Biaxially oriented polyethylene film for water-based ink printing

Abstract

To provide a biaxially oriented polyethylene film for water-based ink printing, which has an excellent recyclability as a base material for a laminate film for a packaging material and is also suitable for water-based ink printing.SOLUTION: There is provided a biaxially oriented polyethylene film for water-based ink printing, the film is a laminate film consisting of multiple layers mainly made of polyethylene resin, which is used as a base material for the laminate film, and is obtained by stretching in two axial directions of a machine direction (MD) and a transverse direction (TD), wherein the biaxially stretched film comprises at least two surface layers and a base layer, one or more kinds of antistatic agents are added to at least one layer other than the two surface layers, a content of the antistatic agent in the biaxially stretched film is 0.05 to 1.00 wt.%, and a content of the antistatic agent having a melting point of 40°C or higher in the layer to which the antistatic agent has been added is 0.60 wt.% or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a laminate film mainly made of polyethylene resin, which is used as a base film for a laminate film, and in particular to a biaxially oriented polyethylene film for water-based ink printing, which is biaxially oriented. [Background technology]

[0002] Generally, in packaging materials for packaging products such as food and daily necessities, a laminate film is used in which a sealant film is laminated (laminated) to a base film that has been subjected to printing processing or the like using an adhesive or the like.

[0003] For the base film of the laminate film, performance such as heat resistance, rigidity, dimensional stability, pinhole resistance, etc. is required, and since it is inexpensive, a biaxially oriented film mainly containing polypropylene as a component is preferably used. This biaxially oriented polypropylene film is produced by blending additives such as antistatic agents to provide suitability for processing steps such as printing and lamination. In addition, for the sealant film of the laminate film, a non-oriented film containing polypropylene and polyethylene as components is used, and a polyethylene-based non-oriented film is particularly preferably used due to its excellent heat sealing suitability.

[0004] For this type of laminate film, organic solvent-based inks are generally used in the printing process. When using organic solvent-based inks, there are issues such as air pollution from the emission and foul odor of organic solvents generated during the drying process, occupational safety and health issues such as the working environment, and compliance with the Fire Service Act regarding the handling of hazardous materials and facilities, making it essential that workers take safety measures such as wearing gas masks.

[0005] In recent years, with the growing interest in environmental issues, and in consideration of the environmental impact of the use of organic solvent-based inks in the printing process, active use of water-based inks using water, alcohol, or the like as a solvent as an alternative to organic solvent-based inks has been considered. However, while conventional base films for printing have good printability for organic solvent-based inks, they tend to have low adhesion to water-based inks, and so it is difficult to say that they necessarily have good printability for water-based inks, and there have been cases where improvements have been required.

[0006] In addition, in laminate films used for packaging materials, there is a trend for multiple types of resins to be laminated and compounded due to the required high level of performance, but from the viewpoint of reducing the environmental load, recycling of waste plastics is desired in the field of resin films. However, films in which multiple types of resins are laminated, such as laminate films in which a sealant film made of a polyethylene film is laminated onto a base film made of a polypropylene film, are difficult to recycle separately for each resin, and even if the resins that make up the film are remelted during recycling, they become a mixture of resins that are not compatible, which significantly reduces the quality of the recycled resources and makes them unsuitable as recycled materials.

[0007] Therefore, in this type of laminate film, there is an increasing demand for the base film and the sealant film to be made of a single material (mono-material).As a mono-material laminate film in which the base film and the sealant film are made of a single material, for example, a polyethylene-based laminate using a polyethylene-based material, which is preferably used as a sealant film, for the base film has been proposed (see Patent Document 1).

[0008] Thus, in the field of packaging materials, the market is changing so that in addition to the optional physical properties that have been conventionally required of films, suitability for recycling is also required. For this reason, the inventors have been making a base film of a single material (mono-material) with the polyethylene resin that constitutes the sealant film, taking into consideration suitability for recycling, and have been conducting intensive research into a film suitable for use in water-based ink printing. As a result, they have invented a biaxially oriented polyethylene film for water-based ink printing that can be suitably used as a base film for a mono-material laminate film. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2019-189333 A Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been proposed in view of the above-mentioned points, and provides a biaxially oriented polyethylene film for water-based ink printing, which has excellent recyclability as a base material for laminate films for packaging materials and is also suitable for water-based ink printing. [Means for solving the problem]

[0011] That is, the first invention relates to a biaxially oriented film for water-based ink printing, which is a laminate film in which multiple layers, mainly made of polyethylene resin used as a base material for a laminate film, are laminated, and which is stretched in two axial directions, that is, the machine direction (MD) and the transverse direction (TD), and which is characterized in that the biaxially oriented film has at least two surface layers and a base layer, and one or more types of antistatic agents are added to at least one layer other than the two surface layers, the content of the antistatic agent in the biaxially oriented film is 0.05 to 1.00% by weight, and the content of the antistatic agent having a melting point of 40°C or higher in the layer to which the antistatic agent is added is 0.60% by weight or less.

[0012] The second invention is the first invention, wherein at least one side of the biaxially stretched film is surface-treated, the surface-treated side has a wet tension of 36 mN / m or more as measured in accordance with JIS K 6768 (1999), and a surface resistivity of 1×10 or more as measured in accordance with JIS K 6911 (2006). 10 ~1×10 14 This relates to a biaxially oriented polyethylene film for water-based ink printing with a modulus of elasticity (Ω / □).

[0013] The third invention relates to a laminate film, characterized in that a sealant film made of a polyethylene resin is laminated on one side of the biaxially oriented polyethylene film for water-based ink printing described in claim 2.

[0014] A fourth invention relates to a laminate film according to the third invention, in which a polyethylene resin film is interposed between the biaxially oriented polyethylene film for water-based ink printing and the sealant film.

[0015] The fifth invention relates to a package comprising the laminate film according to the third or fourth invention. Effect of the Invention

[0016] According to the first aspect of the present invention, the biaxially oriented polyethylene film for water-based ink printing is a laminated film in which a plurality of layers, mainly made of polyethylene resin used as a base material for a laminate film, are laminated, and the biaxially oriented film for water-based ink printing is stretched in two axial directions, namely, the machine direction (MD) and the transverse direction (TD), and the biaxially oriented film has at least two surface layers and a base layer, and one or more types of antistatic agents are added to at least one layer other than the two surface layers, the content of the antistatic agent in the biaxially oriented film is 0.05 to 1.00% by weight, and the content of the antistatic agent having a melting point of 40°C or higher in the layer to which the antistatic agent is added is 0.60% by weight or less. Therefore, while achieving a monomaterial that is advantageous for recycling, the film has good antistatic performance and printability with water-based ink, and can be suitably used as a film for water-based ink printing.

[0017] According to the biaxially oriented polyethylene film for water-based ink printing of the second invention, in the first invention, at least one side of the biaxially oriented film is surface-treated, and the surface-treated side has a wetting tension of 36 mN / m or more as measured in accordance with JIS K 6768 (1999) and a surface resistivity of 1×10 or more as measured in accordance with JIS K 6911 (2006). 10 ~1×10 14 Because it has a resistance of Ω / □, it has improved printability and lamination suitability, and can properly prevent the film from becoming statically charged.

[0018] The laminate film of the third invention has a sealant film made of polyethylene resin laminated on one side of the biaxially oriented polyethylene film for water-based ink printing described in the second invention, and is therefore promising as an alternative to existing laminate films.

[0019] According to the laminate film of the fourth invention, in the third invention, a polyethylene resin film is interposed between the biaxially oriented polyethylene film for water-based ink printing and the sealant film, thereby achieving a single material (mono-material) to improve recyclability and impart appropriate functionality.

[0020] The packaging body of the fifth invention is made of the laminate film according to the third or fourth invention, and is therefore a promising alternative to existing packaging bodies. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The present invention is a biaxially oriented film made of a laminate film in which a plurality of layers mainly made of polyethylene resin are laminated and stretched in two axial directions, namely, the machine direction (MD) and the transverse direction (TD), and is particularly suitable for water-based ink printing. The biaxially oriented polyethylene film for water-based ink printing of the present invention is preferably used mainly as a substrate for a laminate film.

[0022] The polyethylene resin used as the resin raw material for the biaxially oriented polyethylene film for aqueous ink printing of the present invention is appropriately selected from polyethylene resins made from raw materials derived from petroleum, biomass, material recycling, chemical recycling, etc. Preferred polyethylene resins include, for example, random copolymers with α-olefins such as propylene, 1-butene, 1-heptene, 1-hexene, 1-octene, etc., and mixtures of one or more of the above may also be used. Furthermore, using polyethylene resins made from biomass-derived raw materials or recycled polyethylene resins as the resin raw material can contribute to reducing the environmental load.

[0023] In the case of the biaxially oriented polyethylene film of the present invention, when a film is formed by laminating a plurality of layers, the type of resin raw material constituting each layer is not particularly limited as long as it is mainly made of polyethylene resin, so long as it does not impair the effects of the present invention. For example, from the viewpoint of the adhesive strength between each layer, it is preferable that the raw materials used for each layer are the same type.

[0024] The biaxially oriented polyethylene film of the present invention, which is a laminate of multiple layers, comprises at least two surface layers disposed on both surfaces and a base layer disposed between the two surface layers. The surface layer on one side is a layer to which a surface treatment such as printing is applied when the biaxially oriented polyethylene film is used as a base material for a laminate film. The surface layer on the other side is a layer that becomes one end of the outermost layer when the biaxially oriented polyethylene film is used as a laminate film.

[0025] The base layer is the main layer of the biaxially oriented polyethylene film, and is formed to be relatively thicker than the other layers. If necessary, an intermediate layer may be disposed between the base layer and the surface layer. The biaxially oriented polyethylene film of the present invention is preferably a laminate film of 3 to 5 layers.

[0026] In the biaxially stretched polyethylene film of the present invention, any one or more of the layers may be appropriately blended with known additives such as antioxidants, light stabilizers, lubricants, and antiblocking agents, as long as the purpose of the invention is not impaired. For example, in the case of food packaging applications, it is preferable to add an antiblocking agent as an additive. Examples of antiblocking agents include commonly used inorganic silica and organic crosslinked acrylic beads. The antiblocking agent may be used alone or in combination of two or more types.

[0027] In the biaxially oriented polyethylene film, one or more kinds of antistatic agents are added to at least one layer other than the two surface layers in order to impart the desired antistatic performance to the film. When an antistatic agent is added to a layer other than the two surface layers, the antistatic agent added to the layer other than the two surface layers passes through the surface layers and migrates (bleeds out) to the film surface, so that the desired antistatic performance can be imparted to the film. When the layers other than the surface layers are multiple layers such as a substrate layer and an intermediate layer, the antistatic agent can be added only to the substrate layer, or to both the substrate layer and the intermediate layer, or the like, as appropriate.

[0028] On the other hand, if an antistatic agent is added to the surface layer of the film, for example, during the manufacturing process, the antistatic agent is likely to adhere to or accumulate on metal rolls such as guide rolls, and may be transferred to the subsequent film passing through the metal rolls, thereby impairing the appearance and otherwise degrading the quality. In addition, adhesion or accumulation of the antistatic agent on metal rolls or the like means that the antistatic agent added to the film is reduced during the manufacturing process, and there is a risk that the desired antistatic performance cannot be obtained. In order to avoid these problems, the antistatic agent is added to layers other than the two surface layers.

[0029] Antistatic agents generally do not have high heat resistance because they contain oil and fat components. For this reason, in the past, when an antistatic agent was added to a polypropylene film, which is often used as a base film for laminate films, some of the oil and fat components could vaporize when exposed to high temperatures of about 200°C during the stretching process during production. The vaporized oil and fat components turn into smoke, worsening the working environment. There have also been reported cases where oil and fat components and dust accumulated in curved parts of exhaust ducts before exhaust gas treatment, storing heat and igniting, which could be a fire hazard.

[0030] Therefore, in the present invention, a biaxially oriented film mainly made of polyethylene resin is used as the base film of the laminate film. Compared to polypropylene resin, polyethylene resin allows the molding temperature during film production to be lowered to 160°C or less, making it possible to suppress the vaporization of the oil and fat components of the added antistatic agent. Therefore, it is possible to obtain the desired antistatic performance while reducing the amount of antistatic agent added compared to polypropylene film.

[0031] The preferred content of the antistatic agent in the biaxially oriented polyethylene film of the present invention is 0.05 to 1.00% by weight. If the content of the antistatic agent is too small, it is difficult to obtain the desired antistatic performance. If the content of the antistatic agent is excessive, it is likely to have a negative effect on the film performance, such as reducing the adhesive strength of the film, so it is preferable to add a small amount to the extent that the desired antistatic performance is exhibited.

[0032] In addition, since the biaxially oriented polyethylene film is subjected to printing processing by water-based ink printing, printability such as water-based ink transfer (printing) property and adhesion on the film surface is required. Therefore, the inventors have found from the examples described below that the layer to which the antistatic agent is added contains a large amount of an antistatic agent with a high melting point, which tends to inhibit the transfer (printing) and adhesion of the water-based ink to the film surface. That is, in the biaxially oriented polyethylene film, the content of the antistatic agent with a melting point of 40° C. or more in the layer to which the antistatic agent is added is 0.60% by weight or less, preferably 0.50% by weight or less, so that it is possible to improve the printability of water-based ink.

[0033] Since antistatic agents with a high melting point (40°C or higher) are in a solid form at room temperature, it is believed that when they migrate (bleed out) to the film surface, the components of the antistatic agent appear in a solid form. If a large amount of antistatic agent with a high melting point is contained, such solid components will be present in large amounts on the film surface, making it difficult for water-based ink to adhere to the film surface, and it is believed that the transfer of water-based ink will be inhibited. Therefore, by reducing the content of the high-melting antistatic agent in a layer to which an antistatic agent with a content that provides the desired antistatic performance has been added, it is possible to obtain a biaxially oriented polyethylene film that has good antistatic performance and good printability with water-based ink.

[0034] Examples of antistatic agents used in the biaxially stretched polyethylene film of the present invention include aliphatic amine compounds such as lauryl diethanolamine, myristyl diethanolamine, palmityl diethanolamine, oleyl diethanolamine, and stearyl diethanolamine, and aliphatic amine ester compounds which are ester compounds of these compounds, aliphatic amide compounds such as lauryl diethanolamide, myristyl diethanolamide, palmityl diethanolamide, oleyl diethanolamide, and stearyl diethanolamide, and aliphatic amide ester compounds which are ester compounds of these compounds, polyhydric alcohols such as glycerin monooleate, glycerin monostearate, and glycerin distearate, sorbitan fatty acid esters such as sorbitan laurate, sorbitan palmitate, sorbitan oleate, and sorbitan stearate, sulfonic acids such as alkyl sulfonates and alkyl benzene sulfonates, sulfates such as alkyl sulfates and polyoxyethylene alkyl ether sulfates, and phosphoric esters such as alkyl phosphates and polyoxyethylene alkyl ether phosphates. These antistatic agents are selected from one or more types in combination within a range that satisfies the above-mentioned addition conditions.

[0035] In the biaxially oriented polyethylene film of the present invention, it is preferable to perform a surface treatment on at least one side of the film in order to impart printability, lamination suitability, etc. Examples of the surface treatment include known surface treatment methods such as corona treatment, flame treatment, and plasma treatment. The surface-treated film side has a wet tension of 36 mN / m or more measured in accordance with JIS K 6768 (1999) and a surface resistivity of 1×10 or more measured in accordance with JIS K 6911 (2006). 10 ~1×10 14 It is said to be Ω / □.

[0036] Wetting tension is used as an index of the printability and lamination suitability of a film. If the wetting tension value is too low, the film will have insufficient printability and lamination suitability. Surface resistivity is used as an index of the antistatic performance of a film. The higher the surface resistivity value, the more difficult it is for current to flow from the film surface (the easier it is to become charged), resulting in a film with insufficient antistatic performance. By performing surface treatment to satisfy the above wetting tension, the migration (bleed-out) of the added antistatic agent to the film surface is promoted, allowing the antistatic function to be fully expressed while also ensuring sufficient printability and lamination suitability.

[0037] The biaxially oriented polyethylene film of the present invention can be obtained by a known film forming method such as the T-die method or the inflation method. In particular, it is preferable that a sheet shaped by the T-die method is stretched and molded. Film molding by the T-die method is advantageous in that it can provide high thickness precision required for a base film of a laminate film.

[0038] The polyethylene film is a biaxially stretched film that is stretched in two directions, the machine direction (MD) and the transverse direction (TD), of the film. Either sequential biaxial stretching or simultaneous biaxial stretching is preferably used for the biaxial stretching. In film production by biaxial stretching, orientation of the resin occurs in both the machine direction (MD) and the transverse direction (TD) and crystallinity is improved, so that thickness precision for thinning and mechanical properties such as strength can be improved, and mass productivity is also excellent. The stretching ratio of the film is, for example, about 2 to 8 times in the machine direction (MD) and about 4 to 12 times in the transverse direction (TD).

[0039] The thickness of the biaxially oriented polyethylene film of the present invention is not particularly limited and is appropriately determined depending on the demand and the application, for example, 5 to 100 μm, preferably 10 to 70 μm. Of these, the thickness of each of the two surface layers 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. For example, when an antiblocking agent is blended in the surface layer, if the surface layer is too thin, the antiblocking agent may fall off when the film passes through the rolls during processing, whereas if the surface layer is too thick, the amount of antiblocking agent blended may be too large, resulting in poor visibility of the film.

[0040] As described above, the biaxially oriented polyethylene film of the present invention has good antistatic properties and good water-based ink transferability, and therefore can be suitably used as a film for water-based ink printing. In addition, a laminate film can be provided in which the biaxially oriented polyethylene film for water-based ink printing is used as a base film and a sealant film made of polyethylene resin is laminated on one side of the base film. In this laminate film, the biaxially oriented polyethylene film of the present invention is used as the base film, making it possible to make the film from a single material (mono-material), and improving the recyclability.

[0041] In the laminate film of the present invention, the biaxially oriented polyethylene film for aqueous ink printing, which is the base film, is used after being subjected to printing processing with aqueous ink. When a sealant film is laminated on this base film, it may be laminated on either the side that has been printed with aqueous ink or the side that has not been printed with aqueous ink.

[0042] In this laminate film, an appropriate polyethylene resin film may be interposed between the base film and the sealant film. The polyethylene resin film is used for the purpose of imparting appropriate functionality, such as improving the rigidity and tearability, of the laminate film. For example, when used from the viewpoint of improving the rigidity of the laminate film, it is preferable to select a uniaxially stretched film or a biaxially stretched film. In addition, since the polyethylene resin film is composed of the same type of polyethylene resin as the base film and the sealant film, it is possible to achieve a single material (mono-material) and improve the recyclability. Furthermore, in the laminate film, a deposition layer, an adhesive layer, or other layers having functionality may be appropriately laminated between the base film and the sealant film depending on the application. The order of lamination of each layer is appropriate.

[0043] The laminate film of the present invention is suitable as a packaging material for various items such as food, daily necessities, and parts, and is formed into a package for use. The package formed from this laminate film is made of a single material (monomaterial), making it easy to recycle. For this reason, these laminate films and their packages are promising as replacements for existing products. EXAMPLES

[0044] [Preparation of biaxially stretched film] In producing the biaxially stretched films of prototypes 1 to 18, the materials described below were mixed and melted based on a predetermined blending ratio (wt%) corresponding to the substrate layer and both surface layers, extruded into multiple layers (three layers: substrate layer and both surface layers of the substrate layer) by the T-die method, stretched 5 times in the machine direction (MD), and then stretched 8 times in the transverse direction (TD) to form a film. Thereafter, the surface layer on one side was subjected to a surface treatment by corona discharge treatment. The film of each prototype had a total thickness of 20 μm, both surface layers had a thickness of 1 μm, and the substrate layer had a thickness of 18 μm. In each prototype, the blending ratio of the materials was blended so that each layer of the substrate layer or surface layer was 100 wt%.

[0045] [Resin material] PE1: Linear low-density polyethylene (Dow Chemical, "TF80") PE2: High density polyethylene (Japan Polyethylene Co., Ltd., "HY430") PP1: Homopolypropylene (Japan Polypropylene Corporation, "FL203D")

[0046] [Antistatic agent] · AS1: Glycerin monostearate (melting point 70℃) · AS2: Glycerol oleate (melting point 13℃) · AS3: Stearyldiethanolamine (melting point 51°C) · AS4: Oleyldiethanolamine (melting point 28°C) · AS5: Stearyldiethanolamine (melting point 46°C) AS6: Oleyldiethanolamine monolaurate (melting point 25°C) · AS7: Stearyl diethanolamine monostearate (melting point 29°C)

[0047] The melting points (°C) of each antistatic agent (AS1 to AS7) are melting peak temperatures (°C) determined using a differential scanning calorimeter (NETZSCH, "DSC214 Polymer"). The melting peak temperatures (°C) were determined from the DSC curve of the second run, which was obtained by increasing the temperature from -20°C to 100°C at a rate of 10°C / min under a nitrogen stream and holding at 100°C for 3 minutes, then decreasing the temperature from 100°C to -20°C at a rate of 10°C / min and holding at -20°C for 10 minutes (1st run), and then increasing the temperature from -20°C to 100°C at a rate of 10°C / min (2nd run). When multiple melting peaks existed, the highest melting peak temperature was used.

[0048] [Anti-blocking agent] AB1: Antiblocking agent (manufactured by Fuji Silysia Chemical Ltd., "SYLYSIA430")

[0049] [Prototype 1] Prototype example 1 is a biaxially oriented polyethylene film obtained by blending polyethylene resin (99.9% by weight of PE1) and antistatic agent (0.03% by weight of AS1, 0.02% by weight of AS4, and 0.05% by weight of AS6) as a base layer, and polyethylene resin (99.7% by weight of PE1) and antiblocking agent (0.3% by weight of AB1) as both surface layers.

[0050] [Prototype 2] Prototype 2 is an embodiment in which the content of the antistatic agent in the base layer is increased from that in Prototype 1, with the antistatic agent contents being 0.30 wt% AS1, 0.20 wt% AS4, and 0.50 wt% AS6 (PE1 was 99.0 wt% as the polyethylene resin in the base layer); otherwise, this biaxially oriented polyethylene film was obtained identically.

[0051] [Prototype 3] Prototype 3 is an embodiment in which the type and content of the antistatic agent in the base layer was changed from Prototype 1, with the antistatic agents being changed to 0.034% by weight AS1, 0.013% by weight AS5, and 0.053% by weight AS7, but the rest was the same in this biaxially oriented polyethylene film.

[0052] [Prototype 4] Prototype 4 is an embodiment in which the types of polyethylene resin in the base layer and both surface layers of Prototype 1 were changed; the polyethylene resin in the base layer was 79.9% by weight PE1 and 20.0% by weight PE2, and the polyethylene resins in both surface layers were 79.7% by weight PE1, 20.0% by weight PE2, and 0.3% by weight AB1, and the rest was the same, resulting in a biaxially oriented polyethylene film.

[0053] [Prototype 5] Prototype Example 5 is an embodiment in which the type of antistatic agent in the base layer is changed from Prototype Example 1; the antistatic agents were changed to 0.067% by weight AS1 and 0.033% by weight AS3, but the rest was the same as in Prototype Example 1, resulting in a biaxially oriented polyethylene film.

[0054] [Prototype 6] Prototype 6 is an embodiment in which the type and content of the antistatic agent in the base layer was changed from Prototype 1, and the antistatic agents were 0.10% by weight AS1, 0.10% by weight AS2, and 0.10% by weight AS3 (PE1 was 99.7% by weight as the polyethylene resin in the base layer), and the rest was the same, resulting in a biaxially oriented polyethylene film.

[0055] [Prototype 7] Prototype Example 7 is an embodiment in which the type of antistatic agent in the base layer is changed from that in Prototype Example 1; the antistatic agent is changed to 0.1 wt% AS6, and the rest is the same as in Prototype Example 1, resulting in a biaxially oriented polyethylene film.

[0056] [Prototype 8] Trial Example 8 is a biaxially oriented polyethylene film obtained by changing the antistatic agent in the base layer of Trial Example 7 from AS6 to AS7, while keeping everything else the same.

[0057] [Prototype 9] Trial Example 9 is a biaxially oriented polyethylene film obtained in the same manner as Trial Example 7 except that the antistatic agent in the base layer was changed from AS6 to AS4.

[0058] [Prototype 10] Prototype 10 is a biaxially oriented polyethylene film obtained by changing the antistatic agent in the base layer of Prototype 7 from AS6 to AS5, but otherwise remaining the same.

[0059] [Prototype example 11] Prototype Example 11 is an embodiment in which the content of the antistatic agent in the base layer is increased from that of Prototype Example 5, with the antistatic agent contents being 0.333 wt % for AS1 and 0.167 wt % for AS3 (PE1 being 99.5 wt % as the polyethylene resin in the base layer), and the rest being the same, this is a biaxially oriented polyethylene film obtained.

[0060] [Prototype 12] Prototype 12 is a biaxially oriented polyethylene film in which no antistatic agent is added to the base layer, and the base layer and both surface layers are each composed of polyethylene resin (PE1 is 100.0% by weight).

[0061] [Prototype 13] Prototype Example 13 is an embodiment in which the content of the antistatic agent in the base layer is reduced from Prototype Example 1, with the antistatic agent contents being 0.015 wt % AS1, 0.010 wt % AS4, and 0.025 wt % AS6 (PE1 was 99.95 wt % as the polyethylene resin in the base layer), and the rest being the same, this is a biaxially oriented polyethylene film obtained.

[0062] [Prototype 14] Prototype Example 14 is an embodiment in which the content of antistatic agent in the base layer is reduced from that of Prototype Example 3, with the antistatic agent contents being 0.017 wt % for AS1, 0.007 wt % for AS5, and 0.026 wt % for AS7 (PE1 was 99.95 wt % as the polyethylene resin in the base layer), and the rest being the same, this is a biaxially oriented polyethylene film obtained.

[0063] [Prototype 15] Prototype Example 15 is a biaxially oriented polypropylene film obtained by changing the resin material of the base layer and both surface layers of Prototype Example 1 from polyethylene resin (PE1) to polypropylene resin (PP1), and blending polypropylene resin (PP1 is 99.9% by weight) and an anti-blocking agent (AB1 is 0.1% by weight) for each of the two surface layers, while remaining the same as the other prototypes.

[0064] [Prototype 16] Prototype Example 16 is a biaxially oriented polypropylene film obtained by changing the resin material of the base layer and both surface layers of Prototype Example 2 from polyethylene resin (PE1) to polypropylene resin (PP1), and blending polypropylene resin (PP1 is 99.9% by weight) and an anti-blocking agent (AB1 is 0.1% by weight) for each of the two surface layers, while remaining the same as the other prototypes.

[0065] [Prototype 17] Prototype Example 17 is an embodiment in which the content of the antistatic agent in the base layer is increased from Prototype Example 5, and the content is further increased from Prototype Example 11. The antistatic agent contents are 0.467% by weight for AS1 and 0.233% by weight for AS3 (PE1 is 99.3% by weight as the polyethylene resin in the base layer), and the rest is the same for this biaxially oriented polyethylene film.

[0066] [Prototype 18] Prototype Example 18 is an embodiment in which the content of the antistatic agent in the base layer is increased from Prototype Example 5, and the content is further increased from Prototype Example 17. The antistatic agent contents are 0.67% by weight for AS1 and 0.33% by weight for AS3 (PE1 is 99.0% by weight as the polyethylene resin in the base layer), and the rest is the same for this biaxially oriented polyethylene film.

[0067] Regarding the evaluation of the biaxially stretched films of prototypes 1 to 18, the wetting tension (mN / m) and surface resistivity (Ω / □) of the film surface were measured. In addition, the transferability and adhesion of the water-based ink were evaluated as the suitability for printing with water-based ink. The results of each measurement and the evaluation are shown in Tables 1 to 3 below, together with the materials used in each layer of prototypes 1 to 18, the content (weight %) of the antistatic agent in the base layer, the content (weight %) of the antistatic agent in the film, and the content (weight %) of the high melting point (40°C or higher) antistatic agent in the base layer.

[0068] [Wetting tension measurement] Wet tension (mN / m) was measured in accordance with JIS K 6768 (1999). Wet tension is an index of a film's printability and lamination suitability, and a wet tension of 36 mN / m or more was evaluated as good.

[0069] [Measurement of surface resistivity] The surface resistivity (Ω / □) was measured in accordance with JIS K 6911 (2006). Surface resistivity is an index of the antistatic performance of a film, and is 1×10 10 ~1×10 14 The surface resistivity was evaluated as good when Ω / □ was used. 14Films exceeding Ω / □ are marked as "OR" as they are over range.

[0070] [Evaluation of water-based ink printability] The water-based ink printability is the printability of the film for water-based ink, and was evaluated from two viewpoints: transferability (printability) and adhesion of water-based ink. When evaluating the water-based ink printability, the biaxially stretched film surfaces of prototypes 1 to 18 that had been subjected to corona discharge treatment were printed with water-based ink using a CM-type gravure proofing machine (Nissho Gravure Co., Ltd., "GRAVO-PROOF MINI") at a printing speed of 40 m / min and a printing plate of "He, 175L, S130°∠0". The water-based ink was prepared by mixing water-based gravure ink (Toyo Ink Co., Ltd., "JW303 Aquaecole 92 Black") and dilution solvent (Toyo Ink Co., Ltd., "AQ 682 Solvent N") in a ratio of 3:2.

[0071] [Testing water-based ink transferability] The transferability of water-based ink is one of the indicators of water-based ink printability, which evaluates the condition of the ink from the amount of water-based ink attached to the surface of a film printed with water-based ink. In the transferability test, the surface of the film printed with water-based ink was observed using a microscope (Olympus Corporation, "BX51"), an objective lens (Olympus Corporation, "MPlanFL N 5×BDP"), and a camera (Olympus Corporation, "DP74"), and the amount of water-based ink attached was determined by calculating the ink transfer area of ​​the 50% printing tone part of the printing plate "He, 175L, S130°∠0" using analysis software (Evident Corporation, "PRECiV Core").

[0072] The amount of water-based ink attached was measured using a commercially available biaxially oriented polypropylene film for water-based ink printing ("FOR-AQ 20μm" manufactured by Futamura Chemical Co., Ltd.) as a reference film, and the ink transfer area of ​​the water-based ink print relative to the reference film was calculated based on the above transferability test, and the transferability of the water-based ink was evaluated based on the ink transfer area ratio (%) calculated from the following formula (i). The transferability of the water-based ink was evaluated as follows: an ink transfer area ratio of 90% or more is "◎ (good)", an ink transfer area ratio of 60% or more but less than 90% is "○ (passable)", and an ink transfer area ratio of less than 60% is "× (unacceptable)".

[0073]

number

[0074] [Adhesion test for water-based ink] The adhesion of water-based ink is one of the indices of suitability for water-based ink printing, which is evaluated based on the remaining area of ​​ink after peeling off an adhesive tape applied to the surface of a film printed with water-based ink. In the adhesion test, an adhesive tape (Nichiban Co., Ltd., Cellotape (registered trademark) "CT405AP-15") was applied to a length of 150 mm on a portion of the printing plate "He, 175L, S130°∠0" with a print tone of 100%, and a roller with a load of 2 kg was pressed against the adhesive tape and moved back and forth twice. The adhesive tape was then peeled off so that the angle with the printed surface of the film was 90°, and the adhesion of the water-based ink was evaluated based on the remaining area ratio (%) of the ink on the portion where the adhesive tape was applied. The adhesion of water-based ink was evaluated as follows: if the ink remaining area ratio was 90% or more, it was marked "◎ (good)", if it was 50% or more but less than 90%, it was marked "○ (passable)", and if it was less than 50%, it was marked "× (bad)".

[0075] [Antistatic agent content] In the present embodiment, the content (wt%) of the antistatic agent in the base layer is the total content (wt%) of one or more antistatic agents added to the base layer. The content (wt%) of the antistatic agent in the film is the content (wt%) of the antistatic agent added to the 18 μm thick base layer in the 20 μm thick biaxially stretched film, which is 0.9 times the content of the antistatic agent in the base layer. The content (wt%) of the high melting point antistatic agent in the base layer is the total content (wt%) of one or more antistatic agents with a melting point of 40° C. or more added to the base layer.

[0076] [Table 1]

[0077] [Table 2]

[0078] [Table 3]

[0079] [Results and Discussion] As can be seen from Tables 1 to 3, the biaxially stretched films of Prototypes 1 to 11 exhibited good results in both antistatic performance (surface resistivity) and water-based ink printability (water-based ink transferability and water-based ink adhesion). In contrast, the biaxially stretched films of Prototypes 12 to 18 did not exhibit good results in either or both of antistatic performance and water-based ink printability.

[0080] First, the biaxially stretched films of Prototype 1 and Prototype 15 are compared. Prototype 1 is a biaxially stretched polyethylene film mainly made of polyethylene resin, whereas Prototype 15 is a biaxially stretched polypropylene film mainly made of polypropylene resin. The blending ratio of each layer and the type of antistatic agent are the same. Prototype 15, mainly made of polypropylene resin, had good water-based ink transferability as a water-based ink printability, but insufficient adhesion. On the other hand, Prototype 1, mainly made of polyethylene resin, had good water-based ink transferability and adhesion as a water-based ink printability. The same tendency was observed in the relationship between the biaxially stretched polyethylene film of Prototype 2 and the biaxially stretched polypropylene film of Prototype 16. From this, it was confirmed that the biaxially stretched film mainly made of polypropylene resin has insufficient adhesion to water-based ink and is not suitable for use in water-based ink printing, while the biaxially stretched film mainly made of polyethylene resin has excellent water-based ink printability and is suitable for use in water-based ink printing.

[0081] In addition, although the base layers of prototype 1 and prototype 15 contain the same amount of antistatic agent, the antistatic performance of prototype 15 was insufficient. This shows that the biaxially oriented polyethylene film (prototype 1) can obtain sufficient antistatic performance even with a smaller amount of antistatic agent than the biaxially oriented polypropylene film.

[0082] Next, Prototype Example 1 is compared with Prototype Examples 2, 12, and 13. Prototype Example 2 is an embodiment in which the content of the antistatic agent in the base layer is increased from Prototype Example 1. Since Prototype Example 2 had improved antistatic performance compared to Prototype Example 1, it was found that the antistatic performance is improved by including a large amount of antistatic agent.

[0083] On the other hand, Prototype 12 is an embodiment in which the base layer does not contain an antistatic agent, and Prototype 13 is an embodiment in which the content of the antistatic agent in the base layer is reduced from Prototype 1. Both Prototypes 12 and 13 had insufficient antistatic performance compared to Prototype 1. A similar tendency was observed in the relationship between Prototype 3 and Prototype 14. It was found that, in a biaxially oriented polyethylene film, a good antistatic effect can be obtained with a relatively small amount of antistatic agent, but if the content of the antistatic agent is too small (including the case where no antistatic agent is added), sufficient antistatic performance cannot be obtained.

[0084] While Prototype 1 uses one type of polyethylene resin (PE1) as the resin material for the base layer and both surface layers, Prototype 4 uses multiple types of polyethylene resins (PE1, PE2) made of a single material in a different formulation. Prototype 4 had good water-based ink printability, just like Prototype 1. This confirmed that water-based ink printability is good even when different types of polyethylene resins are used for the base layer and both surface layers.

[0085] In prototypes 5, 7 to 10, a different type of antistatic agent was used from that in prototype 1, and the content in the film was the same (0.09% by weight) as in prototype 1. In prototypes 5, 7 to 10, sufficient antistatic performance was obtained, as in prototype 1. This shows that in biaxially oriented polypropylene films, sufficient antistatic performance can be obtained with a small amount of antistatic agent, even when the type of antistatic agent is different.

[0086] In prototypes 6, 11, 17, and 18, a different type of antistatic agent was used than in prototype 1, and the content in the film was increased compared to prototype 1. In prototype 6, the antistatic performance was improved compared to prototype 1. Meanwhile, in prototypes 11, 17, and 18, the antistatic performance was improved compared to prototype 1, but changes were observed in the water-based ink printability.

[0087] Prototypes 11, 17, and 18 use the same type of antistatic agent (AS1 and AS3) as Prototype 5, but the content of the antistatic agent is increased compared to Prototype 5. Prototype 5, which has the lowest content of antistatic agent, was rated as "◎ (good)" for both the transferability and adhesion of the water-based ink. Prototype 11, which has the second lowest content of antistatic agent after Prototype 5, was rated as "○ (fair)" for the transferability and adhesion of the water-based ink. Prototypes 17 and 18, which have a higher content of antistatic agent than Prototypes 5 and 11, were rated as "× (bad)" for both the transferability and adhesion of the water-based ink.

[0088] The content of the antistatic agent in the base layer in each of the prototypes 5, 11, 17, and 18 is 0.10% by weight for prototype 5, 0.50% by weight for prototype 11, 0.70% by weight for prototype 17, and 1.00% by weight for prototype 18. Another prototype with a high content of antistatic agent in the base layer (1.00% by weight) is prototype 2, which has good suitability for printing with water-based ink. The antistatic agents used in prototype 2 are AS1 (0.30% by weight), AS4 (0.20% by weight), and AS6 (0.50% by weight), which are different from the antistatic agents used in each of the prototypes 5, 11, 17, and 18.

[0089] Regarding the properties of the antistatic agent in prototype 2, AS1 was composed of components with a relatively high melting point of 70°C, while AS4 and AS6 were composed of components with relatively low melting points of 28°C and 25°C, respectively. Meanwhile, regarding the properties of the antistatic agents in prototypes 5, 11, 17, and 18, AS1 had a melting point of 70°C, and AS3 had a melting point of 51°C, all of which were composed of components with relatively high melting points. Based on the type and content of the antistatic agent in the base layer, it was found that in biaxially oriented polyethylene film, the content of high-melting-point antistatic agent in the base layer tends to increase, which decreases the suitability for water-based ink printing.

[0090] The high melting point antistatic agents are in a solid form at room temperature because AS1 has a melting point of 70°C and AS3 has a melting point of 51°C. Normally, antistatic agents exert their antistatic performance by migrating (bleeding out) to the film surface, so it is considered that when the content of high melting point antistatic agents is high, the antistatic agent migrating to the film surface contains a large amount of solid components. Therefore, based on the test results of the content of antistatic agents and water-based ink printability of each of the prototypes 5, 11, 17, and 18, it is presumed that the solid components of the high melting point antistatic agents migrating to the film surface as described above hinder the adhesion of water-based ink and are a factor in reducing the water-based ink printability. Considering that the components are in a solid form at room temperature, it is considered that such high melting point antistatic agents have a melting point of 40°C or more.

[0091] Furthermore, in biaxially oriented polyethylene films, the effect on water-based ink printability is suppressed if the content of the high-melting point antistatic agent is small, as in Prototype 5. Therefore, based on Prototypes 17 and 18, which had insufficient water-based ink printability, and Prototype 11, which had test results for water-based ink printability that included a grade of "○ (fair)", it is believed that the preferred content of the high-melting point antistatic agent added to the base layer is about 0.60% by weight or less.

[0092] As described above, biaxially oriented films can be made into a single material (mono-material) by forming a laminate film of multiple layers mainly made of polyethylene resin, and good antistatic performance can be obtained with a small amount of antistatic agent compared to biaxially oriented polypropylene films. In addition, from the results of each prototype, it is considered that a good antistatic effect can be obtained in biaxially oriented polyethylene films if the content of the antistatic agent is 0.05% by weight or more. And, since a negative effect on the film performance is easily caused when the content of the antistatic agent is too high, it is considered that the content of the antistatic agent is preferably about 0.05 to 1.00% by weight based on the results of prototypes 1 to 11, which are good products.

[0093] Furthermore, by setting the content of antistatic agent having a melting point of 40°C or higher (high melting point antistatic agent) in the base layer (layer to which the antistatic agent is added) to 0.60% by weight or less among the antistatic agents contained in the biaxially oriented polyethylene film, it is possible to suppress the deterioration of suitability for water-based ink printing and to make the film suitable for water-based ink printing.

[0094] [Evaluation of oil-based ink printability] The films (samples 5 and 6) that showed good water-based ink printability were also examined for their oil-based ink printability. Oil-based ink printability is the printability of a film for organic solvent-based ink. As the organic solvent-based ink, an oil-based gravure ink ("Rio Alpha R92 Sumi S" manufactured by Toyo Ink Co., Ltd.) and a dilution solvent ("NFKS 103 Solvent N" manufactured by Toyo Ink Co., Ltd.) were used in a 2:1 ratio, and the transferability and adhesion of the organic solvent-based ink were evaluated as the oil-based ink printability using the same procedures as those for the water-based ink printability transferability test and adhesion test. As a result, it was shown that the biaxially oriented polyethylene films (samples 5 and 6) that showed good water-based ink printability also showed good oil-based ink printability ("◎ (good)"). [Industrial Applicability]

[0095] The biaxially oriented polyethylene film for aqueous ink printing of the present invention is made of a single material (mono-material) and has good antistatic properties and suitability for aqueous ink printing. Therefore, it has an advantage in terms of recyclability, and can be suitably printed with aqueous ink without the need for organic solvent-based ink during printing, which can greatly contribute to reducing the burden on the environment and humans.

Claims

1. A laminate film in which multiple layers are laminated together, the main component of which is a polyethylene resin used as a substrate for a laminate film, and which is a biaxially oriented film for water-based ink printing, which is oriented in two axial directions, namely, the machine direction (MD) and the transverse direction (TD), The biaxially stretched film comprises at least two surface layers and a base layer, one or more kinds of antistatic agents are added to at least one layer other than the two surface layers, The content of the antistatic agent in the biaxially stretched film is 0.05 to 1.00% by weight, The content of the antistatic agent having a melting point of 40° C. or higher in the layer to which the antistatic agent is added is 0.60% by weight or less. A biaxially oriented polyethylene film for water-based ink printing, characterized in that

2. At least one surface of the biaxially stretched film is surface-treated; the wet tension of the surface-treated surface measured in accordance with JIS K 6768 (1999) is 36 mN / m or more; The surface resistivity measured according to JIS K 6911 (2006) is 1×10 １０ ~1×10 １４ 2. The biaxially oriented polyethylene film for water-based ink printing according to claim 1, wherein the elastic modulus is Ω / □.

3. 3. A laminate film comprising the biaxially oriented polyethylene film for water-based ink printing according to claim 2 and a sealant film made of a polyethylene resin laminated on one side of the biaxially oriented polyethylene film for water-based ink printing according to claim 2.

4. 4. The laminate film according to claim 3, wherein a polyethylene resin film is interposed between said biaxially oriented polyethylene film for water-based ink printing and said sealant film.

5. A packaging material comprising the laminate film according to claim 3 or 4.

Images