Biaxially oriented polyethylene film, laminate film, and packaging

Abstract

To provide a biaxially stretched polyethylene film that is excellent in scratch resistance of a film surface to be subjected to vapor deposition processing or printing processing, a laminated film, and a package.SOLUTION: A polyethylene film 10 includes a first surface layer 20, a substrate layer 30, and a second surface layer 40 containing an antiblocking agent, and is biaxially stretched in a machine direction (MD) and a transverse direction (TD), wherein when an elastic modulus in a cross section of the first surface layer 20 is determined as E1 (GPa), which is obtained by an atomic force microscopy (AFM), a height of a center surface peak in a three-dimensional surface roughness of the second surface layer 40 is determined as SRp2 (μm), and a pore volume of the antiblocking agent contained in the second surface layer 40 is determined as V2 (ml / g), which has been obtained by a nitrogen adsorption method, a value of the scratch resistance is 16 or smaller.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a biaxially oriented polyethylene film having a first surface layer, a base layer, and a second surface layer containing an antiblocking agent, a laminate film using this polyethylene film, and a package using this laminate film. [Background technology]

[0002] Generally, packaging materials for packaging products such as food and daily necessities use films that are laminated with multiple resin films made of different types of resin materials. This type of laminated film achieves good quality and performance as a film product by laminating films with various functions. In recent years, growing awareness of environmental issues has led to a demand for recycling of this type of resin film. However, when a film made of multiple types of resins is recycled, even if the resins that make up the film are remelted, they become a mixture of incompatible resins, which significantly reduces the quality of the recycled resource and makes it unsuitable as a recycled material.

[0003] Therefore, films have been proposed in which multiple laminated films are made of a single material (monomaterial). Examples of monomaterial laminated films include polyethylene-based laminated films that use the same polyethylene-based material as the polyethylene-based sealant film, which has excellent heat-sealing properties, as the base film. When a laminated film is made of a single material, the individual layers are easily remelted and are compatible with each other, making it suitable for use as a recycled material.

[0004] Laminated films such as biaxially oriented films mainly made of polyethylene resin tend to be more flexible and have a lower melting point than films made of polypropylene resin, and to have inferior film properties such as blocking resistance. In polyethylene resin films, an antiblocking agent such as silica particles is added to the surface layer of the film in order to improve blocking resistance and processability (see, for example, Patent Document 1).

[0005] In such films, the granular antiblocking agent is exposed on the film surface, forming fine irregularities. Fine irregularities on the film surface can cause scratches when films rub against each other during winding, etc. The scratches on the film surface can lead to poor appearance and poor design when the film surface is subjected to surface treatments such as printing and vapor deposition. Therefore, there is a need to prevent scratches on the film surface of polyethylene laminated films that have been given anti-blocking properties by an antiblocking agent. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 7209125 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in consideration of the above points, and provides a biaxially oriented polyethylene film, a laminate film, and a packaging material that have excellent scratch resistance on the film surface to which vapor deposition or printing processing is applied. [Means for solving the problem]

[0008] Specifically, the first invention relates to a biaxially oriented polyethylene film comprising a first surface layer, a base layer, and a second surface layer containing an antiblocking agent, and stretched in biaxial directions, i.e., the machine direction (MD) and the transverse direction (TD), wherein the biaxially oriented polyethylene film satisfies the scratch resistance value given by the following formula (i), where E1 (GPa) is the elastic modulus of a cross section of the first surface layer measured with an atomic force microscope (AFM), SRp2 (μm) is the central peak height in the three-dimensional surface roughness of the second surface layer, and V2 (ml / g) is the pore volume of the antiblocking agent contained in the second surface layer determined by a nitrogen adsorption method.

[0009]

number

[0010] A second invention relates to the biaxially oriented polyethylene film of the first invention, wherein the modulus of elasticity E1 (GPa) of the cross section of the first surface layer measured with an atomic force microscope (AFM) is 0.1 to 5.0 GPa.

[0011] A third aspect of the present invention relates to the biaxially oriented polyethylene film of the first or second aspect of the present invention, wherein the central peak height SRp2 (μm) in the three-dimensional surface roughness of the second surface layer and the pore volume V2 (ml / g) of the antiblocking agent contained in the second surface layer satisfy the scratch resistance value shown in the following formula (ii):

[0012]

number

[0013] A fourth invention relates to the biaxially oriented polyethylene film of the third invention, wherein the central peak height SRp2 (μm) of the three-dimensional surface roughness of the second surface layer is 0.1 to 6.0 μm.

[0014] A fifth invention relates to the biaxially oriented polyethylene film of the third invention, wherein the pore volume V2 (ml / g) of the antiblocking agent contained in the second surface layer is 0.3 to 2.0 ml / g.

[0015] A sixth invention relates to the biaxially oriented polyethylene film of the fourth invention, wherein the pore volume V2 (ml / g) of the antiblocking agent contained in the second surface layer is 0.3 to 2.0 ml / g.

[0016] A seventh aspect of the present invention relates to a laminate film including the biaxially oriented polyethylene film according to the first aspect of the present invention, a printed portion, and a sealant film made of polyethylene resin.

[0017] An eighth aspect of the present invention relates to a laminate film including the biaxially oriented polyethylene film according to the first aspect of the present invention, a vapor deposition layer, a printed portion, and a sealant film made of polyethylene resin.

[0018] A ninth aspect of the present invention relates to a package made of the laminate film according to the seventh or eighth aspect of the present invention. [Effects of the Invention]

[0019] The biaxially oriented polyethylene film according to the first aspect of the present invention is a polyethylene film comprising a first surface layer, a base layer, and a second surface layer containing an antiblocking agent, and stretched in two axial directions, i.e., the machine direction (MD) and the transverse direction (TD), and has a scratch resistance of 16 or less, where E1 (GPa) is the elastic modulus of a cross section of the first surface layer measured with an atomic force microscope (AFM), SRp2 (μm) is the median peak height in the three-dimensional surface roughness of the second surface layer, and V2 (ml / g) is the pore volume of the antiblocking agent contained in the second surface layer determined by a nitrogen adsorption method. Therefore, the film has excellent scratch resistance and can suppress scratches on the first surface layer.

[0020] According to the biaxially oriented polyethylene film of the second invention, in the first invention, the elastic modulus E1 (GPa) of the cross section of the first surface layer measured by atomic force microscope (AFM) is 0.1 to 5.0 GPa, so that good surface rigidity is obtained in the first surface layer.

[0021] According to the biaxially oriented polyethylene film of the third invention, in the first or second invention, the central peak height SRp2 (μm) in the three-dimensional surface roughness of the second surface layer and the pore volume V2 (ml / g) of the antiblocking agent contained in the second surface layer satisfy the scratching property value shown in the following formula (ii), and therefore the second surface layer is less likely to scratch the surface of the film on the first surface layer side when the films rub against each other.

[0022] According to the biaxially oriented polyethylene film of the fourth invention, in the third invention, the central surface peak height SRp2 (μm) of the three-dimensional surface roughness of the second surface layer is 0.1 to 6.0 μm, so that damage to other layers due to the surface roughness of the second surface layer can be suppressed.

[0023] According to the biaxially oriented polyethylene film of the fifth invention, in the third invention, the pore volume V2 (ml / g) of the antiblocking agent contained in the second surface layer is 0.3 to 2.0 ml / g, so that damage to other layers by the antiblocking agent in the second surface layer can be suppressed.

[0024] According to the biaxially oriented polyethylene film of the sixth invention, in the fourth invention, the pore volume V2 (ml / g) of the antiblocking agent contained in the second surface layer is 0.3 to 2.0 ml / g, so that damage to other layers by the antiblocking agent in the second surface layer can be suppressed.

[0025] The laminate film of the seventh invention comprises the biaxially oriented polyethylene film described in the first invention, a printed portion, and a sealant film made of polyethylene resin, so that printing processing can be carried out suitably, and a laminate film with excellent design can be provided.

[0026] The laminate film of the eighth invention comprises the biaxially oriented polyethylene film described in the first invention, a vapor deposition layer, a printed portion, and a sealant film made of polyethylene resin, and therefore can be suitably subjected to vapor deposition and printing processes, providing a laminate film with excellent design.

[0027] The packaging according to the ninth aspect of the invention is made of the laminate film according to the seventh or eighth aspect of the invention, and is therefore easy to recycle, making it a promising alternative to existing packaging. [Brief explanation of the drawings]

[0028] [Figure 1]1 is a schematic cross-sectional view of a biaxially oriented polyethylene film according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view of a laminate film using the biaxially oriented polyethylene film of FIG. 1. [Figure 3] FIG. 2 is a schematic cross-sectional view showing the printed state of a printed portion of a laminate film. [Figure 4] FIG. 2 is a schematic cross-sectional view of a laminate film according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0029] The biaxially oriented polyethylene film 10 according to one embodiment of the present invention shown in Figure 1 is a laminated film comprising a first surface layer 20, a base layer 30, and a second surface layer 40 containing an antiblocking agent, and stretched in two axial directions, 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 which printing, vapor deposition, etc. are applied. This laminate film can be suitably used for various packages (packaging bags) for, for example, food, cosmetics, pharmaceuticals, daily necessities, parts, and other products.

[0030] The biaxially oriented polyethylene film of the present invention is composed of a single material (monomaterial) in which each layer is made primarily of a polyethylene resin. Therefore, it can be suitably used as a recycled material. The term "single material" as used herein means that each layer is made primarily of the same type of resin material, and it is acceptable for the film to contain small amounts of various additives, etc.

[0031] 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.

[0032] 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 resin may be prone to breakage during stretching, making it difficult to form into a film.

[0033] 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.

[0034] The first surface layer 20 corresponds to one surface layer of the biaxially oriented polyethylene film 10, and is the layer to which surface processing such as printing or vapor deposition is applied when the biaxially oriented polyethylene film 10 is used as a base film for a laminate film. An antiblocking agent or the like may be added to the first surface layer 20 as needed.

[0035] The base layer 30 corresponds to the middle layer of the biaxially oriented polyethylene film 10 and is formed to be relatively thicker than the other layers. A surfactant or the like may be added to the base layer 30 as needed. For example, the addition of a surfactant can improve the slip properties and anti-blocking properties of the film 10.

[0036] The second surface layer 40 corresponds to the other surface layer of the biaxially oriented polyethylene film 10, contains an antiblocking agent, and is a layer that becomes one end of the outermost surface layer when used as a laminate film.

[0037] The antiblocking agent added to the 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 viewpoint 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.

[0038] 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 of the surface layer 40 (20) to which it is added, etc. For example, when the surface layer 40 (20) 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 surface layer 40 (20) 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 of the surface layer 40 (20) 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 prone to peeling and deterioration of the see-through feeling.

[0039] The amount of antiblocking agent added to the surface layer 40 (20) 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 anti-blocking properties may not be achieved. For this reason, it is considered that the appropriate amount of antiblocking agent to be added is, for example, 500 to 30,000 ppm, preferably 1,000 to 20,000 ppm. The method for 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.

[0040] The biaxially oriented polyethylene film 10 of the present invention can be obtained by known film forming methods such as the T-die method and the inflation method. In particular, it is preferable to form a sheet shaped by the T-die method by stretching it. 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.

[0041] The polyethylene film 10 is a biaxially stretched film that has been stretched in two directions, the machine direction (MD) and the transverse direction (TD), of the film. Biaxial stretching can be performed by either sequential biaxial stretching or simultaneous biaxial stretching. Film production by biaxial stretching produces resin orientation in both the machine direction (MD) and the transverse direction (TD), which allows for improvements in thickness accuracy (e.g., thinning) and mechanical properties such as strength, and is also suitable for mass production.

[0042] The thickness of the biaxially oriented polyethylene film 10 of the present invention is not particularly limited and may be appropriately determined depending on the demand and application, for example, 5 to 100 μm, preferably 10 to 70 μm. Of these, the thickness of the first surface layer 20 and the second surface layer 40 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 20, 40 are too thin, the antiblocking agent may fall off when the film passes through the rolls during processing. If the surface layers are too thick, the amount of antiblocking agent added may be too large, resulting in poor transparency of the film.

[0043] As described above, in a biaxially oriented polyethylene film 10 having an antiblocking agent added to the second surface layer 40, there is a concern that the fine irregularities on the film surface may scratch the film surface when two films rub against each other. Therefore, in the biaxially oriented polyethylene film 10 of the present invention, an index of scratch resistance for a biaxially oriented polyethylene film 10 containing an antiblocking agent was discovered by focusing on the elastic modulus of the first surface layer 20, the median peak height in the three-dimensional surface roughness of the second surface layer 40 containing the antiblocking agent, and the pore volume of the antiblocking agent contained in the second surface layer 40. Specifically, when the elastic modulus of the first surface layer 20 is E1 (GPa), the median peak height in the three-dimensional surface roughness of the second surface layer 40 is SRp2 (μm), and the pore volume of the antiblocking agent contained in the second surface layer 40, as determined by a nitrogen adsorption method, is V2 (ml / g), the scratch resistance value expressed by the following formula (i) is satisfied:

[0044]

number

[0045] The elastic modulus E1 (GPa) is used as an index of the rigidity of the first surface layer 20 and is obtained by measuring a cross section of the first surface layer 20 with an atomic force microscope (AFM). A higher value of the elastic modulus E1 indicates that the first surface layer 20 has higher rigidity and is less likely to deform.

[0046] The central peak height SRp2 (μm) in the three-dimensional surface roughness is a parameter in the height direction of the surface irregularities of the second surface layer 40, and is a value representing the height from the central plane to the maximum peak. The larger the central peak height in the three-dimensional surface roughness, the higher the peaks, and therefore the higher the value, the more likely it is that the surface of the opposing film will be scratched when rubbing against it. In a polyethylene film, the second surface layer 40 containing the antiblocking agent is the layer that scratches the surface of the opposing first surface layer 20. Therefore, the central peak height SRp2 in the three-dimensional surface roughness of the second surface layer 40 is an indicator of the ease with which the second surface layer 40 scratches the surface of the opposing first surface layer 20. Therefore, it can be said that the smaller the central peak height SRp2, the better the scratch resistance of the polyethylene film.

[0047] The pore volume V2 (ml / g) of the antiblocking agent refers to the volume of the fine pores present in the antiblocking agent and can be used as an indicator of the hardness of the antiblocking agent. This pore volume is determined by nitrogen adsorption. The larger the pore volume of the antiblocking agent, the softer the antiblocking agent, making it less likely to scratch the film surface when it rubs against another film. Conversely, the smaller the pore volume, the harder the antiblocking agent and the more likely it is to scratch the film surface. Since the antiblocking agent forms the ridges on the film surface that can scratch the opposing film when it rubs against the antiblocking agent, it is thought that the softer the antiblocking agent, the less likely it is to scratch the opposing film. Therefore, the pore volume V2 of the antiblocking agent added to the second surface layer 40 serves as an indicator of the susceptibility of the second surface layer 40 to scratching. Therefore, it can be said that the larger the pore volume V2 of the antiblocking agent, the better the scratch resistance of the polyethylene film.

[0048] The left side of the formula (i) represents the scratch resistance of the polyethylene film expressed using these three indices. As will be seen from the examples described later, when the scratch resistance value represented by formula (i) satisfies 16 or less, scratches on the first surface layer 20 by the second surface layer 40 of the biaxially oriented polyethylene film 10 are less likely to occur.

[0049] In formula (i), the elastic modulus E1, which is an index of the rigidity of the first surface layer 20, is the denominator of formula (i). Therefore, as the elastic modulus E1 decreases, the scratch resistance increases, and the rigidity of the first surface layer 20 decreases, making the first surface layer 20 more susceptible to scratches by the second surface layer 40. Therefore, the elastic modulus E1 of the first surface layer 20 is preferably 0.1 to 5.0 GPa, more preferably 0.2 to 4 GPa. If the elastic modulus E1 is too small, the rigidity of the first surface layer 20 may be insufficient, making the first surface layer 20 more susceptible to scratches. If the elastic modulus E1 is too large, the rigidity of the first surface layer 20 may be too high, reducing its functionality as a package.

[0050] The numerator of formula (i) uses the central surface peak height SRp2, which is an index of the scratch susceptibility of the second surface layer 40, and the pore volume V2 of the antiblocking agent determined by nitrogen adsorption. In the present invention, the central surface peak height SRp2 of the second surface layer 40 divided by the pore volume V2, which is an index of the hardness of the antiblocking agent determined by nitrogen adsorption, is used as an index of scratching ability, which indicates the ease with which the first surface layer 20 is scratched, and is used as the numerator of formula (i). The larger the scratching ability value, the larger the scratch resistance value, indicating that the second surface layer 40 is more likely to scratch the first surface layer 20. Therefore, it is preferable that the scratching ability of the second surface layer 40 satisfy the following formula (ii).

[0051]

number

[0052] In addition to the scratch resistance represented by formula (i), the scratch resistance represented by formula (ii) is 10 or less, which further improves the scratch resistance of the biaxially oriented polyethylene film 10. The scratch resistance can be considered as an index of scratch resistance after processing, such as when the film is wound up after surface processing such as vapor deposition or printing. If the scratch resistance of the second surface layer 40 is below a certain level, it can be said that the film has good scratch resistance before and after surface processing such as vapor deposition. This prevents a decrease in commercial value and contributes economically.

[0053] In formula (ii), the central peak height SRp2 of the three-dimensional surface roughness, which is an index of the height of the irregularities of the second surface layer 40, is the numerator of formula (ii). Therefore, as the central peak height SRp2 increases, the scratchability value increases, indicating that the surface peaks of the second surface layer 40 become higher and more likely to scratch the first surface layer 20. Therefore, the central peak height SRp2 of the second surface layer 40 is preferably 0.1 to 6.0 μm, more preferably 0.5 to 5.0 μm. If the central peak height SRp2 is too low, the anti-blocking agent may not provide sufficient blocking resistance. If the central peak height SRp2 is too high, the peak height of the second surface layer 40 may be excessive, making it more likely to scratch the first surface layer 20. Note that the thickness of the second surface layer 40 and the particle size of the anti-blocking agent used are preferably selected so that the central peak height SRp2 of the second surface layer 40 satisfies the preferred range of 0.1 to 6.0 μm.

[0054] Furthermore, since the pore volume V2, which is an index of the hardness of the antiblocking agent, is the denominator of formula (ii), the larger the pore volume V2, the smaller the scratch resistance value, indicating that the first surface layer 20 is less susceptible to scratches. Therefore, the pore volume V2 of the antiblocking agent in the second surface layer 40 is preferably 0.3 to 2 ml / g, more preferably 0.4 to 1.5 ml / g. If the pore volume V2 of the antiblocking agent is too small, the antiblocking agent may be too hard and may easily scratch the first surface layer 20. If the pore volume V2 is too large, the dispersibility of the antiblocking agent may decrease.

[0055] For the biaxially oriented polyethylene film 10 of the present invention, scratch haze was used to evaluate scratch resistance. Scratch haze is an index showing the scratch resistance (scratch resistance) of the film surface when two films are rubbed together, and is a value calculated from the difference between the haze of the film after rubbing and the haze of the film before rubbing. Haze is an index of film transparency measured in accordance with JIS K 7136 (2000), with a lower value indicating better transparency.

[0056] A higher scratch haze value indicates that the film surface is scratched more by rubbing, resulting in a loss of transparency. A lower scratch haze value indicates that the film surface is scratched less by rubbing, resulting in a loss of transparency. Therefore, a preferred scratch haze value is 10% or less, more preferably 7.1% or less. If the scratch haze value is too high, the film's scratch resistance may be insufficient, causing the film surface to appear cloudy, resulting in a loss of design quality. A good scratch haze value can be said to effectively suppress scratches on the first surface layer caused by rubbing. Therefore, it is possible to suppress a loss of design quality due to rubbing between films during transportation or processing.

[0057] In the present invention, as shown in Figure 2, a laminate film 50 can be provided in which the biaxially oriented polyethylene film 10 with excellent scratch resistance is used as a base film, and a printed portion, a vapor deposition layer, a sealant film, etc. are appropriately laminated. In this type of laminate film 50, the biaxially oriented polyethylene film 10, which is the base film, is laminated as the outermost layer on one side, and the sealant film is laminated as the outermost layer on the other side. Since the biaxially oriented polyethylene film 10 has excellent scratch resistance on the film surface, the laminate film 50 can be suitably subjected to printing processes, vapor deposition processes, etc. Furthermore, by using this biaxially oriented polyethylene film 10 as the base film, a laminate film with excellent design properties can be obtained.

[0058] The embodiment shown in FIG. 2 is a laminate film 50A in which a printed area 60 and a sealant film 70 are laminated on a base film 10. The printed area 60 is a portion on the first surface layer 20 side of the base film (biaxially oriented polyethylene film 10) where any desired printed pattern, such as letters, numbers, pictures, or figures, is formed to impart decorative design or aesthetic appeal, or to display various information such as the contents, shelf life, manufacturer, or seller. The printed area 60 may be in any suitable printing state, such as a full-surface print (solid print) 61 in which printing is applied to the entire surface of the first surface layer 20 of the base film 10 as shown in FIG. 3(a) or a partial print 62 in which printing is applied to only a portion of the first surface layer 20 of the base film 10 as shown in FIG. 3(b). The printed area 60 can be processed by known methods such as screen printing, flexographic printing, offset printing, or gravure printing.

[0059] The sealant film 70 is a heat-sealable film made of polyethylene resin. The polyethylene resin used in the sealant film 70 is selected from, for example, linear low-density polyethylene resin (LLDPE), high-density polyethylene (HDPE), low-density polyethylene (LDPE), etc., either singly or in combination. Because the main raw material of the sealant film 70 is the same type of polyethylene resin as the biaxially oriented polyethylene film 10 that serves as the base film, the laminate film 50 is made of a single material (monomaterial). This makes the laminate film 50 easy to recycle.

[0060] The laminate film 50B shown in Fig. 4 is an embodiment in which a vapor deposition layer 80 is further laminated on the first surface layer 20 side of the base film (biaxially oriented polyethylene film). The vapor deposition layer 80 is a layer that provides the laminate film 50B with barrier properties against water vapor, oxygen, etc. The vapor deposition layer 80 is formed on the first surface layer 20 directly or via an anchor coat layer using a known vapor deposition method such as vacuum vapor deposition, sputtering, or ion plating.

[0061] As the material for vapor deposition, an appropriate material such as a metal vapor deposition layer or an inorganic oxide layer is selected. The metal vapor deposition layer is a thin film layer made of known metals such as aluminum, gold, silver, copper, chromium, etc., and may be a thin film layer of oxides, sulfides, or nitrides of these metals. The metal vapor deposition layer may be a single layer or a plurality of layers made of two or more different types or the same type. The inorganic oxide layer is made of known inorganic oxides such as aluminum oxide, silicon oxide, magnesium fluoride, magnesium oxide, etc., and is a thin film layer using one or more types of inorganic oxides.

[0062] The laminate film 50 may further include other polyethylene films or layers with other functionality, such as adhesive layers, as needed. The polyethylene film is a film that is laminated to improve the rigidity and other functions of the laminate film 50. It is made of the same type of polyethylene resin as the biaxially oriented polyethylene film 10 that serves as the base film, and is appropriately selected from unstretched, uniaxially oriented, and biaxially oriented films depending on the purpose. By using a film made of the same type of polyethylene resin as the biaxially oriented polyethylene film 10, a single material (monomaterial) is achieved, making recycling easier. Note that, with regard to polyethylene films, it is preferable to select a uniaxially oriented film or a biaxially oriented film from the perspective of the rigidity of the laminate film 50.

[0063] The adhesive layer is a layer for adhering the various layers together, and can be formed by known methods such as dry lamination, non-solvent lamination, melt extrusion lamination, etc. Suitable adhesives for use in the adhesive layer include known adhesives such as polyurethane adhesives, polyester polyurethane adhesives, and polyether polyurethane adhesives.

[0064] In the laminate film 50, the order in which the printed portion 60, the vapor deposition layer 80, and any other layers, such as an adhesive layer or polyethylene film, that are provided as needed, are laminated is not particularly limited, as long as the functionality of each layer is not impaired. For example, the printed portion may be provided on the first surface layer 20 of the biaxially oriented polyethylene film 10, and then a vapor deposition layer may be provided to form a laminate film, and the layers may be laminated in any appropriate order.

[0065] Furthermore, in order to broaden the range of uses of the biaxially oriented polyethylene film 10 as a substrate film, it is preferable to subject at least one surface layer of the laminate film 50 to a surface treatment so that the wet tension of the surface layer is 36 mN / m or more. The wet tension is measured by a wet tension test method in accordance with JIS K 6768 (1999). If the wet tension is too low, it is not preferable because it can cause poor printing or poor lamination.

[0066] Examples of surface treatments include known surface treatment methods such as atmospheric pressure plasma treatment, flame treatment, and corona discharge treatment. When printing is to be performed on the biaxially oriented polyethylene film 10 of the present invention, the film surface may be subjected to a surface treatment such as corona discharge treatment prior to printing, thereby improving ink compatibility and adhesion.

[0067] The present invention can also be used to produce packaging using the laminate film. This packaging is easy to recycle because it is made of a single-material laminate film, making it a promising alternative to existing packaging. [Example]

[0068] [Preparation of biaxially oriented polyethylene film] To produce the biaxially oriented polyethylene films of Examples 1 to 24, the materials described below were mixed and melted in predetermined blending ratios (by weight), coextruded using a T-die method, stretched 5 times in the machine direction (MD), and then stretched 8 times in the transverse direction (TD) using a tenter to obtain biaxially oriented polyethylene films. The machine direction roll stretching temperature for each of Examples 1 to 24 was 115°C. The transverse direction tenter preheating temperature was 143°C for Examples 1 to 10 and 13 to 24 and 148°C for Examples 11 and 12. The transverse direction stretching temperature was 122°C for Examples 1 to 10 and 13 to 24 and 125°C for Examples 11 and 12. The biaxially oriented polyethylene films had an overall thickness of 20 μm, with the first and second surface layers each having a thickness of 1 μm and the base layer having a thickness of 18 μm. The melt flow rate (MFR) conforms to JIS K 7210 (2014), and the melt flow rate of the polyethylene resin is measured at 190° C. The materials used in each layer of Prototype Examples 1 to 24 are shown in Tables 1 to 4 below.

[0069] [Materials used] The following resin material (polyethylene resin), anti-blocking agent, and surfactant were used for each layer. The melt flow rate (MFR) of each resin material was measured in accordance with JIS K 7210 (2014) at a test temperature of 190°C and a load of 2.16 kg.

[0070] The pore volume of the antiblocking agent was determined by the nitrogen adsorption method as follows. As a pretreatment, the antiblocking agent was subjected to vacuum degassing and drying at 200°C for 2 hours, and the nitrogen adsorption amount was measured and converted into the volume of liquid nitrogen for calculation. The nitrogen adsorption amount was measured using an automatic specific surface area / pore distribution measuring device "BELSORP-mini II (manufactured by Microtrac BEL Co., Ltd.)". Applying Gurvitsch's law to the obtained nitrogen adsorption amount, the nitrogen adsorption amount (V) at a relative pressure of 0.990 was calculated using the following formula (iii) to calculate the volume of liquid nitrogen (V p ) in the formula (iii). g is the molecular weight of the adsorbate (nitrogen: 28.020), ρ g (g / cm 3) is the density of the adsorbate (nitrogen: 0.808).

[0071]

number

[0072] [Resin material] PE1: Linear low-density polyethylene (Dow Chemical; TF80), density 0.926 g / cm 3 , MFR: 1.7g / 10min PE2: High-density polyethylene (Japan Polyethylene Co., Ltd.; HY430), density 0.954 g / cm 3 , MFR: 0.6g / 10min PE3: High-density polyethylene (Japan Polyethylene Co., Ltd.; HF562), density 0.963 g / cm 3 , MFR: 7.5g / 10min PE4: Ethylene-α-olefin random copolymer elastomer (Mitsui Chemicals, Inc.; A-4085S), density 0.885 g / cm 3 , MFR: 3.6g / 10min, comonomer carbon number 4

[0073] [Anti-blocking agent] AB1: Fuji Silysia Chemical Ltd.; SYLYSIA430, average particle size 4.1 μm, pore volume 1.25 ml / g AB2: Fuji Silysia Chemical Ltd.; SYLYSIA550, average particle size 3.9 μm, pore volume 0.8 ml / g AB3: Fuji Silysia Chemical Ltd.; SYLYSIA710, average particle size 2.8 μm, pore volume 0.44 ml / g AB4: Fuji Silysia Chemical Ltd.; SYLYSIA350, average particle size 3.9 μm, pore volume 1.6 ml / g AB5: Fuji Silysia Chemical Ltd.; SYLYSIA730, average particle size 4.0 μm, pore volume 0.44 ml / g AB6: Fuji Silysia Chemical Ltd.; SYLYSIA770, average particle size 6.7 μm, pore volume 0.44 ml / g

[0074] [Surfactants] AS1: Glycerin monostearate AS2: Stearyldiethanolamine

[0075] [Prototype 1] Prototype example 1 is a biaxially oriented polyethylene film obtained by forming a first surface layer containing 99.7% by weight of PE1 as a polyethylene resin and 0.3% by weight of AB1 as an antiblocking agent; a base layer containing 99.7% by weight of PE1 as a polyethylene resin and 0.2% by weight of AS1 and 0.1% by weight of AS2 as surfactants; and a second surface layer containing 99.7% by weight of PE1 as a polyethylene resin and 0.3% by weight of AB1 as an antiblocking agent.

[0076] [Prototype 2] Prototype 2 is a film obtained by forming the same film as in Prototype 1, except that the antiblocking agent in the second surface layer was changed from AB1 to AB2.

[0077] [Prototype 3] Prototype 3 is a film obtained by forming the same film as in Prototype 1, except that the antiblocking agent in the second surface layer was changed from AB1 to AB3.

[0078] [Prototype 4] Prototype 4 is a film obtained by film formation in the same manner as Prototype 1, except that the base layer was made of 100.0 wt% polyethylene resin PE1 (no surfactant added) and the antiblocking agent in the second surface layer was changed from AB1 to AB5.

[0079] [Prototype 5] Prototype 5 is a film obtained by forming the same film as in Prototype 4, except that the antiblocking agent in the first surface layer was changed from AB1 to AB2 and the antiblocking agent in the second surface layer was changed from AB5 to AB2.

[0080] [Prototype 6] Prototype Example 6 is a film obtained by blending 84.7 wt% PE1 and 15.0 wt% PE2 as polyethylene resins in the first surface layer, 0.3 wt% AB1 as an antiblocking agent, and 100.0 wt% PE1, a polyethylene resin, in the base layer (no surfactant added), and forming the second surface layer in the same manner as Prototype Example 1.

[0081] [Prototype 7] Prototype 7 is a film obtained by forming the same film as in Prototype 6, except that the antiblocking agent in the second surface layer was changed from AB1 to AB4.

[0082] [Prototype 8] Prototype Example 8 is a film obtained by forming the first surface layer using the same process as Prototype Example 3, except that the polyethylene resins used were 84.7% by weight of PE1 and 15.0% by weight of PE2, and the anti-blocking agent was 0.3% by weight of AB1.

[0083] [Prototype 9] Prototype 9 is a film obtained by forming the same film as in Prototype 6, except that the antiblocking agent in the second surface layer was changed from AB1 to AB5.

[0084] [Prototype 10] Prototype 10 is a film obtained by forming the same film as in Prototype 8, except that the antiblocking agent in the second surface layer was changed from AB3 to AB6.

[0085] [Prototype 11] Prototype Example 11 is a film obtained by forming a first surface layer containing 80.0 wt% PE1, 13.2 wt% PE2, and 6.8 wt% PE3 as polyethylene resins, a base layer containing 80.0 wt% PE1, 13.2 wt% PE2, and 6.8 wt% PE3 as polyethylene resins, a second surface layer containing 79.7 wt% PE1, 13.2 wt% PE2, and 6.8 wt% PE3 as polyethylene resins, and 0.3 wt% AB1 as an antiblocking agent.

[0086] [Prototype 12] Prototype 12 is a film obtained by forming the film in the same manner as Prototype 11, except that the second surface layer contained 99.7% by weight of PE1 as the polyethylene resin and 0.3% by weight of AB2 as the antiblocking agent.

[0087] [Prototype 13] Prototype 13 is a film obtained by forming the first surface layer using 69.7 wt% PE1, 20.0 wt% PE2, and 10.0 wt% PE3 as polyethylene resins, and 0.3 wt% AB1 as an antiblocking agent, in the same manner as Prototype 1.

[0088] [Prototype 14] Prototype 14 is a film obtained by forming the same film as in Prototype 13, except that the antiblocking agent in the second surface layer was changed from AB1 to AB2.

[0089] [Prototype 15] Prototype Example 15 is a film obtained by forming the first surface layer using the same process as Prototype Example 14, except that the first surface layer contained 89.7 wt% PE1 and 10.0 wt% PE4 as polyethylene resins and 0.3 wt% AB1 as an antiblocking agent.

[0090] [Prototype 16] Prototype 16 is a film obtained by forming the same film as in Prototype 15, except that the antiblocking agent in the second surface layer was changed from AB2 to AB6.

[0091] [Prototype 17] Prototype Example 17 is a film obtained by forming the film in the same manner as Prototype Example 5, except that the first surface layer contained 69.7 wt% PE1 and 30.0 wt% PE4 as polyethylene resins, and 0.3 wt% AB1 as an antiblocking agent.

[0092] [Prototype 18] Prototype 18 is a film obtained by forming the same film as in Prototype 17, except that the antiblocking agent in the second surface layer was changed from AB2 to AB5.

[0093] [Prototype 19] Prototype Example 19 is a film obtained by forming the film in the same manner as Prototype Example 3, except that the first surface layer contained 69.7 wt% PE1 and 30.0 wt% PE4 as polyethylene resins, and 0.3 wt% AB1 as an antiblocking agent.

[0094] [Prototype 20] Prototype Example 20 is a film obtained by film formation in the same manner as Prototype Example 19, except that the first surface layer contained 54.7 wt% PE1 and 45.0 wt% PE4 as polyethylene resins, and 0.3 wt% AB1 as an antiblocking agent, and the antiblocking agent in the second surface layer was changed from AB3 to AB5.

[0095] [Prototype 21] Prototype Example 21 is a film obtained by forming the film in the same manner as Prototype Example 1, except that the first surface layer contained 39.7 wt% PE1 and 60.0 wt% PE4 as polyethylene resins, and 0.3 wt% AB1 as an antiblocking agent.

[0096] [Prototype 22] Prototype 22 is a film obtained by forming the same film as in Prototype 19, except that the antiblocking agent in the second surface layer was changed from AB3 to AB6.

[0097] [Prototype 23] Sample 23 is a film obtained by forming the same film as Sample 20, except that the antiblocking agent in the second surface layer was changed from AB5 to AB6.

[0098] [Prototype 24] Prototype 24 is a film obtained by forming the same film as in Prototype 21, except that the antiblocking agent in the second surface layer was changed from AB1 to AB6.

[0099] [Table 1]

[0100] [Table 2]

[0101] [Table 3]

[0102] [Table 4]

[0103] The polyethylene films of Examples 1 to 24 were evaluated by measuring the modulus of elasticity (GPa) as the stiffness of the first surface layer, the central peak height (SRp2) as the three-dimensional surface roughness (μm) of the second surface layer, and the scratch haze (%). Furthermore, the scratch resistance and scratch resistance were calculated based on the measurement results of the film stiffness and three-dimensional surface roughness, and the pore volume of the antiblocking agent contained in the second surface layer, determined by nitrogen adsorption. The results of each measurement and their evaluation are shown in Tables 5 to 8 below.

[0104] [First surface layer stiffness] Regarding the stiffness of the first surface layer, the modulus of elasticity (GPa) of the first surface layer was measured on the cross section of the film using an atomic force microscope (AFM). For the measurement of the modulus of elasticity, cross sections of the films of prototypes 1 to 24 were cut out in the MD direction and perpendicular thereto using a microtome, and the films were set in the atomic force microscope so that the entire cross section of the film was included in the measurement plane. Measurements were carried out under the following measurement conditions. The obtained measurement results were analyzed using the analysis software "NanoScope Analysis," and the average value of the modulus of elasticity at 512 points corresponding to the first surface layer was calculated as the modulus of elasticity of the first surface layer. Measurement equipment: Bruker AXS NanoScope V / Dimension Icon Measurement mode: AFM-MA mode (PeakForce-QNM) Probe tip curvature radius: 30 nm Probe spring constant: 40N / m Measurement temperature: 23℃ Number of measurement points: 256 x 256 Scanning speed: 0.25Hz Poisson's ratio: 0.3

[0105] [3D surface roughness of the second surface layer] Regarding the three-dimensional surface roughness of the second surface layer, the central peak height (SRp2) of the three-dimensional surface roughness of the second surface layer was measured. The central peak height was measured using a three-dimensional surface roughness measuring instrument "SE3500K (manufactured by Kosaka Laboratory Co., Ltd.)" and an analytical device "TDA-22 (manufactured by Kosaka Laboratory Co., Ltd.)" under the following measurement conditions. The central peak height (SRp2), which corresponds to surface roughness, was measured in accordance with the measurement standard JIS B 0601. 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

[0106] [Calculation of scratch resistance] The scratch resistance value was calculated based on (SRp2 / V2) / E1 using the elastic modulus (E1) of the first surface layer determined by atomic force microscopy, the central peak height (SRp2) of the three-dimensional surface roughness of the second surface layer determined by measuring the three-dimensional surface roughness, and the pore volume (V2) of the antiblocking agent contained in the second surface layer determined by nitrogen adsorption method.

[0107] [Calculation of damage potential] The scratch resistance was calculated based on SRp2 / V2, using the central peak height (SRp2) in the three-dimensional surface roughness of the second surface layer obtained by measuring the three-dimensional surface roughness and the pore volume (V2) of the antiblocking agent contained in the second surface layer.

[0108] [Scratch haze measurement] The haze (%) of the film before rubbing was measured using a haze meter "NDH-8000 (manufactured by Nippon Denshoku Industries Co., Ltd.)" in accordance with JIS K 7136 (2000). Next, three test pieces were prepared for each prototype, and a friction tester "FRICTION TESTER TR (manufactured by Toyo Seiki Seisakusho Co., Ltd.)" was used. Referring to JIS K 7125 (1999), the second surface layer of the test piece was placed on the test table side and the first surface layer on the sliding piece side. The sliding piece was slid three times to rub the first and second surface layers together. The conditions were as follows: Material of the bottom of the slide: Rubber Test speed: 200 mm / min Travel distance: 510mm (170mm x 3 times) Total mass of the sliding piece: 2.17 kg

[0109] Next, the haze of the film on the sliding side that was rubbed together was measured at six points, and the maximum value (maximum haze) was read. Here, the haze of the film measured before rubbing was defined as H1 (%), and the average maximum haze of the three test pieces after rubbing was defined as H2 (%), and the scratch haze (ΔH = H2 - H1) was calculated. The obtained scratch haze value was evaluated as "excellent (◎)" when it was 7.1% or less, "good (○)" when it was 10% or less, and "poor (×)" when it was more than 10%.

[0110] [Table 5]

[0111] [Table 6]

[0112] [Table 7]

[0113] [Table 8]

[0114] [Results and Discussion] As can be seen from Tables 5 to 8, among the biaxially oriented polyethylene films of Prototypes 1 to 24, the films of Prototypes 1 to 21 had good scratch haze, indicating excellent scratch resistance on the film surface to be subjected to deposition processing, printing, etc. Therefore, the trends in film performance were examined from each prototype.

[0115] First, comparing Prototype 1 and Prototype 6, both samples shared the same second surface layer composition but slightly differed in the compositions of the first surface layer and base layer. The elastic modulus (E1), central peak height (SRp2), and antiblocking agent pore volume (V2) were approximately equal, resulting in roughly equivalent scratch haze values. Furthermore, Prototype 3 and Prototype 8 shared the same substrate layer and second surface layer composition but differed in the composition of the first surface layer. However, the elastic modulus (E1), central peak height (SRp2), antiblocking agent pore volume (V2), and scratch haze values ​​tended to be roughly similar. This suggests that the physical properties represented by the elastic modulus (E1), central peak height (SRp2), and antiblocking agent pore volume (V2) have a greater impact on the film surface's scratch susceptibility (scratch haze) than the composition of the first surface layer or base layer.

[0116] Comparing Prototype 3 and Prototype 4, Prototype 3 differed from Prototype 4 in the type of antiblocking agent in the second surface layer, and the elastic modulus (E1) and pore volume (V2) of the antiblocking agent were approximately equal, the central peak height (SRp2) was smaller, and the scratch haze was also lower. Similar trends were also observed between Prototype 8 and Prototype 10, Prototype 19 and Prototype 22, Prototype 20 and Prototype 23, etc. Therefore, it can be said that a smaller central peak height (SRp2) of the second surface layer tends to be less likely to scratch the surfaces of other layers.

[0117] Comparing Prototype 1 and Prototype 4, Prototype 1 differed from Prototype 4 in the type of antiblocking agent in the second surface layer, and the pore volume (V2) of the antiblocking agent was larger, resulting in lower scratch haze. A similar trend was observed for Prototype 6 and Prototype 8. Since a larger value for the pore volume (V2) of the antiblocking agent indicates a softer agent, it can be said that the larger the pore volume (V2) of the antiblocking agent in the second surface layer, i.e., the softer the antiblocking agent, the less likely it is to scratch the surface of other layers.

[0118] Based on the relationship between the central surface peak height (SRp2), pore volume (V2), and film surface scratchability, the formula (SRp2 / V2) can be used as an index of film surface scratchability. For example, when comparing the scratchability (SRp2 / V2) values ​​and scratch haze values ​​of Prototypes 1, 3, and 4, the (SRp2 / V2) values ​​are Prototype 1 < Prototype 3 < Prototype 4, and the scratch haze values ​​are Prototype 1 < Prototype 3 < Prototype 4.

[0119] Furthermore, comparing Prototype 1 and Prototype 2, Prototype 1 differed from Prototype 2 in the type of antiblocking agent in the second surface layer, and had approximately the same elastic modulus (E1), a smaller central peak height (SRp2), and a larger antiblocking agent pore volume (V2). In other words, Prototype 1 tended to be less susceptible to scratching than Prototype 2 in both central peak height (SRp2) and antiblocking agent pore volume (V2). The scratch resistance equation (SRp2 / V2) also satisfies the relationship Prototype 1<Prototype 2. Comparing the scratch haze of Prototype 1 and Prototype 2, Prototype 1 had a smaller value than Prototype 2, demonstrating favorable scratch haze. Similar trends were observed between prototypes 7 and 9, 11 and 12, 15 and 16, 21 and 24, and so on.

[0120] On the other hand, comparing Prototype 1 and Prototype 3, Prototype 1 differed in the type of antiblocking agent in the second surface layer from Prototype 3, had roughly the same elastic modulus (E1), and both the central peak height (SRp2) and the pore volume (V2) of the antiblocking agent were larger. This indicates that Prototype 1 tends to scratch the second surface layer more easily than Prototype 3 in terms of the central peak height (SRp2), while Prototype 1 tends to scratch the second surface layer less easily than Prototype 3 in terms of the pore volume (V2) of the antiblocking agent. Therefore, when comparing scratch haze based on the scratchability formula (SRp2 / V2), the (SRp2 / V2) value was greater for Prototype 1 than for Prototype 3, and the scratch haze value was greater for Prototype 1 than for Prototype 3. Similar trends were observed between Prototype 7 and Prototype 8, and between Prototype 17 and Prototype 18, etc.

[0121] Thus, from a comparison of the above prototype examples, it is believed that there is a correlation between the (SRp2 / V2) formula and the susceptibility to scratching the film surface (scratch haze), such that the smaller the (SRp2 / V2) value, the less likely the film surface is to be scratched, and the larger the value, the more likely the film surface is to be scratched.

[0122] Next, comparing Prototype 12 and Prototype 14, Prototype 14 shared the same composition of the second surface layer as Prototype 12, but differed in the compositions of the first surface layer and the base layer. The central peak height (SRp2) of the second surface layer and the pore volume (V2) of the antiblocking agent were approximately equal, the modulus of elasticity (E1) of the first surface layer were large, and scratch haze was low. Similar trends were observed for Prototype 23 and Prototype 16. Since a higher value of the modulus of elasticity (E1) indicates a higher rigidity of the film (layer), it can be said that the higher the value of the modulus of elasticity (E1) of the first surface layer, i.e., the higher the rigidity of the first surface layer, the more scratch-resistant the first surface layer tends to be.

[0123] Using the modulus of elasticity (E1) of the first surface layer, which is an index of the scratch resistance of the first surface layer, and the scratch resistance (SRp2 / V2) of the second surface layer, which is an index of the scratch susceptibility of the second surface layer, it is believed that the formula {(SRp2 / V2) / E1} can be used as an index of the scratch resistance (scratch resistance) of the film surface when the films are rubbed together. For example, when the scratch resistance {(SRp2 / V2) / E1} values ​​and scratch haze values ​​of Prototypes 12, 14, 16, and 23 are compared, the values ​​of {(SRp2 / V2) / E1} are Prototype 14 < Prototype 12 < Prototype 16 < Prototype 23, and the scratch haze values ​​are Prototype 14 < Prototype 12 < Prototype 16 < Prototype 23.

[0124] Furthermore, comparing Prototype 1 and Prototype 13, Prototype 13 shared the same composition of the base layer and second surface layer as Prototype 1, but differed in composition of the first surface layer, resulting in higher values ​​for both the modulus of elasticity (E1) and scratch resistance (SRp2 / V2) of the first surface layer. This indicates that, from the perspective of modulus of elasticity (E1), the first surface layer of Prototype 13 tends to be less susceptible to scratches than Prototype 1, while from the perspective of scratch resistance (SRp2 / V2), the second surface layer of Prototype 13 tends to be more susceptible to scratches than Prototype 1. Therefore, when comparing scratch haze based on the scratch resistance formula {(SRp2 / V2) / E1}, the value of {(SRp2 / V2) / E1} was greater for Prototype 13 than for Prototype 1, and the scratch haze value was greater for Prototype 13 than for Prototype 1. Similar trends were observed between Prototype Example 2 and Prototype Example 14, Prototype Example 4 and Prototype Example 18, Prototype Example 19 and Prototype Example 8, Prototype Example 21 and Prototype Example 13, and so on.

[0125] Thus, in relation to the relationship between the formula {(SRp2 / V2) / E1} and the resistance to scratches on the film surface when rubbed together (scratch haze), it is thought that there is a correlation such that the smaller the value of {(SRp2 / V2) / E1}, the less likely the film surface is to be scratched when rubbed together, and the larger the value, the more likely the film surface is to be scratched when rubbed together.

[0126] Comparing Prototype 2 and Prototype 5, both have the same composition of the second surface layer but different compositions of the first surface layer and base layer, and are approximately equal in elastic modulus (E1), central surface peak height (SRp2), and pore volume (V2) of the antiblocking agent, but the scratch haze of Prototype 5 was smaller than that of Prototype 2. In Prototype 5, the antiblocking agent used in the first surface layer has a smaller pore volume than the antiblocking agent used in Prototype 2. Since the smaller the pore volume of the antiblocking agent, the harder it is, it is thought that using a harder antiblocking agent in the first surface layer made the first surface layer of Prototype 5 less susceptible to scratches, resulting in better scratch haze than Prototype 2.

[0127] As described above, the scratch resistance of the film surface in each prototype showed that the physical properties of the first and second surface layers significantly affected scratch resistance. Furthermore, for the first surface layer, which is the side that would be scratched when the film was rubbed, the elastic modulus (E1) was used as an indicator of scratch resistance, while for the second surface layer, which is the side that would be scratched, the central peak height (SRp2) and the pore volume (V2) of the antiblocking agent were used as indicators of scratch resistance. It was found that the smaller the value calculated by the formula {(SRp2 / V2) / E1}, the better the film's performance. For biaxially oriented polyethylene films, the scratch haze values ​​of each prototype showed that films with a scratch resistance value of 16 or less had good scratch haze.

[0128] It was also found that the smaller the value calculated by the formula (SRp2 / V2) for the scratch resistance (scratch resistance) of the second surface layer, the better the performance tends to be. For biaxially oriented polyethylene films with a scratch resistance value of 16 or less, it was found that a scratch haze value of more than 10 was likely to increase, which is undesirable, based on the scratch haze values ​​of the various prototypes.

[0129] Furthermore, since the second surface layer does not necessarily have the same surface roughness (center surface peak height) even when the compositions are the same, such as between prototypes 3 and 8, or between prototypes 4 and 9, the significance of using three-dimensional surface roughness (center surface peak height) as an indicator of the scratch resistance of the film can be demonstrated.

[0130] [Creating laminated film] Laminate films were produced using the biaxially oriented polyethylene films of Prototype Examples 1 to 21. The first surface layer of the biaxially oriented polyethylene film of each prototype was subjected to corona treatment, and a two-component curing polyester adhesive was applied to this corona-treated surface at a rate of approximately 3 g / m. 2 The resulting laminated films corresponding to prototypes 1 to 21 were inspected visually for their appearance, and were found to be in good condition with no wrinkles or the like.

[0131] As shown and described above, the polyethylene film of the present invention has excellent scratch resistance by satisfying a scratch resistance value of 16 or less, calculated from the elastic modulus E1 (GPa) of the cross section of the first surface layer measured by atomic force microscopy (AFM), the central peak height SRp2 (μm) of the three-dimensional surface roughness of the second surface layer, and the pore volume V2 (ml / g) of the antiblocking agent contained in the second surface layer determined by nitrogen adsorption. Therefore, even if the first and second surface layers are rubbed against each other during winding or the like, scratching of the surface of the first surface layer is suppressed, allowing for appropriate surface treatments such as vapor deposition. Therefore, the biaxially oriented polyethylene film of the present invention is suitable for use as a laminate film to be subjected to printing or vapor deposition. [Industrial Applicability]

[0132] As described above, the biaxially oriented polyethylene film of the present invention has excellent scratch resistance on one of the film surfaces, which is the processed surface, and can be favorably subjected to vapor deposition and printing processes. Furthermore, by reducing the susceptibility to scratches on the surface other than the processed surface, the scratch resistance of the film after processing can also be improved. Therefore, the biaxially oriented polyethylene film of the present invention is a promising alternative to conventional films for vapor deposition and printing. In addition, by performing printing, vapor deposition, or the like using the biaxially oriented polyethylene film of the present invention, a laminate film can be produced that can suppress deterioration of the printed portion or vapor deposition layer. Therefore, the biaxially oriented polyethylene film of the present invention is a promising alternative to laminate films used in various packaging bags, etc. [Explanation of symbols]

[0133] 10 Biaxially oriented polyethylene film (base film) 20 First surface layer 30 Base material layer 40 Second surface layer 50, 50A, 50B Laminate Film 60 Printing Department 61 Full-page printing 62 partial printing 70 Sealant Film 80 Deposited layer

Claims

1. A polyethylene film comprising a first surface layer, a base layer, and a second surface layer containing an antiblocking agent, and stretched biaxially in the machine direction (MD) and the transverse direction (TD), The scratch resistance value shown in the following formula (i) is satisfied when the elastic modulus of the cross section of the first surface layer measured with an atomic force microscope (AFM) is E1 (GPa), the central peak height of the three-dimensional surface roughness of the second surface layer is SRp2 (μm), and the pore volume of the antiblocking agent contained in the second surface layer determined by a nitrogen adsorption method is V2 (ml / g): A biaxially oriented polyethylene film. [Equation 1]

2. 2. The biaxially oriented polyethylene film according to claim 1, wherein the elastic modulus E1 (GPa) of a cross section of the first surface layer measured with an atomic force microscope (AFM) is 0.1 to 5.0 GPa.

3. 3. The biaxially oriented polyethylene film according to claim 1, wherein a central peak height SRp2 (μm) in the three-dimensional surface roughness of the second surface layer and the pore volume V2 (ml / g) of the antiblocking agent contained in the second surface layer satisfy the value of scratch resistance represented by the following formula (ii): [Equation 2]

4. The biaxially oriented polyethylene film according to claim 3, wherein the central surface peak height SRp2 (μm) in the three-dimensional surface roughness of the second surface layer is 0.1 to 6.0 μm.

5. 4. The biaxially oriented polyethylene film according to claim 3, wherein the pore volume V2 (ml / g) of the antiblocking agent contained in the second surface layer is 0.3 to 2.0 ml / g.

6. 5. The biaxially oriented polyethylene film according to claim 4, wherein the pore volume V2 (ml / g) of the antiblocking agent contained in the second surface layer is 0.3 to 2.0 ml / g.

7. A laminate film comprising the biaxially oriented polyethylene film according to claim 1, a printed portion, and a sealant film made of a polyethylene resin.

8. A laminate film comprising the biaxially oriented polyethylene film according to claim 1, a vapor deposition layer, a printed portion, and a sealant film made of a polyethylene resin.

9. A packaging material comprising the laminate film according to claim 7 or 8.

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