Single-layer or multi-layer polyethylene film

Abstract

Improvement of polyethylene multilayer films. [Solution] A single-layer or multi-layer polyethylene film used as packaging or protective material for electronic devices and / or electronic components, having at least one surface layer (A) and optionally an intermediate layer (B) sandwiched between two A layers. The surface layer (A) comprises a resin mainly composed of high-density polyethylene (A1) polymerized in the presence of a metallocene catalyst, and an antioxidant (a1), a conductive agent (a2), and a dispersant (a3) ​​having a phosphite ester structure and a hindered phenol structure within the same molecule. The intermediate layer (B) comprises high-density polyethylene (B1).

Description

[Technical Field]

[0001] This invention relates to polyethylene-based films. In particular, this invention relates to polyethylene-based films used as packaging or protective materials for electronic devices and / or electronic components. [Background technology]

[0002] Packaging or protective materials for electronic devices and / or electronic components (hereinafter referred to as "films for electronic components") are required to prevent foreign matter from adhering to the packaged items. Particulate matter such as dust collected by static electricity, low molecular weight substances and oily components generated from the film for electronic components itself are particularly undesirable as foreign matter. Cleanliness is required of the film for electronic components itself to avoid damaging the contents. Static electricity is easily generated by friction during the transport and movement of packaged electronic components, or by triboelectric charging or peeling charging when peeling packaging or protective materials from electronic components, so electronic components tend to dislike static electricity itself. For this reason, it is also necessary to impart appropriate conductivity to the film for electronic components to dissipate the generated static electricity.

[0003] Furthermore, because the target electronic components are often thin, small, and sometimes have complex shapes, good film moldability is required for the material of the film used for electronic components.

[0004] On the other hand, polyethylenes are general-purpose resins with excellent film moldability and are widely used as packaging materials. Among polyethylenes, polyethylenes polymerized in the presence of a metallocene catalyst (hereinafter referred to as "metallocene polyethylene") are particularly suitable for avoiding contamination of electronic equipment components because they have a narrow molecular weight distribution and a low content of low molecular weight components. However, relatively high concentrations of additives are required to impart appropriate conductivity to polyethylenes.

[0005] Therefore, as described in Patent Documents 1, 2, and 3, various films and sheets have been proposed to date for use as films for electronic equipment components, in which an antistatic agent is compounded into polyethylene, such as metallocene polyethylene.

[0006] However, when incorporating inorganic conductive agents to prevent static electricity in polyethylenes, there is a problem in that the inorganic conductive agent is difficult to disperse uniformly. If a dispersant is added in this case, the dispersant will bleed out, causing contamination of electronic components.

[0007] Furthermore, it has antistatic properties (for example, a surface resistance value of 1.0 × 10⁻⁶). 10 ~1.0×10 12 While the polyethylene film with a resistance of Ω can prevent static electricity buildup, its high resistance prevents it from dissipating any static electricity that has already been generated.

[0008] Furthermore, when electronic component films are processed to create final products, it is necessary to control the fine surface shape of the electronic component film. In this case, surface defects such as unevenness and discoloration due to the non-uniform dispersion of additives become a problem. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2017-14433 [Patent Document 2] Republished Gazette No. WO2016 / 024529 [Patent Document 3] Japanese Patent Publication No. 2009-19063 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] Therefore, the present inventor has sought a film that has appropriate conductivity, has a low frequency of appearance of surface shape abnormalities detected as foreign substances and / or defect points, etc., and is excellent in film formability and is suitable for packaging and protecting electronic device parts.

Means for Solving the Problems

[0011] As a result, the present inventor has found that a single-layer or multi-layer polyethylene-based film containing a specific polyethylene-based resin and an additive is useful as a packaging material or protective material for articles that dislike foreign matter adhesion and static electricity such as electronic device parts. That is, the present invention is as follows.

[0012] (Invention 1) A single-layer or multi-layer polyethylene-based film having at least one surface layer (A) and optionally having an intermediate layer (B) disposed so as to be sandwiched between two A layers, The surface layer (A) is composed of a resin mainly composed of high-density polyethylene (A1) polymerized in the presence of a metallocene catalyst, and an antioxidant (a1), a conductive agent (a2), and a dispersant (a3) having a phosphite structure and a hindered phenol structure in the same molecule, The intermediate layer (B) is mainly composed of high-density polyethylene (B1), A single-layer or multi-layer polyethylene-based film. (Invention 2) At 780 cm of one open surface layer (A), 2 The number of foreign substances and / or defect points having a short diameter L1 and / or a long diameter L2 exceeding 100 μm detected per is 20 or less, The polyethylene-based film of Invention 1. (Invention 3) The total thickness is 30 μm or more and 300 μm or less, The thickness of the surface layer (A) is 5 μm or more and 100 μm or less, The thickness of the intermediate layer (B) is 20 μm or more and 200 μm or less, The multi-layer polyethylene-based film of Invention 1. (Invention 4) The surface resistance value measured in an atmosphere of a temperature of 23 °C and a humidity of 50% of one open surface layer (A) is 1.0×103 Ω or more 1.0×10 8 A polyethylene-based film of Invention 1, having a value of Ω or less. (Invention 5) A polyethylene film according to Invention 1, used as packaging or protective material for electronic devices and / or electronic components. [Effects of the Invention]

[0013] The polyethylene multilayer film of the present invention possesses the performance required for packaging and protective materials. In particular, when the surface layer (A) consists of high-density polyethylene (A1) polymerized in the presence of a metallocene catalyst and an additive (a1) containing an antioxidant (a1), a conductive agent (a2), and a dispersant (a3), and the intermediate layer consists of high-density polyethylene (B1), the polyethylene multilayer film of the present invention has appropriate conductivity and stain resistance, few foreign matter and / or defects on the film surface, and excellent color stability. In this case, the polyethylene multilayer film of the present invention is useful as a packaging or protective material for precision parts, powders, and medical devices. [Brief explanation of the drawing]

[0014] [Figure 1] An example of a single-layer polyethylene film of the present invention is schematically shown. [Figure 2] An example of a multilayer polyethylene film of the present invention is schematically shown. [Figure 3] An example of a multilayer polyethylene film of the present invention is schematically shown. [Modes for carrying out the invention]

[0015] [Single-layer or multi-layer polyethylene film] The single-layer or multi-layer polyethylene film of the present invention is a single-layer or multi-layer polyethylene film having at least one surface layer (A) and optionally an intermediate layer (B) sandwiched between two A layers.

[0016] The polyethylene-based film of the present invention is, for example, a single-layer film consisting of a surface layer (A). Figure 1 shows a cross-section of such a single-layer film. When the polyethylene-based film of the present invention is a single-layer film consisting of a surface layer (A), the properties of the surface layer (A) are expressed as the properties of the entire film. In this case, for example, the conductivity of the surface layer (A) is directly reflected in the surface resistance and volume resistivity of the film. For this reason, in terms of obtaining the polyethylene-based film of the present invention that achieves the required appropriate surface resistance and volume resistivity, it is fair to say that a single-layer film consisting of a surface layer (A) is relatively advantageous for the polyethylene-based film of the present invention.

[0017] The polyethylene film of the present invention is a two-type, three-layer multilayer film in which a surface layer (A), an intermediate layer (B), and another surface layer (A) are laminated in this order. Figure 2 schematically shows such a two-type, three-layer structure: surface layer (A) / intermediate layer (B) / surface layer (A). Figures 1 and 2 do not show the actual layer thickness, surface shape, or color, but are referred to as reference diagrams for understanding the present invention.

[0018] In addition to the surface layer (A) and intermediate layer (B), the polyethylene film of the present invention may also have other layers, provided that they do not affect the performance of the product of the present invention. For example, a recycled layer (C) can be laminated between the surface layer (A) and the intermediate layer (B) as a recycled layer (C) obtained by melting and forming a layer from scraps (so-called "selvages") generated during the formation of the polyethylene film of the present invention, or from used recycled polyethylene film of the present invention, or from melting and forming a mixture of these scraps or recycled materials with the constituent materials of the surface layer (A) and / or intermediate layer (B). In this case, the layer structure of the polyethylene film of the present invention may be, for example, surface layer (A) / recycled layer (C) / intermediate layer (B) / surface layer (A), surface layer (A) / recycled layer (C) / intermediate layer (B) / recycled layer (C) / surface layer (A), etc. Figure 3 schematically shows a cross-section of the polyethylene film of the present invention having the structure of surface layer (A) / recycled layer (C) / intermediate layer (B) / surface layer (A). Furthermore, a portion or more of the intermediate layer (B) can be replaced with the regenerated layer (C).

[0019] The thickness of each layer and the overall thickness of the polyethylene film of the present invention are not limited, as they can be achieved under the general manufacturing conditions for single-layer or multi-layer films made of polyolefin resin. When the polyethylene film of the present invention is used as a packaging or protective material, the thickness of each surface layer (A) can generally be 5 μm or more and 100 μm or less, preferably 5 μm or more and 50 μm or less. By making the thickness of the surface layer (A) 5 μm or more, it becomes easier to impart appropriate conductivity to the polyethylene film of the present invention. The thickness of the intermediate layer (B) is generally 20 μm or more and 200 μm or less, preferably 40 μm or more and 100 μm or less. Thus, the total thickness of the polyethylene film of the present invention is generally 30 μm or more and 300 μm or less, preferably 60 μm or more and 200 μm or less.

[0020] When adopting the layer structure of the above two types of three-layer multilayer films, generally, the total thickness is within the range described above, and the three layers are symmetrical in the thickness direction, with the front and back open surfaces composed of the same surface layer (A). In this case, the thickness of the intermediate layer (B) is generally 2.5 to 20 times, preferably 3 to 18 times, the thickness of one surface layer (A). That is, if the total thickness of the three-layer multilayer film is conveniently set to 10, the thickness ratio of the three layers (surface layer (A) thickness: intermediate layer (B) thickness: surface layer (A) thickness) is generally in the range of 0.5:9:0.5 to 2:6:2.

[0021] [Surface layer (A)] The surface layer (A) constituting the polyethylene-based film of the present invention comprises a resin mainly composed of high-density polyethylene (A1) polymerized in the presence of a metallocene catalyst, an antioxidant (a1) having a phosphite structure and a hindered phenol structure in the same molecule, a conductive agent (a2), and a dispersant (a3). When the polyethylene-based film of the present invention is used as a packaging material or a protective material, at least one surface of the surface layer (A) may come into contact with the packaged object or the protected object. In this case, the surface layer (A) is required to have appropriate conductivity, strength, control of the surface shape, antifouling properties, etc. in order to prevent contamination and damage to the packaged object or the protected object. By combining the high-density polyethylene (A1) polymerized in the presence of a metallocene catalyst, the antioxidant (a1), the conductive agent (a2), and the dispersant (a3), appropriate conductivity, strength, and antifouling properties are imparted to the surface layer (A), and fine abnormal points such as foreign substances and / or defect points detected on the surface can be reduced.

[0022] The above-mentioned appropriate conductivity means that the surface resistance value measured in an atmosphere with a temperature of 23 °C and a humidity of 50% for one open surface layer (A) is generally 1.0×10 3 Ω or more and 1.0×10 8 Ω or less, preferably 1.0×10 3 Ω or more and 1.0×10 7 Ω or less, particularly preferably 1.0×10 3 Ω or more and 1.0×10 6 Ω or less.

[0023] [High-density polyethylene resin (A1) polymerized in the presence of a metallocene catalyst] The surface layer of the present invention mainly consists of a high-density polyethylene resin (A1) polymerized in the presence of a metallocene catalyst (hereinafter referred to as "metallocene HDPE (A1)"). Metallocene HDPE (A1) generally accounts for 60% or more by weight, preferably 90% or more, of the total amount of resin components constituting the surface layer (A). In addition to metallocene HDPE (A1), the surface layer (A) may also contain polyolefin resins other than metallocene HDPE (A1), such as ethylene homopolymers, ethylene-α-olefin copolymers, and polypropylene polymers, or other thermoplastic resins, to the extent that they do not impair the moldability or surface shape of the surface layer (A).

[0024] The density of metallocene HDPE(A1) generally falls within the range classified as high-density polyethylene in JIS K6922-1 (2018), specifically, a density of 0.935 kg / m³ measured under conditions of 23°C ± 2°C. 3 It is extremely high. The density of metallocene HDPE(A1) is generally 0.935 kg / m³. 3 Super 0.970kg / m 3 The following applies: Metallocene HDPE(A1), like general metallocene PE, exhibits a molecular weight distribution (Mw / Mn) of approximately 2.0, generally between 1.5 and 2.5 (ratio of weight-average molecular weight Mw to number-average molecular weight Mn).

[0025] Considering the film-forming properties of the polyethylene-based film of the present invention, the melt mass flow rate (MFR, measured at 190 °C under a 2.16 kg load according to JIS K 7210) of metallocene HDPE (A1) constituting the surface layer (A) is generally 0.5 g / 10 min or more and 20 g / 10 min or less, preferably 1.0 g / 10 min or more and 15 g / 10 min or less.

[0026] [Antioxidant (a1)] The surface layer (A) contains an antioxidant (a1) having both a phosphite ester structure and a hindered phenol structure within the same molecule. The above antioxidant (a1) is generally a compound represented by the following general formula.

[0027] [ka]

[0028] In the above formula, R 1 , R 2 , R 4 and R 5 Each of these independently represents a hydrogen atom, a C1-C8 alkyl group, a C5-C8 cycloalkyl group, a C6-C12 alkylcycloalkyl group, a C7-C12 aralkyl group, or a phenyl group, and R 3 represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. X represents a single bond, a sulfur atom, or -CHR 6 - Represents the base, R 6 * represents a hydrogen atom, an alkyl group with 1 to 8 carbon atoms, or a cycloalkyl group with 5 to 8 carbon atoms. A represents an alkylene group with 2 to 8 carbon atoms or *-COR 7 - Represents the base, R 7 represents a single bond or an alkylene group having 1 to 8 carbon atoms, and * represents a bond to the oxygen atom in the phosphite structure in formula (V). Y and Z represent either a hydroxyl group, an alkoxy group having 1 to 8 carbon atoms, or an aralkyloxy group having 7 to 12 carbon atoms, and the other represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. However, when Y is a hydroxyl group, R 4 and R 5 One of the C3-C8 alkyl groups, C5-C8 cycloalkyl groups, C6-C12 alkylcycloalkyl groups, C7-C12 aralkyl groups, or phenyl groups. Also, the two R groups in formula (V) 1 These may be the same or different from each other. Furthermore, the two R in equation (V) 2 These may be the same or different from each other. And the two R in equation (V) 3 They may be the same or different from each other.

[0029] The compound represented by the above formula is typically 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butyldibenz[d,f][1.3.2]dioxaphosfepine). This compound can be obtained as "Sumilyzer GP" manufactured by Sumitomo Chemical Co., Ltd.

[0030] [ka]

[0031] The ratio of the antioxidant (a1) to the total amount of metallocene HDPE (A1) and the conductive agent (a2) described later is generally 0.05% by weight or more and 2.0% by weight or less, preferably 0.1% by weight or more and 1.0% by weight or less.

[0032] [Conductive agent (a2)] The surface layer (A) further contains a conductive agent (a2). The conductive agent (a2) can be any commonly used type without limitation, such as conductive carbons like carbon black, graphite, carbon nanotubes, or carbon fibers; metallic conductive fillers made of metals like silver, copper, nickel, tin, or aluminum; metal oxide powders; or powdered or fibrous glass with metal plating. Carbon black, which is particularly known for its conductivity, is preferred as the conductive agent (a2). The amount of conductive carbon black as the conductive agent (a2) blended with metallocene HDPE (A1) is generally 1% by weight or more and 40% by weight or less, preferably 5% by weight or more and 30% by weight or less. By adjusting the amount of conductive carbon black as the conductive agent (a2) blended with metallocene HDPE (A1) as described above, the film of the present invention can be given appropriate conductivity.

[0033] [Dispersant (a3)] In this invention, aggregation of the conductive agent (a2) can be prevented by using a conductive agent (a2) and a dispersant (a3) ​​in combination. As the dispersant (a3), fatty acid metal salts, fatty acid esters, fatty acid amides, acid-modified polyolefins, polyolefin waxes, silane coupling agents, etc., which are commonly used as dispersants for pigments and inorganic fillers, can be used without limitation. Higher fatty acid metal salts such as magnesium stearate, zinc stearate, and aluminum stearate are typical dispersants. The preferred dispersant (a3) ​​is a metal stearate.

[0034] In the sense of using a conductive agent (a2) and a dispersant (a3) ​​in combination, it is also possible to use a conductive agent (a2) that has been surface-treated with a dispersant (a3) ​​beforehand, or to add the conductive agent (a2) as a masterbatch.

[0035] The ratio of the dispersant (a3) ​​to the total amount of metallocene HDPE (A1) and conductive agent (a2) is generally 0.05% by weight or more and 2% by weight or less, preferably 0.1% by weight or more and 1% by weight or less.

[0036] [Other additives (a4)] The surface layer (A) may contain an antioxidant (a4) different from the antioxidant (a1) as an additional additive (a4). Any of these additional antioxidants can be phosphorus-based antioxidants, sulfur-based antioxidants, hindered phenol-based antioxidants, etc.

[0037] The surface layer (A) may include other additives (a4), such as conventional resin additives including antistatic agents, lubricants, mold release agents, antiblocking agents, nucleating agents, flame retardants, dispersants, inorganic or organic fillers, colorants, UV absorbers, and antifogging agents. The amounts of these additives shall follow conventional methods.

[0038] [Intermediate layer (B), high-density polyethylene resin (B1)] The intermediate layer (B) that can constitute the polyethylene film of the present invention mainly consists of a high-density polyethylene resin (B1). As the high-density polyethylene resin (B1), any general so-called HDPE can be used without limitation, such as a high-density polyethylene resin polymerized in the presence of a Ziegler-Natta catalyst or a high-density polyethylene resin polymerized in the presence of a metallocene catalyst.

[0039] The same type of metallocene HDPE (A1) as the metallocene HDPE (A1) contained in the surface layer (A) may be used as the high-density polyethylene resin (B1). For example, the same metallocene HDPE can be used for both the intermediate layer (B) and the surface layer (A).

[0040] The intermediate layer (B) may contain, in addition to the high-density polyethylene resin (B1), such as metallocene HDPE (A1), other polyolefin resins different from the high-density polyethylene resin (B1), such as ethylene homopolymers, ethylene-α-olefin copolymers, and polypropylene polymers, or other thermoplastic resins, as long as the function of the intermediate layer (B) is not impaired. In the present invention, there is no problem if the resin components are the same for the intermediate layer (B) and the surface layer (A). Preferably, both the surface layer (A) and the intermediate layer (B) of the present invention are composed of the same resin components, mainly metallocene HDPE (A1), and the above-mentioned antioxidant (a1), conductive agent (a2), and dispersant (a3) ​​are blended only in the surface layer (A). However, the intermediate layer (B) may also contain antioxidant (a1), conductive agent (a2), dispersant (a3), and various additional additives as needed. There is no problem if the intermediate layer (B) contains the same additives as the surface layer (A).

[0041] [Manufacturing method] To manufacture the polyethylene-based film of the present invention, any method for manufacturing a multilayer film using thermoplastic materials as raw materials can be employed without limitation. For example, either the co-extrusion method using a T-die or the inflation method can be used. The equipment used for film formation and the operating method of the equipment can be selected from within normally permissible ranges.

[0042] [Foreign objects and / or defects] The polyethylene film of the present invention is less prone to the appearance of minute shape abnormalities on its surface. Therefore, it is possible to prevent damage to precision products such as electronic equipment components that come into contact with the polyethylene film of the present invention. Such a polyethylene film is differentiated from conventional products by an objective indicator: the frequency of detection of foreign matter and / or defects in the surface layer (A). The aforementioned foreign matter and / or defects include defects referred to as "bumps," "fish eyes," or "lumps" in the film molding process. These foreign matter and / or defects also include small defects that may be overlooked during visual inspection.

[0043] Shape measuring instruments and roughness meters are used to detect the foreign matter and / or defects mentioned above. For example, a laser microscope for shape measurement can be used to detect irregularities that differ from the surrounding open surface by 10 μm or more as the foreign matter and / or defects mentioned above.

[0044] In this invention, for example, areas on the surface layer (A) detected by a laser microscope for shape measurement, where the minor axis L1 and / or major axis L2 are greater than 100 μm and the shape and / or color differ from the surrounding area, are treated as foreign matter and / or defects. In this case, the open surface layer (A) is 780 cm². 2 The number of foreign objects and / or defects detected per unit is generally 20 or less, preferably 15 or less. Such polyethylene films are useful as packaging or protective materials for precision instruments, medical devices, electronic components, and the like. [Examples]

[0045] [Example of a single-layer polyethylene film] (Film manufacturing) Two 50 μm thick films (Example 1, Comparative Example 1) were produced by melt-extruding a resin composition containing the following metallocene HDPE (A1), antioxidant (a1), conductive agent (a2), and dispersant (a3) ​​in the proportions (parts by weight) shown in Table 1. Each film is a single-layer film consisting of one surface layer (A).

[0046] • Metallocene HDPE (A1): Density 0.937 kg / m³ 3 High-density polyethylene obtained by polymerizing ethylene in the presence of a metallocene catalyst, with an MFR (measured at 190°C and a load of 2.16 according to JIS K 7210) of 2.5 g / 10 min.

[0047] • Antioxidant (a1): "SumiLizer GP" manufactured by Sumitomo Chemical Co., Ltd. • Conductive agent (a2): Carbon black manufactured by Dainichi Seika Kogyo Co., Ltd. • Dispersant (a3): Magnesium stearate.

[0048] Example 1 is a single-layer film consisting of a surface layer (A) that satisfies the conditions of the present invention. Comparative Example 1 is a single-layer film that does not contain an antioxidant (a1).

[0049] [Table 1]

[0050] (Evaluation: Oxidation induction time) The oxidation induction time for the two single-layer films described above (Example 1 and Comparative Example 1) was measured. A Rigaku TG-DTA8122 differential thermal and thermogravimetric analyzer was used. Test pieces of the same dimensions and shape, cut from each of the single-layer films (Example 1 and Comparative Example 1), were placed in the apparatus, and the apparatus was filled with nitrogen. Next, the temperature inside the apparatus was increased and maintained at 220°C for 5 minutes. Then, the temperature inside the apparatus was maintained at 220°C, and the atmosphere inside the apparatus was replaced with oxygen. The time from the completion of the oxygen replacement until the exothermic reaction of the sample was detected, "oxidation induction time (minutes)," was measured. The results are shown in Table 1.

[0051] In Example 1, no endothermic reaction was detected even after 60 minutes had elapsed since the atmosphere inside the apparatus was replaced with oxygen. The oxidation induction time in Comparative Example 1 was 21 minutes. From this, it was confirmed that oxidation of the film was suppressed in Example 1.

[0052] [2. Example of a single-layer polyethylene film] (Film manufacturing) Four films with a thickness of 50 μm (Example 2, Example 3, Comparative Example 2, Comparative Example 3) were produced by melt-extruding a resin composition containing the same materials as in Example 1 and Comparative Example 1 in the proportions (parts by weight) shown in Table 2.

[0053] Four single-layer films for a surface layer (A) with a thickness of 50 μm were manufactured. Examples 2 and 3 are films consisting of a surface layer (A) that satisfies the conditions of the present invention. Comparative Example 2 is a single-layer film that does not contain an antioxidant (a1). Comparative Example 3 is a single-layer film that does not contain an antioxidant (a1) or a dispersant (a3).

[0054] [Table 2]

[0055] (Evaluation: Foreign objects and / or defects) One side of each 30cm x 26cm rectangular sample, cut from four single-layer films (Examples 2 and 3, Comparative Examples 2 and 3), was observed using a Keyence VK-8500 shape-measuring laser microscope. The number of detected foreign objects and / or defects with a minor axis L1 and / or major axis L2 exceeding 100 μm was tallied. Table 2 shows the measurement results for the five samples (780cm). 2 This shows the average number of items per unit. It can be seen that the number of foreign objects and / or defects detected in the single-layer films of Examples 2 and 3 is extremely small.

[0056] [3. Examples of multilayer polyethylene films] (Film manufacturing) Three types of three-layer polyethylene films (Example 4, Comparative Example 4) having a surface layer (A) / intermediate layer (B) / surface layer (A) structure were manufactured. The following polyethylenes were used for the surface layer (A) and intermediate layer (B).

[0057] • Metallocene HDPE (A1): Density of 0.940 kg / m³ 3 High-density polyethylene obtained by polymerizing ethylene in the presence of a metallocene catalyst, with an MFR (measured according to JIS K 7210 at a temperature of 190°C and a load of 2.16 kg) of 2.5 g / 10 min.

[0058] • High-density polyethylene (B1): Density of 0.949 kg / m³ 3 High-density polyethylene (HDPE) with an MFR (measured at 190°C and under a 2.16 kg load according to JIS K 7210) of 1.1 g / 10 min. • High-pressure low-density polyethylene (B2): Manufactured by high-pressure radical polymerization, with a density of 0.925 kg / m³. 3 Polyethylene (HP-LDPE) with an MFR (measured at 190°C under a 2.16 kg load according to JIS K 7210) of 2.3 g / 10 min. The following antioxidants were included as other antioxidants (a4).

[0059] • Other antioxidants (a4): Irganox 1076 (manufactured by BASF Corporation, hindered phenol antioxidant) Three multilayer polyethylene films with two types of three-layer structures—surface layer (A) / intermediate layer (B) / surface layer (A)—were manufactured by laminating the surface layer (A) and intermediate layer (B) using the inflation method with the formulations shown in Table 3.

[0060] [Table 3]

[0061] (Evaluation: Conductivity) The surface resistance values ​​of test pieces cut from the three polyethylene multilayer films (Example 4, Comparative Example 4) were measured under conditions of 23°C and 50% humidity. The results are shown in Table 3.

[0062] The surface resistance of the multilayer film in Example 4 is relatively low. Therefore, the multilayer film in Example 4 is expected to have moderate conductivity. If the multilayer film in Example 4 is used as packaging or protective material for electronic components or powder products, even if static electricity is generated during the transportation of the electronic components or powder products, the moderate conductivity of the multilayer film will allow the static electricity to dissipate, preventing the adhesion of dust and other contaminants.

[0063] In contrast, the polyethylene multilayer film of Comparative Example 4 has a considerably higher surface resistance than that of Example 4. This indicates that the film produced in Comparative Example 4 is inferior to the film of Example 4 in terms of appropriate conductivity. If such a film of Comparative Example 4 is used as packaging material for electronic equipment components, it will be difficult to dissipate the static electricity generated during the movement and transport of the electrical equipment components. For this reason, the film of Comparative Example 4 is unsuitable as packaging or protective material for electrical equipment and / or electrical components.

[0064] From the results of Example 4 and Comparative Example 4, it is considered that the conductive agent (a2) is uniformly dispersed in the surface layer (A) of the polyethylene-based film of the present invention, and as a result, a polyethylene-based multilayer film with excellent conductivity was obtained in Example 4.

[0065] When electronic equipment components are packaged and transported using the polyethylene-based film having appropriate conductivity according to the present invention, it is possible to prevent the generation of electrostatic discharge when the electronic equipment components are separated from the film after transport.

[0066] (Evaluation: Foreign objects and / or defects) Following the method used in the single-layer film example, the number of foreign objects and / or defects in test specimens cut from the three multilayer films mentioned above was measured. The results are shown in Table 3.

[0067] It is understood that the multilayer film of Example 4 has few foreign matter and / or defects. By using the multilayer film of Example 4 as packaging or protective material for precision parts and fragile articles, these precision parts and fragile articles can be transported and stored without damage. Furthermore, if the surface of the multilayer film of Example 4 is further micro-processed, it is expected that complex designs can be realized with high precision without defects.

[0068] In contrast, numerous foreign matter and / or defects were detected on the surface of the polyethylene multilayer film of Comparative Example 4. The polyethylene multilayer film of Comparative Example 4 has poor scratch prevention properties for articles that come into contact with it and is not suitable for fine surface processing.

[0069] [Overall rating: Quality] Considering the evaluation results described above, it can be said that Example 4 yielded a polyethylene-based multilayer film that met the requirements for stain resistance, shape precision, reduced frequency of foreign matter and defects on the surface, and appearance stability. In contrast, Comparative Example 4, which had a different layer composition, failed to meet one or more of the requirements for stain resistance, shape precision, reduced frequency of foreign matter and defects on the surface, and appearance stability, and had quality problems. The polyethylene-based film of the present invention can be said to be useful as a packaging material or protective material. Furthermore, the polyethylene-based film of the present invention is advantageous for secondary processing involving microfabrication because it achieves shape precision and reduced frequency of foreign matter and defects on the surface. [Industrial applicability]

[0070] This invention provides the market with high-quality polyethylene multilayer films. It also contributes to improving the quality and multi-functionality of packaging materials, particularly those used for packaging and protecting electronic components. [Explanation of symbols]

[0071] 1. Single-layer polyethylene film 12 Surface layer (A) 2. Multilayer polyethylene film 22 Surface layer (A) 23 Middle layer (B) 3. Multilayer polyethylene film 32 Surface layer (A) 33 Middle layer (B) 34 Reproduction layer (C)

Claims

1. A single-layer or multi-layer polyethylene film having at least one surface layer (A) and optionally an intermediate layer (B) sandwiched between two A layers, The surface layer (A) comprises a resin mainly composed of high-density polyethylene (A1) polymerized in the presence of a metallocene catalyst, and an antioxidant (a1), a conductive agent (a2), and a dispersant (a3) ​​having both a phosphite ester structure and a hindered phenol structure within the same molecule. The intermediate layer (B) is mainly composed of high-density polyethylene (B1). Single-layer or multi-layer polyethylene films.

2. 780 cm of one open surface layer (A) ２ The number of foreign objects and / or defect points detected per unit, with a short diameter L1 and / or long diameter L2 exceeding 100 μm, is 20 or less. The polyethylene film according to claim 1.

3. Total thickness is 30 μm or more and 300 μm or less. The thickness of the surface layer (A) is 5 μm or more and 100 μm or less. The thickness of the intermediate layer (B) is between 20 μm and 200 μm. A multilayer polyethylene film according to claim 1.

4. The surface resistance of one open surface layer (A) measured in an atmosphere of 23°C and 50% humidity was 1.0 × 10⁻⁶. ３ Ω or more 1.0×10 ８ A polyethylene film according to claim 1, wherein the Ω value is less than or equal to Ω.

5. A polyethylene film according to claim 1, used as packaging or protective material for electronic devices and / or electronic components.

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