Stretched film and method for manufacturing the same

Abstract

This stretched film is mainly composed of polyethylene having a density of 0.950 g / cm3 or more, wherein the amount of polyethylene having a density of 0.950 g / cm3 or more exceeds 50 mass% relative to the entire stretched film, and the thermal shrinkage rate in the film stretching direction when heated at 120°C for 10 min is 3% or less.

Description

[Technical Field] 【0001】 The present invention relates to a stretched film used in packaging films and the like, and a method for producing the same. [Background technology] 【0002】 Conventionally, packaging films used for pouches and the like have employed laminates, which consist 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 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). [Prior art documents] [Patent Documents] 【0006】 [Patent Document 1] Japanese Patent Publication No. 2019-171860 [Overview of the project] [Problems that the invention aims to solve] 【0007】 In packaging films, various functions are required, but it is known that thermal shrinkage occurs when the film is stretched. In the packaging film described in Patent Document 1 above, the density is 0.950 g / cm³. 3 Because it is primarily composed of polyethylene, it has a high thermal shrinkage rate, which causes the base film to shrink during heat sealing in the bag-making process, resulting in wrinkles and a poor appearance. 【0008】 Therefore, the present invention has been made in view of the above problems, and aims to provide a stretched film with excellent heat resistance. [Means for solving the problem] 【0009】 To achieve the above objective, the stretched film of the present invention has a density of 0.950 g / cm³. 3 A stretched film mainly composed of polyethylene, wherein the density of the stretched film as a whole is 0.950 g / cm³. 3 The polyethylene content is more than 50% by mass, and the thermal shrinkage rate when heated at 120°C for 10 minutes in the stretching direction of the film is 3% or less. 【0010】 Furthermore, the method for producing the stretched film of the present invention has a density of 0.950 g / cm³. 3 A method for manufacturing a stretched film, comprising at least the steps of preparing a base film mainly composed of polyethylene and stretching the base film, wherein the density of the base film is 0.950 g / cm³. 3 The polyethylene content is more than 50% by mass, and the stretching temperature during the stretching process is 125°C or higher and less than 130°C. 【Advantages of the Invention】 【0011】 According to the present invention, it becomes possible to provide a stretched film having excellent heat resistance. 【Brief Description of the Drawings】 【0012】 [Figure 1] It is a cross-sectional view for explaining a laminate using the stretched film of the present invention. [Figure 2] It is a plan view for explaining a laminate using the stretched film of the present invention. 【Modes for Carrying Out the Invention】 【0013】 Hereinafter, the stretched film of the present invention will be specifically described. Note that the present invention is not limited to the following embodiments, and can be appropriately modified and applied without changing the gist of the present invention. 【0014】 FIG. 1 is a cross-sectional view showing a laminate using the stretched film of the present invention. 【0015】 The laminate 1 includes a polyethylene film (stretched film) 3 serving as a base film and a sealant film 2 laminated on the polyethylene film 3. 【0016】 <Sealant Film> From the perspective of a single material, the sealant film 2 of the present invention preferably uses a polyethylene-based resin. More specifically, high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and the like can be mentioned. 【0017】 In addition, from the perspective of improving heat sealability, in order to provide a melting point difference from the base film, low-density polyethylene (LDPE) or linear low-density polyethylene (LLDPE) having a lower melting point than the base film is preferable. 【0018】 Also, the content of polyethylene in the sealant film 2 is preferably 70% or more, more preferably 90% or more, still more preferably 95% or more, and most preferably 100%. 【0019】 Also, the thickness of the sealant film 2 is preferably 20 μm to 200 μm, more preferably 30 μm to 150 μm. 【0020】 Also, the sealant film 2 may contain other components other than the above-mentioned polyethylene-based resin within a range that does not impair the properties of the sealant film 2. 【0021】 Examples of other components include olefin-based resins, amide-based antiblocking agents (such as stearic acid amide), plasticizers, ultraviolet absorbers, antioxidants, weather stabilizers, antistatic agents, colorants, antifogging agents, metal soaps, waxes, fungicides, antibacterial agents, nucleating agents, flame retardants, lubricants, and the like. 【0022】 <Polyethylene film> The polyethylene film 3 of the present invention is composed mainly of high-density polyethylene (HDPE). In the present invention, the density of 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 polyethylene becomes low, so the heat shrinkage rate increases and the heat resistance decreases, and at the same time the film strength decreases. 【0023】 Incidentally, the density of high-density polyethylene is preferably less than 0.970 g / cm 3 This is because when the density is 0.970 g / cm 3 or more, it becomes hard and is likely to crack, so it may be difficult to produce a stretched film. 【0024】 Furthermore, the melting point of high-density polyethylene is preferably in the range of 130 to 140°C, and more preferably in the range of 132 to 140°C. If the melting point is below 130°C, stretching to the stretching temperature (125°C) described later may not be possible, and the heat resistance of the stretched film may decrease. 【0025】 The "melting point" mentioned above refers to the melting point measured in accordance with JIS K 7121:1987, which is determined by measuring the temperature at which the main endothermic peak appears using a differential scanning calorimeter (DSC). 【0026】 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. 【0027】 The melt mass flow rate mentioned above is obtained by measurement in accordance with the provisions of JIS K7210:1999. 【0028】 Furthermore, from the viewpoint of further improving heat resistance, the content of high-density polyethylene relative to the total polyethylene film is preferably more than 50% by mass and 70% or more by mass of 100% by mass of the polyethylene film. 【0029】 Furthermore, the polyethylene film 3 of the present invention may also contain ultra-high molecular weight polyethylene (UHMWPE) in addition to the high-density polyethylene, which is the main component mentioned above. By using a mixture of high-density polyethylene, which is the main component, and ultra-high molecular weight polyethylene as the polyethylene constituting the polyethylene film 3, it becomes possible to stretch the film at a higher temperature without melting the film, thereby further improving its heat resistance. 【0030】 This ultra-high molecular weight polyethylene is a solid powder, and can be used with a viscosity-average molecular weight (Mv) of 500,000 to 3,000,000. This is because if the viscosity-average molecular weight (Mv) is less than 500,000, the melt tension will be small, and the effect obtained by mixing with ultra-high molecular weight polyethylene (i.e., the effect of being able to stretch at a higher temperature without causing the film to melt) may be reduced. Also, if the viscosity-average molecular weight (Mv) is greater than 3,000,000, the ultra-high molecular weight polyethylene may not melt and may not mix with high-density polyethylene (gelation may occur during mixing and molding). 【0031】 As ultra-high molecular weight polyethylene, commercially available products such as Hyzex Million 030S (manufactured by Mitsui Chemicals, viscosity-average molecular weight: 500,000) can be used. 【0032】 Alternatively, crosslinked polyethylene obtained by crosslinking agents or electron beam irradiation, or polyethylene with a high molecular weight of 500,000 to 3,000,000 (synthesized) may be used. 【0033】 Furthermore, the "viscosity-average molecular weight" mentioned above refers to the value calculated in accordance with JIS K 7367-3:1999. 【0034】 Furthermore, as ultra-high molecular weight polyethylene, those with a melting point in the range of 130 to 140°C after recrystallization are preferred, and those with a melting point in the range of 132 to 140°C are more preferred. 【0035】 Furthermore, when using ultra-high molecular weight polyethylene, the content of ultra-high molecular weight polyethylene relative to the total polyethylene film is preferably more than 0% by mass and 30% by mass or less of 100% by mass of the polyethylene film. This is because if the content of ultra-high molecular weight polyethylene is greater than 30% by mass, the transparency of the film may decrease. 【0036】 Furthermore, the polyethylene content (i.e., high-density polyethylene and ultra-high molecular weight polyethylene) relative to the total polyethylene film is preferably 90% by mass or more, and more preferably 95% by mass or more, of 100% by mass of the polyethylene film. When the polyethylene content is greater than 90% by mass, the entire laminate 1 can be considered as a single material made of polyethylene, thereby improving recyclability. 【0037】 <Other ingredients> The polyethylene film may contain other components besides the high-density polyethylene and ultra-high molecular weight polyethylene mentioned above, as long as they do not impair the heat resistance of the polyethylene film. 【0038】 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. 【0039】 <Method for manufacturing laminates> Next, an example of a method for manufacturing a laminate using the stretched film of the present invention will be described in detail. 【0040】 First, a polyethylene film is produced by forming the raw material containing the high-density polyethylene mentioned above into a film shape using an extruder. 【0041】 More specifically, high-density polyethylene and, if necessary, other components such as the aforementioned ultra-high molecular weight polyethylene 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. 【0042】 Furthermore, similar to the content of polyethylene film as described above, the content of high-density polyethylene in the raw film is more than 50% by mass of 100% by mass of the raw film, and the content of ultra-high molecular weight polyethylene in the raw film is more than 0% by mass and 30% by mass or less of 100% by mass of the raw film. 【0043】 Then, by subjecting the raw film to a uniaxial stretching process, a stretched film that becomes polyethylene film 3, as shown in Figures 1 and 2, is produced. The stretching method is not particularly limited and examples include roll stretching and tenter stretching. 【0044】 Furthermore, 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. Alternatively, biaxial stretching, which stretches in both the MD and TD directions, may also be performed. 【0045】 Furthermore, the stretching temperature in the uniaxial stretching process is 125°C or higher and less than 129°C, preferably 127°C or higher and less than 129°C, when the polyethylene film 3 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 129°C, the film may melt and break. 【0046】 In other words, if the stretching temperature is within the above range, the effect of heat fixation becomes greater, so the thermal shrinkage rate at high temperatures (120°C) decreases, and the heat resistance can be improved. 【0047】 Furthermore, when the polyethylene film 3 is composed of high-density polyethylene and ultra-high molecular weight polyethylene, the temperature is 125°C or higher and less than 130°C, preferably 127°C or higher and less than 130°C. By mixing ultra-high molecular weight polyethylene with high-density polyethylene, it becomes possible to stretch the film at a higher temperature without melting, thereby further improving its 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 less than 4 times, unstretched portions remain, which may reduce transparency. Also, if the stretching ratio is greater than 10 times, the film may break. Moreover, from the viewpoint of improving transparency and preventing film breakage, a stretching ratio of 5 to 8 times is preferable. 【0049】 The polyethylene 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. When heated at 120°C for 10 minutes in the stretching direction of the film, the thermal shrinkage rate is 3% or less, resulting in high dimensional stability after heat treatment and excellent heat resistance. 【0050】 Furthermore, from the viewpoint of improving heat resistance, the thermal shrinkage rate of the polyethylene film is preferably 2% or less, and more preferably 1% or less. 【0051】 Furthermore, the aforementioned "thermal shrinkage rate" can be determined by the method described in the examples below. 【0052】 Furthermore, in the polyethylene film of the present invention, the haze is 20% or less, making it possible to obtain excellent transparency. 【0053】 Furthermore, from the viewpoint of further improving transparency, the haze of the polyethylene film is preferably 10% or less, more preferably 7% or less, and even more preferably 5% or less. 【0054】 Furthermore, the term "haze" used here refers to an index of cloudiness measured in accordance with JIS K 7361. 【0055】 Furthermore, in the polyethylene film of the present invention, it is preferable that the tensile breaking stress in at least one direction among MD and TD is 100 MPa or more. If the tensile breaking stress is 100 MPa or more, it is possible to provide a polyethylene film that has improved transparency and sufficient strength as a base film. 【0056】 Furthermore, from the viewpoint of further improving transparency, the tensile breaking stress of the polyethylene film is preferably 200 MPa or higher. 【0057】 Furthermore, the "tensile fracture stress" mentioned above refers to the stress measured in accordance with JIS K 7127. 【0058】 Furthermore, 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. Also, 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 polyethylene film after stretching is preferably 10 μm to 50 μm, and more preferably 20 μm to 40 μm. If the thickness of the polyethylene film after stretching is 10 μm or more, sufficient strength can be obtained as a base film. Also, if the thickness of the polyethylene film after stretching is 50 μm or less, sufficient transparency can be obtained. 【0060】 By the above method, the present invention makes it possible to obtain a polyethylene film that has excellent heat resistance as well as excellent strength and transparency. 【0061】 The polyethylene film used as the base film may be a single layer or a multi-layered film of two or more layers. If the polyethylene film is multi-layered, the composition and thickness of each layer may be the same or different. The thickness of the multi-layered polyethylene film refers to the total thickness of the multi-layered film. 【0062】 Next, raw materials containing polyethylene-based resins such as high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE) are prepared, and sealant film 2 is produced by forming it into a film using an extruder in the same manner as the polyethylene film described above. 【0063】 Then, for example, by laminating the polyethylene film 3 and the sealant film 2 via an adhesive, the laminate 1 shown in Figure 1 is manufactured. [Examples] 【0064】 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. 【0065】 The materials used to produce the stretched film are listed below. (1) HDPE1: High-density polyethylene (density: 0.951 g / cm³) 3 (Melting point: 133.6℃, ​​MFR: 1.0g / 10min, manufactured by Tosoh Corporation) (2) HDPE2: High-density polyethylene (density: 0.958 g / cm³) 3 Melting point: 133℃, MFR: 0.98g / 10min, manufactured by Prime Polymer Co., Ltd., product name: Hyzex 3600F) (3) HDPE3: High-density polyethylene (density: 0.960 g / cm³) 3 (Melting point: 135℃, 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: 126℃, MFR: 0.24g / 10min, manufactured by Prime Polymer Co., Ltd., product name: Hyzex 5100E) (5) UHMWPE: Ultra-high molecular weight polyethylene (viscosity average molecular weight: 500,000, density: 0.949g / cm 3 (Melting point after recrystallization: 132.8℃, manufactured by Mitsui Chemicals, product name: Hyzex Million 030S) 【0066】 (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 (manufactured by LABTECH) equipped with a T-die, and the film was wound onto a winding roll to obtain a raw film roll before stretching with the thickness shown in Table 1. 【0067】 Then, the raw film was stretched by uniaxial stretching using MD under the stretching temperature and stretching ratio conditions shown in Table 1, thereby producing a stretched film (polyethylene film) made of high-density polyethylene with the thickness shown in Table 1. 【0068】 <Calculation of thermal shrinkage rate> A sample of a predetermined size (7cm x 7cm) was cut from the prepared stretched film. Five perpendicular gauge lines, each 5cm long and parallel to the edge, were marked 1cm 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 allowed to cool to room temperature. The distance between the gauge lines 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 gauge lines 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. 【0069】 Thermal shrinkage rate in the stretching direction [%] = [(gauge distance before heating - gauge distance after heating) / gauge distance before heating] × 100 (1) 【0070】 <Measurement of tensile fracture stress> The tensile breaking stress [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, and tensile tests were performed using a tensile testing machine (Shimadzu Corporation, product name: Autograph AG-5000A) at a temperature of 25°C and a tensile speed of 100 mm / min. The tensile breaking stress [MPa] in the MD and TD directions was measured. The results are shown in Table 1. 【0071】 <Haze Measurement> Using a spectrophotometer (manufactured by Nippon Denshoku Industries Co., Ltd., product name: HAZE METER NDH5000), the haze [%] of polyethylene in the visible light range (360-750 nm) was measured in accordance with JIS K 7361 as an indicator of the haze of the stretched film prepared. The results are shown in Table 1. 【0072】 (Examples 2-7, Comparative Examples 1-6) A stretched film was produced by stretching a raw film having the thickness shown in Table 1, in the same manner as in Example 1 described above, except that the composition of the stretched film (i.e., the polyethylene used) and the conditions for uniaxial stretching were changed to those shown in Table 1. 【0073】 Then, in the same manner as in Example 1 described above, the thermal shrinkage rate was calculated, the tensile fracture stress was measured, and the haze was measured. The results are shown in Tables 1 and 2. 【0074】 In Comparative Example 2, 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 129°C, resulting in the melting of the stretched film. Therefore, in Comparative Example 2, it was not possible to calculate the thermal shrinkage rate, measure the tensile breaking stress, or measure the haze. 【0075】 Furthermore, in Comparative Example 4, the raw film before stretching was composed solely of medium-density polyethylene. 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 4, it was not possible to calculate the thermal shrinkage rate, measure the tensile fracture stress, or measure the haze. 【0076】 Furthermore, in Comparative Example 5, the raw film before stretching was composed solely of medium-density polyethylene, and due to the low density of the polyethylene, the stretched film fractured at the stretch ratio (5 times) during film formation in the uniaxial stretching process. Consequently, in Comparative Example 5, it was not possible to calculate the thermal shrinkage rate, measure the tensile fracture stress, or measure the haze. 【0077】 Furthermore, in Comparative Example 6, the raw film before stretching was composed of high-density polyethylene and ultra-high molecular weight polyethylene, and the stretching temperature during film formation in the uniaxial stretching process was 130°C, causing the stretched film to melt. Therefore, in Comparative Example 6, it was not possible to calculate the thermal shrinkage rate, measure the tensile breaking stress, or measure the haze. 【0078】 (Comparative Example 7) First, two types of polyethylene (HDPE3 and MDPE mentioned above) were prepared as shown in Table 3. Next, using an extruder equipped with a T-die (manufactured by LABTECH), the two types of polyethylene were co-extruded at an extrusion temperature of 200°C to form a three-layer film in which the first, second, and third base layers were laminated in that 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. 【0079】 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 (polyethylene film) with a three-layer structure formed from two types of polyethylene and having the thickness shown in Table 3. 【0080】 Then, in the same manner as in Example 1 described above, the thermal shrinkage rate was calculated, the tensile fracture stress was measured, and the haze was measured. The results are shown in Table 3. 【0081】 (Comparative Example 8) A stretched film was produced by stretching a raw film having the thickness shown in Table 3, in the same manner as in Comparative Example 7 described above, except that the stretching temperature for the uniaxial stretching process was changed to the conditions shown in Table 3 (125°C). 【0082】 In Comparative Example 8, the entire second base material layer in the raw film before stretching was composed of medium-density polyethylene with a low density (low melting point). Therefore, at the stretching temperature (125°C) during film formation in the uniaxial stretching process, the second base material layer made of medium-density polyethylene melted. Consequently, in Comparative Example 8, it was not possible to calculate the thermal shrinkage rate, measure the tensile fracture stress, or measure the haze. 【0083】 [Table 1] 【0084】 [Table 2] 【0085】 [Table 3] 【0086】 As shown in Table 1, the stretched films of Examples 1 to 7 had a density of 0.950 g / cm³. 3The film contains high-density polyethylene, with a high-density polyethylene content exceeding 50% by mass relative to the total length of the stretched film. Furthermore, the thermal shrinkage rate when heated at 120°C for 10 minutes in the stretching direction of the film is 3% or less, indicating high dimensional stability under heat treatment and excellent heat resistance. 【0087】 In particular, the stretched films of Examples 6 and 7 are composed of high-density polyethylene and ultra-high molecular weight polyethylene with a viscosity-average molecular weight (Mv) of 500,000. Since the ultra-high molecular weight polyethylene content relative to the total stretched film is 30% by mass or less, stretching can be performed at higher temperatures (128-129°C) without melting the film, and the heat shrinkage rate is 1% or less, indicating excellent heat resistance. 【0088】 On the other hand, as shown in Table 2, in the stretched film of Comparative Example 1, the stretching temperature was low at 120°C, resulting in a large thermal shrinkage rate and poor heat resistance. 【0089】 Furthermore, in the stretched film of Comparative Example 3, since it is composed solely of medium-density polyethylene and the stretching temperature is low at 120°C, the thermal shrinkage rate is very large, indicating poor heat resistance. In addition, the haze is greater than 20%, indicating poor transparency. 【0090】 Furthermore, as shown in Table 3, in Comparative Example 7, the low stretching temperature of 120°C resulted in a large thermal shrinkage rate and poor heat resistance. [Industrial applicability] 【0091】 As described above, the present invention is suitable for stretched films used, for example, in packaging films. [Explanation of symbols] 【0092】 1. Laminate 2. Sealant film 3. Polyethylene film (stretched film)

Claims

[Claim 1] Density is 0.950 g / cm³ ３ A uniaxially oriented film having polyethylene as its main component and a stretching ratio of 4 to 6 times, The density of the stretched film as a whole is 0.950 g / cm³. ３ The polyethylene content is more than 50% by mass, A stretched film characterized in that, in the stretching direction of the film, the thermal shrinkage rate when heated at 120°C for 10 minutes is 3% or less. [Claim 2] The density is 0.950 g / cm³. ３ The stretched film according to claim 1, characterized in that it consists only of polyethylene as described above. [Claim 3] It further contains ultra-high molecular weight polyethylene with a viscosity-average molecular weight (Mv) of 500,000 to 3,000,000. The stretched film according to claim 1, characterized in that the content of the ultra-high molecular weight polyethylene relative to the total stretched film is 30% by mass or less. [Claim 4] The stretched film according to any one of claims 1 to 3, A sealant film laminated on the stretched film and A laminate characterized by comprising the following features. [Claim 5] Density is 0.950 g / cm³ ３ The process involves preparing a raw film mainly composed of polyethylene, A step of performing uniaxial stretching on the aforementioned raw film roll. A method for manufacturing a stretched film comprising at least the following: The density of the aforementioned raw film is 0.950 g / cm³. ３ The polyethylene content is more than 50% by mass, A method for manufacturing a stretched film, characterized in that the stretching temperature in the uniaxial stretching process is 125°C or higher and less than 130°C, and the stretching ratio is 4 times or higher and 6 times or lower. [Claim 6] The aforementioned raw film has a density of 0.950 g / cm³. ３ The method for producing a stretched film according to claim 5, characterized in that it consists only of polyethylene as described above. [Claim 7] The aforementioned raw film further contains ultra-high molecular weight polyethylene having a viscosity-average molecular weight (Mv) of 500,000 to 3,000,000. The method for producing a stretched film according to claim 5, characterized in that the content of the ultra-high molecular weight polyethylene relative to the total amount of the raw film is 30% by mass or less.

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