Biaxially oriented polyethylene film, laminate film, and packaging

Abstract

To provide a biaxially stretched polyethylene film which can obtain good performance of blocking resistance and slipperiness of a film surface while appropriately using an anti-blocking agent without special adjustment, and a laminate film, and a package.SOLUTION: A stretched film contains a polyethylene resin as a main component and contains an anti-blocking agent, and is stretched in a biaxial direction of a vertical (MD) direction and a transverse (TD) direction, wherein more than 0.05 wt.% and 4 wt.% or less of a surface active agent having a ratio of a melting heat quantity at 40°C or higher to a total melting heat quantity measured by differential scan calorimetry according to JIS K 7122 (2012) of 40% or more is contained in the stretched film, or 0.25 wt.% or more and 1.25 wt.% or less of a polymer type anti-static agent having a ratio of a melting heat quantity at 40°C or more to the total melting heat quantity measured by differential scan calorimetry according to JIS K 7122 (2012) of 90% or more is contained therein.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a biaxially oriented polyethylene film and a laminate film and a package using the biaxially oriented polyethylene film, and in particular to a biaxially oriented polyethylene film, a laminate film, and a package that are excellent in properties such as blocking resistance and slipperiness. [Background technology]

[0002] In recent years, growing awareness of environmental issues has led to environmentally conscious efforts being made in various fields. For example, recycling, which involves collecting used products and processing them into new products for reuse, is known as one of the most representative efforts to address environmental issues.

[0003] In general, in the field of packaging food and other products, laminated films made of multiple different types of synthetic resin films are used to achieve high quality requirements. From an environmentally conscious perspective, it is desirable to reduce the environmental impact of this type of laminated film through recycling, etc. However, when discarded laminated films are recycled, the resins that make up the film typically become a mixture of incompatible resins even when remelted, significantly reducing the quality of the recycled resource, making them unsuitable as recycled materials.

[0004] In order to solve these problems, a laminate film has been proposed in which the base layer of the laminate film and the heat seal layer are made of a single material (see, for example, Patent Document 1). This type of laminate film uses a polyethylene resin that constitutes the heat seal layer in the base layer and in the surface layer laminated on the outer surface thereof, which allows for good compatibility upon remelting and makes it possible to use the film as a recycled material.

[0005] It is known that laminated films, such as biaxially oriented films, mainly made of polyethylene resin tend to be more flexible and have a lower melting point than polypropylene resin films, resulting in poorer film performance, such as blocking resistance. To improve the blocking resistance of polyethylene resin films, an antiblocking agent is added to the surface layer of the film. The blocking resistance of the antiblocking agent can be improved by adjusting the average particle size and the amount added.

[0006] However, if the average particle size of the antiblocking agent is large, the height of the protrusions on the film surface increases, and if the amount of antiblocking agent added is increased, the number of protrusions increases, making it more likely that ink will leak through when printing is performed on the film surface.In order to prevent ink leaks, it is possible to reduce the average particle size of the antiblocking agent or the amount of antiblocking agent added, but if the average particle size is reduced or the amount of antiblocking agent added is reduced, there is a concern that other problems such as a decrease in blocking resistance and slippage may occur.

[0007] Thus, when trying to improve film performance such as blocking resistance and slippage in polyethylene resin films, there are limits to how much can be achieved by adjusting the particle size or amount of the anti-blocking agent used, etc. Therefore, when constructing a biaxially oriented polyethylene film that can be used as a recyclable material from a single material (monomaterial), whether single-layer or multi-layer, it is desired to improve the blocking resistance and slippage of the film surface without making any particular adjustments to the anti-blocking agent used. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 8-300581 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made in consideration of the above points, and provides a biaxially oriented polyethylene film, a laminate film, and a package that can provide good performance in terms of the blocking resistance and slipperiness of the film surface while using an antiblocking agent appropriately without any special adjustment. [Means for solving the problem]

[0010] That is, the first invention is a stretched film mainly made of polyethylene resin, containing an antiblocking agent, and stretched in biaxial directions, i.e., machine direction (MD) and transverse direction (TD), The stretched film comprises a base layer and surface layers disposed on both sides of the base layer and containing the antiblocking agent, and a surfactant is added to layers other than the surface layers, and the surfactant is The ratio of the heat of fusion at 40°C or higher to the total heat of fusion measured by differential scanning calorimetry in accordance with JIS K 7122 (2012) is 40% or more. The surfactant is contained in the stretched film in an amount of more than 0.05% by weight and not more than 4% by weight. The present invention relates to a biaxially oriented polyethylene film characterized by the above-mentioned.

[0011] No. 2 The invention is 1 The present invention relates to a biaxially oriented polyethylene film in which the substrate layer contains the surfactant in an amount of 0.06% by weight or more and 4% by weight or less.

[0012] No. 3 The invention of the first or 2 In any one of the above aspects, the present invention relates to a biaxially oriented polyethylene film, wherein the oriented film has a dynamic friction coefficient of 0.9 or less as measured in accordance with JIS K 7125 (1999).

[0013] No. 4 The invention of the first or 2 The present invention relates to a laminate film using any one of the biaxially oriented polyethylene films of the above-mentioned invention, characterized in that a sealant film mainly made of polyethylene resin is laminated on the biaxially oriented polyethylene film.

[0014] No. 5 The invention is 3The present invention relates to a laminate film using the biaxially oriented polyethylene film of the present invention, characterized in that a sealant film mainly made of polyethylene resin is laminated on the biaxially oriented polyethylene film.

[0015] No. 6 The invention is 4 The present invention relates to a packaging body made of the laminate film of the present invention.

[0016] No. 7 The invention is 5 The present invention relates to a packaging body made of the laminate film of the present invention. [Effects of the Invention]

[0017] The biaxially oriented polyethylene film according to the first aspect of the present invention is a stretched film mainly made of polyethylene resin, containing an antiblocking agent, and stretched in two axial directions, i.e., the machine direction (MD) and the transverse direction (TD), The stretched film comprises a base layer and surface layers disposed on both sides of the base layer and containing the antiblocking agent, and a surfactant is added to layers other than the surface layers, and the surfactant is The ratio of the heat of fusion at 40°C or higher to the total heat of fusion measured by differential scanning calorimetry in accordance with JIS K 7122 (2012) is 40% or more. The surfactant is contained in the stretched film in an amount of more than 0.05% by weight and not more than 4% by weight. Therefore, it is possible to use anti-blocking agents appropriately without making any special adjustments. The surfactant contained in the base layer passes through the surface layer and migrates to the film surface. The desired blocking resistance and slipperiness are imparted to the film, thereby making it possible to obtain a film with excellent processability.

[0018] No. 2 According to the biaxially oriented polyethylene film of the present invention, 1 In the invention, the substrate layer contains the surfactant in an amount of 0.06% by weight or more and 4% by weight or less, so that the amount of surfactant added to the substrate layer can be adjusted to a predetermined amount to impart desired blocking resistance and slip properties to the film surface.

[0019] No. 3 According to the biaxially oriented polyethylene film of the present invention, or 2In any one of the above aspects, the stretched film has a dynamic friction coefficient of 0.9 or less as measured in accordance with JIS K 7125 (1999), and therefore good slip properties can be obtained.

[0020] No. 4 According to the laminate film of the present invention, or 2 Since the biaxially oriented polyethylene film of any one of the inventions is laminated with a sealant film mainly made of polyethylene resin, it is possible to achieve a monomaterial laminate film that is easy to recycle and has improved blocking resistance.

[0021] No. 5 According to the laminate film of the present invention, 3 The biaxially oriented polyethylene film of the present invention is laminated with a sealant film mainly made of polyethylene resin, thereby achieving a mono-material laminate film that is easy to recycle and has improved blocking resistance.

[0022] No. 6 According to the packaging of the present invention, 4 Since the packaging body is made of the laminate film of the present invention, it can be made recyclable by being made of an easily recyclable laminate film.

[0023] No. 7 According to the packaging of the present invention, 5 Since the packaging body is made of the laminate film of the present invention, it can be made recyclable by being made of an easily recyclable laminate film. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is an explanatory diagram for calculating the heat of fusion of all surfactants contained in a biaxially oriented polyethylene film according to one embodiment of the present invention. [Figure 2]FIG. 2 is an explanatory diagram for calculating the heat of fusion of the surfactant contained in the biaxially oriented polyethylene film at 40° C. or higher. DETAILED DESCRIPTION OF THE INVENTION

[0025] A biaxially oriented polyethylene film according to one embodiment of the present invention is a stretched film made primarily of polyethylene resin and containing an antiblocking agent, stretched in two axial directions, i.e., the machine direction (MD) and the transverse direction (TD). The biaxially oriented polyethylene film of the present invention can be used as a base film for a laminate film to be subjected to printing, vapor deposition, etc. This laminate film is suitably used as a packaging material for various items such as food, daily necessities, and parts.

[0026] The biaxially oriented polyethylene film of the present invention is made of a single material (monomaterial) with polyethylene resin as the main raw material. Therefore, it can be suitably used as a recycled material. Note that the term "single material" here means that the main raw material of each layer is the same type of resin material, and it is acceptable for small amounts of various additives to be contained.

[0027] The polyethylene resin used as the resin raw material for the biaxially oriented polyethylene film is appropriately selected from polyethylene resins derived from petroleum, biomass, material recycling, chemical recycling, etc., and is an ethylene homopolymer or a random copolymer of ethylene and an α-olefin having 3 or more carbon atoms, such as propylene, 1-butene, 1-heptene, 1-hexene, 1-octene, etc. The polyethylene resin may also be a mixture of one or more of the above.

[0028] The melt flow rate (MFR) of the polyethylene resin is not particularly limited. For example, polyethylene resins having an MFR of 0.1 to 30 g / 10 min, particularly 0.1 to 20 g / 10 min, measured in accordance with JIS K 7210 at 190°C and a load of 2.16 kg, are preferably used. If the MFR of the polyethylene resin used is too low, the extruder pressure may become excessively high, which may result in reduced productivity. If the MFR is too high, the melt viscosity of the resin may decrease, making it more susceptible to breakage during stretching and making it difficult to form into a film.

[0029] The resin raw material used for the biaxially oriented polyethylene film may contain a polyolefin elastomer such as an ethylene-α-olefin random copolymer elastomer, as appropriate, within the scope of the present invention, and may also contain additives such as antioxidants, neutralizing agents, anti-fogging agents, lubricants, nucleating agents, and colorants.

[0030] The antiblocking agent added to the biaxially oriented polyethylene film of the present invention is not particularly limited in type, and organic or inorganic particles, or a mixture thereof, are preferably used. Organic particles can be obtained, for example, by emulsion polymerization or suspension polymerization. Examples of organic particles include polymethyl methacrylate, polystyrene, polyamide, etc. Examples of inorganic fine particles include silica, zeolite, talc, etc. These antiblocking agents may be used alone or in combination of two or more. From the viewpoints of the blocking resistance and see-through properties of the film, polymethyl methacrylate is preferably used as the organic particles, and silica and zeolite are preferably used as the inorganic particles.

[0031] The average particle size of the antiblocking agent is not particularly limited. The average particle size of the antiblocking agent that can be used is determined depending on the layer thickness to which it is added, etc. For example, when the layer thickness is thin, an antiblocking agent with a relatively small average particle size tends to be suitable, while an antiblocking agent with a relatively large average particle size tends to be unsuitable. On the other hand, when the layer thickness is thick, an antiblocking agent with a relatively large average particle size tends to be suitable, while an antiblocking agent with a relatively small average particle size tends to be unsuitable. Specifically, an antiblocking agent with an average particle size appropriate for the layer thickness is appropriately selected from the range of 1 to 15 μm, preferably 1 to 13 μm. If the average particle size of the antiblocking agent used is too small, the antiblocking performance may be insufficient, while if the average particle size is too large, it is likely to cause detachment, deterioration of see-through feeling, etc.

[0032] The amount of antiblocking agent added is not particularly limited. If the amount added is too large, costs will increase, the film's transparency will deteriorate, and the antiblocking agent will easily fall off after film formation. If the amount added is too small, desired performance such as antiblocking properties may not be achieved. Therefore, for example, an appropriate amount of antiblocking agent added is considered to be a concentration of 500 to 30,000 ppm, preferably 1,000 to 20,000 ppm. The method of adding the antiblocking agent is not particularly limited, and the agent can be added by known methods, such as mixing a high-concentration masterbatch with the resin raw material of the film or mixing by dry blending.

[0033] Anti-blocking agents are typically added to biaxially oriented polyethylene films used in packaging materials and the like to impart anti-blocking properties. Conventionally, a large average particle size of an anti-blocking agent improves anti-blocking properties, but tends to cause ink breakthrough when printing on the film surface. In contrast, reducing the average particle size of the anti-blocking agent to prevent ink breakthrough can result in problems such as reduced anti-blocking properties and slippage on the film surface, limiting the ability to improve film performance by adjusting the particle size of the anti-blocking agent used. Therefore, the present inventors conducted extensive research to obtain desired film properties such as anti-blocking properties and slippage without adjusting the particle size of the anti-blocking agent. As a result, they discovered that adding a surfactant to the resin raw material of the film, by selecting a surfactant whose heat of fusion satisfies certain conditions, contributes to improving the slippage and anti-blocking properties of the film. That is, the surfactant must have a heat of fusion at 40°C or higher that accounts for 40% or more of the heat of fusion of the entire surfactant, and must be contained in the stretched film in an amount exceeding 0.05% by weight and not exceeding 4% by weight.

[0034] The surfactants added to the resin raw material include aliphatic amine compounds such as lauryl diethanolamine, myristyl diethanolamine, palmityl diethanolamine, oleyl diethanolamine, and stearyl diethanolamine, and aliphatic amine ester compounds which are ester compounds of these compounds; aliphatic amide compounds such as lauryl diethanolamide, myristyl diethanolamide, palmityl diethanolamide, oleyl diethanolamide, and stearyl diethanolamide, and aliphatic amide ester compounds which are ester compounds of these compounds; polyhydric alcohols such as glycerin monooleate, glycerin monostearate, and glycerin distearate; sorbitan fatty acid esters such as sorbitan laurate, sorbitan palmitate, sorbitan oleate, and sorbitan stearate; sulfonic acids such as alkyl sulfonates and alkyl benzene sulfonates; sulfate esters such as alkyl sulfates and polyoxyethylene alkyl ether sulfates; and phosphate esters such as alkyl phosphates and polyoxyethylene alkyl ether phosphates, and are appropriately selected and used.

[0035] The heat of fusion of a surfactant is measured by differential scanning calorimetry (DSC) in accordance with JIS K 7122 (2012). The heat of fusion of the entire surfactant is calculated by determining the peak area M enclosed by the DSC curve R obtained by measurement and a line L drawn from the baseline, which is the flat portion of the DSC curve R, to the low-temperature side, as shown in Figure 1. Surfactants with a large heat of fusion above a certain temperature exhibit little change in properties in high-temperature environments, and are therefore thought to suppress deterioration in anti-blocking performance during film storage in high-temperature environments, such as in summer. Therefore, as shown in the examples below, when the ratio of the heat of fusion of a surfactant above 40°C to the total surfactant is 40% or more, the desired blocking performance can be obtained without any special adjustment of the anti-blocking agent. The ratio of the heat of fusion of a surfactant above 40°C to the total surfactant is calculated by determining the peak area M1 in the region above 40°C relative to the total peak area M (Figure 1), as shown in the shaded area in Figure 2. As will be seen from the examples below, if the proportion of heat of fusion at 40°C or higher is small, i.e., if the proportion of heat of fusion at temperatures below 40°C is large, the surfactant that migrates to the film surface will be more likely to melt during film storage in a high-temperature environment, causing the film surface to become sticky, which may result in the desired blocking resistance not being achieved. Therefore, the preferred proportion of heat of fusion at 40°C or higher is 40% or more. Note that the symbol L1 in Figure 2 indicates a portion of the line L (Figure 1).

[0036] The surfactant that satisfies the above heat of fusion requirement is contained in the biaxially oriented polyethylene film in an amount of more than 0.05% by weight and not more than 4% by weight, preferably not less than 0.1% by weight and not more than 3% by weight. If the surfactant content is too low, it becomes difficult to sufficiently compensate for blocking resistance, while if the surfactant content is too high, the dynamic friction coefficient increases, which may deteriorate the slipperiness of the film.

[0037] The inventors also found that adding a polymeric antistatic agent to the resin raw material of the film and selecting a polymeric antistatic agent whose heat of fusion satisfies certain conditions contributes to improving the slipperiness and blocking resistance of the film. That is, the polymeric antistatic agent must have a heat of fusion at 40°C or higher that accounts for 90% or more of the heat of fusion of the entire polymeric antistatic agent, and must be contained in an amount of 0.25% by weight or more and 1.25% by weight or less in the stretched film.

[0038] The polymeric antistatic agent added to the resin raw material is a copolymer of a hydrophilic polymer and a modified polyolefin. Preferred hydrophilic polymers include those commonly referred to as polyethers, such as polyether diols, polyether diamines, polyether ester amides, polyether amide imides, polyether urethanes, polyether esters, polyether amides, and modified versions thereof. Modified polyolefins include polyolefins containing a carbonyl group, a carboxyl group, an amino group, a hydroxyl group, or the like, introduced as a modifying group at at least one end of a suitable polyolefin. Preferred examples include carboxyl group-modified polyolefins.

[0039] The heat of fusion of the polymeric antistatic agent is measured by differential scanning calorimetry (DSC) in accordance with JIS K 7122 (2012). The heat of fusion of the entire polymeric antistatic agent is calculated by determining the peak area M as shown in Figure 1. Even polymeric antistatic agents with a large heat of fusion above a certain temperature are thought to have excellent thermal stability and therefore suppress deterioration of anti-blocking performance during film storage in high-temperature environments. Therefore, as shown in the examples below, even when the ratio of the heat of fusion of the polymeric antistatic agent at 40°C or above to the total polymeric antistatic agent is 90% or more, the desired blocking performance can be obtained without any special adjustment of the anti-blocking agent. The ratio of the heat of fusion of the polymeric antistatic agent at 40°C or above to the total polymeric antistatic agent is calculated by determining the peak area M1 (see Figure 2) in the region above 40°C relative to the total peak area M (see Figure 1), similar to the ratio of the heat of fusion of the surfactant at 40°C or above. If the proportion of the heat of fusion of the polymer-type antistatic agent at 40°C or higher is small, i.e., if the proportion of the heat of fusion at temperatures below 40°C is large, the polymer-type antistatic agent will be more likely to melt on the film surface during storage in a high-temperature environment, causing the film surface to become sticky, which may make it difficult to achieve the desired blocking resistance. Therefore, the proportion of the heat of fusion of the polymer-type antistatic agent at 40°C or higher is preferably 90% or more.

[0040] The polymeric antistatic agent satisfying the above heat of fusion requirement is contained in the biaxially oriented polyethylene film in an amount of 0.25% by weight or more and 1.25% by weight or less, preferably 0.5% by weight or more and 1.0% by weight or less, and more preferably 0.75% by weight or more and 1.0% by weight or less. If the amount of polymeric antistatic agent is too small, it becomes difficult to sufficiently compensate for the blocking resistance, while if the amount is too large, the see-through feeling of the film may be deteriorated and the cost may increase.

[0041] The biaxially oriented polyethylene film can be a single-layer film or a laminate film. In the case of a single-layer biaxially oriented polyethylene film, an antiblocking agent and a surfactant are appropriately added to the polyethylene resin as the main raw material to form the film.

[0042] On the other hand, a biaxially oriented polyethylene film, which is a laminate film, comprises a substrate layer containing a surfactant that satisfies the above-mentioned heat of fusion condition, and surface layers A and B, which are disposed on both sides of the substrate layer and contain an antiblocking agent. In this laminate film, other layers such as an intermediate layer may be laminated between the substrate layer and the surface layer as needed. The biaxially oriented polyethylene film of the present invention is preferably a laminate film of 3 to 5 layers.

[0043] In the case of a laminated film, it is preferable to add the surfactant to a layer other than the surface layer A and the surface layer B. For example, it is possible to add the surfactant only to the substrate layer, or to the substrate layer and the intermediate layer. A surfactant added to a layer other than the surface layer A and the surface layer B can impart the desired blocking resistance and slipperiness to the film surface by passing through the surface layer and migrating to the film surface. To impart the desired blocking resistance and slipperiness to the film surface, the amount of surfactant added is appropriately adjusted. In the laminated film of the present invention, it is preferable that the substrate layer contains a surfactant in an amount of 0.06 wt % or more and 4 wt % or less. In general, surfactants with a small carbon number in the fatty acid, which is the main component, tend to migrate easily to the film surface, while surfactants with a large carbon number in the fatty acid tend to migrate less easily to the film surface.

[0044] On the other hand, surfactants may also be added to the surface layer. When surfactants are added to the surface layer of a laminate film, the surfactants tend to adhere to or accumulate on metal rolls, such as guide rolls, during the film production process. The surfactants accumulated on the metal rolls may be transferred to the subsequent film passing through the metal rolls, potentially leading to quality degradation, such as damage to the appearance. This requires the work of removing the surfactants adhered to or accumulated on the metal rolls, which increases the burden on workers and reduces the efficiency of film production.

[0045] If the surfactant adheres or accumulates on the metal roll as described above, the surfactant added to the film may be reduced during the production process, and the resulting biaxially oriented polyethylene film may not have the desired blocking resistance and slip properties. Because of this potential problem, it is preferable to add the surfactant to a layer other than the surface layer. When adding the surfactant to the surface layer, it is preferable to add a small amount of surfactant to the extent that the above-mentioned problems do not occur and the desired blocking resistance and slip properties are exhibited. It is also desirable to add the surfactant to the substrate layer and / or intermediate layer in addition to the surface layer. The method for adding the surfactant is not particularly limited, and it can be added by any known method, such as mixing a high-concentration masterbatch with the resin raw material of the film or mixing by dry blending.

[0046] Furthermore, when a polymeric antistatic agent is added to a biaxially oriented polyethylene film that is a laminate film, the biaxially oriented polyethylene film comprises a base layer and surface layers A and B that are disposed on both sides of the base layer and contain an antiblocking agent, and the polymeric antistatic agent is contained in at least one of surface layers A and B. Again, the biaxially oriented polyethylene film is preferably a laminate film of 3 to 5 layers.

[0047] Unlike the surfactants mentioned above, polymeric antistatic agents do not migrate to the film surface even when added to the base layer, and are therefore added to at least one of the surface layers A and B. In biaxially oriented polyethylene films, a small amount of polymeric antistatic agent added to the surface layer can impart blocking resistance and slipperiness to the film surface, and increasing the amount of polymeric antistatic agent added improves antistatic performance. Furthermore, adding an excessive amount of polymeric antistatic agent does not sufficiently improve film performance and may result in a decrease in see-through quality. The preferred amount of polymeric antistatic agent added to the surface layer is, for example, approximately 5% by weight to 25% by weight, preferably approximately 10% by weight to 20% by weight, and more preferably approximately 15% by weight to 20% by weight. The method of adding the polymeric antistatic agent is not particularly limited; for example, it can be added by known methods, such as mixing a high-concentration masterbatch with the resin raw material of the film or by dry blending.

[0048] In the biaxially stretched polyethylene film of the present invention, the dynamic friction coefficient of the stretched film is preferably 0.9 or less. The dynamic friction coefficient is used as an index of the slipperiness of a film and can be measured by a method in accordance with JIS K 7125 (1999). If the dynamic friction coefficient is too high, the slipperiness of the film may be insufficient. By ensuring that this dynamic friction coefficient is 0.9 or less, the film can achieve good slipperiness.

[0049] In the biaxially oriented polyethylene film of the present invention, the antistatic properties are such that the surface resistivity of the film is 1×10 14 It is preferable that the surface resistivity is Ω / □ or less. The surface resistivity is measured by a surface resistivity test in accordance with JIS K 6911 (2006). If the surface resistivity of the film is too high, the antistatic performance will be insufficient and static electricity problems will easily occur during the film manufacturing process. If the surface resistivity is 1×10 14 Ω / □ or less, static electricity problems during the manufacturing process can be effectively suppressed. Regarding antistatic performance, the surface resistivity of either surface layer A or surface layer B is 1×10 14It is good if the surface resistivity of both surface layer A and surface layer B is 1×10 14 It is even better if the resistance is Ω / □ or less. In the biaxially oriented polyethylene film of the present invention, the surfactant added to the resin raw material also functions as an antistatic agent. Therefore, in the biaxially oriented polyethylene film to which the surfactant has been added as described above, there is no need to add a separate antistatic agent for the purpose of improving antistatic performance.

[0050] In the biaxially oriented polyethylene film of the present invention, at least one surface is surface-treated to broaden the range of use as a substrate film for laminate films. The surface-treated surface preferably has a wet tension of 36 mN / m or more. Examples of surface treatments include atmospheric pressure plasma treatment, flame treatment, and corona discharge treatment. The wet tension is measured using a wet tension test method in accordance with JIS K 6768 (1999). A wet tension of less than 36 mN / m is undesirable because it can cause poor printing and lamination. When the biaxially oriented polyethylene film is a laminate film, surface treatment of the film surface by corona discharge treatment or the like can promote migration of surfactants added to layers other than surface layer A and surface layer B to the film surface. This allows the surfactant's functions, such as anti-blocking, slip properties, and antistatic performance, to be more efficiently exhibited.

[0051] The biaxially oriented polyethylene film of the present invention can be obtained by known film forming methods such as the T-die method or the inflation method. In particular, it is preferable to stretch and form a sheet formed by the T-die method. Film forming by the T-die method is advantageous in that it can achieve the high thickness precision required for a base film of a laminate film. The biaxially oriented polyethylene film is a biaxially oriented film that has been stretched in two axial directions, the machine direction (MD) and the transverse direction (TD) of the film. For biaxial stretching, either sequential biaxial stretching or simultaneous biaxial stretching can be used successfully.

[0052] As an example, we will explain a method for producing a biaxially oriented film by sequentially stretching it in the machine direction (MD) and the transverse direction (TD). Polyethylene resin is melted and kneaded in an extruder, extruded into a sheet from a T-die, and cooled on a chill roll at a temperature of 10 to 70°C. The sheet is stretched 3 to 8 times in the machine direction (MD) by inter-roll stretching using stretching rolls at 70 to 130°C. Next, it is stretched 5 to 15 times in the transverse direction (TD) at a temperature of 100 to 160°C, at least one surface is subjected to a corona discharge treatment, and the biaxially oriented polyethylene film is wound up on a winder.

[0053] The lower limit of the longitudinal (MD) stretching ratio is approximately 3 times. If it is less than 3 times, unevenness in the film thickness may occur. The upper limit of the longitudinal (MD) stretching ratio is 8 times, preferably 7 times. If it exceeds 8 times, transverse (TD) stretching may become difficult. The lower limit of the longitudinal (MD) stretching temperature is 70°C, preferably 80°C. If it is less than 70°C, uniform stretching may not occur, and unevenness in the film thickness may occur. The upper limit of the longitudinal (MD) stretching temperature is 130°C. If it exceeds 130°C, the adhesion between the sheet and the roll may increase, making stretching impossible. The lower limit of the transverse (TD) stretching ratio is 5 times, preferably 6 times. If it is less than 5 times, unevenness in the film thickness may occur. The upper limit of the transverse (TD) stretching ratio is 15 times, preferably 14 times, and more preferably 13 times. If it exceeds 15 times, breakage may occur during stretching. The lower limit of the transverse (TD) stretching temperature is 100°C. If the temperature is less than 100°C, there is a risk of uneven film thickness. The upper limit of the transverse (TD) stretching temperature is 160°C. If the temperature exceeds 160°C, there is a risk of the film breaking during stretching.

[0054] The thickness of the biaxially oriented polyethylene film of the present invention is not particularly limited and may be appropriately determined depending on the demand, application, etc., and is, for example, 5 to 100 μm, preferably 10 to 70 μm. Of these, the thickness of surface layer A and surface layer B of the biaxially oriented polyethylene film is preferably 0.3 to 5 μm, preferably 0.4 to 4 μm, and more preferably 0.5 to 2 μm. If the surface layers are too thin, the antiblocking agent may fall off when the film passes through the rolls during processing, while if they are too thick, the amount of antiblocking agent added may increase, resulting in a poor transparency of the film.

[0055] The present invention can provide a laminate film in which the above-mentioned biaxially oriented polyethylene film is used as a base film and a printing process, a gas barrier layer, a sealant film, etc. are appropriately laminated. The printing process is carried out on the surface of the biaxially oriented polyethylene film, and known methods such as screen printing, flexographic printing, offset printing, and gravure printing are used. Furthermore, when printing is carried out on the biaxially oriented polyethylene film of the present invention, the film surface is subjected to the above-mentioned surface treatment such as corona discharge treatment prior to printing, thereby improving ink compatibility and adhesion.

[0056] The gas barrier layer is disposed on the surface layer directly or via an anchor coat layer for the purpose of imparting barrier properties to water vapor, oxygen, etc. When a gas barrier layer is disposed on the biaxially oriented polyethylene film of the present invention, the film surface is previously subjected to a surface treatment such as corona discharge treatment, thereby improving the wettability and adhesion of the anchor coat layer and gas barrier layer.

[0057] The anchor coat layer is not particularly limited, and examples thereof include polyurethane-based resins and polyester-based resins. The gas barrier layer is also not particularly limited, and examples thereof include metal thin film layers and inorganic oxide layers. The metal thin film layer is a thin film layer made of known metals such as aluminum, gold, silver, copper, and chromium, and may be a thin film layer of oxides, sulfides, or nitrides of these metals. The metal thin film layer may be a single layer or a plurality of layers made of two or more different or identical types. The inorganic oxide layer is made of known inorganic oxides such as aluminum oxide, silicon oxide, magnesium fluoride, and magnesium oxide, and may be a thin film layer using one or more inorganic oxides.

[0058] A sealant film is a heat-sealable film made of polyethylene resin. The polyethylene resin used in the sealant film is selected from, for example, linear low-density polyethylene resin (LLDPE), high-density polyethylene (HDPE), low-density polyethylene (LDPE), and the like, either singly or in combination. By using a sealant layer made of the same polyethylene resin as the biaxially oriented polyethylene film used as the base film, a monomaterial laminate film can be obtained, facilitating recycling and improving blocking resistance. Furthermore, the laminate film can also be used to make packaging. This makes it a promising alternative to existing laminate films and packaging, as it allows for easy recycling. [Example]

[0059] [Preparation of biaxially oriented polyethylene film] The materials described below were blended, melted, and kneaded. The resulting extrusions were then formed into three layers (surface layer A, substrate layer, and surface layer B) using a T-die method. The extrusions were stretched 5 times in the machine direction (MD) and then 8 times in the transverse direction (TD) to form films. Subsequently, in Prototype Examples 6, 9-13, 20 and 21, and 23 and 24, one surface layer (surface layer A) was treated with corona discharge, while in the other examples, both surface layers (surface layer A and surface layer B) were treated with corona discharge to obtain biaxially oriented polyethylene films. In each prototype, the resin content of each substrate layer or surface layer was 100% by weight. The materials used in each layer (surface layer A, substrate layer, and surface layer B) of Prototype Examples 1-24 are shown in Tables 1-3. In each prototype film, the thickness was 20 μm, the thickness of the surface layers A and B was 1 μm, and the thickness of the base layer was 18 μm.

[0060] [Materials used] The following resins, antiblocking agents, surfactants, and polymeric antistatic agents were used as materials for each layer. The melt flow rate (MFR) of each resin material was measured at a test temperature of 190°C in accordance with JIS K 7210 (2014).

[0061] [Resin material] PE1: Linear low-density polyethylene (Dow Chemical; TF80), density 0.926 g / cm 3 MFR (190℃ / 2.16kg): 1.7g / 10min PE2: High-density polyethylene (Japan Polyethylene Co., Ltd.; HY340), density 0.952 g / cm 3 MFR (190℃ / 2.16kg): 1.4g / 10min

[0062] [Anti-blocking agent (AB agent)] AB1: Fuji Silysia Chemical Ltd.; SYLYSIA430, average particle size 4.1 μm AB2: Fuji Silysia Chemical Ltd.; SYLYSIA530, average particle size 2.7 μm AB3: Fuji Silysia Chemical Ltd.; SYLYSIA450, average particle size 8.0 μm AB4: Fuji Silysia Chemical Ltd.; SYLYSIA470, average particle size 14.1 μm

[0063] [Surfactants] AS1: Glycerin monostearate, fatty acid with 18 carbon atoms AS2: Stearyldiethanolamine, fatty acid with 18 carbon atoms AS3: Myristyldiethanolamine, fatty acid with 14 carbon atoms AS4: Oleyldiethanolamine, fatty acid with 18 carbon atoms AS5: Oleyldiethanolamine monolaurate, fatty acid with 18 carbon atoms AS6: Oleyldiethanolamine, fatty acid with 18 carbon atoms AS7: Phosphate ester

[0064] [Polymer-type antistatic agent] AA1: Polymer antistatic agent (Sanyo Chemical Industries, Ltd.; Pelestat LM230), melting point 115°C, MFR: 15.0g / 10min (190°C, load 21.18N)

[0065] [Prototype 1] Prototype example 1 is a biaxially oriented polyethylene film in which surface layer A is made of 99.7 wt% PE1 and 0.3 wt% AB1, the base layer is made of 99.0 wt% PE1 and 1 wt% AS1, and surface layer B is made of 99.7 wt% PE1 and 0.3 wt% AB1.

[0066] [Prototype 2] Prototype example 2 is a biaxially oriented polyethylene film in which surface layer A is made of 99.7 wt% PE1 and 0.3 wt% AB1, the base layer is made of 99.0 wt% PE1 and 1 wt% AS2, and surface layer B is made of 99.7 wt% PE1 and 0.3 wt% AB1.

[0067] [Prototype 3] Prototype example 3 is a biaxially oriented polyethylene film in which surface layer A contains 99.7 wt% PE1 and 0.3 wt% AB1, base layer contains 99.0 wt% PE1, 0.30 wt% AS1, 0.50 wt% AS5, and 0.20 wt% AS6, and surface layer B contains 99.7 wt% PE1 and 0.3 wt% AB1.

[0068] [Prototype 4] Prototype example 4 is a biaxially oriented polyethylene film in which surface layer A contains 99.7 wt% PE1 and 0.3 wt% AB1, the base layer contains 99.0 wt% PE1, 0.667 wt% AS1, and 0.333 wt% AS2, and surface layer B contains 99.7 wt% PE1 and 0.3 wt% AB1.

[0069] [Prototype 5] Prototype example 5 is a biaxially oriented polyethylene film in which surface layer A is made of 99.7 wt% PE1 and 0.3 wt% AB1, the base layer is made of 99.9 wt% PE1 and 0.1 wt% AS2, and surface layer B is made of 99.7 wt% PE1 and 0.3 wt% AB1.

[0070] [Prototype 6] Prototype Example 6 is a biaxially oriented polyethylene film in which surface layer A contains 99.7% by weight of PE1 and 0.3% by weight of AB1, the base layer contains 99.7% by weight of PE1, 0.2% by weight of AS1, and 0.1% by weight of AS2, and surface layer B contains 99.7% by weight of PE1 and 0.3% by weight of AB1.

[0071] [Prototype 7] Prototype example 7 is a biaxially oriented polyethylene film in which surface layer A contains 99.7 wt% PE1 and 0.3 wt% AB1, the base layer contains 84.25 wt% PE1, 15 wt% PE2, and 0.75 wt% AS1, and surface layer B contains 99.7 wt% PE1 and 0.3 wt% AB1.

[0072] [Prototype 8] Prototype Example 8 is a biaxially oriented polyethylene film in which surface layer A contains 99.7 wt% PE1 and 0.3 wt% AB1, the base layer contains 96.0 wt% PE1, 2.666 wt% AS1, and 1.334 wt% AS2, and surface layer B contains 99.7 wt% PE1 and 0.3 wt% AB1.

[0073] [Prototype 9] Prototype Example 9 is a biaxially oriented polyethylene film in which surface layer A contains 99.7% by weight of PE1 and 0.3% by weight of AB2, the base layer contains 99.7% by weight of PE1, 0.2% by weight of AS1, and 0.1% by weight of AS2, and surface layer B contains 99.7% by weight of PE1 and 0.3% by weight of AB2.

[0074] [Prototype 10] Prototype example 10 is a biaxially oriented polyethylene film in which surface layer A contains 99.7% by weight of PE1 and 0.3% by weight of AB3, the base layer contains 99.7% by weight of PE1, 0.2% by weight of AS1, and 0.1% by weight of AS2, and surface layer B contains 99.7% by weight of PE1 and 0.3% by weight of AB3.

[0075] [Prototype 11] Prototype Example 11 is a biaxially oriented polyethylene film in which surface layer A is made of 99.7 wt% PE1 and 0.3 wt% AB4, the base layer is made of 99.7 wt% PE1, 0.2 wt% AS1, and 0.1 wt% AS2, and surface layer B is made of 99.7 wt% PE1 and 0.3 wt% AB4.

[0076] [Prototype 12] Prototype Example 12 is a biaxially oriented polyethylene film in which surface layer A contains 99.8% by weight of PE1 and 0.2% by weight of AB1, the base layer contains 99.7% by weight of PE1, 0.2% by weight of AS1, and 0.1% by weight of AS2, and surface layer B contains 99.7% by weight of PE1 and 0.3% by weight of AB1.

[0077] [Prototype 13] Prototype Example 13 is a biaxially oriented polyethylene film in which surface layer A contains 99.8 wt% PE1 and 0.2 wt% AB1, the base layer contains 99.7 wt% PE1, 0.2 wt% AS1, and 0.1 wt% AS2, and surface layer B contains 99.6 wt% PE1 and 0.4 wt% AB1.

[0078] [Prototype 14] Prototype 14 is a biaxially oriented polyethylene film in which surface layer A contains 99.7% by weight of PE1 and 0.3% by weight of AB1, the base layer contains 100% by weight of PE1, and surface layer B contains 99.7% by weight of PE1 and 0.3% by weight of AB1. Prototype 14 is a biaxially oriented polyethylene film in which no surfactant is added to the base layer or the entire film.

[0079] [Prototype 15] Prototype Example 15 is a biaxially oriented polyethylene film in which surface layer A is made of 99.7 wt% PE1 and 0.3 wt% AB1, the base layer is made of 99.0 wt% PE1 and 1 wt% AS4, and surface layer B is made of 99.7 wt% PE1 and 0.3 wt% AB1.

[0080] [Prototype 16] Prototype Example 16 is a biaxially oriented polyethylene film in which surface layer A is made of 99.7 wt% PE1 and 0.3 wt% AB1, the base layer is made of 99.0 wt% PE1 and 1 wt% AS5, and surface layer B is made of 99.7 wt% PE1 and 0.3 wt% AB1.

[0081] [Prototype 17] Prototype Example 17 is a biaxially oriented polyethylene film in which surface layer A contains 99.7 wt% PE1 and 0.3 wt% AB1, the base layer contains 95.0 wt% PE1, 3.333 wt% AS1, and 1.667 wt% AS2, and surface layer B contains 99.7 wt% PE1 and 0.3 wt% AB1.

[0082] [Prototype 18] Prototype Example 18 is a biaxially oriented polyethylene film in which surface layer A is made of 99.7 wt% PE1 and 0.3 wt% AB1, the base layer is made of 99.9 wt% PE1 and 0.1 wt% AS7, and surface layer B is made of 99.7 wt% PE1 and 0.3 wt% AB1.

[0083] [Prototype 19] Prototype Example 19 is a biaxially oriented polyethylene film in which surface layer A contains 99.7 wt% PE1 and 0.3 wt% AB1, base layer contains 99.95 wt% PE1, 0.033 wt% AS1, and 0.017 wt% AS2, and surface layer B contains 99.7 wt% PE1 and 0.3 wt% AB1.

[0084] [Prototype 20] Prototype Example 20 is a biaxially oriented polyethylene film in which surface layer A contains 99.7% by weight of PE1 and 0.3% by weight of AB1, the base layer contains 99.95% by weight of PE1 and 0.05% by weight of AS2, and surface layer B contains 99.7% by weight of PE1 and 0.3% by weight of AB1.

[0085] [Prototype 21] Prototype Example 21 is a biaxially oriented polyethylene film in which surface layer A contains 99.7% by weight of PE1 and 0.3% by weight of AB1, the base layer contains 99.90% by weight of PE1, 0.05% by weight of AS1, and 0.05% by weight of AS3, and surface layer B contains 99.7% by weight of PE1 and 0.3% by weight of AB1.

[0086] [Prototype 22] Prototype Example 22 is a biaxially oriented polyethylene film in which surface layer A contains 99.7% by weight of PE1 and 0.3% by weight of AB1, the base layer contains 99.93% by weight of PE1 and 0.07% by weight of AS2, and surface layer B contains 99.7% by weight of PE1 and 0.3% by weight of AB1.

[0087] [Prototype 23] Prototype 23 is a biaxially oriented polyethylene film in which surface layer A contains 89.7% by weight of PE1, 0.3% by weight of AB1, and 10% by weight of AA1, the base layer contains 100% by weight of PE1, and surface layer B contains 99.7% by weight of PE1 and 0.3% by weight of AB1. Prototype 23 is a biaxially oriented polyethylene film in which surface layer A contains a polymeric antistatic agent.

[0088] [Prototype 24] Prototype 24 is a biaxially oriented polyethylene film in which surface layer A contains 79.7% by weight of PE1, 0.3% by weight of AB1, and 20% by weight of AA1, the base layer contains 100% by weight of PE1, and surface layer B contains 99.7% by weight of PE1 and 0.3% by weight of AB1. Prototype 24 is also a biaxially oriented polyethylene film in which surface layer A contains a polymeric antistatic agent.

[0089] [Table 1]

[0090] [Table 2]

[0091] [Table 3]

[0092] The surfactant concentration, heat of fusion of the surfactant, polymeric antistatic agent concentration, heat of fusion of the polymeric antistatic agent, kinetic friction coefficient, blocking strength, and surface resistivity were measured for Prototype Examples 1 to 24. The area ratio of the heat of fusion of the surfactant at 40°C or higher shown in Tables 4 to 6 means the ratio of the peak area M1 in Figure 2 to the total peak area M in Figure 1, and the area ratio of the heat of fusion of the polymeric antistatic agent at 40°C or higher means the ratio of the peak area M1 similar to Figure 2 to the total peak area M similar to Figure 1.

[0093] [Calculation of surfactant concentration] For the evaluation of the biaxially oriented polyethylene films of Prototype Examples 1 to 22, the surfactant concentrations in the substrate layer and the entire biaxially oriented polyethylene film were calculated. The surfactant concentration in the substrate layer was calculated by dividing the surfactant used in the substrate layer by the resin and surfactant used in the substrate layer. The surfactant concentration in the entire biaxially oriented polyethylene film was calculated by multiplying the surfactant used in the substrate layer by the ratio of the thickness of the substrate layer to the thickness of the entire film.

[0094] [Measurement of calorimetry of fusion of surfactants] The heats of fusion of the surfactants in Examples 1 to 22 were calculated in accordance with JIS K 7122 (2012) using a differential scanning calorimeter "DSC214Polyma (NETZSCH-Geratebau GmbH)" by measuring the sample in a series of steps: cooling the sample to -70°C at a rate of 10°C / min, holding the sample at -70°C for 10 minutes, and then heating the sample to 100°C at a rate of 10°C / min. The heat of fusion was calculated by determining the total peak area enclosed by the melting curve, including the endothermic peak, and the baseline. When measuring the heat of fusion of two or more surfactants, the sample for heat of fusion measurement was prepared as follows: The surfactants were mixed in the ratio of each sample to 2 g, placed in a sample vial, and capped. The sample vial was heated in hot water at 90°C until the surfactants dissolved, and then cooled and solidified in water. The cooled and solidified surfactant was used as the sample for heat of fusion measurement.

[0095] [Calculation of polymer antistatic agent concentration] For the evaluation of the biaxially oriented polyethylene films of Samples 23 and 24, the concentrations of the polymeric antistatic agent contained in the surface layer and the entire biaxially oriented polyethylene film were calculated. The concentration of the polymeric antistatic agent contained in the surface layer was calculated by dividing the polymeric antistatic agent used in the surface layer by the resin, antiblocking agent (AB agent), and polymeric antistatic agent used in the surface layer. The concentration of the polymeric antistatic agent contained in the entire biaxially oriented polyethylene film was calculated by multiplying the polymeric antistatic agent used in the surface layer by the ratio of the thickness of the surface layer to the thickness of the entire film.

[0096] [Measurement of calorie of fusion of polymeric antistatic agents] The heat of fusion of the polymer-type antistatic agents of Prototype Examples 23 and 24 was calculated in the same manner as in the measurement of the heat of fusion of the surfactant described above, except that the temperature was increased at a rate of 10°C / min up to 150°C.

[0097] [Measurement of dynamic friction coefficient] The dynamic friction coefficients of prototypes 1 to 24 were measured at a test speed of 100 mm / min using a "FRICTION TESTER TR-2 (manufactured by Toyo Seiki Seisakusho Co., Ltd.)" in accordance with the test method of JIS K 7125 (1999). A dynamic friction coefficient of 0.9 or less was considered good.

[0098] [Measurement of blocking strength] Blocking strength of prototypes 1 to 24 (N / 4cm 2 ) was measured by overlapping the surface layers of each biaxially oriented polyethylene film and measuring 4cm test pieces, assuming that the film will be stored in a high temperature environment such as in summer. 2 A load of 1 kg was applied to the film and the film was left at 40°C for 24 hours. Thereafter, the shear peel strength was measured using a tensile tester "Autograph AGS-X 50N (Shimadzu Corporation)" and used as the blocking strength. This blocking strength refers to the shear force of the film after the load is applied when the film is pulled at a pulling speed of 50 mm / min using the tensile tester. The blocking strength was 6.9 (N / 4 cm 2 ) The following cases were considered good.

[0099] [Measurement of surface resistivity] The surface resistivity (Ω / □) of Prototype Examples 1 to 24 was measured in accordance with JIS K 6911 (2006). It can be said that the higher the surface resistivity, the poorer the antistatic performance of the film. The surface resistivity is 1×10 14 For example, the surface resistivity of prototype 3 in Table 4 is 1E+11, which is the surface resistivity of 1×10 11 Ω / □, and the surface resistivity of prototype 1, 4E+12, is 4×10 12 Ω / □. Note that the surface resistivity is 1×10 14 Films exceeding Ω / □ are marked as "OR" in Tables 4 to 6 as being over-range.

[0100] [Table 4]

[0101] [Table 5]

[0102] [Table 6]

[0103] [Results and Discussion] The film of prototype 14 is a film to which an antiblocking agent has only been added without adjusting the particle size, and does not have the desired anti-blocking properties or antistatic properties. The films of prototypes 1 to 13 and 15 to 22 are the film of prototype 14 to which a surfactant has been added to the base layer, and the film performance has been examined. The films of prototypes 23 and 24 are the film of prototype 14 to which a polymeric antistatic agent has been added to surface layer A, and the film performance has been examined.

[0104] For the films of Prototype Examples 1 to 8 and 22, the surfactant content of the entire film was changed by changing the surfactant content of each substrate layer. For the films of Prototype Examples 1 to 8 and 22, the blocking strength of the film was 6.9 (N / 4 cm 2 ) or less, the dynamic friction coefficient was 0.9 or less, the area ratio of the heat of fusion of the surfactant at 40°C or more was 50% to 100%, and the surfactant concentration in the entire film was 0.06% by weight to 3.60% by weight, and all of the prototypes 1 to 8 and 22 had good blocking resistance and slip properties.

[0105] Furthermore, for the films of Samples 9 to 11, antiblocking agents of different types (average particle size) were added to the surface layers A and B, respectively, and for the films of Samples 12 and 13, the amount of antiblocking agent added to the surface layers A or B was changed to a different amount than that of Samples 9 to 11. For the films of Samples 9 to 13, the blocking strength of the film was 6.9 (N / 4cm 2 ) or less, the coefficient of dynamic friction was 0.9 or less, and the area ratio of the heat of fusion of the surfactant at 40°C or more was 90%, and all of Prototypes 9 to 13 had good blocking resistance and slip properties.

[0106] In the film of Prototype 15, the surfactant in the base layer was changed from AS1 to AS4 compared to Prototype 1. In Prototype 15, the surface area ratio of the heat of fusion of the surfactant at 40°C or higher was 0%, and the blocking strength of the film was 6.9 (N / 4cm 2 ) and the blocking resistance deteriorated.

[0107] In the film of Prototype 16, the surfactant in the base layer was changed from AS1 to AS5, as compared with Prototype 1. In Prototype 16, the area ratio of the heat of fusion of the surfactant at 40°C or higher was 0%, as in Prototype 15, and the blocking strength of the film was 6.9 (N / 4cm 2 ) and the blocking resistance deteriorated.

[0108] The film of Prototype 17 differs from Prototype 8 in that the types of surfactants (AS1 and AS2) in the base layer are the same but the content is different, resulting in a different surfactant content throughout the film. In Prototype 17, the surfactant concentration in the base layer was 5.00 wt % and the surfactant concentration in the entire film was 4.50 wt %, resulting in a dynamic friction coefficient exceeding 0.9.

[0109] In the film of Prototype 18, compared to Prototype 5, the type of surfactant in the base layer was changed from AS2 in Prototype 5 to AS7. In Prototype 18, the surface area ratio of the heat of fusion of the surfactant at 40°C or higher was set to 2%, and the blocking strength of the film was 6.9 (N / 4cm 2 ) and the blocking resistance deteriorated.

[0110] In comparison with Prototype 8, Prototype 19 has the same surfactant type (AS1 and AS2) in the base layer but a different content, and the surfactant content of the entire film is different. In Prototype 19, the surfactant concentration in the base layer is 0.05 wt % and the surfactant concentration in the entire film is 0.05 wt %, and the blocking strength of the film is 6.9 (N / 4 cm 2 ) and the blocking resistance deteriorated.

[0111] In comparison with Prototype 5, Prototype 20 has the same type of surfactant (AS2) in the base layer but a different content, and the surfactant content of the entire film is different. In Prototype 20, the surfactant concentration in the base layer is 0.05 wt % and the surfactant concentration in the entire film is 0.05 wt %, and the blocking strength of the surface layer A is 6.9 (N / 4 cm 2 ) and the blocking resistance deteriorated.

[0112] In the film of Prototype 21, compared to Prototype 5, the type of surfactant in the base layer was changed from AS2 in Prototype 5 to AS1 and AS3. In Prototype 21, the surface area ratio of the heat of fusion of the surfactant at 40°C or higher was set to 38%, and the blocking strength of the surface layer A was 6.9 (N / 4cm 2 ) and the blocking resistance deteriorated.

[0113] As described above, the effects of adding a surfactant to the base layer on film performance were examined. For Prototype 3, the area ratio of the surfactant's heat of fusion above 40°C was 50%, and the surfactant concentration throughout the film was 0.90 wt%. This resulted in good film anti-blocking and slipperiness. In contrast, for Prototype 21, the area ratio of the surfactant's heat of fusion above 40°C was 38%, resulting in poor film anti-blocking. Since the surfactant migrated to the film surface is likely to melt under high-temperature conditions (40°C, 24 hours), resulting in a decrease in anti-blocking properties, Prototype 21 likely did not achieve the desired anti-blocking properties due to the low proportion of the surfactant's heat of fusion above 40°C. Based on these findings, it is considered preferable for the surfactant's heat of fusion above 40°C to be 40% or greater relative to the total heat of fusion of the surfactant.

[0114] Furthermore, when the film performance was examined by adding a surfactant to the base layer, the blocking resistance and slipperiness of the film were good for Prototype 5, when the surfactant concentration in the entire film was 0.09 wt%. Similarly, the blocking resistance and slipperiness of the film were good for Prototype 8, when the surfactant concentration in the entire film was 3.60 wt%. In contrast, the slipperiness of the film was poor for Prototype 17, when the surfactant concentration in the entire film was 4.50 wt%. Similarly, it was confirmed that the blocking resistance of Prototypes 19 and 20 was poor when the surfactant concentration in the entire film was 0.05 wt%. Based on these findings, it is considered preferable for the surfactant content of the entire film to be more than 0.05 wt% and not more than 4 wt%.

[0115] Regarding the antistatic performance of the films, in Prototypes 1 to 13, 15 to 21, and 22, the surface resistivity of the corona discharge-treated surface layer was generally good, indicating that excellent antistatic performance was imparted. Therefore, when imparting antistatic performance to a film, it is preferable to subject the surface layer to a surface treatment such as corona discharge treatment. In Prototype 21, excellent antistatic performance was obtained even though the surface layer B was not subjected to corona discharge treatment. This is thought to be because the fatty acid, which is the main component of the surfactant in Prototype 21, has a carbon number of 14, which is smaller than the carbon number of the fatty acid, which is the main component of the surfactant in Prototypes 1 to 20 and 22, and therefore the surfactant migrates more easily from the base layer to the surface layer.

[0116] Furthermore, when Prototype 21 is compared with Prototype 5, in which the surfactant concentration is the same in both the base layer and the entire film, it is clear that the area ratio of the heat of fusion at 40°C or higher is smaller than that of Prototype 5. This suggests that when the number of carbon atoms in the fatty acid, which is the main component of the surfactant, is small, as in Prototype 21, the area ratio of the heat of fusion at 40°C or higher is smaller, and that there is a proportional relationship between the number of carbon atoms in the surfactant and the area ratio of the heat of fusion at 40°C or higher.

[0117] For the films of Samples 23 and 24, which contain a polymeric antistatic agent, the content of the polymeric antistatic agent AA1 in each surface layer A was changed, thereby changing the content of the polymeric antistatic agent in the entire film. In the films of Samples 23 and 24, the blocking strength of the film was 6.9 (N / 4cm 2 ) or less, the dynamic friction coefficient was 0.9 or less, the area ratio of the heat of fusion of the polymer-type antistatic agent at 40°C or higher was 100%, and the concentration of the polymer-type antistatic agent in the entire film was 0.50% by weight to 1.00% by weight, and both prototypes 23 and 24 had good anti-blocking properties and slip properties. From this, it is thought that it is preferable to add about 0.25% by weight to 1.25% by weight of a polymer-type antistatic agent with a high area ratio of the heat of fusion of 40°C or higher (90% or more) to surface layer A.

[0118] In addition, it is believed that the desired anti-blocking properties and slip properties can be imparted to biaxially oriented polyethylene films by adding a small amount (approximately 5% to 10% by weight) of a polymeric antistatic agent to the surface layer. Furthermore, it is believed that the desired anti-static properties can be achieved by increasing the amount of polymeric antistatic agent added (approximately 15% by weight or more).

[0119] From the above, it was shown that in the biaxially oriented polyethylene film containing the antiblocking agent of the present invention, when the surfactant has a heat of fusion at 40°C or above of 40% or more of the total heat of fusion of the surfactant, and is contained in the entire biaxially oriented polyethylene film in an amount greater than 0.05% by weight and less than 4% by weight, the antiblocking agent can be used appropriately without any special adjustments, and the surfactant added to the entire biaxially oriented polyethylene film can provide good anti-blocking and slip properties to the film surface. As seen in the above-mentioned Prototype 17, even if the surfactant has a heat of fusion at 40°C or above of 40% or more, if the surfactant contained in the entire biaxially oriented polyethylene film exceeds 4% by weight, slip properties are poor. Furthermore, as seen in the above-mentioned Prototype 18, even if the surfactant has a heat of fusion at 40°C or above of 40% or less of the total heat of fusion of the surfactant, if the surfactant has a heat of fusion at 40°C or above of 40% or less, anti-blocking properties are poor. These findings indicate that in order to improve the blocking resistance and slipperiness of the film surface, it is significant to use both the ratio of the heat of fusion of the surfactant at 40°C or above to the heat of fusion of the entire surfactant added to the biaxially oriented polyethylene film and the surfactant content (surfactant concentration) of the entire biaxially oriented polyethylene film as indicators.

[0120] Furthermore, it was shown that in the biaxially oriented polyethylene film of the present invention, when the substrate layer contains 0.06 wt% or more and 4 wt% or less of a surfactant, the blocking resistance and slipperiness of the film surface are improved. Looking at the above-mentioned Prototype 17, even if the proportion of the heat of fusion of the surfactant at 40°C or more is 40% or more, slipperiness is poor when the surfactant content in the substrate layer exceeds 4 wt%. Therefore, in order to improve the blocking resistance and slipperiness of the film surface, it is also significant to use the surfactant content (surfactant concentration) in the substrate layer as an indicator.

[0121] Furthermore, in a biaxially oriented polyethylene film containing the antiblocking agent of the present invention, when the polymeric antistatic agent has a high ratio (90% or more) of the heat of fusion at 40°C or higher relative to the heat of fusion of the entire polymeric antistatic agent and is contained in an amount of approximately 0.25% by weight to 1.25% by weight throughout the biaxially oriented polyethylene film, it is believed that the polymeric antistatic agent added throughout the biaxially oriented polyethylene film, while being used appropriately without any particular adjustment of the antiblocking agent, will improve the blocking resistance and slip properties of the film surface.

[0122] Furthermore, in the biaxially oriented polyethylene film of the present invention, it is believed that the desired blocking resistance and slippage can be imparted by adding a small amount (about 5% to 10% by weight) of a polymeric antistatic agent to at least one surface layer. Since it is unlikely that adding a large amount of a polymeric antistatic agent to the surface layer will significantly improve blocking resistance and slippage, it is believed that in order to improve blocking resistance and slippage, it is preferable to add about 5% to 25% by weight of a polymeric antistatic agent to the surface layer. [Industrial Applicability]

[0123] As described above, the biaxially oriented polyethylene film of the present invention can be made into a film with excellent processability and excellent surface anti-blocking properties due to the addition of a surfactant or polymeric antistatic agent to the entire biaxially oriented polyethylene film while using an anti-blocking agent appropriately without any special adjustment. In addition, by laminating a sealant film primarily made of polyethylene resin onto the biaxially oriented polyethylene film of the present invention, a mono-material laminate film can be obtained, facilitating recycling and improving anti-blocking properties. Furthermore, the laminate film can also be used in packaging. Therefore, it is promising as an easily recyclable packaging material.

Claims

1. A stretched film made of a polyethylene resin as a main component, containing an antiblocking agent, and stretched in biaxial directions, i.e., the machine direction (MD) and the transverse direction (TD), the stretched film comprises a base layer and surface layers disposed on both sides of the base layer and containing the antiblocking agent, and a surfactant is added to layers other than the surface layers; The surfactant has a ratio of heat of fusion at 40°C or higher to the total heat of fusion measured by differential scanning calorimetry in accordance with JIS K 7122 (2012) of 40% or more, The surfactant is contained in the stretched film in an amount of more than 0.05 wt % and not more than 4 wt %. A biaxially oriented polyethylene film.

2. 2. The biaxially oriented polyethylene film according to claim 1, wherein the substrate layer contains the surfactant in an amount of 0.06% by weight or more and 4% by weight or less.

3. 3. The biaxially oriented polyethylene film according to claim 1, wherein the stretched film has a dynamic friction coefficient of 0.9 or less as measured in accordance with JIS K 7125 (1999).

4. 3. A laminate film comprising the biaxially oriented polyethylene film according to claim 1 or 2, and a sealant film mainly made of polyethylene resin laminated thereon.

5. A laminate film, comprising the biaxially oriented polyethylene film according to claim 3 and a sealant film mainly made of polyethylene resin laminated thereon.

6. A package comprising the laminate film according to claim 4.

7. A package comprising the laminate film according to claim 5.

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