Polyethylene-based sealant film and laminate

Abstract

To provide a polyethylene-based sealant film which holds performance as a sealant film while improving elastic modulus using a high density resin material, and can suppress warpage of a film, and a laminate.SOLUTION: A film body 10 is formed by laminating a laminate layer 20, a base layer 30 and a sealant layer 40 in this order, and consists mainly of a polyethylene resin, wherein the film body 10 has layer density (D2) of the base layer 30 of 0.935 g / cm3 or more, has layer density (D3) of the sealant layer 40 of 0.924 g / cm3 or less, and total density (DA) of 0.930 to 0.935 g / cm3, a sum (MD+TD) of elastic moduli in a longitudinal (MD) direction and a lateral (TD) direction is 0.66 GPa or more, layer density (D1) of the laminate layer 20 and the layer density (D3) of the sealant layer 40 satisfy a relation of |D1-D3|≤0.020, and layer thickness of the sealant layer 40 to the total layer thickness is 15% or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a polyethylene sealant film and a laminate using the sealant film. [Background technology]

[0002] In recent years, with the promotion of Sustainable Development Goals (SDGs), various efforts have been made to reduce environmental impact, such as by using renewable energy to curb emissions of greenhouse gases such as carbon dioxide. In the field of resin films, for example, progress has been made in the production of films using plant-derived raw materials (biomass raw materials) instead of petroleum-derived raw materials (see, for example, Patent Document 1).

[0003] Plant-derived raw materials are carbon-neutral resources because they absorb carbon dioxide from the atmosphere during the plant growth process, and even if carbon dioxide is released during combustion, no new carbon dioxide is released into the atmosphere. Therefore, compared to petroleum-derived raw materials, which increase carbon dioxide in the atmosphere when burned, plant-derived raw materials are effective as resources that can contribute to reducing environmental impact.

[0004] SDG initiatives in the field of resin films are required to go beyond utilizing biomass raw materials and contribute to reducing environmental impact from various angles. One method is to reduce the volume of film. When reducing the volume of film, for example, in the case of polyethylene sealant film, the rigidity of the film decreases as the volume is reduced. Therefore, using a high-density resin can prevent the film's physical properties from deteriorating. However, simply using a high-density resin can cause problems such as higher heat-sealing temperatures and reduced bag-breaking strength during bag production.

[0005] Furthermore, with this type of film, warping (curling) may occur at the edges of the film roll after film formation and winding. When warping occurs in the film, problems are likely to occur during processing of the film, such as making it difficult to process film products such as packaging bags. Therefore, with regard to polyethylene sealant films, it is necessary to reduce the volume of the film while suppressing deterioration in the film's physical properties, and to suppress a decrease in bag-breaking strength and film warping. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2021-171969 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been proposed in light of the above circumstances, and provides a polyethylene sealant film and laminate that uses a high-density resin material to reduce the volume of the film, thereby improving the elastic modulus, while maintaining the performance of the sealant film and suppressing warping of the film. [Means for solving the problem]

[0008] That is, the first invention is a film body mainly made of polyethylene resin, which is composed of three or more layers of at least a laminate layer, a base layer, and a sealant layer, and in which the laminate layer, the base layer, and the sealant layer are laminated in this order, and in which the layer density (D2) of the base layer is 0.935 g / cm 3 The layer density (D3) of the sealant layer is 0.924 g / cm 3 Below, and the overall density (D A ) is 0.930~0.935g / cm 3the sum of the modulus of elasticity in the machine direction (MD) and the transverse direction (TD) (MD+TD) measured based on the test method for tensile properties of plastics in accordance with JIS K 7127 (1999) is 0.66 GPa or more, the layer density (D1) of the laminate layer and the layer density (D3) of the sealant layer satisfy the relationship |D1-D3|≦0.020, and the thickness of the sealant layer accounts for 15% or more of the total layer thickness.

[0009] The second invention relates to a laminate obtained by laminating a stretched surface substrate having at least one layer structure on the surface of the laminate layer of the polyethylene sealant film according to the first invention.

[0010] The third invention relates to the laminate of the second invention, wherein the surface substrate is made of one or more of a biaxially oriented polypropylene film, a uniaxially oriented polyethylene film, a biaxially oriented polyethylene film, a biaxially oriented polyethylene terephthalate film, and a biaxially oriented polyamide film. [Effects of the Invention]

[0011] The polyethylene sealant film according to the first aspect of the present invention is a film body mainly made of polyethylene resin, which comprises three or more layers, namely, at least a laminate layer, a base layer, and a sealant layer, and in which the laminate layer, the base layer, and the sealant layer are laminated in this order, and the film body has a layer density (D2) of the base layer of 0.935 g / cm 3 The layer density (D3) of the sealant layer is 0.924 g / cm 3 Below, and the overall density (D A ) is 0.930~0.935g / cm 3The sum of the modulus of elasticity in the machine direction (MD) and the transverse direction (TD) (MD+TD) measured based on the test method for tensile properties of plastics in accordance with JIS K 7127 (1999) is 0.66 GPa or more, the layer density (D1) of the laminate layer and the layer density (D3) of the sealant layer satisfy the relationship |D1-D3|≦0.020, and the thickness of the sealant layer is 15% or more of the total layer thickness. Therefore, it is possible to reduce the volume by improving the modulus of elasticity while maintaining the performance of the sealant film, thereby contributing to a reduction in the environmental load, and furthermore, warping of the film can be suppressed, resulting in good film formability.

[0012] According to the laminate of the second invention, a stretched surface substrate having at least one layer structure is laminated to the surface layer of the laminate layer of the polyethylene sealant film described in the first invention, so that it is possible to provide a laminate using a sealant film that can contribute to reducing the environmental burden by reducing volume through improved elastic modulus while appropriately avoiding deterioration of low-temperature sealing properties and bag rupture resistance.

[0013] According to the laminate of the third invention, in the second invention, the surface substrate is made of one or more of a biaxially oriented polypropylene film, a uniaxially oriented polyethylene film, a biaxially oriented polyethylene film, a biaxially oriented polyethylene terephthalate film, and a biaxially oriented polyamide film, and therefore is inexpensive, has excellent processability and strength, and is suitable for protecting a sealant film. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic cross-sectional view of a laminate using a polyethylene sealant film according to one embodiment of the present invention. [Figure 2] FIG. 1 is a schematic diagram of a bag rupture test. DETAILED DESCRIPTION OF THE INVENTION

[0015] 1 shows a polyethylene sealant film 10 according to one embodiment of the present invention, which is a film body mainly made of polyethylene resin and which is composed of at least three layers: a laminate layer 20, a base layer 30, and a sealant layer 40. The laminate layer 20, the base layer 30, and the sealant layer 40 are laminated in this order. In the sealant film 10, a surface substrate 60 is laminated on the surface of the laminate layer 20 to form a laminate 50.

[0016] The sealant film 10 is manufactured by a known film manufacturing method such as the T-die method. Furthermore, by forming the sealant film 10 into a laminate 50, it is suitable for use in various packaging materials (packaging bags) for foods, cosmetics, medicines, daily necessities, parts, and other products, as well as in industrial film products.

[0017] The polyethylene resin used in the sealant film 10 may be selected from linear low-density polyethylene resin (LLDPE), high-density polyethylene (HDPE), low-density polyethylene (LDPE), etc., either singly or in combination. Each layer of the sealant film may contain other resins. For example, other resins, such as masterbatches for additives, may be contained within the range that does not impair the properties of the film.

[0018] From the viewpoint of reducing the environmental load, the polyethylene resin may contain polyolefin resin derived from recycled raw materials such as material recycling and chemical recycling, or biomass. Examples of biomass-derived polyolefin resins include polyethylene-based resins obtained by processing plant raw materials. Specifically, these are polyethylene-based resins produced by subjecting sugar solution extracted from plant raw materials such as sugarcane to alcoholic fermentation using yeast to produce ethanol, which is then converted into ethylene, and then subjected to a known resinification process. The higher the weight proportion of biomass-derived polyolefin resin, the greater the contribution to reducing the environmental load.

[0019] Furthermore, additives such as lubricants, antistatic agents, antiblocking agents, crystal nucleating agents, heat stabilizers, antioxidants, light stabilizers, ultraviolet absorbers, colorants, etc. may be added to each layer as needed within the range that does not impair the properties of the film of the present invention. The type of additive may be determined appropriately depending on the application, and for example, low-density polyethylene may be added as a crystal nucleating agent.

[0020] The laminate layer 20 corresponds to one surface layer of the sealant film 10, and is the surface onto which the surface substrate 60 described below is laminated. A resin mainly composed of linear low-density polyethylene or a resin mainly composed of a combination of linear low-density polyethylene and high-density polyethylene is preferably selected as the resin constituting the laminate layer 20. The laminate layer 20 may be subjected to a surface treatment such as corona treatment, flame treatment, or plasma treatment to improve adhesion to the surface substrate 60.

[0021] The base layer 30 corresponds to the middle layer of the sealant film 10. The resin constituting the base layer 30 is preferably selected from resins mainly made of linear low-density polyethylene or a combination of linear low-density polyethylene and high-density polyethylene.

[0022] The sealant layer 40 corresponds to the surface layer on the other side of the sealant film 10, and when used as a packaging material (packaging bag), for example, it becomes the inner surface of the bag and is the surface (sealing surface) that is bonded to other films, etc. A resin mainly containing linear low-density polyethylene is preferably selected as the resin constituting the sealant layer 40.

[0023] In this type of resin film, if a high-density resin is used to reduce the volume, the heat-sealing temperature and bag-breaking strength during bag formation may deteriorate, and warping (curling) may occur at the edges of the film. The present inventors have conducted extensive research, focusing on the layer density and layer thickness of each layer of the film, to produce a film that can reduce the volume by improving the elastic modulus of the film while avoiding deterioration in bag-breaking resistance and suppressing warping, and have found that the above-mentioned multiple problems can be solved at once by making the layer density and layer thickness of a specific layer satisfy a predetermined relationship.

[0024] That is, in the sealant film 10 of the present invention, the layer density (D2) of the base layer 30 is 0.935 g / cm 3 The layer density (D3) of the sealant layer 40 is 0.924 g / cm 3 Below, and the overall density (D A ) is 0.930~0.935g / cm 3 The laminate layer 20 has a layer density (D1) and the sealant layer 40 has a layer density (D3) that satisfy the relationship |D1-D3|≦0.020, and the thickness of the sealant layer 40 is 15% or more of the total layer thickness.

[0025] The layer density (D1) of the laminate layer 20 is set to an appropriate density that provides good film properties such as rigidity and elastic modulus. For example, from the viewpoint of obtaining excellent film properties, a preferred layer density (D1) is 0.919 g / cm. 3 More preferably, it is 0.924 g / cm 3 More preferably, 0.931 g / cm 3 The upper limit of the layer density (D1) of the laminate layer 20 is not particularly limited, but from the viewpoint of improving the bag rupture resistance, it is set to 0.955 g / cm 3 is preferred, and 0.950 g / cm 3 is more preferred.

[0026] The layer density (D2) of the base layer 30 contributes to the bag rupture resistance and rigidity of the sealant film 10. A preferred layer density (D2) of the base layer 30 is 0.935 g / cm 3More preferably, 0.940 g / cm 3 That is all. When the base layer 30 satisfies the above layer density (D2) condition, the rigidity of the film becomes good. Furthermore, although there is no particular upper limit for the layer density (D2) of the base layer 30, from the viewpoint of improving the bag-breaking resistance, it is set to 0.955 g / cm 3 is preferred, and 0.950 g / cm 3 is more preferred.

[0027] The layer density (D3) of the sealant layer 40 contributes to the low-temperature sealing properties of the sealant film 10. By adjusting the layer density (D3) of the sealant layer 40, which forms the sealing surface of the film, to a relatively low value, an increase in the heat sealing temperature, etc., is suppressed. The preferred layer density (D3) of the sealant layer 40 is 0.924 g / cm 3 or less, more preferably 0.919 g / cm 3 The low-temperature sealability is improved when the sealant layer 40 satisfies the above layer density (D3) condition. Although the lower limit of the layer density (D3) of the sealant layer 40 is not particularly limited, from the viewpoint of improving the rigidity of the film, it is set to 0.890 g / cm. 3 is preferred, and 0.904 g / cm 3 is more preferred.

[0028] Overall density of sealant film 10 (D A ) contributes to the performance of the bag, such as rupture resistance, rigidity, and elastic modulus. A ) is 0.930 to 0.935 g / cm while satisfying at least the layer density (D2) of the base layer 30 and the layer density (D3) of the sealant layer 40. 3 The total density (D A If the overall density (D) is too small, the elastic modulus may decrease and the film may not have sufficient rigidity, while if it is too large, the bag rupture resistance may decrease. A By appropriately adjusting the above, it is possible to obtain a sealant film that has an excellent elastic modulus, a good balance between film rigidity and bag-breaking resistance, and allows for volume reduction.

[0029] Furthermore, in the sealant film 10, as will be described in the examples below, the difference in density between the surface laminate layer 20 and the sealant layer 40 is small, and the thickness of the sealant layer 40 is relatively thick relative to the overall film, thereby suppressing warping of the film during the production of a volume-reduced film. Specifically, the layer density (D1) of the laminate layer 20 and the layer density (D3) of the sealant layer 40 satisfy the relationship |D1-D3|≦0.020, and the thickness of the sealant layer 40 is 15% or more of the overall layer thickness.

[0030] The density difference (|D1-D3|) between the laminate layer 20 and the sealant layer 40 is an index showing the balance of densities of the two surface layers of the sealant film 10. Furthermore, the thickness (layer ratio) of the sealant layer 40 relative to the overall thickness of the sealant film 10 contributes to suppressing warpage of the sealant film 10. If the density difference (|D1-D3|) is too large, the balance of densities of the two surface layers is lost, or if the layer ratio of the sealant layer 40 is too small, making the sealant layer 40 too thin relative to the overall film, there is a risk of significant warpage of the film. When the density difference (|D1-D3|) value is reduced to achieve a balance of densities of the two surface layers, and when the layer ratio of the sealant layer 40 is increased to make the sealant layer 40 relatively thick relative to the overall film, warpage of the film is suppressed.

[0031] In addition, it is preferable to adjust the relationship between the layer density and the layer ratio of the laminate layer 20 and the sealant layer 40 so that the layer ratio is relatively small when the layer density is relatively large and relatively large when the layer density is relatively small. Furthermore, it is more preferable to adjust the layer ratio of the laminate layer 20 to be smaller than that of the sealant layer 40 when the layer density (D1) of the laminate layer 20 is larger than the layer density (D3) of the sealant layer 40, and to adjust the layer ratio of the laminate layer 20 to be larger than that of the sealant layer 40 when the layer density (D1) of the laminate layer 20 is smaller than the layer density (D3) of the sealant layer 40. By adjusting the relationship between the layer density and the layer ratio of the laminate layer 20 and the sealant layer 40 as described above, warping of the film can be effectively suppressed.

[0032] The layer ratio of the sealant layer 40 also contributes to the elastic modulus and bag rupture resistance of the film. If the layer ratio of the sealant layer 40 is too small, the bag rupture resistance may deteriorate. By setting the layer ratio of the sealant layer 40 to 15% or more, preferably 20% or more, and more preferably 25% or more, it is possible to achieve both an elastic modulus and bag rupture resistance of the film. There is no particular upper limit for the layer ratio of the sealant layer 40, but as the layer ratio of the sealant layer 40 increases, the density of the film as a whole decreases, reducing the elastic modulus. Therefore, from the viewpoint of increasing the elastic modulus of the film, the layer ratio is preferably 40% or less, more preferably 35% or less.

[0033] In the sealant film 10, the preferred modulus of elasticity is 0.66 GPa or more, where MD+TD is the sum of the modulus of elasticity in the machine direction and the modulus of elasticity in the transverse direction. It is more preferred that the modulus of elasticity in the machine direction is 0.31 GPa or more, and the modulus of elasticity in the transverse direction is 0.34 GPa or more. If the modulus of elasticity of the sealant film 10 is insufficient, the film may not be adequately reduced in volume. The modulus of elasticity is measured based on the test method for tensile properties of plastics in accordance with JIS K 7127 (1999).

[0034] In this way, the sealant film 10 of the present invention has a layer density (D2) of the base layer 30, a layer density (D3) of the sealant layer, and a density of the entire film (D A ) in a predetermined high-density range, while keeping the density difference between the layer density (D1) of the laminate layer 20 and the layer density (D3) of the sealant layer small and controlling the layer ratio of the sealant layer 40 relatively high, it is possible to take advantage of the improved elastic modulus that results from the use of a high-density resin, while appropriately avoiding deterioration in low-temperature sealability and bag-breaking resistance, and further suppressing film warping (curl). Therefore, the sealant film 10 of the present invention can achieve volume reduction by improving the elastic modulus while maintaining the performance of a sealant film, contributing to a reduction in environmental impact, and further suppressing film warping, resulting in good film formability.

[0035] A laminate 50 using the sealant film 10 of the present invention is formed by laminating a surface substrate 60 onto the surface layer of the laminate layer 20 of the sealant film 10. As a method for laminating the surface substrate 60 onto the sealant film 10, known methods such as dry lamination and melt extrusion lamination can be used.

[0036] The surface substrate 60 is a stretched film having at least one layer. The surface substrate 60 protects the underlying sealant film 10, and corresponds to the exterior surface when the laminate 50 is used as a packaging material, for example. This surface substrate 60 is subjected to printing and the like, and various functions depending on the application, such as durability, weather resistance, light resistance, etc., are imparted to it by adding appropriate additives.

[0037] One or more films selected from biaxially oriented polypropylene film, uniaxially oriented polyethylene film, biaxially oriented polyethylene film, biaxially oriented polyethylene terephthalate film, and biaxially oriented polyamide film are preferably selected for the front substrate 60. These films are inexpensive and have excellent processability and strength, making them suitable for protecting the sealant film 10. [Example]

[0038] [Preparation of sealant film] In producing the sealant films of Prototype Examples 1 to 13, the materials described below were fed into an extrusion device, melted and kneaded, and extruded into three layers using a T-die method: a laminate layer, a base layer, and a sealant layer, to produce a film with an overall thickness (total thickness) of 50 μm. The layer thickness (layer ratio) of each layer relative to the total thickness was adjusted. After film production, the laminate layer was subjected to a surface treatment using a corona discharge treatment. In Prototype Examples 1 to 13, the resin content of each layer was adjusted to 100% by weight. Additives such as antiblocking agents were omitted.

[0039] [Materials used] The following resins were used as the resin materials for the laminate layer, base layer, and sealant layer. The materials used for each layer in prototypes 1 to 13 are shown in Tables 1 and 2 below, along with the layer ratios of each layer and the film thickness (total film thickness).

[0040] PE1: Linear low-density polyethylene (FX307, manufactured by Sumitomo Chemical Co., Ltd.), density 0.890 g / cm 3 PE2: Linear low-density polyethylene (Ube Maruzen Polyethylene Co., Ltd.; 0540F), density 0.904 g / cm 3 PE3: Linear low-density polyethylene (Ube Maruzen Polyethylene Co., Ltd.; 1540FC), density 0.913 g / cm 3 PE4: Linear low-density polyethylene (Ube Maruzen Polyethylene Co., Ltd.; 2040FC), density 0.919 g / cm 3 PE5: Linear low-density polyethylene (Prime Polymer Co., Ltd.; SP2540), density 0.924 g / cm 3 PE6: Linear low-density polyethylene (Ube Maruzen Polyethylene Co., Ltd.; 3570FC), density 0.931 g / cm 3 PE7: Linear low-density polyethylene (Ube Maruzen Polyethylene Co., Ltd.; 4040F), density 0.937 g / cm 3 PE8: Linear low-density polyethylene (Ube Maruzen Polyethylene Co., Ltd.; 4540F), density 0.944 g / cm 3 PE9: High-density polyethylene (Japan Polyethylene Co., Ltd.; HF562), density 0.963 g / cm 3 PE10: Low-density polyethylene (Ube Maruzen Polyethylene Co., Ltd.; R300), density 0.920 g / cm 3

[0041] [Prototype 1] The sealant film of prototype 1 was composed of 100.0 wt% PE6 for the laminate layer, 69.0 wt% PE6 and 31.0 wt% PE9 for the base layer, and 100.0 wt% PE4 for the sealant layer, with the layer ratio of the laminate layer being 16.0%, the layer ratio of the base layer being 59.0%, and the layer ratio of the sealant layer being 25.0%.

[0042] [Prototype 2] The sealant film of prototype 2 had the same structure as prototype 1, except that the layer ratio of the base layer was changed to 54.0% and the layer ratio of the sealant layer was changed to 30.0%.

[0043] [Prototype 3] The sealant film of Prototype 3 had the same structure as Prototype 1, except that PE3 was blended in place of PE4 in the sealant layer.

[0044] [Prototype 4] The sealant film of prototype 4 was the same as prototype 1 except that the base layer consisted of 86.0% by weight PE6 and 14.0% by weight PE9, the layer ratio of the base layer was changed to 68.0%, and the layer ratio of the sealant layer was changed to 16.0%,

[0045] [Prototype 5] The sealant film of prototype 5 had the same structure as prototype 1, except that PE5 was blended in place of PE4 in the sealant layer.

[0046] [Prototype 6] The sealant film of prototype 6 had the same structure as prototype 1, except that the layer ratio of the base layer was changed to 71.5% and the layer ratio of the sealant layer was changed to 12.5%.

[0047] [Prototype 7] The sealant film of prototype 7 had the same structure as prototype 1, except that the layer ratio of the base layer was changed to 74.0% and the layer ratio of the sealant layer was changed to 10.0%.

[0048] [Prototype 8] The sealant film of prototype 8 had the same structure as prototype 1, except that PE2 was blended in place of PE4 in the sealant layer.

[0049] [Prototype 9] The sealant film of Prototype Example 9 had the same structure as Prototype Example 1, except that PE1 was blended in place of PE4 in the sealant layer.

[0050] [Prototype 10] The sealant film of prototype 10 was composed of 93.0 wt% PE7 and 7.0 wt% PE10 for the laminate layer, 93.0 wt% PE7 and 7.0 wt% PE10 for the base layer, and 100.0 wt% PE4 for the sealant layer, with a layer ratio of 12.5% ​​for the laminate layer, 75.0% for the base layer, and 12.5% ​​for the sealant layer.

[0051] [Prototype 11] The sealant film of prototype 11 had the same structure as prototype 5, except that the base layer contained 100.0 wt % PE5.

[0052] [Prototype 12] The sealant film of prototype 12 had the same configuration as prototype 1, except that PE2 was blended in instead of PE6 in the laminate layer and PE6 was blended in instead of PE4 in the sealant layer.

[0053] [Prototype 13] The sealant film of prototype 13 was the same as prototype 1 except that the base layer contained 100.0% PE8 by weight, the layer ratio of the base layer was 68.0%, and the layer ratio of the sealant layer was 16.0%, but the rest of the structure was the same.

[0054] [Table 1]

[0055] [Table 2]

[0056] To evaluate the performance of the sealant films of prototypes 1 to 13, the layer densities of the laminate layer, base layer, and sealant layer (D1, D2, D3), and the overall density of the film (D A ), and the density difference (|D1-D3|) between the layer density of the laminate layer (D1) and the layer density of the sealant layer (D3) was calculated. The tensile modulus, heat seal initiation temperature (low-temperature sealability), film curl amount, and bag rupture strength were also measured. For the overall evaluation, a product that was judged to be good in all of the tensile modulus, heat seal initiation temperature, film curl amount, and bag rupture resistance was rated as "Good (○)," and a product that was judged to be defective in any one of the categories was rated as "Poor (×)." The measurement results are shown in Tables 3 and 4 below.

[0057] [Density calculation] For prototypes 1 to 13, the density of each layer (D1, D2, D3) of the laminate layer, base layer, and sealant layer and the overall density (D A )(g / cm 3 ) was calculated based on the following formula (i). The density difference (|D1-D3|) was calculated from the calculated layer density (D1) of the laminate layer and the layer density (D3) of the sealant layer. Formula (i) is used to calculate the density (ρ blend ) and ρ X is the density of raw material X, ρ Y is the density of raw material Y, ρ Z is the density of raw material Z, x is the blending ratio of raw material X, y is the blending ratio of raw material Y, and z is the blending ratio of raw material Z.

[0058]

number

[0059] [Measurement of tensile modulus] The tensile modulus (GPa) is an index of processability. Measurements were made using a tensile testing machine (Orientec Co., Ltd., RTF-1310) in both the machine direction (MD) and the transverse direction (TD) based on the test method for plastic tensile properties in accordance with JIS K 7127 (1999). A product was deemed good if the sum of the machine direction modulus and the transverse direction modulus (MD + TD) was 0.66 or greater, and a product was deemed best if the machine direction modulus was 0.32 GPa or greater, the transverse direction modulus was 0.35 GPa or greater, and the sum of the machine direction and transverse direction modulus (MD + TD) was 0.66 or greater.

[0060] [Measurement of heat seal initiation temperature] The heat-sealing initiation temperature (°C) is one indicator of processability. This measurement was based on the heat-sealing initiation temperature test in accordance with JIS Z 1713 (2009). First, the films prepared in Examples 1 to 13 were cut into rectangular shapes measuring 50 mm in the transverse (TD) direction and 250 mm in the longitudinal (MD) direction to prepare test specimens. The sealant layers of two test specimens were placed together and heat-sealed using a heat-sealing tester (Toyo Seiki Seisakusho Co., Ltd.; "Thermal Gradient Tester") at a heat-sealing pressure of 0.4 MPa, a heat-sealing time of 1 second, and a temperature gradient (heat rise) of 5°C. During heat-sealing, a cellophane film was sandwiched between the heat sealer's hot plate and the test specimen to prevent adhesion. After heat-sealing, the fused test specimens were opened 180°, and the unsealed portion of the test specimen was clamped between the zipper and the sealed portion using a small tabletop tester (Shimadzu Corporation; "EZ-SX"). The temperature at which the heat seal strength reached 3 (N / 15 mm) was taken as the heat seal initiation temperature, which was calculated by interpolation. From the measurement results, products were judged to be good when the temperature was 120°C or less.

[0061] [Film curl amount] The sealant films of prototypes 1 to 13 were cut into squares measuring 10 cm in the transverse (TD) direction and 10 cm in the longitudinal (MD) direction to prepare test specimens. The test specimens were placed on a flat table, and the highest point of the height of the edge where warping occurred on the test specimen was measured as the amount of curl of the film. A curl amount of 4.0 mm or less was considered a pass, and the warp suppression performance was evaluated.

[0062] [Bag resistance performance] To evaluate the bag rupture resistance of the sealant films of Prototype Examples 1 to 13, laminate films were produced using the sealant films of Prototype Examples 1 to 13 as described below, assuming actual products (packaging bags), and these laminate films were made into bags to obtain sample bags. The resulting sample bags corresponding to each of Prototype Examples 1 to 13 were subjected to the bag rupture test described below.

[0063] For the laminate film, a 15 μm thick biaxially oriented nylon film (Mitsubishi Chemical Corporation; "Santonir SNR") was used as the front substrate. An adhesive prepared for dry lamination (Toyo-Morton Co., Ltd.; base: TM-329, curing agent: CAT-8B, solvent: ethyl acetate) was applied to the film surface of the front substrate at a rate of approximately 3 g / m. 2 After coating and drying the adhesive, the surface substrate was attached to the surface of the laminate layer of the sealant film of prototypes 1 to 13, and the sealant film and the surface substrate were adhered together by sequentially passing a roller through the surface substrate to produce a laminate film.

[0064] Sample bags were prepared by heat-sealing three sides of a 130 mm x 180 mm bag, with the sealant film side (sealant layer) of the laminate film facing the inner surface of the bag. Heat-sealing was performed using an impulse sealer (Fuji Impulse Co., Ltd.; "OPL-350-MD NP") under the following conditions: sealing temperature 160°C, heating time 1.0 second, and cooling temperature 60°C. After pouring 200 mL of tap water into the prepared bag, the unsealed opening was heat-sealed under the same conditions to seal the bag. The prepared sample bags were stored in water at 0°C in a refrigerator for 24 hours. Five sample bags were prepared for each of Prototype Examples 1 to 13.

[0065] In the bag-breaking test, a bag-breaking test apparatus 100 shown in FIG. 2 was used. A sample bag S stored in a refrigerator was placed on the loading section 101 of the bag-breaking test apparatus 100, and a 3 kg iron plate section 102 was tilted from the 90° position shown in the figure toward the sample bag S on the loading section 101 via a rotating section 103 to apply an impact to the sample bag S. This operation was counted as one cycle and repeated up to 50 times. The number of sample bags for which breakage was confirmed before the 50th cycle (number of broken bags) was calculated. In this bag-breaking test, for each of the prototypes 1 to 13, the operation was repeated 50 times with five sample bags, and if no breakage was confirmed even once, the product was deemed to be a good product and its resistance to bag breakage was evaluated.

[0066] [Table 3]

[0067] [Table 4]

[0068] [Results and Discussion] As shown in Tables 3 and 4, prototypes 1 to 5 were judged to be good products in terms of modulus of elasticity, sealing start temperature (low-temperature sealing), curl amount, and number of broken bags (bag-breaking resistance), while prototypes 6 to 13 were judged to be poor (unacceptable) in terms of at least one of modulus of elasticity, sealing start temperature (low-temperature sealing), curl amount (curl suppression performance), and number of broken bags (bag-breaking resistance).

[0069] First, an examination of curl suppression performance showed that the films of prototypes 6 to 10 and 12 had large curl amounts and insufficient curl suppression performance. Comparing prototype 1, which had an extremely good curl amount of 0.0 mm, with prototypes 2, 6 and 7, which had different sealant layer ratios, prototype 2, which had an increased sealant layer ratio from prototype 1, showed extremely good curl suppression performance similar to prototype 1, whereas prototypes 6 and 7, which had a decreased sealant layer ratio, showed significantly reduced curl suppression performance.

[0070] Furthermore, when Prototype 1 was compared with Prototypes 3, 5, 8, and 9, which had different sealant layer types, Prototypes 3 and 5 had a small density difference (|D1-D3|) between the laminate layer and the sealant layer, the amount of curl was within the acceptable range, and the curl suppression performance was good. On the other hand, Prototypes 8 and 9 had a large density difference (|D1-D3|) between the laminate layer and the sealant layer, the amount of curl exceeded the acceptable range, and the curl suppression performance was significantly reduced.

[0071] Here, we examine the layer ratio of the sealant layer and the density difference (|D1-D3|) between the laminate layer and the sealant layer for Prototypes 1 to 5, which are good products, and Prototypes 6 to 10 and 12, which have insufficient curl-suppressing performance. The layer ratio of the sealant layer was 12.5% ​​for Prototypes 6 and 10, and 10.0% for Prototype 7, while all of Prototypes 1 to 5 had values ​​greater than those for Prototypes 6, 7, and 10. Furthermore, the density difference (|D1-D3|) between the laminate layer and the sealant layer was 0.0270 for Prototypes 8 and 12, and 0.0410 for Prototype 9, while all of Prototypes 1 to 5 had values ​​smaller than those for Prototypes 8, 9, and 12. Therefore, to obtain good curl-suppressing performance, it is considered preferable to increase the layer ratio of the sealant layer relatively and reduce the density difference between the laminate layer and the sealant layer. From the above prototypes 1 to 5 and prototypes 6 to 10 and 12, it is considered preferable that the layer ratio of the sealant layer is about 15% or more and the density difference (|D1-D3|) between the laminate layer and the sealant layer is about 0.020 or less.

[0072] When examining the elastic modulus of the film, in prototype 11, the elastic modulus in the machine direction (MD) and the transverse direction (TD) and the sum of these (MD + TD) were insufficient. When prototype 11 was compared with prototype 5, which was a good prototype and differed only in the type of resin in the base layer, prototype 11 had a layer density (D2) of the base layer and an overall density (D A ) was lower than that of Prototype 5. In addition, in Prototype 9, the modulus of elasticity in the machine (MD) direction and the sum of the modulus of elasticity in the machine (MD) direction and the transverse (TD) direction (MD+TD) were insufficient. In Prototype 9, the overall density (D A ) was almost the same value as that of Prototype 11. From this, it can be seen that the layer density (D2) of the base layer and the overall density (D A ) is too low, the elastic modulus of the film is thought to decrease.

[0073] When examining low-temperature sealability, Prototype 12 had a high heat-sealing initiation temperature and insufficient low-temperature sealability. Prototype 12 had a higher layer density (D3) of the sealant layer than did the good-quality products of Prototypes 1 to 5. This suggests that if the layer density (D3) of the sealant layer is too high, the low-temperature sealability of the film will be reduced.

[0074] When examining the bag rupture resistance, in prototypes 6, 7, 10, 12, and 13, the sample bags were found to be broken in the bag rupture test, and sufficient bag rupture resistance was not obtained. When comparing the above prototypes with prototypes 1 to 5, which are good products, prototypes 6 and 7 have a small layer ratio of the sealant layer and a low overall density (D A ) is a high value, the layer ratio of the sealant layer is a small value in prototype 10, the layer density (D3) of the sealant layer is a high value in prototype 12, and the overall density (D A ) was high. From this, it was found that the layer ratio of the sealant layer, the layer density (D3), and the overall density (D A ) is not an appropriate value, the film's resistance to bag rupture is thought to be reduced.

[0075] As mentioned above, when considering prototypes 1 to 13 comprehensively, the layer density of the base layer (D2) is 0.935 g / cm 3 The layer density of the sealant layer (D3) is 0.924 g / cm 3 Below, the total density (D A ) is 0.930~0.935g / cm 3 By satisfying the following requirements: the density difference (|D1-D3|) between the laminate layer and the sealant layer is 0.020 or less, and the layer ratio of the sealant layer is 15% or more, it is believed that the film's elastic modulus, low-temperature sealing properties, bag-breaking resistance, and curl suppression properties will all be good. [Industrial Applicability]

[0076] As described above, the polyethylene sealant film of the present invention can solve multiple problems that tend to occur when attempting to reduce the volume, such as deterioration in the film's elastic modulus, low-temperature sealability, bag-breaking resistance, and curl suppression performance, etc. Therefore, the polyethylene sealant film of the present invention and a laminate using this film can exhibit good film-forming properties and contribute to reducing the environmental load, and are promising alternatives to conventional polyethylene sealant films and laminates. [Explanation of symbols]

[0077] 10 Polyethylene sealant film 20 laminate layers 30 Base layer 40 Sealant Layer 50 laminate 60 Table base material 100 Bag Breaking Testing Device 101 Placement section 102 Iron Plate Section 103 Rotating part S sample bag

Claims

1. A film body mainly made of polyethylene resin, which comprises at least three or more layers, namely, a laminate layer, a base layer, and a sealant layer, and in which the laminate layer, the base layer, and the sealant layer are laminated in this order, The film body has a layer density (D ２ ) is 0.935 g / cm ３ The layer density (D ３ ) is 0.924 g / cm ３ Below, and the overall density (D Ａ ) is 0.930 to 0.935 g / cm ３ and The sum of the elastic modulus in the machine direction (MD) and the elastic modulus in the transverse direction (TD) (MD+TD) measured based on the test method for tensile properties of plastics in accordance with JIS K 7127 (1999) is 0.66 GPa or more, The layer density (D １ ) and the layer density (D ３ ) is |D １ -D ３ |≦0.020 and the thickness of the sealant layer is 15% or more of the total thickness of the sealant layer. A polyethylene sealant film characterized by:

2. A laminate obtained by laminating a stretched surface substrate having at least one layer structure on the surface layer of the laminate layer of the polyethylene sealant film according to claim 1.

3. 3. The laminate according to claim 2, wherein the surface substrate comprises at least one of a biaxially oriented polypropylene film, a uniaxially oriented polyethylene film, a biaxially oriented polyethylene film, a biaxially oriented polyethylene terephthalate film, and a biaxially oriented polyamide film.

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