Biaxially oriented polyethylene film and laminate film

Abstract

To provide an oriented polyethylene film with excellent blocking resistance among biaxially oriented films accommodating monomaterialization of a laminate.SOLUTION: A biaxially oriented film is formed by stretching a laminate film, which consists of a plurality of layers including at least a base layer and a surface layer A that is arranged on one side thereof, in two axial directions, namely, longitudinal (MD) and transverse (TD) directions. The base layer and the surface layer A are made of polyethylene resin. The skewness (Ssk) in the three-dimensional surface roughness of the surface layer A is greater than 1.0.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a laminate used for general packaging applications, and in particular to a biaxially oriented polyethylene film and a laminate film mainly made of polyethylene. [Background technology]

[0002] Generally, packaging materials made of synthetic resin films are constructed as laminates in which a printed substrate film and a sealant film are laminated together (laminated) with an adhesive or the like. The substrate film of the laminate is required to have properties such as heat resistance, rigidity, and pinhole resistance, and is typically a biaxially oriented film made of polyester, polyamide, or polypropylene. The sealant film of the laminate is typically a non-oriented film made of polypropylene or polyethylene, with polyethylene-based non-oriented films being particularly preferred due to their excellent heat-sealing properties.

[0003] As described above, synthetic resin packaging materials tend to be composites formed by laminating multiple types of resins. However, despite the growing interest in environmental issues in recent years and the desire to recycle waste plastics, it has been difficult to separate and recycle films in which multiple types of resins are laminated. Therefore, in this type of synthetic resin packaging material, it has become necessary for the base film and sealant film to be made of a single material (monomaterial).

[0004] Among packaging materials in which the base film and sealant film are made from a single material, for example, a polyethylene-based laminate in which a polyethylene material that is preferably used as a sealant film is used as the base film is known (see Patent Document 1). This polyethylene-based laminate includes a stretched polyethylene film as the base film and a heat-sealable polyethylene film as the sealant film, and is configured so that the adhesive layer contains a solventless adhesive from the viewpoint of reducing the environmental load.

[0005] Also, a polyethylene film with excellent abrasion resistance has been proposed (see, for example, Patent Document 2). This film has a surface roughness (RaA) of 4.0 to 10.0, and is thought to have poor surface roughness and poor anti-blocking performance. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-189333 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-93885 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been proposed in view of the above circumstances, and provides a biaxially oriented polyethylene film and a laminate film that are particularly excellent in blocking resistance, among oriented films that are compatible with the mono-materialization of laminates. [Means for solving the problem]

[0008] That is, the first invention relates to a biaxially oriented film formed by stretching a laminated film consisting of multiple layers, at least a base layer and a surface layer A arranged on one side of the base layer, in two axial directions, that is, the machine direction (MD) and the transverse direction (TD), wherein the base layer and the surface layer A are made of a polyethylene resin, and the skewness (Ssk) in the three-dimensional surface roughness of the surface layer A is greater than 1.0.

[0009] A second invention relates to the biaxially oriented polyethylene film of the first invention, wherein the skewness (Ssk) in the three-dimensional surface roughness of the surface layer A is greater than 4.0.

[0010] A third invention relates to the biaxially oriented polyethylene film of the first invention, wherein the arithmetic mean roughness (SRa) of the three-dimensional surface roughness of the surface layer A is greater than 0.01 μm.

[0011] A fourth invention relates to the biaxially oriented polyethylene film of the third invention, wherein the surface layer A has an arithmetic mean roughness (SRa) of more than 0.04 μm in three-dimensional surface roughness.

[0012] A fifth invention relates to the biaxially oriented polyethylene film according to the first or third invention, wherein the surface layer A has a ten-point average roughness (SRz) of more than 1.00 μm in three-dimensional surface roughness.

[0013] A sixth aspect of the present invention relates to the biaxially oriented polyethylene film of the fifth aspect, wherein the surface layer A has a ten-point average roughness (SRz) of more than 1.30 μm in three-dimensional surface roughness.

[0014] A seventh aspect of the present invention relates to the biaxially oriented polyethylene film according to the first or third aspect of the present invention, wherein the maximum height (SRmax) of the three-dimensional surface roughness of the surface layer A is greater than 1.00 μm.

[0015] An eighth aspect of the present invention relates to the biaxially oriented polyethylene film of the seventh aspect, wherein the maximum height (SRmax) of the three-dimensional surface roughness of the surface layer A is greater than 1.70 μm.

[0016] A ninth aspect of the present invention relates to the biaxially oriented polyethylene film according to the first or third aspect of the present invention, wherein the number of peaks having a height of 0.1 μm or more in the three-dimensional surface roughness of the surface layer A is 100 or more.

[0017] A tenth aspect of the present invention relates to the biaxially oriented polyethylene film of the ninth aspect, wherein the number of peaks having a height of 0.1 μm or more in the three-dimensional surface roughness of the surface layer A is 170 or more.

[0018] An eleventh invention relates to the biaxially oriented polyethylene film of the first invention, in which a surface layer B is disposed on the other side of the base layer, and at least the surface layer A contains an antiblocking agent.

[0019] A twelfth aspect of the invention relates to a laminate film obtained by laminating a sealant film made of a polyethylene resin onto the biaxially oriented polyethylene film of the first or third aspect of the invention.

[0020] A thirteenth aspect of the present invention relates to a laminate film obtained by laminating a sealant film made of a polyethylene resin on the biaxially oriented polyethylene film of the fifth aspect of the present invention.

[0021] A fourteenth aspect of the present invention relates to a laminate film obtained by laminating a sealant film made of a polyethylene resin onto the biaxially oriented polyethylene film of the seventh aspect of the present invention.

[0022] A fifteenth aspect of the present invention relates to a laminate film obtained by laminating a sealant film made of a polyethylene resin onto the biaxially oriented polyethylene film of the ninth aspect of the present invention. [Effects of the Invention]

[0023] The biaxially oriented polyethylene film of the first invention is a biaxially oriented film formed by stretching a laminate film consisting of multiple layers, at least a base layer and a surface layer A arranged on one side of the base layer, in two axial directions, that is, the machine direction (MD) and the transverse direction (TD), wherein the base layer and the surface layer A are made of a polyethylene-based resin, and the skewness (Ssk) in the three-dimensional surface roughness of the surface layer A is greater than 1.0, thereby making it possible to obtain a biaxially oriented polyethylene film that is particularly excellent in blocking resistance while being compatible with the mono-materialization of laminates.

[0024] According to the biaxially oriented polyethylene film of the second invention, in the first invention, the skewness (Ssk) in the three-dimensional surface roughness of the surface layer A is greater than 4.0, so that the biaxially oriented polyethylene film can have even better blocking resistance.

[0025] According to the biaxially oriented polyethylene film of the third invention, in the first invention, the arithmetic mean roughness (SRa) of the three-dimensional surface roughness of the surface layer A is greater than 0.01 μm, so that the biaxially oriented polyethylene film has better blocking resistance.

[0026] According to the biaxially oriented polyethylene film of the fourth invention, in the third invention, the arithmetic mean roughness (SRa) of the three-dimensional surface roughness of the surface layer A is greater than 0.04 μm, so that the biaxially oriented polyethylene film can have even better blocking resistance.

[0027] According to the biaxially oriented polyethylene film of the fifth invention, in the first or third invention, the ten-point average roughness (SRz) of the three-dimensional surface roughness of the surface layer A is greater than 1.00 μm, so that the biaxially oriented polyethylene film can have better blocking resistance.

[0028] According to the biaxially oriented polyethylene film of the sixth invention, in the fifth invention, the ten-point average roughness (SRz) of the three-dimensional surface roughness of the surface layer A is greater than 1.30 μm, so that the biaxially oriented polyethylene film can have even better blocking resistance.

[0029] According to the biaxially oriented polyethylene film of the seventh invention, in the first or third invention, the maximum height (SRmax) of the three-dimensional surface roughness of the surface layer A is greater than 1.00 μm, so that the biaxially oriented polyethylene film can have better blocking resistance.

[0030] According to the biaxially oriented polyethylene film of the eighth invention, in the seventh invention, the maximum height (SRmax) of the three-dimensional surface roughness of the surface layer A is greater than 1.70 μm, so that the biaxially oriented polyethylene film can have even better blocking resistance.

[0031] According to the biaxially oriented polyethylene film of the ninth invention, in the first or third invention, the number of peaks with a height of 0.1 μm or more in the three-dimensional surface roughness of the surface layer A is 100 or more, so that the biaxially oriented polyethylene film has better blocking resistance.

[0032] According to the biaxially oriented polyethylene film of the tenth invention, in the ninth invention, the number of peaks with a height of 0.1 μm or more in the three-dimensional surface roughness of the surface layer A is 170 or more, so that the biaxially oriented polyethylene film can have even better blocking resistance.

[0033] The biaxially oriented polyethylene film of the eleventh invention is the same as that of the first invention, except that a surface layer B is disposed on the other side of the base layer, and at least the surface layer A contains an antiblocking agent, so that the biaxially oriented polyethylene film has desired physical properties and excellent blocking resistance on at least one side.

[0034] The laminate film of the 12th invention is formed by laminating a sealant film made of polyethylene resin onto the biaxially oriented polyethylene film of the first or third invention, thereby achieving a mono-material structure and making it a promising alternative to existing laminate films.

[0035] The laminate film of the thirteenth invention is formed by laminating a sealant film made of polyethylene resin onto the biaxially oriented polyethylene film of the fifth invention, thereby achieving a mono-material structure and making it a promising alternative to existing laminate films.

[0036] The laminate film of the 14th invention is formed by laminating a sealant film made of polyethylene resin onto the biaxially oriented polyethylene film of the 7th invention, thereby achieving a mono-material structure and making it a promising alternative to existing laminate films.

[0037] The laminate film of the 15th invention is formed by laminating a sealant film made of polyethylene resin onto the biaxially oriented polyethylene film of the 9th invention, thereby achieving a mono-material structure and making it a promising alternative to existing laminate films. DETAILED DESCRIPTION OF THE INVENTION

[0038] The biaxially oriented polyethylene film according to the present invention is a laminated film composed of multiple layers, including at least a base layer and a surface layer A disposed on one side thereof, and is a biaxially oriented film stretched in two directions, namely, the machine direction (MD) and the transverse direction (TD). The raw material resin of each layer constituting the laminated film is preferably a polyethylene-based resin, and by forming the biaxially oriented polyethylene film from a single material (monomaterial), the film becomes suitable for recycling. The biaxially oriented polyethylene film is suitably used as a packaging material for various goods, such as food, daily necessities, and parts. It is not intended to limit the resin raw material of the laminated film, and other films made of polypropylene resin or polyester resin may be laminated depending on the desired physical properties and application.

[0039] The polyethylene resin used as the resin raw material for the biaxially oriented polyethylene film of the present invention is appropriately selected from polyethylene resins derived from petroleum, biomass, recycled materials, chemically recycled materials, 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.

[0040] 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.

[0041] The resin raw material 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, antistatic agents, antifogging agents, lubricants, nucleating agents, and colorants.

[0042] In order to provide the biaxially oriented polyethylene film of the present invention with excellent blocking resistance, it is specified by various physical properties of the surface layer A. The indices include the skewness (Ssk) of the three-dimensional surface roughness, the arithmetic mean roughness (SRa) of the three-dimensional surface roughness, the ten-point mean roughness (SRz) of the three-dimensional surface roughness, the maximum height (SRmax) of the three-dimensional surface roughness, and the number of peaks with a height of 0.1 μm or more of the three-dimensional surface roughness, and are specified as follows:

[0043] In order to impart excellent blocking resistance to the biaxially oriented polyethylene film, the skewness (Ssk) in the three-dimensional surface roughness of the surface layer A is specified to be greater than 1.0. As will be shown in the examples described later, a skewness (Ssk) of greater than 4.0 is more preferable, as this will result in even better blocking resistance.

[0044] The skewness (Ssk) in three-dimensional surface roughness is a parameter in the height direction, which is a quantified height statistic. The skewness (Ssk) in three-dimensional surface roughness is the cube mean of Z(x) in a reference length that is made dimensionless by the cube of the root mean square roughness (SRq), and is derived by the following formula (i):

[0045]

number

[0046] Next, in order to impart excellent blocking resistance to the biaxially oriented polyethylene film, the arithmetic mean roughness (SRa) of the three-dimensional surface roughness of the surface layer A is preferably greater than 0.01 μm. As shown in the examples described later, the arithmetic mean roughness (SRa) is more preferably 0.04 μm or greater. Although there is no particular upper limit, it is preferably 0.10 μm or less because there is a concern that the sense of see-through may be impaired.

[0047] Furthermore, the blocking resistance of biaxially oriented polyethylene films can also be determined by the ten-point average roughness (SRz) of the three-dimensional surface roughness, and it is preferably greater than 1.00 μm. As shown in the examples below, the ten-point average roughness (SRz) is more preferably 1.30 μm or greater. Although there is no particular upper limit, it is preferably 5.00 μm or less due to concerns about deterioration of the see-through feeling.

[0048] In addition, the blocking resistance of biaxially oriented polyethylene films can also be determined by the maximum height (SRmax) of the three-dimensional surface roughness, which is preferably greater than 1.00 μm. As shown in the examples below, the maximum height (SRmax) is more preferably 1.70 μm or greater. Although there is no particular upper limit, it is preferably 6.00 μm or less due to concerns about deterioration of the see-through feeling.

[0049] The arithmetic mean roughness (SRa) of three-dimensional surface roughness, the ten-point mean roughness (SRz) of three-dimensional surface roughness, and the maximum height (SRmax) of three-dimensional surface roughness are defined as follows: Each numerical value is an index showing the unevenness of the film surface, i.e., the degree to which the film surface is rough.

[0050] The arithmetic mean roughness (SRa) in three-dimensional surface roughness is a parameter in the height direction, and is the value obtained by dividing the volume of the area enclosed by the roughness surface and the center plane by the measurement range, with the X and Y axes being orthogonal coordinate axes placed on the center plane from the roughness surface and the Z axis being the axis perpendicular to the center plane.

[0051] The ten-point mean roughness (SRz) in three-dimensional surface roughness is a parameter in the height direction, and is a value that represents the distance between the average height of the fifth highest peak and the average depth of the fifth deepest peak relative to the average surface of the curved surface.

[0052] The maximum height (SRmax) in three-dimensional surface roughness is a parameter in the height direction, and is a value that represents the distance between two planes that are parallel to the average plane of the curved surface when the curved surface is sandwiched between them.

[0053] The blocking resistance of a biaxially oriented polyethylene film can also be determined by the number of peaks of 0.1 μm or more in three-dimensional surface roughness, and the number of peaks of 0.1 μm or more is preferably 100 or more, more preferably 170 or more. Although there is no particular upper limit, it is desirable that the number be 3000 or less, since there is a concern that the sense of see-through may be deteriorated. The number of peaks is determined by the number of peaks (convex portions) of 0.1 μm or more on the film surface per unit area (1 mm 2 ) and is an index of the roughness of the film surface. In the present invention, the number of peaks is a value obtained by measuring an area equivalent to a unit area using the measurement method described in the Examples.

[0054] The surface layer A is imparted with anti-blocking properties by adding an anti-blocking agent. There are no particular restrictions on the amount of anti-blocking agent added, but if the amount added is too large, costs will increase, the film's transparency will deteriorate, and the anti-blocking agent will tend to fall off after film formation. For this reason, it is considered that the appropriate amount of anti-blocking agent added is, for example, a concentration of 500 ppm to 30,000 ppm, preferably more than 1,000 ppm to 20,000 ppm.

[0055] The type of antiblocking agent is not particularly limited, but 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, and polyamide. Examples of inorganic fine particles include silica, zeolite, and talc. These antiblocking agents may be used alone or in combination. From the viewpoint of the blocking resistance and see-through feel of the film, polymethyl methacrylate is preferably used as the organic particles, and silica and zeolite are preferably used as the inorganic particles. The average particle size of the antiblocking agent is not particularly limited, but is 1 to 15 μm, preferably 1 to 13 μm. If the particle size is too small, the surface roughness will be small and the blocking resistance will tend to be poor, while if the particle size is too large, the antiblocking agent will tend to fall off and the see-through feel of the film will tend to be poor.

[0056] In the biaxially oriented polyethylene film of the present invention, it is also conceivable that a surface layer B is disposed on the other side of the surface layer A. The antiblocking agent needs to be contained in at least the surface layer A, and may also be contained in both surface layers. By providing the surface layer B with the same physical properties as the surface layer A, good anti-blocking properties can be imparted. The type and amount of the antiblocking agent added to both surface layers may be the same or different, and the type and amount can be appropriately selected and adjusted depending on the desired physical properties. The method of adding the antiblocking agent is not particularly limited, and it 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.

[0057] The thickness of surface layer A or surface layer B is preferably 0.3 to 5.0 μm, and more preferably 0.4 to 4.5 μm. If the surface layer is too thin, the antiblocking agent may fall off when the film passes through the rolls during processing. If the surface layer is too thick, the amount of antiblocking agent added may increase, resulting in poor transparency of the film. The thickness of the biaxially oriented polyethylene film is not particularly limited and may be determined appropriately depending on demand and application, and is preferably 5 to 100 μm, and more preferably 10 to 70 μm.

[0058] From the perspective of see-through, it is considered preferable that the biaxially oriented polyethylene film has an image clarity of 80% or more. Image clarity indicates the sharpness of an image seen through the film and is an index of see-through.

[0059] 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 substrate film. The biaxially oriented film is a biaxially oriented film that is 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 effectively.

[0060] 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.

[0061] 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.

[0062] In the biaxially oriented polyethylene film of the present invention, at least one surface is surface-treated to broaden the range of applications as a substrate film. 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 by 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 printing defects and lamination defects.

[0063] The biaxially oriented polyethylene film of the present invention may be subjected to a printing process on its surface. Printing on the surface of the biaxially oriented polyethylene film can be performed by known methods such as screen printing, flexographic printing, offset printing, and gravure printing. When printing is performed 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.

[0064] Furthermore, a gas barrier layer may be disposed on the surface layer directly or via an anchor coat layer in order to impart 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 may be subjected to a surface treatment such as corona discharge treatment in advance to improve the wettability and adhesion of the anchor coat layer and gas barrier layer.

[0065] 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 foil 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 is a thin film layer using one or more inorganic oxides.

[0066] Furthermore, the biaxially oriented polyethylene film of the present invention can be provided with a sealant layer made of polyethylene resin to form a laminate film. By using a sealant layer made of the same polyethylene resin as the biaxially oriented polyethylene film serving as the base film, a laminate film can be obtained that is monomaterial, facilitating recycling and improving blocking resistance. Furthermore, the laminate film can also be used to form packaging. This makes it a promising alternative to existing laminate films and packaging, as it allows for easy recycling. [Example]

[0067] [Preparation of biaxially oriented polyethylene film] The materials described below were blended, melted, and kneaded, extruded into three layers (surface layer A, base layer, and surface layer B) by the T-die method, biaxially stretched to form a film, and surface layer A was surface-treated by corona discharge treatment to obtain biaxially stretched polyethylene films of Prototype Examples 1 to 11 and Comparative Example 1. In each of Prototype Examples 1 to 11 and Comparative Example 1, the blending ratio of the resin in each of the base layer or surface layer was 100% by weight.

[0068] [Materials used] Polyethylene resin 1 (PE-1): Linear low-density polyethylene (Dow Chemical; TF80), density 0.926 g / cm 3 , MFR(190℃ / 2.16kg):1.7g / 10min Polyethylene resin 2 (PE-2): High-density polyethylene (Japan Polyethylene Co., Ltd.; HY430), density 0.956 g / cm 3 , MFR(190℃ / 2.16kg):0.8g / 10min Polyethylene resin 3 (PE-3): Ethylene-α-olefin random copolymer elastomer (Mitsui Chemicals, Inc.; A-4085S), density 0.885 g / cm 3 , MFR (190℃ / 2.16kg): 3.6g / 10min, comonomer carbon number 4 Antiblocking agent 1 (AB-1): Fuji Silysia Chemical Ltd.; SYLYSIA430, average particle size 4.1 μm, bulk density 55 mL / 5 g Antiblocking agent 2 (AB-2): Fuji Silysia Chemical Ltd.; SYLYSIA350, average particle size 3.9 μm, bulk density 90 mL / 5 g Antiblocking agent 3 (AB-3): Fuji Silysia Chemical Ltd.; SYLYSIA550, average particle size 3.9 μm, bulk density 30 mL / 5 g

[0069] [Prototype 1] The materials used for surface layer A were 99.9% by weight of resin (PE-1) and 0.1% by weight of antiblocking agent (AB-1), the base layer was 100.0% by weight of resin (PE-1), and the materials used for surface layer B were 99.9% by weight of resin (PE-1) and 0.1% by weight of antiblocking agent (AB-1).The ratio of surface layer A:base layer:surface layer B = 1:18:1 was extruded to a thickness of 20 μm and biaxially stretched in the machine direction (MD) and transverse direction (TD) to form a film.The surface layer A was subjected to a surface treatment by corona treatment to obtain the biaxially stretched polyethylene film of prototype example 1.

[0070] [Prototype 2] The biaxially oriented polyethylene film of Prototype Example 2 was obtained in the same manner as Prototype Example 1, except that 99.7% by weight of resin (PE-1) and 0.3% by weight of antiblocking agent (AB-1) were used for surface layer A, and 99.7% by weight of resin (PE-1) and 0.3% by weight of antiblocking agent (AB-1) were used for surface layer B.

[0071] [Prototype 3] The biaxially oriented polyethylene film of Prototype Example 3 was obtained in the same manner as in Prototype Example 1, except that 99.5% by weight of resin (PE-1) and 0.5% by weight of antiblocking agent (AB-1) were used for surface layer A, and 99.5% by weight of resin (PE-1) and 0.5% by weight of antiblocking agent (AB-1) were used for surface layer B.

[0072] [Prototype 4] A biaxially stretched polyethylene film of Sample 4 was obtained in the same manner as Sample 2, except that the ratio of surface layer A:base layer:surface layer B was 3:14:3.

[0073] [Prototype 5] A biaxially stretched polyethylene film of Sample 5 was obtained in the same manner as Sample 2, except that the antiblocking agent (AB-2) was added to the surface layers A and B instead of (AB-1).

[0074] [Prototype 6] A biaxially stretched polyethylene film of Sample 6 was obtained in the same manner as Sample 2, except that the antiblocking agent (AB-3) was added to the surface layers A and B instead of (AB-1).

[0075] [Prototype 7] The biaxially oriented polyethylene film of Prototype Example 7 was obtained in the same manner as in Prototype Example 2, except that 84.7 wt% of resin (PE-1), 15.0 wt% of (PE-2), and 0.3 wt% of antiblocking agent (AB-1) were used in surface layer A.

[0076] [Prototype 8] The biaxially oriented polyethylene film of Prototype Example 8 was obtained in the same manner as in Prototype Example 2, except that 79.7 wt% of resin (PE-1), 20.0 wt% of (PE-3), and 0.3 wt% of antiblocking agent (AB-1) were used in the surface layer A.

[0077] [Prototype 9] The same procedure as in Prototype Example 1 was repeated except that 99.8% by weight of resin (PE-1) and 0.2% by weight of antiblocking agent (AB-1) were used for surface layer A and surface layer B, and a biaxially oriented polyethylene film of Prototype Example 9 was obtained.

[0078] [Prototype 10] A biaxially stretched polyethylene film of Sample 10 was obtained in the same manner as Sample 9, except that the ratio of surface layer A:base layer:surface layer B was 2:17:1.

[0079] [Prototype 11] A biaxially oriented polyethylene film of Prototype Example 11 was obtained in the same manner as in Prototype Example 2, except that 100% by weight of resin (PE-1) was used for the surface layer B.

[0080] [Comparative Example 1] A biaxially oriented polyethylene film of Comparative Example 1 was obtained in the same manner as in Prototype Example 1, except that no antiblocking agent was added to surface layer A and surface layer B, and each layer contained 100.0% by weight of resin (PE-1).

[0081] The biaxially stretched polyethylene films of each prototype and comparative example were evaluated for haze (%), image clarity (%), skewness in three-dimensional surface roughness (Ssk), arithmetic mean roughness in three-dimensional surface roughness (SRa) (μm), ten-point mean roughness in three-dimensional surface roughness (SRz) (μm), maximum height in three-dimensional surface roughness (SRmax) (μm), number of peaks in three-dimensional surface roughness, and blocking strength (N / 4cm 2 ) was measured or calculated.

[0082] [Haze measurement] The haze (%) was measured in accordance with JIS K 7136 (2000) using an NDH-5000 (manufactured by Nippon Denshoku Industries Co., Ltd.) The lower the value, the better the transparency of the film.

[0083] [Measurement of image clarity] Image clarity (%) was measured in accordance with JIS K 7374 (2007) using an ICM-1T (manufactured by Suga Test Instruments Co., Ltd.) with an optical comb width of 0.125 mm. A higher value indicates a better transparency of the film.

[0084] [Measurement of skewness (Ssk), various roughnesses (SRa, SRz, SRmax), and number of peaks] Skewness (Ssk), various roughnesses (SRa, SRz, SRmax) (μm), and the number of peaks (number) were measured using a three-dimensional surface roughness measuring instrument "SE3500K (manufactured by Kosaka Laboratory Co., Ltd.)" and an analyzer "TDA-22 (manufactured by Kosaka Laboratory Co., Ltd.)" under the following measurement conditions. Skewness (Ssk), various roughnesses (SRa, SRz, SRmax), and the number of peaks were measured according to the measurement standard JIS B 0601. The number of peaks was calculated using particle analysis (multiple levels) under the conditions of a hysteresis width of 0 μm and slice level intervals of 0.1 μm. Measurement direction: longitudinal (MD) direction X measurement length: 2 mm X feed pitch: 4 μm X feed rate: 0.2 mm / s Y measurement length: 0.5 mm Y feed pitch: 10 μm Z magnification: 20000 Polarity: Positive Leveling: Least Squares Low-frequency cutoff: 0.250 mm High frequency cutoff: 0.000mm Phase characteristics: Gaussian Number of Y lines: 51 Detector: PU-DJ2S Stylus tip radius: 2μm Stylus apex angle: 60° Measuring force: 0.7mN or less

[0085] [Measurement of blocking strength] Blocking strength (N / 4cm 2 ) is a 4cm test piece made by overlapping the surface layers of each biaxially oriented polyethylene film. 2 A load of 1 kgf was applied to the film and the film was left at 30°C for 24 hours. The shear peel strength was then measured using a tensile tester, Autograph AGS-X 50N (Shimadzu Corporation), and the result was taken as the blocking strength. This blocking strength is the maximum strength measured when the film shear-peels at a tensile speed of 50 mm / min. In the table, "-" indicates that the overlapping portion of the test piece broke at another location before shear peeling occurred, making it impossible to measure.

[0086] The types and weight ratios of the resins and antiblocking agents in the biaxially oriented polyethylene films of Prototype Examples 1 to 11 and Comparative Example 1, as well as the concentrations and thicknesses of the antiblocking agents (referred to as "AB agents" in the tables) for each layer are shown in Tables 1 and 2, and the measurement and calculation results are shown in Tables 3 and 4.

[0087] [Table 1]

[0088] [Table 2]

[0089] [Table 3]

[0090] [Table 4]

[0091] [Results and Discussion] As shown in Comparative Example 1 and Prototype Examples 1 to 3 in each table, it was found that as the amount of antiblocking agent added increases, the skewness (Ssk), various roughnesses (SRa, SRz, SRmax), and number of peaks increase, and the blocking strength decreases accordingly, resulting in a film with excellent blocking resistance. Furthermore, since the haze increases and image clarity decreases in proportion to the amount of antiblocking agent added, resulting in poor see-through, it was shown that when using a biaxially oriented polyethylene film as a transparent film, it is better not to add too much antiblocking agent.

[0092] Comparing prototypes 2 and 4, in which the thicknesses of surface layers A and B were varied, prototype 4, in which surface layers A and B were thicker, contained a greater total amount of antiblocking agent in each surface layer, presumably resulting in greater skewness (Ssk), various roughnesses, and the number of peaks. As a result, although the haze increased, image clarity decreased, and the sense of see-through was poor, the blocking strength decreased, resulting in a film with better blocking resistance.

[0093] Comparing prototypes 9 and 10, in which the thickness of surface layer A was varied, it was found that the thicker the surface layer A, the greater the total amount of antiblocking agent present in surface layer A, and the greater the values ​​of skewness (Ssk), various roughnesses, and number of peaks, which in turn reduced the blocking strength, resulting in a film with excellent blocking resistance. Furthermore, the thicker the surface layer A, the higher the haze and the lower the image clarity, resulting in poor see-through, and therefore it was shown that when using a biaxially oriented polyethylene film as a transparent film, it is better not to make the surface layer too thick.

[0094] Comparing Prototypes 2, 5, and 6, which used different types of antiblocking agents, it was found that the lower the bulk density of the antiblocking agent, the greater the skewness (Ssk), various roughnesses, and number of peaks. It was also found that image clarity tends to decrease roughly in proportion to the skewness (Ssk), which is an index of surface roughness, various roughnesses, and number of peaks, and that blocking strength tends to decrease and blocking resistance tends to improve.

[0095] Furthermore, when comparing Prototypes 2, 7, and 8, in which the type or amount of polyethylene resin constituting the surface layer was changed, it is believed that the degree to which the antiblocking agent particles were exposed from the surface of Surface Layer A changed depending on the type or amount of resin added. As a result, the skewness (Ssk), various roughnesses, and number of peaks varied in each example, and it is believed that there were some changes in the transparency and blocking resistance. Although there were some changes, all of these films can be said to have good blocking resistance, and therefore it is believed that the amount and concentration of the antiblocking agent added have a greater impact on blocking resistance than the type or amount of polyethylene resin constituting the surface layer.

[0096] Comparison is made between Prototype Example 2 and Prototype Example 11, in which no antiblocking agent is added to surface layer B. It is believed that the transfer of roughness from surface layer B, which has small skewness (Ssk) and various roughnesses, to surface layer A during winding in film production is reduced, resulting in a higher skewness (Ssk) of surface layer A in Prototype Example 11 and a smaller arithmetic mean roughness (SRa) in three-dimensional surface roughness. Therefore, it is believed that Prototype Example 11, which has a smaller arithmetic mean roughness (SRa) than Prototype Example 2, had a higher blocking strength.

[0097] Furthermore, looking at the skewness (Ssk) and blocking strength of each prototype, it appears that when the skewness (Ssk) is approximately 4 or greater, there is a threshold at which the blocking strength changes significantly. Therefore, by increasing the skewness (Ssk) of the film surface layer to greater than 4.0, the blocking strength will be below a certain level, and it is believed that a biaxially oriented polyethylene film with excellent blocking resistance can be produced.

[0098] [Creating laminated film] Laminate films were prepared using the biaxially oriented polyethylene films of Samples 1, 2, 7, and 8. A two-component curing polyester adhesive was applied to the corona-treated surface at a rate of approximately 3 g / m. 2The laminated films were then attached to a polyethylene non-oriented film (Futamura Chemical Co., Ltd.; LL-XMTN#50) by dry lamination to produce laminated films. The appearance of each laminated film was visually inspected and found to be in good condition with no wrinkles. [Industrial Applicability]

[0099] As described above, the biaxially oriented polyethylene film of the present invention can be suitably used as a film that is excellent in blocking resistance while also being compatible with mono-material laminates.

Claims

1. A biaxially stretched film obtained by stretching a laminated film consisting of multiple layers including at least a base layer and a surface layer A arranged on one side of the base layer in two axial directions, i.e., a machine direction (MD) and a transverse direction (TD), The surface layer A is made of a polyethylene resin, The skewness (Ssk) in the three-dimensional surface roughness of the surface layer A is greater than 1.0 A biaxially oriented polyethylene film.

2. 2. The biaxially oriented polyethylene film according to claim 1, wherein the skewness (Ssk) in the three-dimensional surface roughness of the surface layer A is greater than 4.

0.

3. 2. The biaxially oriented polyethylene film according to claim 1, wherein the arithmetic mean roughness (SRa) of the three-dimensional surface roughness of the surface layer A is greater than 0.01 μm.

4. 4. The biaxially oriented polyethylene film according to claim 3, wherein the arithmetic mean roughness (SRa) of the three-dimensional surface roughness of the surface layer A is greater than 0.04 μm.

5. 4. The biaxially oriented polyethylene film according to claim 1, wherein the surface layer A has a ten-point average roughness (SRz) of more than 1.00 μm in three-dimensional surface roughness.

6. 6. The biaxially oriented polyethylene film according to claim 5, wherein the ten-point average roughness (SRz) of the three-dimensional surface roughness of the surface layer A is greater than 1.30 μm.

7. 4. The biaxially oriented polyethylene film according to claim 1, wherein the maximum height (SRmax) of the three-dimensional surface roughness of the surface layer A is greater than 1.00 μm.

8. 8. The biaxially oriented polyethylene film according to claim 7, wherein the maximum height (SRmax) of the three-dimensional surface roughness of the surface layer A is greater than 1.70 μm.

9. 4. The biaxially oriented polyethylene film according to claim 1, wherein the number of peaks having a height of 0.1 μm or more in the three-dimensional surface roughness of the surface layer A is 100 or more.

10. 10. The biaxially oriented polyethylene film according to claim 9, wherein the number of peaks having a height of 0.1 μm or more in the three-dimensional surface roughness of the surface layer A is 170 or more.

11. 2. The biaxially oriented polyethylene film according to claim 1, wherein a surface layer B is disposed on the other side of the base layer, and at least the surface layer A contains an antiblocking agent.

12. A laminate film comprising the biaxially oriented polyethylene film of claim 1 or 3 laminated with a sealant film made of a polyethylene resin.

13. A laminate film comprising the biaxially oriented polyethylene film of claim 5 and a sealant film made of a polyethylene resin laminated thereon.

14. A laminate film comprising the biaxially oriented polyethylene film of claim 7 and a sealant film made of a polyethylene resin laminated thereon.

15. A laminate film comprising the biaxially oriented polyethylene film of claim 9 and a sealant film made of a polyethylene resin laminated thereon.