Heat-resistant sealant film

Abstract

To provide a sealant film for heat resistance having heat resistance, and furthermore excellent in tearability in a machine direction (MD) of the film, and a film for packaging a food.SOLUTION: A sealant film for heat resistance is a multilayer film having at least an innermost layer, and other layers, where the inner most layer contains 65-100 wt.% of straight chain medium density polyethylene (A) obtained by copolymerizing ethylene having (a-1) a density of 0.925-0.940 g / cm3 and (a-2) a MFR of 0.1-20 g / 10 min, and α-olefin with 6 or more carbons, and a layer contacting the innermost layer contains straight chain low density polyethylene (B) obtained by copolymerizing ethylene having (b-1) a density of 0.910-0.950 g / cm3 and (b-2) a MFR of 0.1-15 g / 10 min, and α-olefin with four carbons.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a heat-resistant sealant film excellent in tearability in the machine direction (MD) of a film, and a food packaging film using the same.

Background Art

[0002] In recent years, due to the spread of the individual food culture and the increase in convenience stores, the required performance of food packaging bags has also changed according to the times. For example, food packaging bags are required to withstand high-temperature heat sterilization for long life, and to have strength suitability in a wide temperature range where they are heated by a microwave oven or a retort after low-temperature distribution by freezing or chilling. Since such foods are heated after refrigerated or frozen transportation and storage, the packaging bags are required to have both cold resistance and heat resistance. Furthermore, there is also a problem that it is difficult to open the bag manually because the film becomes easy to stretch in the high-temperature state after heat cooking such as boiling or using a microwave oven. In addition, in terms of visibility at the storefront and shape retention during heat cooking, a stand-up pouch type packaging design is adopted, and higher rigidity is required for the constituting film. Conventionally, polypropylene-based resins with a high melting point have been frequently used for the seal layer in packaging bags corresponding to microwave ovens or retorts. However, polypropylene has no cold resistance and has a problem that the bag breaks during transportation. On the other hand, although polyethylene, which is frequently used for sealant films, is known to have excellent cold resistance (Patent Document 1), it has a lower melting point than polypropylene and is inferior in heat resistance, and there is a problem that the films fuse together after retorting. Furthermore, as the aging of the population with low birthrate and high age progresses rapidly, the demand for barrier-free features such as easy opening of packaging bags has been increasing.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In view of the above problems of the prior art, an object of the present invention is to provide a heat-resistant sealant film having heat resistance and excellent tear resistance in the machine direction (MD) of the film, and a food packaging film using the same.

Means for Solving the Problems

[0005] As a result of various studies to solve the above problems, the present inventor has recently used a linear medium-density polyethylene resin newly manufactured and developed with specific physical properties, and further in a multilayer film having an innermost layer and other layers. It has been found that the above problems can be solved by using a film having a specific resin layer structure, and based on these findings, the present invention has been completed.

[0006] That is, according to a first invention of the present invention, there is provided a multilayer film having at least an innermost layer and other layers, wherein the innermost layer contains (a-1) a density of 0.925 to 0.940 g / cm 3 , (a-2) 65 to 100% by weight of linear medium-density polyethylene (A) obtained by copolymerizing ethylene with an α-olefin having 6 or more carbon atoms and having an MFR of 0.1 to 20 g / 10 min, and the layer adjacent to the innermost layer contains (b-1) a density of 0.910 to 0.950 g / cm 3 , (b-2) A heat-resistant sealant film is provided, which contains linear low-density polyethylene (B) obtained by copolymerizing ethylene with an α-olefin having 4 carbon atoms and having an MFR of 0.1 to 15 g / 10 min. According to a second invention, the linear medium-density polyethylene (A) is an ethylene·α-olefin copolymer having the following physical properties (a-3) and (a-4), and the heat-resistant sealant film according to the first invention is provided. (a-3) The molecular weight distribution (Mw / Mn) is 1.8 to 3.5 (a-4) The elution temperature-elution amount curve obtained by the continuous temperature-rising elution fractionation method (TREF) has a plurality of peaks According to the third invention, there is provided a heat-resistant sealant film as described in the first or second invention, wherein in the Elmendorf tear test measured in accordance with JIS K7128-2, the tear strength in the machine direction (MD) of the film is 20 N / mm or less. According to the fourth invention, in the Elmendorf tear test measured in accordance with JIS K7128-2, the ratio of the tear strength (S MD ) in the machine direction (MD) to the tear strength (S TD ) in the transverse direction (TD) of the film is S MD / S TD < 0.5, and there is provided a heat-resistant sealant film as described in any one of the first to third inventions. According to the fifth invention, there is provided a heat-resistant sealant film as described in any one of the first to fourth inventions, wherein at least one base material layer selected from PET, Ny, OPP, and AL is laminated on the layer opposite to the innermost layer. According to the sixth invention, there is provided a heat-resistant sealant film as described in any one of the first to fifth inventions, wherein the innermost layers are brought into close contact with each other, and no fusion of the innermost layers is observed after heat and pressure treatment at 115°C. According to the seventh invention, there is provided a food packaging film using the heat-resistant sealant film as described in any one of the first to sixth inventions.

Effect of the Invention

[0007] The heat-resistant sealant film of the present invention is excellent in easy tearability in the machine direction (MD) of the film, and has the characteristics that no fusion of the films is observed after heat and pressure treatment at 115°C, and the easy tearability is continuously maintained. Therefore, by using the heat-resistant sealant film, it is possible to provide a food packaging film and a medical product packaging film having easy peelability even after heat and pressure sterilization treatment or retort treatment.

Modes for Carrying Out the Invention

[0008] The present invention relates to a heat-resistant sealant film comprising an innermost layer made of linear medium-density polyethylene (A) and a layer in contact with the innermost layer made of C4LLDPE (B). Hereinafter, the components constituting each ethylene copolymer composition, each ethylene copolymer composition, its properties, and the food packaging film using them will be described in detail.

[0009] (1) Linear medium-density polyethylene (A) Specifically, the linear medium-density polyethylene (A) of the present invention is an ethylene-α-olefin copolymer having a medium-density and linear molecular structure, which is obtained by copolymerizing ethylene and an α-olefin having 6 to 18 carbon atoms by a catalytic polymerization method. Here, examples of the α-olefin having 6 to 18 carbon atoms include 1-hexene, 4-methyl-1-hexene, 1-heptene, 1-octene, 1-decene, 1-octadecene, etc. Among them, those having 6 to 12 carbon atoms are preferable, and those having 6 to 10 carbon atoms such as 1-hexene, 4-methyl-1-hexene, 1-heptene, 1-octene, 1-decene are particularly preferable.

[0010] Also, the content of the α-olefin in the ethylene-α-olefin copolymer is preferably 3 to 24% by weight, more preferably 5 to 20% by weight, and still more preferably 7 to 15% by weight. When the content of the α-olefin is less than 3% by weight, the pinhole resistance of the film tends to be inferior.

[0011] Furthermore, the linear medium-density polyethylene of component (A) in the present invention needs to satisfy the following characteristics (a-1) to (a-2). (a-1) Density The density of component (A) is 0.925 to 0.940 g / cm 3 and preferably 0.928 to 0.940 g / cm 3 , more preferably 0.930 g / cm 3 above ~ 0.938 g / cm 3It is as follows. Here, the density is a value measured in accordance with Method D (density gradient tube method) of "Plastics - Methods of measuring density and specific gravity of non-foamed plastics" in JIS K7112-1999.

[0012] (a-2) Melt flow rate (MFR) The MFR of component (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, when forming into a film, the resin pressure increases and the processability deteriorates. On the other hand, if the MFR exceeds 20 g / 10 min, the processability such as the mechanical strength as a packaging film and the bubble stability during film forming processing deteriorates. Here, the MFR is a value measured in accordance with "Plastics - Test methods for melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of thermoplastic plastics" in JIS K7210-1999 under the test conditions: 190 °C, 21.18 N (2.16 kg) load.

[0013] As the linear medium-density polyethylene (A) used in the present invention, it is preferably copolymerized in the presence of a Kaminsky type catalyst rather than copolymerized in the presence of a Ziegler-Natta type catalyst, a Phillips type catalyst, or the like. Ethylene-α-olefin copolymers using Kaminsky catalysts are described, 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, US Patent No. 5055438, and International Publication WO91 / 04257, etc. They are produced using metallocene catalysts, particularly metallocene-alumoxane catalysts, or, for example, catalysts composed of a metallocene compound and a compound that reacts with the compound to form a stable anion as described in International Publication WO92 / 07123, etc. They can be produced by polymerization methods such as gas phase method, slurry method, solution method, and high pressure ionic polymerization method.

[0014] Among them, the ethylene-α-olefin copolymer in the present invention is preferably polymerized using a catalyst having a tetravalent transition metal compound such as titanium, zirconium, nickel, palladium, hafnium, or platinum having a mono-, di-, or tri-cyclopentadienyl ring or a substituted cyclopentadienyl ring as a ligand as a metallocene compound, particularly preferably polymerized using a catalyst having a transition metal compound having a hafnium compound as a central metal as a metallocene compound. More preferably, an ethylene-α-olefin copolymer produced by a special catalyst species as described in Patent No. 3539801, etc. is preferred. As the linear medium density polyethylene (A), an ethylene-α-olefin copolymer having the following physical properties (a-3) is preferred. (a-3) The molecular weight distribution (Mw / Mn) is 1.8 to 3.5 (a-4) The elution temperature-elution amount curve by continuous temperature rising elution fractionation (TREF) has a plurality of peaks The copolymer satisfying (a-3) and (a-4) is a copolymer characterized in that, in addition to having a narrower molecular weight distribution than the polymer obtained by a conventional Ziegler-Natta type catalyst, it has a plurality of peaks in the elution temperature - elution amount curve, while the copolymer by a typical metallocene catalyst usually has one peak. The catalyst used for producing the ethylene-α-olefin copolymer, the production method thereof, and the measurement methods of the molecular weight distribution and TREF are as described in Patent No. 3539801 and the like.

[0015] In recent years, the applicant has succeeded in producing linear medium-density polyethylene having the above physical properties in the medium-density region where production control is difficult using the above catalyst species. As the linear medium-density polyethylene (A) used in the present invention, for example, it is available as a new resin in the medium-density region of the "Harmolex" (trademark) series by the applicant (Nippon Polyethylene Co., Ltd.). In addition to having a narrower molecular weight distribution than the polymer obtained by a conventional Ziegler-Natta type catalyst, such a copolymer has strength and high rigidity in a wide temperature range, and optimizes the heat sealability, impact strength, and basic qualities such as low odor and low fish eyes required for polyethylene films. It is a polyethylene resin.

[0016] (2) Linear low-density polyethylene (B) Specifically, the linear low-density polyethylene (B) of the present invention is an ethylene-α-olefin copolymer obtained by copolymerizing ethylene and an α-olefin having 4 carbon atoms by a catalytic polymerization method. Hereinafter, it is also referred to as C4LLDPE. As the linear low-density polyethylene (B), it is preferable to use an ethylene-α-olefin in which the comonomer species is limited to an α-olefin having 4 carbon atoms, because a heat-resistant sealing film excellent in easy tearability in the MD direction can be obtained while satisfying the heat resistance. In addition, the content of the α-olefin having 4 carbon atoms (referred to as C4) in the linear low-density polyethylene (B) is preferably 3 to 24% by weight, more preferably 5 to 20% by weight, and still more preferably 7 to 15% by weight. When the content of the α-olefin is less than 3% by weight, the pinhole resistance of the film tends to be inferior.

[0017] Furthermore, the linear low-density polyethylene (B) in the present invention preferably satisfies the following characteristics (b-1) and (b-2). (b-1) Density The density of component (B) is 0.910 to 0.950 g / cm 3 and preferably 0.915 to 0.940 g / cm 3 More preferably, it is 0.915 to 0.938 g / cm 3 or less. Here, the density is a value measured in accordance with Method D (density gradient tube method) of "Plastics - Methods for Measuring the Density and Specific Gravity of Non-Cellular Plastics" in JIS K7112-1999.

[0018] (b-2) Melt flow rate (MFR) The MFR of the linear low-density polyethylene (B) is 0.1 to 15 g / 10 min, and preferably 0.3 to 10 g / 10 min. When the MFR is less than 0.1 g / 10 min, the processability deteriorates due to an increase in resin pressure during film forming. On the other hand, when the MFR exceeds 15 g / 10 min, the processability such as the mechanical strength as a packaging film and the bubble stability during film forming deteriorates. Here, the MFR is a value measured in accordance with "Plastics - Test Methods for Melt Mass Flow Rate (MFR) and Melt Volume Flow Rate (MVR) of Thermoplastic Plastics" in JIS K7210-1999 under the test conditions: 190 °C, 21.18 N (2.16 kg) load.

[0019] As the linear low-density polyethylene (B) used in the present invention, it can be selected from known linear low-density polyethylenes such as those copolymerized in the presence of a Ziegler-Natta type catalyst. Among them, a linear low-density polyethylene containing a C4 component as an essential component can be selected. For example, resins containing a C4 component as an essential component can be exemplified from "Novatec LL" (trademark name) manufactured by Nippon Polyethylene Co., Ltd.

[0020] (3) Other additives In the ethylene-based copolymer composition constituting each layer of the present invention, other resins, rubbers, and various additives usually 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, fluidity improvers, mold release agents, adhesion-imparting agents, flame retardants, colorants, fillers, etc., may be added as long as the effects of the present invention are not impaired. These components may be contained in each component or may be blended during the production of the ethylene-based copolymer composition.

[0021] (4) Film forming The method for producing the film is not particularly limited, and in addition to coextrusion molding methods such as the multilayer inflation molding method in which the resin melted by an extruder is joined at the tip of the die using a multilayer die to form a laminated structure, and the multilayer T-die molding method, ordinary molding methods such as the multilayer blow molding method are applicable.

[0022] (5) Structure of multilayer film The heat-resistant sealing film of the present invention is composed of at least two layers, namely, the innermost layer and the layer in contact with the innermost layer. The innermost layer is the layer located on the surface of the multilayer film, and when a bag or the like is formed with the film, the layer located inside is referred to as the innermost layer. In the multilayer structure, an arbitrary other layer having barrier properties or adhesiveness or the like may be provided between the innermost layer and the other layers, but a simple structure is preferred. Also, 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.

[0023] (6) Innermost layer The innermost layer of the present invention contains 65 to 100% by weight of linear medium density polyethylene (A) having (a-1) a density of 0.925 to 0.940 g / cm 3 , (a-2) an MFR of 0.1 to 20 g / 10 minutes, which is preferable for obtaining a film having excellent easy tearability even after heat and pressure treatment. In particular, it is preferable to contain 70 to 100% by weight of linear medium density polyethylene (A). The preferable characteristics of the linear medium density polyethylene (A) are as described above.

[0024] (7) Layer in contact with the innermost layer The layer in contact with the innermost layer of the present invention preferably contains 50 to 100% by weight of C4LLDPE (B) having (b-1) a density of 0.910 to 0.950 g / cm 3 , (b-2) an MFR of 0.1 to 15 g / 10 minutes. With this configuration, it is possible to impart easy tearability while maintaining the heat resistance required for the heat-resistant sealant film.

[0025] (8) Tear characteristics The heat-resistant sealant film of the present invention is characterized by having a specific Elmendorf tear strength as a preferable characteristic. That is, the Elmendorf tear strength measured in accordance with JIS K7128-2 is preferably 20 N / mm or less in the machine direction (MD) of the film. The lower limit is not particularly limited. Also, in the Elmendorf tear test measured in accordance with JIS K7128-2, the ratio of the tear strength (S MD ) in the machine direction (MD) of the film to the tear strength (S TD ) in the transverse direction (TD) is S MD / S TD <0.5, which is preferable because it indicates easy tearability in the MD direction.

[0026] (9) Heat resistance The heat-resistant sealant film of the present invention is characterized by the fact that the innermost layers do not fuse even after heat and pressure treatment at 115°C as a preferable characteristic. The pressure and treatment time during this heating are not particularly limited, but for example, heating is performed at 115°C for 30 minutes.

[0027] (10) Combination with other substrates Using the heat-resistant sealant film of the present invention, the sealant film may be disposed on the content side of a substrate film having oxygen barrier properties to form a pouch. Specifically, a substrate layer selected from PET, Ny, OPP, and Al is laminated on the layer of the heat-resistant sealant film opposite to the side where the innermost layer is provided. By combining with other substrates having functions, it becomes a suitable form as a retort food package or a long-life food package.

Examples

[0028] Hereinafter, examples and comparative examples of the present invention will be shown for more specific explanation. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded. 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 "Plastics - Methods for Measuring the Density and Specific Gravity of Non-Cellular Plastics" in JIS K7112-1999. (2) MFR: Measured in accordance with the "Test Method for Melt Mass Flow Rate (MFR) and Melt Volume Flow Rate (MVR) of Plastics - Thermoplastic Plastics" in JIS K7210-1999 under the test conditions of 190°C and a load of 21.18 N (2.16 kg). (3) Elmendorf tear strength Measured using the following apparatus and conditions in accordance with JIS K7128-2. MD is the flow direction (MD: Machine Direction), and TD is the value in the vertical direction (TD: Transverse Direction). Apparatus: Digital Elmendorf Tear Tester Model SA (manufactured by Toyo Seiki Seisakusho Co., Ltd.) Measurement environment: Temperature 23°C, humidity 50% (4) Heat and pressure treatment The heat and pressure treatment was carried out under the following apparatus and conditions. For the treatment, a pouch was prepared by combining the nylon film "EMBLEM(ONM)" manufactured by Unitika Ltd. of the heat-resistant sealant film and adding an appropriate amount of water therein. Apparatus: High-temperature and high-pressure shower sterilization (sterilization) apparatus YRF-40 / 50E (manufactured by Sakura ES AI Co., Ltd.) Treatment conditions: Treatment at 115°C for 30 minutes Regarding the heat resistance, it was judged according to the following criteria. 〇: Visually, no fusion is observed between the innermost layers. ×: Visually, fusion is observed between the innermost layers.

[0030] 2. Materials (1) Component (A) (i) A: Density is 0.935 g / cm 3 , MFR is 1.5 g / 10 min, Mw / Mn is 3.42, metallocene linear medium-density polyethylene LL(A) (Using a metallocene catalyst, the manufacturing conditions were set to have a predetermined density and MFR range, and the manufactured polyethylene resin was used. The peak of the elution temperature - elution amount curve of this resin by continuous temperature rise elution fractionation method (TREF) was plural.) (2) Component (B) (B-1) Density is 0.927 g / cm 3 , MFR is 2.1 g / 10 min linear low-density polyolefin LL (manufactured by Japan Polyethylene Corporation "UF641") (B-2) Density is 0.938 g / cm 3 , MFR is 2.1 g / 10 min linear low-density polyolefin LL (manufactured by Japan Polyethylene Corporation "UF943") (3) AB agent (anti-blocking agent) "Harmolex MBN560B" manufactured by Japan Polyethylene Corporation (4) Slip agent "Harmolex MBN560S" manufactured by Japan Polyethylene Corporation

[0031] (Example 1) According to the formulation in Table 1, a multilayer T-die forming machine (die lip: 1 mm, die temperature: 220 °C) was used to form a sheet-like film with a total thickness of 50 μm and three layers. The thickness of the innermost layer: middle layer: outermost layer was 10 μm: 30 μm: 10 μm. The Elmendorf tear strength and heat resistance of the obtained film were evaluated. The results are shown in Table 3.

[0032] (Example 2) According to the formulation in Table 1, a film was prepared in the same manner as in Example 1. The results are shown in Table 3.

[0033] (Example 3) According to the formulation in Table 1, a film was prepared in the same manner as in Example 1. The results are shown in Table 3.

[0034] (Example 4) According to the formulation in Table 1, a film was prepared in the same manner as in Example 1. The results are shown in Table 3.

[0035] (Comparative Example 1) According to the formulation in Table 2, a film was prepared in the same manner as in Example 1. The results are shown in Table 3.

[0036] (Comparative Example 2) According to the formulation in Table 2, a film was prepared in the same manner as in Example 1. The results are shown in Table 3.

[0037]

Table 1

[0038]

Table 2

[0039]

Table 3

[0040] From Table 3, it can be seen that Examples 1 to 4 have heat resistance and are excellent in tearability in the machine direction (MD) of the film (the Elmendorf tear strength S TD in the machine direction (MD) of the film with respect to the tear strength S MD in the transverse direction (TD) of the film, and the ratio S MD / S TD (indicated as TD, MD, and MD / TD in the table) is less than 0.5). Therefore, it is clear that the heat-resistant sealant film of the present invention has both heat resistance to heat and pressure treatment at a temperature corresponding to retort sterilization treatment and easy tearability (easy opening property) that can be easily torn by hand, and has great technical significance.

Industrial Applicability

[0041] The heat-resistant sealant film composed of a multilayer structure of the ethylene-based copolymer composition of the present invention does not cause fusion between the innermost layers even after heat and pressure treatment at 115°C, and has excellent tearability (easy opening property). Therefore, it is suitably used as a food packaging film for retort foods that require heat and pressure sterilization treatment, as well as for medical product packaging.

Claims

1. A multilayer film having at least an innermost layer and other layers, wherein the innermost layer contains (a-1) a linear medium density polyethylene (A) obtained by copolymerizing ethylene and an α-olefin having 6 or more carbon atoms, having a density of 0.925 to 0.940 g / cm ３ , (a-2) an MFR of 0.1 to 20 g / 10 min, (a-3) a molecular weight distribution (Mw / Mn) of 1.8 to 3.5, and (a-4) a plurality of peaks in the elution temperature-elution amount curve by continuous temperature rise elution fractionation (TREF), in an amount of 65 to 100% by weight, and the layer adjacent to the innermost layer contains (b-1) a linear low density polyethylene (B) obtained by copolymerizing ethylene and an α-olefin having 4 carbon atoms, having a density of 0.927 to 0.950 g / cm ３ , (b-2) an MFR of 0.1 to 15 g / 10 min. The heat-resistant sealing film is characterized by containing the same.

2. The heat-resistant sealant film according to claim 1, wherein in the Elmendorf tear test measured in accordance with JIS K7128-2, the tear strength in the flow direction (MD) of the film is 20 N / mm or less.

3. In the Elmendorf tear test measured in accordance with JIS K7128-2, the ratio of the tear strength (S ＭＤ in the machine direction (MD) of the film) to the tear strength (S ＴＤ in the transverse direction (TD)) is S ＭＤ / S ＴＤ < 0.5, and the heat-resistant sealant film according to claim 1 or 2 is characterized by this.

4. The heat-resistant sealant film according to any one of claims 1 to 3, wherein at least one base material layer selected from PET, Ny, OPP, and Al is laminated on the layer opposite to the innermost layer.

5. The heat-resistant sealant film according to any one of claims 1 to 4, wherein the innermost layers are adhered to each other, and no fusion of the innermost layers is observed after the heat and pressure treatment at 115°C.

6. A film for food packaging using the heat-resistant sealant film according to any one of claims 1 to 5.

Images