Foamed electrical cable, communication cable and method for producing the same

Abstract

A foamed electric wire (10) comprises a conductor (12) and a covering layer that covers the conductor and is formed from one or more layers. At least one layer of the covering layer is a foamed covering layer (14) made of a resin composition containing a polypropylene resin and formed by foam extrusion molding. An average foam diameter of the foamed covering layer (14) is 30 µm or less in a cross-sectional direction and 60 µm or less in a longitudinal direction. The foaming ratio of the foamed covering layer (14) is 25% or more and 55% or less. The arithmetic average height of a surface of the foamed electric wire (10) is 20 µm or less.

Description

Technical area

[0001] The present invention relates to a foamed electrical cable, a communication cable and a method for producing the same. State of the art

[0002] In a physical foaming extrusion process using an inert gas for a small-diameter electrical wire for a foamed electrical cable that can be used as a high-speed communication cable for the GHz band, it has been found that foaming is difficult to control and communication properties tend to deteriorate due to fluctuations in foaming. Therefore, a conventional chemical foaming process is often used, in which foaming is relatively gentle and the foam diameter can be easily stabilized.In Patent Literature 1, it is disclosed that a foamed covering layer is formed by kneading a base resin and a masterbatch containing a heat-decomposition type chemical foaming agent and a polypropylene-based resin, and that the foam diameter and the foam ratio are controlled by, for example, controlling the melt tension of the resin. Citation listPatent documents

[0003] Patent Document 1: Japanese Patent No. 5,420,662 Summary of the invention

[0004] However, in Patent Literature 1, the chemical foaming agent is kneaded into the masterbatch, and the two are mixed through a foam extrusion process. Therefore, the dispersion of the chemical foaming agent during melting is poor, and it is difficult to achieve a uniform foam diameter. Because the foaming agent and masterbatch must be sufficiently melted in a cylinder, the production rate is low and the production efficiency is low. Furthermore, since azodicarbonamide (ADCA) is used as the chemical foaming agent, there was the problem of not being able to comply with REACH regulations.

[0005] It is an object of the present invention to provide a foamed electrical wire with excellent abrasion resistance and heat distortion temperature, designed for a vehicle environment while ensuring communication stability, and enabling control of the foam diameter even in a physical foaming process using an inert gas. Another object of the present invention is to provide a communication cable using the foamed electrical wire and a method for manufacturing the same.

[0006] A foamed electric wire according to one aspect of the present invention comprises: a conductor; and a covering layer covering the conductor and having one or more layers, wherein at least one layer of the covering layer is a foamed covering layer made of a resin composition containing a polypropylene resin formed by foam extrusion molding, an average foam diameter of the foamed covering layer is 30 μm or less in a cross-sectional direction and 60 μm or less in a longitudinal direction, a foaming ratio of the foamed covering layer is 25% or more and 55% or less, and an arithmetic average height of a surface of the foamed electric wire is 20 μm or less.

[0007] A communication cable according to another aspect of the present invention comprises the foamed electrical wire described above.

[0008] A method for producing a foamed electric wire according to another aspect of the present invention comprises: a step of forming a covering layer that covers a conductor and has one or more layers; and a step of forming a foamed covering layer from a resin composition containing a polypropylene resin formed by foam extrusion molding as at least one layer of the covering layer, in which an average foam diameter of the foamed covering layer is 30 μm or less in a cross-sectional direction and 60 μm or less in a longitudinal direction, a foaming ratio of the foamed covering layer is 25% or more and 55% or less, and an arithmetic average height of a surface of the foamed electric wire is 20 μm or less.

[0009] According to the present invention, it is possible to provide a foamed electrical wire with excellent abrasion resistance and heat distortion temperature, designed for a vehicle environment while ensuring communication stability, and enabling control of the foam diameter even in a physical foaming process using an inert gas. Furthermore, it is possible to provide a communication cable using the foamed electrical wire and a method for manufacturing the same. Short description of the drawings [ Fig. 1] Fig. 1 shows an example of a case where a covering layer of a foamed electric wire according to the present embodiment has a single layer, and is a cross-sectional view taken perpendicular to a longitudinal direction of the foamed electric wire. [ Fig. 2] Fig.2 shows an example of a case where the covering layer of the foamed electric wire according to the present embodiment has two layers, and is a cross-sectional view taken perpendicular to the longitudinal direction of the foamed electric wire. [ Fig. 3] Fig. 3 shows an example of a case where the covering layer of the foamed electric wire according to the present embodiment has three layers, and is a cross-sectional view taken perpendicular to the longitudinal direction of the foamed electric wire. Description of the embodiments

[0010] A foamed electric wire according to the present embodiment will be described in detail below with reference to the drawings. The dimensional proportions in the drawings are exaggerated for simplicity and may differ from the actual conditions. [Foamed electrical cable]

[0011] A foamed electrical wire according to the present embodiment comprises a conductor and covering layers covering the conductor. The covering layers consist of one or more layers. At least one of the covering layers is a foamed covering layer composed of a resin composition containing a polypropylene resin and formed by foam extrusion molding. Preferably, the foamed covering layer is formed using an inert gas in the foam extrusion process (physical foaming process).

[0012] As in Fig. 1, a foamed electrical cable 10 comprises a conductor 12 and a foamed covering layer 14 covering the outer periphery of the conductor 12. The conductor 12 and the foamed covering layer 14 form an insulated electrical cable. As shown in Fig.As shown in Figure 1, the conductor 12 of the foamed electrical wire 10 is covered only with the foamed covering layer 14 when the covering layer of the foamed electrical wire 10 is a single layer. This type of foamed electrical wire 10 with a single covering layer can be manufactured by covering the conductor 12 with a resin composition containing a polypropylene resin by foam extrusion molding.

[0013] As in Fig.As shown in Figure 2, when the covering layer of the foamed electric wire 10 has two layers, the foamed electric wire 10 includes the conductor 12, the foamed covering layer 14 covering the outer periphery of the conductor 12, and an outer layer 16 covering the outer periphery of the foamed covering layer 14. Similar to the foamed electric wire with a single covering layer, the foamed covering layer 14 of the foamed electric wire 10 with two covering layers is formed by covering the conductor 12 with a resin composition containing a polypropylene resin by foam extrusion molding. Meanwhile, the outer layer 16 can be formed by general extrusion molding, but from the viewpoint of improving productivity, it is preferable to form the foamed covering layer 14 and the outer layer 16 by coextrusion.

[0014] As in Fig.As shown in Figure 3, the foamed electrical wire 10 comprises the conductor 12, an inner layer 18 covering the outer periphery of the conductor 12, the foamed covering layer 14 covering the outer periphery of the inner layer 18, and an outer layer 16 covering the outer periphery of the foamed covering layer 14 when the covering layer of the foamed electrical wire 10 has three layers. To produce the foamed electrical wire 10 with three covering layers, the conductor 12 is first covered with the inner layer 18 by extrusion molding. Subsequently, as previously described, the electrical wire 10 can be produced with two covering layers by covering the inner layer 18 with the foamed covering layer 14 and the outer layer 16.

[0015] The covering layer of the foamed electrical wire 10 may be formed of four or more layers. Furthermore, there are no particular restrictions on the number of covering layers or the configuration of the foamed electrical wire 10. It is not necessary for an outer layer or an inner layer of the foamed covering layer 14 to contain a non-foamed layer, and the covering layer of the foamed electrical wire 10 may be formed only from the foamed covering layer 14.

[0016] The arithmetic average height of a surface of the foamed electric wire 10 is 20 μm or less. The arithmetic average height is a parameter for evaluating three-dimensional surface properties (surface roughness). Since the arithmetic average height is 20 μm or less, abrasion resistance can be ensured when used as a communication cable. The arithmetic average height of the surface of the foamed electric wire 10 is measured as the arithmetic average height Sa by analyzing an image of the surface of the foamed electric wire 10 taken with a 3D optical profilometer (manufactured by KEYENCE CORPORATION) or the like, in accordance with the international standard ISO 25178, which defines evaluation methods for surface roughness. [Foamed cover layer]

[0017] The foamed cover layer 14 is made of a resin composition containing a polypropylene resin. Examples of the polypropylene resin used in the resin composition include homopolypropylene (homo-PP), random polypropylene (random-PP), block polypropylene (block-PP), and copolymers with components such as other olefins copolymerizable with propylene. Examples of other olefins copolymerizable with propylene include α-olefins such as ethylene, 1-butene, isobutylene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3,4-dimethyl-1-butene, 1-heptene, and 3-methyl-1-hexene.

[0018] The melt stress of the resin composition, measured with a capillary rheometer at 200°C, is 15 mN or more and 45 mN or less, preferably 18 mN or more and 35 mN or less. Since the melt stress of the resin composition is 15 mN or more, foam breakage on the surface of the foamed covering layer is prevented, and the surface of the foamed covering layer is less likely to be roughened. In addition, since the melt stress of the resin composition is 45 mN or less, a foam is prevented from excessively expanding in a longitudinal direction of the foamed electrical wire, it is easy for a foam to maintain a spherical shape, and communication stability can be ensured when used as a communication cable. The melt stress can be measured with a capillary rheometer such as the CAPILOGRAPH (registered trademark) (manufactured by Toyo Seiki Seisaku-sho, Ltd.).

[0019] The melt viscosity of the resin composition, measured with a capillary rheometer at 200°C, is 120 Pa s or more and 200 Pa s or less, preferably 130 Pa s or more and 170 Pa s or less. When the melt viscosity of the resin composition is 120 Pa s or more, foam formation is promoted. When the melt viscosity of the resin composition is 200 Pa s or less, foam coalescence is prevented, and the foam diameter can be easily adjusted to a desired diameter. The melt viscosity can be measured according to JIS K 7199:1999 using a capillary rheometer such as the CAPILOGRAPH (registered trademark) (manufactured by Toyo Seiki Seisaku-sho, Ltd.).

[0020] The average foam diameter of the foamed covering layer 14 is 30 μm or less in a cross-sectional direction of the foamed electric wire 10 and 60 μm or less in a longitudinal direction of the foamed electric wire 10. Further, the average foam diameter of the foamed covering layer 14 is preferably 20 μm or less in the cross-sectional direction of the foamed electric wire 10 and 55 μm or less in the longitudinal direction of the foamed electric wire 10. Since the average foam diameter of the foamed covering layer 14 is 30 μm or less in the cross-sectional direction and 60 μm or less in the longitudinal direction, it is easy to form nearly spherical and fine foams with a uniform foam diameter. Therefore, it is possible to ensure communication stability when used as a communication cable.The average foam diameter can be confirmed by observing a cross-sectional area obtained by cutting the foamed electrical wire 10 in the transverse or longitudinal direction with an electron microscope, measuring the foam diameters, and calculating an average value. Alternatively, the average foam diameter can be confirmed by non-destructive observation of a cross-sectional area obtained by cutting the foamed electrical wire 10 in the transverse or longitudinal direction using an X-ray CT microscope, measuring the foam diameters, and calculating an average value.

[0021] The foaming ratio of the foamed covering layer 14 is 25% or more and 55% or less. The characteristic impedance of an in-vehicle communication cable is preferably in a range of 95 Ω to 105 Ω. Since the foaming ratio of the foamed covering layer 14 is 25% or more and 55% or less, the characteristic impedance of the foamed electric wire 10 can be controlled to be within the above-mentioned range. Taking the area occupied by foams in a cross-sectional area of ​​the foamed covering layer 14 as the foaming ratio, the foaming ratio can be confirmed in the same way as the average foam diameter by observing a sectional area of ​​the foamed electric wire 10 and calculating average values ​​of the foaming ratios in the cross-sectional direction and the longitudinal direction.

[0022] The foamed cover layer 14 is preferably produced by a foam extrusion process using an inert gas. Specifically, at the time of molding, an inert gas, such as a foaming agent, is injected into a heated and molten resin composition to cause foaming. The above-described foaming ratio can be controlled by adjusting the injection amount, temperature, and inert gas pressure.

[0023] Examples of the inert gas used for foam extrusion molding include nitrogen, carbon dioxide, argon, water vapor, helium, and isobutane. From the viewpoint of solubility in a polypropylene resin and environmental consideration, the inert gas is preferably at least one selected from the group consisting of nitrogen gas, carbon dioxide gas, and argon gas, and more preferably nitrogen gas or carbon dioxide gas. Nitrogen gas or carbon dioxide gas is used for general foam extrusion molding of a polypropylene resin. One inert gas may be used alone, or two or more may be used in combination.

[0024] In addition to a polypropylene resin, a suitable amount of various additives may be added to a resin composition to the extent that the effects of the present embodiment are not impaired. Examples of additives include flame retardants, inorganic fillers, flame retardant aids, antioxidants, processing aids, crosslinking agents, metal deactivators, copper inhibitors, antiaging agents, fillers, reinforcing agents, ultraviolet absorbers, stabilizers, plasticizers, pigments, dyes, colorants, and antistatic agents. (flame retardants)

[0025] A flame retardant increases the flame retardancy of a resin composition. The flame retardant can be at least either an organic flame retardant or an inorganic flame retardant. Examples of organic flame retardants that can be used include halogen-based flame retardants such as bromine- and chlorine-based flame retardants, and phosphorus-based flame retardants such as phosphate esters, condensed phosphate esters, cyclic phosphorus compounds, and red phosphorus. Examples of inorganic flame retardants that can be used include at least one metal hydroxide selected from the group consisting of aluminum hydroxide, magnesium hydroxide, and calcium hydroxide. One of the flame retardants can be used alone, or a mixture of several flame retardants can be used. Examples of organic flame retardants that can be used include an organic flame retardant and an inorganic flame retardant.The amount of flame retardant added can be adjusted accordingly, taking into account the flame-retardant effect and the influence on the mechanical properties. (antioxidant)

[0026] An antioxidant suppresses the oxidation of a resin composition. Known antioxidants for thermoplastic resins and the like can be used as the antioxidant, including radical inhibitors such as phenol-based antioxidants, hindered phenol-based antioxidants, and amine-based antioxidants; peroxide decomposers such as phosphorus-based antioxidants and sulfur-based antioxidants; and metal deactivators such as hydrazine-based antioxidants and amine-based antioxidants. One of the antioxidants can be used alone, or a mixture of multiple antioxidants can be used. The added amount of an antioxidant can be adjusted accordingly, taking into account the antioxidant effect and any deficiencies caused by bleeding. (copper inhibitor)

[0027] If copper or a copper alloy is used for the conductor 12, copper can cause decomposition of the covering layers of the foamed electrical wire 10, which is referred to as copper damage. For this reason, a copper inhibitor can be added to a resin forming the covering layers of the foamed electrical wire 10. For example, a salicylic-based copper inhibitor or a hydrazine-based copper inhibitor is used as the copper inhibitor. The added amount of a copper inhibitor can be adjusted accordingly, taking into account the effect of preventing copper damage and any defects caused by bleeding.

[0028] Known means can be used as a method for adding the above-described additive to the polypropylene resin to obtain the resin composition. The resin composition can be obtained by kneading the resin and the additive using a known kneading device such as a Banbury mixer, a kneader, a rolling mill, a twin-screw extruder, or a single-screw extruder. [Director]

[0029] As the conductor 12, a single wire consisting of a single element wire or a twisted wire conductor formed by twisting a plurality of element wires can be used. For the twisted wire conductor, a concentric twisted wire in which the element wires are concentrically twisted around one or more element wires, an aggregate twisted wire in which multiple element wires are twisted together in the same direction, and a composite twisted wire in which multiple aggregate twisted wires are concentrically twisted can be used. There are no particular restrictions on the diameter of the conductor and the diameter of the individual element wires constituting the twisted wire conductor. The conductor 12 can be a compacted conductor or a non-compacted conductor.Furthermore, there are no particular restrictions on the materials of the conductor and the twisted conductor, and it is possible to use known conductive metal materials such as copper, a copper alloy, aluminum, and an aluminum alloy. Furthermore, the surfaces of the conductor and the twisted wire conductor can be coated, and tin plating, silver plating, or nickel plating can be applied.

[0030] The outer diameter of the conductor 12 is not particularly limited, but it is preferably 0.45 mm or more. Since the outer diameter of the conductor 12 is 0.45 mm or more, it is possible to reduce the resistance of the conductor 12. Further, it is preferable that the outer diameter of the conductor 12 is 0.80 mm or less. Since the outer diameter of the conductor 12 is 0.80 mm or less, the foamed electric wire 10 can be easily arranged in a path even if the path is narrow and short. [Outer layer]

[0031] For the material and thickness of the outer layer 16, which forms the outermost part of the Fig. 2 and Fig.3, there are no particular restrictions as long as the electrical insulation of the conductor can be ensured. For the outer layer 16, electrically insulating resins can optionally be used, including olefin resins such as cross-linked polyethylene and polypropylene, and vinyl chloride resins. Specifically, as the resin material constituting the outer layer 16, it is possible to use, for example, polyvinyl chloride, heat-resistant polyvinyl chloride, cross-linked polyvinyl chloride, polyethylene, cross-linked polyethylene, foamed polyethylene, cross-linked foamed polyethylene, chlorinated polyethylene, polypropylene, polyamide (nylon), polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene, perfluoroalkoxyalkane, natural rubber, chloroprene rubber, butyl rubber, ethylene-propylene rubber, chlorosulfonated polyethylene rubber, or silicone rubber.One of the materials can be used alone, or two or more can be used in combination.

[0032] As in the Fig. 2 and Fig. As shown in Figure 3, the foamed cover layer 14 can be covered with the outer layer 16 by known means. The outer layer 16 can be formed, for example, by general extrusion. As the extruder for extrusion, a single-screw extruder or twin-screw extruder equipped with a screw, breaker plate, crosshead, distributor, nozzle, and die can be used. In extrusion, a resin material is charged into an extruder set at a temperature at which the resin melts sufficiently. At this time, in addition to the resin material, various additives to be added to the above-described resin composition, such as an antioxidant, can be charged into the extruder if necessary. [Inner layer]

[0033] There are no particular restrictions on the material and thickness of the inner layer 18, which Fig. 3, as long as the electrical insulation of the conductor 12 can be ensured, and it is possible to use resin materials similar to those for the previously described outer layer 16. Furthermore, the conductor 12 can be covered with the inner layer 18 using known means, and general extrusion molding can be used as in the case of forming the previously described outer layer 16.

[0034] As described above, the foamed electric wire 10 includes the conductor 12 and the covering layers covering the conductor 12, which are formed of one or more layers. At least one of the covering layers is the foamed covering layer 14, which is made of a resin composition containing a polypropylene resin and is formed by foam extrusion molding. The average foam diameter of the foamed covering layer 14 is 30 μm or less in the cross-sectional direction and 60 μm or less in the longitudinal direction. The foaming ratio of the foamed covering layer 14 is 25% or more and 55% or less. The arithmetic average height of the surface of the foamed electric wire 10 is 20 μm or less.Therefore, it is possible to control the foam diameter even by a physical foaming process using an inert gas, and it is possible to provide a foamed electrical wire with excellent abrasion resistance and heat deformation resistance, designed for a vehicle environment while ensuring communication stability.

[0035] As described above, a method for manufacturing the foamed electric wire 10 further includes a step of forming cover layers that cover the conductor 12 and are formed of one or more layers, and a step of forming the foamed cover layer 14 from a resin composition containing a polypropylene resin formed by foam extrusion molding as at least one of the cover layers. The average foam diameter of the foamed cover layer 14 is 30 μm or less in the cross-sectional direction and 60 μm or less in the longitudinal direction. The foaming ratio of the foamed cover layer 14 is 25% or more and 55% or less.

[0036] The arithmetic average height of the surface of the foamed electric wire 10 is 20 µm or less. [Communication cable]

[0037] The communication cable according to the present embodiment includes the foamed electric wire 10 described above. The communication cable can be manufactured by a known method, such as general extrusion molding. Specifically, a covering can be formed by bundling one or more foamed electric wires 10 and then extruding a covering material onto the outer surface of the foamed electric wires 10 and covering the outer surface. The communication cable including the foamed electric wire 10 can be used as a coaxial cable or a twisted-pair cable. As the resin for the covering of the communication cable, known insulating resins can optionally be used, including olefin resins such as cross-linked polyethylene and polypropylene, and vinyl chloride, and a plasticizer can be included. As the plasticizer, a known plasticizer added to polyvinyl chloride can be used.

[0038] The communication cable according to the present embodiment includes the foamed electric wire 10. Thanks to the foamed electric wire 10, it is possible to control the foam diameter even through a physical foaming process using an inert gas. The foamed electric wire 10 has excellent abrasion resistance and heat deformation resistance and is designed for in-vehicle use, ensuring communication stability. Therefore, the communication cable including this type of foamed electric wire 10 can be preferably used as a transmission cable in a vehicle, for example. [Examples]

[0039] The present embodiment will be described in more detail below using examples and comparative examples, but the present embodiment is not limited to these examples. [Composition of the resin](resin) • PP1: Polypropylene: manufactured by Japan Polypropylene Corporation, Product Name: WAYMAX (Registered Trademark) EX4000 • PP2: Polypropylene: manufactured by Prime Polymer Co., Ltd, Product Name: Prime Polypro (Registered Trademark) E150GK • PP3: Polypropylene: manufactured by Prime Polymer Co, Ltd, Product Name: Prime Polypro (Registered Trademark) J715M • PP4: Polypropylene: manufactured by Prime Polymer Co., Ltd, Product Name: Prime Polypro (Registered Trademark) J-452HP • PP5: Polypropylene: manufactured by SunAllomer Ltd, product name: Qualear (registered trademark) CM688A • EP1: Soft polypropylene (propylene / ethylene copolymer resin): manufactured by SunAllomer Ltd, product name: Adflex (registered trademark) Q200F • PE1: Low-density polyethylene (LDPE): manufactured by DOW-MITSUI POLYCHEMI-CALS CO. LTD, product name: MIRASON (registered trademark) 3530 (antioxidant)

[0040] Phenol-based antioxidant: manufactured by ADEKA CORPORATION, product name: ADK STAB (registered trademark) AO-60 (copper inhibitor)

[0041] Hydrazine-based copper inhibitor: manufactured by BASF SE, product name: IRGANOX (registered trademark) MD1024 [Evaluation of resin composition]

[0042] The resin compositions of Examples 1 to 10 and Comparative Examples 1 to 7 were prepared by melt-kneading the above-described resins, the antioxidant, and the copper inhibitor in the blending amounts shown in Tables 1 and 2. Then, as material properties of each resin composition, the melt tension and melt viscosity were measured using the following method. Tables 1 and 2 show the evaluation results. (melting voltage)

[0043] Melt tension was measured using CAPILOGRAPH (registered trademark) (manufactured by Toyo Seiki Seisaku-sho, Ltd.). The L / D of the capillary was set to 10, and the oven temperature was set to 200°C. After addition of the materials, they were held and dissolved for 3 minutes. A resin was extruded at a piston speed of 20 mm / min, and the resin was taken up by a take-up roller (manufactured by Toyo Seiki Seisaku-sho, Ltd.) in speed increments of 10 mm / min, increasing the take-up speed within a range of 10 to 200 mm / min. The resin was held at each take-up speed for 30 seconds, and if the resin had not been detached, the take-up speed was changed to the next take-up speed. The tension at which the resin detached was set as the melt tension. (melt viscosity)

[0044] Melt viscosity was measured using a CAPILOGRAPH (registered trademark) (manufactured by Toyo Seiki Seisaku-sho, Ltd.). The measurement conditions were a capillary L / D of 10 and a furnace temperature of 200 °C. The melt viscosity was defined as a value measured at a piston speed of 100 mm / min when the piston speed was changed to values ​​of 300 mm / min, 200 mm / min, 100 mm / min, 50 mm / min, and 10 mm / min. [Table 1] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Resin composition PP1 20 - 30 60 70 - 80 - - 80 PP2 - - - - - - - - - 20 PP3 80 70 70 40 30 - 20 60 50 - PP4 - 30 - - - 100 - - - - PP5 - - - - - - - - - - EP1 - - - - - - - 40 50 - PE1 - - - - - - - - - - Antioxidants 0,1 0,1 0,1 0,1 0,1 0,1 0,1 0,1 0,1 0,1 copper inhibitor 0,1 0,1 0,1 0,1 0,1 0,1 0,1 0,1 0,1 0,1 Material properties Melting stress (mN) 15 15 18 29 32 18 35 15 25 45 Melt viscosity (Pa s) 120 125 130 135 160 150 170 180 200 200 [Table 2] Comparison example 1 Comparison example 2 Comparison example 3 Comparison example 4 Comparison example 5 Comparison example 6 Comparison example 7 Comparison example 8 Comparison example 9 Resin composition PP1 - - - 10 20 80 20 100 - PP2 - - 100 - - 20 - - - PP3 - 100 - 90 80 - - - - PP4 - - - - - - - - - PP5 100 - - - - - - - - EP1 - - - - - - - - - PE1 - - - - - - 80 - 100 Antioxidants 0,1 0,1 0,1 0,1 0,1 0,1 0,1 0,1 0,1 copper inhibitor 0,1 0,1 0,1 0,1 0,1 0,1 0,1 0,1 0,1 Material properties Melting stress (mN) 9 7 15 14 15 45 45 50 51 Melt viscosity (Pa s) 110 120 350 120 120 200 210 170 280 [Evaluation of foamed electrical cables]

[0045] The Fig. The foamed electric wire (three-layer insulated electric wire) shown in Fig. 3 was manufactured by the following method using the resin compositions of Examples 1 to 10 and Comparative Examples 1 to 9.

[0046] In the method for producing the foamed electric wire, a polypropylene-based resin was first foamed (at an extrusion temperature of 170°C to 220°C) onto a compressed or uncompressed twisted wire conductor (with an outer diameter of 0.45 mm to 0.80 mm), and the conductor was covered with an inner layer having a thickness of 0.03 mm to 0.1 mm. Using the electric wire, the resin compositions of Examples 1 to 10 and Comparative Examples 1 to 9 were covered by foam extrusion molding, whereby the outer diameter of the electric wire was in a range of 1.00 mm to 2.20 mm, and accordingly, a foamed covering layer was formed.The temperature of the extruder used for foam extrusion molding was set within a range of 170°C to 220°C, and a high-pressure nitrogen gas obtained by pressurizing with a gas booster was injected from a central part of the extruder and mixed. At this time, the manufacturing of the electrical wire was carried out under conditions where the foaming ratio of the foamed cover was a low foaming ratio (25% or 20%) and a high foaming ratio (55% or 60%), as shown in Tables 3 and 4. Furthermore, a polypropylene-based resin was extrusion-molded simultaneously with the foamed cover layer using a sub-extruder (set temperature 210°C to 240°C), and the foamed cover layer was covered with a 0.03 mm to 0.1 mm thick outer layer.The properties of the resulting foamed electrical wire were evaluated using the following method: foaming ratio, average foam diameter, arithmetic average height, abrasion resistance, heat distortion temperature, LCTL, and characteristic impedance. Tables 3 and 4 show the evaluation results. (Foaming ratio and average foam diameter)

[0047] A CT image of the foamed electrical cable (in the transverse and longitudinal directions) was acquired using an X-ray CT microscope (nano3DX). The acquisition conditions were as follows: spatial resolution of 4.31 µmNoxel, X-ray camera lens L1080, binning of 3, exposure time of 4 seconds, X-ray source Cu (40 kV, 30 mA), field of view of 3.626 mm * 2.719 mm, and the number of acquired images of 400. The foaming ratio and average foam diameter were calculated using the analysis software ImageJ as average values ​​for the acquired images. (Arithmetic mean)

[0048] An image of the foamed electrical wire surface was acquired using a 3D optical profilometer (manufactured by KEYENCE CORPORATION), and the arithmetic average height Sa of the foamed electrical wire surface was calculated using analysis software. The image acquisition conditions were as follows: magnification power 25, measurement range 10 x 10 mm, and the number of acquired images 5. (Abrasion resistance)

[0049] The abrasion resistance test was conducted according to the abrasion test described in ISO 19642-12. Specifically, a needle was placed vertically on a test sample of the cut-out foamed electrical cable, the covering layer was removed by reciprocating the needle with a fixed load (4 N), and the number of reciprocations until the needle touched the conductor was measured. If the number of reciprocations until the needle touched the conductor was 300 or more, it was rated as very good (symbol ⊚); if the number of reciprocations was 100 or more and less than 300, it was rated as passed (symbol ◯); and if the number of reciprocations was less than 100, it was rated as failed (symbol x). (heat deformation)

[0050] A heat distortion test was conducted according to a high-temperature compression test specified in ISO 19642-12. Specifically, a test specimen of the cut-out foamed electrical wire was applied with a fixed load from above at a set temperature of 100°C (Class B) for four hours, and then a voltage of 1 kV was applied to a conductor of the test specimen using a withstand voltage device to conduct a withstand voltage test. The applied load varies depending on the thickness of the covering layer and the outer diameter of the electrical wire and can be determined based on the following formula (1). If the insulation was maintained for one minute, it was evaluated as passed (symbol o), and if the insulation was maintained for less than one minute, it was evaluated as failed (symbol x). Load(N)=0.8*(thickness of the covering layer*(2*outer diameter of the electrical wire−thickness of the covering layer))0.5 (LCTL)

[0051] The communication stability when used as a communication cable was evaluated based on the longitudinal conversion loss (LCTL). Specifically, two foamed electrical wires were twisted together with a 30 mm pitch and wrapped with a metal foil vertically or horizontally. Then, a tinned soft copper wire braid was covered, and a 0.5 mm thick vinyl chloride (PVC) resin was applied as a sheath to prepare a test sample. For the resulting test sample, the same voltage was applied to the two foamed electrical wires using a network analyzer, and the LCTL was calculated by converting the ratio of the potential differences caused by the imbalance of the foamed electrical wires into decibels.If LCTL was 18 dB / m or less, it was rated as very good (symbol ⊚), if LCTL was 20 dB / m or less, it was rated as pass (symbol ◯), and if LCTL was more than 20 dB / m, it was rated as fail (symbol x). (Characteristic impedance)

[0052] Communication stability when used as a communication cable was evaluated based on the characteristic impedance. Specifically, the characteristic impedance of a test sample of the cut-out foamed electrical wire was measured using a vector network analyzer (VNA) (E5071C, manufactured by Keysight Technologies). If the characteristic impedance was within a range of 95 to 105 Ω, it was evaluated as passed (symbol ◯), and if the characteristic impedance was less than 95 Ω or more than 105 Ω, it was evaluated as failed (symbol x). [Table 3] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Electrical conduction properties Foaming ratio (%) 25 25 25 25 25 25 25 25 25 25 Average foam diameter (µm) Cross-sectional direction 29 29 20 15 13 20 12 30 20 10 Longitudinal direction 40 40 45 50 53 40 55 45 40 60 Arithmetic mean height (µm) 20 19 15 15 15 17 14 20 16 14 Abrasion resistance ◯ ◯ ⊚ ⊚ ⊚ ◯ ⊚ ◯ ◯ ⊚ Heat deformation ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ LCTL ◯ ◯ ⊚ ⊚ ⊚ ◯ ⊚ ◯ ⊚ ◯ Characteristic impedance ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ Foaming ratio (%) 55 55 55 55 55 55 55 55 55 55 Average foam diameter (µm) Cross-sectional direction 30 30 22 16 15 21 15 28 22 10 Longitudinal direction 43 44 44 50 52 42 54 46 45 50 Arithmetic mean height (µm) 19 19 17 15 15 15 13 18 17 15 Abrasion resistance ◯ ◯ ◯ ⊚ ⊚ ◯ ⊚ ◯ ◯ ⊚ Heat deformation ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ LCTL ◯ ◯ ◯ ⊚ ⊚ ◯ ⊚ ◯ ◯ ◯ Characteristic impedance ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ [Table 4] Comparison example 1 Comparison example 2 Comparison example 3 Comparison example 4 Comparison example 5 Comparison example 6 Comparison example 7 Comparison example 8 Comparison example 9 Electrical conduction properties Foaming ratio (%) 25 25 - 25 20 20 25 25 25 average foam diameter (µm) Cross-sectional direction 38 35 No foaming 32 29 10 15 10 20 Longitudinal direction 45 40 40 40 60 55 70 65 Arithmetic mean height (µm) 33 30 - 22 20 14 13 13 17 Abrasion resistance × × - × ◯ ⊚ ⊚ ⊚ ◯ Heat deformation ◯ ◯ ◯ ◯ ◯ ◯ × ◯ × LCTL ◯ ◯ - ◯ ◯ ◯ ◯ × × Characteristic impedance ◯ ◯ ◯ ◯ × × ◯ ◯ ◯ Foaming ratio (%) 55 55 - 55 60 60 55 55 55 average foam diameter (µm) Cross-sectional direction 40 37 No foaming 33 30 10 12 15 21 Longitudinal direction 50 48 42 43 50 56 65 66 Arithmetic mean height (µm) 35 33 - 22 19 15 12 12 17 Abrasion resistance × × - × ◯ ⊚ ⊚ ⊚ ◯ Heat deformation ◯ ◯ ◯ ◯ ◯ ◯ × ◯ × LCTL ◯ ◯ - ◯ ◯ ◯ ◯ × × Characteristic impedance ◯ ◯ ◯ ◯ × × ◯ ◯ ◯

[0053] As shown in Table 1, the melt tension of the resin compositions of Examples 1 to 10 at 200 °C, measured with a capillary rheometer, was 15 mN or more and 45 mN or less, and the melt viscosity was 120 Pa s or more and 200 Pa s or less.

[0054] As shown in Table 3, in both cases where the foaming ratio was 25% and the foaming ratio was 55%, the average foam diameter of the foamed electric wire prepared using the resin compositions of Examples 1 to 10 was 30 μm or less in the cross-sectional direction of the foamed electric wire and 60 μm or less in the longitudinal direction of the foamed electric wire. Furthermore, the arithmetic average height of the foamed electric wire was 20 μm or less, and the results of abrasion resistance, heat deformation, LCTL, and characteristic impedance were favorable.

[0055] As shown in Table 2, the melt tension of the resin compositions of Comparative Examples 1, 2, 4, 8, and 9 at 200°C, measured by a capillary rheometer, was less than 15 mN or more than 45 mN. Furthermore, the melt viscosity of the resin compositions of Comparative Examples 1, 3, 7, and 9 at 200°C, measured by a capillary rheometer, was less than 120 Pa s or more than 200 Pa s.

[0056] As can be seen from Table 4, in both cases where the foaming ratio was 25% and the foaming ratio was 55%, the average foam diameter of the foamed electric wire produced using the resin compositions of Comparative Examples 1, 2, and 4 was more than 30 μm in the cross-sectional direction. In both cases where the foaming ratio was 25% and the foaming ratio was 55%, the average foam diameter of the foamed electric wire produced using the resin compositions of Comparative Examples 8 and 9 was more than 60 μm in the longitudinal direction. Furthermore, in both cases where the foaming ratio was 25% and the foaming ratio was 55%, the arithmetic average height of the foamed electric wire produced using the resin compositions of Comparative Examples 1, 2, and 4 was more than 20 μm.The resin compositions of Comparative Examples 1, 2, 4, and 7 to 9 failed all of the abrasion resistance, heat distortion, and LCTL results. Furthermore, from Table 2, the melt tension of the resin compositions of Comparative Examples 5 and 6 was 15 mN or more and 45 mN or less, and the melt viscosity of the compositions was 120 Pa s or more and 200 Pa s or less. From Table 4, the foaming ratio of the resin compositions of Comparative Examples 5 and 6 was 20% and 60%, respectively, so the characteristic impedance of the compositions was missed. The resin composition of Comparative Example 3 could not be foamed and therefore was unable to produce a foamed electrical wire.

[0057] Although the present embodiment has been described above, the present embodiment is not limited to the above description, and various changes may be made within the scope of the present embodiment.

[0058] The entire contents of Japanese Patent Application No. 2022-161080 (filed on October 5, 2022) are incorporated herein. List of reference symbols 10 Foamed electrical cable 12 ladders 14 Foamed cover layer 16 Outer layer 18 Inner layer QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 5 420 662

[0003] JP 2022-161 080

[0058]

Claims

[1] Foamed electrical cable, comprising: a leader; and a covering layer covering the conductor and formed from one or more layers, wherein at least one layer of the cover layer is a foamed cover layer made of a resin composition containing a polypropylene resin produced by foam extrusion molding, an average foam diameter of the foamed cover layer is 30 µm or less in a cross-sectional direction and 60 µm or less in a longitudinal direction, a foaming ratio of the foamed covering layer is 25% or more and 55% or less and the arithmetic mean height of a surface is 20 µm or less. [2] Foamed electric cable according to claim 1, wherein the foamed cover layer is formed by foam extrusion molding using an inert gas, and the resin composition has a melt tension of 15 mN or more and 45 mN or less as measured by a capillary rheometer at 200°C, and a melt viscosity of 120 Pa s or more and 200 Pa s or less. [3] The foamed electric wire according to claim 2, wherein the inert gas is at least one selected from the group consisting of a nitrogen gas, a carbon dioxide gas and an argon gas. [4] Communication cable, comprising: the foamed electrical cable according to claim 1 or 2. [5] A method for producing a foamed electrical cable, comprising: a step of forming a covering layer covering a conductor and formed of one or more layers; and a step of forming a foamed cover layer from a resin composition containing a polypropylene resin formed by foam extrusion molding as at least one layer of the cover layer, wherein an average foam diameter of the foamed cover layer is 30 µm or less in a cross-sectional direction and 60 µm or less in a longitudinal direction, a foaming ratio of the foamed cover is 25% or more and 55% or less and an arithmetic average height of a surface of the foamed electrical cable is 20 µm or less.

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