stretched film

Abstract

The objective is to provide a stretched film that has excellent water vapor barrier properties and heat resistance, as well as excellent transparency. [Solution] The stretched film has a density of 0.950 g / cm³. 3 The main component is polyethylene, and the water vapor transmission rate per 100 μm is 1.0 g / m². 2 The film has a minimum of 10 days, a haze of 20% or less, and a thermal shrinkage rate of 10% or less when heated at 100°C for 10 minutes in the MD (Metal Dynamics) of the film.

Description

[Technical Field]

[0001] This invention relates to a stretched film used in packaging films and the like. [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 Initiative] [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 of polyethylene is 0.950 g / cm³. 3 When the stretching temperature is below a certain value (e.g., 80°C), the water vapor barrier properties improve, but the heat shrinkage rate at 100°C increases, causing the base film to shrink during heat sealing in bag making, resulting in wrinkles and poor appearance. Conversely, when the stretching temperature is high (e.g., 120°C), the heat fixing effect increases, resulting in a smaller heat shrinkage rate at 100°C, but the water vapor barrier properties decrease. As a result, it was difficult to achieve both water vapor barrier properties and heat resistance.

[0008] Therefore, the present invention has been made in view of the above problems, and aims to provide a stretched film that has excellent water vapor barrier properties and heat resistance, as well as excellent transparency. [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 water vapor transmission rate per 100 μm is 1.0 g / m². 2 The film is characterized by being less than or equal to 10 days, having a haze of 20% or less, and having a thermal shrinkage rate of 10% or less when heated at 100°C for 10 minutes in the MD (Metal Modulation) of the film. [Effects of the Invention]

[0010] According to the present invention, it becomes possible to provide a stretched film having excellent water vapor barrier properties and heat resistance, and also excellent transparency.

Brief Description of Drawings

[0011] [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

[0012] 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 changed and applied within the scope not changing the gist of the present invention.

[0013] FIG. 1 is a cross-sectional view showing a laminate using the stretched film of the present invention.

[0014] The laminate 1 includes a polyethylene film 3 serving as a base film and a sealant film 2 laminated on the polyethylene film 3.

[0015] <Sealant Film> From the viewpoint 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), etc. can be mentioned.

[0016] In addition, from the viewpoint 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.

[0017] Furthermore, the polyethylene content in the sealant film 2 is preferably 70% or more, more preferably 90% or more, even more preferably 95% or more, and most preferably 100%.

[0018] Furthermore, the thickness of the sealant film 2 is preferably 20 μm to 200 μm, and more preferably 30 μm to 150 μm.

[0019] 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.

[0020] 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.

[0021] <Polyethylene film> The polyethylene film 3 of the present invention is 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. The density is 0.950 g / cm³. 3 In the above cases, the degree of crystallinity of polyethylene is improved, which can enhance its water vapor barrier properties.

[0022] Furthermore, from the perspective of further improving water vapor barrier properties, the density of high-density polyethylene is set to 0.955 g / cm³. 3 Preferably, it is 0.962 g / cm³ or more. 3 It is more preferable that the amount be greater than or equal to 0.970 g / cm³. 3 It is even more preferable that the above conditions are met.

[0023] Also, 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. When the melt mass flow rate (MFR) is 0.01 g / 10 min or more, it can be molded with a general-purpose extruder without using special equipment. When it is 3.00 g / 10 min or less, sufficient film strength can be achieved.

[0024] The melt mass flow rate described above is obtained by measuring in accordance with the provisions of JIS K7210:1999.

[0025] Also, from the perspective of obtaining excellent water vapor barrier properties, the content of high-density polyethylene in the entire polyethylene film is preferably 90% by mass or more, more preferably 95% by mass or more, out of 100% by mass of the polyethylene film.

[0026] From the above, as the resin for forming the polyethylene film, high-density polyethylene with a density of 0.950 g / cm 3 By using the above high-density polyethylene, the water vapor permeability per 100 μm of the polyethylene film is 1.0 g / m<000e010>·day or less, so it is possible to provide a polyethylene film with excellent water vapor barrier properties.

[0027] <000e0133>From the perspective of improving the water vapor barrier properties, the water vapor permeability per 100 μm of the polyethylene film is preferably 0.8 g / m 2 ·day or less, more preferably 0.5 g / m 2 ·day or less.

[0028] Here, the "water vapor permeability" refers to the value measured using a water vapor permeability measuring machine in accordance with JIS K 7129-1 under an atmosphere of 40°C and 90% humidity.

[0029] <Other components> The stretched film may contain other components besides the high-density polyethylene described above, to the extent that it does not impair the stretchability of the stretched film.

[0030] 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.

[0031] <Method for manufacturing laminates> Next, a method for manufacturing a laminate using the stretched film of the present invention will be described in detail.

[0032] 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.

[0033] 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.

[0034] Then, by subjecting the raw film to a uniaxial stretching process, a stretched film that becomes polyethylene film is produced, as shown in Figures 1 and 2. The stretching method is not particularly limited and examples include roll stretching and tenter stretching.

[0035] 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.

[0036] Furthermore, the stretching temperature during uniaxial stretching is between 80°C and 125°C. This is because if the temperature is below 80°C, the film may become cloudy. Also, if the stretching temperature is above 125°C, the film may melt and break.

[0037] Furthermore, the stretching ratio in the uniaxial stretching process is between 5 and 9 times. This is because if the stretching ratio is less than 5 times, unstretched portions remain, which may reduce transparency. Also, if the stretching ratio is greater than 9 times, the film may break. Moreover, from the viewpoint of improving transparency and preventing film breakage, a stretching ratio of 6 to 8 times is preferable.

[0038] Furthermore, the polyethylene film produced by the stretching process described above has a haze of 20% or less, making it possible to obtain excellent transparency.

[0039] 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.

[0040] Furthermore, the term "haze" used here refers to an index of cloudiness measured in accordance with JIS K 7361.

[0041] Furthermore, in the polyethylene film of the present invention, the thermal shrinkage rate when heated at 100°C for 10 minutes in the stretching direction of the film is 10% or less. Since the dimensional stability after heat treatment is high when the thermal shrinkage rate is 10% or less, a polyethylene film with excellent heat resistance can be provided.

[0042] Furthermore, increasing the density of high-density polyethylene, the main component of polyethylene film, raises the melting point of the high-density polyethylene, which makes it possible to suppress the increase in thermal shrinkage rate.

[0043] Furthermore, from the viewpoint of improving heat resistance, the thermal shrinkage rate of the polyethylene film is preferably 6% or less, more preferably 4% or less, and even more preferably 2% or less.

[0044] Furthermore, the aforementioned "thermal shrinkage rate" can be determined by the method described in the examples below.

[0045] 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, the dimensions will be stable during transport and the transportability will be excellent during post-processing such as printing and lamination, thus providing a polyethylene film with sufficient strength as a base film.

[0046] Furthermore, from the viewpoint of improving transparency, the tensile breaking stress of the polyethylene film is preferably 300 MPa or higher.

[0047] Furthermore, the "tensile fracture stress" mentioned above refers to the stress measured in accordance with JIS K 7127.

[0048] Furthermore, the thickness of the raw film before stretching is preferably 50 to 400 μm, and more preferably 80 to 300 μm. If the thickness of the raw film is 50 μm or more, sufficient strength to withstand the stress during stretching can be obtained. Also, if the thickness of the raw film is 400 μm or less, sufficient transparency can be obtained after stretching.

[0049] Furthermore, the thickness of the polyethylene film after stretching is preferably 10 to 50 μm, and more preferably 15 to 40 μm. If the thickness of the polyethylene film after stretching is 10 μm or more, sufficient strength and water vapor barrier properties 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.

[0050] By the above method, the present invention makes it possible to obtain a polyethylene film that has excellent water vapor barrier properties and heat resistance, as well as excellent transparency.

[0051] 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.

[0052] 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 films are produced by forming them into films using an extruder in the same manner as the polyethylene films described above.

[0053] Then, for example, by laminating a polyethylene film and a sealant film via an adhesive, the laminate 1 shown in Figure 1 is manufactured. [Examples]

[0054] 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.

[0055] The materials used to produce the stretched film are listed below. (1) HDPE1: High-density polyethylene (density: 0.971 g / cm³) 3 (Melting point: 134℃, MFR: 1.2g / 10min, manufactured by Dow Chemical, product name: ELITE AT6900) (2) HDPE2: High-density polyethylene (density: 0.962 g / cm³) 3Melting point: 133℃, MFR: 0.24g / 10min, manufactured by Prime Polymer Co., Ltd., product name: Hyzex 520MB) (3) HDPE3: 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) (4) HDPE4: High-density polyethylene (density: 0.950 g / cm³) 3 (Melting point: 133℃, MFR: 0.3g / 10min, manufactured by Prime Polymer Co., Ltd., product name: Hyzex 6800S) (5) HDPE5: High-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)

[0056] (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 (manufactured by Nagata Seisakusho Co., Ltd.), and the film was wound onto a winding roll to obtain a raw film roll before stretching with the thickness shown in Table 1.

[0057] 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.

[0058] <Calculation of water vapor transmission rate per 100 μm> Next, the water vapor transmission rate of the stretched film [g / m²] 2The water vapor transmission rate [g / m²] was measured using a water vapor transmission meter (SYSTEC illinois, product name: Water Vapor Transmission Meter Lyssy L80-6000) in accordance with JIS K 7129-1, under conditions of 40°C and 90% humidity. The measured water vapor transmission rate was then multiplied by the thickness of the stretched film [μm] / 100 [μm] to obtain the water vapor transmission rate per 100 μm [g / m²]. 2 The number of days was calculated. The results are shown in Table 1.

[0059] <Measurement of haze and total light transmittance> Using a spectrophotometer (manufactured by Suga Test Instruments Co., Ltd., product name: Haze Meter HZ-V3), the haze [%] in the visible light range (360-750 nm) of the stretched polyethylene film was measured in accordance with JIS K 7361 as an indicator of the degree of cloudiness of the stretched film. In addition, the total light transmittance [%] of the stretched film was measured in accordance with JIS K 7361-1. The results are shown in Table 1.

[0060] <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 100°C oven and heated for 10 minutes. After removal, it was allowed to cool to room temperature. The distance between gauge lines in the stretching direction (i.e., MD or TD) was measured in the heat-treated sample. The thermal shrinkage rate [%] was calculated from the change in the distance between 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.

[0061] Thermal shrinkage rate in the stretching direction [%] = [(gauge distance before heating - gauge distance after heating) / gauge distance before heating] × 100 (1)

[0062] <Measurement of tensile fracture stress> The tensile breaking stress [MPa] of the stretched film was measured in accordance with JIS K 7127. More specifically, a test film of type 3 dumbbell was prepared, and a tensile test was 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] for MD and TD was measured. The results are shown in Table 1.

[0063] (Examples 2-16, Comparative Examples 1-8) 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 high-density polyethylene used) and the conditions for uniaxial stretching were changed to those shown in Table 1.

[0064] Then, in the same manner as in Example 1 described above, water vapor transmission rate, haze, and total light transmittance were measured, the thermal shrinkage rate was calculated, and the tensile fracture stress was measured. The results are shown in Tables 1 to 3.

[0065] In Comparative Example 7, the stretching temperature during film formation in the uniaxial stretching process was higher than 125°C (130°C), causing the stretched film to melt and break. Therefore, in Comparative Example 7, it was not possible to measure water vapor transmission, haze, total light transmittance, calculate thermal shrinkage, or measure tensile fracture stress.

[0066] Furthermore, in Comparative Example 8, the material was unstretched and therefore not subject to thermal shrinkage. Also, as described later, it lacked transparency and did not meet the required physical properties regardless of the thermal shrinkage rate, so the thermal shrinkage rate was not calculated.

[0067] [Table 1]

[0068] [Table 2]

[0069] [Table 3]

[0070] As shown in Tables 1 and 2, the stretched films of Examples 1 to 16 had a polyethylene density of 0.950 g / cm³. 3 The above conditions are met, and the water vapor transmission rate per 100 μm is 1.0 g / m³. 2 The film has a lifespan of less than 10 days and a haze of less than 20%, indicating excellent water vapor barrier properties and transparency. Furthermore, the film exhibits a thermal shrinkage rate of less than 10% when heated at 100°C for 10 minutes in the stretching direction, demonstrating high dimensional stability and excellent heat resistance after heat treatment.

[0071] On the other hand, as shown in Table 3, the stretched film of Comparative Example 1 had a polyethylene density of 0.950 g / cm³. 3 Since it is less than 10%, and the melting point of high-density polyethylene is low, when the stretching temperature is as low as 80°C, the thermal shrinkage rate becomes considerably larger than 10%, indicating poor heat resistance.

[0072] Furthermore, in the stretched film of Comparative Example 2, the density of polyethylene was 0.950 g / cm³. 3 Since it is less than 10%, and the melting point of high-density polyethylene is low, when the stretching temperature is as low as 90°C, the thermal shrinkage rate becomes considerably larger than 10%, indicating poor heat resistance.

[0073] Furthermore, in the stretched films of Comparative Examples 3-5, the density of polyethylene was 0.950 g / cm³. 3 Since it is less than [a certain value], it can be seen that it has poor water vapor barrier properties.

[0074] In the case of the stretched film in Comparative Example 5, the stretching temperature was high at 120°C, resulting in a greater heat-fixing effect, thus reducing the thermal shrinkage rate and exhibiting excellent heat resistance. However, the density of the polyethylene was 0.950 g / cm³. 3 Since it is less than [a certain value], it can be seen that it has poor water vapor barrier properties.

[0075] Furthermore, in the stretched film of Comparative Example 6, since the stretching temperature was less than 80°C, the film became cloudy and the haze was considerably greater than 20%, indicating poor transparency.

[0076] Furthermore, in the stretched film of Comparative Example 8, the stretching ratio is less than 5 times (i.e., unstretched), so the haze is considerably larger than 20%, indicating poor transparency. [Industrial applicability]

[0077] As described above, the present invention is suitable for stretched films used, for example, in packaging films. [Explanation of Symbols]

[0078] 1. Laminate 2. Sealant film 3. Polyethylene film (stretched film)

Claims

1. Density is 0.950 g / cm³ ３ A stretched film mainly composed of polyethylene, Water vapor transmission rate per 100 μm is 1.0 g / m². ２ - less than or equal to day, The haze is below 20%, A stretched film characterized in that, in the MD (Metal Modulation) of the film, the thermal shrinkage rate when heated at 100°C for 10 minutes is 10% or less.

2. The aforementioned water vapor transmission rate is 0.8 g / m³. ２ The stretched film according to claim 1, characterized in that it is less than or equal to day.

3. The stretched film according to claim 1 or 2, characterized in that the haze is 10% or less.

4. The stretched film according to claim 1 or 2, characterized in that the thermal shrinkage rate is 6% or less.

5. The stretched film according to claim 3, characterized in that the thermal shrinkage rate is 6% or less.

6. The stretched film according to claim 1, characterized in that its thickness is 13.8 μm or more and 44.4 μm or less.

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