Biaxially oriented polyethylene film, laminate film, and packaging

Abstract

The present invention provides a biaxially oriented polyethylene film, a laminate film, and a packaging that can suppress tearing and separation when the packaging is opened. [Solution] A biaxially oriented film is formed by stretching a polyethylene resin mainly in the longitudinal (MD) direction and the transverse (TD) direction, wherein at least one layer constituting the biaxially oriented film is a mixed resin layer in which the polyethylene resin is mixed with another resin different from the polyethylene resin, and the biaxially oriented film satisfies the relationship 0.040 ≤ [internal haze (%)] / [film thickness (μm)] ≤ 0.170, using the internal haze (%) calculated excluding the influence of the film surface and the film thickness (μm).

Description

Technical Field

[0001] The present invention relates to a biaxially stretched polyethylene film, a laminated film using this biaxially stretched polyethylene film, and a package using this laminated film.

Background Art

[0002] Generally, as packaging materials for products such as foods and daily necessities, films in which a plurality of resin films made of different types of resin materials are laminated are used. This type of laminated film can obtain good quality and performance as a film product by laminating films with various functions. Due to the increasing awareness of environmental issues in recent years, recycling has been demanded in the field of this type of resin film.

[0003] [[ID=1५]] However, in a film in which a plurality of types of resins are laminated, even if the resins constituting the film are remelted during recycling, they become a mixture of incompatible resins, so the quality of the recycled resources is greatly reduced and they are unsuitable as recycled materials. Therefore, films in which a plurality of laminated films are made of a single material (monomaterial) have been proposed.

[0004] In a laminated film of a single material, a polypropylene-based resin is generally used to obtain performance such as rigidity and heat resistance. In recent years, however, polyethylene-based laminated films have attracted attention as laminated films of a single material. As a polyethylene-based laminated film, for example, a polyethylene-based laminated film in which a polyethylene-based sealant film excellent in heat sealability and a base film made of a stretched film using the same type of polyethylene-based material as the sealant film are laminated is known (see Patent Document 1).

[0005] Laminated films of this type generally have poor tear resistance, which tends to result in poor opening when used to construct packaging. For example, when tearing open a package, a phenomenon called "separation" is more likely to occur, where the tear positions of the film on one side of the package and the other side are misaligned, especially at points further from the starting point of the tear. When separation occurs when tearing open a package, it can lead to problems such as contents spilling out easily or the torn pieces becoming difficult to separate from the package.

[0006] Therefore, conventionally, when manufacturing packaging using this type of laminated film as a packaging material, predetermined perforations were made to improve ease of opening. However, when perforations are made on packaging, other problems arise, such as an increase in the number of manufacturing steps and a decrease in tear resistance. Therefore, the inventors diligently studied means to suppress the separation of packaging when it is torn open, and found that the separation of packaging can be suppressed if the polyethylene-based stretched film used as the base film of the packaging possesses certain physical properties. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2024-55581 [Overview of the project] [Problems that the invention aims to solve]

[0008] The present invention has been made in view of the above points, and provides a biaxially oriented polyethylene film, a laminate film, and a packaging that can suppress tearing and separation when the packaging is torn open. [Means for solving the problem]

[0009] In other words, the first invention is a biaxially oriented film made mainly of polyethylene resin and stretched in two axial directions, the longitudinal (MD) direction and the transverse (TD) direction, wherein at least one layer constituting the biaxially oriented film is made of the polyethylene resin and the polyethylene resin incompatibility The present invention relates to a biaxially oriented polyethylene film, characterized in that it is a mixed resin layer obtained by mixing a resin with a biaxially oriented film, and the biaxially oriented film satisfies the following formula (i) using the internal haze (%) calculated excluding the influence of the film surface and the film thickness (μm).

[0010] 0.040 ≤ [Internal haze (%)] / [Film thickness (μm)] ≤ 0.170 …(i)

[0011] The second invention relates to the first invention, wherein the polyethylene resin and incompatibility The present invention relates to a biaxially oriented polyethylene film in which the resin is a polypropylene-based resin, and the entire biaxially oriented film contains 1 to 25% by weight of the polypropylene-based resin.

[0012] The third invention relates to a biaxially oriented polyethylene film in the first or second invention, wherein the biaxially oriented film consists of at least three layers: a surface layer A, a base layer, and a surface layer B.

[0013] The fourth invention relates to a biaxially oriented polyethylene film in which the base layer is the mixed resin layer, in the third invention.

[0014] The fifth invention relates to a biaxially oriented polyethylene film in which the thickness ratio of the base material layer in the biaxially oriented film is 70 to 95%, as described in the third invention.

[0015] The sixth invention relates to a biaxially oriented polyethylene film in which the thickness ratio of the base material layer in the biaxially oriented film is 70 to 95%, as described in the fourth invention.

[0016] The seventh invention relates to a laminated film, wherein a laminated film mainly composed of a polyethylene resin is laminated on at least one side of the biaxially stretched polyethylene film described in the first or second invention, and the proportion of the polyethylene-based single material is 80% by weight or more as a whole.

[0017] The eighth invention relates to a laminated film, wherein a laminated film mainly composed of a polyethylene resin is laminated on at least one side of the biaxially stretched polyethylene film described in the third invention, and the proportion of the polyethylene-based single material is 80% by weight or more as a whole.

[0018] The ninth invention relates to a laminated film, wherein a laminated film mainly composed of a polyethylene resin is laminated on at least one side of the biaxially stretched polyethylene film described in the fourth invention, and the proportion of the polyethylene-based single material is 80% by weight or more as a whole.

[0019] The tenth invention relates to a laminated film, wherein a laminated film mainly composed of a polyethylene resin is laminated on at least one side of the biaxially stretched polyethylene film described in the fifth invention, and the proportion of the polyethylene-based single material is 80% by weight or more as a whole.

[0020] The eleventh invention relates to a laminated film, wherein a laminated film mainly composed of a polyethylene resin is laminated on at least one side of the biaxially stretched polyethylene film described in the sixth invention, and the proportion of the polyethylene-based single material is 80% by weight or more as a whole.

[0021] The twelfth invention relates to a laminated film according to the seventh invention, wherein the tear separation amount measured by the following [1] is 90 mm or less.

[0022] [1] Delamination separation amount (mm): Overlap the laminated films of two A4-sized laminated films, heat one short side at 120°C for 1 second, then cool at 60°C to form a heat seal part. Make a cut at a position 60 mm from the end of the heat seal part and tear it to the other short side in the longitudinal direction. The maximum distance between the tear positions on the front and back sides of the two-layered laminated film after tearing is defined as the delamination separation amount.

[0023] The 13th invention relates to a laminated film in which the delamination separation amount measured in the above [1] is 90 mm or less in the 8th invention.

[0024] The 14th invention relates to a laminated film in which the delamination separation amount measured in the above [1] is 90 mm or less in the 9th invention.

[0025] The 15th invention relates to a laminated film in which the delamination separation amount measured in the above [1] is 90 mm or less in the 10th invention.

[0026] The 16th invention relates to a laminated film in which the delamination separation amount measured in the above [1] is 90 mm or less in the 11th invention.

[0027] The 17th invention relates to a package characterized by being made of the laminated film described in the 7th invention.

[0028] The 18th invention relates to a package characterized by being made of the laminated film described in the 8th invention.

[0029] The 19th invention relates to a package characterized by being made of the laminated film described in the 9th invention.

[0030] The 20th invention relates to a package characterized by being made of the laminated film described in the 10th invention.

[0031] The 21st invention relates to a package characterized by being made of the laminated film described in the 11th invention. [Effects of the Invention]

[0032] According to the first invention, a biaxially oriented polyethylene film is formed by stretching a polyethylene resin mainly in the longitudinal (MD) direction and the transverse (TD) direction, wherein at least one layer constituting the biaxially oriented film is made of the polyethylene resin and the polyethylene resin incompatibility The mixed resin layer is a mixture of resins, and the biaxially oriented film satisfies the relationship 0.040 ≤ [internal haze (%)] / [film thickness (μm)] ≤ 0.170, which is calculated using the internal haze (%) and film thickness (μm) after removing the influence of the film surface. Therefore, it is possible to suppress tearing and separation when a package is torn open using this film as a packaging material.

[0033] According to the biaxially oriented polyethylene film of the second invention, in the first invention, the polyethylene resin and incompatibility Since the resin is a polypropylene-based resin, and the entire biaxially oriented film contains 1 to 25% by weight of this polypropylene-based resin, it is inexpensive and readily available as another resin, and it enables the film to be made from a single material.

[0034] According to the biaxially oriented polyethylene film of the third invention, in the first or second invention, the biaxially oriented film consists of at least three layers: a surface layer A, a base layer, and a surface layer B, thus providing a film with excellent convenience.

[0035] According to the biaxially oriented polyethylene film of the fourth invention, in the third invention, since the base material layer is the mixed resin layer, tear resistance is easily obtained.

[0036] According to the biaxially oriented polyethylene film of the fifth invention, in the third invention, since the thickness ratio of the base material layer in the biaxially oriented film is 70-95%, tear resistance can be obtained more effectively.

[0037] According to the biaxially oriented polyethylene film of the sixth invention, in the fourth invention, since the thickness ratio of the base material layer in the biaxially oriented film is 70-95%, tear resistance can be obtained more effectively.

[0038] According to the seventh invention, the laminate film is formed by laminating a film mainly composed of polyethylene resin onto at least one side of the biaxially oriented polyethylene film described in the first or second invention, and the proportion of the polyethylene-based single material as a whole is 80% by weight or more. Therefore, the film can be made from a single material and can be suitably used as a recycled material.

[0039] According to the eighth invention, the laminate film is formed by laminating a film mainly composed of polyethylene resin onto at least one side of the biaxially oriented polyethylene film described in the third invention, and the proportion of the polyethylene-based single material as a whole is 80% by weight or more. This makes it possible to achieve a single material for the film, and it can be suitably used as a recycled material.

[0040] According to the laminate film of the ninth invention, a laminated film mainly composed of polyethylene resin is laminated on at least one side of the biaxially oriented polyethylene film described in the fourth invention, and the proportion of polyethylene-based single material as a whole is 80% by weight or more. Therefore, the film can be made from a single material and can be suitably used as a recycled material.

[0041] According to the laminate film of the 10th invention, a laminated film mainly composed of polyethylene resin is laminated on at least one side of the biaxially oriented polyethylene film described in the 5th invention, and the proportion of polyethylene-based single material as a whole is 80% by weight or more. Therefore, it is possible to achieve a single material for the film, and it can be suitably used as a recycled material.

[0042] According to the laminate film of the 11th invention, a laminated film mainly composed of polyethylene resin is laminated on at least one side of the biaxially oriented polyethylene film described in the 6th invention, and the proportion of polyethylene-based single material as a whole is 80% by weight or more. Therefore, it is possible to achieve a single material for the film, and it can be suitably used as a recycled material.

[0043] According to the laminate film of the 12th invention, in the 7th invention, since the tear-off distance is 90 mm or less, problems are less likely to occur when the film is used as packaging and torn open.

[0044] According to the laminate film of the 13th invention, in the 8th invention, since the tear-off distance is 90 mm or less, problems are less likely to occur when the film is used as packaging and torn open.

[0045] According to the laminate film of the 14th invention, in the 9th invention, since the tear-off distance is 90 mm or less, problems are less likely to occur when the film is used as packaging and torn open.

[0046] According to the laminate film of the 15th invention, in the 10th invention, since the tear-off distance is 90 mm or less, problems are less likely to occur when the film is used as packaging and torn open.

[0047] According to the laminate film of the 16th invention, in the 11th invention, since the tear-off distance is 90 mm or less, problems are less likely to occur when the film is used as packaging and torn open.

[0048] The packaging according to the 17th invention is made of the laminate film described in the 7th invention, and therefore is a promising alternative to existing packaging.

[0049] The packaging according to the 18th invention is made of the laminate film described in the 8th invention, and therefore is a promising alternative to existing packaging.

[0050] The packaging according to the 19th invention is made of the laminate film described in the 9th invention and is therefore a promising alternative to existing packaging.

[0051] The packaging according to the 20th invention is made of the laminate film described in the 10th invention, and is therefore a promising alternative to existing packaging.

[0052] The packaging according to the 21st invention is made of the laminate film described in the 11th invention, and is therefore a promising alternative to existing packaging. [Brief explanation of the drawing]

[0053] [Figure 1] This is a schematic diagram of the first procedure for measuring the amount of tearing and delamination of laminate film. [Figure 2] This is a second schematic diagram of the procedure for measuring the amount of tearing and delamination of laminate film. [Figure 3] This graph shows the relationship between the internal haze value per unit film thickness of the biaxially oriented polyethylene film in the example and the amount of tear separation (edge ​​side) of the laminate film. [Figure 4] This graph shows the relationship between the internal haze value per unit film thickness of the biaxially oriented polyethylene film in the example and the amount of tear separation (center side) of the laminate film. [Modes for carrying out the invention]

[0054] The biaxially oriented polyethylene film according to the present invention is a biaxially oriented film mainly composed of a polyethylene resin, stretched in two axial directions: the longitudinal (MD) direction and the transverse (TD) direction. This biaxially oriented polyethylene film can be used in various film products such as packaging materials, and is particularly suitable as a base film for laminate films. The laminate film is formed by laminating a film to be laminated on at least one side of the biaxially oriented polyethylene film of the present invention, and can be suitably used in various packaging materials (packaging bags) for products such as food, cosmetics, pharmaceuticals, daily necessities, parts, and other products.

[0055] The biaxially oriented polyethylene film of the present invention is composed of a single layer or multiple layers. A multi-layer biaxially oriented polyethylene film is preferably composed of at least three layers, for example, a surface layer A, a base layer, and a surface layer B. This biaxially oriented polyethylene film is obtained by known film forming methods such as the T-die method or the inflation method. In particular, it is preferable that a sheet formed by the T-die method is stretched and formed. Film forming by the T-die method is advantageous in that it provides the high thickness-to-thinness accuracy required for base films of laminate films.

[0056] In the biaxially oriented polyethylene film of the present invention, both sequential biaxial stretching and simultaneous biaxial stretching are well applicable. Because the formation of the biaxially oriented film results in resin orientation in both the longitudinal (MD) and transverse (TD) directions, improvements in thickness accuracy (such as thinness) and mechanical properties (such as strength) can be achieved, and it also offers excellent mass production capabilities. The stretching ratio is approximately 2 to 8 times in the longitudinal (MD) direction and 4 to 12 times in the transverse (TD) direction.

[0057] In the biaxially oriented polyethylene film of the present invention, it is preferable that the constituent material is a single material (monomaterial) of polyethylene resin. Here, a single material means that the constituent material of the entire film is mainly composed of the same type of resin material, for example, it is sufficient if the main material is blended in a proportion of about 75% or more, preferably about 85% or more, as the constituent material of the entire film. Because the film is made of a single material in this way, it can be suitably used as a recycled material.

[0058] The polyethylene resin that serves as the main raw material for biaxially oriented polyethylene film is appropriately selected from polyethylene resins derived from petroleum, biomass, material recycling, chemical recycling, etc., and is either a homopolymer of ethylene or a random copolymer of ethylene and α-olefins having 3 or more carbon atoms, such as propylene, 1-butene, 1-heptene, 1-hexene, 1-octene, and other α-olefins. A mixture of one or more of the above polyethylene resins may also be used.

[0059] In a biaxially oriented polyethylene film with at least three layers, the base layer is formed to be relatively thicker than the other layers. This base layer is mainly composed of a polyethylene resin. In the base layer, surfactants and the like may be added as needed, as long as they do not impair the objectives of the present invention. For example, by adding a surfactant, the slipperiness and antiblocking properties of the biaxially oriented polyethylene film can be improved.

[0060] Surface layer A corresponds to one side of the surface layer of the biaxially oriented polyethylene film, and can be used as the processed surface when surface processing such as vapor deposition is applied to the film surface. This surface layer A is mainly composed of a polyethylene resin. The polyethylene resin used for surface layer A is preferably the same type of polyethylene resin as the base layer, for example, it may be the same polyethylene resin as the base layer, or it may be a different polyethylene resin of the same type. Antiblocking agents and the like may be added to surface layer A as needed, as long as they do not impair the objectives of the present invention.

[0061] Surface layer B is the surface layer of the biaxially oriented polyethylene film opposite to surface layer A, and like surface layer A, it can be used as the processed surface when surface processing such as vapor deposition is applied to the film surface. Therefore, both sides of the biaxially oriented polyethylene film can be used as processed surfaces, which is highly convenient. Surface layer B is mainly composed of polyethylene resin, similar to surface layer A. The polyethylene resin used for surface layer B is preferably the same type of polyethylene resin as the base layer and surface layer A, for example, it may be the same polyethylene resin as the base layer and surface layer A, or it may be a different polyethylene resin of the same type. Antiblocking agents and the like may be added to surface layer B as needed, as long as they do not impair the objectives of the present invention.

[0062] In biaxially oriented polyethylene film, there are no particular restrictions on thickness, and it is determined appropriately according to demand and application, for example, it is preferably 5 to 100 μm, and more preferably 10 to 70 μm. Furthermore, when the biaxially oriented polyethylene film consists of multiple layers, for example three layers, it is preferable that the thickness ratio of the base layer is about 70 to 95%, and the thickness ratio of surface layer A and surface layer B is about 2.5 to 30%. If surface layer A or surface layer B is too thin, there is a risk of appearance defects due to uneven film thickness, and for example, if an antiblocking agent is added, it may fall off. If surface layer A or surface layer B is too thick, it may not be possible to impart functionality to surface layer A or surface layer B because the conditions for single-material formation cannot be met, and if an antiblocking agent is added, there is a risk of reduced transparency due to the relative increase in its amount.

[0063] The biaxially oriented polyethylene film of the present invention is characterized in that at least one layer constituting the film is a mixed resin layer, and satisfies the following formula (i) using internal haze (%) and film thickness (μm). 0.040 ≤ [Internal haze (%)] / [Film thickness (μm)] ≤ 0.170 …(i)

[0064] The mixed resin layer is a resin layer formed by mixing a polyethylene-based resin with another resin different from the polyethylene-based resin. The other resin different from the polyethylene-based resin is a resin that is incompatible with the polyethylene-based resin. In the mixed resin layer, since the incompatible resin is mixed with the polyethylene-based resin, a sea-island structure is formed within the resin layer. In this sea-island structure, the polyethylene-based resin is the "sea" portion, and the incompatible resin that does not mix with the polyethylene-based resin exists as "island" portions dispersed within the sea portion, imparting straight-line tearing properties to the biaxially oriented polyethylene film. This is thought to be because the island portions dispersed within the "sea" portion of the mixed resin layer restrict the tearing direction of the film.

[0065] However, if there are too few island portions dispersed in the sea portion of the mixed resin layer, proper straight-line tear resistance may not be achieved. This is thought to be because there are insufficient island portions to regulate the tearing direction of the film, making it difficult to adequately regulate the tearing direction. Conversely, if there are too many island portions dispersed in the sea portion of the mixed resin layer, proper straight-line tear resistance may not be achieved. This is thought to be because the excessively dispersed island portions hinder the progression of tearing, impairing straight-line tear resistance. Therefore, it is believed that by appropriately distributing island portions in the sea portion of the mixed resin layer, the tearing direction of the film is appropriately regulated, thereby improving straight-line tear resistance.

[0066] In biaxially oriented polyethylene films, if the film is composed of a single layer, the film is composed of a mixed resin layer. If the biaxially oriented polyethylene film is composed of multiple layers, one or more of the layers are composed of a mixed resin layer. For example, in a biaxially oriented polyethylene film with at least three layers, such as surface layer A, base layer, and surface layer B, one or more of the layers—surface layer A, base layer, and surface layer B—are mixed resin layers. In this case, it is preferable that the base layer is a mixed resin layer. Since the base layer is formed to be relatively thicker than the other layers, using a mixed resin layer increases the number of sea-island structures in the film, making it easier to obtain tear resistance. Furthermore, if the thickness ratio of the base layer is about 70-95%, tear resistance can be obtained more effectively.

[0067] Other resins different from polyethylene resins include, for example, polypropylene resins, polybutene resins, cycloolefin copolymers, and polystyrene resins. Of these miscible resins, polypropylene resins are preferred because they are commonly used as constituent materials for films, are inexpensive, and readily available. The preferred blending ratio of polypropylene resin in the mixed resin layer is 1 to 25% by weight for the entire biaxially oriented polyethylene film. If the blending ratio of polypropylene resin is too low, the sea-island structure in the biaxially oriented polyethylene film may be insufficient, and appropriate straight-line tear resistance may not be obtained. If the blending ratio is too high, it becomes impossible to monomaterialize the biaxially oriented polyethylene film.

[0068] The polypropylene resin used can be appropriately selected from polypropylene resins derived from petroleum, biomass, material recycling, chemical recycling, etc. The polypropylene resin can also be a mixture of one or more types from propylene homopolymers (homopolypropylene), copolymers of propylene with other olefins such as ethylene and butene (propylene-ethylene random copolymer, propylene-ethylene-butene random copolymer, etc.), propylene-ethylene block copolymer, propylene plastomer, propylene elastomer, etc.

[0069] Furthermore, the MFR is not particularly limited for polypropylene resins. From the viewpoint of resin fluidity, a preferred MFR for propylene resins is, for example, 0.5 to 20 g / 10 min, more preferably 1 to 15 g / 10 min, as measured under the conditions of 230°C and a load of 2.16 kg as described in JIS K 7210 (2014). If the MFR value is too low, the fluidity of the resin may be insufficient, which may hinder film formation, etc. If the MFR value is too high, the resin may flow excessively, which may impair the stretchability.

[0070] Equation (i) above is an index for understanding the sea-island structure in biaxially oriented polyethylene film, and is expressed using internal haze (%) and film thickness (μm). Internal haze is an index of the transparency inside the film, excluding the effect of surface irregularities, and is calculated using a measurement method compliant with JIS K 7136 (2000).

[0071] In internal haze, light transmitted through the film is scattered according to the film's internal structure, resulting in varying haze values. Therefore, the sea-island structure and film thickness affect the internal haze; for example, the more islands present in the sea-island structure or the thicker the film, the larger the internal haze value. By calculating the internal haze per unit film thickness, it is possible to understand the state of the sea-island structure in biaxially oriented polyethylene film, excluding the influence of film thickness.

[0072] In the biaxially oriented polyethylene film of the present invention, as shown in the examples described later, when the films to be laminated are laminated to form a laminate film, tearing is suppressed when the value of internal haze per unit film thickness falls within a predetermined range, and tearing tends to worsen when the value of internal haze per unit film thickness is too small or too large. A value of internal haze per unit film thickness that is too small is thought to be a state in which there are insufficient island portions in the sea-island structure and the restriction of the tearing direction is inadequate, and a value of internal haze per unit film thickness that is too large is thought to be a state in which there are too many island portions in the sea-island structure and the progression of tearing is hindered.

[0073] When the internal haze value per unit film thickness satisfies equation (i), it is considered that the island portions of the sea-island structure are appropriately dispersed, and the tearing direction of the film is appropriately regulated by the island portions. Therefore, by using a biaxially oriented polyethylene film having a mixed resin layer and a predetermined sea-island structure that satisfies the relationship of equation (i) as the base film for a laminate film, the laminate film itself becomes relatively easy to tear in a straight line. Accordingly, the biaxially oriented polyethylene film of the present invention can be suitably used as a packaging material to obtain a package that is less prone to tearing and separation when opened by tearing.

[0074] In the biaxially oriented polyethylene film of the present invention, the appearance, such as transparent or matte (non-glossy), can be appropriately selected depending on the application, such as the type of contents when used as packaging. The preferred appearance of the biaxially oriented polyethylene film can be defined by the haze (total haze) measured in accordance with JIS K 7136 (2000). For transparent films, the haze is preferably 20% or less, and more preferably 10% or less. For matte films, the haze is preferably 30% or more, and more preferably 40% or more. If the haze of the transparent or matte film does not meet the above conditions, it is undesirable because the appearance generally required for each application may not be obtained.

[0075] In the biaxially oriented polyethylene film of the present invention, it is preferable to apply a surface treatment to one or both surfaces in order to broaden the range of applications as a base film for laminate films. Examples of surface treatments include atmospheric pressure plasma treatment, flame treatment, and corona discharge treatment. On the surface-treated surface, it is preferable that the wetting tension measured by the wetting tension test method in accordance with JIS K 6768 (1999) is 36 mN / m or higher. If the wetting tension is too low, it is undesirable as it may cause printing defects or lamination defects. Surface treatment may also be applied to surface layer B as needed.

[0076] In the laminate film using the biaxially oriented polyethylene film of the present invention as the base film, the film to be laminated is laminated on at least one side of the biaxially oriented polyethylene film. From the viewpoint of improving recyclability by monomaterialization as a laminate film, the film to be laminated is preferably a film mainly composed of polyethylene resin. In this case, it is preferable that the proportion of polyethylene-based monomaterial as the overall constituent material of the laminate film is 80% by weight or more, preferably about 90% or more. This makes it possible to suitably utilize the laminate film as a recyclable material.

[0077] Examples of laminated films primarily composed of polyethylene resins include heat-sealable sealant films and other polyethylene films used to improve the functionality of the laminate film, such as its rigidity. The polyethylene resin used in the sealant film is selected from, for example, linear low-density polyethylene resin (LLDPE), high-density polyethylene (HDPE), and low-density polyethylene (LDPE), either individually or in appropriate combinations. Other polyethylene films can be selected from unoriented, uniaxially oriented, and biaxially oriented films depending on the purpose, but it is preferable to select a uniaxially oriented or biaxially oriented film from the viewpoint of the rigidity of the laminate film. When laminating a sealant film or the like to the surface layer of a biaxially oriented polyethylene film, it is preferable to improve adhesion by applying a surface treatment to the surface layer.

[0078] In the laminate film of the present invention, it is preferable that the tear separation amount is 90 mm or less. The tear separation amount (mm) is an indicator of the degree of separation of the laminate film. In measuring the tear separation amount, first, as shown in Figure 1(a), two A4-sized laminate films 10A and 10B were overlapped to form the test specimen 10C shown in Figure 1(b), and one short side 11 was heated at 120°C for 1 second, then cooled to 60°C to form a heat-sealed portion 15. Next, a cut 20 was made 60 mm from the edge of the heat-sealed portion 15, and the film was torn to the other short side 12 with the longitudinal direction (MD direction) as the tearing direction 25.

[0079] As shown in Figure 2, the tear line 26 on the front film 10A and the tear line 27 on the back film 10B of the torn test specimen 10D were defined as the tearing position, and the maximum distance D between them (in the illustrated example, the position on the other short side 12) was defined as the tear separation amount (mm). In laminate films where this tear separation amount exceeds 90 mm, the displacement of the tearing position is too large, making it easy for problems to occur when the package is used and torn open, such as contents spilling out or difficulty in separating the torn pieces. If the tear separation amount is 90 mm or less, the separation when the package is used and torn open is suppressed to a level that does not affect practicality, and problems when the package is torn open are less likely to occur.

[0080] In the laminate film of the present invention, the lamination strength between the biaxially oriented polyethylene film and the laminated film is preferably 0.4 N / 15 mm or higher, and more preferably 0.8 N / 15 mm or higher. The lamination strength is measured in accordance with JIS K 68954-3 (1999). If the lamination strength is too low, problems such as reduced tear resistance when used as packaging or increased tear strength making it difficult to tear may occur. By ensuring an appropriate lamination strength between the biaxially oriented polyethylene film and the laminated film, appropriate film performance such as tear resistance and tearability can be ensured.

[0081] Furthermore, in the case of laminate films, printing processes, gas barrier layers, etc., may be appropriately laminated onto the biaxially oriented polyethylene film, which is the base film, as needed. Printing processes are applied to the film surface of the biaxially oriented polyethylene film, and known methods such as screen printing, flexographic printing, offset printing, and gravure printing are used. When printing is performed on a biaxially oriented polyethylene film, it is preferable to perform the above-mentioned surface treatment, such as corona discharge treatment, on the film surface prior to printing in order to improve ink absorption and adhesion.

[0082] The gas barrier layer is applied directly to the surface layer or via an anchor coat layer to provide barrier properties against water vapor, oxygen, etc. When a gas barrier layer is applied to a biaxially oriented polyethylene film, the film surface is pre-treated by corona discharge treatment or the like to improve wettability and adhesion to the anchor coat layer and the gas barrier layer.

[0083] The anchor coat layer is not particularly limited and can be made of polyurethane resin, polyester resin, etc. The gas barrier layer is also not particularly limited and can be made of a metal thin film layer or an inorganic oxide layer. The metal thin film layer is a thin film layer made of known metals such as aluminum, gold, silver, copper, and chromium, and may also be a thin film layer of oxides, sulfides, or nitrides of these metals. Furthermore, the metal thin film layer may be a single layer or multiple layers of two or more different or identical types. The inorganic oxide layer consists 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 types of inorganic oxides.

[0084] The laminate film of the present invention can be used to produce a package by appropriately manufacturing a bag using a known bag-making method. Since this package is made of a single-material (monomaterial) laminate film, it is easily recyclable and is promising as a replacement for existing package materials. In particular, in this package, since the laminate film uses a biaxially oriented polyethylene film with a mixed resin layer that satisfies the relationship of formula (i) as the base film, tearing and separation when opening is effectively suppressed. [Examples]

[0085] [Preparation of biaxially oriented polyethylene film] Biaxially oriented polyethylene films, consisting of three layers—surface layer A, base layer, and surface layer B—were prepared by blending each material described later in predetermined proportions (by weight) according to the following procedure. First, each material was supplied to an extruder, melted, kneaded, and formed into a sheet by co-extrusion of the three layers—surface layer A, base layer, and surface layer B—using the T-die method. Subsequently, the co-extruded sheet was stretched five times in the longitudinal (MD) direction by inter-roll stretching and eight times in the transverse (TD) direction by tenter stretching. After that, the surface of surface layer A was subjected to corona treatment to obtain a biaxially oriented polyethylene film. The stretching conditions were as follows: roll preheating temperature in the longitudinal (MD) direction was 110-112°C, roll stretching temperature was 115-117°C, and transverse (TD) direction preheating temperature was 143-151°C, stretching temperature was 122-124°C. The materials used in each layer of each prototype are shown in Tables 1-4 below.

[0086] The following resins were used as constituent materials for surface layer A, base layer, and surface layer B. For each material, the melt flow rate (MFR) was measured in accordance with JIS K 7210 (2014) under conditions of 190°C and 2.16 kg, or 230°C and 2.16 kg. Additives were omitted.

[0087] [Polyethylene resin] PE1: Linear low-density polyethylene (Dow Chemical Company; "TF80"), MFR (190℃, 2.16kg): 1.7g / 10min, density 0.926g / cm³ 3 , melting point 127℃ • PE2: High-density polyethylene (manufactured by Nippon Polyethylene Co., Ltd.; "HY430"), MFR (190℃, 2.16kg): 0.8g / 10min, density 0.954g / cm³ 3 , melting point 136℃ • PE3: High-density polyethylene (manufactured by Nippon Polyethylene Co., Ltd.; "HF562"), MFR (190℃, 2.16kg): 7.5g / 10min, density 0.963g / cm³ 3 , melting point 135℃ • PE4: Polyethylene elastomer (manufactured by Mitsui Chemicals, Inc.; "A-4085S"), MFR (190℃, 2.16kg): 3.6g / 10min, density 0.885g / cm³ 3 , melting point 66℃

[0088] [Resins other than polyethylene-based resins] • PP1: Propylene-ethylene random copolymer (manufactured by Nippon Polypropylene Co., Ltd.; "WFX4M"), MFR (230℃, 2.16kg): 7.0g / 10min, melting point 125℃ • PP2: Propylene-ethylene random copolymer (manufactured by Nippon Polypropylene Co., Ltd.; "WFW4M"), MFR (230℃, 2.16kg): 7.0g / 10min, melting point 135℃ • PP3: Propylene-ethylene-butene random copolymer (manufactured by Nippon Polypropylene Co., Ltd.; "FW4BA"), MFR (230℃, 2.16kg): 7.0g / 10min, melting point 139℃ • PP4: Homopolypropylene copolymer (manufactured by Nippon Polypropylene Co., Ltd.; "FB3B"), MFR (230℃, 2.16kg): 7.5g / 10min, melting point 165℃ • PP5: Propylene-ethylene block copolymer (manufactured by Nippon Polypropylene Co., Ltd.; "BC3HF"), MFR (230℃, 2.16kg): 8.5g / 10min, melting point 165℃ • PP6: Propylene-ethylene random copolymer (manufactured by Nippon Polypropylene Co., Ltd.; "WFX6"), MFR (230℃, 2.16kg): 2.0g / 10min, melting point 125℃ • COC: Cyclic olefin copolymer (manufactured by Polyplastics Co., Ltd.; "8007F-600"), density 1.010 g / cm³ 3 BC1: Butene copolymer (manufactured by Mitsui Chemicals, Inc.; "BL2491M"), MFR (190℃, 2.16kg): 4.0g / 10min, melting point 100℃

[0089] [Prototype Example 1] Prototype Example 1 is a biaxially oriented polyethylene film in which surface layer A is composed of PE1:80.0% by weight and PE4:20.0% by weight, the base layer is composed of PE1:95.0% by weight and PP2:5.0% by weight, and surface layer B is composed of PE1:100% by weight. The film thickness (total thickness) is 25 μm, the layer thickness (layer ratio) of each layer relative to the total thickness is surface layer A / base layer / surface layer B = 1 / 18 / 1, and the thickness ratio of the base layer relative to the total thickness is 90.0%.

[0090] [Prototype Example 2] Prototype Example 2 is a biaxially oriented polyethylene film that is identical to Prototype Example 1 except that the base layer is changed to PE1:90.0% by weight and PP2:10.0% by weight.

[0091] [Prototype Example 3] Prototype Example 3 is a biaxially oriented polyethylene film that is identical to Prototype Example 1 except that the base layer is changed to PE1:80.0% by weight and PP2:20.0% by weight.

[0092] [Prototype Example 4] Prototype Example 4 is a biaxially oriented polyethylene film that is identical to Prototype Example 2 except that the base layer is changed to PE1:90.0% by weight and PP1:10.0% by weight.

[0093] [Prototype Example 5] Prototype Example 5 is a biaxially oriented polyethylene film that is identical to Prototype Example 2, except that the base layer is changed to PE1:90.0% by weight and PP3:10.0% by weight.

[0094] [Prototype Example 6] Prototype 6 is a biaxially oriented polyethylene film in which the base layer of prototype 3 is changed to PE1: 60.0% by weight, PE2: 13.2% by weight, PE3: 6.8% by weight, and PP2: 20.0% by weight, while all other aspects remain the same.

[0095] [Prototype Example 7] Prototype example 7 is a biaxially oriented polyethylene film in which surface layer A is composed of PE1:50.0% by weight, PE4:20% by weight, and PP2:30.0% by weight, the base layer is PE1:100.0% by weight, and surface layer B is PE1:100.0% by weight.

[0096] [Prototype Example 8] Prototype Example 8 is a biaxially oriented polyethylene film that is identical to Prototype Example 7, except that the layer thickness (layer ratio) of each layer relative to the total thickness is changed to Surface Layer A / Base Layer / Surface Layer B = 3 / 16 / 1, and the thickness ratio of the base layer relative to the total thickness is changed to 80.0%.

[0097] [Prototype Example 9] Prototype Example 9 is a biaxially oriented polyethylene film in which the surface layer B of Prototype Example 2 is changed to PE1:70.0% by weight and PP2:30.0% by weight, while all other aspects remain the same.

[0098] [Prototype Example 10] Prototype 10 is a biaxially oriented polyethylene film that is identical to that of Prototype 2, except that the base layer is changed to PE1:90.0% by weight and PP4:10.0% by weight.

[0099] [Prototype Example 11] Prototype 11 is a biaxially oriented polyethylene film that is identical to that of Prototype 2, except that the base layer is changed to PE1:90.0% by weight and PP5:10.0% by weight.

[0100] [Prototype Example 12] Prototype Example 12 is a biaxially oriented polyethylene film in which surface layer A is PE1:100.0 wt%, base layer is PE1:80.0 wt% and COC:20.0 wt%, and surface layer B is PE1:100 wt%, the film thickness (total thickness) is 20 μm, and the layer thickness (layer ratio) of each layer relative to the total thickness is surface layer A / base layer / surface layer B = 1 / 18 / 1.

[0101] [Prototype Example 13] Prototype 13 is a biaxially oriented polyethylene film that is identical to Prototype 3 except that the layer thickness (layer ratio) of each layer relative to the total thickness is changed to Surface Layer A / Base Layer / Surface Layer B = 2 / 15 / 3, and the thickness ratio of the base layer relative to the total thickness is changed to 75.0%.

[0102] [Prototype Example 14] Prototype 14 is a biaxially oriented polyethylene film that is identical to Prototype 3 except that the layer thickness (layer ratio) of each layer relative to the total thickness is changed to Surface Layer A / Base Layer / Surface Layer B = 0.5 / 19 / 0.5, and the thickness ratio of the base layer to the total thickness is changed to 95.0%.

[0103] [Prototype Example 15] Prototype 15 is a biaxially oriented polyethylene film that is identical to that of Prototype 1, except that the base layer is changed to PE1:70.0% by weight and PP2:30.0% by weight.

[0104] [Prototype Example 16] Prototype 16 is a biaxially oriented polyethylene film in which the base layer of Prototype 1 is changed to PE1:60.0% by weight and PP2:40.0% by weight, while all other aspects remain the same.

[0105] [Prototype Example 17] Prototype 17 is a biaxially oriented polyethylene film that is identical to that of Prototype 2, except that the base layer is changed to PE1:90.0% by weight and BC1:10.0% by weight.

[0106] [Prototype Example 18] Prototype 18 is a biaxially oriented polyethylene film that is identical to prototype 13, except that the surface layer B is made of PE1:70.0% by weight and PP6:30.0% by weight, the layer thickness (layer ratio) of each layer relative to the total thickness is changed to surface layer A / base layer / surface layer B = 1 / 17 / 2, and the thickness ratio of the base layer relative to the total thickness is changed to 85.0%.

[0107] [Prototype Example 19] Prototype 19 is a biaxially oriented polyethylene film that is identical to prototype 18 except that the surface layer B is changed to PE1:40.0% by weight and PP6:60.0% by weight.

[0108] [Prototype Example 20] Prototype example 20 is a biaxially oriented polyethylene film in which surface layer A is PE1:100.0% by weight, base layer is PE1:100.0% by weight, and surface layer B is PE1:100.0% by weight, with the layer thickness (layer ratio) of each layer relative to the total thickness being surface layer A / base layer / surface layer B = 1 / 18 / 1.

[0109] [Prototype Example 21] Prototype 21 is a biaxially oriented polyethylene film in which the base layer of Prototype 1 is changed to PE1:100.0% by weight, while all other aspects remain the same.

[0110] [Prototype Example 22] Prototype 22 is a biaxially oriented polyethylene film that is identical to that of Prototype 6, except that the base layer is changed to PE1: 80.0% by weight, PE2: 13.2% by weight, and PE3: 6.8% by weight.

[0111] [Table 1]

[0112] [Table 2]

[0113] [Table 3]

[0114] [Table 4]

[0115] For the biaxially oriented polyethylene films of prototype examples 1 to 22, the proportion of polypropylene in the entire biaxially oriented polyethylene film was calculated. In addition, the internal haze was measured, and the value of internal haze per unit film thickness was calculated. The obtained results are shown in Tables 5 to 8 below.

[0116] [Percentage of materials other than polyethylene] The percentage (by weight) of non-polyethylene materials in the biaxially oriented polyethylene films of prototype examples 1 to 22 was calculated based on the blending ratio of non-polyethylene resins (PP1 to PP6, COC, BC1) and the layer ratio of the resin layers containing non-polyethylene resins.

[0117] [Internal haze] For the biaxially oriented polyethylene films of prototype examples 1 to 22, the internal haze was calculated using a measurement method compliant with JIS K 7136 (2000). Internal haze (%) is an indicator of the transparency inside the film, excluding the influence of the film surface. In calculating the internal haze, oil (Olympus Corporation; "IMMERSION OIL") was first dropped onto the film surface, and the film was sandwiched between slides whose haze had been previously measured to create a test specimen. The haze of the test specimen was then measured as the haze of the film. The haze was measured using a haze meter (Nippon Denshoku Industries Ltd.; "Haze Meter NDH-8000"). Then, the measured film haze was designated as H, and the hazes of the two slides as G0 and G1, and the internal haze was calculated using the following formula. Internal haze = H - G0 - G1

[0118] [Internal haze per unit film thickness] For the biaxially oriented polyethylene films of prototype examples 1 to 22, the internal haze per unit film thickness ([internal haze (%)] / [film thickness (μm)]) was calculated based on the calculated internal haze value and film thickness.

[0119] Laminate films corresponding to prototypes 1-22 were fabricated by dry laminating (adhesive layer) a 50 μm thick unoriented polyethylene film (Futamura Chemical Co., Ltd.; LL-XUMN#50) onto the surface layer A of the biaxially oriented polyethylene films of prototypes 1-22. For the dry lamination, the adhesive layer was prepared by mixing the main agent (Toyo Morton Co., Ltd.; TM-329), the curing agent (Toyo Morton Co., Ltd.; CAT-26B), and ethyl acetate, and applying approximately 3 g / m² to the surface of surface layer A. 2 After applying the coating and drying it at 80°C, an unstretched polyethylene film was laminated to it.

[0120] For the laminate films corresponding to prototype examples 1 to 22, the proportion of polyethylene in the entire laminate film was calculated. In addition, the lamination strength of the biaxially oriented polyethylene film and the unoriented polyethylene film for prototype examples 1 to 22, and the amount of tear separation of the laminate films corresponding to prototype examples 1 to 22 were measured. The obtained results are shown in Tables 5 to 8 below.

[0121] [Percentage of polyethylene] The percentage of polyethylene (by weight) in the laminate film corresponding to prototype examples 1 to 22 was calculated based on the blending ratio of polyethylene-based resin in each film (layer) and the layer ratio, assuming the laminate film consisted of a biaxially oriented polyethylene film, an adhesive layer, and an unoriented polyethylene film.

[0122] [Lamination strength] Lamination strength was measured in accordance with JIS K 6854-3 (1999). In this measurement, rectangular test pieces measuring 15 mm x 200 mm (TD direction x MD direction of the film) were cut from the laminate film corresponding to prototype examples 1 to 22. The unoriented polyethylene film and biaxially oriented polyethylene film were spread 180 degrees vertically and fixed to a tensile testing machine (Shimadzu Corporation; EZ-SX). The unoriented polyethylene film and biaxially oriented polyethylene film were then pulled 180 degrees vertically (MD direction) at a test speed of 50 mm / min, and the adhesive portion of the two films was peeled off to determine the lamination strength. Lamination strength was rated as "Excellent (◎)" if it was 0.8 N / 15 mm or higher, "Good (○)" if it was 0.4 N / 15 mm or higher, and "Poor (×)" if it was less than 0.4 N / 15 mm.

[0123] [Amount of tearing and divergence] Biaxially oriented polyethylene films for prototypes 1-22 were cut to A4 size from the end of the film roll, and laminated with unoriented polyethylene film by dry lamination as described above to produce laminated films for the roll end corresponding to prototypes 1-22. Two of each of the laminated films for the roll end corresponding to prototypes 1-22 were prepared, and the unoriented polyethylene films were overlapped. On one of the shorter sides, a heat-sealed section was formed by heating at 120°C for 1 second using a heat-temperature controlled electric sealer (manufactured by Fuji Impulse Co., Ltd.; OPL-350-MD NP), followed by cooling to 60°C, to produce test specimen A.

[0124] Furthermore, the biaxially oriented polyethylene films of prototype examples 1 to 22 were cut to A4 size from the center of the film roll, and after creating a laminated film in the same manner as test specimen A above, the unoriented polyethylene films were overlapped and a heat-sealed section was formed on one of the short sides to create test specimen B.

[0125] For test specimens A and B corresponding to prototype examples 1-22, a cut was made 60 mm from the edge of the heat-sealed portion, and the specimens were torn along the longitudinal direction (MD direction) to the other short side. During tearing, test specimens A and B were placed on a table, weights were placed on the right side of test specimens A and B to prevent the film from lifting, and the left side was positioned towards the user. For the torn test specimens A and B, the maximum distance of the displacement at the tear line between the tear line of the front film and the tear line of the back film was measured using calipers. The same procedure was performed three times for each test specimen A and B corresponding to prototype examples 1-22, and the average of the obtained measurements was calculated as the tear separation amount (mm). A tear separation amount of 90 mm or less was classified as "Good (○)", and an amount exceeding 90 mm was classified as "Unacceptable (×)". The tear separation amount for test specimen A is denoted as "Tear separation amount (end side)," and the tear separation amount for test specimen B is denoted as "Tear separation amount (center side)."

[0126] [comprehensive evaluation] For the overall evaluation of prototypes 1 to 22, a "○ (Good)" rating was given if all evaluations for each item—laminate strength, tear separation amount (edge ​​side), and tear separation amount (center side)—received a "○ (Good)" or higher rating, while a "× (Unacceptable)" rating was given if even one item received an "× (Unacceptable)" rating.

[0127] [Table 5]

[0128] [Table 6]

[0129] [Table 7]

[0130] [Table 8]

[0131] [Results and Discussion] Prototypes 20-22 are conventional biaxially oriented polyethylene films, and as shown in Table 4, all layers—surface layer A, base layer, and surface layer B—are composed of polyethylene resin. As shown in Table 8, in the laminate films using the biaxially oriented polyethylene films of prototypes 20 and 21, the tear separation amount (center side) was good, but the tear separation amount (edge ​​side) was large, and the separation during tearing could not be sufficiently suppressed. In addition, in the laminate film using the biaxially oriented polyethylene film of prototype 22, both the tear separation amount (edge ​​side) and the tear separation amount (center side) were large, and the separation during tearing could not be sufficiently suppressed.

[0132] In particular, in the laminate films of prototype examples 20 and 21, as can be seen from the comparison of tear separation amount (center side) and tear separation amount (edge ​​side), the degree of tear separation differs depending on whether the biaxially oriented polyethylene film is cut from the edge side of the film roll or from the center side of the film roll. This is thought to be due to the bowing phenomenon, which occurs when there is a difference in molecular orientation between the film edge side and the film center side during the manufacturing of biaxially oriented polyethylene film, indicating that the tear performance of the laminate film differs depending on the position of the film roll used (e.g., edge side or center side). In other words, in the laminate films of prototype examples 20 and 21, even if biaxially oriented polyethylene film with the same composition is used, it may not be possible to obtain tear performance that meets practical requirements, and it may be difficult to stably supply products with appropriate performance.

[0133] On the other hand, the biaxially oriented polyethylene films of prototype examples 1 to 19, as shown in Tables 1 to 4, are examples in which at least one of the layers—surface layer A, base layer, and surface layer B—is a mixed resin layer in which a resin other than polyethylene resin (polypropylene resin, cyclic olefin copolymer, butene copolymer) is mixed. As shown in Tables 5 to 8, the laminate films using the biaxially oriented polyethylene films of prototype examples 1 to 19 showed good tear separation (edge ​​side) and tear separation (center side), and the separation during tearing was suppressed to a level that does not affect practicality.

[0134] Examples 1-3, 15, and 16 are examples where the blending ratio of polypropylene resin in the base layer was changed. In Examples 1-3, 15, and 16, the blending ratio of polypropylene resin increased in the order of Examples 1, 2, 3, 15, and 16, but the amount of tear separation decreased in the order of Examples 1, 15, 16, 2, and 3, indicating that the amount of tear separation does not necessarily decrease in proportion to the blending ratio of polypropylene resin. Examples 2, 4, 5, 10, and 11 are examples where the type of polypropylene resin was changed while keeping the blending ratio of polypropylene resin in the base layer the same. Examples 2, 4, 5, 10, and 11 showed that even with the same blending ratio of polypropylene resin, there were slight differences in the amount of tear separation depending on the type. On the other hand, Examples 3 and 6 are examples where the type of polyethylene resin in the base layer was changed. As shown in prototype examples 3 and 6, slight differences in tearing and delamination occur even when different types of polyethylene resin are used.

[0135] Examples 7 and 8 show that the surface layer A, which is laminated with unoriented polyethylene film, is a mixed resin layer, and in particular, example 8 is an example in which the layer ratio of surface layer A is increased compared to example 7. It was shown that tearing and separation is suppressed even when the mixed resin layer is surface layer A, which is laminated with unoriented polyethylene film. Furthermore, it was shown that when the layer ratio of surface layer A, which is the mixed resin layer, is increased and the proportion of polypropylene resin is increased, the amount of tearing and separation decreases. On the other hand, examples 18 and 19 show that the surface layer B is a mixed resin layer. It was shown that tearing and separation is suppressed even when the mixed resin layer is surface layer B, which is not laminated with unoriented polyethylene film. Therefore, it can be said that tearing and separation can be appropriately suppressed even when the mixed resin layer is a layer other than the base layer.

[0136] Prototype Example 9 is an example of a mixed resin layer with multiple layers (base layer, surface layer B). It was shown that separation is suppressed even when there are multiple mixed resin layers. Furthermore, in Prototype Example 9, although the proportion of polypropylene resin (10.5 wt%) is lower than that of Prototype Examples 3 and 6 (18 wt%), it was shown that the amount of tear separation was extremely small, to a similar degree.

[0137] Examples 12 and 17 are examples in which resins other than polyethylene-based resins were used, specifically resins different from polypropylene-based resins (cyclic olefin copolymers and butene copolymers). In example 12, which incorporated cyclic olefin copolymers, it was shown that the amount of tear separation was extremely small, and particularly excellent straight-line tearing properties were obtained. In example 17, which incorporated butene copolymers, it was shown that straight-line tearing properties comparable to those obtained when polypropylene-based resins were incorporated were obtained.

[0138] Prototype examples 3, 13, and 14 are examples in which the thickness of the base layer (mixed resin layer) of the biaxially oriented polyethylene film was changed. In prototype examples 3, 13, and 14, the thickness of the base layer (mixed resin layer) increased in the order of prototype example 13, 3, and 14, but the amount of tear separation decreased in the order of prototype example 13, 14, and 3, indicating that the amount of tear separation does not necessarily decrease in proportion to the thickness of the base layer (mixed resin layer).

[0139] A comparison of prototypes 1-19 and 20-22 showed that biaxially oriented polyethylene films tended to effectively suppress tearing by incorporating a mixed resin layer containing a resin other than polyethylene. However, differences in tearing and delamination arose due to various factors such as the type and proportion of resins used, and which of the multiple layers was designated as the mixed resin layer. Therefore, it is considered difficult to identify a correlation between the proportion of the resin other than polyethylene and the amount of tearing and delamination.

[0140] Therefore, we focused on the sea-island structure between the polyethylene-based resin and other resins that make up the mixed resin layer, and considered using internal haze to understand its state, calculating the internal haze per unit film thickness. As a result, we found that when the internal haze per unit film thickness is approximately 0.040 or higher (Prototype Examples 1-19), separation can be suppressed, but when it is less than 0.040 (Prototype Examples 20-22), separation cannot be sufficiently suppressed.

[0141] Furthermore, Figure 3 shows a graph plotting the amount of tear separation (edge ​​side) corresponding to the internal haze value per unit film thickness for each prototype example 1 to 22, with the internal haze per unit film thickness on the horizontal axis and the amount of tear separation on the vertical axis. Figure 4 shows a graph plotting the amount of tear separation (center side) corresponding to the internal haze value per unit film thickness for each prototype example 1 to 14.

[0142] As can be seen from Figures 3 and 4, in the laminate films of prototypes 1 to 22, regardless of the usage position of the roll of biaxially oriented polyethylene film (e.g., end or center), prototypes with relatively large tear separation amounts were distributed in the range where the internal haze per unit film thickness was below approximately 0.040, prototypes with relatively small tear separation amounts were distributed in the range of approximately 0.080 to 0.100, and prototypes with relatively large tear separation amounts were distributed in the range above approximately 0.120. From this, it can be considered that if the value of the internal haze per unit film thickness is too small or too large, the tear separation amount increases and the straight tear resistance deteriorates, and when the value of the internal haze per unit film thickness approaches a predetermined value (around 0.080 to 0.100), the tear separation amount decreases and the straight tear resistance improves.

[0143] Since internal haze is thought to manifest as a high or low haze value depending on the state of the sea-island structure in the biaxially oriented polyethylene film, a low internal haze value indicates a state where there are few island portions dispersed in the sea portion of the mixed resin layer, while a high value indicates a state where there are many island portions dispersed in the sea portion of the mixed resin layer. Furthermore, since the amount of tear separation tends to decrease as the internal haze value per unit film thickness approaches a predetermined value, it is thought that good straight-line tear resistance can be obtained when the island portions are appropriately dispersed in the sea portion of the mixed resin layer. From these points, it is thought that if the island portions are appropriately dispersed in the mixed resin layer, the island portions appropriately restrict the tear direction and impart straight-line tear resistance, if there are few island portions, the restriction of the tear direction by the island portions does not work sufficiently, and if there are many island portions, the island portions hinder the progression of tearing and impede straight-line tear resistance.

[0144] Therefore, in biaxially oriented polyethylene film, there is generally a correlation between the internal haze per unit film thickness and the amount of tear separation of the laminate film, as shown by the curves in Figures 3 and 4. Thus, the internal haze per unit film thickness is useful as an indicator of the degree of tear separation of the laminate film. Considering the curves in Figures 3 and 4, it is considered that an internal haze of approximately 0.040 to 0.170 per unit film thickness is sufficient to satisfy the acceptable tear separation amount of 90 mm or less for the laminate film. [Industrial applicability]

[0145] As described above, in the biaxially oriented polyethylene film of the present invention, at least one layer constituting the film is a mixed resin layer in which a polyethylene-based resin is mixed with another resin different from the polyethylene-based resin, and the internal haze per unit film thickness satisfies the relationship of 0.040 to 0.170, thereby suppressing tearing and separation when a package using this film as a packaging material is torn open. For this reason, it is promising as a replacement for conventional biaxially oriented polyethylene films, laminate films using this biaxially oriented polyethylene film, and packaging products using this laminate film. [Explanation of Symbols]

[0146] 10A, 10B Laminating Film 10C test specimen 10D Torn specimen 11 One of the shorter sides 12 The other short side 15 Heat seal section 20 cuts 25. Tear direction 26,27 Tear line D tear deviation amount

Claims

1. A biaxially oriented film made mainly of polyethylene resin, stretched in two axial directions: the longitudinal (MD) direction and the transverse (TD) direction. At least one layer constituting the biaxially oriented film is a mixed resin layer obtained by mixing the polyethylene resin with a resin that is incompatible with the polyethylene resin. The biaxially oriented polyethylene film is characterized by satisfying the following formula (i) using the internal haze (%) calculated after removing the influence of the film surface and the film thickness (μm). 0.040 ≤ [Internal haze (%)] / [Film thickness (μm)] ≤ 0.170 …(i)

2. The biaxially oriented polyethylene film according to claim 1, wherein the resin that is incompatible with the polyethylene resin is a polypropylene resin, and the entire biaxially oriented film contains 1 to 25% by weight of the polypropylene resin.

3. The biaxially oriented polyethylene film according to claim 1 or 2, wherein the biaxially oriented film comprises at least three layers: a surface layer A, a base layer, and a surface layer B.

4. The biaxially oriented polyethylene film according to claim 3, wherein the base material layer is the mixed resin layer.

5. The biaxially oriented polyethylene film according to claim 3, wherein the thickness ratio of the base layer in the biaxially oriented film is 70 to 95%.

6. The biaxially oriented polyethylene film according to claim 4, wherein the thickness ratio of the base layer in the biaxially oriented film is 70 to 95%.

7. A laminate film characterized in that a laminated film mainly composed of polyethylene resin is laminated on at least one side of the biaxially oriented polyethylene film according to claim 1 or 2, and the proportion of the polyethylene single material as a whole is 80% by weight or more.

8. A laminate film characterized in that a laminated film mainly composed of polyethylene resin is laminated on at least one side of the biaxially oriented polyethylene film described in claim 3, and the proportion of the polyethylene single material as a whole is 80% by weight or more.

9. A laminate film characterized in that a laminated film mainly composed of polyethylene resin is laminated on at least one side of the biaxially oriented polyethylene film described in claim 4, and the proportion of polyethylene-based single material as a whole is 80% by weight or more.

10. A laminate film characterized in that a laminated film mainly composed of polyethylene resin is laminated on at least one side of the biaxially oriented polyethylene film described in claim 5, and the proportion of the polyethylene single material as a whole is 80% by weight or more.

11. A laminate film characterized in that a laminated film mainly composed of polyethylene resin is laminated on at least one side of the biaxially oriented polyethylene film described in claim 6, and the proportion of a single polyethylene material overall is 80% by weight or more.

12. The laminate film according to claim 7, wherein the tear separation amount measured in [1] below is 90 mm or less. [1] Amount of tear separation (mm): Two A4-sized laminate films were placed on top of each other, and one short side was heated at 120°C for 1 second, then cooled to 60°C to form a heat-sealed area. A cut was made 60 mm from the edge of the heat-sealed area and torn in the longitudinal direction to the other short side. The maximum distance between the torn front and back surfaces of the two layered laminate films was defined as the amount of tear separation.

13. The laminate film according to claim 8, wherein the tear separation amount measured in [1] below is 90 mm or less. [1] Amount of tear separation (mm): Two A4-sized laminate films were placed on top of each other, and one short side was heated at 120°C for 1 second, then cooled to 60°C to form a heat-sealed area. A cut was made 60 mm from the edge of the heat-sealed area and torn in the longitudinal direction to the other short side. The maximum distance between the torn front and back surfaces of the two layered laminate films was defined as the amount of tear separation.

14. The laminate film according to claim 9, wherein the tear separation amount measured in [1] below is 90 mm or less. [1] Amount of tear separation (mm): Two A4-sized laminate films were placed on top of each other, and one short side was heated at 120°C for 1 second, then cooled to 60°C to form a heat-sealed area. A cut was made 60 mm from the edge of the heat-sealed area and torn in the longitudinal direction to the other short side. The maximum distance between the torn front and back surfaces of the two layered laminate films was defined as the amount of tear separation.

15. The laminate film according to claim 10, wherein the amount of tear separation measured in [1] below is 90 mm or less. [1] Amount of tear separation (mm): Two A4-sized laminate films were placed on top of each other, and one short side was heated at 120°C for 1 second, then cooled to 60°C to form a heat-sealed area. A cut was made 60 mm from the edge of the heat-sealed area and torn in the longitudinal direction to the other short side. The maximum distance between the torn front and back surfaces of the two layered laminate films was defined as the amount of tear separation.

16. The laminate film according to claim 11, wherein the amount of tear separation measured in [1] below is 90 mm or less. [1] Amount of tear separation (mm): Two A4-sized laminate films were placed on top of each other, and one short side was heated at 120°C for 1 second, then cooled to 60°C to form a heat-sealed area. A cut was made 60 mm from the edge of the heat-sealed area and torn in the longitudinal direction to the other short side. The maximum distance between the torn front and back surfaces of the two layered laminate films was defined as the amount of tear separation.

17. A packaging body characterized by being made of the laminate film described in claim 7.

18. A packaging body characterized by being made of the laminate film described in claim 8.

19. A packaging body characterized by being made of the laminate film described in claim 9.

20. A packaging body characterized by being made of the laminate film described in claim 10.

21. A packaging body characterized by being made of the laminate film described in claim 11.

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