Stretched polyethylene film

Abstract

To provide, in a base film corresponding to mono-materialization of a laminate using a heat-sealable polyethylene film, a stretched polyethylene film which is excellent in performance such as rigidity, toughness, and thermal resistance.SOLUTION: Provided is a stretched polyethylene film formed of an ethylenic resin composition comprising: 20-90 wt.% of either or both of an ethylene homopolymer or a copolymer component of ethylene-olefin comonomer, having a density of 0.940-0.970 g / cm3 and an MFR of 0.1-10 g / 10 min; and 10-80 wt.% of a copolymer component of ethylene and an olefin comonomer having a density of 0.860-0.926 g / cm3 and an MFR of 1.0-30.0 g / 10 min, where the ethylenic resin composition has a density of 0.930-0.960 g / cm3, an MFR of 0.5-10 g / 10 min, an amount of heat of fusion (ΔHtotal) of 110.0-200.0 J / g, and an amount of heat of fusion (ΔH124 upward arrow) at a fractionation temperature of 124°C or more of 80.0-190.0 J / g.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyethylene film used as a base film for a laminate, and more particularly to a stretched polyethylene film that is stretched in at least one direction. [Background technology]

[0002] Generally, packaging materials made of synthetic resin film are composed of laminates formed by bonding a base film (which has been printed or otherwise processed) and a sealant film together with an adhesive (lamination process). The base film of the laminate is required to have properties such as heat resistance, rigidity, and pinhole resistance, and biaxially oriented films mainly composed of polyester, polyamide, and polypropylene are used. The sealant film of the laminate is an unoriented film composed of polypropylene or polyethylene, and polyethylene-based unoriented films are particularly preferred due to their excellent heat-sealability.

[0003] As described above, synthetic resin packaging materials tend to be composites made by laminating multiple types of resins. However, with the growing concern for environmental issues in recent years and the desire for recycling waste plastics, it has been difficult to recycle each resin separately in films made by laminating multiple types of resins. Therefore, in this type of synthetic resin packaging material, it is necessary to construct the base film and sealant film from a single material (monomaterial).

[0004] In packaging materials that use a base film and a sealant film as a single material, for example, a polyethylene laminate is known in which a polyethylene-based material, which is preferably used as the sealant film, is used as the base film (see Patent Document 1). This polyethylene laminate comprises an oriented polyethylene film as the base film and a heat-sealable polyethylene film as the sealant film, and is configured so that the adhesive layer contains a solvent-free adhesive from the viewpoint of reducing environmental impact.

[0005] In the case of a laminate which is this type of packaging material, the performance such as rigidity, toughness, heat resistance, etc. depends on the performance of the base film. Therefore, in the base film of the laminate, it is required to use a stretched polyethylene film corresponding to the monomerization of the laminate using a heat-sealing polyethylene film to further improve the performance such as rigidity, toughness, heat resistance, etc.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention has been proposed in view of the above situation, and provides a stretched polyethylene film excellent in performance such as rigidity, toughness, heat resistance, etc. in a base film corresponding to the monomerization of a laminate using a heat-sealing polyethylene film.

Means for Solving the Problems

[0008] That is, the invention of claim 1 is a stretched polyethylene film used as a base film of a laminate used for a packaging material for packaging contents by heat sealing, which is stretched in at least one direction, and the density is 0.952~0.960 g / cm 3 , the MFR is 0.1 to 10 g / 10 min High-density polyethylene is 20 to 90% by weight, and the density is 0.890 ~0.926 g / cm 3 , the MFR is 1.0 to 4.0 g / 10 min Ultra-low density polyethylene or linear low-density polyethylene is 10 to 80% by weight, and is composed of an ethylene resin composition (A), and the density of the ethylene resin composition (A) is 0.930 to 0.960 g / cm 3and the MFR is 0.5 to 10 g / 10 min, and the heat of fusion (ΔH total ) obtained by measuring using a differential scanning calorimeter (DSC) with the SSA method is 110.0 to 200.0 J / g, and the heat of fusion (ΔH 124↑ ) at a fractionation temperature of 124°C or higher is 80.0 to 190.0 J / g, and in the heating shrinkage rate measured at 120°C, the shrinkage rate in the longitudinal direction is 15% or less, and the sum of the shrinkage rates in the longitudinal and transverse directions is 25% or less, which relates to a stretched polyethylene film.

[0009] The invention according to claim 2 relates to the stretched polyethylene film according to claim 1, wherein the tensile fracture elongation measured in accordance with JIS K 7127 (1999) is 40% or more in at least one of the longitudinal direction or the transverse direction.

[0011] Claim 3 The invention of relates to the stretched polyethylene film according to claim 1, which is formed by stretching a sheet shaped by the T-die method. Or to 2 described.

[0012] Claim 4 The invention of relates to the stretched polyethylene film according to any one of claims 1 to, wherein at least one surface is surface-treated to have a wetting tension of 36 mN / m or more. 3

Advantages of the Invention

[0013] According to the stretched polyethylene film according to the invention of claim 1, it is a stretched polyethylene film used as a base film of a laminate used as a packaging material for packaging contents by heat sealing and stretched in at least one direction, and the density is 0.952~0.960 g / cm 3 , the MFR is 0.1 to 10 g / 10 min High-density polyethylene is 20 to 90% by weight, and the density is 0.890 ~0.926 g / cm 3 , the MFR is 1.0 to 4.0 g / 10 min Ultra-low density polyethylene or linear low-density polyethyleneIt consists of an ethylene-based resin composition (A) comprising 10 to 80% by weight, and the density of the ethylene-based resin composition (A) is 0.930 to 0.960 g / cm 3 and the MFR is 0.5 to 10 g / 10 min. The heat of fusion (ΔH total ) obtained by measuring using a differential scanning calorimeter (DSC) and the SSA method is 110.0 to 200.0 J / g, and the heat of fusion (ΔH 124↑ ) at a fractionation temperature of 124 °C or higher is 80.0 to 190.0 J / g. In the heat shrinkage rate measured at 120 °C, the shrinkage rate in the longitudinal direction is 15% or less, and the sum of the shrinkage rates in the longitudinal and transverse directions is 25% or less. Therefore, it has excellent properties such as rigidity, toughness, and heat resistance, and can be suitably used as a base film corresponding to the monomaterialization of a laminate using a heat-sealable polyethylene film. Also, high dimensional accuracy at high temperatures required for a base film can be obtained.

[0014] According to the stretched polyethylene film according to the invention of claim 2, in the invention of claim 1, since the tensile fracture elongation measured in accordance with JIS K 7127 (1999) is 40% or more in at least one of the longitudinal and transverse directions, good processing suitability is obtained, and the range of use as a base film is expanded.

[0016] Claim 3 According to the stretched polyethylene film according to the invention of, in the invention of claim 1 or 2 Since the sheet shaped by the T-die method is stretched, high thickness accuracy required for a base film can be obtained.

[0017] Claim 4 According to the stretched polyethylene film according to the invention of, in the inventions of claims 1 to 3 Since at least one surface is surface-treated to have a wetting tension of 36 mN / m or more, good printing processing suitability and lamination processing suitability required for processing into a packaging material are obtained, and the range of use as a base film is expanded. [Modes for carrying out the invention]

[0018] An oriented polyethylene film according to one embodiment of the present invention is a film stretched in at least one direction and used as a base film for a laminate. The laminate includes a base film and a sealant film made of a single polyethylene resin material (monomaterial), and is suitably used as packaging material for various articles such as food, daily necessities, and parts.

[0019] Stretched polyethylene film has a density of 0.940 to 0.970 g / cm³. 3 The first component consists of either an ethylene homopolymer or a copolymer of ethylene and an olefin comonomer, or both, with an MFR of 0.1 to 10 g / 10 min, in an amount of 20 to 90% by weight, and a density of 0.860 to 0.926 g / cm³. 3 The ethylene-based resin composition (A) consists of 10 to 80% by weight of a second component consisting of a copolymer of ethylene and an olefin comonomer having an MFR of 1.0 to 30.0 g / 10 min. The ethylene homopolymer refers to a polymer derived from ethylene monomers, and low-density polyethylene and high-density polyethylene are selectable, selected within the density range. The copolymer of ethylene and an olefin comonomer is selectable from ultra-low-density polyethylene, linear low-density polyethylene, and high-density polyethylene, selected within the density range.

[0020] Ethylene-based resin composition (A) is prepared by mixing a first component and a second component, which have different polyethylene densities and MFRs, in the aforementioned mixing ratio, so that the overall density of ethylene-based resin composition (A) is 0.930 to 0.960 g / cm³. 3 The device is configured so that the MFR (measuring fiber intake) is 0.5 to 10 g / 10 min.

[0021] The density of the ethylene resin composition (A) is 0.930 g / cm³. 3 If the density is less than 0.960 g / cm³, the heat resistance of the base film will be poor, and shrinkage or melting of the film may occur during processing. 3If the value is greater, the toughness of the base film may decrease. If the MFR of the ethylene-based resin composition (A) falls outside the range of 0.5 to 10 g / 10 min, properties such as extrusion suitability, stretchability (break resistance), and thickness-to-thickness characteristics (thickness uniformity) may decrease, potentially leading to poor moldability.

[0022] Furthermore, the ethylene-based resin composition (A) has a heat of fusion (ΔH) measured by a scanning calorimeter (DSC). total The heat of fusion (ΔH) is 110.0-200.0 J / g, and the heat of fusion at a fractionation temperature of 124°C or higher is ΔH 124↑ The irradiance is 80.0 to 190.0 J / g.

[0023] Heat of fusion (ΔH) total The total heat of fusion below 150°C was determined from the endothermic peaks obtained by measuring the self-seeding and annealing temperature (Ts) from 139°C to 59°C in 5°C increments using a scanning calorimeter and the SSA (Successive Self-Nucleation / Annealing) method described in Polymer Bulletin 39, 465-472 (1997). The total heat of fusion was calculated by taking a baseline horizontally starting from 150°C.

[0024] Heat of fusion (ΔH) at fractionation temperature of 124°C or higher 124↑ ) refers to the heat of fusion between 124°C and 150°C, obtained by fractionating the total heat of fusion below 150°C, from the endothermic peaks obtained using the SSA (Successive Self-Nucleation / Annealing) method described in Polymer Bulletin 39, 465-472 (1997), with the Self-seeding and annealing temperature (Ts) set from 139°C to 59°C in 5°C increments. The total heat of fusion is calculated by taking a baseline horizontally starting from 150°C, and the heat of fusion above the fractionation temperature of 124°C (ΔH) is calculated. 124↑ The same baseline was used for ).

[0025] In the ethylene-based resin composition (A), the heat of fusion (ΔH total If the heat of fusion (ΔH) is less than 110.0 J / g, or if the fractionation temperature is 124°C or higher, 124↑ If the heat of fusion (ΔH) is less than 80.0 J / g, the heat resistance and rigidity as a base material fill will decrease. total If the heat of fusion (ΔH) is greater than 200.0 J / g, or if the fractionation temperature is 124°C or higher, 124↑ If the value is greater than 190.0 J / g, the toughness of the base film decreases.

[0026] The stretched polyethylene film of the present invention is provided with excellent heat resistance by being stretched in at least one direction. In this case, it is preferable that the tensile elongation at break, measured in accordance with JIS K 7127 (1999), is 40% or more in at least one of the longitudinal or transverse directions, as this provides good processing suitability and broadens the range of applications as a base film. The tensile elongation at break is the value measured using a tensile testing machine in accordance with JIS K 7127 (1999), at a tensile speed of 200 mm / min and a test specimen sample width of 15 mm. If the tensile elongation at break is less than 40%, the film itself becomes brittle, and there is a concern that processing suitability will decrease and problems such as tearing and ripping may occur when used as a base film.

[0027] This stretched polyethylene film can be obtained by any suitable film forming method, but it is preferable to obtain it by stretching a sheet formed by the T-die method. Film forming by the T-die method allows for the high thickness-to-thinness accuracy required for a base film.

[0028] Furthermore, in the stretched polyethylene film of the present invention, in order to obtain the high dimensional accuracy required for a base film at high temperatures, it is preferable that the thermal shrinkage rate measured at 120°C is 15% or less in the longitudinal direction and 25% or less in the sum of the longitudinal and transverse shrinkage rates. The thermal shrinkage rate is expressed as a percentage change obtained by, for example, heating a test piece of the film at 120°C for a predetermined time, then slowly cooling it to room temperature, measuring the dimensions of the test piece after heating, and comparing them with the dimensions of the test piece measured before heating. If this thermal shrinkage rate exceeds the above value, there is a risk that the dimensional accuracy required for a base film at high temperatures cannot be obtained.

[0029] Furthermore, in order to broaden the range of applications of the stretched polyethylene film of the present invention as a base film, it is preferable that at least one surface of the film be surface-treated to have a wetting tension of 36 mN / m or more. Examples of surface treatments include atmospheric pressure plasma treatment, flame treatment, and corona discharge treatment. The wetting tension is measured by the wetting tension test method in accordance with JIS K 6768 (1999). A wetting tension of less than 36 mN / m is undesirable because it can cause printing defects and lamination defects. [Examples]

[0030] [Production of stretched polyethylene film] Each of the materials described below was blended as the first or second component, melted, and kneaded. The mixture was then extruded into a single layer (intermediate layer only) or multiple layers (intermediate layer and surface layers on both sides of the intermediate layer) using a T-die method. The films were then uniaxially or biaxially stretched to form films, and the surfaces were treated with corona discharge to achieve a wetting tension of 36 mN / m to obtain the stretched polyethylene films (base films) of prototypes 1 to 7. In each of prototypes 1 to 7, the resin blending ratio was 100% by weight for each of the intermediate or surface layers.

[0031] [Materials used] • Resin 1: High-density polyethylene (manufactured by Keiyo Polyethylene Co., Ltd.; E8080), density 0.958 g / cm³ 3, MFR(190℃ / 2.16kg):1.0g / 10min • Resin 2: High-density polyethylene (manufactured by Nippon Polyethylene Co., Ltd.; HY430), density 0.956 g / cm³ 3 , MFR(190℃ / 2.16kg):0.8g / 10min • Resin 3: High-density polyethylene (manufactured by Nippon Polyethylene Co., Ltd.; HY340), density 0.952 g / cm³ 3 , MFR(190℃ / 2.16kg):1.4g / 10min • Resin 4: High-density polyethylene (manufactured by Nippon Polyethylene Co., Ltd.; HF562), density 0.960 g / cm³ 3 , MFR(190℃ / 2.16kg):7.5g / 10min • Resin 5: Ultra-low density polyethylene (manufactured by Sumitomo Chemical Co., Ltd.; FX307), density 0.890 g / cm³ 3 , MFR(190℃ / 2.16kg):3.2g / 10min • Resin 6: Linear low-density polyethylene (Dow Chemical; TF80), density 0.926 g / cm³ 3 , MFR(190℃ / 2.16kg):1.7g / 10min • Resin 7: Linear low-density polyethylene (manufactured by Prime Polymer Co., Ltd.; SP2040), density 0.918 g / cm³ 3 , MFR(190℃ / 2.16kg):4.0g / 10min

[0032] [Prototype Example 1] Prototype Example 1 is an ethylene-based resin composition consisting of a single layer of an intermediate layer with a thickness of 25 μm, which is extruded and then uniaxially stretched in the longitudinal direction (MD) to form a film. The intermediate layer is composed of a first component, which is a mixture of 71.2% by weight of resin 1 and 10.4% by weight of resin 2, and a second component, which is 18.4% by weight of resin 5. The density of the ethylene-based resin composition of Prototype Example 1 is 0.944 g / cm³. 3 The MFR (190℃ / 2.16kg) is 1.2g / 10min.

[0033] [Prototype Example 2] Prototype Example 2 is an ethylene-based resin composition consisting of three layers (20 μm thick): an intermediate layer with a thickness of 18 μm, a first surface layer with a thickness of 1 μm on one side of the intermediate layer, and a second surface layer with a thickness of 1 μm on the other side of the intermediate layer. The film is produced by extrusion molding and biaxial stretching in the longitudinal (MD) and width (TD) directions. The intermediate layer is composed of a first component consisting of 30.0% by weight of resin 2 and a second component consisting of 70.0% by weight of resin 6. Each surface layer is composed of a first component consisting of 30.0% by weight of resin 2 and a second component consisting of 70.0% by weight of resin 6. The density of the ethylene-based resin composition of Prototype Example 2 is 0.934 g / cm³. 3 The MFR (190℃ / 2.16kg) is 1.4g / 10min.

[0034] [Prototype Example 3] Prototype Example 3 is an ethylene-based resin composition consisting of three layers (20 μm thick): an intermediate layer with a thickness of 18 μm, a first surface layer with a thickness of 1 μm on one side of the intermediate layer, and a second surface layer with a thickness of 1 μm on the other side of the intermediate layer. The film is produced by extrusion molding and biaxial stretching in the longitudinal (MD) and width (TD) directions. The intermediate layer is composed of a first component with 20.0% by weight of resin 2 and a second component with 80.0% by weight of resin 6. Each surface layer is composed of a first component with 30.0% by weight of resin 2 and a second component with 70.0% by weight of resin 6. The density of the ethylene-based resin composition of Prototype Example 3 is 0.932 g / cm³. 3 The MFR (190℃ / 2.16kg) is 1.5g / 10min.

[0035] [Prototype Example 4] Prototype Example 4 is an ethylene-based resin composition consisting of three layers (20 μm thick): an intermediate layer with a thickness of 18 μm, a first surface layer with a thickness of 1 μm on one side of the intermediate layer, and a second surface layer with a thickness of 1 μm on the other side of the intermediate layer. The film is produced by extrusion molding and biaxial stretching in the longitudinal (MD) and width (TD) directions. The intermediate layer is composed of a first component consisting of 20.0% by weight of resin 4 and a second component consisting of 80.0% by weight of resin 6. Each surface layer is composed of a first component consisting of 20.0% by weight of resin 2 and a second component consisting of 80.0% by weight of resin 6. The density of the ethylene-based resin composition of Prototype Example 4 is 0.932 g / cm³. 3The MFR (190℃ / 2.16kg) was 2.2g / 10min.

[0036] [Prototype Example 5] Prototype Example 5 is an ethylene-based resin composition consisting of a single layer of an intermediate layer with a thickness of 50 μm, which is extruded and then uniaxially stretched in the longitudinal direction (MD) to form a film. The intermediate layer is composed of a first component, which is a mixture of 6.0% by weight of resin 2 and 94.0% by weight of resin 3. The density of the ethylene-based resin composition of Prototype Example 5 is 0.952 g / cm³. 3 The MFR (190℃ / 2.16kg) is 1.4g / 10min.

[0037] [Prototype Example 6] Prototype Example 6 is an ethylene-based resin composition consisting of a single layer of an intermediate layer with a thickness of 50 μm, which is extruded and then uniaxially stretched in the longitudinal direction (MD) to form a film. The intermediate layer is composed of a second component, with resin 7 at 100.0% by weight. The density of the ethylene-based resin composition in Prototype Example 6 is 0.918 g / cm³. 3 The MFR (190℃ / 2.16kg) is 4.0g / 10min.

[0038] [Prototype Example 7] Prototype Example 7 is an ethylene-based resin composition consisting of three layers (20 μm thick): an intermediate layer with a thickness of 18 μm, a first surface layer with a thickness of 1 μm on one side of the intermediate layer, and a second surface layer with a thickness of 1 μm on the other side of the intermediate layer. The film is produced by extrusion molding and biaxial stretching in the longitudinal (MD) and width (TD) directions. The intermediate layer is composed of a first component with 10.0% by weight of resin 2 and a second component with 90.0% by weight of resin 6. Each surface layer is composed of a first component with 30.0% by weight of resin 2 and a second component with 70.0% by weight of resin 6. The density of the ethylene-based resin composition of Prototype Example 7 is 0.929 g / cm³. 3 The MFR (190℃ / 2.16kg) is 1.6g / 10min.

[0039] As a performance evaluation of the stretched polyethylene films in prototype examples 1-7, the heat of fusion (ΔH) was used. total ), heat of fusion (ΔH) at fractionation temperature of 124°C or higher 124↑The tensile fracture strength, tensile elongation at fracture, tensile modulus, and heat shrinkage rate at 120°C were measured.

[0040] [Measurement of total heat of fusion] Total heat of fusion (ΔH) total For the measurement of ;J / g), a scanning calorimeter (NETZSCH DSC 214 Polyma) was used, and the SSA (Successive Self-Nucleation / Annealing) method described in Polymer Bulletin 39, 465-472 (1997) was employed, with the self-seeding and annealing temperature (Ts) set from 139°C to 59°C in 5°C increments. Measurements with a result of 110.0 to 200.0 J / g were considered good quality.

[0041] [Measurement of heat of fusion at fractionation temperatures of 124°C or higher] Heat of fusion (ΔH) 124↑ (Unit: J / g) is the heat of fusion (ΔH total Of the total heat of fusion at temperatures below 150°C (measured in J / g), the heat of fusion at fractionation temperatures above 124°C was determined. Measurement results between 80.0 and 190.0 J / g were considered acceptable.

[0042] [Measurement of tensile fracture strength] Tensile fracture strength (MPa) was measured using a tensile testing machine (A&D Company, Limited; RTF-1310) and the tensile properties test method in accordance with JIS K 7127. A 15 mm wide test specimen was pulled at a tensile speed of 200 mm / min, and the stress at fracture was determined. Products with a longitudinal (MD) measurement result of at least 50 MPa were considered good.

[0043] [Measurement of tensile fracture elongation] The tensile elongation at fracture (%) was measured using a tensile testing machine (A&D Co., Ltd.; RTF-1310) and the tensile properties test method in accordance with JIS K 7127. A 15 mm wide test specimen was pulled at a tensile speed of 200 mm / min, and the displacement was calculated from the dimensions of the test specimen at the fracture point. The tensile elongation at fracture was determined as the percentage of displacement from the initial length. A good product was defined as one in which the measurement result in at least one direction, either longitudinal (MD) or transverse (TD), was 40% or more of the initial length.

[0044] [Measurement of Tensile Modulus] The tensile modulus (GPa) was measured using a tensile testing machine (A&D Company, Limited; RTF-1310) and the tensile properties test method in accordance with JIS K 7127, by pulling a 15 mm wide test specimen at a tensile speed of 200 mm / min. A specimen was considered good if the measurement result in the longitudinal direction (MD) was at least 0.5 GPa.

[0045] [Measurement of heat shrinkage rate] In measuring the heat shrinkage rate (%), a square (100mm x 100mm) test sample was prepared, cut so that two adjacent sides of the test specimen were either in the vertical (MD) direction or the horizontal (TD) direction. The distance between the midpoints of two opposite sides in the vertical (MD) and horizontal (TD) directions was measured to determine the dimensions of the test sample before heating in both directions. Next, the test specimen was placed in a precision constant temperature chamber (DF610, manufactured by Yamato Scientific Co., Ltd.) at a predetermined temperature (120°C) for 15 minutes. After removing it from the chamber and allowing it to cool to room temperature, the distance between the midpoints of two opposite sides was measured to determine the dimensions of the test specimen after heating. The percentage change in the dimensions of the test specimen before and after heating was defined as the heat shrinkage rate (%). A good product was defined as one in which the shrinkage rate in the vertical direction (MD) was 15% or less, and the sum of the shrinkage rates in the vertical (MD) and horizontal (TD) directions (MD+TD) was 25% or less.

[0046] The test results for the stretched polyethylene films of prototype examples 1 to 7 are shown in Table 1. In Table 1, the overall evaluation was rated "Good (○)" if all test results were good, and "Unacceptable (×)" if even one good result was not obtained.

[0047] [Table 1]

[0048] [Results and Discussion] As shown in Table 1, prototypes 1-4 received an overall evaluation of "Good (〇)" for film performance, while prototypes 5-7 received an overall evaluation of "Unacceptable (×)". As can be seen from prototypes 1-4 (good products) and prototypes 5-7 (defective products), it is preferable for the stretched polyethylene film (ethylene-based resin composition) to contain both the first and second components, and the preferred blending ratio is considered to be approximately 20-90% by weight of the first component and 10-80% by weight of the second component. Furthermore, the density of the stretched polyethylene film is 0.930-0.960 g / cm³. 3 The MFR is approximately 0.5-10.0 g / 10 min, more preferably 1.0-2.5 g / 10 min.

[0049] In the stretched polyethylene films of prototype examples 1-4, the heat of fusion, which serves as an indicator of the film's rigidity and toughness, is the total heat of fusion (ΔH total The heat of fusion (ΔH) is 110.0 to 200.0 J / g, more preferably 140.0 to 190.0 J / g, and the heat of fusion (ΔH) is obtained at a fractionation temperature of 124°C or higher. 124↑ The saturation level is 80.0 to 190.0 J / g, more preferably 90.0 to 180.0 J / g.

[0050] Regarding the tensile breaking strength in the longitudinal direction (MD), a minimum of 50 MPa, more preferably 60 MPa, and even more preferably 70 MPa is required. The stretched polyethylene films of prototype examples 1 to 7 all had a tensile breaking strength in the longitudinal direction (MD) of 50 MPa or higher, demonstrating excellent tensile breaking strength.

[0051] Tensile elongation at break is an indicator of the handling properties of a film, and the preferred condition is that at least one of the longitudinal or transverse direction is 40% or more, more preferably 100% or more, and even more preferably 150% or more. In prototype example 5, the tensile elongation at break was below 40% in both the longitudinal and transverse directions. When the tensile elongation at break is less than 40% in both the longitudinal and transverse directions, the film itself is brittle, and there is a concern that problems may occur, especially in the case of a base film that goes through many processes before final consumption, such as printing, lamination, bag making, storage, and distribution, compared to a sealant film or when used alone. Prototype example 5 differs from the good prototype example 1 in that the intermediate layer is composed of the first component (does not contain the second component), so it is thought that the handling properties of the film will decrease if the second component is not contained in the intermediate layer in a predetermined proportion.

[0052] Furthermore, the tensile modulus is an indicator of stiffness, and a preferred condition is 0.5 GPa or higher, more preferably 0.6 GPa or higher, and even more preferably 0.7 GPa or higher. In prototype example 6, the modulus of elasticity in the longitudinal direction (MD) was below 0.5 MPa. When the modulus of elasticity in the longitudinal direction (MD) is less than 0.5 MPa, the stiffness of the film is low and it is unsuitable as a base film. Prototype example 6 differs from the good prototype example 1 in that the intermediate layer is composed of the second component (it does not contain the first component), so it is thought that the stiffness of the film decreases if the first component is not contained in the intermediate layer in a predetermined mixing ratio.

[0053] The heat shrinkage rate is an indicator of the dimensional accuracy of the film at high temperatures. Preferred conditions are that, when measured at 120°C, the shrinkage in the longitudinal direction (MD) is 15% or less, and the sum of the shrinkage rates in the longitudinal direction (MD) and the transverse direction (TD) (MD+TD) is 25% or less. In prototype example 6, measurement was impossible due to the melting of the film. In prototype example 7, the heat shrinkage rate in the longitudinal direction (MD) exceeded 15%, and the sum of the shrinkage rates in the longitudinal direction (MD) and the transverse direction (TD) (MD+TD) exceeded 25%. If the value of the heat shrinkage rate is greater than the required physical properties, it is expected that defects will occur during processing at high temperatures. As mentioned above, prototype example 6 differs from the good prototype example 1 in that the intermediate layer is composed of the second component (does not contain the first component), and prototype example 7 differs from the good prototype examples 2 and 3 in that the proportion of the second component in the intermediate layer is excessive. Based on these findings, it is believed that if the proportion of the second component in the intermediate layer is excessive, proper dimensional accuracy cannot be obtained at high temperatures, and in particular, if the intermediate layer is composed solely of the second component, there is a risk that the film will melt.

[0054] As described above, the stretched polyethylene film of the present invention exhibits extremely good performance in terms of rigidity, toughness, heat resistance, and other properties. Furthermore, since this film is made of an ethylene-based resin composition, it is suitable as a base film for laminates used in packaging materials and the like, and is particularly ideal as a base film for laminates using heat-sealable polyethylene film, which is widely used in sealant films, to support the monomaterialization of laminates. [Industrial applicability]

[0055] As described above, the stretched polyethylene film of the present invention has excellent properties such as rigidity, toughness, and heat resistance, and can be suitably used as a base film for monomaterialization of laminates using heat-sealable polyethylene film.

Claims

1. A stretched polyethylene film that is stretched in at least one direction and used as a base film for a laminate used in packaging materials that package contents by heat sealing, Density of 0.952–0.960 g / cm³ ３ , 20 to 90% by weight of high-density polyethylene with an MFR of 0.1 to 10 g / 10 min, and a density of 0.890 to 0.926 g / cm³ ３ It consists of an ethylene-based resin composition (A) comprising 10 to 80% by weight of ultra-low density polyethylene or linear low density polyethylene having an MFR of 1.0 to 4.0 g / 10 min, The density of the ethylene-based resin composition (A) is 0.930 to 0.960 g / cm³. 3 The MFR is 0.5 to 10 g / 10 min, The heat of fusion (ΔH) obtained by measuring using the SSA method with a scanning calorimeter (DSC) is obtained. ｔｏｔａｌ The heat of fusion (ΔH) is 110.0 to 200.0 J / g, and the heat of fusion at a fractionation temperature of 124°C or higher is ΔH １２４↑ ) is 80.0 to 190.0 J / g, In the heat shrinkage rate measured at 120°C, the vertical shrinkage rate is 15% or less, and the sum of the vertical and horizontal shrinkage rates is 25% or less. A stretched polyethylene film characterized by the following features.

2. The stretched polyethylene film according to claim 1, wherein the tensile break elongation measured in accordance with JIS K 7127 (1999) is 40% or more in at least one of the longitudinal or transverse direction.

3. A stretched polyethylene film according to claim 1 or 2, which is obtained by stretching a sheet formed by the T-die method.

4. The stretched polyethylene film according to any one of claims 1 to 3, wherein at least one surface is surface-treated and has a wetting tension of 36 mN / m or more.

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