Insulated wire

Abstract

Insulated wire (10), comprising: a wire conductor (12) consisting of a single-core wire or of a strand formed by twisting together a plurality of strands (12a); and an insulating coating (14) made from a resin composition for covering an outer circumference of the wire conductor (12), wherein a cross-sectional area ratio S, which is defined as a ratio S2 / S1 of a cross-sectional area S2 of the insulating coating (14) to a conductor cross-sectional area S1, and an oxygen index Ol of the resin composition forming the insulating coating (14) satisfy a relationship of S ≤ Ol-17,2, the cross-sectional area ratio S is 1.5 or less, the conductor cross-sectional area S1 0.10 mm 2 or less, and the resin composition forming the insulating coating (14) contains a flame retardant produced from a phosphate ester compound and the flame retardant content is 5 parts by mass or less per 100 parts by mass of a resin component.

Description

[Technical field]

[0001] The present invention relates to an insulated wire. [Technical background]

[0002] Insulated wires used in vehicles such as automobiles and various devices must have high flame retardancy. For example, when a halogen-free resin such as a polyolefin resin is used as the material of an insulating coating constituting an insulated wire, flame retardancy is ensured by blending it with a flame retardant made of a phosphorus-based compound. For example, Patent Literature 1 describes containing 30 parts by mass or more of a flame retardant in 100 parts by mass of a polyolefin-based resin having a predetermined composition. Furthermore, Patent Literature 2 discloses a flame-retardant poly(arylene ether) composition and the use of the same as a cover for a coated wire. Furthermore, Patent Literature 3 discloses a structured cable and a method for producing the same. [Citations][Patent Literature] Patent literature 1: JP 2017 - 066 345 A Patent literature 2: WO 2009 / 042 369 A2 Patent Literature 3: CN 1 04 361 938 A (Summary of the invention)[Object of the invention]

[0003] As also described in Patent Literature 1, the flame retardancy of the insulation coating can be improved by incorporating the flame retardant into the insulation coating constituting the insulated wire. However, the mechanical properties and the like of the resin material constituting the insulation coating may be adversely affected by a large amount of the flame retardant. Therefore, the content of the flame retardant is preferably kept low enough to ensure the required flame retardancy. Accordingly, in addition to increasing the content of the flame retardant, a means for increasing the flame retardancy of the insulated wire is also desired.

[0004] Accordingly, it is desired to provide an insulated wire whose flame retardancy can be improved by a method other than a method of increasing the content of a flame retardant in an insulating coating. [Means of solving the problem]

[0005] The present invention is directed to an insulated wire having a wire conductor consisting of a single-core wire or a stranded wire formed by twisting a plurality of strands, and an insulating coating made of a resin composition for covering an outer periphery of the wire conductor, wherein a cross-sectional area ratio S, which is defined as a ratio S2 / S1 of a cross-sectional area S2 of the insulating coating to a conductor cross-sectional area S1, and an oxygen index Ol of the resin composition forming the insulating coating satisfy a relationship of S ≤ Ol-17.2, the cross-sectional area ratio S is 1.5 or less, the conductor cross-sectional area S1 is 0.10 mm 2or less, and the resin composition forming the insulation coating contains a flame retardant made of a phosphate ester compound, and a content of the flame retardant is 5 parts by mass or less based on 100 parts by mass of a resin component. [Effect of the invention]

[0006] The insulated wire according to the present invention can also improve its flame retardancy by a method other than a method of increasing the content of a flame retardant in the insulation coating. [Brief description of the drawings] Fig. 1A and Fig. 1B are views showing an insulated wire according to an embodiment of the present invention, wherein Fig. 1A is a perspective view and Fig. 1B is a circumferential section, Fig.2 is a graph showing a relationship between an oxygen index, a cross-sectional area ratio and flame retardancy for experimental data, and Fig. Figure 3A is a graph showing a relationship between oxygen index and flame retardancy for experimental data, and Fig. Figure 3B is a graph showing a relationship between the oxygen index, insulation thickness, and flame retardancy for experimental data. (Embodiments of the Invention)[Description of the Embodiments of the Present Invention]

[0007] First, the embodiments of the present invention will be listed and described.

[0008] The insulated wire of the present invention includes a wire conductor made of a single-core wire or a stranded wire formed by twisting a plurality of strands, and an insulating coating made of a resin composition for covering an outer periphery of the wire conductor, wherein a cross-sectional area ratio S defined as a ratio S2 / S1 of a cross-sectional area S2 of the insulating coating to a conductor cross-sectional area S1 and an oxygen index Ol of the resin composition constituting the insulating coating satisfy a relationship of S ≤ Ol-17.2, the cross-sectional area ratio S is 1.5 or less, the conductor cross-sectional area S1 is 0.10 mm 2or less, and the resin composition forming the insulation coating contains a flame retardant made of a phosphate ester compound, and a content of the flame retardant is 5 parts by mass or less based on 100 parts by mass of a resin component.

[0009] In the above-mentioned insulated wire, the cross-sectional area ratio S and the oxygen index Ol of the insulation coating satisfy the relationship S ≤ Ol-17.2. By reducing the cross-sectional area of ​​the insulation coating with respect to the conductor cross-sectional area, the heat of the insulation coating is more easily dissipated to the wire conductor, and the temperature of the insulation coating is less likely to rise. This increases the flame retardancy of the insulated wire. Even if the oxygen index of the resin composition constituting the insulation coating is low due to the inclusion of only a small amount of the flame retardant, the insulation coating is formed thin to reduce the cross-sectional area S2 of the insulation coating with respect to the conductor cross-sectional area S1.Therefore, if the cross-sectional area ratio S is lowered to satisfy the above relationship, high flame retardancy can be ensured in the insulated wire.

[0010] The formation of a thin insulation coating also leads to a reduction in the diameter of the insulated wire. If a large amount of flame retardant is included during the thinning of the insulation coating, there is a possibility that the mechanical properties of the insulation coating, such as abrasion resistance, will be reduced. However, since the oxygen index in the aforementioned insulated wire may be low, if the cross-sectional area ratio is sufficiently low, the flame retardant content can be suppressed to a low level. Therefore, the influences on the mechanical properties of a resin component can be suppressed to a low level by adding the flame retardant.

[0011] According to the present invention, the cross-sectional area ratio S is 1.5 or less. Even if the oxygen index of an insulating material constituting the insulation coating is relatively low, high flame retardancy of the insulated wire is achieved. Furthermore, by thinning the insulation coating, a reduction in the diameter of the insulated wire is more easily achieved.

[0012] As long as the cross-sectional area ratio S is 1.5 or less, the effect of improving the flame retardancy of the insulated wire and the effect of reducing the diameter of the insulated wire are particularly good.

[0013] The resin composition forming the insulation coating can contain polypropylene and polyphenylene ether. Even if the insulation coating is thinned to reduce the cross-sectional area ratio and improve the flame retardancy of the insulated wire, high abrasion resistance is easily ensured. Furthermore, the chemical resistance and heat resistance of the insulation coating are also improved.

[0014] According to the present invention, the resin composition forming the insulation coating contains a flame retardant made from a phosphate ester compound. The content of the flame retardant is 5 parts by mass or less per 100 parts by mass of a resin component. This allows the oxygen index of the resin composition to be increased by the content of the flame retardant. By suppressing the content of the flame retardant to 5 parts by mass or less, a reduction in the mechanical properties of the insulation coating, such as abrasion resistance, due to a large content of the flame retardant can be suppressed.

[0015] Since the cross-sectional area ratio S is 1.5 or less and the content of the flame retardant in the resin composition is 5 parts by mass or less based on 100 parts by mass of the resin component, the insulation coating can be thinned while effectively combining the flame retardancy and abrasion resistance of the insulated wire.

[0016] This also makes the effect of thinning the insulation coating particularly good, while combining the flame retardancy and abrasion resistance of the insulated wire.

[0017] According to the present invention, the conductor cross-sectional area S1 is 0.10 mm 2 or less. By reducing the diameter of the conductor, the effect of reducing the diameter of the entire insulated wire is particularly good, along with the effect of thinning the insulation coating. [Details of the embodiment of the present invention]

[0018] An insulated wire according to an embodiment of the present invention will be described in detail below with reference to the drawings. In this description, various physical properties of materials indicate values ​​measured at room temperature in the atmosphere, unless otherwise stated. Insulated wire configuration

[0019] Fig. 1 schematically shows an insulated wire 10 according to an embodiment of the present invention. As in Fig. 1, the insulated wire 10 includes a wire conductor 12 and an insulating coating 14 made of a resin composition for covering the outer circumference of the wire conductor 12. The insulated wire 10 can be obtained by extruding the resin composition, which becomes the insulating coating 14, onto the outer circumference of the wire conductor 12 so as to cover the outer circumference.

[0020] In the insulated wire 10 according to this embodiment, a cross-sectional area ratio S and an oxygen index Ol of the resin composition constituting the insulation coating 14 satisfy the following equation (1), where A is set to 17.2. S≤OI−A

[0021] Herein, the cross-sectional area ratio S of the insulated wire 10 is expressed as follows S=S2 / S1 wherein a conductor cross-sectional area, ie a cross-sectional area of ​​the wire conductor 12 in a cross section ( Fig. 1B) perpendicular to an axis of the insulated wire 10, is denoted by S1 and an insulation cross-sectional area, ie a cross-sectional area of ​​the insulation coating 14 in the same cross section, is denoted by S2.

[0022] The oxygen index Ol is a minimum oxygen concentration (volume percent) necessary to maintain combustion of a material and can be measured, for example, according to JIS K7201-2.

[0023] In the insulated wire 10 according to this embodiment, when A is set to 17.2, the cross-sectional area ratio S and the oxygen index Ol satisfy equation (1), whereby the insulated wire 10 has sufficiently high flame retardancy for use in a vehicle such as an automobile. Even higher flame retardancy can be ensured when equation (1) is satisfied with A set to a value greater than 17.2. For example, A can be set to 17.5 or further to 18.0.

[0024] In the insulated wire 10, even if the insulation coating 14 is heated by an external environment or by spontaneous combustion, the heat of the insulation coating 14 can be dissipated to the wire conductor 12, and the heat of the insulation coating 14 can be absorbed by the wire conductor 12. Through this phenomenon, a rapid temperature rise of the insulation coating 14 can be suppressed (heat dissipation). This heat dissipation effect is greater the larger the volume of the wire conductor 12 relative to the volume of the insulation coating 14. In other words, the thinner the insulation coating 14 is relative to the wire conductor 12, the greater the heat dissipation effect. That is, the heat dissipation effect can be enhanced as the cross-sectional area ratio S defined by equation (2) decreases.

[0025] The higher the oxygen index Ol of the resin composition of the insulated wire 10, the lower the probability of the insulation coating 14 burning. However, even if the oxygen index Ol of the resin composition is low, the insulation coating 14 can be made less likely to burn by utilizing the heat dissipation through the wire conductor 12. Furthermore, even if the insulation coating 14 ignites, it can be quickly extinguished. In the insulated wire 10, the heat dissipation effect can be increased and the flame retardancy of the insulated wire 10 can be improved by forming the thin insulation coating 14 in proportion to the conductor cross-sectional area S1 to reduce the cross-sectional area ratio S.

[0026] When the insulation coating 14 is thinned, in addition to the effect of increasing the cross-sectional area ratio S and improving the flame retardancy of the insulated wire 10, an effect of reducing the diameter of the insulated wire 10 can also be achieved. In an automobile or the like, there is a great demand for reducing the diameter of the insulated wire 10 in terms of space saving.

[0027] When the cross-sectional area ratio S of the insulated wire 10 is suppressed to be equal to or less than an upper limit determined in a relationship with the oxygen index Ol of the resin composition as in equation (1), sufficient flame retardancy can be ensured in the insulated wire 10 even when the insulating coating 14 is formed using a resin composition having a low oxygen index Ol. The oxygen index Ol of the resin composition depends on the types and formulations of a resin component and additive components other than the resin component, but adding a flame retardant is an example of a method for efficiently increasing the oxygen index Ol. However, when a large amount of the flame retardant is added, the mechanical properties of the resin component constituting the insulating coating 14, such as abrasion resistance, are more easily deteriorated.

[0028] When the addition amount of the flame retardant is reduced to maintain mechanical properties, the oxygen index Ol of the resin composition forming the insulating coating 14 is reduced. However, even in this case, sufficient flame retardancy can be ensured by thinning the insulating coating 14 to utilize the heat dissipation in the insulated wire 10. As the insulating coating 14 thins, the abrasion resistance of the insulating coating 14 tends to decrease, but a reduction in abrasion resistance due to the addition of the flame retardant is suppressed by keeping the addition amount of the flame retardant small.That is, by thinning the insulation coating 14 and reducing the addition amount of the flame retardant within a range satisfying the relationship between the cross-sectional area ratio S and the oxygen index Ol shown by equation (1), the diameter of the insulated wire 10 can be reduced while maintaining both the flame retardancy and the abrasion resistance of the insulated wire 10.

[0029] The use of the insulated wire 10 according to this embodiment is not particularly limited, and the insulated wire 10 can be used in various applications such as vehicles such as automobiles, appliances, information communications, electric power, ships, and aircraft. Among them, the insulated wire 10 can be suitably used as an automotive wire. In the field of automotive wires, high flame retardancy is required of the insulated wire 10 due to requirements such as fire prevention. Furthermore, a reduction in the diameter of the insulated wire 10 is required for space saving. In addition, the automotive wire easily comes into contact with the vehicle body and other parts during assembly and easily rubs against the vehicle body and other parts during use, and thus is required to have excellent abrasion resistance.In the insulated wire 10 according to this embodiment, the insulated wire 10 can be reduced in diameter while combining flame retardancy and abrasion resistance, and the above-mentioned properties required for automotive wires can be satisfied.

[0030] The insulated wire 10 according to this embodiment can be used individually or in the form of a wiring harness comprising multiple insulated wires. All of the insulated wires constituting the wiring harness may be the insulated wires 10 according to this embodiment, or some of them may be the insulated wires 10 according to this embodiment.

[0031] The constituent materials and specific dimensions of the wire conductor 12, which is made of a single-core wire or a stranded wire formed by twisting a plurality of strands 12a, and the insulation coating 14 constituting the insulated wire 10 according to this embodiment, are not particularly limited as long as the relationship of the above equation (1) is satisfied, the cross-sectional area ratio S is 1.5 or less, the conductor cross-sectional area S1 is 0.10 mm 2 or less, and the resin composition forming the insulation coating contains a flame retardant made from a phosphate ester compound, and a content of the flame retardant is 5 parts by mass or less based on 100 parts by mass of a resin component. Preferred embodiments are listed below. Wire conductor

[0032] Various metal materials that commonly form a wire as a conductor can be used as the wire conductor 12. Copper, aluminum, iron, magnesium, or alloys of these metals, and other metals can be used as such metal materials. Of these metals, copper or a copper alloy is most suitable. Among the various metal materials, copper and copper alloys have high thermal conductivity and offer a particularly high effect in improving the flame retardancy of the insulated wire 10 through heat dissipation.

[0033] As mentioned above, the wire conductor 12 is made of a single-core wire or a stranded wire formed by twisting a plurality of strands 12a. To ensure the flexibility and the like of the insulated wire 10, the wire conductor 12 is preferably made of a stranded wire. In this case, all strands 12a may be made of the same material, or strands 12a made of a plurality of different materials may be used.

[0034] As mentioned above, the conductor cross-sectional area S1 of the wire conductor 12 is 0.10 mm 2 or less. The conductor cross-sectional area S1 is preferably small in the sense of reducing the diameter of the insulated wire 10. Since the conductor cross-sectional area S1 is 0.10 mm 2 or less or 0.05 mm 2or less, the insulated wire 10 can be effectively reduced in diameter by the action of the thin wire conductor 12 and by the action of the thinning of the insulation coating 14 to satisfy equation (1) when the wire conductor 12 is reduced in diameter. A lower limit of the conductor cross-sectional area S1 is not specifically designated, but is preferably 0.03 mm 2 or more, as in terms of enhancing the effect of heat dissipation. Insulation coating

[0035] The thickness of the insulating coating 14 is not particularly limited as long as the ratio S to the conductor cross-sectional area S1 and the oxygen index Ol of the insulating coating 14 satisfy the relationship of Equation (1). However, the insulating coating 14 is preferably thin from the viewpoint of improving flame retardancy by making the cross-sectional area ratio S as small as possible and from the viewpoint of reducing the diameter of the insulated wire 10. When the thickness of the insulating coating 14 is 0.20 mm or less, further 0.15 mm or less, or 0.10 mm or less, the flame retardancy and diameter reduction of the insulated wire 10 can be effectively improved. A lower limit of the thickness is not particularly specified, but is preferably 0.08 mm or more, for example, from the viewpoint of easily ensuring the abrasion resistance of the insulating coating 14.

[0036] As mentioned above, the cross-sectional area ratio S is 1.5 or less. Since the cross-sectional area ratio S is set to 1.5 or less, the effect of improving flame retardancy and the effect of reducing the diameter of the insulated wire 10 tend to be excellent. The cross-sectional area ratio S easily satisfies the relationship of equation (1) for the oxygen index Ol of each of the various resin compositions adopted as the material of the insulation coating 14, and high flame retardancy can be ensured in the insulated wire 10.

[0037] A component composition of the resin composition forming the insulation coating 14 influences the flame retardancy of the insulated wire 10 through the oxygen index Ol. Provided that the resin composition forming the insulation coating 14 contains a flame retardant made of a phosphate ester compound and a content of the flame retardant is 5 parts by mass or less with respect to 100 parts by mass of a resin component, the component composition of the resin composition can be arbitrarily selected as long as it provides an oxygen index Ol that satisfies the equation (1) with respect to the desired cross-sectional area ratio S.

[0038] Various polymer materials can be used as the resin component, which is a main component of the resin composition. Polyolefins such as polyethylene and polypropylene; engineering plastics such as polyvinyl chloride, polyphenylene ether, and polyamide; thermoplastic elastomers, rubber, and the like can be represented as such polymer materials. One type of polymer material can be used, or multiple types of polymer materials can be blended and used.

[0039] Among all the above, blends of polyolefin and engineering plastic can be examples of a preferred resin component. These blends easily yield a relatively high oxygen index O1 among various polymer materials. Since polyolefins have excellent chemical resistance and oil resistance, and engineering plastics have excellent abrasion resistance, the insulating coating 14 can be easily formed with abrasion resistance and excellent chemical resistance and oil resistance by blending and using these materials, even if the insulating coating 14 is made thin to reduce the cross-sectional area ratio S.

[0040] Examples of polyolefins from which the above-mentioned blends consist are polypropylene (PP) and polyethylene (PE). Other examples of engineering plastics are polyphenylene ether (PPE), polyamide (PA), polybutylene terephthalate (PBT), and polycarbonate (PC). Polyolefin and engineering plastic preferably form a polymer alloy. The blending ratio of polyolefin and engineering plastic is preferably 30:70 to 70:30, with a mass ratio of polyolefin to engineering plastic that sufficiently exhibits the properties of each material.

[0041] Of the blends mentioned above, a particularly preferred example is a blend (PP / PPE) of polypropylene (PP) and polyphenylene ether (PPE), particularly a polymer alloy thereof. PP / PPE is a relatively inexpensive material, yet it is characterized by excellent abrasion resistance, chemical resistance, and oil resistance.

[0042] Another polymer material may be added to the mixture of polyolefin and engineering plastic. Thermoplastic elastomers, including SEBS, can be examples of such a polymer material. By adding thermoplastic elastomer, the flexibility and mechanical properties of the insulation coating 14 can be improved. The addition amount of the thermoplastic elastomer may be 5 parts by mass or more, with the amount of the total resin component constituting the resin composition being set to 100 parts by mass in order to achieve a sufficient addition effect. On the other hand, the addition amount may be 20 parts by mass or less, for example, from the viewpoint of ensuring sufficient abrasion resistance.

[0043] The resin composition forming the insulating coating 14 may contain various additives in addition to the resin component. According to the present invention, the resin composition forming the insulating coating contains a flame retardant made from a phosphate ester compound to improve compatibility with the resin component and suppress deterioration in mechanical properties.

[0044] The oxygen index Ol of the resin composition can be increased by adding the flame retardant. However, if the content of the flame retardant is increased as described above, the mechanical properties of the resin composition, such as abrasion resistance, tend to be impaired. In particular, if a large amount of the flame retardant is contained when the insulating coating 14 is formed thin, it becomes difficult to ensure sufficient abrasion resistance. Accordingly, it is preferable to improve the flame retardancy of the insulated wire 10 not by increasing the content of the flame retardant, but by thinning the insulating coating 14 and decreasing the cross-sectional area ratio S. That is, it is better to reduce the content of the flame retardant.

[0045] As long as the cross-sectional area ratio S of the insulated wire 10 is 1.5 or less, the insulated wire 10 satisfying the equation (1) and having high flame retardancy can be easily manufactured even if the content of the flame retardant made of the phosphate ester compound is 5 parts by mass or less relative to 100 parts by mass of a resin component.

[0046] There is no particular limit on the specific value of the oxygen index Ol itself. However, the oxygen index Ol of the resin composition intended for use as the insulation coating 14 is generally 18 or more. Furthermore, it is preferable if the oxygen index Ol is 21 or more. On the other hand, it is preferable if the oxygen index Ol is 23 or less to avoid a high flame retardant content.

[0047] The resin composition forming the insulation coating 14 may contain various additives besides the flame retardant. Examples of such additives include a filler, an antioxidant, an anti-aging agent, a lubricant, a plasticizer, a pigment, and the like. However, the content of additives other than the flame retardant is also preferably low to easily ensure abrasion resistance during thinning of the insulation coating 14. For example, the content of various additives including the flame retardant is preferably less than 30 parts by mass, further 20 parts by mass or less, or 10 parts by mass based on 100 parts by mass of the resin component.

[0048] The insulation coating 14 can be formed by stacking multiple layers of different resin compositions. In this case, a total value of the cross-sectional areas of the respective layers can be used as the insulation cross-sectional area S2 using Equation (1). Furthermore, a value obtained by weight-averaging the oxygen indices of the materials constituting the respective layers according to the cross-sectional areas can be used as the oxygen index O1. Examples

[0049] The following examples, which are non-limiting reference examples, serve to illustrate the present invention. Flame retardancy and abrasion resistance were evaluated for insulated wires with various conductor cross-sectional areas, oxygen indices, and insulation coating thicknesses. [Test procedure](1) Preparation of samples

[0050] Initially, stranded copper alloy wires were produced as wire conductors. Three types of wire conductors with different cross-sectional areas were produced. In particular, three types of wire conductors with nominal conductor sizes of 0.05 mm 2 (strand diameter of 0.11 mm, the number of strands is 7), 0.13 mm 2 (strand diameter of 0.18 mm, the number of strands is 7) and 0.35 mm 2 (strand diameter of 0.26 mm, the number of strands is 7).

[0051] Furthermore, the components shown in Tables 1 and 2 were kneaded at a predetermined content ratio at 280°C to prepare resin compositions used in the preparation of Samples A1 to A13 and Samples B1 to B5. The obtained resin compositions were extruded onto the outer peripheries of the wire conductors with the thicknesses shown in Tables 1 and 2, thereby forming insulating coatings.

[0052] The following materials are used as respective components of the resin compositions that make up the insulation coatings. PPE: “Zylon S201A”, manufactured by Asahi Kasei Corporation PP: “Novatec EC9”, manufactured by Japan Polypropylene Corporation SEBS: “Tough-Tek H1043” manufactured by Asahi Kasei Corporation Flame retardant: Phosphate ester-based flame retardant (aromatic condensed phosphate ester), “PX-200”, manufactured by Daihachi Chemical Industry Co., Ltd. Antioxidant: Hindered phenol-based antioxidant, “Irganox 1010”, manufactured by BASF (2) Evaluation of the oxygen index

[0053] The resin compositions with the component compositions shown in Tables 1 and 2 were molded into sheets, and an oxygen index was evaluated for each IV test piece according to JIS K7201-2. (3) Assessment of flame retardancy

[0054] The flame retardancy of the insulated wire was evaluated according to ISO 6722. Specifically, each wire was cut to 600 mm, fixed at a 45° inclination to a horizontal surface, and the flame of a gas burner was applied to the cut wire at a position 500 mm from its upper end. A case where the burning time until flame extinguishment was 70 seconds or less was rated as "A" with high flame retardancy. A case where the burning time until flame extinguishment was more than 70 seconds and a case where the flame did not extinguish was rated as "B" with low flame retardancy. (4) Assessment of abrasion resistance

[0055] The abrasion resistance of the insulated wire was evaluated using a blade stroke method according to ISO 6722. At this time, the load to be applied to a blade was 4 N when the conductor nominal size was 0.05 mm2 or 0.13 mm 2 and 7 N when the conductor nominal size was 0.35 mm 2 A case where the number of reciprocating movements of the knife until the conductor was exposed was equal to or greater than a predetermined standard was rated as "A" with high abrasion resistance, and a case where this number was below the predetermined standard was rated as "B" with low abrasion resistance. The specified standard was 50 when the nominal conductor size was 0.05 mm. 2 was 100, if the conductor nominal size was 0.13 mm 2 and 150 if the conductor nominal size was 0.35 mm 2 fraud. [Result]

[0056] Tables 1 and 2 show the evaluation results of flame retardancy and abrasion resistance, along with the content (unit: parts by mass) and oxygen index (Ol) of each component in the resin composition forming the insulation coating, the conductor cross-sectional area (S1), and the insulation thickness for each of Samples A1 to A13 and Samples B1 to B5. The insulation cross-sectional areas (S2) and cross-sectional area ratios (S) are also listed in Tables 1 and 2. The insulation cross-sectional area (S2) is calculated by subtracting the conductor cross-sectional area (S1) from an actual measurement of the cross-sectional area of ​​the insulated wire. The cross-sectional area ratio (S) is calculated by dividing the insulation cross-sectional area (S2) by the conductor cross-sectional area (S1). [Table 2] Sample number B1 B2 B3 B4 B5 Content (parts by mass) PPE 45 45 45 45 50 - PP 45 45 45 45 40 SEBS 10 10 10 10 10 Flame retardants 5 10 20 30 5 antioxidant 0,5 0,5 0,5 0,5 0,5 Oxygen index (Ol) 20,0 21,0 22,0 22,5 20,3 Conductor cross-sectional area S1 (mm 2 ) - - 0,1451 0,0491 0,0491 0,0491 0,1475 Conductor size (mm 2 ) 0,13 0,05 0,05 0,05 0,13 Insulation thickness (mm) 0,20 0,20 0,20 0,20 0,23 Insulation cross-sectional area S2 (mm 2 ) 0,431 0,431 0,431 0,283 0,515 Cross-sectional area ratio (S = S2 / S1) 3,0 8,8 8,8 5,8 3,5 Flame retardancy (burning time) B (80 s) B (not extinguished) B (not extinguished) B (80 s) B (85 s) Abrasion resistance (number of back and forth movements) A (1300) A (750) A (300) B (40) A (2000)

[0057] Furthermore, Fig.Figure 2 shows a relationship between the cross-sectional area ratio, the oxygen index, and the flame retardancy evaluation result. The vertical axis represents the cross-sectional area ratio, the horizontal axis represents the oxygen index. Data points of samples A1 to A13 with an evaluation result of "A" are represented by circles (•), and data points of samples B1 to B5 with an evaluation result of "B" are represented by rectangles (□).

[0058] According to Fig. 2, it is understood that high flame retardancy is achieved in a region where the cross-sectional area ratio is small at any oxygen index. That is, the flame retardancy of the insulated wire can be improved by forming the thin insulation coating in proportion to the conductor cross-sectional area.

[0059] However, the cross-sectional area ratios that can achieve high flame retardancy, rated as "A," vary depending on the oxygen index. As the oxygen index increases, high flame retardancy is achieved even when the cross-sectional area ratio is large. As the solid line in Fig.As shown in Figure 2, the cases where high flame retardancy, rated as "A," was achieved and the cases where high flame retardancy was not achieved can be divided by an upward straight line of Ol = S + A, where A is set to 17.2, and high flame retardancy is achieved in a region below the straight line, that is, in a region where the cross-sectional area ratio is small. As just described, the relationship between the cross-sectional area ratio and flame retardancy can be evaluated using a linear function of the oxygen index, and the insulated wire with high flame retardancy can be obtained by assuming a cross-sectional area ratio equal to or less than a value specified by this linear function. Fig.In Figure 2, the straight lines with A = 17.5 and A = 18.0 are also represented by a dashed line and a dotted line, respectively. These straight lines allow for more stringent selection of a region with high flame retardancy.

[0060] When the content of the flame retardant in the resin composition is reduced, the oxygen index tends to decrease. However, in this case, sufficient flame retardancy can be ensured by reducing the cross-sectional area ratio. For example, when the cross-sectional area ratio is set to 2.5 or less, high flame retardancy is achieved even when the flame retardant content is reduced to 10 parts by mass or less (Samples A1, A2, A5 to A7, A9, and A13). When the cross-sectional area ratio is set to 1.5 or less, as is the case according to the present invention, high flame retardancy is achieved even when the flame retardant content is reduced to 5 parts by mass or less (Samples A1, A5, A6, and A13).

[0061] Fig.Figure 3A shows the burning time obtained in the test to evaluate flame retardancy as a function of the oxygen index. According to this result, the data points are distributed in regions that exhibit largely different burning times, even with the same oxygen index. The oxygen index is an index that correlates with the flame retardancy of the resin composition. Fig. 3A shows that the flame retardancy of the insulated wire cannot be adequately evaluated solely by the oxygen index of the resin composition forming the insulation coating.

[0062] Fig. Figure 3B shows a relationship between insulation thickness, oxygen index, and flame retardancy evaluation result. Fig. Figure 3B corresponds to a diagram obtained by substituting the cross-sectional area ratio on the vertical axis of Fig. 2 is obtained by the insulation thickness. In contrast to Fig.2, the data points (·) that were evaluated as having high flame retardancy and the data points (□) that were evaluated as having low flame retardancy are not distributed in regions shown in the graph in Fig. 3B are clearly divided. For example, data points (•) with high flame retardancy and data points (□) with low flame retardancy overlap at two positions where the insulation thickness is 0.20 mm. From this, it can be deduced that the ratio to the conductor cross-sectional area, rather than the insulation coating thickness and the cross-sectional area value, should be used as an index to evaluate the flame retardancy of the insulated wire, along with the oxygen index of the resin composition.

[0063] Finally, the abrasion resistance evaluation results for the respective samples are compared in Tables 1 and 2. The abrasion resistance is low for samples A12 and B4, where the flame retardant content is 30 parts by mass. For sample A11, the number of reciprocating movements during evaluation is also relatively low. To achieve sufficiently high abrasion resistance, the flame retardant content is preferably suppressed to less than 30 parts by mass. Furthermore, although the SEBS content is different in samples A6 and A13, similar flame retardancy is achieved under the same oxygen index, but the abrasion resistance is higher in sample A13 with a lower SEBS content. List of reference symbols 10 insulated wire 12 wire conductors 12a stranded wire 14 Insulation coating

Claims

[1] Insulated wire (10) comprising: a wire conductor (12) consisting of a single-core wire or a strand formed by twisting a plurality of strands (12a); and an insulation coating (14) made of a resin composition for covering an outer periphery of the wire conductor (12), wherein a cross-sectional area ratio S, which is defined as a ratio S2 / S1 of a cross-sectional area S2 of the insulation coating (14) to a conductor cross-sectional area S1, and an oxygen index Ol of the resin composition forming the insulation coating (14) satisfy a relationship of S ≤ Ol-17.2, the cross-sectional area ratio S is 1.5 or less, the conductor cross-sectional area S1 0.10 mm 2 or less, and the resin composition forming the insulation coating (14) contains a flame retardant made of a phosphate ester compound, and a content of the flame retardant is 5 parts by mass or less based on 100 parts by mass of a resin component. [2] The insulated wire (10) according to claim 1, wherein the resin composition forming the insulation coating (14) contains polypropylene and polyphenylene ether.

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