Laminate for packaging

Abstract

The objective is to provide a laminated packaging material that offers excellent heat resistance and can be used for a wide range of applications. [Solution] Density is 0.950 g / cm³ 3 The packaging laminate 1 comprises a stretched film having at least a base layer 3 mainly composed of high-density polyethylene, and a sealant film 2 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%, and the relationship Mp1[°C]-Mp2[°C]<24.0[°C] holds when the melting point of the base layer 3 is Mp1[°C] and the melting point of the sealant film 2 is Mp2[°C].

Description

[Technical Field]

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

[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 an example of a packaging film using polyethylene, a laminate has been proposed comprising a base film and a sealant film, wherein both the base film and the 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). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2019-171860 [Patent Document 2] Japanese Patent Publication No. 2021-120204 [Overview of the Initiative] [Problems that the invention aims to solve]

[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, for example, high-temperature contents (e.g., 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 an object thereof is to provide a packaging laminate having excellent heat resistance and being usable for various applications.

Means for Solving the Problems

[0011] In order to achieve the above object, the packaging laminate of the present invention is a stretched film having at least a base material layer mainly composed of high-density polyethylene with a density of 0.950 g / cm 3 or more, and a sealant film mainly composed of polyethylene laminated on the stretched film, wherein the heat shrinkage rate of the stretched film in the stretching direction when heated at 120 °C for 10 minutes is less than 5%, and when the melting point of the base material layer is Mp1 [°C] and the melting point of the sealant film is Mp2 [°C], the relationship Mp1 [°C] - Mp2 [°C] < 24.0 [°C] holds.

Effects of the Invention

[0012] According to the present invention, it becomes possible to provide a packaging laminate having excellent heat resistance and being usable for various applications.

Brief Description of the Drawings

[0013] [Figure 1] It is a cross-sectional view for explaining the packaging laminate of the present invention. [Figure 2] It is a plan view for explaining the packaging laminate of the present invention. [Figure 3] It is a cross-sectional view for explaining a modified example of the packaging laminate of the present invention. [Figure 4] It is a cross-sectional view for explaining a modified example of the packaging laminate of the present invention. [Figure 5] It is a cross-sectional view for explaining a modified example of the packaging laminate of the present invention.

Mode for Carrying Out the Invention

[0014] The laminated packaging material 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 base film 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 More than 0.929g / cm 3 (Below) Linear low-density polyethylene (LLDPE, density: 0.910 g / cm³) 3 More than 0.925g / cm 3 The following are examples of medium-density polyethylene (MDPE), with a density of 0.930 g / cm³. 3 More than 0.949g / cm 3 Examples include the following:

[0018] Of these, linear low-density polyethylene (LLDPE) is preferred from the viewpoint of having excellent heat-sealing properties, impact resistance, and transparency.

[0019] Furthermore, the melting point of the polyethylene resin is preferably in the range of 116°C or higher, and more preferably 120°C or higher. When the melting point is 116°C or higher, the rigidity of the sealant film 2 is improved, making it possible to use it as a sealant film in packaging films used for packaging high-temperature contents, or in packaging films that are self-supporting on their own, such as stand-up pouches.

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

[0021] Furthermore, in order to improve heat-sealability, a polyethylene-based resin with a lower melting point than the base film is used to create a difference in melting points with the base film.

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

[0023] Furthermore, 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 if the thickness is less than 50 μm, the rigidity of the sealant film 2 decreases, making it difficult to apply to packaging films that are self-supporting on their own, such as the aforementioned packaging films and stand-up pouches. If the thickness is 150 μm or more, the cost increases, and prolonged heating is required during bag making, which can reduce productivity.

[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 material layer> The base material layer 3 of the present invention is a stretched film composed mainly of high-density polyethylene (HDPE). In the present invention, the density of the high-density polyethylene is 0.950 g / cm 3 or more. This is because when the density is less than 0.950 g / cm 3 , the melting point of the polyethylene becomes low, so the heat shrinkage rate increases, the heat resistance decreases, and the film strength decreases. Also, from the viewpoint of improving the heat resistance and the film strength, the density of the high-density polyethylene is preferably 0.960 g / cm 3 or more.

[0027] Also, the density of the high-density polyethylene is preferably 0.971 g / cm 3 or less. This is because when the density is greater than 0.971 g / cm 3 , it becomes hard and prone to cracking, which may make it difficult to produce the stretched film.

[0028] That is, in the present invention, the density of the high-density polyethylene constituting the base material layer 3 is 0.950 g / cm 3 or more, and the melting point of the polyethylene becomes high, so uniaxial stretching treatment at the stretching temperature described later becomes possible, and it is possible to suppress an increase in the heat shrinkage rate (that is, the heat shrinkage rate when the stretched film in the stretching direction is heated at 120°C for 10 minutes is less than 5% as described later), so the heat resistance can be improved and the film strength can be improved.

[0029] Also, from the viewpoint of further improving the heat resistance, the content of high-density polyethylene with respect to the entire base material layer 2 (100% by mass) is preferably 50% by mass or more (that is, it is the main component of the base material layer 3). From the viewpoint of improving the recyclability, 70% by mass or more is more preferable, 90% by mass or more is further preferable, and 95% by mass or more is particularly preferable.

[0030] Furthermore, it is preferable to use high-density polyethylene (m-HDPE) polymerized using a metallocene catalyst as the high-density polyethylene constituting the base layer 3. Polymerization using a metallocene catalyst results in a uniform active site structure, making it possible to perform polymerization with fewer low molecular weight components and a smaller molecular weight distribution. Consequently, the entanglement of molecular chains increases, making it possible to improve the impact strength and puncture strength of the base layer 3.

[0031] Furthermore, the melting point of high-density polyethylene is preferably 130°C or higher and less than 140°C, more preferably 132°C or higher and less than 140°C, and even more preferably 135°C or higher and less than 140°C. This is because if the melting point is below 130°C, stretching to the stretching temperature (125°C) or higher, as described later, may not be possible, and the heat resistance of the stretched film may decrease.

[0032] Furthermore, a feature of the laminate 1 of the present invention is that, when the melting point of the base layer 3 is Mp1 [°C] and the melting point of the sealant film 2 is Mp2 [°C], the difference between the melting point of the base layer 3 Mp1 [°C] and the melting point of the sealant film 2 Mp2 [°C] is less than 24°C (i.e., the relationship Mp1 [°C] - Mp2 [°C] < 24.0 [°C] holds).

[0033] Furthermore, this configuration makes it possible to use a sealant film 2 made of polyethylene resin with a high melting point, allowing the laminate 1 to be used, for example, as a packaging film that allows self-supporting packaging films or stand-up pouches used for packaging high-temperature contents. Thus, it becomes possible to obtain a packaging laminate that has excellent heat resistance and can be used for a wide range of applications.

[0034] Furthermore, the difference between the melting point Mp1 [°C] of the base layer 3 and the melting point Mp2 [°C] of the sealant film 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] Note that 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 a packaging laminate 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 predetermined proportions, 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 in the 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, resulting in a thermal shrinkage rate of less than 5% when heated at 120°C for 10 minutes in the stretching direction of the film. Therefore, dimensional stability after heat treatment is enhanced, and the occurrence of wrinkles due to thermal shrinkage during the heat sealing process in bag making can be prevented, thus enabling the acquisition of 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 elongation 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, a tensile modulus of elasticity of 2500 MPa or higher is more preferable, and 3000 MPa or higher is even more preferable.

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

[0055] Furthermore, it is preferable that the puncture strength of the stretched film be 1.5N or higher. If the puncture strength is less than 1.5N, 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, raw materials containing polyethylene-based resins such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and medium-density polyethylene (MDPE) are prepared, and sealant film 2 is produced by forming them 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 forms> Furthermore, although the above-described embodiment described an example of a packaging laminate 1 comprising a base layer (stretched film) 3 and a sealant film 2 laminated on the base layer 3, the packaging laminate of the present invention only needs to have the above-described base layer 3 and sealant film 2. 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 is 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 composed 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. [Examples]

[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 listed below. (1) HDPE1: High-density polyethylene (density: 0.951 g / cm³)3 Melting point (measured according to JIS K 7121): 133.6°C, Molecular weight distribution (Mw / Mn) = 2.4, MFR (190°C): 1.0g / 10min, manufactured by Tosoh Corporation. (2) HDPE2: High-density polyethylene (density: 0.954 g / cm³) 3 Melting point (measured according to JIS K 7121): 134°C, Molecular weight distribution (Mw / Mn) = 2.6, MFR: 1.0 g / 10 min, Manufactured by Prime Polymer Co., Ltd., Product name: Neozex 5510F) (3) HDPE3: High-density polyethylene (density: 0.960 g / cm³) 3 Melting point (measured according to JIS K 7121): 135°C, Molecular weight distribution (Mw / Mn) = 8.7, MFR: 1.0g / 10min, Manufactured by Nippon Polyethylene Co., Ltd., Product name: Novatec HY540) (4) MDPE: Medium-density polyethylene (density: 0.943 g / cm³) 3 Melting point (measured according to JIS K 7121): 126°C, Molecular weight distribution (Mw / Mn) = 22.4, MFR: 0.24 g / 10 min, Manufactured by Prime Polymer Co., Ltd., Product name: Hyzex 5100E) (5) EVOH: Ethylene-vinyl alcohol copolymer (Density: 1.19 g / cm³) 3 Melting point (measured according to JIS K 7121): 183°C, MFR: 1.6g / 10min, Ethylene content: 32mol%, manufactured by Kuraray Co., Ltd. (EVAL F171B) (6) Acid-modified polyethylene: (Density: 0.91 g / cm³) 3 Melting point (measured in accordance with JIS K 7121): 120°C, MFR: 2.3g / 10min, manufactured by Mitsui Chemicals, Inc. (Admer NF587) (7) LLDPE1: Linear low-density polyethylene (density: 0.925 g / cm³) 3 Melting point (measured according to JIS K 7121): 122°C, MFR (190°C): 1.9g / 10min, manufactured by Prime Polymer, product name: Evolu SP2520) (8) LLDPE2: Linear low-density polyethylene (density: 0.916 g / cm³) 3Melting point (measured according to JIS K 7121): 116°C, MFR (190°C): 2.3g / 10min, 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 MD manner 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 thermal shrinkage rate at 120°C> A sample of a predetermined size (12 cm × 12 cm) was cut from the prepared stretched film. Orthogonal markings, each 10 cm long and parallel to the edge, were marked 1 cm inward from each side of the sample. The sample was then placed in a 120°C oven 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 thermal 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] <Measuring the 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 30 ml / min, and the temperature was increased at a heating 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 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 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 conditions of a temperature of 25°C and a humidity of 65% RH, with 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 with a strain of 0-1% was calculated, and this 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 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 names: TKS-250N / EMX-1000N), a needle with a diameter of φ1.0 mm × 0.5 mmR was inserted into the 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] 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> Furthermore, the seal strength [N / 15mm] of the heat-sealed portion of the film formed by heat-sealing the two aforementioned packaging laminates was 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 conditions of a tensile speed of 500 mm / min and a test specimen 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) Except for changing 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) to the conditions shown in Tables 1 and 2, a roll of film having the thickness shown in Tables 1 and 2 was stretched in the same manner as in Example 1 described above to produce a stretched film.

[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. This 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 using MD 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 was calculated, the melting point was measured, the tensile modulus was measured, and the puncture strength was 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 fabricated 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 fabricated 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] [Table 1]

[0103] [Table 2]

[0104] [Table 3]

[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, since the difference between the melting point Mp1 [°C] of the base layer and the melting point Mp2 [°C] of the sealant film is less than 24°C, it is possible to use a sealant film made of a polyethylene resin with a high melting point (linear low-density polyethylene), and it is possible to obtain a packaging laminate that can be used for a wide range of applications. [Industrial applicability]

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

[0107] 1. Laminate for packaging 2. Sealant film 3. Substrate layer (stretched film) 4 Coating layer 6 Deposited layer 9. Barrier layer

Claims

1. 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 Mp 1 [°C], the melting point of the sealant film is Mp ２ When set to [℃], Mp 1 [℃] - Mp ２ A laminate for packaging characterized by the relationship [°C] < 24.0 [°C].

2. 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.

3. The packaging laminate according to claim 1, characterized in that the sealant film has a melting point of 116°C or higher.

4. 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.

5. 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.

6. 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.

7. 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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