Insulated electrical cable

Abstract

Insulated electrical cable (10) comprising: a wire conductor (12); and an insulating sheath (14) covering the outer circumference of the wire conductor (12), wherein the insulation sheath (14) contains a polymer component comprising a polypropylene resin and a flame retardant made of a metal hydroxide, the polypropylene resin has a melting enthalpy of at least 35J / g, in a molecular weight distribution of the polymer component, the number-average molecular weight, calculated at the peak with the largest area, is at least 5.00 × 10 4 is, and the polypropylene resin contains homo-polypropylene and block-polypropylene, wherein the block polypropylene contains three phases, a polypropylene phase, a polyethylene phase and an ethylene-propylene copolymer phase.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to insulated electrical cables. TECHNICAL BACKGROUND

[0002] For insulated electrical cables used in vehicles such as cars or various appliances, halogen-free electrical cables with an insulation sheath made of a plastic composition containing no halogens are used, for example, with the aim of achieving environmental sustainability. A representative example of an insulation sheath of a halogen-free electrical cable is an insulation sheath using a polypropylene resin as the base resin and a metal hydroxide such as magnesium hydroxide as the flame retardant. An insulated electrical cable with an insulation sheath containing a base resin made of polypropylene resin and a metal hydroxide is described, for example, in JP 2002-212354 A and JP 2010-174113 A.Although the addition of metal hydroxide particles to the base resin can affect the properties of the base resin, in JP 2002 - 212 354 A and JP 2010 - 174 113 A, properties such as wear resistance and resistance to low temperatures are improved by, for example, modifying the metal hydroxide through a surface treatment or adjusting the composition of the base resin.

[0003] JP 2002-348417 A discloses an olefin polymer having an elastic recovery factor of 70-100%, as defined by the following formula (1). Preferably, the olefin polymer is a random copolymer, a thermoplastic composition comprising 99 to 1% by weight of the olefin polymer and 1 to 99% by weight of the thermoplastic resin. Elastic recovery rate = residual stress recovery × 100 / elongational deformation (1). In the formula, the residual stress recovery rate and the elongational deformation rate are the residual stress recovery rate and the elongational deformation rate obtained from a 100% strain hysteresis curve of the resin composition to be evaluated, which comprises 70% by weight of the olefin polymer and 30% by weight of the specific polypropylene resin. The extent of elongational deformation, wherein at least one of the resin compositions to be evaluated must meet the above requirements.

[0004] US 2017 / 0 011 816 A1 discloses a resin composition for a cable material and a cable used for a vehicle, as well as a method for producing such a cable. Specifically, by controlling components such as the polypropylene content, the flame retardant content, and the like in a base resin, and by containing a highly crystalline homopolypropylene (PP) resin and a highly crystalline block polypropylene resin in the base resin in a specific ratio, the resin composition offers excellent physical properties such as abrasion resistance and flexibility resistance, and has a reduced weight effect when a cable is produced using the resin composition. OVERVIEW OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0005] Insulated electrical cables with an insulation sheath made of a material that uses polypropylene resin as the base resin and to which a metal hydroxide is added as a flame retardant tend to have reduced low-temperature resistance. One possible method to increase low-temperature resistance is to use polypropylene with a large amount of amorphous components (i.e., low crystallinity) and a large average molecular weight. However, in this case, due to the low crystallinity, the wear resistance of the insulation sheath tends to be reduced.

[0006] To prevent a reduction in wear resistance caused by using a polypropylene resin with a high proportion of amorphous components and a high average molecular weight, a method is conceivable in which a highly crystalline polypropylene resin is blended into the plastic composition. This improves the wear resistance of the insulation sheath by increasing the number of crystals, but it is difficult to achieve satisfactory resistance to low temperatures.

[0007] As described above, it is difficult to sufficiently improve the wear resistance and low-temperature resistance of an electrically insulated cable with an insulation jacket using polypropylene resin as the base resin with a metal oxide added. Therefore, careful consideration of the physical properties of the polypropylene resin used as the base resin is necessary to improve wear resistance and low-temperature resistance. Therefore, the present objective is to provide an insulated electrical cable containing a base resin containing polypropylene resin and a metal hydroxide as a flame retardant, which exhibits high wear resistance and low-temperature resistance. MEANS FOR SOLVING THE TASK

[0008] An insulated electrical cable of the present disclosure has the features of claim 1. EFFECT OF THE INVENTION

[0009] An insulated electrical cable according to the present disclosure contains a base resin containing a polypropylene resin and a metal hydroxide used as a flame retardant, and has high wear resistance and high low temperature resistance. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view illustrating an insulated electrical wire according to a first embodiment of the present disclosure. Fig. 2 is a DCS curve measured on a sample A1 EMBODIMENTS OF THE INVENTION Description of embodiments of the present disclosure

[0010] First, embodiments of the present disclosure are cited and described.

[0011] An insulated electric cable according to the present disclosure comprises: a wire conductor; and an insulation sheath covering the outer periphery of the wire conductor, wherein the insulation sheath contains a polymer component including a polypropylene resin and a flame retardant made of a metal hydroxide, the polypropylene resin has an enthalpy of fusion of at least 35 J / g, and in a molecular weight distribution of the polymer component, the number-average molecular weight calculated at the peak having the largest area is at least 5.00 × 10 4 is.

[0012] In the insulation sheath used in the insulated electrical cable, the polypropylene resin has a melting enthalpy of at least 35 J / kg, and a sufficient amount of crystalline polypropylene can be ensured. A large amount of crystalline polypropylene contributes to improving the wear resistance of the insulation sheath. Since the number-average molecular weight calculated at the peak with the largest area in the molecular weight distribution of the polymer component is at least 35 J / kg, the insulation sheath exhibits preferable low-temperature resistance. By appropriately adjusting the melting enthalpy and molecular weight distribution of the polymer component containing the polypropylene resin, it is possible to improve both the wear resistance and the low-temperature resistance of the insulation sheath.

[0013] Here, a polydispersity Mw / Mn is determined at the peak with the largest area in the molecular weight distribution of the polymer component. This polydispersity is defined as the ratio of the mass-average molecular weight Mw to the number-average molecular weight Mn, and is at least 5.90. Accordingly, a broad molecular weight distribution improves the processability of the insulation jacket and improves the external appearance of the insulation jacket formed by extrusion or similar processes. Improving the external appearance means that the insulation jacket has fewer unevennesses, which simultaneously leads to improved wear resistance and low-temperature resistance.

[0014] Preferably, the polypropylene contains homopolypropylene and block polypropylene. By blending homopolypropylene and block polypropylene, a desired melting enthalpy and molecular weight distribution can be achieved by adjusting the blending ratio. Homopolypropylene is also very effective in improving the crystallinity of the polymer component. On the other hand, block polypropylene is very effective in improving the processability of the insulation jacket. By blending homopolypropylene and block polypropylene, it is possible to effectively implement improvements in wear resistance and low-temperature resistance.

[0015] Preferably, the polymer component also contains a thermoplastic elastomer. This improves the distribution of the metal hydroxide particles throughout the polymer component, resulting in significantly improved wear resistance and resistance to low temperatures.

[0016] The metal hydroxide is preferably magnesium hydroxide. Magnesium hydroxide is available at a low price and provides the insulation jacket with high flame retardancy.

[0017] Preferably, the mean roughness Ra of the surface of the insulation coating is less than or equal to 3.00 µm. This gives the insulation coating an attractive external appearance and, consequently, makes high wear resistance and low-temperature resistance easy to achieve. Details of embodiments of the present disclosure

[0018] Insulated electrical cables according to embodiments of the present disclosure will now be described in detail with reference to the attached drawings. Unless otherwise stated, in the embodiment presented, the various physical properties of the materials are all measured at room temperature and atmospheric pressure. Designs of insulated electrical cables

[0019] Fig. 1 shows an overview of an insulated electrical cable 10 according to an embodiment of the present disclosure. As in Fig.As shown in Figure 1, the insulated electrical cable 10 consists of a wire conductor 12 and an insulating coating 14 that surrounds the outer periphery of the wire conductor 12 and is made of a plastic composition. The insulated electrical cable 10 can be obtained, for example, by extruding a plastic composition acting as an insulating coating 14 onto the outer periphery of the wire conductor 12.

[0020] The material from which the wire conductor 12 is made is not particularly limited; copper is usually used. However, a metal material such as aluminum or iron can also be used instead of copper. Alloys can also function as such a metal material. For example, alloys can be made of metal materials such as iron, nickel, magnesium, silicon, and any combination thereof. The wire conductor 12 can consist of a single wire or a twisted wire obtained by twisting several individual wires 12a together. To ensure the flexibility of the insulated electrical cable 10, the wire conductor 12 is preferably a twisted wire conductor.

[0021] The insulation jacket 14 is made of a resin mixture containing a base resin comprising a polymer component with polypropylene resin and a flame retardant with metal hydroxide. Although the resin mixture constituting the insulation jacket 14 will be described in detail below, the polypropylene resin contained in the resin mixture constituting the insulation jacket 14 has a predetermined minimum enthalpy of fusion, and the polymer component containing the polypropylene resin has a predetermined molecular weight distribution.

[0022] In the embodiment of the insulated electrical cable 10 described here, there is no limitation on the size of the components, such as the cross-section of the wire conductor 12 and the thickness of the insulation sheath 14. Furthermore, the use of the insulated electrical cable 10 according to the present embodiment is not further specified. The insulated electrical cable can be used for various types of electrical cables in automobiles, electrical / electronic equipment, information and telecommunications, power supplies, boats and ships, and aircraft. As described later, the insulation sheath 14 has excellent flame resistance, as well as high wear resistance and low-temperature durability. Therefore, the insulated electrical cable 10 is particularly suitable for use as an electrical cable for automobiles.

[0023] The insulated electrical wire 10 according to the present embodiment can be used as a standalone wire or in a wiring harness consisting of multiple insulated electrical wires. When the insulated electrical wire is used in a wiring harness, all or only a portion of the wires in the wiring harness may be insulated electrical wires 10 according to the present embodiment. Insulation sheath made of plastic composition

[0024] The resin mixture used to manufacture the insulation sheath 14 of the insulated electric wire 10 according to the present embodiment will be described in detail below.

[0025] The plastic composition from which the insulation sheath 14 is made contains a base resin and a flame retardant containing a metal hydroxide. The polymer component forming the base resin contains a polypropylene resin (PP resin), wherein the PP resin has a melting enthalpy of at least 35 J / g and the polymer component has a molecular weight distribution of at least 5.00 × 10 4 has. Physical properties of the resin mixture

[0026] The enthalpy of fusion of a plastic material serves as a proxy for the crystallinity of the plastic material. The higher the enthalpy of fusion, the greater the crystallinity, i.e., the greater the proportion of crystalline solid. In the present embodiment, the PP resin contained in the plastic composition from which the insulation jacket 14 is made has a fusion enthalpy of at least 35 J / g. By ensuring that the PP resin has a fusion enthalpy of at least 35 J / g, it can be ensured that the insulation jacket 14 contains sufficient crystalline polypropylene. If the plastic composition from which the insulation jacket 14 is made contains a sufficient amount of crystalline polypropylene, the wear resistance of the insulation jacket increases.To further improve wear resistance, the enthalpy of fusion should be at least 37 J / g, and preferably at least 39 J / g. There is no specific upper limit for the enthalpy of fusion, but the enthalpy of fusion should not exceed approximately 80 J / g. This is because such a high enthalpy of fusion and the associated excessive increase in crystalline solids inhibit the absorption of additives such as flame retardants.

[0027] The melting temperature of the PP resin can be measured using a differential scanning calorimeter (DSC) in accordance with JIS K 7122. This involves measuring the heat of phase transition when the PP resin is heated. When the polymer component, such as the PP resin, contains a homopolypropylene and a block copolypropylene, it is important to note that the melting points of these two types of polypropylene, as shown in the examples, typically do not occur separately. Instead, only one melting point occurs, which results from the crystal structure of the two types of polypropylene (see Fig. 2). The melting temperature can be measured for the PP resin alone, or for the entire polymer component, which also contains other resins. Alternatively, the melting temperature can be measured for the entire resin mixture, which also contains other components besides the polymer component, such as a flame retardant.

[0028] The polymer component forming the insulating coating 14 according to the present embodiment has a number-average molecular weight of at least 5.00 x 10 4 If several peaks occur in the molecular weight distribution, a number-average molecular weight is calculated using the peak with the largest area. This value is defined as the number-average molecular weight of a polymer component. Accordingly, the number-average molecular weight, determined at the peak with the largest area in the molecular weight distribution, is at least 5.00 x 10 4 .

[0029] If the number average molecular weight of the polymer component constituting the insulation sheath 14 is at least 5.00 x 10 4, low-temperature resistance is advantageous. This means that embrittlement of the insulation sheath 14 is suppressed in a low-temperature environment and the extensibility of the insulation sheath 14 is ensured. To further improve these properties, the number-average molecular weight should be at least 5.50 × 10 4 , even better 5.70 × 10 4 In particular, there is no upper limit for the number average molecular weight, but the number average molecular weight should ideally not exceed approximately 1.00 × 10 5 to suppress, for example, a deterioration in the flowability of the resin mixture.

[0030] As described above, the molecular weight distribution of the polymer component constituting the insulating sheath 14 has a predetermined number-average molecular weight. Furthermore, the molecular weight distribution of the polymer component constituting the insulating sheath 14 preferably has a polydispersity of at least 5.90, which is defined as the ratio Mw / Mn of the mass-average molecular weight Mw to the number-average molecular weight Mn. If multiple maxima occur in the molecular weight distribution, the polydispersity Mw / Mn at the maximum with the largest area is defined as the polydispersity Mw / Mn, comparable to the definition of the molecular weight distribution described above. Accordingly, the polydispersity Mw / Mn at the maximum of the molecular weight distribution with the largest area is preferably at least 5.90.

[0031] The polydispersity Mw / Mn describes the breadth of the molecular weight distribution of a polymer component. The higher the polydispersity Mw / Mn, the broader the molecular weight distribution. If the polydispersity Mw / Mn is at least 5.90, the breadth of the molecular weight distribution is broad, and thus the flowability of the plastic composition forming the insulation jacket 14 is high. This increases the processability of the plastic composition, and if the insulation jacket 14 is produced by extrusion or similar, an insulation jacket 14 with an attractive external appearance can be achieved. An attractive external appearance of the insulation jacket 14 also means that the surface contains hardly any unevenness, which is a good indicator of high abrasion resistance and cold resistance, since these properties are adversely affected by an uneven structure.With a view to further improving these effects, the polydispersity Mw / Mn is preferably at least 6.00, even more preferably at least 6.20. In particular, there is no upper limit for the polydispersity Mw / Mn, but the polydispersity should not be greater than 8.00 in order to avoid properties of the insulation jacket 14 that occur when the molecular weight distribution is too broad.

[0032] The molecular weight distribution of the polymer component can be determined, for example, by size-exclusion chromatography (GPC). It should be noted that if the polymer component contains multiple types of plastic, it is sufficient if the above-mentioned molecular weight distribution parameters, i.e., the number-average molecular weight and the polydispersity Mw / Mn, of the polymer component as a whole fall within the above-mentioned predetermined ranges. However, the above-mentioned numerical values ​​for the PP resin in the polymer component should preferably also fall within the above-mentioned numerical range.

[0033] The unevenness of the surface of the insulation sheath 14 can be quantitatively evaluated as roughness. For example, a roughness Ra (average roughness) is preferably no greater than 4.00 µm. Thus, the high evenness of the surface of the insulation sheath 14 is a good indicator of an attractive external appearance of the insulated electrical cable 10, high wear resistance, and high resistance to low temperatures. The average roughness Ra is particularly preferably no greater than 3.00 µm or no greater than 2.50 µm. In many cases, the average roughness Ra of the surface of the insulation sheath 14 is not substantially affected by the addition of a solid such as a flame retardant; rather, it is a result of the composition of the polymer component. Using a roughness meter, the average roughness Ra of a surface can be determined in accordance with JIS B0601.

[0034] According to the present embodiment of the insulated electric wire 10 as described above, the insulation coating 14 has excellent wear resistance and low temperature resistance when the PP resin contained as the polymer component has a melting enthalpy of at least 35 J / g and the polymer component has a number-average molecular weight of at least 5.00 × 10 4 If the polydispersity Mw / Mn of the polymer component is at least 5.90 and the mean roughness is not greater than 4.00 µm, the cable also has an attractive external appearance and its wear resistance and resistance to low temperatures are positively influenced. Material components of the plastic composition

[0035] The specific components of the plastic composition constituting the insulation sheath 14 are not further limited, as long as the plastic composition contains a polymer component of PP resin and a flame retardant of metal hydroxide and has the properties described above. The following describes preferable components. (1) Polymer component

[0036] The percentage of PP resin is not specifically restricted. However, PP resin preferably contributes at least 50% of the mass of the total plastic composition, and even better, 80% of the mass.

[0037] "PP resin" refers to a polymer containing a propylene unit and can be one of three types: homopolypropylene (homo-PP), block polypropylene (block-PP), or random polypropylene (random-PP). Details of the resin type constituting the PP resin, i.e., which of the above-mentioned types is contained in the PP resin, and the specific resin used therein, are not particularly limited. It is possible to use only one type or multiple types as long as the resin has the above-described enthalpy of fusion and contributes to the number-average molecular weight of the polymer component.

[0038] The PP resin preferably contains homo-PP and block-PP, given that it is comparatively easy to achieve the desired enthalpy of fusion and molecular weight distribution. Homo-PP is highly crystalline and thus contributes significantly to the wear resistance of the insulation sheath 14. On the other hand, block-PP is effective in improving the long-term heat resistance of an electrical cable and contributes to low-temperature resistance due to its good absorption of additives such as flame retardants. In addition, block-PP contributes to improving the processability of the plastic composition.By blending homo-PP and block-PP, the melting enthalpy and molecular weight distribution described above can be easily realized, and as a result, it is easy to obtain an insulation jacket 14 having excellent heat resistance and low temperature resistance.

[0039] The blend ratio of homo-PP and block-PP can be selected as needed to ensure that physical properties, such as enthalpy of fusion and molecular weight distribution, correspond to the predetermined values. However, the mass ratio of homo-PP to block-PP should be between 1:4 and 4:1 to achieve a balanced application of the properties of both polypropylene types. The blend ratio is preferably between 1:3 and 3:1 or between 1:2 and 2:1.

[0040] When block PP is used, the exact molecular structure of the block PP is not restricted. However, it is better to use block PP that contains an ethylene unit in addition to the propylene unit, although this unit accounts for less than 10% of the total ethylene content. Block PP advantageously contains three phases: a polypropylene (PP) phase, a polyethylene (PE) phase, and an ethylene-propylene copolymer (EPR) phase. The melting point of block PP should also be at least 160°C. This melting point corresponds to the melting point of homo-PP. When block PP and homo-PP are used in a mixture, a corresponding peak in the phase transition heat is observed when the mixture is heated using a DSC or similar device.To further enhance the effect of improving low-temperature resistance by blending block PP and homo-PP, the block PP preferably also has a larger number-average molecular weight and polydispersity Mw / Mn than the homo-PP. Furthermore, the addition of the block PP should ideally increase the number-average molecular weight and polydispersity Mw / Mn of the polymer component when added to it.

[0041] Even if a PP resin contains multiple components such as homo-PP and block PP, each of the components can exhibit any physical property, as long as the PP resin formed by combining the individual components as a whole possesses predetermined physical properties. However, to simply improve the flow properties and the like of the plastic composition, the melt flow index (MFR) of homo-PP should be approximately 0.3 to 2.0 g / 10 min, and the melt flow index (MFR) of block PP should be approximately 0.3 to 2.0 g / 10 min.

[0042] The PP resin forming the insulation sheath 14 may or may not be subjected to modification, such as acid modification. Examples of PP resins that are not subjected to acid modification include polypropylene, ethylene-propylene copolymer, 1-butene-propylene copolymer, propylene-1-butene-ethylene copolymer, propylene-1-hexene copolymer, propylene-1-hexene-ethylene copolymer, and propylene-4 (or 5)-methyl-1,4-hexadiene copolymer. The acid-modified PP resin may be a PP resin obtained by subjecting one of the above-mentioned PP resins to acid modification and using a PP resin such as a self-adhesive polyolefin, polyolefin-based self-adhesive polymer, self-adhesive plastic, polyolefin-based self-adhesive plastic, or the like.However, it is preferable to use a PP resin that has not undergone any modification, as this prevents the wire conductor 12 and the insulation sheath 14 from sticking to each other and improves processability when the insulation sheath 14 is removed at the end portion, etc. In addition, the PP resin from which the insulation sheath 14 is made should preferably not be crosslinked.

[0043] The polymer component constituting the insulation sheath 14 may contain only PP resin or may contain other polymers in addition to PP resin. Preferably, the polymer component contains not only PP resin but also a thermoplastic elastomer. The thermoplastic elastomer serves to improve dispersity and compatibility with the flame retardant contained in the polymer component. Examples of usable thermoplastic elastomers are SEBS and TPO (polyolefin-based elastomer). The thermoplastic elastomer may be acid-modified or non-acid-modified. To obtain sufficient effects through addition, the added mass fraction of the thermoplastic elastomer should preferably be at least 5% of the total polymer component, with a mass fraction of 10% being even better.On the other hand, the added amount of a thermoplastic elastomer should not exceed 20% by mass to avoid adversely affecting the properties of the PP resin. Additionally, it is noted that the polymer component preferably does not contain a halogen-containing polymer to realize a halogen-free insulated electrical cable 10. (2) Flame retardants

[0044] In the present embodiment, the flame retardant in the insulation sheath 14 contains metal hydroxide. The flame retardant should preferably contain at least 50% metal hydroxide by mass, particularly preferably at least 80% by mass. Furthermore, the flame retardant preferably contains only metal hydroxide, apart from small amounts of other ingredients such as surfactants.

[0045] Examples of metal hydroxides included in flame retardants are magnesium hydroxide and aluminum hydroxide. Of these types of metal hydroxides, magnesium hydroxide is preferable because it is inexpensive and can offer high flame retardancy. The flame retardant is included in the plastic composition in the form of particles.

[0046] The average particle size of the metal hydroxide contained in the flame retardant is preferably at least 0.1 µm or at least 0.5 µm to avoid secondary aggregation of the particles when the metal hydroxide is mixed with the plastic composition and to enable its use at a low cost. On the other hand, the average particle size of the metal hydroxide should be no larger than 10 µm or no larger than 5 µm to avoid adversely affecting the properties of the plastic composition, especially the PP resin. The metal hydroxide can be subjected to a surface treatment using a silane coupling agent, polyhydric fatty acid, or polyolefin wax to improve dispersibility, etc.In the present embodiment, the insulation sheath 14 has excellent properties such as wear resistance and low temperature resistance by virtue of the polymer component having a predetermined enthalpy of fusion and a predetermined molecular weight distribution even if the metal hydroxide is not subjected to surface treatment.

[0047] The flame retardant components contained in the plastic composition from which the insulation jacket 14 is formed preferably comprise at least 30 parts by mass, or at least 50 parts by mass to 100 parts by mass of the polymer component to provide sufficient flame protection. On the other hand, the flame retardant should preferably comprise no more than 200 parts by mass, and even better, less than 100 parts by mass to 100 parts by mass of the polymer component, to avoid reducing the properties of the insulation jacket 14 due to an excessive amount of flame retardant. (3) Other ingredients

[0048] In the present embodiment of the insulated electrical cable 10, the plastic composition forming the insulation sheath 14 may contain, in addition to the above-described polymer component and flame retardant, other appropriate components such as various types of additives. Examples of additives besides flame retardants include antioxidants such as sulfur compounds and hindered phenol compounds, preservatives such as zinc oxide and imidazole compounds, metal deactivators, lubricants, stabilizers, ultraviolet absorbers, pigments, and dyes.

[0049] The composition of the additives is not particularly limited as long as the properties of the polymer component and the flame retardant are not adversely affected. For example, the total proportion of additives other than the metal hydroxide should preferably be no more than 20 parts by mass, more preferably no more than 10 parts by mass, relative to 100 parts by mass of the polymer component. Preferably, the plastic composition forming the insulation sheath 14 does not contain any additives containing halogens in order to realize a halogen-free insulated electrical cable 10. Practical examples

[0050] Practical examples are described below. Note that the present disclosure is not limited to these practical examples. The composition of the polymer component constituting the insulation coating was changed here to change the physical properties of the polymer component, and the relationship between the physical properties and the properties of the insulation coating was tested. Samples were prepared below, and various tests were conducted at room temperature and normal pressure, unless otherwise specified. [Test method](1) Preparation of samples

[0051] The components listed in Table 1 were mixed in a predetermined ratio and kneaded at 260°C. Plastic compositions were prepared according to samples A1 to A5 and B1 to B5. The table shows the composition of the individual components as a percentage of 100 mass parts of the total polymer components. Furthermore, the plastic compositions were pelletized and then extruded to a thickness of 0.20 mm around the circumference of a twisted wire conductor with a nominal cross-sectional area of ​​0.35 mm. 2 was applied, an insulated electrical cable was produced.

[0052] The materials used in the plastic composition forming the insulation sheath were as follows: Block PP - EC9: “NOVATEC EC9” manufactured by Japan Polypropylene Corporation, MFR = 0.5 g / 10 min; shear viscosity 890 Pa s (temperature 230°C, shear rate 100 / s) - EC9GD: “NOVATEC EC9GD” manufactured by Japan Polypropylene Corporation, MFR = 0.5 g / 10 min; shear viscosity 1040 Pa s (temperature 230°C, shear rate 100 / s) Homo-PP - FY6H: “NOVATEC FY6H” manufactured by Japan Polypropylene Corporation, MFR = 1.9 g / 10 min - EA9FTD: “NOVATEC EA9FTD” manufactured by Japan Polypropylene Corporation, MFR = 0.4 g / 10 min Thermoplastic elastomer - H1041: Hydrogenated SEBS (unmodified), “Tuftec H1041” manufactured by Asahi Kasei Corporation, MFR = 5.0 g / 10 min - M1913: Maleic acid-modified SEBS, “Tuftec M1913” manufactured by Asahi Kasei Corporation, MFR = 5.0 g / 10 min Other components - Magnesium hydroxide: “Magnifin H10” manufactured by Huber Engineered Materials - sulfur-based antioxidants: “NOCRAC MB” manufactured by Ouchi Shinko Chemical Industrial Co., Ltd. - sterically hindered phenol-based antioxidants: “Irganox 1010” manufactured by BASF - Preservative: Zinc oxide, “Second Type” manufactured by Hakusui Tech Co., Ltd. - Metal deactivator: “Irganox MD 1024” manufactured by BASF (2) Evaluation methodMeasurement of phase transition heat by heating

[0053] The phase transition heat upon heating was measured using a differential scanning calorimeter (DSC) for each plastic composition of the individual insulation jacket samples. The melting point was determined from the obtained results, and the enthalpy of fusion was determined based on JIS K 7122. Evaluation of the molecular weight distribution

[0054] For each plastic composition of the insulation jacket of each sample, the molecular weight distribution was measured by size-rejection chromatography (GPC). Then, the number-average molecular weight Mn and the polydispersity Mw / Mn were determined at the peak with the largest area. Measurement of roughness

[0055] The mean roughness Ra of the surface of the insulated electrical cable from each sample was measured using a roughness meter in accordance with JIS B0601. The measurement was performed at three points, and the average value was recorded. Measuring the manufacturability of the cable

[0056] If pellet production and extrusion were possible during the insulated electrical cable manufacturing process with a sample, an "A" rating was assigned to demonstrate the cable's manufacturability. On the other hand, if either pellet production or extrusion was not possible, a "B" rating was assigned to demonstrate the cable's poor manufacturability. Wear resistance test

[0057] The wear resistance of the insulation sheath of the insulated electrical cable of each sample was evaluated in accordance with ISO6722 using a scraper wear test (reciprocating knife test). In this test, the force applied to the knife was set to 7.00 ± 0.05 N. The number of reciprocating movements performed by the knife until the conductor was visible was then measured. This test was performed on three insulated electrical cables of each sample, and the average number of reciprocating movements was recorded. If the number of reciprocating movements was at least 450, an "A" rating was given to indicate high wear resistance. If the number of reciprocating movements was less than 450, a "B" rating was given to indicate less high wear resistance. Evaluation of resistance to low temperatures

[0058] To evaluate low-temperature resistance, the wire core was removed from the insulated electrical conductor of each sample, leaving only the insulation sheath. At low temperatures, the elongation of the insulation sheath was measured. The elongation was performed using a tensile strength test at an ambient temperature of 0°C and a test speed of 50 mm / min, in accordance with JIS K 7161. If the elongation was more than 200%, an "A" was awarded to indicate good low-temperature resistance. If the elongation was less than 200%, a "B" was awarded to indicate less good low-temperature resistance. [Test results]

[0059] Fig.Figure 2 shows a representative DSC curve obtained by measuring the phase transition heat upon heating of sample A1. The horizontal axis represents the temperature. The vertical axis represents the DSC value (heat flow), with negative values ​​representing an endothermic process.

[0060] After Fig.2, an endothermic peak was observed at 165°C. This peak is a result of the melting of the crystalline polypropylene, since the melting temperature of homo-PP is approximately 165°C. This peak has a broader shoulder toward the lower temperature, but is still a single peak. Therefore, the PP resin included in the plastic composition contains both homo-PP and block-PP, but the homo-PP and block-PP do not have independent peaks. It appears that the polypropylene structures contained in the two types of PP form crystals that melt at similar temperatures. For samples A2 to A5 and B1 and B2, a melting point between approximately 160°C and 165°C was observed, respectively.

[0061] Table 1 also lists the component composition (unit: mass fraction) of the plastic composition used to form the insulation sheath for each sample. The evaluation results are also summarized, including the results of the heat melt measurement described above. For wear resistance and low-temperature resistance, the measured values ​​and an additional classification of the measured values ​​are also given in square brackets [ ]. It should be noted that no pellets could be produced from sample B3, and therefore no insulated electrical cable could be produced as a sample, and therefore no evaluation could be performed. Table 1 Sample number A1 A2 A3 A4 A5 B1 B2 B3 Components Composition Block PP EC9 - - - - - 90 - - EC9GD 48,75 69,4 48,75 28,1 48,75 - 90 - Homo-PP FY6H 41,25 20,6 41,25 61,9 - - - 90 EA9FTD - - - - 41,25 - - - Thermoplastic elastomer H1041 10 - - - - - - - M1913 - 10 10 10 10 10 10 10 Magnesium hydroxide 70 70 70 70 70 70 70 70 Sulfur system antioxidant 3 3 3 3 3 3 3 3 Metal oxides 3 3 3 3 3 3 3 3 sterically hindered phenol system antioxidants 3 3 3 3 3 3 3 3 Metal deactivator 0,5 0,5 0,5 0,5 0,5 0,5 0,5 0,5 Evaluation Measurement of phase transition heat by heating Melting point (°C) 165 163 165 165 162 163 161 - Enthalpy of fusion (J / g) 39 37 39 41 37 36 33 - Molar mass distribution Number average molecular mass Mn 5,76×10 4 5,98×10 4 5,78×10 4 5,53×10 4 7,06×10 4 4,51×10 4 6,30×10 4 - PolydispersityMw / Mn 6,02 6,27 6,05 5,92 5,81 8,39 6,45 - Average roughness Ra (µm) 2,31 2,98 2,36 2,34 3,93 2,10 5,61 - Cable manufacturability A A A A A A A B (pellet stove not possible) Wear resistance (average back and forth with the knife / number) 530[A] 455[A] 501[A] 585[A] 455[A] 1232[A] 160[B] - Resistance to low temperatures (elongation at 0°C / %) 390[A] 450[A] 410[A] 385[A] 300[A] 170[B] 540[A] -

[0062] According to Table 1, the PP resins of samples A1 to A5 have a melting enthalpy of at least 35 J / kg and the polymer component has a number-average molecular weight of at least 5.00 × 10 4 . Consequently, the insulation coating has high wear resistance and favorable resistance to low temperatures.

[0063] Comparing the results of samples A1 to A5, the higher the melting enthalpy of the PP resin, the greater the wear resistance (the greater the number of reciprocal movements). Generally, the higher the number-average molecular weight Mn of the polymer component, the greater the low-temperature resistance (the greater the elongation at low temperatures). Based on these results, there is a clear correlation between the melting enthalpy of the PP resin and wear resistance. Likewise, there is a clear correlation between the number-average molecular weight Mn of the polymer component and low-temperature resistance. It is assumed that the PP resin has a high melting enthalpy because an increase in crystallinity contributes to an improvement in wear resistance.

[0064] Furthermore, there is a general tendency that the greater the polydispersity Mw / Mn, the smaller the surface roughness Ra. Specifically, sample A5 has a polydispersity Mw / Mn of less than 5.90, a mean roughness Ra of less than 4.00 µm, but far exceeds 3.00 µm. In contrast, samples A1 to A4 have a polydispersity Mw / Mn of at least 5.90, but a mean roughness Ra of less than 3.00 µm. It is assumed that the extrusion processability of the plastic composition is improved by the wide molecular weight distribution described by the polydispersity Mw / Mn, and therefore the mean roughness of the resulting insulation coatings is reduced. Also, in sample A5, where the roughness is large, the resistance to low temperatures is much lower than in the other samples A1 to A4 and the wear resistance is also reduced.Sample A5 has an identical composition to sample A3, except for the homo-PP used. The main reason why the manufactured insulation jackets appear different, exhibit different wear resistance, and exhibit different resistance to low temperatures may be that the selection of a specific homo-PP results in different molecular weight distributions, described by the polydispersity Mw / Mn.

[0065] Samples A2 to A4 have the same components, but with different ratios of block PP to homo PP. As the proportion of homo PP increases from sample A2 to sample A4, so does the wear resistance. Conversely, as the proportion of block PP increases from sample A4 to sample A2, so does the low-temperature resistance. These results demonstrate that homo PP, due to its high crystallinity, contributes significantly to the improvement in wear resistance. Conversely, block PP contributes significantly to the improvement in the low-temperature resistance of the insulated electrical cable.

[0066] Samples A1 and A3 differ in the type of thermoplastic elastomer added, specifically in whether they are acid-modified or not. Nevertheless, the wear resistance and low-temperature resistance results do not differ significantly. Therefore, it can be stated that the type of thermoplastic elastomer does not significantly influence the properties of the insulation jacket.

[0067] Finally, samples B1 and B2 are evaluated. In sample B1, the number-average molecular weight Mn of the polymer component is less than 5.00 × 10 4Accordingly, in the low temperature resistance evaluation, the elongation of at least 200% was not achieved, meaning the low temperature resistance is insufficient. On the other hand, the fusion enthalpy of the PP resin in sample B2 is less than 35 J / kg. Accordingly, in the wear resistance evaluation, less than 450 reciprocal movements were achieved, meaning the wear resistance is insufficient. Both samples B1 and B2 contain only block PP as the PP resin, although they are different types of block PP, but in both samples B1 and B2, sufficient wear resistance and low temperature resistance could not be achieved. Sample B3 contains only homo-PP as the PP resin and has significantly low flow properties, which is why it was not possible to produce an insulation jacket from it by extrusion.It may be impossible to produce an insulation jacket with high wear resistance and high low temperature resistance using only a single PP resin unless the PP resin has a sufficiently large fusion enthalpy and a sufficient molecular weight distribution Mn.

[0068] The embodiments of the present disclosure have been described in detail, but the present invention is not limited to the above-described embodiments. Various modifications are possible without departing from the spirit of the invention. LIST OF REFERENCE SYMBOLS 10 Insulated electrical cable 12 wire conductors 12a bare wire 14 Insulation sheath

Claims

[1] Insulated electrical cable (10) comprising: a wire conductor (12); and an insulating sheath (14) covering the outer circumference of the wire conductor (12), wherein the insulation sheath (14) contains a polymer component comprising a polypropylene resin and a flame retardant made of a metal hydroxide, the polypropylene resin has a melting enthalpy of at least 35J / g, in a molecular weight distribution of the polymer component, the number-average molecular weight, calculated at the peak with the largest area, is at least 5.00 × 10 4 is, and the polypropylene resin contains homo-polypropylene and block-polypropylene, wherein the block polypropylene contains three phases, a polypropylene phase, a polyethylene phase and an ethylene-propylene copolymer phase. [2] The insulated electrical cable (10) according to claim 1, wherein in the molecular weight distribution of the polymer component, a polydispersity Mw / Mn defined as a ratio of mass-average molecular weight Mw to number-average molecular weight Mn at the peak having the largest area is at least 5.

90. [3] An insulated electrical cable (10) according to claim 1 or 2, wherein the polypropylene resin contributes at least 50% by mass of the total plastic composition. [4] An insulated electrical cable (10) according to any one of claims 1 to 3, wherein neither the homo-polypropylene nor the block-polypropylene is acid-modified. [5] An insulated electrical cable (10) according to any one of claims 1 to 4, wherein the polymer component further contains thermoplastic elastomer. [6] An insulated electrical cable (10) according to any one of claims 1 to 5, wherein the metal hydroxide is magnesium hydroxide. [7] An insulated electrical cable (10) according to any one of claims 1 to 6, wherein the centerline roughness Ra of the surface of the insulation sheath (14) is less than or equal to 3.00 µm.

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