Laminate for packaging

Abstract

Provided is a packaging laminate (1) comprising: a stretched film having at least a base material layer (3) mainly composed of a high-density polyethylene having a density of 0.950 g / cm3 or more; and a sealant film (2) laminated on the stretched film and mainly composed of polyethylene. The thermal shrinkage rate of the stretched film in the stretching direction when heated at 120°C for 10 minutes is less than 5%. When the melting point of the base material layer (3) is Mp1 (°C) and the melting point of the sealant film (2) is Mp2 (°C), the relation Mp1 (°C) - Mp2 (°C) < 24.0 (°C) is satisfied.

Description

Laminate for packaging

[0001] This invention relates to a packaging laminate used in packaging films and the like.

[0002] Conventionally, packaging films used for pouches and the like have employed a packaging laminate (hereinafter sometimes simply referred to as "laminated") which consists of a base film made of a resin material and a sealant film made of a material different from the resin material that makes up the base film.

[0003] While there is a demand for reducing the environmental impact of plastics in general, and recyclability is also required for packaging films, the problem with laminates made of different materials is that separating the materials is difficult, making recycling challenging.

[0004] Therefore, in recent years, there has been a growing movement towards monomaterialization, where packaging films are made from a single material. Examples of resins used in monomaterial packaging films include polyethylene, polypropylene, and polyethylene terephthalate. Of these, polyethylene has the highest usage rate in existing packaging films and is a material for which monomaterialization is particularly in demand.

[0005] As a packaging film using polyethylene, for example, a laminate has been proposed comprising a base film and a sealant film, wherein the base film and sealant film are made of polyethylene, and the base film is subjected to a stretching treatment. It has been stated that such a configuration can provide a laminate with high recyclability, printability, and strength, as well as improved transparency of the base film (see, for example, Patent Document 1).

[0006] Furthermore, for example, a laminate has been proposed comprising a first layer containing only a first polyethylene and a second layer laminated on the first layer and containing only a second polyethylene, wherein the difference in melting points between the two layers is 24.0°C or more. It is stated that with such a configuration, the heat resistance of the first layer can be improved while the second layer can be melted at a low temperature, thus providing a laminate with excellent heat sealability and suitability for reuse (see, for example, Patent Document 2).

[0007] Japanese Patent Publication No. 2019-171860 Japanese Patent Publication No. 2021-120204

[0008] In packaging films, various functions are required, but it is known that thermal shrinkage occurs when the film is stretched. In the laminate described in Patent Document 1 above, the density is 0.950 g / cm³. ３ Because it is less than [amount missing] and mainly composed of polyethylene with a low melting point, it has a high thermal shrinkage rate, and during heat sealing performed in bag making, the base film shrinks, causing wrinkles and resulting in a poor appearance.

[0009] Furthermore, in the laminate described in Patent Document 2, the melting point of the second layer (corresponding to the sealant film) is low, so it cannot be used as a packaging film for packaging high-temperature contents (for example, boiled food). Also, polyethylene with a low melting point is soft and lacks rigidity, so it cannot be used as a packaging film that is self-supporting on its own, such as a stand-up pouch. Therefore, the laminate described in Patent Document 2 has the problem of having limited applications.

[0010] Therefore, the present invention has been made in view of the above problems, and aims to provide a packaging laminate that has excellent heat resistance and can be used for a wide range of applications.

[0011] To achieve the above objective, the packaging laminate of the present invention has a density of 0.950 g / cm³. ３A packaging laminate comprising a stretched film having at least a base layer mainly composed of high-density polyethylene, and a sealant film laminated on the stretched film and mainly composed of polyethylene, wherein the thermal shrinkage rate of the stretched film in the stretching direction when heated at 120°C for 10 minutes is less than 5%, the melting point of the base layer is Mp1 [°C], and the melting point of the sealant film is Mp ２ When given as [°C], Mp1[°C] - Mp ２ This is characterized by the relationship [°C] < 24.0 [°C] being true.

[0012] According to the present invention, it is possible to provide a packaging laminate that has excellent heat resistance and can be used for a wide range of applications.

[0013] This is a cross-sectional view illustrating the packaging laminate of the present invention. This is a plan view illustrating the packaging laminate of the present invention. This is a cross-sectional view illustrating a modified example of the packaging laminate of the present invention. This is a cross-sectional view illustrating a modified example of the packaging laminate of the present invention. This is a cross-sectional view illustrating a modified example of the packaging laminate of the present invention.

[0014] The packaging laminate of the present invention will be described in detail below. However, the present invention is not limited to the following embodiments, and can be modified and applied as appropriate without altering the essence of the invention.

[0015] Figure 1 is a cross-sectional view showing a packaging laminate of the present invention using a stretched film.

[0016] The packaging laminate 1 comprises a base film substrate layer (stretched film) 3 and a sealant film 2 laminated on the substrate layer 3.

[0017] <Sealant Film> From the viewpoint of monomaterials, polyethylene resins are preferred as the resin constituting the sealant film 2 of the present invention. More specifically, low-density polyethylene (LDPE, density: 0.910 g / cm³) is preferred. ３ 0.929g / cm or more ３ Below), linear low-density polyethylene (LLDPE, density: 0.910 g / cm³) ３ 0.925g / cm or more ３as follows), and medium-density polyethylene (MDPE, density: 0.930 g / cm ３ or more and 0.949 g / cm or less ３ etc. may be mentioned.

[0018] Among these, from the viewpoint of excellent heat sealability, impact resistance, and transparency, it is preferable to use linear low-density polyethylene (LLDPE).

[0019] Further, the melting point of the polyethylene-based resin is preferably in the range of 116°C or more, and more preferably 120°C or more. When the melting point is 116°C or more, the rigidity of the sealant film 2 is improved, so for example, it can be used as a sealant film in a packaging film that can stand on its own only with a film such as a packaging film used for packaging high-temperature contents or a stand-up pouch.

[0020] Note that the above "melting point" refers to the one measured in accordance with JIS K 7121, and is obtained by measuring the temperature at which the main endothermic peak appears using a differential scanning calorimeter (DSC).

[0021] Further, from the viewpoint of improving heat sealability, a polyethylene-based resin having a lower melting point than the base film is used to provide a melting point difference from the base film.

[0022] The content of polyethylene in the entire sealant film 2 is preferably 70% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and particularly preferably 100% by mass.

[0023] Further, the thickness of the sealant film 2 is preferably 50 μm to 150 μm, and more preferably 80 μm to 150 μm. This is because when the thickness is less than 50 μm, the rigidity of the sealant film 2 decreases, so it may be difficult to apply it to a packaging film that can stand on its own only with a film such as the above-mentioned packaging film or stand-up pouch. When the thickness is 150 μm or more, the cost increases and long-time heating is required during bag making, so the productivity may decrease.

[0024] Furthermore, the sealant film 2 may contain other components besides the polyethylene resin described above, as long as they do not impair the properties of the sealant film 2.

[0025] Other components include olefin resins, amide antiblocking agents (such as amide stearate), plasticizers, UV absorbers, antioxidants, weather stabilizers, antistatic agents, colorants, antifogging agents, metal soaps, waxes, antifungal agents, antibacterial agents, nucleating agents, flame retardants, and lubricants.

[0026] <Base Layer> The base layer 3 of the present invention is a stretched film mainly composed of high-density polyethylene (HDPE), and in the present invention, the density of the high-density polyethylene is 0.950 g / cm³. ３ That's all. This has a density of 0.950 g / cm³. ３ If the density is less than 0.960 g / cm³, the melting point of polyethylene decreases, which increases the thermal shrinkage rate, reduces heat resistance, and lowers film strength. Furthermore, from the viewpoint of improving heat resistance and film strength, the density of high-density polyethylene is 0.960 g / cm³. ３ It is preferable that the above conditions are met.

[0027] Furthermore, the density of high-density polyethylene is 0.971 g / cm³. ３ Preferably, the density is 0.971 g / cm³. ３ If the size is larger than this, it becomes harder and more prone to tearing, which can make it difficult to produce stretched film.

[0028] In other words, in the present invention, the density of the high-density polyethylene constituting the base layer 3 is 0.950 g / cm³. ３ As described above, the melting point of polyethylene is increased, which makes uniaxial stretching at the stretching temperature described later possible and suppresses the increase in thermal shrinkage rate (i.e., the thermal shrinkage rate of the stretched film when heated at 120°C for 10 minutes in the stretching direction is less than 5%), thereby improving heat resistance and film strength.

[0029] Further, from the perspective of further improving heat resistance, the content of high-density polyethylene in the entire substrate layer 2 (100% by mass) is preferably 50% by mass or more (that is, it is the main component of the substrate layer 3), more preferably 70% by mass or more from the perspective of improving recyclability, still more preferably 90% by mass or more, and particularly preferably 95% by mass or more.

[0030] Further, as the high-density polyethylene constituting the substrate layer 3, it is preferable to use high-density polyethylene (m-HDPE) polymerized using a metallocene catalyst. By polymerizing using a metallocene catalyst, the active site structure becomes uniform, so that it is possible to perform polymerization with few low-molecular-weight components and a small molecular weight distribution. Therefore, since the entanglement of molecular chains increases, it is possible to improve the impact strength and puncture strength of the substrate layer 3.

[0031] Further, the melting point of the high-density polyethylene is preferably 130°C or more and less than 140°C, more preferably 132°C or more and less than 140°C, and still more preferably 135°C or more and less than 140°C. This is because when the melting point is less than 130°C, stretching at a temperature equal to or higher than the stretching temperature (125°C) described later cannot be performed, and the heat resistance of the stretched film may decrease.

[0032] Further, in the laminate 1 of the present invention, when the melting point of the substrate layer 3 is Mp1 [°C] and the melting point of the sealant film 2 is Mp ２ [°C], the difference between the melting point Mp1 [°C] of the substrate layer 3 and the melting point Mp ２ [°C] of the sealant film 2 is less than 24°C (that is, Mp1 [°C] - Mp ２ [°C] < 24.0 [°C]) holds).

[0033] And with such a configuration, it becomes possible to use the sealant film 2 made of a polyethylene-based resin having a high melting point. Therefore, the laminate 1 can be used as a packaging film that stands alone with only films such as packaging films used for packaging high-temperature contents and films such as stand-up pouches. Therefore, it is possible to obtain a packaging laminate that is excellent in heat resistance and can be used for a variety of applications.

[0034] Note that the melting point Mp1 [°C] of the base layer 3 and the melting point Mp of the sealant film ２ The difference from [°C] is preferably 20°C or less, and more preferably 15°C or less.

[0035] Furthermore, it is preferable that the molecular weight distribution (Mw / Mn), which is the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) of the high-density polyethylene, be 3.0 or less. With this configuration, the molecular weight distribution (Mw / Mn) becomes smaller, which increases the entanglement of molecular chains and makes it possible to improve the impact strength and puncture strength of the base layer 3.

[0036] The weight-average molecular weight (Mw) and number-average molecular weight (Mn) mentioned above refer to polystyrene-converted values ​​obtained by gel permeation chromatography (GPC) measurement.

[0037] Furthermore, the melt mass flow rate (MFR) of high-density polyethylene is preferably 0.01 to 3.00 g / 10 min, more preferably 0.02 to 2.50 g / 10 min, and even more preferably 0.1 to 2.00 g / 10 min. This is because when the melt mass flow rate (MFR) is 0.01 g / 10 min or higher, it can be molded using a general-purpose extruder without the need for special equipment, and when it is 3.00 g / 10 min or lower, it is possible to achieve sufficient film strength.

[0038] The melt mass flow rate mentioned above is obtained by measurement in accordance with the provisions of JIS K7210:1999.

[0039] Furthermore, the base layer 3 may contain other components as described above, to the extent that they do not impair the heat resistance of the base layer 3.

[0040] <Method for Manufacturing Laminated Packaging Materials> Next, an example of a method for manufacturing laminated packaging materials using the stretched film of the present invention will be described in detail.

[0041] First, the raw material containing the high-density polyethylene described above is formed into a film using an extruder to produce the base layer 3.

[0042] More specifically, high-density polyethylene and, if necessary, other components mentioned above are mixed in a predetermined ratio, and the mixture is formed into a film by melt extrusion using an extruder equipped with a T-die to obtain a raw film roll before stretching.

[0043] Furthermore, similar to the content of the base material layer 3 described above, the content of high-density polyethylene relative to the entire raw film is 50% by mass or more of 100% by mass of the raw film.

[0044] Then, by subjecting the raw film to a uniaxial stretching process, a stretched film that will become the base layer 3, as shown in Figures 1 and 2, is manufactured. The stretching method is not particularly limited and examples include roll stretching and tenter stretching.

[0045] The uniaxial stretching process described above is a stretching process performed in either the direction of the machine axis (longitudinal) of the film (hereinafter referred to as "MD") or the direction perpendicular to the MD (hereinafter referred to as "TD"), as shown in Figure 2. By performing uniaxial stretching, the high-density polyethylene is oriented and the elastic modulus of the film is improved, making it possible to prevent printing misalignment caused by elongation during the printing process.

[0046] In uniaxial stretching, the stretching temperature is 125°C or higher and less than 130°C, preferably 127°C or higher and less than 128°C, when the stretched film is composed solely of high-density polyethylene. This is because if the stretching temperature is below 125°C, the thermal shrinkage rate increases, which can reduce heat resistance, and if the stretching temperature is above 130°C, the film may melt and break.

[0047] In other words, if the stretching temperature is within the above range, the effect of heat fixation becomes greater, thus improving heat resistance.

[0048] Furthermore, the stretching ratio in the uniaxial stretching process is between 4 and 10 times. This is because if the stretching ratio is 4 times or less, the film stretches unevenly, making it difficult to suppress printing misalignment caused by film stretching during the printing process. Also, if the stretching ratio is greater than 10 times, the film may break. Moreover, from the viewpoint of suppressing printing misalignment and preventing film breakage, the stretching ratio is preferably between 5 and 8 times, more preferably between 5 and 7 times, and even more preferably between 5 and 6 times.

[0049] The stretched film produced by the stretching process described above has a density of 0.950 g / cm³. ３ The main component is high-density polyethylene, and because high-density polyethylene has a high melting point, it is possible to suppress the increase in the thermal shrinkage rate, and the thermal shrinkage rate when heated at 120°C for 10 minutes in the stretching direction of the film is less than 5%. Therefore, the dimensional stability after heat treatment is increased, and the occurrence of wrinkles due to thermal shrinkage during the heat sealing process in bag making can be prevented, making it possible to obtain excellent heat resistance.

[0050] Furthermore, from the viewpoint of improving heat resistance, the thermal shrinkage rate of the stretched film is preferably less than 3%, more preferably less than 2%, and particularly preferably less than 1%.

[0051] Furthermore, the aforementioned "thermal shrinkage rate" can be determined by the method described in the examples below.

[0052] Furthermore, for stretched films, it is preferable that the tensile modulus of elasticity in the stretching direction of the film is 2000 MPa or more and less than 5000 MPa. This is because if the tensile modulus of elasticity is less than 2000 MPa, it may be difficult to suppress the occurrence of printing misalignment due to the stretching of the film when transporting the film during the printing process. Also, if the tensile modulus of elasticity is 5000 MPa or more, the flexibility of the film decreases, which may cause cracks or fissures.

[0053] Furthermore, the tensile modulus is more preferably 2500 MPa or higher, and even more preferably 3000 MPa or higher.

[0054] Furthermore, the above-mentioned "tensile modulus" can be obtained by measurement in accordance with JIS K 7127.

[0055] Furthermore, it is preferable that the puncture strength of the stretched film be 1.5 N or higher. If the puncture strength is less than 1.5 N, the film may rub against the packaged item or the transport container (cardboard, etc.) and tear during transport.

[0056] Furthermore, a puncture strength of 2.0 N or higher is more preferable, 2.5 N or higher is even more preferable, and 3.0 N or higher is particularly preferable.

[0057] Furthermore, the above-mentioned "puncture strength" is obtained by measuring it in accordance with JIS Z 1707 ("General Rules for Plastic Films for Food Packaging," "7.4 Puncture Strength Test").

[0058] The thickness of the raw film before stretching is preferably 100 μm to 300 μm, and more preferably 100 μm to 250 μm. If the thickness of the raw film is 100 μm or more, sufficient strength to withstand the stress during stretching can be obtained. Furthermore, if the thickness of the raw film is 300 μm or less, sufficient transparency can be obtained after stretching.

[0059] Furthermore, the thickness of the stretched film after stretching is preferably 10 μm to 40 μm, more preferably 15 μm to 35 μm, and even more preferably 20 μm to 30 μm. If the thickness of the stretched film after stretching is 10 μm or more, sufficient strength can be obtained as a base film. Also, if the thickness of the stretched film after stretching is 40 μm or less, sufficient transparency can be obtained, costs can be reduced, and especially when used for flexible packaging, the amount of plastic used can be reduced, thus providing an environmentally friendly packaging film.

[0060] The stretched film used as the base film may be a single layer or a multi-layered film of two or more layers. If the stretched film is multi-layered, the composition and thickness of each layer may be the same or different.

[0061] Next, a raw material containing polyethylene-based resins such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and medium-density polyethylene (MDPE) is prepared, and a sealant film 2 is produced by forming it into a film using the extruder described above.

[0062] Then, by laminating the stretched film (base layer 3) and the sealant film 2, the packaging laminate (packaging film) 1 shown in Figure 1 is manufactured.

[0063] Furthermore, it is preferable that the seal strength of the packaging film (i.e., the seal strength of the heat-sealed portion when the two sealant films of the two prepared packaging films are overlapped facing each other and the two packaging films are heat-sealed using a heat sealer) is 50 N / 15 mm or more. If the seal strength is less than 50 N / 15 mm, the packaging film will tear easily, and in particular, if the packaged product is a liquid, the liquid may leak.

[0064] The above-mentioned "seal strength" is obtained by measurement in accordance with JIS Z 0238 (1998).

[0065] By the above method, the present invention makes it possible to obtain a packaging laminate that has excellent heat resistance and can be used for a wide range of applications.

[0066] <Other Embodiments> In the embodiments described above, a packaging laminate 1 comprising a base layer (stretched film) 3 and a sealant film 2 laminated on the base layer 3 was used as an example. However, the packaging laminate of the present invention only needs to have the base layer 3 and sealant film 2 described above. For example, as shown in Figure 3, a coating layer 4 made of polyvinyl alcohol or the like is provided on at least one surface of the base layer 3 (in Figure 3, the surface of the base layer 3 on the sealant film 2 side), and the packaging laminate 20 may have a three-layer structure in which the sealant film 2 / coating layer 4 / base layer 3 are laminated in that order.

[0067] Furthermore, by providing such a coating layer 4, it becomes possible to impart high gas barrier properties (characteristics that suppress the permeation of gases such as oxygen and water vapor).

[0068] Furthermore, as shown in Figure 4, a packaging laminate 30 may also have a five-layer structure in which a vapor-deposited layer 6 made of silica, aluminum, alumina, etc. is provided on at least one side of the base layer (stretched film) 3 (in Figure 4, the side of the base layer 3 opposite to the sealant film 2 side) via an anchor coat layer 5, and a top coat layer 7 is provided on the surface of the vapor-deposited layer 6, and the layers are stacked in the order of sealant film 2 / base layer 3 / anchor coat layer 5 / vapor-deposited layer 6 / top coat layer 7.

[0069] Furthermore, by providing such a vapor-deposited layer 6, it becomes possible to impart high gas barrier properties (characteristics that suppress the permeation of gases such as oxygen and water vapor).

[0070] Furthermore, although the above-described embodiment described an example of a packaging laminate 1 comprising a stretched film having a single-layer structure consisting only of the base material layer 3, the stretched film of the present invention only needs to have at least a base material layer. For example, as shown in Figure 5, the packaging laminate 40 may comprise a stretched film 12 having a five-layer structure in which a base material layer (first base material layer) 3 / first adhesive layer 8 / barrier layer 9 / second adhesive layer 10 / second base material layer 11 are laminated in that order (i.e., a base material layer is provided on at least one side of the barrier layer), and a sealant film 2 laminated on the stretched film 12.

[0071] The barrier layer 9 is made of a barrier resin that has the function of suppressing the permeation of gases such as oxygen and water vapor, and at least one of ethylene-vinyl alcohol copolymer (EVOH) and butenediol-vinyl alcohol copolymer (BVOH) can be used as the barrier resin.

[0072] In this case, first, resin materials for forming each layer are prepared, and then, using a co-extruder equipped with a T-die for five types and five layers, the resin materials for forming each layer are extruded at a predetermined temperature to form a five-layer film in which the first base layer, the first adhesive layer, the barrier layer, the second adhesive layer, and the second base layer are laminated in this order, thereby obtaining a raw film before stretching. Then, the raw film is stretched by performing uniaxial stretching in MD or TD under predetermined stretching temperature and stretching ratio conditions, thereby producing a stretched film having the five-layer structure shown in Figure 5.

[0073] The present invention will be described below based on examples. However, the present invention is not limited to these examples, and these examples can be modified and altered in accordance with the spirit of the invention; such modifications do not exclude them from the scope of the invention.

[0074] The materials used to produce the stretched film are as follows: (1) HDPE1: High-density polyethylene (density: 0.951 g / cm³) ３ (1) HDPE2: High-density polyethylene (density: 0.954 g / cm³) ３ (3) HDPE3: High-density polyethylene (density: 0.960 g / cm³) ３ (4) MDPE: Medium-density polyethylene (density: 0.943 g / cm³) ３(5) EVOH: Ethylene-vinyl alcohol copolymer (density: 1.19 g / cm³) ３ (6) Acid-modified polyethylene: (Density: 0.91 g / cm³) ３ (7) LLDPE1: Linear low-density polyethylene (density: 0.925 g / cm³) ３ (8) LLDPE2: Linear low-density polyethylene (density: 0.916 g / cm³) ３ Melting point (measured according to JIS K 7121): 116°C, MFR (190°C): 2.3 g / 10 min, manufactured by Prime Polymer, product name: Evolu SP2020)

[0075] (Example 1) <Preparation of stretched film> First, high-density polyethylene as shown in Table 1 was prepared. Next, the prepared high-density polyethylene was formed into a film by melt extrusion (extrusion temperature: 200°C) using an extruder equipped with a T-die (LABTECH Co., Ltd., product name: LCR-350), and the film was wound onto a winding roll to obtain a raw film roll before stretching with the thickness shown in Table 1.

[0076] Then, using a stretching machine (LABTECH, product name: LMDO-350), the raw film was subjected to uniaxial stretching in the medium-density direction (MD) under the stretching temperature and stretching ratio conditions shown in Table 1, thereby stretching the raw film and producing a single-layer stretched film made of high-density polyethylene with the thickness shown in Table 1.

[0077] <Calculation of Heat Shrinkage Rate at 120°C> A sample of a predetermined size (12 cm x 12 cm) was cut from the prepared stretched film. Orthogonal markings, each 10 cm long and parallel to the edge, were drawn 1 cm inward from each edge of the sample. The sample was placed in an oven at 120°C and heated for 10 minutes. After removal, it was cooled to room temperature (approximately 25°C). The distance between the markings in the stretching direction (i.e., MD) was measured in the heat-treated sample. The heat shrinkage rate [%] was calculated from the change in the distance between the markings before and after heating in the stretching direction using the following formula (1), and this was used as an indicator of heat resistance. The results are shown in Table 1.

[0078] Thermal shrinkage rate in the stretching direction [%] = [(gauge distance before heating - gauge distance after heating) / gauge distance before heating] × 100 (1)

[0079] <Measurement of Melting Point> The melting point of the fabricated stretched film was measured by differential calorimetry (DSC measurement). More specifically, a 5 mg sample was prepared from the fabricated stretched film, and in accordance with JIS K 7121, the sample was sealed in a differential calorimetry meter (Hitachi High-Tech Science Corporation, product name: DSC7000X). Nitrogen was then flowed as a carrier gas at a rate of 30 ml / min, and the temperature was increased at a rate of 10 °C / min in the temperature range of 30 °C to 200 °C, and the melting point was measured. The results are shown in Table 1.

[0080] <Measurement of Tensile Modulus> The tensile modulus [MPa] of the prepared stretched film was measured in accordance with JIS K 7127. More specifically, strip-shaped test pieces measuring 200 mm in the MD direction and 10 mm in the TD direction were prepared from the prepared stretched film. Using a tensile testing machine (Shimadzu Corporation, product name: Autograph AG-5000A), the test pieces were pulled in the stretching direction (MD) under the conditions of a temperature of 25°C and a humidity of 65% RH, a chuck distance of 80 mm, and a tensile speed of 10 mm / min. The ratio of the tensile stress corresponding to the strain between two points of strain from 0 to 1% and the corresponding strain was calculated, and the calculated value was defined as the tensile modulus [MPa]. The results are shown in Table 1.

[0081] <Measurement of Puncture Strength> The puncture strength [N] of the prepared stretched film was measured in accordance with JIS Z 1707 ("General Rules for Plastic Films for Food Packaging," "7.4 Puncture Strength Test"). More specifically, using a puncture tester (manufactured by IMADA Corporation, product name: TKS-250N / EMX-1000N), a needle with a diameter of φ1.0 mm × 0.5 mmR was punctured into the prepared stretched film at a puncture speed of 50 mm / min, and the strength [N] at which the needle penetrated the stretched film was measured.

[0082] Furthermore, the puncture strength was measured five times (N=5) when the stretched film was pierced from the surface side, and the average value was defined as the puncture strength [N]. The results are shown in Table 1.

[0083] <Appearance after heat sealing> A packaging laminate (packaging film) comprising a stretched film (base layer) and a sealant film laminated to the stretched film was prepared by laminating a sealant film made of linear low-density polyethylene (LLDPE) as shown in Table 1 onto one side of the prepared stretched film. Next, the sealant films of the two prepared packaging laminates were placed facing each other and the two packaging laminates were heat-sealed at a temperature of approximately 120°C using a heat sealer. The appearance of the heat-sealed surface was then visually evaluated based on the following evaluation criteria. The results are shown in Table 1.

[0084] ◎: No wrinkles are observed on the heat-sealed surface. ○: Almost no wrinkles are observed on the heat-sealed surface. ×: Wrinkles are clearly visible on the heat-sealed surface.

[0085] <Seal Strength> The seal strength [N / 15mm] of the heat-sealed portion of the film obtained by heat-sealing the two packaging laminates described above was also measured. More specifically, in accordance with JIS Z 0238 (1998), the measurement was performed using a tensile testing machine (Shimadzu Corporation, product name: Autograph AG-5000A) under the conditions of a tensile speed of 500 mm / min and a test piece width of 15 mm.

[0086] Furthermore, if the seal strength was 50 N / 15 mm or higher, the heat seal strength of the packaging laminate was evaluated as excellent. The results are shown in Table 1.

[0087] (Examples 2-8, Comparative Examples 1-7) Stretched films were produced by stretching raw film rolls having the thicknesses shown in Tables 1-2, in the same manner as in Example 1 described above, except that the composition of the stretched film (i.e., the high-density polyethylene used), the conditions for uniaxial stretching, or the composition of the sealant film (i.e., the linear low-density polyethylene used) were changed to the conditions shown in Tables 1-2.

[0088] Then, in the same manner as in Example 1 described above, the thermal shrinkage rate at 120°C was calculated, the melting point was measured, the tensile modulus was measured, the puncture strength was measured, the appearance after heat sealing was evaluated, and the seal strength was evaluated. The results are shown in Tables 1 and 2.

[0089] In Comparative Example 1, the stretched film was composed solely of medium-density polyethylene. Due to the low density (low melting point) of polyethylene, the stretched film (base layer) underwent thermal shrinkage during the heat sealing process (i.e., the thermal shrinkage rate exceeded 5%), resulting in clear wrinkle formation on the heat-sealed surface. Consequently, it was not possible to evaluate the seal strength in Comparative Example 1.

[0090] Furthermore, in Comparative Example 2, the raw film before stretching was composed solely of medium-density polyethylene, and because polyethylene has a low density (low melting point), the stretched film melted at the stretching temperature (125°C) during film formation in the uniaxial stretching process. Consequently, in Comparative Example 2, it was not possible to calculate the thermal shrinkage rate at 120°C, measure the melting point, measure the tensile modulus, measure the puncture strength, evaluate the appearance after heat sealing, or evaluate the seal strength.

[0091] Furthermore, in Comparative Example 3, the stretched film was composed solely of high-density polyethylene, and the stretching temperature during film formation in the uniaxial stretching process was low (115°C). As a result, the stretched film (base layer) underwent thermal shrinkage during the heat sealing process (i.e., the thermal shrinkage rate exceeded 5%), and wrinkles were clearly observed on the heat-sealed surface. Therefore, it was not possible to evaluate the seal strength in Comparative Example 1.

[0092] Furthermore, in Comparative Example 4, the raw film before stretching was composed solely of high-density polyethylene, and the stretching temperature during film formation in the uniaxial stretching process was 130°C, causing the stretched film to melt. Consequently, in Comparative Example 4, it was not possible to calculate the thermal shrinkage rate at 120°C, measure the melting point, measure the tensile modulus, measure the puncture strength, evaluate the appearance after heat sealing, or evaluate the seal strength.

[0093] Furthermore, in Comparative Example 5, the raw film before stretching was composed solely of high-density polyethylene, and the stretching ratio during film formation in the uniaxial stretching process was high (11 times), resulting in the stretched film breaking. Consequently, in Comparative Example 5, it was not possible to calculate the thermal shrinkage rate at 120°C, measure the melting point, measure the tensile modulus, measure the puncture strength, evaluate the appearance after heat sealing, or evaluate the seal strength.

[0094] Furthermore, in Comparative Example 6, the raw film before stretching was composed solely of high-density polyethylene, and the stretching ratio during film formation in the uniaxial stretching process was low (3 times), resulting in uneven film elongation. Consequently, in Comparative Example 6, it was not possible to calculate the thermal shrinkage rate at 120°C, measure the melting point, measure the tensile modulus, measure the puncture strength, evaluate the appearance after heat sealing, or evaluate the seal strength.

[0095] Furthermore, in Comparative Example 7, the stretched film was composed solely of medium-density polyethylene, and because polyethylene has a low density (low melting point), the stretched film (base layer) underwent thermal shrinkage during the heat sealing process (i.e., the thermal shrinkage rate exceeded 5%), resulting in clear wrinkle formation on the heat-sealed surface. Consequently, it was not possible to evaluate the seal strength in Comparative Example 1.

[0096] (Example 9) First, high-density polyethylene, ethylene-vinyl alcohol copolymer, and acid-modified polyethylene were prepared as shown in Table 3. Next, using a multilayer extruder equipped with a T-die (manufactured by LABTECH), the prepared high-density polyethylene, ethylene-vinyl alcohol copolymer, and acid-modified polyethylene were co-extruded in layers at an extrusion temperature of 200°C to form a five-layer film in which a first base layer, a first adhesive layer, a barrier layer, a second adhesive layer, and a second base layer were laminated in this order. The film was then wound onto a winding roll to obtain a raw film roll before stretching with the thickness shown in Table 3.

[0097] The thickness of the first substrate layer in the raw film was 58.5 μm, the thickness of the first adhesive layer was 9.4 μm, the thickness of the barrier layer was 20.8 μm, the thickness of the second adhesive layer was 9.4 μm, and the thickness of the second substrate layer was 58.5 μm, resulting in a total thickness of 156.6 μm for the raw film.

[0098] Then, the raw film was stretched by uniaxial stretching in the medium-density (MD) direction under the stretching temperature and stretching ratio conditions shown in Table 3, thereby producing a stretched film having the thickness shown in Table 3 and the five-layer structure shown in Figure 5.

[0099] In the stretched film, the thickness of the first substrate layer was 9.3 μm, the thickness of the first adhesive layer was 1.5 μm, the thickness of the barrier layer was 3.3 μm, the thickness of the second adhesive layer was 1.5 μm, and the thickness of the second substrate layer was 9.3 μm, resulting in a total thickness of 24.9 μm for the stretched film.

[0100] Then, in the same manner as in Example 1 described above, the thermal shrinkage rate at 120°C, the melting point, the tensile modulus, and the puncture strength were measured. The results are shown in Table 3.

[0101] Furthermore, similar to Example 1 described above, a packaging laminate comprising a stretched film and a sealant film laminated to the stretched film was prepared by laminating linear low-density polyethylene (LLDPE) shown in Table 3 to one side of the first base layer of the stretched film having a five-layer structure, as shown in Figure 5. Next, the sealant films of the two prepared packaging laminates were placed facing each other and the two packaging laminates were heat-sealed at a temperature of approximately 120°C using a heat sealer. Then, the appearance and seal strength after heat sealing were evaluated in the same manner as in Example 1 described above. The results are shown in Table 3.

[0102]

[0103]

[0104]

[0105] As shown in Tables 1 and 3, in the packaging laminates of Examples 1 to 9, the base layer constituting the stretched film has a density of 0.950 g / cm³. ３ The above-mentioned high-density polyethylene is the main component, and the thermal shrinkage rate of the stretched film when heated at 120°C for 10 minutes in the stretching direction is less than 5%, indicating high dimensional stability after heat treatment and excellent heat resistance. Furthermore, the melting point Mp1 [°C] of the base layer and the melting point Mp of the sealant film are... ２ Since the difference with [°C] is less than 24°C, it becomes possible to use a sealant film made of polyethylene resin (linear low-density polyethylene) with a high melting point, and it can be seen that a packaging laminate that can be used for various applications can be obtained.

[0106] As described above, the present invention is suitable for packaging laminates used, for example, in packaging films and the like.

[0107] 1. Packaging laminate 2. Sealant film 3. Substrate layer (stretched film) 4. Coating layer 6. Vapor deposition layer 9. Barrier layer

Claims

Density is 0.950 g / cm³ ３ A stretched film having at least a base layer mainly composed of high-density polyethylene, A sealant film mainly composed of polyethylene is laminated on the stretched film. A packaging laminate comprising, The thermal shrinkage rate of the stretched film in the stretching direction when heated at 120°C for 10 minutes is less than 5%. The melting point of the substrate layer is Mp1 [°C], and the melting point of the sealant film is Mp ２ When given as [°C], Mp1[°C] - Mp ２ A laminate for packaging characterized by the relationship [°C] < 24.0 [°C]. The packaging laminate according to claim 1, characterized in that the molecular weight distribution (Mw / Mn), which is the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) of the high-density polyethylene obtained by gel permeation chromatography (GPC) measurement, is 3.0 or less. 　 The packaging laminate according to claim 1, characterized in that the sealant film has a melting point of 116°C or higher. 　 The stretched film has a barrier layer formed of a barrier resin, The packaging laminate according to any one of claims 1 to 3, characterized in that the base material layer is provided on at least one surface of the barrier layer. 　 The packaging laminate according to claim 4, characterized in that the barrier resin is formed of at least one of an ethylene-vinyl alcohol copolymer and a butenediol-vinyl alcohol copolymer. 　 The packaging laminate according to any one of claims 1 to 3, characterized in that a vapor-deposited layer is provided on at least one surface of the stretched film. 　 The packaging laminate according to any one of claims 1 to 3, characterized in that a coating layer is provided on at least one surface of the stretched film.

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