Retort-resistant sealant film

Abstract

To provide a sealant film which can withstand retort treatment at 125°C, and a film for food packaging using the same.SOLUTION: A multilayer sealant film capable of withstanding retort treatment has at least an innermost layer, an intermediate layer, and an outermost layer, wherein the innermost layer contains 55 to 100 wt.% of a resin (A) satisfying the following conditions (a-1) to (a-3), and the intermediate layer contains 20 to 100 wt.% of a resin (B) satisfying the following conditions (b-1) and (b-2). Resin (A): (a-1) linear medium-density polyethylene in which ethylene and an α-olefin having 6 or more carbon atoms are copolymerized; (a-2) density of 0.930 to 0.950 g / cm3; and (a-3) MFR of 0.1 to 20 g / 10 min. Resin (B): (b-1) density of 0.950 to 0.970 g / cm3; and (b-2) MFR of 0.05 to 10 g / 10 min.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a sealant film that can be used in retort treatment at 125°C, and a food packaging film using the same. [Background technology]

[0002] In recent years, with the spread of individual eating culture and the increase in convenience stores, the performance requirements for food packaging bags have changed with the times. For example, food packaging bags are now required to withstand high-temperature sterilization to extend the shelf life of food, and to have strength suitable for a wide range of temperatures, including heating in a microwave oven or retort pouch after low-temperature distribution in frozen or chilled conditions. Because such foods are heated after refrigerated or frozen storage, packaging bags are now required to be both cold-resistant and heat-resistant. Additionally, stand-up pouch packaging designs are being adopted to improve visibility at stores and maintain shape during cooking, requiring the film that makes up the packaging to be highly rigid. Conventionally, polypropylene resins with high melting points have often been used in the sealing layer of packaging bags compatible with microwave ovens and retort pouches. However, polypropylene lacks cold resistance, leading to the problem of bags breaking during transportation. On the other hand, polyethylene, which is often used in sealant films, is known to have excellent cold resistance (Patent Document 1), but has a lower melting point than polypropylene and poorer heat resistance, resulting in the problem of films fusing together after retort pouches. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2020-15804 Summary of the Invention [Problem to be solved by the invention]

[0004] In view of the above-mentioned problems of the prior art, an object of the present invention is to provide a sealant film that can withstand retort treatment at 125°C, and a food packaging film using the same. [Means for solving the problem]

[0005] As a result of extensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by using a linear medium-density polyethylene resin having specific physical properties, which has been newly manufactured and developed in recent years, and further by using a film with a specific resin layer configuration in a multilayer film having an innermost layer and other layers.Based on these findings, the present invention has been completed.

[0006] That is, according to the first aspect of the present invention, there is provided a retort-compatible multilayer sealant film having at least an innermost layer, an intermediate layer, and an outermost layer, wherein the innermost layer contains 55 to 100% by weight of a resin (A) that satisfies the following conditions (a-1) to (a-3), and the intermediate layer contains 20 to 100% by weight of a polyethylene resin (B) that satisfies the following conditions (b-2) and (b-2): Resin (A) (a-1) Linear medium-density polyethylene copolymerized with ethylene and an α-olefin having 6 or more carbon atoms (a-2) Density: 0.930 to 0.950 g / cm 3 (a-3) MFR is 0.1 to 20 g / 10 min Resin (B) (b-1) Density is 0.950 to 0.970 g / cm 3 (b-2) MFR is 0.05 to 10 g / 10 min According to the second invention, there is provided the retort-compatible multilayer sealant film according to the first invention, characterized in that the resin (A) of the innermost layer has a maximum melting peak measured by DSC at 125°C or higher. According to a third invention, there is provided a retort-compatible multilayer sealant film according to the first or second invention, characterized in that the multilayer sealant film has a 1% tensile modulus of elasticity of 400 MPa or more in both the longitudinal and transverse directions. According to a fourth invention, there is provided a retort-compatible multilayer sealant film according to any one of the first to third inventions, characterized in that the multilayer sealant film has an impact strength of 10 J / mm or more as measured using a film impact tester (using a 1 / 2 inch head). According to the fifth invention, there is provided a retort-compatible multilayer sealant film according to any one of the first to fourth inventions, characterized in that a pouch made using the multilayer sealant film shows no fusion after being subjected to heat-pressure sterilization at 125°C for 30 minutes. According to a sixth aspect of the present invention, there is provided a retort-compatible multilayer sealant film according to any one of the first to fifth aspects of the present invention, characterized in that at least one substrate layer selected from PET (polyethylene terephthalate), Ny (nylon), OPP (biaxially oriented polypropylene), and Al (aluminum) is laminated adjacent to the outermost layer of the multilayer sealant film. According to a seventh aspect of the present invention, there is provided a food packaging film using the retort-compatible multilayer sealant film according to any one of the first to sixth aspects of the present invention. [Effects of the Invention]

[0007] The retort-compatible multilayer sealant film of the present invention is characterized by the absence of film-to-film fusion after heat and pressure treatment at 125° C. Therefore, by using this sealant film, it is possible to provide a food packaging film and a retort food packaging film that can withstand higher-temperature heat and pressure sterilization treatment and retort treatment. DETAILED DESCRIPTION OF THE INVENTION

[0008] The present invention provides a retort-compatible sealant film having at least an innermost layer, an intermediate layer, and an outermost layer, the innermost layer containing a resin (A) and the intermediate layer containing a polyethylene resin (B). The components constituting each resin, their properties, and food packaging films using them are described in detail below.

[0009] Resin (A) (a-1) Specifically, the resin (A) of the present invention is a linear medium-density polyethylene copolymerized with an α-olefin having 6 or more carbon atoms. Examples of α-olefins having 6 or more carbon atoms include 1-hexene, 4-methyl-1-hexene, 1-heptene, 1-octene, 1-decene, and 1-octadecene. Of these, α-olefins having 6 to 12 carbon atoms are preferred, and those having 6 to 10 carbon atoms, such as 1-hexene, 4-methyl-1-hexene, 1-heptene, 1-octene, and 1-decene, are particularly preferred.

[0010] The ethylene-α-olefin copolymer preferably has an α-olefin content of 3 to 24% by weight, more preferably 5 to 20% by weight, and even more preferably 7 to 15% by weight. If the α-olefin content is less than 3% by weight, the film tends to have poor pinhole resistance.

[0011] Furthermore, the resin (A) in the present invention must satisfy the following properties (a-2) and (a-3). (a-2) Density The density of resin (A) is 0.930 to 0.950 g / cm 3 and preferably 0.932 to 0.950 g / cm 3 , more preferably 0.934 to 0.948 g / cm 3 Here, the density is a value measured in accordance with Method D (density gradient tube method) of JIS K7112-1999 "Method for measuring density and specific gravity of plastics - non-foamed plastics."

[0012] (a-3) Melt flow rate (MFR) The MFR of resin (A) is 0.1 to 20 g / 10 min, preferably 0.3 to 15 g / 10 min, and more preferably 0.5 to 10 g / 10 min. If the MFR is less than 0.1 g / 10 min, the resin pressure increases during molding and processing into a film, resulting in poor processability. On the other hand, if the MFR exceeds 20 g / 10 min, the mechanical strength required for a packaging film and processability such as bubble stability during film molding and processing will be poor. Here, MFR is a value measured in accordance with JIS K7210-1999 "Test method for melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of plastics - thermoplastic plastics" under test conditions of 190°C and a load of 21.18N (2.16kg).

[0013] The resin (A) used in the present invention is preferably one copolymerized in the presence of a Kaminsky catalyst rather than one copolymerized in the presence of a Ziegler-Natta catalyst or a Phillips catalyst. Ethylene-α-olefin copolymers produced using Kaminsky-type catalysts are disclosed, for example, in JP-A-58-19309, JP-A-59-95292, JP-A-60-35005, JP-A-60-35006, JP-A-60-35007, JP-A-60-35008, JP-A-60-35009, JP-A-61-130314, JP-A-3-163088, European Patent Publication No. 420436, U.S. Pat. No. 505543 The polyimide can be produced by a polymerization method such as a gas phase method, a slurry method, a solution method, or a high-pressure ionic polymerization method using a metallocene catalyst, particularly a metallocene-alumoxane catalyst, as described in the specification of International Publication No. 8 and International Publication No. WO91 / 04257, or by a catalyst comprising a metallocene compound and a compound that reacts with the metallocene compound to form a stable anion, as described in International Publication No. WO92 / 07123.

[0014] Among these, the ethylene-α-olefin copolymer of the present invention is preferably one polymerized using a catalyst in which the metallocene compound is a tetravalent transition metal compound such as titanium, zirconium, nickel, palladium, hafnium, or platinum, with a mono-, di-, or tri-cyclopentadienyl ring or a substituted cyclopentadienyl ring as a ligand, and more preferably one polymerized using a catalyst in which the metallocene compound is a transition metal compound with a hafnium compound as the central metal. More preferred are ethylene-α-olefin copolymers produced using special catalysts, such as those described in Japanese Patent No. 3539801.

[0015] (2) Polyethylene resin (B) The polyethylene resin (B) of the present invention preferably satisfies the following properties (b-1) and (b-2): (Note that the polyethylene resin (B) does not include those corresponding to the resin (A)). (b-1) Density The density of polyethylene resin (B) is 0.950 to 0.970 g / cm 3 and preferably 0.955 to 0.970 g / cm 3 More preferably, it is 0.958 to 0.968 g / cm 3 Here, the density is a value measured in accordance with Method D (density gradient tube method) of JIS K7112-1999 "Method for measuring density and specific gravity of plastics-non-foamed plastics."

[0016] (b-2) Melt flow rate (MFR) The MFR of the polyethylene resin (B) is 0.05 to 10 g / 10 min, preferably 0.1 to 10 g / 10 min, and more preferably 0.5 to 10 g / 10 min. If the MFR is less than 0.05 g / 10 min, the resin pressure increases during molding into a film, resulting in poor processability. On the other hand, if the MFR exceeds 10 g / 10 min, the mechanical strength required for a packaging film and processability such as bubble stability during film molding and processing will be poor. Here, MFR is a value measured in accordance with JIS K7210-1999 "Test method for melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of plastics - thermoplastic plastics" under test conditions of 190°C and a load of 21.18N (2.16kg).

[0017] The polyethylene resin (B) used in the present invention can be selected from known high-density polyethylenes such as those produced in the presence of a Ziegler catalyst or a chromium catalyst. For example, resins such as "Novatec HD" (trade name) manufactured by Japan Polyethylene Corporation can be used.

[0018] (3) Other additives The ethylene copolymer composition constituting each layer of the present invention may contain, if necessary, other resins or rubbers, as well as various additives commonly used in thermoplastic resins, such as heat stabilizers, light stabilizers, ultraviolet absorbers, nucleating agents, neutralizing agents, lubricants, antistatic agents, antiblocking agents, slip agents, antifogging agents, dispersants, flow improvers, release agents, adhesion promoters, flame retardants, colorants, fillers, etc., within the scope of not impairing the effects of the present invention. These components may be contained in each component, or may be blended during the production of the ethylene copolymer composition.

[0019] (4) Film molding The method for producing the film is not particularly limited, and includes common molding methods such as multi-layer inflation molding, in which resins melted in an extruder are joined at the tip of a die using a multi-layer die to form a laminated structure, co-extrusion molding such as multi-layer T-die molding, and multi-layer blow molding.

[0020] (5) Multilayer film structure The sealant film of the present invention is composed of at least three layers: an innermost layer, an intermediate layer, and an outermost layer. The innermost layer is the layer located on the surface of the multilayer film, and when the film is used to construct a bag or the like, the layer located on the inside is called the innermost layer. In a multilayer structure, any other layer having barrier properties or adhesive properties may be provided between the innermost layer and the other layers, but a simple structure is preferable. The layer ratio between the innermost layer and the other layers is not particularly limited. The total thickness of the multilayer film is 10 to 500 μm, preferably 20 to 200 μm.

[0021] (6) Innermost layer The innermost layer of the present invention is (a-1) a linear medium-density polyethylene obtained by copolymerizing ethylene with an α-olefin having 6 or more carbon atoms, and (a-2) a density of 0.930 to 0.950 g / cm 3 (a-3) The resin (A) has an MFR of 0.1 to 20 g / 10 min and is contained in an amount of 55 to 100% by weight, which is preferable for obtaining a film that can be used in a retort treatment. The preferable properties of the resin (A) are as described above.

[0022] (7) Middle class The intermediate layer of the present invention has (b-1) a density of 0.950 to 0.970 g / cm 3 It is preferable that the resin composition contains 20 to 100% by weight of (b-2) polyethylene resin (B) having an MFR of 0.05 to 10 g / 10 min. This configuration makes it possible to impart the heat resistance required for a sealant film that can withstand retort treatment.

[0023] (8) Melting Peak A preferred characteristic of the retort-compatible sealant film of the present invention is that the melting peak of the resin (A) in the innermost layer measured by DSC is at or above a specific temperature. That is, it is preferred that the maximum melting peak of the resin (A) measured by DSC is at or above 125°C. The upper limit is not particularly limited.

[0024] (9) 1% tensile modulus The retort-compatible sealant film of the present invention preferably has a 1% tensile modulus of elasticity equal to or greater than a specific value, i.e., the 1% tensile modulus of elasticity measured with reference to JIS K7127 is preferably 400 MPa or greater in both the machine direction (MD) and transverse direction (TD) of the film.

[0025] (10) Impact strength The retort-compatible sealant film of the present invention preferably has an impact strength of at least a specific level, i.e., an impact strength of at least 10 J / mm as measured using a film impact tester. This impact strength can be measured using a film impact tester manufactured by Toyo Seiki Seisakusho Co., Ltd., and it is preferable to use a 1 / 2 inch head.

[0026] (11) Heat resistance A preferred characteristic of the retort-compatible sealant film of the present invention is that the innermost layers do not fuse together even after heating and pressurizing at 125° C. The pressure and treatment time during heating are not particularly limited, but for example, heating is performed at 125° C. for 30 minutes.

[0027] (12) Combination with other substrates The retort-compatible sealant film of the present invention, i.e., the retort sealant film, may be used to construct a pouch by placing the sealant film on the content side of a substrate film having oxygen barrier properties. Specifically, a substrate layer selected from PET (polyethylene terephthalate), Ny (nylon), OPP (biaxially oriented polypropylene), and Al (aluminum) is laminated on the layer (outermost layer) opposite the side on which the innermost layer of the sealant film is provided. By combining it with a substrate having other functions, it becomes a suitable embodiment for use as a package for retort foods (a film for packaging retort foods) or a package for long-life foods. [Example]

[0028] The present invention will be explained in more detail below by showing examples and comparative examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. The test and evaluation methods and materials used in the examples are as follows.

[0029] 1. Test and evaluation methods (1) Density: Measured in accordance with Method D (density gradient tube method) of JIS K7112-1999 "Method for measuring density and specific gravity of plastics - non-foamed plastics." (2) MFR: Measured in accordance with JIS K7210-1999 "Test method for melt mass flow rate (MFR) and melt volume flow rate (MVR) of plastics - thermoplastics" under test conditions of 190°C and a load of 21.18N (2.16kg). (3) Melting Peak Measurement was carried out using the following equipment and conditions. Equipment: DSC7020 (Hitachi High-Tech Science Corporation) Measurement conditions: Heat to 200°C at 10°C / minute, hold for 5 minutes, then cool to 20°C at 10°C / minute and hold for 5 minutes. After that, heat again to 200°C at 10°C / minute, and determine the peak with the greatest melting energy as the melting peak. (4) 1% tensile modulus Measurements were made with the following equipment and conditions, with reference to JIS K7127. MD is the machine direction, and TD is the value in the transverse direction. Equipment: Tensilon universal testing machine (Orientec Co., Ltd.) Measurement environment: temperature 23℃, humidity 50% Measurement conditions: Chuck distance: 100 mm, Test speed: 25 mm / min (5) Impact strength Measurement was carried out using the following equipment and conditions. Device: Film impact tester (manufactured by Toyo Seiki Seisakusho Co., Ltd.) Measurement environment: temperature 23℃, humidity 50% Measurement conditions: 1 / 2 inch impact head (6) Heat and pressure treatment Heat and pressure treatment was carried out using the following equipment and conditions: For the treatment, the heat-resistant sealant film was combined with a nylon film "EMBLEM (ONY)" manufactured by Unitika Ltd., and a pouch was prepared by adding an appropriate amount of water therein. Equipment: High-temperature, high-pressure shower sterilization (disinfection) equipment YRF-40 / 50E (manufactured by Sakura SI Co., Ltd.) Treatment conditions: 125°C x 30 minutes Heat resistance was judged according to the following criteria. ○: No fusion between the innermost layers is visible to the naked eye △: Slight blocking is observed visually, but there is no practical problem. ×: Fusion between the innermost layers is visually observed

[0030] 2.Material Density is 0.935g / cm 3 Metallocene-based linear medium-density polyethylene LL(1) (a copolymer of ethylene and C6 α-olefin) with an MFR of 4.4 g / 10 min. Density is 0.963g / cm 3 High density polyethylene HD (1) with a MFR of 7.0 g / 10 min Density is 0.931g / cm 3 Metallocene-based linear medium-density polyethylene LL(2) (a copolymer of ethylene and C6 α-olefin) with an MFR of 4.0 g / 10 min. Density is 0.912g / cm 3 , Linear medium density polyethylene LL (3) with MFR of 2.0 g / 10 min Density is 0.927g / cm 3 , Linear medium density polyethylene LL (4) with MFR of 2.1 g / 10 min Density is 0.938g / cm 3 , Linear medium density polyethylene LL (5) with MFR of 2.1 g / 10 min

[0031] Example 1 Using a multi-layer T-die molding machine (die lip: 1 mm, die temperature: 240°C) and following the formulation in Table 1, a three-layer sheet film with a total thickness of 60 μm was molded. The thicknesses of the innermost layer, middle layer, and outermost layer were 12 μm, 36 μm, and 12 μm. The elastic modulus, impact strength, and heat resistance of the resulting film were evaluated. The results are shown in Table 1.

[0032] Example 2 A film was produced in the same manner as in Example 1 according to the formulation in Table 1. The results are shown in Table 1.

[0033] (Comparative Example 1) A film was produced in the same manner as in Example 1 according to the formulation in Table 1. The results are shown in Table 1.

[0034] (Comparative Example 2) A film was produced in the same manner as in Example 1 according to the formulation in Table 1. The results are shown in Table 1.

[0035] (Comparative Example 3) A film was produced in the same manner as in Example 1 according to the formulation in Table 1. The results are shown in Table 1.

[0036] [Table 1]

[0037] From Table 1, it can be seen that in Examples 1 and 2, no fusion that would cause problems in use was observed even after retort treatment at 125°C, and the impact strength was excellent compared to Comparative Examples 1 to 3. Therefore, the sealant film of the present invention has heat resistance to heating and pressure treatment at a temperature of 125°C, which is equivalent to the high temperature of retort treatment, and has the strength required for packaging film, and it is clear that it has great technical significance. [Industrial Applicability]

[0038] The sealant film of the present invention, which has a multilayer structure, does not fuse together between the innermost layers even after heating and pressurizing treatment at 125°C, and has sufficient impact strength, so it is suitable for use as a food packaging film, including retort foods that require heating and pressurizing sterilization treatment.

Claims

1. A retort-compatible multilayer sealant film having at least an innermost layer, an intermediate layer, and an outermost layer, wherein the innermost layer contains 55 to 100% by weight of a resin (A) that satisfies the following conditions (a-1) to (a-3), and the intermediate layer contains 20 to 100% by weight of a polyethylene resin (B) that satisfies the following conditions (b-2) and (b-2): Resin (A) (a-1) Linear medium-density polyethylene copolymerized with ethylene and an α-olefin having 6 or more carbon atoms (a-2) Density is 0.930 to 0.950 g / cm ３ (a-3) MFR is 0.1 to 20 g / 10 min Resin (B) (b-1) Density is 0.950 to 0.970 g / cm ３ (b-2) MFR is 0.05 to 10 g / 10 min

2. 2. The retortable multilayer sealant film according to claim 1, wherein the resin (A) in the innermost layer has a maximum melting peak at 125°C or higher as measured by DSC.

3. 3. The retort-compatible multilayer sealant film according to claim 1, wherein the multilayer sealant film has a 1% tensile modulus of elasticity of 400 MPa or more in both the longitudinal and transverse directions.

4. A retort-compatible multilayer sealant film according to claim 1 or 2, characterized in that the impact strength of the multilayer sealant film measured using a film impact tester (using a 1 / 2 inch head) is 10 J / mm or more.

5. 3. The retort-compatible multilayer sealant film according to claim 1 or 2, wherein a pouch made using the multilayer sealant film shows no fusion after being subjected to heat and pressure sterilization at 125°C for 30 minutes.

6. 3. The retort-resistant multilayer sealant film according to claim 1, wherein at least one substrate layer selected from PET, Ny, OPP, and Al is laminated adjacent to the outermost layer of the multilayer sealant film.

7. A food packaging film using the retort-compatible multilayer sealant film according to claim 1 or 2.

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