means at least one of X and Y, and means three possibilities: X only, Y only, and X and Y. In the present specification, when numerical ranges are described in stages, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of another numerical range. In addition, in the numerical ranges described herein, the upper or lower limit of the numerical range can also be replaced with the values shown in the examples or formulation examples.

[0014] In this specification, the term "film" encompasses a wide range of materials from thick sheets to thin films.

[0015] In addition, in this specification, "easy-open property" means that the peel strength measured according to the peel test in the examples described later is 200 gf / 15 mm width or more and 2000 gf / 15 mm width or less.

[0016] <<Easy-to-open film>> An easy-open film according to one embodiment of the present invention (hereinafter referred to as "the film") has at least a seal layer, and the seal layer contains a polypropylene resin (a) having a melting point of 145°C or higher and a polyethylene resin (b) having a melting point of 105°C or higher, with the polypropylene resin (a) being the main component of the seal layer. The film can be suitably used as a base or lid material film for deep-drawn packaging, and is particularly suitable for use as a base material film for deep-drawn packaging.

[0017] In addition to the sealing layer, the present film may have, for example, a thermoplastic resin layer, a barrier resin layer, an adhesive resin layer, etc. The present film may have one of these layers or two or more of them. The "thermoplastic resin layer" means a layer containing a thermoplastic resin as a main component, the "barrier resin layer" means a layer containing a barrier resin as a main component, and the "adhesive resin layer" means a layer containing an adhesive resin as a main component.

[0018] In particular, the present film preferably has a thermoplastic resin layer adjacent to the sealing layer from the viewpoints of improving film strength and heat resistance and adjusting thickness.

[0019] In addition, the present film preferably has a barrier resin layer from the viewpoint of gas barrier properties. Each layer of the film will now be described.

[0020] <Sealing layer> As described above, the sealing layer contains a polypropylene-based resin (a) having a melting point of 145°C or higher and a polyethylene-based resin (b) having a melting point of 105°C or higher, with the polypropylene-based resin (a) being the main component of the sealing layer. By having a sealing layer containing the polypropylene-based resin (a) as the main component, the present film can be endowed with heat resistance and sealing properties.

[0021] [Polypropylene resin (a)] The melting point (JIS K7121) of the polypropylene resin (a) is 145° C. or higher, preferably 150° C. or higher, and more preferably 155° C. or higher, from the viewpoint of heat resistance. The upper limit of the melting point is not particularly limited, but is usually 170° C. or lower.

[0022] The melt flow rate (MFR) (JIS K7210, 230°C, load 2.16 kg) of the polypropylene resin (a) is preferably 0.1 g / 10 min or more and less than 50 g / 10 min, more preferably 0.5 g / 10 min or more and less than 40 g / 10 min, and even more preferably 0.5 g / 10 min or more and less than 15 g / 10 min, from the viewpoint of film-forming properties.

[0023] The density (JIS K7121) of the polypropylene resin (a) is usually 0.880 to 0.905 g / cm 3 and preferably 0.890 to 0.900 g / cm 3 is.

[0024] Examples of the polypropylene resin (a) include random polypropylene (rPP), block polypropylene (bPP), homopolypropylene (hPP), propylene-α-olefin copolymer, ethylene-propylene-α-olefin copolymer, etc. These may be used alone or in combination of two or more. Among them, from the viewpoint of heat resistance, block polypropylene (bPP) and homopolypropylene (hPP) are preferred, and homopolypropylene (hPP) is more preferred.

[0025] [Polyethylene resin (b)] From the viewpoint of heat resistance during high-temperature treatment, the polyethylene resin (b) has a melting point (JIS K7121) of 105° C. or higher, preferably 110° C. or higher, and more preferably 120° C. or higher. The upper limit of the melting point is not particularly limited as long as it is within the range of commonly available polyethylene resins, but from the viewpoint of imparting sealability, it is usually 140° C. or lower, preferably 135° C. or lower, and more preferably 130° C. or lower.

[0026] The melt flow rate (MFR) (JIS K7210, 190°C, 2.16 kg load) of the polyethylene resin (b) is usually 0.1 g / 10 min or more, preferably 0.5 g / 10 min or more, from the viewpoint of film-forming properties. The upper limit is usually less than 15 g / 10 min, preferably less than 10 g / 10 min, more preferably less than 2.4 g / 10 min.

[0027] The density (JIS K7121) of the polyethylene resin (b) is usually 0.940 g / cm 3 less than 0.935 g / cm 3 less than 0.930 g / cm 3 The lower limit is not particularly limited, but is usually less than 0.870 g / cm 3 or more, preferably 0.890 g / cm 3 More preferably, 0.900 g / cm 3 If the density is higher than the above range, the heat sealability tends to be difficult to exhibit, and if the density is too low, the heat resistance tends to be insufficient.

[0028] Examples of the polyethylene resin (b) include ultra-low density polyethylene, linear low density polyethylene (LLDPE), low density polyethylene (LDPE), medium density polyethylene (MDPE), and high density polyethylene (HDPE). These may be used alone or in combination of two or more. Among these, LLDPE and LDPE are preferred, with LLDPE being more preferred, from the viewpoint of providing sealability.

[0029] The mass ratio of the polypropylene resin (a) to the polyethylene resin (b) is preferably propylene resin (a):polyethylene resin (b)=90:10 to 50:50, more preferably 85:15 to 55:45, and even more preferably 80:20 to 60:40. By setting the mass ratio of the polypropylene resin (a) to the polyethylene resin (b) within the above range, there is a tendency that heat resistance to high-temperature sterilization and the like and heat sealability can be improved.

[0030] The monomers constituting the polypropylene-based resin (a) and / or polyethylene-based resin (b) may be petroleum-derived or plant-derived biomass materials, but are preferably plant-derived biomass materials from an environmental perspective. That is, the polypropylene-based resin (a) is preferably a biomass polypropylene-based resin, and the polyethylene-based resin (b) is preferably a biomass polyethylene-based resin.

[0031] Furthermore, for the purpose of improving or adjusting various properties such as moldability and productivity, the sealing layer may contain additives such as antifogging agents, antistatic agents, heat stabilizers, nucleating agents, antioxidants, lubricants, antiblocking agents, mold release agents, and ultraviolet absorbers, as long as the effects of the present invention are not significantly impaired. These additives may be used alone or in combination of two or more.

[0032] The sealing layer can be obtained by the manufacturing method described below, and the softening temperature of the sealing layer measured by nano thermal analysis (nano TA) is preferably 125° C. or lower, more preferably 120° C. or lower, from the viewpoint of heat sealing properties. On the other hand, the lower limit is preferably 95° C. or higher, more preferably 100° C. or higher, from the viewpoint of imparting heat resistance.

[0033] The storage modulus (10 Hz tension) of the sealing layer at 25°C measured in accordance with JIS K7244-4 (1999) is usually 9.0 x 10 8 Pa or more, preferably 1.0 × 10 9 The upper limit is not particularly limited, but is usually 3.0 × 10 9 It is Pa.

[0034] The storage modulus (10 Hz tensile) of the sealing layer at 120°C measured in accordance with JIS K7244-4 (1999) was 8.0 × 10 7 Pa or more is preferable, and 9.0×10 7 Pa or more, more preferably 1.0 × 10 8 The upper limit is not particularly limited, but is usually 5.0 × 10 8By setting the storage modulus at 120°C within the above range, there is a tendency that heat resistance to high-temperature sterilization and the like can be better imparted.

[0035] The storage modulus (10 Hz tensile) of the sealing layer at 140°C measured in accordance with JIS K7244-4 (1999) is usually 1.0 x 10 8 Pa or less, preferably 9.0 × 10 7 Pa or less, more preferably 8.0 × 10 7 The lower limit is not particularly limited, but is usually 1.0 × 10 6 By setting the storage modulus at 140°C within the above range, there is a tendency that better heat sealability can be imparted.

[0036] The biomass ratio of the sealing layer is preferably 5% or more, more preferably 10% or more, and even more preferably 20% or more. The biomass ratio can be calculated by the following method. [How to calculate biomass ratio] Biomass ratio (%) = "Biomass ratio of biomass raw material" (%) x "mass ratio of biomass raw material"

[0037] The biomass ratio is determined by measuring the content of carbon derived from plants (biomass) using a commonly known method, using radiocarbon ( 14 It can also be calculated by measuring carbon-12( 12 C), carbon-13( 13 C), carbon-14( 14Carbon-14 exists in three isotopes, each with a different number of neutrons (C). Carbon-14 exists in the atmosphere at a constant rate and decreases periodically, becoming half of its original amount in 5,730 years (half-life). Furthermore, plants absorb carbon dioxide from the atmosphere to grow, so the carbon-14 they contain is in the same proportion as that in the atmosphere. On the other hand, fossil resources such as petroleum do not contain carbon-14, so carbon-14 correlates with biomass. Therefore, the biomass level of a sample can be calculated by measuring the types of carbon contained in the sample and their respective proportions using an accelerator mass spectrometer (AMS) or similar.

[0038] The thickness of the seal layer is usually 3 μm or more, preferably 4 μm or more, and more preferably 5 μm or more. The upper limit of the thickness is usually 60 μm or less, preferably 50 μm or less, more preferably 30 μm or less, even more preferably 20 μm or less, and particularly preferably 15 μm or less. When the thickness of the seal layer is equal to or greater than the above-mentioned numerical value, the film formability during co-extrusion tends to be more stable, and when the thickness is equal to or less than the above-mentioned numerical value, the occurrence of fluffing (roughness of the opening surface) and stringiness when the package is opened tends to be suppressed, and a good peel appearance tends to be obtained.

[0039] <Thermoplastic resin layer> The present film preferably has a thermoplastic resin layer for the purposes of improving film strength and heat resistance and adjusting thickness. Furthermore, it is preferable that the thermoplastic resin layer is adjacent to the seal layer of the present film in terms of improving film strength and heat resistance.

[0040] Examples of the thermoplastic resin include polyolefin resin (PO) and polyamide resin (PA).

[0041] [Polyolefin resin] Examples of the polyolefin resin include polyethylene resin (PE), polypropylene resin (PP), and α-olefin copolymer. These may be used alone or in combination of two or more. Among these, polyethylene resin and polypropylene resin are preferred.

[0042] The present film preferably has a layer containing a polyethylene resin as a main component (polyethylene resin layer) as an adjacent layer adjacent to the seal layer.

[0043] In addition, the present film preferably has a layer (polypropylene-based resin layer) containing a polypropylene-based resin as a main component as an outer layer (a layer located on the opposite side of the sealing layer). By providing a polypropylene-based resin layer as the outer layer of the package, curling of the flange portion (the sealing portion around the containing portion in the package) after high-temperature treatment tends to be suppressed.

[0044] Examples of the polyethylene resin include resins containing ethylene structural units as a main component, such as linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE).

[0045] The melting point (JIS K7121) of the polyethylene resin is usually 100°C or higher, preferably 110°C or higher, and more preferably 120°C or higher.

[0046] Examples of the polypropylene resin include resins containing propylene structural units as a main component, such as random polypropylene (rPP), block polypropylene (bPP), homopolypropylene (hPP), etc. Among these, homopolypropylene, which has heat resistance, is preferred from the viewpoint of preventing curling and whitening after high-temperature sterilization.

[0047] The melting point (JIS K7121) of the polypropylene resin is usually 120°C or higher, preferably 130°C or higher, and more preferably 140°C or higher.

[0048] Examples of the α-olefin copolymer include copolymers of α-olefins having 2 to 10 carbon atoms, such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, and 1-octene. Specific examples include ethylene-α-olefin copolymers, propylene-α-olefin copolymers, and ethylene-propylene-α-olefin copolymers.

[0049] [Polyamide resin] When the present film has a layer mainly composed of a polyamide resin (polyamide resin layer), it tends to be able to impart pinhole resistance. Furthermore, when the present film is used as a deep-draw base material, the provision of a polyamide resin layer tends to improve the deep-draw formability of the present film. From the viewpoint of pinhole resistance, it is preferable that the polyamide resin layer is located in the middle layer of the present film (the layer sandwiched between the sealing layer and the outer layer).

[0050] The polyamide resin is not particularly limited, but examples thereof include homopolymers or copolymers obtained by polycondensation of lactams with three or more ring members, polymerizable ω-amino acids, diamines and dicarboxylic acids, and the like.

[0051] Furthermore, when the polyamide-based resin is a copolymer, the structural units derived from the lactam having a three or more membered ring, the polymerizable ω-amino acid, the diamine and the dicarboxylic acid are preferably contained in the polyamide-based resin in an amount of 50 mol% or more, more preferably 80 mol% or more, even more preferably 85 mol% or more, and particularly preferably 90 mol% or more.

[0052] Examples of the lactam having a three or more membered ring include ε-caprolactam, ω-enantholactam, ω-laurolactam, and α-pyrrolidone.

[0053] Examples of the polymerizable ω-amino acid include ω-aminocaproic acid, ω-aminoheptanoic acid, ω-aminononanoic acid, ω-aminoundodecanoic acid, and ω-aminododecanoic acid.

[0054] Examples of the diamine include aliphatic amines such as tetramethylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, undecamethylenediamine, dodecamethylenediamine, 2,2,4-trimethylhexamethylenediamine, and 2,4,4-trimethylhexamethylenediamine; alicyclic diamines such as 1,3 / 1,4-bis(aminomethyl)cyclohexane, isophoronediamine, piperazine, bis(4-aminocyclohexyl)methane, and 2,2-bis-(4'-aminocyclohexyl)propane; and aromatic diamines such as metaxylylenediamine and paraxylylenediamine.

[0055] Examples of the dicarboxylic acid include aliphatic dicarboxylic acids such as glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, nonanedioic acid, decanedioic acid, undecanedioic acid, and dodecanedioic acid; alicyclic carboxylic acids such as hexahydroterephthalic acid and hexahydroisophthalic acid; and aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid (1,2-isomer, 1,3-isomer, 1,4-isomer, 1,5-isomer, 1,6-isomer, 1,7-isomer, 1,8-isomer, 2,3-isomer, 2,6-isomer, and 2,7-isomer), and metal-isophthalic sulfonic acid.

[0056] Specific examples of polyamide resins include nylon resins such as nylon 4, nylon 6, nylon 7, nylon 11, nylon 12, nylon 46, nylon 66, nylon 69, nylon 610, nylon 611, nylon 6T, nylon 6I, 6-66, nylon 6-610, nylon 6-611, nylon 6-12, nylon 6-612, nylon 6-6T, nylon 6-6I, nylon 6-66-610, nylon 6-66-12, nylon 6-66-612, nylon 66-6T, nylon 66-6I, nylon 6T-6I, and nylon 66-6T-6I.

[0057] As the polyamide resin, it is preferable to use a nylon resin from the viewpoint of imparting pinhole resistance to the film, and among these, it is particularly preferable to use nylon 6 or nylon 6-66.

[0058] The thermoplastic resin layer may contain the additives described above for the sealing layer, provided that the additives do not significantly impair the effects of the present invention. The additives may be used alone or in combination of two or more.

[0059] When the present film has a thermoplastic resin layer, the thickness thereof (single layer) is usually 5 to 150 μm, preferably 10 to 120 μm, and more preferably 20 to 100 μm.

[0060] When the present film has a polypropylene-based resin layer, its thickness (single layer) is usually 5 to 150 μm, preferably 10 to 120 μm, and more preferably 15 to 100 μm. By making the thickness of the polypropylene-based resin layer equal to or greater than the above-mentioned numerical value, curling of the flange portion after high-temperature sterilization tends to be suppressed, and by making the thickness equal to or less than the above-mentioned numerical value, the present film tends to maintain good deep-draw formability.

[0061] When the present film has a polyethylene-based resin layer, its thickness (single layer) is usually 5 to 150 μm, preferably 10 to 120 μm, and more preferably 15 to 100 μm. By making the thickness of the polyethylene-based resin layer equal to or greater than the above-mentioned numerical value, stable film formation tends to become possible, and by making the thickness equal to or less than the above-mentioned numerical value, the cuttability and deep drawability of the film tend to be maintained well.

[0062] When the present film has a polyamide-based resin layer, its thickness (single layer) is usually 5 to 150 μm, preferably 10 to 120 μm, and more preferably 20 to 100 μm. By making the thickness of the polyethylene-based resin layer equal to or greater than the above-mentioned numerical value, good pinhole resistance tends to be obtained, and by making the thickness equal to or less than the above-mentioned numerical value, the cuttability and deep drawability of the film tend to be maintained good.

[0063] <Barrier resin layer> The present film preferably has a barrier resin layer for the purpose of imparting barrier properties, and from the viewpoint of barrier properties, the barrier resin layer is preferably located as an intermediate layer of the present film (a layer sandwiched between the seal layer and the outer layer).

[0064] Examples of the barrier resin include ethylene vinyl alcohol copolymer (EVOH), MXD-6 nylon resin (MXD), and the like.

[0065] [EVOH] The EVOH is a resin obtained by saponifying a copolymer of ethylene and vinyl acetate with an alkali catalyst or the like.

[0066] The ethylene content in the EVOH is not particularly limited, but from the viewpoint of film formation stability, it is usually 23 mol% or more, preferably 25 mol% or more, and from the viewpoint of gas barrier properties, it is usually 47 mol% or less, preferably 44 mol% or less.

[0067] The saponification degree of EVOH is usually 96 mol % or more, preferably 99 mol % or more. By maintaining the ethylene content and degree of saponification in the EVOH within the above ranges, good gas barrier properties can be maintained.

[0068] It should be noted that the EVOH is not limited to those produced by saponification, as long as they have a similar chemical structure.

[0069] [MXD] The MXD is a crystalline polyamide resin obtained by polycondensation reaction of metaxylenediamine and adipic acid.

[0070] The barrier resin layer may contain the additives described above for the sealing layer, provided that the additives do not significantly impair the effects of the present invention. The additives may be used alone or in combination of two or more.

[0071] When the present film has a gas barrier resin layer, its thickness (single layer) is usually 5 to 50 μm, preferably 7 to 40 μm, and more preferably 10 to 30 μm. If the thickness of the barrier resin layer is equal to or greater than the above-mentioned numerical value, good oxygen barrier properties tend to be obtained, and if the thickness is equal to or less than the above-mentioned numerical value, the deep drawability of the film tends to be good.

[0072] <Adhesive resin layer> The film may also be provided with an adhesive resin layer to increase the adhesive strength between the layers.

[0073] The adhesive resin may be a known modified polyolefin resin, such as a resin obtained by modifying a polyolefin resin with an unsaturated carboxylic acid or a derivative thereof.

[0074] The modified polyolefin resin has a density (JIS K7121) of 0.870 g / cm in order to ensure sufficient interlayer adhesion when subjected to high-temperature treatment. 3 or more, preferably 0.880 to 0.950 g / cm 3 It is preferable that: The melting point (JIS K7121) of the modified polyolefin resin is usually 100°C or higher, preferably 120°C or higher, and although there are no particular upper limits, it is usually 170°C or lower.

[0075] Among these, preferred examples of the adhesive resin include ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, maleic anhydride-modified polyethylene, and maleic anhydride-modified polypropylene.

[0076] The adhesive resin layer may contain the additives described above for the sealing layer, provided that the additives do not significantly impair the effects of the present invention. The additives may be used alone or in combination of two or more.

[0077] When the present film has an adhesive resin layer, the lower limit of its thickness (single layer) is usually 5 μm or more, preferably 8 μm or more, more preferably 10 μm or more, from the viewpoint of obtaining sufficient interlayer strength. The upper limit of the thickness is not particularly limited, but is usually 25 μm or less, preferably 20 μm or less, more preferably 15 μm or less, from the viewpoint of preventing the total film thickness from becoming too thick and increasing production costs.

[0078] [Method for manufacturing the present film] The present film can be produced by forming each of the layers by a known method, such as coextrusion, extrusion lamination, dry lamination, etc. Among these, the coextrusion method is preferred because it allows the production process to be integrated.

[0079] As a preferred layer structure of the present film, the following layer structure can be exemplified, omitting the adhesive resin layer and listing the layers in the order of outer layer (each layer) / sealing layer. (1) PP layer / sealing layer (2) PP layer / PE layer / sealing layer (3) PA layer / {sealing layer, or PO layer / sealing layer} (3) PA layer / EVOH layer / {sealing layer, or PO layer / sealing layer} (4) EVOH layer / {sealing layer, or PO layer / sealing layer} (5) PP layer / PA layer / EVOH layer / {sealing layer, or PO layer / sealing layer} (6) PP layer / EVOH layer / PA layer / {sealing layer, or PO layer / sealing layer} (7) PP layer / EVOH layer / PA layer / MXD layer / {sealing layer, or PO layer / sealing layer} (8) PP layer / EVOH layer / PA layer / MXD layer / PA layer / {sealing layer, or PO layer / sealing layer} In the layer structure, the layers are represented as PP layer (polypropylene resin layer), PE layer (polyethylene resin layer), PA layer (polyamide resin layer), PO layer (polyolefin resin layer), EVOH layer (ethylene-vinyl alcohol copolymer layer), and MXD layer (MXD-6 nylon resin layer).

[0080] The lower limit of the thickness of the present film is usually 70 μm or more, preferably 80 μm or more, and more preferably 90 μm or more. The upper limit of the thickness is usually 300 μm or less, preferably 250 μm or less, and more preferably 200 μm or less. When the thickness of the present film is equal to or greater than the lower limit, good pinhole resistance tends to be obtained. When the thickness of the present film is equal to or less than the upper limit, good easy-open properties (easy peel properties) tend to be easily obtained, and in deep drawing molding, the molding heating time can be set relatively short, and deep drawing tends to be able to be formed faithfully to the mold shape.

[0081] The film has easy-open properties, and the peel strength when the seal layer of the film is sealed to the thermoplastic resin is usually 200 gf / 15 mm width or more and 2000 gf / 15 mm width or less, preferably 220 gf / 15 mm width or more and 1500 gf / 15 mm width or less, and more preferably 250 gf / 15 mm width or more and 1000 gf / 15 mm width or less. If the peel strength of the seal layer is above this value, the bag tends to be less likely to tear when treated at high temperatures after being made into a package, and if the peel strength is below this value, good easy-open properties tend to be achieved. The peel strength of the sealing layer is preferably smaller than the interlayer peel strengths of the thermoplastic resin layer, the barrier layer and the adhesive resin layer.

[0082] <Package> This film has both sufficient sealing properties and easy-opening properties (easy peel properties) even when heat-sealed at high temperatures, and can also withstand high-temperature treatments such as high-temperature sterilization, making it suitable for use as a base film or lid material for deep-drawn packages. A package can be made by heat-sealing a base or lid material of a deep-drawn package made from this film to a film (lid material) or container made of a thermoplastic resin.

[0083] The thermoplastic resin is not particularly limited as long as it can be used as a lid material or a base material for deep-draw packaging.

[0084] The package according to one embodiment of the present invention obtained in this manner has sufficient sealing properties and is easy to open even when heat-sealed at high temperatures, and is also heat-resistant, making it useful for packaging food, daily necessities, miscellaneous goods, medical supplies, and various other items. [Example]

[0085] Examples will be shown below, but the present invention is not limited to these. Prior to the examples, the following raw materials were prepared.

[0086] [Polypropylene resin (a)] hPP: hPP (Melting point: 168°C, MFR: 3.2 g / 10 min (230°C), density: 0.90 g / cm 3 , manufactured by Lyondelbasell, biomass content 42% [Polyethylene resin (b)] PE1: LLDPE (melting point: 126°C, MFR: 2.3 g / 10 min (190°C), density: 0.916 g / cm 3 , manufactured by Braskem, biomass content 87% [Thermoplastic resin] rPP: rPP (melting point: 144°C, MFR: 7.0 g / 10 min (230°C), manufactured by Prime Polymer) PE2: LDPE (melting point: 104°C, MFR: 8.3g / 10min (190°C), manufactured by Braskem, biomass content 95%) PE3: LLDPE (melting point: 123°C, MFR: 2.3g / 10min (190°C), manufactured by Prime Polymer) The melting point of each resin was determined by differential scanning calorimetry in accordance with JIS K7121 using a thermal analyzer (Diamond DSC (product name): manufactured by PerkinElmer Japan) at a heating rate of 10°C / min, in a temperature range of -50 to 220°C, and with a sample weight of 10 mg, by performing measurements in the steps of heating → cooling → heating again.

[0087] <Examples 1 to 3 and Comparative Examples 1 to 4> Each resin was co-extruded using a single-screw extruder by the T-die method at a die temperature of 220°C to form a multilayer structure as shown in Table 1 below, and then rapidly cooled using a cast roll at 90°C to form a film, producing the easy-open films of Examples 1 to 3 and Comparative Examples 1 to 4. In addition, each seal layer of the easy-open films of Examples 1 and 2 and Comparative Examples 1 to 4 was produced by molding only the seal layer using a single-screw extruder by the T-die method at a die temperature of 220°C, followed by rapid cooling to form a film using a casting roll at 90°C.

[0088] The following evaluations were carried out using the obtained easy-open films and each seal layer of Examples 1 to 3 and Comparative Examples 1 to 4. The results are shown in Table 1 below.

[0089] [Elastic modulus evaluation] The storage modulus E' (Pa) of the obtained easy-open film of Example 2 and each seal layer was measured at 25°C, 120°C and 140°C in a tensile mode at a frequency of 10 Hz according to JIS K7244-4 (1999).

[0090] [Surface softening temperature] The obtained easy-open film of Example 2 and each seal layer were measured for softening point on the seal layer surface using a nanosearch microscope (Lext OLS3500 / SFT-3500 (Olympus) and nANOta2 NANOtHERMAL aNALYZER (Anasys Instruments)) while heating from 40°C at 10°C / sec with the tip of the probe (measuring needle) in contact with the seal layer surface.

[0091] [Peel test] The obtained easy-open films of Examples 1 to 3 and Comparative Examples 1 to 4 were used as a sealant to seal PE and rPP under the following conditions, and then a peel test was carried out.

[0092] [Sealing material PE] A film made by dry laminating PE (thickness 60 μm) and biaxially oriented nylon 6 film (melting point 220°C, thickness 15 μm) was used as the sealing material, and the sealing layer of the easy-open film and the PE layer of the sealing material were sealed using a deep-draw packaging machine ("FV6300", manufactured by Omori Machinery Industry Co., Ltd.) under conditions of a seal width of 7 mm, a seal time of 1.5 seconds, and a seal temperature of 140°C to prepare a test specimen.

[0093] [Sealing material rPP] The seal layer of the easy-open film and rPP (thickness 50 μm) were sealed using a heat sealing machine (manufactured by Sagawa Corporation) under conditions of a seal width of 20 mm, a seal time of 1.5 seconds, and a seal temperature of 150°C to prepare a test specimen.

[0094] [Peel test] Each test piece obtained was cut into a 15 mm wide strip and then subjected to a 180° peel test at a peel speed of 200 mm / min to measure the peel strength in the machine direction (MD) of the film and in the direction perpendicular to the machine direction (TD). The releasability and peel surface were evaluated according to the following criteria. (Removability evaluation criteria) 〇: 200gf / 15mm width or more, 2000gf / 15mm or less ×: Less than 200gf / 15mm width, or more than 2000f / 15mm (too much peeling strength to peel off), or not able to be measured due to not being able to seal -:Not measured (Peeling surface evaluation criteria) 〇: No seal layer remains on the sealant side and no stringiness △: The seal layer remains partially on the seal material side, but there is no stringiness ×: Stringiness occurs or peel strength is too high and the film cannot be peeled off -:Not measured

[0095] [Retort test] The obtained easy-open films of Examples 1 to 3 and Comparative Examples 1 to 4 were cut into two pieces measuring 10 cm x 10 cm, the sealing layers were joined together, and a bag was produced by heat-sealing the four sides of the film periphery under conditions of a seal width of 7 mm, a sealing time of 2 seconds, and a sealing temperature of 150° C. The bag was subjected to a retort treatment at 121° C. for 30 minutes, and the presence or absence of fusion between the films was visually observed and evaluated according to the following evaluation criteria. (Evaluation criteria) 〇: No fusion ×: Fusion

[0096] 〔comprehensive evaluation〕 Based on the evaluation results of the peel test and the retort test, a comprehensive evaluation was made according to the following criteria. (Evaluation criteria) 〇: No "×" marks in any test ×: There is an "×" in any test

[0097] [Table 1]

[0098] The easy-open films of Examples 1 to 3 had good easy-open properties for the sealing materials PE and rPP. Furthermore, the easy-open films of Examples 1 to 3 maintained a high storage modulus E' at 120°C, and no fusion between the sealing layers was observed in a retort test, demonstrating their excellent heat resistance. On the other hand, the easy-open film of Comparative Example 1, which was mainly composed of a polyethylene-based resin, had a high peel strength against the sealing material PE, was difficult to peel off, and had poor openability. The easy-open films of Comparative Examples 1, 2, and 4 had a low storage modulus E' at 120°C, and the seal layers were fused together in a retort test, resulting in poor heat resistance. Furthermore, the easy-open film of Comparative Example 3 did not contain a polyethylene-based resin in the seal layer, and therefore could not be sealed with a sealant even at 140°C. [Industrial Applicability]

[0099] The easy-open film of the present invention has both sufficient sealing properties and easy-open properties (easy peel properties) even when heat-sealed at high temperatures, and can also withstand high-temperature treatments such as high-temperature sterilization, so it can be suitably used as a base film or lid material for deep-draw packaging.

Claims

1. An easy-to-open film having at least a seal layer, wherein the seal layer contains a polypropylene-based resin (a) having a melting point of 145°C or higher and a polyethylene-based resin (b) having a melting point of 105°C or higher, and the polypropylene-based resin (a) is the main component of the seal layer.

2. The easy-open film according to claim 1 , wherein the polypropylene-based resin (a) is a homopolypropylene.

3. 2. The easy-open film according to claim 1, wherein the polyethylene resin (b) is a linear low-density polyethylene resin.

4. The easy-open film according to claim 1, wherein the surface softening temperature of the sealing layer measured by nano thermal analysis is 125°C or lower.

5. The storage modulus of the sealing layer at 120°C measured in accordance with JIS K7244-4 (1999) was 8.0 x 10 7 2. The easy-open film according to claim 1, wherein the elastic modulus is 100 Pa or more.

6. 2. The easy-open film according to claim 1, wherein the monomers constituting the polypropylene-based resin (a) and / or the polyethylene-based resin (b) are plant-derived biomass raw materials.

7. The easy-open film according to claim 1 , further comprising a thermoplastic resin layer adjacent to the seal layer.

8. The easy-open film according to claim 7 , further comprising a barrier resin layer.

9. A package obtained by heat-sealing the easy-open film according to any one of claims 1 to 8 to a film or a container made of a thermoplastic resin.

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