stretched film

Abstract

To provide a stretched film that offers excellent handling properties after heat processing and suppresses zipping and / or adhesion defects. [Solution] A stretched film containing polyethylene resin, wherein the average linear expansion coefficient from 30°C to 85°C when heated at a rate of 10°C / min in at least one direction, both longitudinal and transverse, is 8.00 × 10 -4 A stretched film having a temperature of 7°C or lower, and a peel force of 4.00 N / 25 mm or less when measured in a 180° peel test on at least one side at a peel speed of 50 mm / min.

Description

[Technical Field]

[0001] This invention relates to stretched films and the like. [Background technology]

[0002] Polyolefin films, such as polyethylene and polypropylene films, are widely used as industrial material films, including for packaging, due to their excellent lightweight properties, thermal stability, and mechanical characteristics. In recent years, polyolefin films have become increasingly valuable due to their superior release properties, and are widely used as protective materials and release agents in the manufacturing processes of electronic components and circuit boards, as well as in thermosetting resin components such as fiber-reinforced plastics.

[0003] When used as a protective film, thermal lamination is sometimes performed to obtain a laminate with other layers. However, curling occurs during thermal lamination, which reduces handling in subsequent processes and lowers production efficiency. Patent document 1 proposes a polyethylene film formed by an inflation method that reduces fisheye as a cover film for dry film resists, but this film is prone to curling.

[0004] Furthermore, when used as a protective film for an adhesive resin layer, problems can arise such as zipping (stick-slip) occurring when peeling off the protective film at operating speed, resulting in horizontal stripes on the adhesive surface, or the protective film lifting due to poor adhesion. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2020 / 255194 [Overview of the project] [Problems that the invention aims to solve]

[0006] An object of the present invention is to provide a film that has excellent handling properties after heat processing and suppresses dipping and / or adhesion failures.

Means for Solving the Problems

[0007] As a result of intensive studies in view of the above problems, the present inventors have found that a stretched film containing a polyethylene resin, having an average linear expansion coefficient of 8.00×10 -4 / °C or less from 30°C to 85°C when the temperature is raised at 10°C / min in at least one of the longitudinal direction and the width direction, and a peel force of 4.00 N / 25 mm or less at a peel rate of 50 mm / min measured by a 180° peel test on at least one surface, can solve the above problems. Based on this finding, the present inventors further conducted research and completed the present invention. That is, the present invention includes the following aspects.

[0008] Item 1. A stretched film containing a polyethylene resin, having an average linear expansion coefficient of 8.00×10 -4 / °C or less from 30°C to 85°C when the temperature is raised at 10°C / min in at least one of the longitudinal direction and the width direction, and a peel force of 4.00 N / 25 mm or less at a peel rate of 50 mm / min measured by a 180° peel test on at least one surface, a stretched film.

[0009] Item 2. The stretched film according to Item 1, wherein the average linear expansion coefficient is 1.20×10 -4 / °C or more and 8.00×10 -4 / °C or less, and the peel force is 0.05 N / 25 mm or more and 4.00 N / 25 mm or less. The stretched film according to Item 1.

[0010] Item 3. The stretched film according to Item 1 or 2, having a curl curvature of less than 0.21 / mm at a lamination temperature of 85°C.

[0011] Item 4. The stretched film according to any one of Items 1 to 3, having a tensile strength in the longitudinal direction of 30 MPa or more and a tensile strength in the width direction of 50 MPa or more.

[0012] Item 5. The stretched film according to any one of Items 1 to 4, which is a biaxially stretched film.

[0013] Item 6. The stretched film according to any one of Items 1 to 5, having a thickness of 10 μm or more and 50 μm or less.

[0014] Item 7. A protective film, a release film, or a packaging film including the stretched film according to any one of Items 1 to 6.

[0015] Item 8. A laminate including the stretched film according to any one of Items 1 to 6 and another layer.

Advantages of the Invention

[0016] According to the present invention, it is possible to provide a film having excellent handling properties after heat processing and suppressing dipping and / or adhesion failure.

Modes for Carrying Out the Invention

[0017] In this specification, the expressions "containing" and "including" include the concepts of "containing", "including", "substantially consisting of", and "consisting only of".

[0018] In this specification, "~" in a numerical range means "or more" and "or less". That is, the notation α~β means α or more and β or less, or β or more and α or less, and includes α and β as a range.

[0019] In this specification, when the upper limit value and the lower limit value are described separately, a range formed by arbitrarily combining the described upper limit value and the lower limit value is also disclosed in this specification.

[0020] In identifying the inventions encompassed by the present disclosure, the respective configurations (properties, structures, functions, etc.) described in each embodiment of the present disclosure may be combined in any manner. That is, the present disclosure encompasses all the subject matters consisting of any combinations of the respective combinable configurations described in this specification.

[0021] 1. Stretched film In one aspect, the present invention relates to a stretched film containing a polyethylene resin, wherein the average linear expansion coefficient from 30°C to 85°C when the temperature is raised at 10°C / min is 8.00×10 -4 / °C or less in at least one of the longitudinal and width directions, and the peel force at a peel rate of 50 mm / min measured by a 180° peel test on at least one surface is 4.00 N / 25 mm or less. (In this specification, it may also be referred to as "the stretched film of the present invention".) The following will explain this.

[0022] The stretched film of the present invention is excellent in handling properties after heat processing and suppresses dipping and / or adhesion failure.

[0023] The present inventor has found that, from the viewpoints of handling properties after heat processing, dipping (especially dipping under high-speed operation), adhesion failure, etc., the average linear expansion coefficient from 30°C to 85°C when the temperature is raised at 10°C / min (hereinafter, may also be simply referred to as "average linear expansion coefficient"), and the peel force at a peel rate of 50 mm / min measured by a 180° peel test (hereinafter, may also be simply referred to as "peel force") are important. By adjusting these within the above ranges, it is possible to improve the handling properties after heat processing and suppress dipping and / or adhesion failure.

[0024] From the viewpoint of handling properties after heat processing (especially from the viewpoint of handling properties after heat processing), the average linear expansion coefficient is preferably 0.80×10 -4 / °C or more and 8.00×10 -4 / °C or less, more preferably 0.90×10 -4 / °C or more and 8.00×10 -4 / ℃ or lower, more preferably 1.00 × 10 -4 / ℃ or higher 8.00×10 -4 / ℃ or lower, particularly preferably 1.10 × 10 -4 / ℃ or higher 7.50×10 -4 / ℃ or lower, especially more preferably 1.20 × 10 -4 / ℃ or higher 7.00×10 -4 / ℃ or less, and more preferably 1.30 × 10 -4 / ℃ or higher 6.50×10 -4 / ℃ or less, and more preferably 1.30 × 10 -4 / ℃ or higher 6.00×10 -4 It is below / ℃. In one embodiment of the present invention, the average coefficient of linear expansion is, for example, 1.50 × 10⁻⁶. -4 / ℃ or higher, 2.00 × 10 -4 / ℃ or higher, 2.50 × 10 -4 / ℃ or higher, 3.00 × 10 -4 / ℃ or higher, or 3.50 × 10 -4 It is above / ℃, and also, for example, 5.50 × 10 -4 / ℃ or below, or 5.00 × 10 -4 It is below / ℃.

[0025] The mean coefficient of linear expansion is a value measured according to the method of (4-1) in the example described below.

[0026] The peeling force is preferably 0.05 N / 25 mm to 4.00 N / 25 mm, more preferably 0.05 N / 25 mm to 3.50 N / 25 mm, even more preferably 0.05 N / 25 mm to 3.00 N / 25 mm, even more preferably 0.05 N / 25 mm to 2.50 N / 25 mm, and most preferably 0.06 N / 25 mm to 2.30 N / 25 mm, from the viewpoint of zipping (especially zipping under high-speed operation) and poor adhesion (especially from the viewpoint of zipping and poor adhesion). In one embodiment of the present invention, the peeling force is, for example, 0.10 N / 25 mm or more, 0.20 N / 25 mm or more, 0.30 N / 25 mm or more, 0.40 N / 25 mm or more, 0.50 N / 25 mm or more, or 0.60 N / 25 mm or more, and also, for example, 2.00 N / 25 mm or less, 1.50 N / 25 mm or less, 1.20 N / 25 mm or less, or 1.00 N / 25 mm or less.

[0027] The peeling force is a value measured according to the method of (4-2) in the example described below.

[0028] From the viewpoint of handling after heat processing (particularly from the viewpoint of handling after heat processing), the stretched film of the present invention preferably has a curl curvature of less than 0.21 / mm at a lamination temperature of 85°C. The curl curvature is more preferably 0.01 / mm or more and less than 0.21 / mm, even more preferably 0.01 / mm or more and 0.20 / mm or less, even more preferably 0.02 / mm or more and 0.20 / mm or less, particularly preferably 0.03 / mm or more and 0.20 / mm or less, particularly more preferably 0.05 / mm or more and 0.20 / mm or less, particularly more preferably 0.07 / mm or more and 0.20 / mm or less, even more preferably 0.07 / mm or more and 0.18 / mm or less, and particularly preferably 0.07 / mm or more and 0.16 / mm or less. In one embodiment of the present invention, the curl curvature is, for example, 0.09 / mm or more, 0.11 / mm or more, or 0.12 / mm or more, and also, for example, 0.15 / mm or less.

[0029] The above curl curvature is a value measured according to the method of (4-3) in the example described below.

[0030] The stretched film of the present invention preferably has a tensile strength of 30 MPa or more in the longitudinal direction and a tensile strength of 50 MPa or more in the width direction, from the viewpoint of preventing film breakage, handling after heat processing, zipping (especially zipping under high-speed operation), and poor adhesion.

[0031] The longitudinal tensile strength is more preferably 30 MPa to 200 MPa, even more preferably 30 MPa to 150 MPa, even more preferably 30 MPa to 120 MPa, and particularly preferably 30 MPa to 100 MPa, from the viewpoint of suppressing film breakage. In one embodiment of the present invention, the longitudinal tensile strength is, for example, 40 MPa or more, 50 MPa or more, or 60 MPa or more, and also, for example, 90 MPa or less.

[0032] The tensile strength in the width direction is more preferably 50 MPa to 350 MPa, even more preferably 70 MPa to 300 MPa, and even more preferably 90 MPa to 280 MPa. In one embodiment of the present invention, the tensile strength in the width direction is, for example, 100 MPa or more, 120 MPa or more, 140 MPa or more, or 160 MPa or more, and also, for example, 250 MPa or less, 230 MPa or less, or 220 MPa or less.

[0033] The tensile strength in the longitudinal and transverse directions is measured according to the method described in (4-4) of the embodiment below. By increasing this tensile strength, impact resistance can be improved.

[0034] The stretched film of the present invention contains polyethylene resin. The stretched film of the present invention contains polyethylene resin as a main component. In this specification, "containing polyethylene resin as a main component" means that the stretched film of the present invention contains 30% by mass or more of polyethylene resin relative to the entire stretched film of the present invention (when the entire stretched film of the present invention is considered to be 100% by mass). The polyethylene resin content relative to the entire stretched film of the present invention is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, particularly preferably 90% by mass or more, particularly more preferably 95% by mass or more, and especially preferably 99% by mass or more. The upper limit of the polyethylene resin content is, for example, 100% by mass and 99.9% by mass relative to the entire stretched film of the present invention.

[0035] Polyethylene resin is not particularly limited in its origin; for example, it can be a resin made from petroleum-derived raw materials, or it can be a resin made from plant-derived raw materials (so-called biomass plastic).

[0036] Among polyethylene resins, low-density polyethylene or high-density polyethylene is preferred, and linear low-density polyethylene, so-called LLDPE, is preferred.

[0037] The weight-average molecular weight (Mw) of polyethylene resin is preferably between 200,000 and 400,000, and more preferably between 210,000 and 300,000, from the viewpoint of thickness uniformity, mechanical properties, and thermal-mechanical properties.

[0038] The number-average molecular weight (Mn) of the polyethylene resin is preferably 80,000 or less, and more preferably between 10,000 and 70,000, from the viewpoint of suppressing the elastic modulus after stretching and obtaining a flexible film.

[0039] The molecular weight distribution (Mw / Mn) of polyethylene resin, calculated as the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn), is preferably 3 to 13, and more preferably 3.3 to 12, from the viewpoint of obtaining appropriate resin fluidity during biaxial stretching and efficiently obtaining a film without breakage.

[0040] The melt flow rate (MFR) of polyethylene resin at 190°C and a load of 2.16 kg is not particularly limited, but from the viewpoint of reducing the mechanical load in the film-forming process, it is preferably 5 g / 10 min or less, and from the viewpoint of making the thickness of the stretched film of the present invention, it is more preferably 0.2 g / 10 min or more and 4 g / 10 min or less. Furthermore, from the viewpoint of handling after heat processing, the MFR is preferably 0.8 g / 10 min or more, and more preferably 1.2 g / 10 min or more.

[0041] The average molecular weight (Mz) of polyethylene resin is, for example, between 500,000 and 1,800,000.

[0042] The density of polyethylene resin is, for example, 0.910 g / cm³. 3 More than 0.970g / cm 3 Preferably, 0.915 g / cm³ 3 More than 0.960g / cm 3 More preferably, 0.918 g / cm³ 3 More than 0.950g / cm 3 More preferably, 0.920 g / cm³ 3 More than 0.940g / cm 3 The following is particularly preferred: 0.922 g / cm³ 3 More than 0.930g / cm 3 The following applies:

[0043] The average molecular weight and molecular weight distribution of the polyethylene resin are values ​​measured according to the method of (2-1) in the example described below. The MFR of the polyethylene resin is a value measured according to the method of (2-2) in the example described below. The density of the polyethylene resin is a value measured according to the method of (2-3) in the example described below.

[0044] The stretched film of the present invention may contain other resins besides the polyethylene resin, as long as the effects of the present invention are not hindered. Examples of other resins include polyolefin resins other than polyethylene resin. Polyolefin resins can broadly include polyolefin resins used for manufacturing films. For example, a polymer obtained by polymerizing an olefin compound can be used as a polyolefin resin. Such olefin compounds preferably have 2 to 20 carbon atoms, more preferably 2 to 10 carbon atoms, and even more preferably 3 to 6 carbon atoms. Specific examples of polyolefin resins include polypropylene resin, poly(1-butene) resin, polyisobutene resin, poly(1-pentene) resin, poly(4-methylpentene-1) resin, etc. Furthermore, the polyolefin resin may be a copolymer containing two or more structural units derived from different olefin compounds, such as an ethylene-propylene copolymer. The content of other resins in the total stretched film of the present invention is, for example, less than 70% by mass, preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, even more preferably 20% by mass or less, particularly preferably 10% by mass or less, particularly more preferably 5% by mass or less, and especially preferably 1% by mass or less. In one embodiment, the stretched film of the present invention does not contain other resins.

[0045] The stretched film of the present invention may contain other components besides the resin, as long as the effects of the present invention are not hindered. Examples of other components include additives contained in known resin films, such as antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, plasticizers, lubricants, crosslinking agents, flame retardants, antistatic agents, heat resistance improvers, blocking inhibitors, inorganic particles, resin particles, chlorine scavenging agents, antifogging agents, hydrolysis inhibitors, and the like. Each of these components may be used individually or in combination as needed. When the stretched film of the present invention contains the above-mentioned other components, their content is 10% by mass or less, preferably 5% by mass or less, more preferably 1% by mass or less, and particularly preferably 0.5% by mass or less, based on the total mass of the stretched film of the present invention.

[0046] The stretched film of the present invention is a stretched film that is stretched in at least one axial direction, either in the longitudinal direction (MD direction) or the TD direction (width direction). The stretched film of the present invention may also be a biaxially oriented film that is stretched in two axial directions. When the stretched film of the present invention is a biaxially oriented film, it is preferable that it is a biaxially oriented film that is stretched in two axial directions, either in the longitudinal direction or the width direction. The stretched film of the present invention is particularly preferable to be a sequentially biaxially oriented film from the viewpoint of stably achieving uniform thickness and easily adjusting the mechanical strength of the film.

[0047] The stretched film of the present invention can have a single-layer structure or a multilayer structure (for example, 2 to 7 layers, 2 to 5 layers, 2 to 3 layers, or 3 layers). A multilayer structure is preferable for the stretched film of the present invention. If the stretched film of the present invention has a multilayer structure, at least one layer (for example, 2 to 6 layers, 2 to 4 layers, or 2 layers, preferably all layers) contains the aforementioned polyethylene resin (preferably as the main component). When polyethylene resin is contained in multiple layers, the polyethylene resin contained in each layer may be the same as those in each layer, or at least one or all of them may be different.

[0048] The thickness of the stretched film of the present invention is not particularly limited and can be set to any desired thickness depending on the intended application. From the viewpoint of avoiding film breakage and obtaining a stable and uniform thickness, the lower limit of the thickness is preferably 2 μm or more, more preferably 5 μm or more, even more preferably 10 μm or more, and even more preferably 15 μm or more. On the other hand, from the viewpoint of suppressing production costs and reducing the mechanical load of the film-forming process, the upper limit of the thickness is preferably 100 μm or less, more preferably 70 μm or less, even more preferably 50 μm or less, and even more preferably 30 μm or less. In the case where the stretched film of the present invention has the multilayer structure described above, the thickness of the stretched film of the present invention refers to the sum of the thicknesses of each layer.

[0049] 2. Manufacturing method The method for manufacturing the stretched film of the present invention is not particularly limited, and a wide range of methods similar to those used for known films can be employed. Specifically, for example, the stretched film of the present invention can be manufactured by a manufacturing method that includes the step of obtaining a cast sheet containing polyethylene resin and stretching the cast sheet in the MD direction and the TD direction. An example of such a method will be described in detail below.

[0050] Cast sheets, which are the stretching precursors, can be obtained using known methods. For example, polyethylene resin pellets, dry-mixed polyethylene resin pellets, or mixed polyethylene resin pellets prepared by pre-melting and kneading can be supplied to an extruder, heated and melted, foreign matter and modified polymers removed through a filter, then extruded into a sheet from a T-die, and cooled and solidified in at least one cooling drum to obtain a cast sheet.

[0051] Inside the extruder, polyethylene resin undergoes some degree of degradation due to thermal and oxidative stress. From the viewpoint of suppressing such polymer degradation, the resin temperature during melt extrusion should be between 170°C and 320°C, preferably between 200°C and 300°C. Furthermore, degradation can be suppressed by adjusting the nitrogen purging inside the extruder, the screw shape, the internal shape of the T-die during casting, and the amount of antioxidant added.

[0052] The temperature of the cooling drum is preferably between 20°C and 90°C, and more preferably maintained between 40°C and 80°C. Any method can be used to adhere the sheet resin to the cooling drum, such as the air knife method, touch roll method, electrostatic application method, or water-cooled casting method, but the air knife method is preferred because it is easy to adjust when adhering the sheet resin to the cooling drum and can be handled simply. When using an air knife, the temperature of the blown air (AK air temperature) is preferably between 10°C and 90°C, more preferably between 20°C and 80°C.

[0053] Cast sheets obtained by adjusting the cooling drum temperature and AK air temperature within the above range exhibit suppressed crystallization and reduced mechanical load during stretching. As a result, it is believed that the desired physical properties of the present invention can be easily obtained.

[0054] In one embodiment, the stretched film of the present invention can be obtained by stretching a cast sheet in two axes: longitudinal and transverse (MD and TD directions).

[0055] First, the cast sheet is heated to a temperature of 70°C to 130°C, preferably 80°C to 120°C. The method of heating the cast sheet is not particularly limited, but it is preferable to alternately heat both sides of the cast sheet using a group of four or more rolls arranged in the flow direction, and to heat both sides of the sheet simultaneously just before longitudinal stretching. By maintaining this temperature range, the cast sheet does not undergo excessive thermal expansion and can be stretched longitudinally as described later while maintaining its flatness.

[0056] A cast sheet is stretched longitudinally (MD stretching), and then immediately relaxed to obtain an MD stretched sheet. The stretching ratio in the longitudinal direction (MD ratio) is 3 times or more and 11 times or less, preferably 3.5 times or more and 9 times or less. The relaxation rate (MD relaxation rate) is preferably 0% or more and 12% or less, more preferably 5% or more and 11% or less, and even more preferably 6% or more and 10% or less.

[0057] The MD stretched sheet obtained by adjusting within the above range maintains its flatness and suppresses oriented crystallization, thus reducing the mechanical load during stretching in the width direction, as described later. The method of stretching and relaxing in the longitudinal direction is not particularly limited, but a method that utilizes the difference in peripheral speed of two or more roll groups arranged in the flow direction is preferred.

[0058] Next, the stretched sheet is guided to a tenter and stretched in the width-to-width direction (TD stretching). The temperature for stretching in the width-to-width direction (TD temperature) is preferably 150°C to 190°C, more preferably 155°C to 185°C, even more preferably 160°C to 180°C, and even more preferably 165°C to 180°C. The stretching ratio in the width-to-width direction (TD ratio) is 4 times to 13 times, preferably 5 times to 12 times, and even more preferably 6 times to 11 times.

[0059] By adjusting within the above range, stretching breakage caused by unstretched residue (remaining material) can be suppressed, and a stretched film of uniform thickness can be efficiently obtained.

[0060] Finally, the biaxially oriented film is relaxed in the width direction to obtain the stretched film of the present invention.

[0061] The lateral relaxation rate (TD relaxation rate) is 0% or more and less than 23%, preferably 5% or more and 20%, and more preferably 8% or more and 15%.

[0062] It is believed that the desired physical properties of the present invention can be easily obtained by adjusting within the above range. In particular, it is believed that the desired physical properties of the present invention can be easily obtained by adjusting the stretching temperature (especially the preheating temperature for TD stretching) within the above range, and further relaxing the material so that the relaxation rate is above a certain level after MD stretching and at least one of (preferably both) after TD stretching. More specifically, by stretching, orientation and crystallization can be adjusted, and the average coefficient of linear expansion can be adjusted. By setting a high preheating temperature for TD stretching, it is difficult for minute crystals to grow due to rapid heating, and large crystals can grow, thus adjusting the coefficient of linear expansion. By setting a high MD relaxation rate, the unoriented polymer chains are loosened by MD relaxation, making it easier for them to be oriented and crystallized during subsequent TD stretching. By setting a high TD relaxation rate, the stress in the TD direction is weakened, making it easier for stress to be applied in the MD direction, and thus strong orientation and crystallization can be achieved in the MD direction.

[0063] The film fed from the tenter is wound into a roll by a winding machine to obtain the stretched film of the present invention. Furthermore, the stretched film of the present invention can be surface-treated according to its application, as long as its properties are not impaired. Examples of surface treatments include corona discharge treatment, plasma treatment, and flame treatment.

[0064] 3.Applications The stretched film of the present invention can be applied to a variety of uses. In particular, the stretched film of the present invention is especially suitable as a protective film for electronic components. Furthermore, the stretched film of the present invention can also be used as a protective film, release film, and packaging film other than those mentioned above.

[0065] The stretched film of the present invention can be used as a protective film for dry film resists. The type of dry film resist is not particularly limited, and can be broadly applied to known dry film resists, for example. Such a protective film is provided to protect the adhesive layer of the dry film resist. In one embodiment, the dry film resist may be a film in which the stretched film of the present invention, a resist layer, and a base film (for example, a film containing polyethylene terephthalate (PET)) are laminated in that order.

[0066] The stretched film of the present invention can be used for various applications by arranging other layers on one or both of its surfaces as needed. For example, the stretched film of the present invention can be used as a protective film, release film, etc., by arranging a release layer containing a release agent (such as a silicone coating) on ​​one or both of its surfaces as needed. As another example, the stretched film of the present invention can be used as a packaging film, etc., by arranging a coating layer (such as a gas barrier layer) on one or both of its surfaces as needed. [Examples]

[0067] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0068] (1) Preparation of resin The resins used in the examples and comparative examples are as follows: PE refers to polyethylene resin, and PP refers to polypropylene resin. • PE1: Dow Chemical's "TF80" (LLDPE) • PE2: SABIC "BX202" (LLDPE) • PE3: LG Chem Co., Ltd. "LO4904P" (HDPE) • PE4: "LC520" (LDPE) manufactured by Japan Polyethylene Co., Ltd. • PE5: "LF128" (LDPE) manufactured by Nippon Polyethylene Co., Ltd. • PP: Prime Polymer's "F-300SP" The physical properties of these resins are shown below. The measurement method is as follows. In the table, "-" indicates that the measurement was not performed.

[0069] [Table 1]

[0070] (2) Measurement of the physical properties of resins (2-1) Measurement of the average molecular weight and molecular weight distribution of various resins Using SEC (size exclusion chromatography), the average molecular weight and molecular weight distribution of various materials were measured under the following conditions. Equipment: HLC-8321GPC / HT (Detector: Differential Refractometer (RI)) (Manufactured by Tosoh Corporation) Column: TSKgel guardcolumnH HR (30)HT(7.5mmI.D.×7.5cm)×1 + TSKgel GMH HR -H(20)HT (7.8mm I.D. x 30cm) x 3 pieces (manufactured by Tosoh Corporation) Eluent: 1,2,4-Trichlorobenzene (for GPC, manufactured by Fujifilm Wako Pure Chemical Industries) + Dibutylhydroxytoluene (0.05%) Flow rate: 1.0mL / min Detection condition: polarization=(-) Injection volume: 300μL Column temperature: 140℃ Temperature: 40°C Sample concentration: 1 mg / mL Pretreatment: The sample was weighed, and dissolved in a solvent (1,2,4-trichlorobenzene with 0.1% dibutylhydroxytoluene) by shaking at 140°C for 1 hour. The solution was then filtered by heating through a 0.5 μm sintered filter. No insoluble material was observed in any of the sample solutions during visual inspection. Calibration Curve: A calibration curve for a quintic approximation curve was created using standard polystyrene manufactured by Tosoh Corporation. Therefore, the obtained values ​​represent the molecular weight on a polystyrene basis.

[0071] From the obtained calibration curve and SEC chromatogram, the number-average molecular weight (Mn), weight-average molecular weight (Mw), and Z-average molecular weight (Mz) were obtained using analysis software for the measurement device. The molecular weight distribution (Mw / Mn) was then obtained using these Mw and Mn values.

[0072] (2-2) Measurement of Melt Flow Rate (MFR) For each resin, the melt flow rate (MFR) in the form of raw resin pellets was measured using a melt indexer from Toyo Seiki Co., Ltd., in accordance with condition M of JIS K 7210. Specifically, first, a weighed 4g sample was inserted into a cylinder heated to the test temperature (190°C for PE, 230°C for PP), and preheated for 3.5 minutes under a load of 2.16kg. Then, the weight of the sample extruded from the bottom hole in 30 seconds was measured, and the MFR (g / 10min) was determined. The above measurement was repeated three times, and the average value was taken as the measured value of MFR.

[0073] (2-3) Measurement of density For each resin, the density in the form of raw resin pellets was measured in accordance with JIS K7112 using a density gradient tube type specific gravity measuring device (Type A) manufactured by Shibayama Scientific Instruments Co., Ltd. Specifically, ethanol / water was used as the gradient solution, and the measurement was taken at a temperature of 23°C approximately 24 hours after the gradient solution was added. The above measurement was repeated three times, and the average value was used as the density measurement value.

[0074] (3) Preparation of stretched film (Example 1) As shown in Table 2 below, a stretched film was manufactured in which surface layer A and surface layer B were arranged on both sides of the base layer. First, 100 parts by mass of PE1 (hereinafter referred to as pellet 1) was prepared as the resin for forming the base layer, and 100 parts by mass of PE1 (hereinafter referred to as pellet 2) was prepared as the resin for forming surface layer A and surface layer B. Pellet 1 was fed from a hopper into a single-screw type extruder a, and pellet 2 was fed from a hopper into a single-screw type extruder b, which was separate from extruder a. Pellet 1 and pellet 2 were melted at 260°C, and these were laminated in a three-layer configuration inside a three-layer multi-manifold die. Then, they were cooled and solidified while being pressed with air pressure using an air knife on a cooling drum. The temperature of the blown air was set to 25°C. As a result, a raw material sheet was obtained in which layers of PE2 derived from pellet 2 were directly formed on both sides of the PE-1 layer derived from pellet 1.

[0075] The obtained cast sheet was preheated to 100°C, stretched six times in the longitudinal direction (MD direction), then relaxed by 0% in the same direction, and immediately returned to room temperature. The stretched film was then guided to a tenter, held at both ends with clips, preheated to 155°C, stretched 7.8 times in the width-to-length direction (TD direction) in a stretching zone at 125°C, and then relaxed by 10% in the same direction to obtain a stretched film with a thickness of 20 μm. The obtained stretched film was a stretched film in which surface layer A, a base layer, and surface layer B were laminated in this order, with a thickness ratio of 1:2:1 (surface layer A: base layer: surface layer B). In such a stretched film, surface layer B was the layer that was in direct contact with the cooling drum, and surface layer A was the layer that was not in contact with the cooling drum.

[0076] The film thickness was measured using a micrometer (JIS-B7502) in accordance with JIS-C2330.

[0077] (Example 2) A stretched film was obtained in the same manner as in Example 1, except that relaxation was applied 8% in the longitudinal direction and 0% in the transverse direction.

[0078] (Example 3) A stretched film was obtained in the same manner as in Example 1, except that an 8% relaxation was applied in the longitudinal direction.

[0079] (Example 4) A stretched film was obtained in the same manner as in Example 3, except that the preheating temperature before stretching in the width direction was set to 165°C.

[0080] (Example 5) A stretched film was obtained in the same manner as in Example 3, except that the preheating temperature before stretching in the width direction was set to 175°C.

[0081] (Example 6) A stretched film was obtained in the same manner as in Example 5, except that PE2 was used as the resin for forming the base layer and PE2 was used as the resin for forming surface layer A and surface layer B.

[0082] (Example 7) A stretched film was obtained in the same manner as in Example 5, except that PE3 was used as the resin for forming the base layer and PE3 was used as the resin for forming surface layer A and surface layer B.

[0083] (Example 8) A stretched film was obtained in the same manner as in Example 1, except that the resin used to form the base layer was changed to PP1 and the preheating temperature during stretching in the TD direction was changed to 195°C.

[0084] (Comparative Example 1) PE4 pellets were fed from a hopper into a single-screw extruder and melted at a resin temperature of 200°C. After removing foreign matter and modified polymers through a filter installed in the polymer tube, the melted material was extruded using a ring die and wound onto a pinch roll. Air was then introduced into the ring, causing the resin to inflate into a balloon shape between the ring die and the pinch roll. The ends of the folded balloon, after passing through the pinch roll, were cut off, and each was wound onto a separate film to obtain a polyethylene film with a thickness of 20 μm.

[0085] (Comparative Example 2) A polyethylene film was obtained in the same manner as in Comparative Example 1, except that the resin fed into the extruder was PE5.

[0086] (Comparative Example 3) A stretched film was obtained in the same manner as in Example 1, except that 0% relaxation was applied in the width direction.

[0087] (Comparative Example 4) A stretched film was obtained in the same manner as in Example 3, except that the preheating temperature before stretching in the width direction was set to 145°C.

[0088] (Comparative Example 5) A stretched film was obtained in the same manner as in Example 5, except that the resin fed into the extruder was changed to PP, the preheating temperature when stretching in the MD direction was set to 130°C, and the stretching zone temperature when stretching in the TD direction was set to 160°C.

[0089] (4) Measurement of the physical properties of the film (4-1) Measurement of the mean coefficient of linear expansion The average linear thermal expansion coefficient (1 / °C) of the films in the examples and comparative examples was measured in the longitudinal direction using a thermomechanical analyzer (Seiko Instruments Inc., TMA / SS6000) in accordance with JIS K7197, as follows: A film was cut to a length of 30 mm and a width of 4 mm in the longitudinal direction. The sample was set in the thermomechanical analyzer with a chuck distance of 15 mm, and while applying a load of 0.2 N / mm in the tensile direction, the temperature was increased from 25°C to 105°C (as ambient temperature) at a heating rate of 10°C / min and held for 7 minutes. At this time, the average linear thermal expansion coefficient (1 / °C) obtained in the temperature range of 30°C to 85°C (as sample temperature) was measured.

[0090] (4-2) Measurement of peeling force A 25mm wide x 150mm long adhesive tape (Nitto Denko Corporation NO.31B tape, total thickness 53μm, acrylic adhesive) was applied to the surface of the film in the examples and comparative examples that was to be bonded to the adherend by rolling a 2kg roller back and forth twice to obtain a laminate. The obtained laminate was left to stand for 20 hours in an environment of 70°C and 50% humidity, then cooled to room temperature, and this was used as the measurement sample. The measurement sample was peeled 180° at a speed of 50mm / min using a tensile testing machine (Minebea Co., Ltd. universal tensile testing machine "Technograph TGI-1kN"), and the peeling force was measured. Measurements were performed for n=10 for each peeling speed, and the average value was taken as the measurement result.

[0091] (4-3) Measurement of curl curvature A 25mm wide x 150mm long adhesive tape (Nitto Denko Corporation NO.31B tape, total thickness 53μm, acrylic adhesive) was applied to the surface of the film of the example and comparative example that was to be bonded to the adherend by passing a 2kg roller back and forth twice to obtain a laminate. The obtained laminate was placed on a 0.1mm thick SUS plate with the 31B tape side facing up. A 38μm thick PET film was then used to cover it, and it was passed through a laminator (Aurora Japan Co., Ltd. LM-A3). The heating temperature confirmed by a thermolabel was 85°C. After passing through the laminator, the laminate was removed from the paper and SUS plate and cut to a size of 25mm wide x 70mm long. The laminate was then placed on graph paper with the long side facing down, and the curl diameter of the laminate was measured. The curl curvature was calculated as the reciprocal of the curl radius (2 / curl diameter). The measurement was performed with n=3, and the average value was used as the measurement result.

[0092] (4-4) Measurement of tensile strength The tensile strength in the longitudinal and transverse directions of the films in the examples and comparative examples was measured using the Tensilon universal material tester RTG-1210 (product name) manufactured by A&D Co., Ltd. Specifically, the film was cut into 15 × 150 mm pieces with the longitudinal and transverse directions as the longer sides, and the tensile strength was measured under conditions of a chuck distance of 100 mm and a tensile speed of 200 mm / min, and the strength at the breaking point (unit: MPa) was determined.

[0093] (4-5) Measurement of impact resistance The impact strength of the films in the examples and comparative examples was measured using a Yasuda Seiki film impact tester, based on ASTM-D3420. A weight of 15 kgf·cm was used for the measurement, and a metal sphere with a radius of 6.35 mm was used as the impact ball. Three impact strength measurements were performed per sample, and the average value was taken as the impact strength.

[0094] (5) Evaluation of film performance (5-1) Evaluation of handling A 150mm wide x 250mm long adhesive tape (Nitto Denko Corporation NO.31B tape, total thickness 53μm, acrylic adhesive) was applied to the surface of the film of the example and comparative example that was to be bonded to the adherend by passing a 2kg roller back and forth twice to obtain a laminate. The obtained laminate was placed on a 0.1mm thick SUS plate with the 31B tape side facing up. A 38μm thick PET film was then used to cover it, and it was passed through a laminator. The heating temperature confirmed by a thermolabel was 85°C. After the obtained samples were left to stand at room temperature for 24 hours, the stretched film was peeled off again. The obtained 31B tape was bonded to a 50μm thick PET film using a desktop laminator, and the presence or absence of defects was checked. The evaluation was performed with n=10, and the number of sheets with appearance defects such as folds, wrinkles, and unevenness was calculated, and the handling performance was evaluated according to the following evaluation criteria.

[0095] ◎: The number of measurement samples that showed defects was 0.

[0096] ○: The number of measurement samples that showed defects was 1 to 5.

[0097] ×: The number of measurement samples that showed defects was between 6 and 10.

[0098] (5-2) Evaluation of Zipping A 25mm wide x 150mm long adhesive tape (Nitto Denko Corporation NO.31B tape, total thickness 53μm, acrylic adhesive) was applied to the surface of the film of the examples and comparative examples that was to be bonded to the adherend by rolling a 2kg roller back and forth twice to obtain a laminate. The obtained laminate was left to stand for 20 hours in an environment of 70°C and 50% humidity, then cooled to room temperature, and this was used as the measurement sample. The measurement sample was peeled 180° at a speed of 1250mm / min using an adhesive / film peel analyzer (Kyowa Interface Science Co., Ltd. "VPA"), and the occurrence of zipping was confirmed. The measurement was performed with n=10, and the number of measurement samples in which zipping occurred was calculated, and zipping was evaluated according to the following evaluation criteria.

[0099] ◎: The number of measurement samples that experienced zipping was 0.

[0100] ○: The number of measurement samples that experienced zipping was between 1 and 5.

[0101] ×: The number of measurement samples that experienced zipping was between 6 and 10.

[0102] (5-3) Evaluation of poor adhesion A 25mm wide x 150mm long adhesive tape (Nitto Denko Corporation NO.31B tape, acrylic adhesive) was applied to the surface of the film in the examples and comparative examples that was to be bonded to the adherend by rolling a 2kg roller back and forth twice to obtain a laminate. The obtained laminate was left to stand for 20 hours in an environment of 70°C and 50% humidity. It was then left to stand at room temperature for 24 hours, and the occurrence of film lifting (natural delamination) from the adhesive tape was confirmed. Measurements were performed with n=10, and the number of measurement samples in which lifting occurred was calculated, and adhesion failure was evaluated according to the following evaluation criteria.

[0103] ◎: The number of measurement samples that showed floating was 0.

[0104] ○: The number of measurement samples in which floating occurred was 1 to 5.

[0105] ×: The number of measurement samples that showed floating was 6 to 10.

[0106] (6) Results Table 2 shows the resin composition, manufacturing conditions, physical property measurement results, and performance evaluation results.

[0107] [Table 2]

Claims

1. A stretched film containing polyethylene resin, When the temperature is increased at a rate of 10°C / min in at least one direction, both longitudinally and transversely, the average coefficient of linear expansion from 30°C to 85°C is 8.00 × 10⁻⁶. －４ It is below / ℃, and The peeling force is 4.00 N / 25 mm or less when the peeling speed measured in a 180° peel test on at least one side is 50 mm / min. Stretched film.

2. The aforementioned average coefficient of linear expansion is 1.20 × 10 －４ / ℃ or higher 8.00 × 10 －４ It is below / ℃, and The peeling force is 0.05 N / 25 mm or more and 4.00 N / 25 mm or less. The stretched film according to claim 1.

3. The stretched film according to claim 1, wherein the curl curvature at a lamination temperature of 85°C is less than 0.21 / mm.

4. The stretched film according to claim 1, wherein the tensile strength in the longitudinal direction is 30 MPa or more, and the tensile strength in the width direction is 50 MPa or more.

5. The stretched film according to claim 1, which is a biaxially oriented film.

6. The stretched film according to claim 1, wherein the thickness is 10 μm or more and 50 μm or less.

7. A protective film, release film, or packaging film comprising the stretched film described in any one of claims 1 to 6.

8. A laminate comprising the stretched film and other layers according to any one of claims 1 to 6.

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