JP2013020783A - Insulated wire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an insulated wire having an insulation layer containing crosslinked silicone rubber and having excellent low temperature resistance and wear resistance in which deterioration of various physical properties due to poor appearance of the insulation layer caused by foam formation during the crosslinking is minimized.SOLUTION: In the insulated wire where the circumference of a conductor is coated with an insulation layer containing crosslinked silicone rubber, the insulation layer contains surface treatment magnesium hydroxide obtained by performing surface treatment of magnesium hydroxide with a surface treatment agent consisting of an organic polymer, and white carbon powder.

Description

  The present invention relates to an insulated wire, and more particularly to an insulated wire that is suitably used in a vehicle such as an automobile.

  Insulating materials for insulated wires used in vehicles such as automobiles are required to have various characteristics such as mechanical characteristics, flame retardancy, heat resistance, and cold resistance. Conventionally, as this type of insulating material, a material containing halogen such as a compound containing a vinyl chloride resin or a halogen-based flame retardant is often used.

  Since this type of insulating material contains halogen, corrosive gas may be generated when discarded by incineration. Therefore, there is an attempt to use an insulating material that does not contain a halogen from the viewpoint of environmental protection.

  For example, Patent Document 1 describes that a non-halogen insulating material in which aluminum hydroxide is blended with uncrosslinked silicone rubber is used as an insulating material for an insulated wire. Since this non-halogenous insulating material contains uncrosslinked silicone rubber, it is necessary to crosslink the uncrosslinked silicone rubber by heating after coating the outer periphery of the conductor.

Japanese Patent No. 3555101

  However, in the insulating material described in the above-mentioned Patent Document 1, by heating when cross-linking uncrosslinked silicone rubber, crystal water of aluminum hydroxide is released and dehydration occurs, and the insulating material is foamed by the generated water. There's a problem. If the insulating material is foamed, the appearance of the insulating layer may be poor, and various physical properties may be deteriorated.

  In addition, since the insulating material described in Patent Document 1 uses a rubber material (silicone rubber), there is a problem that the insulating layer is softer and more likely to be worn than when a vinyl chloride resin is used, for example.

  The problem to be solved by the present invention is an insulated wire having an insulating layer containing a crosslinked silicone rubber, which suppresses deterioration of various physical properties due to poor appearance of the insulating layer caused by foaming at the time of crosslinking, as well as cold resistance and wear resistance. An object of the present invention is to provide an insulated wire that is excellent in performance.

  In order to solve the above problems, an insulated wire according to the present invention is an insulated wire in which a conductor is covered with an insulating layer containing a crosslinked silicone rubber, and the insulating layer is water-treated with a surface treatment agent made of an organic polymer. The gist of the invention is that it contains surface-treated magnesium hydroxide whose surface is treated with magnesium oxide and white carbon powder.

  The said insulated wire WHEREIN: It is preferable that content of the said white carbon powder exists in the range of 0.1-100 mass parts with respect to 100 mass parts of the said crosslinked silicone rubber.

  The said insulated wire WHEREIN: It is preferable that content of the said surface treatment magnesium hydroxide exists in the range of 0.1-100 mass parts with respect to 100 mass parts of the said crosslinked silicone rubber.

  In the insulated wire, the surface treatment agent is preferably at least one selected from polyethylene, polypropylene, ethylene-ethyl acrylate copolymer, ethylene-vinyl acetate copolymer, and derivatives thereof.

  The said insulated wire WHEREIN: It is preferable that the surface treatment amount with respect to the said magnesium hydroxide of the said surface treating agent exists in the range of 0.1-10 mass% of the total amount of the said surface treating agent and the said magnesium hydroxide.

  The insulated wire according to the present invention is the insulated wire in which the periphery of the conductor is covered with an insulating layer containing a crosslinked silicone rubber, and the insulating layer is surface-treated with magnesium hydroxide with a surface treatment agent made of an organic polymer. Because it contains surface-treated magnesium hydroxide and white carbon powder, it does not foam when the silicone rubber is crosslinked, thus preventing deterioration of various physical properties due to poor appearance of the insulating layer and providing excellent cold resistance and wear resistance. It is done.

  That is, the temperature at which magnesium hydroxide dehydrates is higher than the temperature at which aluminum hydroxide dehydrates. Magnesium hydroxide is unlikely to be dehydrated like aluminum hydroxide at the temperature of heat crosslinking of silicone rubber. By using magnesium hydroxide, the appearance defect of the insulating layer due to dehydration does not occur.

  Moreover, since the insulated wire of this invention uses the surface treatment magnesium hydroxide in which magnesium hydroxide is surface-treated with the surface treating agent which consists of organic polymers, it is excellent in the dispersibility of magnesium hydroxide in silicone rubber. Thereby, it is excellent in cold resistance. When the dispersibility of magnesium hydroxide is good, the load when kneading silicone rubber and magnesium hydroxide is reduced, and the temperature rise during kneading can be suppressed. As a result, it is possible to use a material that is sensitive to temperature rise, and the effect that the width of a material that can be used as an insulated wire is widened can be obtained.

  Furthermore, the insulated wire of the present invention contains white carbon powder together with surface-treated magnesium hydroxide. White carbon, like magnesium hydroxide, is an additive that does not cause poor appearance. Furthermore, the addition of white carbon has the effect of increasing the elastic modulus of the crosslinked silicone rubber and improving the strength of the insulating layer. Therefore, the insulated wire can obtain good wear resistance.

  Hereinafter, embodiments of the present invention will be described in detail. The insulated wire according to the present invention has a conductor and an insulating layer covering the periphery of the conductor. The insulating layer contains a crosslinked silicone rubber, surface-treated magnesium hydroxide as a flame retardant, and white carbon powder. The surface-treated magnesium hydroxide is one in which the surface of magnesium hydroxide is surface-treated with a surface treatment agent made of an organic polymer.

  This insulating layer is formed using the rubber composition for insulating layers containing uncrosslinked silicone rubber. The uncrosslinked silicone rubber may be either a millable type (heat-crosslinked type) that becomes an elastic body by kneading a cross-linking agent and then heat-crosslinked, or a liquid rubber type that is liquid before cross-linking. The liquid rubber type silicone rubber includes a room temperature crosslinking type (RTV) capable of crosslinking near room temperature and a low temperature crosslinking type (LTV) capable of crosslinking when heated near 100 ° C. after mixing.

  As the uncrosslinked silicone rubber, a millable silicone rubber is preferable. Millable silicone rubber has the advantage that it is easy to mix during kneading and has excellent workability because the crosslinking temperature is relatively high at 180 ° C. or higher and has good stability. On the other hand, since the liquid rubber type silicone rubber has a low cross-linking temperature of about 120 ° C., it is necessary to suppress heat generation during kneading because of low stability. is there. Millable silicone rubber is a commercially available rubber compound that contains linear organopolysiloxane as the main raw material (raw rubber) and contains reinforcing filler, filler, dispersion accelerator, and other additives. May be.

  Magnesium hydroxide used in surface-treated magnesium hydroxide is pulverized from synthetic magnesium hydroxide such as one synthesized from seawater by crystal growth method, one synthesized by reaction of magnesium chloride and calcium hydroxide, or naturally produced minerals. Natural magnesium hydroxide can be used.

  The average particle size of the magnesium hydroxide is preferably in the range of 0.1 to 20 μm. If the average particle size of the magnesium hydroxide is within this range, the mechanical properties of the insulating layer are hardly affected. For example, when the average particle diameter of magnesium hydroxide is less than 0.1 μm, secondary aggregation of the magnesium hydroxide particles tends to occur. When the dispersibility of the magnesium hydroxide particles in the insulating layer is lowered, the mechanical properties of the insulating layer are likely to be lowered. In addition, a decrease in cold resistance is likely to occur. For example, when the average particle size of magnesium hydroxide exceeds 20 μm, the appearance of the insulating layer may be deteriorated. The average particle size of magnesium hydroxide is preferably 0.2 to 10 μm, more preferably 0.5 to 5 μm.

  The average particle size of the surface-treated magnesium hydroxide after the surface treatment is substantially the same as the average particle size of the magnesium hydroxide before the surface treatment.

  The organic polymer used as the surface treatment agent for magnesium hydroxide is preferably a hydrocarbon resin such as a paraffin resin or an olefin resin. Specific examples of the hydrocarbon resin include homopolymers of α-olefins such as 1-heptene, 1-octene, 1-nonene, and 1-decene, or interpolymers, or mixtures thereof, polypropylene (PP ), Polyethylene (PE), ethylene-ethyl acrylate copolymer (EEA), ethylene-vinyl acetate copolymer (EVA), and derivatives thereof. The surface treating agent should just contain 1 or more types of the said resin at least.

  The organic polymer as the surface treatment agent may be modified. As the modifier, an unsaturated carboxylic acid or a derivative thereof can be used. Specific examples of the unsaturated carboxylic acid include maleic acid and fumaric acid. Examples of the derivative of unsaturated carboxylic acid include maleic anhydride (MAH), maleic acid monoester, maleic acid diester and the like. Of these, maleic acid and maleic anhydride are preferred. These organic polymer modifiers as the surface treatment agent may be used alone or in combination of two or more.

  Examples of a method for introducing an acid into an organic polymer as a surface treatment agent include a graft method and a direct method. The amount of acid modification is 0.1 to 20% by mass, preferably 0.2 to 10% by mass, and more preferably 0.2 to 5% by mass of the organic polymer as the surface treatment agent.

  The surface treatment method using a surface treatment agent for magnesium hydroxide is not particularly limited. As the surface treatment method of magnesium hydroxide, for example, the surface treatment may be performed on magnesium hydroxide having a predetermined particle diameter, or at the same time as synthesis. Moreover, as a processing method, the wet process using a solvent may be sufficient and the dry process which does not use a solvent may be sufficient. In the wet treatment, examples of suitable solvents include aliphatic solvents such as pentane, hexane, and heptane, and aromatic solvents such as benzene, toluene, and xylene. Moreover, when preparing the composition of an insulating layer, you may knead | mix a surface treating agent simultaneously with materials, such as another rubber raw material.

  The surface treatment amount of the surface treatment agent with respect to magnesium hydroxide (sometimes referred to as the coating amount) ranges from 0.1 to 10% by mass of the total amount of the surface treatment agent and magnesium hydroxide as the addition amount of the surface treatment agent. It is preferable to be within. If the coating amount of the surface treatment agent is less than 0.1% by mass, the dispersion may be poor, and if it exceeds 10% by mass, aggregation may occur.

  The content of the surface-treated magnesium hydroxide is preferably in the range of 0.1 to 100 parts by mass with respect to 100 parts by mass of the crosslinked silicone rubber. The content of the surface-treated magnesium hydroxide is more preferably 0.5 to 95 parts by mass. If the content of the surface-treated magnesium hydroxide is less than 0.1 parts by mass, the flame retardancy of the insulating layer may be deteriorated, and if it exceeds 100 parts by mass, the heat resistance of the insulating layer may be deteriorated.

The white carbon powder is a white fine powder having an effect of enhancing the reinforcing property of rubber when blended with rubber. For example, synthetic amorphous silica or the like is used. Synthetic amorphous silica includes anhydrous silicic acid, hydrous silicic acid, silicate and the like. Silicic anhydride is obtained by a dry method in which silicon halide is thermally decomposed. Examples of the dry method include a combustion method and an arc method. The hydrous silicic acid is obtained by a wet method by acid decomposition of sodium silicate. The wet method includes a sedimentation method and a gel method. The synthetic amorphous silica is amorphous in both silicic anhydride and hydrous silicic acid, has an average primary particle size of 10 to 50 nm, a secondary particle size of 1 to 40 μm, and a bulk density (apparent specific gravity) of 0. The thing of 005-1.0 g / ml and a BET specific surface area of about 50-400 m < ² > / g can be used.

  The white carbon powder preferably has a bulk density of 0.01 to 0.8 g / ml. If the bulk density is less than 0.01 g / ml, mixing may take time, and if it exceeds 0.8 g / ml, the reinforcing effect may be reduced.

  As the white carbon powder, a commercially available product marketed for the rubber industry can be used. Examples of commercially available white carbon powders include “Nipseal VN3”, “Nipseal NA”, “Nipseal HD-2”, “Nipseal AQ”, “Nipseal LP”, and trade names “Fuji Silysia Chemical” Examples include "Silicia 310P", "Silicia 420", "Siriciria 530", "Siriciria 710", Tokuyama's trade names "Tocseale", "Fine Seal", "Leoseale", "Excelica", and the like.

  When white carbon powder is added to the crosslinked silicone rubber, it has the effect of improving the elastic modulus of the insulating layer. The insulating layer preferably has an elastic modulus of 3 MPa or more from the viewpoint of improving wear resistance. The elastic modulus of the insulating layer can be adjusted by appropriately adjusting the type of the crosslinked silicone rubber constituting the insulating layer, the type and amount of white carbon powder added to the insulating layer, and the like.

  The insulating layer has a higher elastic modulus and improved strength by adding white carbon powder to the crosslinked silicone rubber. As a result, the wear resistance of the insulating layer can be improved. Moreover, the white carbon powder, like magnesium hydroxide, has no risk of foaming when heated to the degree of crosslinking of the silicone rubber, and the appearance of the insulating layer is good.

  The content of the white carbon powder is preferably in the range of 0.1 to 100 parts by mass with respect to 100 parts by mass of the crosslinked silicone rubber. More preferably, it exists in the range of 1-95 mass parts, More preferably, it exists in the range of 5-90 mass parts. When the content of the white carbon powder is within a specific range, it is easy to improve the wear resistance and the kneading operation can be easily performed. If content of white carbon powder is less than 0.1 mass part, the effect which improves abrasion resistance will fall easily. In addition, kneading with silicone rubber tends to take time. On the other hand, when the content of the white carbon powder exceeds 100 parts by mass, the impact on wear resistance is small, but the elongation at break may be deteriorated. In this case, cold resistance may be affected.

  In the rubber composition for the insulating layer, the uncrosslinked silicone rubber can be crosslinked by heating or the like, but may be crosslinked using a crosslinking agent (vulcanizing agent). The crosslinking agent can be appropriately selected depending on the type of uncrosslinked rubber, the crosslinking conditions, and the like. Examples of the crosslinking agent include radical generators such as organic peroxides, compounds such as metal soaps, amines, thiols, thiocarbamates, and organic carboxylic acids. As the crosslinking agent, an organic peroxide or the like is preferable from the viewpoint of improving the crosslinking rate.

  Examples of the organic peroxide include dialkyl peroxides such as dihexyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, and 2,5-dimethyl-2,5-bis (t-butylperoxy) hexane. Examples thereof include peroxyketals such as oxide and n-butyl 4,4-di (t-butyl peroxide) valerate.

  The amount of the crosslinking agent can be determined as appropriate. It is preferable to mix | blend the compounding quantity of a crosslinking agent in 0.01-10 mass% with respect to the total amount of uncrosslinked rubber | gum and a crosslinking agent, for example.

In addition to the crosslinked silicone rubber, surface-treated magnesium hydroxide, and white carbon powder, the insulating layer may contain various additives as long as the characteristics of the insulating layer are not impaired. As such an additive, the common additive used for the insulating layer of an insulated wire can be mentioned. Specifically, other flame retardants, crosslinking agents, fillers, antioxidants, anti-aging agents, pigments and the like can be mentioned.

  The insulated wire according to the present invention can be manufactured, for example, as follows. That is, first, a rubber composition for an insulating layer for forming an insulating layer is prepared. Next, the prepared rubber composition is extruded around the conductor to form a coating layer containing uncrosslinked rubber around the conductor. Next, the uncrosslinked rubber of the coating layer is crosslinked by crosslinking means such as heating. Thereby, the insulated wire by which the circumference | surroundings of the conductor were coat | covered with the insulating layer containing crosslinked rubber can be manufactured. The insulated wire according to the present invention can also be formed by coating a rubber composition for an insulating layer around a conductor to form a coating layer, and crosslinking the uncrosslinked rubber of the coating layer by a crosslinking means such as heating. Can be manufactured.

  The rubber composition for the insulating layer is obtained by melt-kneading an uncrosslinked silicone rubber, surface-treated magnesium hydroxide, white carbon powder, and various additives such as a crosslinking agent blended as necessary. And uniformly dispersed. When kneading the components of the rubber composition, for example, a conventional kneader such as a Banbury mixer, a pressure kneader, a kneading extruder, a biaxial kneading extruder, or a roll can be used.

  For extruding the rubber composition for the insulating layer, an electric wire extruding machine or the like used for manufacturing a normal insulated wire can be used. What is used for a normal insulated wire can be utilized for a conductor. Examples of the conductor include a single wire conductor and a stranded wire conductor made of a copper-based material or an aluminum-based material. Moreover, the diameter of a conductor, the thickness of an insulating layer, etc. are not specifically limited, According to the use etc. of an insulated wire, it can determine suitably.

  The insulated wire according to the present invention having the above-described structure contains a surface-treated magnesium hydroxide and a silica powder in which magnesium hydroxide is surface-treated with a surface treatment agent made of an organic polymer in an insulating layer containing a crosslinked silicone rubber. ing. Magnesium hydroxide is not dehydrated like aluminum hydroxide when heated during crosslinking of the silicone rubber. That is, the temperature at which magnesium hydroxide is dehydrated is higher than the temperature at which aluminum hydroxide is dehydrated, and there is no risk of dehydration at the temperature of heat crosslinking of silicone rubber. Therefore, according to the insulated wire according to the present invention, an appearance defect of the insulating layer due to dehydration of magnesium hydroxide does not occur, and a good appearance can be obtained. Thereby, the fall of various physical properties is suppressed.

  Further, since magnesium hydroxide is surface-treated with a surface treatment agent made of an organic polymer, it is excellent in dispersibility of magnesium hydroxide in silicone rubber. Thereby, it is excellent in cold resistance. Thus, when the dispersibility of magnesium hydroxide is good, the load at the time of kneading silicone rubber and magnesium hydroxide becomes small, and the temperature rise at the time of kneading can be suppressed. As a result, it is possible to use a material that is sensitive to temperature rise, and the effect that the width of a material that can be used as an insulated wire is widened can be obtained.

  Furthermore, by using white carbon powder together with magnesium hydroxide, it is possible to improve the elastic modulus of the insulating layer while maintaining flame retardancy, and to suppress the decrease in wear resistance when using a rubber material for the insulating layer. it can.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention. For example, although the insulated wire of the said aspect was comprised from the single layer insulation layer, you may comprise the insulated wire of this invention from two or more layers of insulation layers.

  The insulated wire according to the present invention can be used for insulated wires used in automobiles, electronic / electrical equipment. It is particularly suitable as an insulated wire for applications that require high heat resistance and flame resistance. For example, in an insulated electric wire for automobiles, such high heat resistance is required for high voltage and large current applications such as a power cable connecting an engine and a battery of a hybrid vehicle or an electric vehicle.

[Examples 1-7]
Each component such as uncrosslinked silicone rubber 1-4, surface-treated magnesium hydroxide (PE 5% water mug), white carbon powder (Nipseal VN3 or Cicilia 310P), and a crosslinking agent so as to have the composition shown in Table 1 A rubber composition for an insulating layer was prepared by mixing at room temperature using a Banbury mixer. Next, using an extruder, the rubber composition for the insulating layer was extruded and coated at a thickness of 0.2 mm on the outer periphery of a conductor (cross-sectional area 0.5 mm ² ) of an annealed copper twisted wire obtained by twisting 7 annealed copper wires. A coating layer containing uncrosslinked rubber was formed. Thereafter, the coating layer was heat-treated at 200 ° C. for 4 hours to crosslink the uncrosslinked silicone rubber to form an insulating layer. Thereby, the insulated wire of Examples 1-7 was obtained.

[Comparative Examples 1-7]
Ingredients such as uncrosslinked silicone rubber 1 to 4, aluminum hydroxide, and crosslinking agent were mixed at room temperature using a Banbury mixer in the same manner as in Examples 1 to 7 so that the composition shown in Table 2 was obtained. A rubber composition for the layer was prepared. Subsequently, the insulated wire of Comparative Examples 1-7 was obtained like Example 1-7 using this rubber composition.

[Reference Example 1]
For the insulating layer, the components such as uncrosslinked silicone rubber 1, surface-treated magnesium hydroxide (PE 5% water mug), and crosslinking agent are mixed at room temperature using a Banbury mixer so as to have the composition shown in Table 1. A rubber composition was prepared. Subsequently, the insulated wire of the reference example 1 was obtained like Example 1-7 using this rubber composition.

  About the insulated wire of Examples 1-7, Comparative Examples 1-7, and Reference Example 1, the cold resistance test, the external appearance observation of the wire, and the abrasion resistance test were performed and evaluated. The results are shown in Tables 1 and 2. In addition, each component composition of Table 1 and Table 2, a test method, and evaluation are as follows.

[Ingredients in Tables 1 and 2]
Silicone rubber 1: manufactured by Shin-Etsu Chemical Co., Ltd., 931 (composition: dimethylsiloxane)
Silicone rubber 2: manufactured by Shin-Etsu Chemical Co., Ltd., 541 (composition: dimethylsiloxane)
Silicone rubber 3: manufactured by Toshiba Corporation, 2267 (composition: dimethylsiloxane)
Silicone rubber 4: manufactured by Toshiba Corporation, 2277 (composition: dimethylsiloxane)
・ PE5% coated water mug (surface treated magnesium hydroxide)
Magnesium hydroxide: crystal growth method, average particle size 1.0 μm
Surface treatment agent: Polyethylene (Mitsui Chemicals, 800P)
Use amount of surface treatment agent: 5% by mass of the total amount of polyethylene and magnesium hydroxide
Nipsil VN3: White carbon powder manufactured by Tosoh Silica Co., Ltd., trade name “Nipsil VN3”, average primary particle size 40 nm, bulk density 0.20 g / ml
・ Cycilia 310P: White carbon powder manufactured by Fuji Syria, trade name “Cycilia 310P”, average primary particle size 30 nm, bulk density 0.15 g / ml
Crosslinking agent: manufactured by NOF Corporation, perhexyl D (di-t-hexyl peroxide)
Aluminum hydroxide: Heidilite H42 manufactured by Showa Denko

[Cold resistance test method for electric wires]
This was performed in accordance with JIS C3055. That is, the produced insulated wire was cut into a length of 38 mm to obtain a test piece. The test piece was mounted on a cold resistance tester, cooled to a predetermined temperature, hit with a hitting tool, and the state after hitting the test piece was observed. Using five test pieces, the temperature at which all five test pieces were broken was defined as the cold resistant temperature.

[Evaluation method of the appearance of electric wires]
The case where unevenness and roughness were not observed on the surface of the insulated wire was evaluated as “good”, and the case where unevenness and roughness were observed on the surface of the insulated wire was rated as “bad”.

[Wire wear resistance test method]
The test was conducted by the blade reciprocation method in accordance with the automobile technical standard “JASO D618”. That is, the insulated wire of an Example and a comparative example was cut out to the length of 750 mm, and it was set as the test piece. Then, at a room temperature of 23 ± 5 ° C., the blade is reciprocated at a speed of 50 mm / min with a length of 10 mm or more in the axial direction with respect to the coating material (insulating layer) of the test piece, and the number of reciprocations until contact with the conductor Was measured. At this time, the load applied to the blade was 7N. About the number of times, the thing of 200 times or more was made into the pass "(circle)", and the thing less than 200 times was made into the disqualified "x". In addition, “◎” is particularly excellent when the number of times is 300 times or more.

  As shown in Table 1, it was confirmed that all of the insulated wires of Examples 1 to 7 had excellent appearance and cold resistance and excellent wear resistance. In particular, when the content of the white carbon powder was 0.1 parts by mass or more with respect to 100 parts by mass of the silicone rubber, it was confirmed that the wear resistance was further improved.

  On the other hand, as shown in Table 2, the insulated wires of Comparative Examples 1 to 7 were foamed on the surface of the insulating layer and had poor appearance. In addition, the cold resistance and wear resistance of the insulated wires of Comparative Examples 1 to 7 are lower than those of the Examples as compared to the cold resistance and wear resistance of the corresponding insulated wires of Examples 1 to 7, respectively. It was.

  Moreover, about the composition of Examples 1-7 and Reference Example 1, the elastic modulus at the time of setting it as crosslinked silicone rubber was measured, and the result is shown in Table 1. It can be seen that in Examples 1 to 7, the elastic modulus is improved by adding white carbon as compared with Reference Example 1 in which white carbon is not added. The elastic modulus of the crosslinked silicone rubber was measured with a tensile tester after preparing a conductor-extracted sample.

Claims (5)

  In the insulated wire in which the periphery of the conductor is coated with an insulating layer containing a crosslinked silicone rubber, the insulating layer is a surface-treated magnesium hydroxide in which magnesium hydroxide is surface-treated with a surface treating agent made of an organic polymer, and white An insulated wire characterized by containing carbon powder.   2. The insulated wire according to claim 1, wherein a content of the white carbon powder is in a range of 0.1 to 100 parts by mass with respect to 100 parts by mass of the crosslinked silicone rubber.   The insulated wire according to claim 1 or 2, wherein a content of the surface-treated magnesium hydroxide is in a range of 0.1 to 100 parts by mass with respect to 100 parts by mass of the crosslinked silicone rubber.   The surface treatment agent is at least one selected from polyethylene, polypropylene, ethylene-ethyl acrylate copolymer, ethylene-vinyl acetate copolymer, and derivatives thereof. An insulated wire given in any 1 paragraph. 5. The surface treatment amount of the surface treatment agent with respect to the magnesium hydroxide is within a range of 0.1 to 10% by mass of a total amount of the surface treatment agent and the magnesium hydroxide. The insulated wire according to any one of the above.