Method for increasing the smoking temperature of insulated wire

Abstract

To provide an insulated wire having improved smoke generation property without increasing a conductor cross-section area and an insulated wire having excellent smoke generation property even in an aspect having a plurality of insulated layers.MEANS FOR SOLVING THE PROBLEM: It is characterized in that a total remaining amount of volatile organic compounds and semi-volatile organic compounds having boiling points in the range of 150°C. to 360°C. remaining in the insulated layer is 1500 ppm or less. In particular, when the insulated layer contains organopolysiloxane, low molecular weight cyclic siloxanes of D4 to D10 are reduced. In addition, in the case of an insulated wire in which the conductor is coated with at least two insulated layers including a first insulated layer and a second insulated layer, a total remaining amount of the volatile organic compounds and semi-organic compounds having the boiling point remaining in all the insulated layers is in the range of 150°C to 360°C is 1500 ppm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an insulated electric wire, and is particularly suitable for use in high voltage power cables used in automobiles. [Background technology]

[0002] Insulated wires used in vehicles such as automobiles are required to have various properties such as mechanical properties, flame retardancy, heat resistance, and cold resistance, and one of the required properties is smoke generation resistance.

[0003] Recently, electric vehicles that use electric motor drive and hybrid vehicles that use both motor drive and conventional gasoline engine drive have appeared. Vehicles that use such motor drive require a high voltage and large current supply to drive the motor. Insulated wires that supply high voltages and currents are prone to high temperatures, and the smoke generation characteristics of insulated wires generally decrease in high-temperature environments.

[0004] One method for improving smoke generation characteristics is to increase the conductor cross-sectional area of ​​the insulated wire to reduce heat generation when current is passed through it. However, insulated wires that supply high voltages and currents are often designed with a large conductor cross-sectional area to begin with, and further increasing the conductor cross-sectional area leads to the insulated wire becoming larger, making it difficult to secure space for installing the insulated wire and resulting in problems such as worsening fuel efficiency due to increased weight.

[0005] Known methods for reducing the amount of smoke emitted during combustion include a method in which halogens are not used in the insulating material used for the insulated wire (Patent Document 1), and a method in which a fluorine-containing elastomer composition is used that contains a base polymer that includes a tetrafluoroethylene-α-olefin copolymer obtained by polymerizing tetrafluoroethylene and an α-olefin having 2 to 4 carbon atoms (Patent Document 2).

[0006] However, these methods are intended to reduce the amount of smoke generated in an emergency situation such as when an insulated wire burns, and do not necessarily contribute to improving smoke generation characteristics, which are more important as a safety indicator before combustion occurs.

[0007] Furthermore, when there are multiple insulating layers as shown in FIG. 2, the smoke generation characteristics tend to be worse than insulated wires with only one insulating layer.

[0008] Some high-voltage power cables for automobiles have a configuration in which a shielding layer is provided around the first insulating layer and a second insulating layer is also provided, as shown in Figure 4, and there is a demand for improved smoke generation characteristics even in such high-voltage power cables. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-191845 [Patent Document 2] Japanese Patent Application Publication No. 2017-33784 Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide an insulated wire having improved smoke-generating properties without increasing the cross-sectional area of ​​the conductor, and to provide an insulated wire having excellent smoke-generating properties even in an embodiment having multiple insulating layers. [Means for solving the problem]

[0011] As a result of a detailed analysis of the smoke generation mechanism of insulated electric wires, the inventors have been able to solve the conventional problem by reducing the volatile components contained in the insulating layer and by focusing on the behavior of volatile organic compounds during treatment to reduce them, thereby suppressing the phenomenon of re-adsorption onto the inner insulating layer.

[0012] The present invention is an insulated wire having an insulating layer covering the periphery of a conductor, characterized in that the total amount of volatile organic compounds and semi-volatile organic compounds with boiling points in the range of 150°C to 360°C remaining in the insulating layer is 1500 ppm or less.

[0013] The present invention also provides an insulated wire having a conductor covered with at least two insulating layers, including a first insulating layer and a second insulating layer, characterized in that the total amount of volatile organic compounds and semi-volatile organic compounds with boiling points in the range of 150°C to 360°C remaining in all of the insulating layers is 1500 ppm or less. [Effects of the Invention]

[0014] According to the present invention, it is possible to improve smoke generation characteristics without increasing the cross-sectional area of ​​the conductor, and even insulated wires having multiple insulating layers can have good smoke generation characteristics. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a diagram showing the basic structure of an insulated wire according to the present invention. FIG. [Figure 2] FIG. 1 is a diagram showing an example of an insulated wire of the present invention having a plurality of insulating layers. [Figure 3] FIG. 2 is a diagram showing an example of an insulated wire of the present invention having a permeation suppressing layer. [Figure 4] FIG. 1 is a diagram showing an example of an insulated wire of the present invention having a shielding layer. [Figure 5] FIG. 1 is a diagram showing an example of an insulated wire of the present invention, having a permeation suppressing layer and a shielding layer. DETAILED DESCRIPTION OF THE INVENTION

[0016] The basic configuration of the present invention will be described below with reference to the accompanying drawings. In Fig. 1, 1 denotes an insulated wire of the present invention, 10 denotes a conductor, and 12 denotes an insulating layer. Note that the configuration of the present invention is not limited to Fig. 1 and can be modified within the scope of the concept of the present invention. A feature of the present invention is that the total amount of volatile organic compounds and semi-volatile organic compounds with boiling points in the range of 150°C to 360°C remaining in the insulating layer 12 is 1500 ppm or less.

[0017] Volatile organic compounds (VOCs) are a general term for organic compounds that exist in the atmosphere as gases and have boiling points of around 50 to 260°C, while semi-volatile organic compounds (SVOCs) are a general term for organic compounds that exist in the atmosphere as gases and have boiling points of around 260 to 400°C. Hereafter, unless otherwise specified, the term "VOC" will be used to refer to both volatile organic compounds and semi-volatile organic compounds.

[0018] The smoke generation characteristics of insulated wire 1 are measured by the test specified in the automotive standard JASO D609. Specifically, a certain length of insulated wire 1 is prepared as a sample and kept horizontally in an environment set at the test temperature. Several types of direct current are passed through the sample with different current values, and the time until smoke generation is confirmed is measured. Several test temperatures are set, and the relationship between the current value and the time when smoke generation begins is determined for each test temperature, and the results are used as the smoke generation characteristics of insulated wire 1.

[0019] In the smoke generation characteristic test, smoke is generated when an electric current is passed through the insulated wire 1 placed in a high-temperature environment, and the high temperature and heat generated by the current cause the insulating layer 12 to deteriorate, causing the deteriorated material of the insulating layer 12 to evaporate and scatter as visible smoke.

[0020] However, if VOCs remain in the insulating layer 12, the VOCs begin to evaporate and disperse before the heat resistance temperature of the insulating layer 12 or the short-time allowable temperature of the insulated wire 1 is reached, and the dispersed VOCs turn into visible smoke. Therefore, even if the insulated wire 1 and the insulating layer 12 have high heat resistance, there are situations in which the smoke-emitting characteristics deteriorate.

[0021] Therefore, by reducing the VOCs remaining in the insulating layer 12, smoke generated by the VOCs is reduced, and the insulating layer 12 can obtain smoke generation characteristics according to its inherent heat resistance, thereby improving the smoke generation characteristics of the insulated wire 1.

[0022] Insulated wires 1 that generally require smoke-emission characteristics are often also required to have heat resistance, and the smoke-emission characteristics (smoke temperature) of wires that have a heat resistance temperature of about 150 to 200°C are often required to be sufficiently higher than the heat resistance temperature. For this reason, reducing VOCs with a boiling point of 150°C or higher can effectively improve the smoke-emission characteristics of insulated wire 1.

[0023] Specifically, by keeping the remaining amount of VOCs with boiling points between 150°C and 360°C to 1,500 ppm or less, most of the VOCs that cause smoke in smoke characteristic tests are removed, thereby improving smoke characteristics.

[0024] As the amount of remaining VOCs decreases, smoke generation characteristics tend to improve, so it is more preferable to keep the amount of remaining VOCs with boiling points in the range of 150°C to 360°C to 1000 ppm or less.

[0025] The present invention can be particularly suitably used when the material constituting the insulating layer 12 contains organopolysiloxane.

[0026] A typical example of an insulating material containing organopolysiloxane is silicone rubber, which is known for its excellent flexibility, insulating properties, heat resistance, cold resistance, etc. Silicone rubber is usually made by compounding and kneading a silicone rubber compound with a vulcanizing agent, pigment, etc., and then heating and vulcanizing it under specified conditions to harden it before use.

[0027] Silicone rubber compounds are primarily composed of dimethylpolysiloxane, which is obtained by ring-opening polymerization of cyclic dimethylsiloxane tetramer (D4). However, because this ring-opening polymerization reaction is reversible, so-called low-molecular-weight cyclic siloxanes remain in the silicone rubber compound.

[0028] That is, when the material constituting the insulating layer 12 contains organopolysiloxane, low molecular weight cyclic siloxane remains in the insulating layer 12. Low molecular weight cyclic siloxane is a type of VOC, and is one of the factors that deteriorate the smoke generation characteristics of the insulated wire 1.

[0029] Generally, cyclic dimethylsiloxane trimer (D3) to cyclic dimethylsiloxane decamer (D10) are considered low-molecular-weight cyclic siloxanes. Among cyclic dimethylsiloxanes, the boiling point of D3 is 134°C at atmospheric pressure, and that of D4 is 175°C at atmospheric pressure. As the molecular weight increases to D5, D6, and so on, the boiling point increases, and the boiling point of D10 is estimated to be around 360°C at atmospheric pressure. Because the boiling point of D3 is relatively low, most of it evaporates during the manufacturing process of insulated electric wire 1, leaving only a small amount remaining, but D4 to D10 remain in larger amounts than D3.

[0030] The low-molecular-weight cyclic siloxane, which is one of the factors that reduces the smoke generation characteristics of the insulated wire 1, is not limited to cyclic dimethylsiloxane. The organic substituent bonded to the silicon atom of the siloxane bond is not limited to a methyl group, but also includes an ethyl group, a vinyl group, a phenyl group, and the like, and any combination of these groups is also possible. Furthermore, factors that reduce the smoke generation characteristics of insulated wire 1 include sublimable substances such as benzoic acid and derivatives of benzoic acid, in addition to low-molecular-weight cyclic siloxane.

[0031] Therefore, in an insulated wire 1 using an insulating layer 12 containing organopolysiloxane, the smoke generation characteristics of the insulated wire 1 can be improved by limiting the total residual amount of low molecular weight cyclic siloxanes D4 to D10, which are VOCs with boiling points in the range of 150°C to 360°C, to 1500 ppm or less.

[0032] As the material for the insulating layer 12 containing organopolysiloxane, various types of silicone rubber or a mixture of silicone rubber and other materials can be used.

[0033] When insulating layer 12 is a mixture of silicone rubber and other materials, the higher the silicone rubber content, the greater the amount of residual low molecular weight cyclic siloxane, which tends to worsen smoke-emission characteristics. However, even when the silicone rubber content is high, smoke-emission characteristics can be improved by keeping the total amount of residual low molecular weight cyclic siloxane with a boiling point in the range of 150°C to 360°C below 1500 ppm.

[0034] Even in the case of an insulating layer 12 made of silicone rubber alone, which originally contains a particularly large amount of residual low molecular weight cyclic siloxane, the smoke-producing characteristics can be improved by reducing the total amount of residual low molecular weight cyclic siloxane with a boiling point in the range of 150°C to 360°C to 1500 ppm or less, which is particularly effective when the insulating layer 12 is made of silicone rubber alone.

[0035] When the insulated wire 1 is constructed using the insulating layer 12 containing the organopolysiloxane, it is preferable that the amount of at least one of the low molecular weight cyclic siloxanes D4 to D6 remaining in the insulating layer 12 be 1000 ppm or less.

[0036] The low molecular weight cyclic siloxanes D4 to D6 belong to the volatile organic compounds, and despite their high boiling points, have high vapor pressures, making them relatively volatile even at room temperature and tending to account for the majority of VOCs remaining in insulating layer 12. By keeping the remaining amount of at least one of the low molecular weight cyclic siloxanes D4 to D6, which have such properties, to 1000 ppm or less, smoke generation characteristics are improved.

[0037] Although the effect of improving smoke generation characteristics can be obtained by making the remaining amount of at least one of the low molecular weight cyclic siloxanes D4 to D6 1000 ppm, it is preferable to make the remaining amount of D6 100 ppm or less in order to make the total remaining amount of the low molecular weight cyclic siloxanes 1500 ppm or less.It is more preferable that the total remaining amount of the low molecular weight cyclic siloxanes D4 to D6 is 100 ppm or less.

[0038] Of the low molecular weight cyclic siloxanes D4 to D6, a relatively large amount of D6 tends to remain in insulating layer 12, so smoke generation characteristics can be effectively improved by concentrating on reducing the amount of remaining D6. Furthermore, as the amount of remaining D6 decreases, the amounts of remaining D4 and D5 also tend to decrease, and smoke generation characteristics are further improved by keeping the total amount of remaining low molecular weight cyclic siloxanes D4 to D6 at 100 ppm or less.

[0039] When the insulated wire 1 is constructed using the insulating layer 12 containing organopolysiloxane, it is preferable in consideration of a practical design range that the total residual amount of the low molecular weight cyclic siloxanes D4 to D8 is 500 ppm or less.

[0040] In addition to the low molecular weight cyclic siloxanes D4 to D6, D7 and D8 The low molecular weight cyclic siloxane Since D8 is a VOC that is particularly likely to produce visible smoke in a smoke generation characteristic test, by concentrating on reducing the remaining amount of D8 and, concomitantly, reducing the remaining amount of D7, the smoke generation characteristic of the insulated wire 1 can be more effectively improved. It is desirable to keep the residual amount of low molecular weight cyclic siloxane in D8 at 300 ppm or less.

[0041] When the insulated wire 1 is constructed using the insulating layer 12 containing organopolysiloxane, it is more preferable that the total amount of the remaining low molecular weight cyclic siloxanes D4 to D10 is 400 ppm or less.

[0042] The low molecular weight cyclic siloxanes D9 and D10 tend to evaporate around 300°C, the short-term allowable temperature for typical silicone rubber insulated wires as defined in JCS (Japanese Electric Wire & Cable Makers' Association) Standard No. 168, and affect smoke generation characteristics at high temperatures. Taking into consideration the remaining amounts of D9 and D10, the total remaining amount of low molecular weight cyclic siloxane in D10 is set to 200 ppm or less, and by reducing the remaining amount of D9 as well, the smoke generation temperature of insulated wire 1 can be brought closer to the short-term allowable temperature for silicone rubber insulated wires, further improving smoke generation characteristics. It is desirable that the total amount of residual low molecular weight cyclic siloxanes D9 and D10 be 300 ppm or less.

[0043] The amount of VOC remaining in the insulating layer 12 can be reduced by the following methods.

[0044] (Method 1) The insulated wire 1 is heated at a predetermined temperature for a predetermined time to forcibly evaporate the VOCs in the insulating layer 12.

[0045] (Method 2) The insulated wire 1 is immersed in a solvent, and the VOCs in the insulating layer 12 are dissolved into the solvent.

[0046] (Method 3) A low-VOC insulating material is used for the insulating layer 12.

[0047] (Method 4) A material formed by mixing a material mainly containing organopolysiloxane with a low-VOC insulating material is used for the insulating layer 12.

[0048] Of the above-mentioned methods, method 1 is the most preferable. Method 1 can be used regardless of the type of insulating material, and can be carried out using a heating means such as a heating furnace, which is easy to handle industrially.

[0049] Furthermore, the insulated wire 1 of the present invention may contain substances other than VOCs that have the property of evaporating and scattering due to an increase in temperature. Therefore, in order to improve the smoke generation characteristics, it is preferable to reduce the amount of remaining substances other than VOCs.

[0050] Sublimation substances, other than VOCs, are substances that evaporate and disperse as the temperature rises. Sublimation substances change directly from a solid to a gas state as the temperature rises, making them prone to evaporation and dispersal, and like VOCs, they can cause visible smoke.

[0051] In the insulated wire 1 of the present invention, examples of sublimable substances that are likely to be contained in the insulating layer 12 include benzoic acid (boiling point: about 249° C.) and its derivatives.

[0052] Benzoic acid and its derivatives are generated as decomposition products of the organic peroxides used as reaction initiators when forming the silicone rubber insulating layer 12 using peroxide vulcanization, which has a high crosslinking rate, and are contained in the insulating layer 12. The main derivatives include 2,4-dichlorobenzoic acid (boiling point: approximately 200°C) and 4-methylbenzoic acid (boiling point: approximately 274°C).

[0053] Benzoic acid and its derivatives have a boiling point similar to that of VOCs and begin to sublimate at temperatures below the boiling point, so they are contained in the smoke generated in smoke characteristic tests and act to worsen the smoke characteristics.

[0054] As with VOCs, reducing the amount of sublimable substances remaining in insulating layer 12 reduces the amount of smoke generated by the sublimable substances, thereby enabling insulating layer 12 to obtain smoke generation characteristics that correspond to its inherent heat resistance, thereby improving the smoke generation characteristics of insulated wire 1.

[0055] Normally, the amount of sublimable substances remaining in the insulating layer 12 is small compared to the amount of VOCs remaining, and good smoke-generating properties can be obtained if the sum of the total amount of VOCs remaining in the insulating layer 12 with boiling points in the range of 150°C to 360°C and the total amount of sublimable substances remaining in the insulating layer 12 is 1500 ppm or less.

[0056] More preferably, the total amount of sublimable substances remaining in the insulating layer 12 is set to 300 ppm or less.

[0057] The amount of sublimable substance remaining in the insulating layer 12 can be reduced by the following methods.

[0058] (Method 1) The insulated wire 1 is heated at a predetermined temperature for a predetermined time to forcibly evaporate the sublimable substance in the insulating layer 12.

[0059] (Method 2) The insulated wire 1 is immersed in a solvent, and the sublimable substance in the insulating layer 12 is dissolved into the solvent.

[0060] (Method 3) When the insulating layer 12 is made of silicone rubber, the insulating layer 12 is formed of silicone rubber using a vulcanization method (addition vulcanization, etc.) that does not use organic peroxides.

[0061] Furthermore, an embodiment of the present invention having multiple insulating layers will be described with reference to the accompanying drawings. In Figures 2 to 5, 2 to 5 indicate the insulated wire of the present invention, 20 indicates a conductor, and 22 indicates an insulating layer. Of the insulating layers 22, 23 located on the inner periphery of the insulated wires 2 to 5 is a first insulating layer, and 24 located on the outer periphery of the first insulating layer 23 is a second insulating layer. Note that the configuration of the present invention is not limited to Figures 2 to 5 and can be modified within the scope of the concept of the present invention. Figures 2 to 5 show the first insulating layer 23 and the second insulating layer 24 as at least two insulating layers 22, but additional insulating layers may be provided. Each of the first insulating layer 23 and the second insulating layer 24 may have uniform physical properties within the layer, or may have physical properties that vary in the thickness direction and / or the length direction of the insulated wire.

[0062] A feature of the present invention is that the insulated wires 2 to 5 are coated around the conductor 20 with at least two insulating layers 22, including a first insulating layer 23 and a second insulating layer 24, and the total amount of volatile organic compounds and semi-volatile organic compounds with a boiling point in the range of 150°C to 360°C remaining in all insulating layers 22, including the first insulating layer 23, the second insulating layer 24, and any additional insulating layers, is 1500 ppm or less. In other words, the sum of the total amount of VOCs with a boiling point in the range of 150°C to 360°C remaining in the first insulating layer 23, the total amount of VOCs with a boiling point in the range of 150°C to 360°C remaining in the second insulating layer 24, and the total amount of VOCs with a boiling point in the range of 150°C to 360°C remaining in the third insulating layer and / or fourth insulating layer, if any, is 1500 ppm or less.

[0063] By keeping the sum of the remaining amounts of VOCs with boiling points in the range of 150°C to 360°C remaining in each of the first insulating layer 23 and the second insulating layer 24 at 1500 ppm or less, most of the VOCs that cause smoke generated in the smoke characteristic test are removed, thereby improving the smoke characteristic.

[0064] Since smoke generation characteristics tend to improve as the amount of remaining VOCs decreases, it is more preferable that the sum of the remaining amounts of VOCs with boiling points in the range of 150°C to 360°C remaining in each of the first insulating layer 23 and the second insulating layer 24 be 1000 ppm or less.

[0065] In addition, in the present invention, as shown in Figure 3, it is preferable to provide a permeation suppression layer 26 between the first insulating layer 23 and the second insulating layer 24, which exhibits low permeability to VOCs with boiling points in the range of 150°C to 360°C.

[0066] When reducing VOCs using the above method 1 or 2 for an insulated wire 2 having two insulating layers, the VOCs contained in the second insulating layer 24, which is the outermost layer, are reduced, but the presence of the second insulating layer 24 hinders the VOCs contained in the first insulating layer 23, which is located on the inside, and it takes time to sufficiently reduce them.

[0067] The above problem can be addressed by first treating the first insulating layer 23 to reduce VOCs and then providing the second insulating layer 24. However, in this case, when treating the second insulating layer 24 to reduce VOCs, some of the VOCs that have desorbed from the second insulating layer 24 may be re-adsorbed onto the first insulating layer 23, and the total amount of VOCs contained in the insulated wire 2 may not be significantly reduced.

[0068] As shown in Figure 3, by providing a permeation suppression layer 26 that exhibits low permeability to VOCs between the first insulating layer 23 and the second insulating layer 24, the phenomenon in which VOCs contained in the second insulating layer 24 are re-adsorbed onto the first insulating layer 23 is suppressed, contributing to a reduction in the total amount of VOCs contained in the insulated wire 3.

[0069] The permeation suppression layer 26 is selected from materials that have low permeability to the VOCs contained in the insulating layer and minimize VOC adsorption, and various metal materials, polyethylene, PET (polyethylene terephthalate), fluorine, etc. can be suitably used. From the viewpoint of suppressing the permeation of VOCs, crystalline materials with high gas barrier properties are particularly suitable. PET, which is prone to forming many crystalline regions due to its molecular structure, and metallic materials that form metallic crystals are particularly preferred. Among metallic materials, copper and aluminum are suitable, as they form a dense oxide film that has gas barrier properties.

[0070] One example of a method for providing the permeation suppressing layer 26 is to wrap a tape-like member such as a metal foil tape, a resin tape, or a metal-deposited resin tape around the first insulating layer 23. The wrapping method may be selected appropriately from the wrapping methods used for wrapping tape around electric wires and cables, such as horizontal wrapping or vertical wrapping.

[0071] When the permeation suppression layer 26 is provided by wrapping a tape-shaped member around the first insulating layer 23, it is preferable to wrap it so that it wraps at least 1 / 6 of the way around. By wrapping it at least 1 / 6 of the way around, the occurrence of gaps in the wrapped portion is suppressed, improving the permeation suppression function for VOCs. It is more preferable to wrap it at least 1 / 4 of the way around.

[0072] When using a tape-shaped member as the permeation suppression layer 26, it is preferable to use a member made of a solid material in order to ensure low permeability to VOCs, but a porous material may also be used as long as low permeability to VOCs can be maintained.

[0073] When a tape-shaped member is used as the permeation suppression layer 26, there is no particular limitation on the thickness of the member. A thicker member is preferable from the viewpoint of ensuring low permeability to VOCs, but a thinner member is acceptable if low permeability is ensured by the selected material, and a thinner member is preferable from the viewpoint of reducing the outer diameter of the insulated wire 3.

[0074] The members and modes used for the permeation suppressing layer 26 are not limited to those described above, and various members, materials and modes can be selected and used within the scope of the technical concept of the present invention. For example, there is an embodiment in which a coating layer exhibiting low permeability to VOCs is provided, such as by providing a metal vapor deposition on the outer periphery of the first insulating layer 23, or an embodiment in which the gaps present in the shield layer 28 in Figure 5 described below are filled with a material exhibiting low permeability to VOCs, making it serve as both the permeation suppression layer 26 and the shield layer 28.

[0075] The present invention is intended for use as a high-voltage power cable for automobiles. However, some insulated wires for this application have a shielding layer 28 as shown in FIG. 4 , and the insulated wire 4 of this embodiment usually has a first insulating layer 23 and a second insulating layer 24. The present invention can be particularly suitably used to improve the smoke generation characteristics of an insulated wire 4 having a shielding layer 28 as shown in FIG.

[0076] When the insulated wire 5 of the present invention is constructed by providing both the permeation suppression layer 26 and the shielding layer 28, an embodiment in which the permeation suppression layer 26 is provided between the shielding layer 28 and the second insulating layer 24 (Figure 5), or an embodiment in which the permeation suppression layer is provided between the first insulating layer and the shielding layer (not shown) can be appropriately selected and used.

[0077] Furthermore, the insulated wires 2 to 5 of the present invention can be particularly suitably used when the material constituting at least one of the first insulating layer 23 and the second insulating layer 24 contains organopolysiloxane.

[0078] Insulated wires 2 to 5 using insulating layers containing organopolysiloxane, the smoke generation characteristics of insulated wires 2 to 5 can be improved by setting the sum of the remaining amounts of low molecular weight cyclic siloxanes D4 to D10, which are VOCs with boiling points in the range of 150°C to 360°C, remaining in first insulating layer 23 and second insulating layer 24 to 1500 ppm or less.

[0079] When insulating layer 22 is a mixture of silicone rubber and other materials, the higher the silicone rubber content, the greater the amount of remaining low molecular weight cyclic siloxane, which tends to worsen smoke-producing characteristics. However, even when the silicone rubber content is high, smoke-producing characteristics can be improved by keeping the sum of the remaining amounts of low molecular weight cyclic siloxanes with boiling points in the range of 150°C to 360°C in first insulating layer 23 and second insulating layer 24 to 1500 ppm or less.

[0080] Even if the insulating layer is originally made of silicone rubber alone, which contains a particularly large amount of low molecular weight cyclic siloxane, the smoke-producing characteristics can be improved by keeping the total amount of low molecular weight cyclic siloxane with a boiling point in the range of 150°C to 360°C remaining in each of the first insulating layer 23 and the second insulating layer 24 to 1500 ppm or less, which is particularly effective when the insulating layer 22 is made of silicone rubber alone.

[0081] When the insulated wires 2 to 5 are constructed using an insulating layer containing an organopolysiloxane, the total amount of the low molecular cyclic siloxanes D4 to D6 remaining in the insulating layer is preferably 100 ppm or less.

[0082] The low molecular weight cyclic siloxanes D4 to D6 are volatile organic compounds that have a high vapor pressure despite their high boiling points, making them relatively prone to volatilization even at room temperature. By keeping the total remaining amount of low molecular weight cyclic siloxanes D4 to D6, which have such properties, to 100 ppm or less, smoke generation characteristics are improved.

[0083] When insulated wires 2 to 5 are constructed using an insulating layer containing organopolysiloxane, it is preferable in consideration of practical design that the total residual amount of low molecular weight cyclic siloxanes D4 to D8 be 500 ppm or less.

[0084] Since the low molecular weight cyclic siloxanes D4 to D8 are VOCs that are particularly likely to produce visible smoke in the smoke generation characteristics test, the smoke generation characteristics of insulated wires 2 to 5 can be more effectively improved by concentrating on reducing the remaining amounts of these VOCs.

[0085] When the insulated wires 2 to 5 are constructed using an insulating layer containing an organopolysiloxane, it is more preferable that the total amount of the remaining low molecular cyclic siloxanes D4 to D10 is 1000 ppm or less.

[0086] The low molecular weight cyclic siloxanes D9 and D10 tend to evaporate around 300°C, the short-term allowable temperature for typical silicone rubber insulated wires as defined in JCS (Japanese Electric Wire & Cable Makers' Association) Standard No. 168, and affect smoke generation characteristics at high temperatures. By taking into consideration the remaining amounts of D9 and D10 and keeping the total remaining amount of low molecular weight cyclic siloxanes D4 to D10 at 1,000 ppm or less, the smoke generation temperature of insulated wires 2 to 5 can be brought closer to the short-term allowable temperature for silicone rubber insulated wires, further improving smoke generation characteristics.

[0087] When there is only one insulating layer containing organopolysiloxane, it is sufficient that the insulating layer satisfies the above-mentioned preferable remaining amount of low molecular weight cyclic siloxane.

[0088] When there are multiple insulating layers containing organopolysiloxane, it is preferable that the sum of the total amounts of low molecular weight cyclic siloxane remaining in each layer, i.e., the total amount of low molecular weight cyclic siloxane remaining in the entire insulated wire, is the preferred remaining amount.

[0089] Although details are omitted, even in the case of multiple insulating layers (insulated wires 2 to 5), the effect of reducing the remaining amount of substances other than VOCs, such as benzoic acid and its derivatives, which are sublimable substances, is expected.

[0090] As will be described later, the insulated wires 1 to 5 of the present invention described above have high smoke generation properties compared to conventional insulated wires. [Example]

[0091] Examples of the present invention will be described below. It should be noted that Example 1 will be referred to as Reference Example 1, and Example 4 will be referred to as Reference Example 4.

[0092] [Example 1] An insulated wire 1 having a single insulating layer 12 as shown in FIG. 1 was produced. Specifically, first, a child stranded conductor was prepared by twisting together nine soft copper wires with a diameter of 0.32 mm, and then 19 of these child stranded conductors were twisted together in a concentric twist structure to form a conductor 10 with a cross-sectional area equivalent to 15 mm2 and a diameter of 5.1 mm. Next, using an extrusion molding machine, the outer periphery of the conductor 10 was coated with silicone rubber to form the insulating layer 12 to a thickness of 1.0 mm, and then heat treatment was carried out to crosslink the silicone rubber, thereby obtaining an insulated wire 1 with an outer diameter of 7.1 mm.

[0093] Next, the insulated wire 1 was cut to a length of 2000 mm and heated in a heating furnace at 90°C for 11 hours and then at 150°C for 11 hours, thereby evaporating the VOCs in the insulating layer 12 and obtaining the insulated wire 1-1 of Example 1. When the amount of VOCs remaining in the insulating layer 12 was measured by the method described below, the total amount of low molecular weight cyclic dimethylsiloxanes D4 to D10 was 987 ppm, of which the total amount of D4 to D6 was 42 ppm, the total amount of D7 and D8 was 324 ppm, and the total amount of D9 and D10 was 621 ppm.

[0094] [Example 2] An insulated wire 1 identical to that of Example 1 was cut to a length of 2000 mm, immersed in acetone at room temperature for 3 hours, thoroughly dried at room temperature, and then heated under the same conditions as in Example 1 to obtain an insulated wire 1-2 of Example 2. The VOCs remaining in the insulating layer 12 were low molecular weight cyclic dimethylsiloxanes D4 to D10, with the total amount of D4 to D6 being 25 ppm, D7 and D8 being 138 ppm, and D9 and D10 being 196 ppm.

[0095] [Example 3] An insulated wire 1 similar to that of Example 1 was produced using silicone rubber whose VOC content had been reduced by previously subjecting it to heat treatment at 90°C for 5 hours, and the silicone rubber was then subjected to the same VOC reduction treatment as in Example 2, yielding an insulated wire 1-3 of Example 3. The VOCs remaining in insulating layer 12 were low molecular weight cyclic dimethylsiloxanes D4 to D10, with the total amount of D4 to D6 being 31 ppm, D7 and D8 being 33 ppm, and D9 and D10 being 134 ppm.

[0096] [Comparative Example 1] An insulated wire 1'-1 of Comparative Example 1 was the same as that of Example 1, except that it was not subjected to VOC reduction treatment. The VOCs remaining in insulating layer 12 were low molecular weight cyclic dimethylsiloxanes D4 to D10, with the total amount of D4 to D6 being 7430 ppm, D7 and D8 being 1909 ppm, and D9 and D10 being 759 ppm.

[0097] [Example 4] A child stranded conductor was prepared by twisting together 23 soft copper wires with a diameter of 0.32 mm, and 19 of these child stranded conductors were twisted together in a concentric twist structure to form a conductor 10 with a cross-sectional area equivalent to 35 mm2 and a diameter of 8.1 mm. Next, using an extrusion molding machine, the outer periphery of the conductor 10 was coated with silicone rubber to form the insulating layer 12 to a thickness of 1.3 mm, and then heat treatment was performed to crosslink the silicone rubber, thereby obtaining an insulated wire 1 with an outer diameter of 10.7 mm.

[0098] Next, the insulated wire 1 was heated under the same conditions as in Example 1 to evaporate the VOCs in the insulating layer 12, thereby obtaining an insulated wire 1-4 of Example 4. With regard to the VOCs remaining in the insulating layer 12, the total amount of low molecular weight cyclic dimethylsiloxanes D4 to D10 was 951 ppm, of which the total amount of D4 to D6 was 19 ppm, the total amount of D7 and D8 was 318 ppm, and the total amount of D9 and D10 was 614 ppm, which are the same remaining amounts as in Example 1.

[0099] [Example 5] The same insulated wire 1 as in Example 4 was immersed in acetone and heated under the same conditions as in Example 2 to obtain an insulated wire 1-5 of Example 5. With regard to the VOCs remaining in the insulating layer 12, the total amount of low molecular weight cyclic dimethylsiloxanes D4 to D10 was 361 ppm, of which the total amount of D4 to D6 was 30 ppm, the total amount of D7 and D8 was 94 ppm, and the total amount of D9 and D10 was 237 ppm, which are the same remaining amounts as in Example 2.

[0100] [Example 6] An insulated wire 1 similar to that of Example 4 was produced using silicone rubber whose VOC content had been reduced by previously subjecting it to heat treatment at 90°C for 5 hours, and the silicone rubber was then subjected to the same VOC reduction treatment as in Example 3, yielding an insulated wire 1-6 of Example 6. The VOCs remaining in insulating layer 12 were 201 ppm in total for low molecular weight cyclic dimethylsiloxanes D4 to D10, of which the total for D4 to D6 was 35 ppm, the total for D7 and D8 was 31 ppm, and the total for D9 and D10 was 135 ppm, which are the same remaining amounts as in Example 3.

[0101] Comparative Example 2 An insulated wire 1'-2 of Comparative Example 2 was the same as that of Example 3, except that it was not subjected to VOC reduction treatment. The VOCs remaining in insulating layer 12 were 10,142 ppm in total for low molecular weight cyclic dimethylsiloxanes D4 to D10, of which D4 to D6 were 7,563 ppm in total, D7 and D8 were 1,843 ppm in total, and D9 and D10 were 736 ppm in total, which were the same remaining amounts as in Comparative Example 1.

[0102] [VOC residual amount measurement method] The amount of VOC (low molecular weight cyclic siloxane) remaining in the insulating layer 12 of each of the insulated wires of the examples and comparative examples was measured by gas chromatography using acetone extraction. The specific method is described below.

[0103] The insulating layer 12 collected from the insulated wire is cut into small pieces, and then 0.5 mg of the shredded piece is weighed out and placed in a 10 ml sample bottle.

[0104] Five ml of acetone was poured into the sample bottle so that the shredded insulating layer 12 was immersed, and ultrasonic treatment was carried out for 30 minutes to elute the VOC into the acetone.

[0105] 1 μl of the acetone from which the VOCs had eluted was sampled, introduced into a gas chromatograph, heated, and compared with a calibration curve prepared in advance using standard samples of known concentrations to measure the amount of low molecular weight cyclic siloxanes D4 to D10. The heating conditions for gas chromatography were as follows: hold at 40°C for 1 minute → heat to 80°C at a rate of 10°C / min → heat to 120°C at a rate of 20°C / min → heat to 310°C at a rate of 7°C / min and hold for 10 minutes.

[0106] [Method for measuring residual amount of sublimable substance] For the insulated wires of Example 4 and Comparative Example 2, the amounts of sublimable substances (benzoic acid and its derivatives) remaining in the insulating layer 12 were measured by thermal desorption gas chromatography. The specific method is described below.

[0107] The insulating layer 12 is collected from the insulated wire, and 15 mg is weighed out and placed in a sample tube of a thermal desorption device.

[0108] The thermal desorption device is operated under the conditions shown in Table 1 to generate gas from the sample.

[0109] [Table 1]

[0110] The generated gas was introduced into a gas chromatograph, and the amount of benzoic acid and its derivatives was measured by comparing with a calibration curve prepared in advance using standard samples of known concentrations. The heating conditions for gas chromatography were: hold at 40°C for 7 minutes, heat to 120°C at a rate of 10°C / min, heat to 270°C at a rate of 20°C / min, and hold for 30 minutes.

[0111] [Smoke generation characteristics test] The smoke generation characteristics were confirmed with reference to the automotive standard JASO D609. Normally, smoke generation characteristics are measured by summarizing the relationship between current values ​​at various temperatures and the time it takes for smoke generation to begin. However, in this application, a current was passed through the insulated wire 1 at room temperature, and the current value was gradually increased until smoke generation occurred. The temperature of the insulated wire 1 and the magnitude of the current value were used as indicators of smoke generation characteristics. The specific test method is as follows.

[0112] (1. Sample Preparation) The insulated wire 1 was cut into a length of 1000 mm, and the insulating layer 12 was removed from both ends by a length of 20 mm to prepare a sample. A thermocouple was used to measure the surface temperature of the insulating layer 12 at a position 50 mm to the left of the center of the sample, and a thermocouple was used to measure the conductor temperature at a position 50 mm to the right of the center of the sample.

[0113] (2. Measurement environment) Measurements were taken at room temperature (27±5°C).

[0114] (3. Recording of current application and smoke temperature) A constant voltage / constant current DC power supply is connected to the removed portions of the insulating layer 12 at both ends of the insulated wire 1, and a predetermined initial current set according to the conductor cross-sectional area is passed through it, and the conductor is left to stand until the temperature becomes constant. After the conductor temperature became constant, the current value was increased by 10 A every 5 minutes. As the current value increased, the conductor temperature and the surface temperature of the insulating layer also increased, and the conductor temperature at which smoke was confirmed to be coming from the insulating layer 12 was recorded as the smoke temperature. The results of each example and comparative example are shown in Table 2.

[0115] [Table 2]

[0116] "<5" in Table 2 indicates that the amount was below the detection limit and is not included in the total residual amount.

[0117] The insulated wire 1'-1 of Comparative Example 1, which was not subjected to VOC reduction treatment, emitted smoke at 220 A and 210°C, whereas the insulated wire 1-1 of Example 1, which was subjected to VOC reduction treatment and had a total residual VOC amount of 1500 ppm or less, especially a total residual amount of D4 to D6 of 100 ppm or less and a total residual amount of D7 and D8 of 500 ppm or less, emitted smoke at 250 A and 260°C, confirming that the reduction in VOCs improved the smoke generation characteristics.

[0118] Insulated wire 1-2 of Example 2, which had an additional VOC reduction process to reduce the total residual amount of D9 and D10 to 300 ppm or less, emitted smoke at 270 A and 300° C., confirming further improvement in smoke emission characteristics.

[0119] Insulated wire 1-3 of Example 3, which had an additional VOC reduction process to reduce the total residual amount of D4 to D10 to about 200 ppm, emitted smoke at 270 A and 300° C., and had smoke emission characteristics equivalent to those of Example 2. From the above results, it can be said that sufficient smoke generation characteristics can be obtained by reducing the amount of low molecular weight cyclic siloxane so that the total amount of remaining D9 and D10 is 300 ppm or less.

[0120] The insulated wire 1'-2 of Comparative Example 2, which was not subjected to VOC reduction treatment and had a larger conductor cross-sectional area than the insulated wire 1'-1 of Comparative Example 1, emitted smoke at 380A and 200°C. Because the conductor cross-sectional area is larger than in Comparative Example 1, the temperature rise when the same current is applied is more gradual than in Comparative Example 1, and as a result, it is thought that the current value that can be passed before smoking is generated has increased.

[0121] On the other hand, the smoke generation characteristics of the insulated wire 1'-2 of Comparative Example 2 were found to be worse than those of the insulated wire 1'-1 of Comparative Example 1. In a typical insulated wire, as the cross-sectional area of ​​the conductor 10 increases, the thickness required for the insulating layer 12 also increases. Furthermore, even if the thickness of insulating layer 12 is designed to be the same, the amount of insulating layer 12 increases because the outer diameter of insulating layer 12 increases as the cross-sectional area of ​​conductor 10 increases. In the case of insulated wire 1'-2 of Comparative Example 2, the amount of insulating layer 12 per unit length is approximately twice that of insulated wire 1'-1 of Comparative Example 1.

[0122] Since the conductor temperature at which smoke generation is visually confirmed is taken as the smoke generation temperature, the greater the absolute amount of VOC remaining in the sample, the easier it is to visually detect smoke generation, which tends to be disadvantageous for the smoke generation characteristic test. Even if the amount of VOC remaining per unit weight of the insulating layer 12 is the same, the absolute amount of VOC remaining in the insulating layer 12 is proportional to the amount of the insulating layer 12, so it is thought that the absolute amount of VOC remaining in the insulated wire 1'-2 of Comparative Example 2 is about twice the amount remaining in the insulated wire 1'-1 of Comparative Example 1. As a result, it is thought that the insulated wire 1'-2 of Comparative Example 2 began to generate smoke at a lower temperature in the measurement.

[0123] The insulated wire 1-4 of Example 4, which can be said to be a configuration in which the VOC reduction treatment was performed on the insulated wire 1'-2 of Comparative Example 2 to reduce the total residual VOC amount to 1500 ppm or less, and in particular the total residual amount of D4 to D6 to 100 ppm or less, and the total residual amount of D7 and D8 to 500 ppm or less, emitted smoke at 440 A and 250°C, confirming the improvement in smoke generation characteristics due to the reduction in VOCs.

[0124] Additionally, the amount of benzoic acid and its derivatives remaining in insulated wire 1-4 of Example 4 was significantly reduced compared to insulated wire 1'-2 of Comparative Example 2, and the sum of the remaining amounts of D4 to D10 was 1500 ppm or less. Furthermore, the total amount of remaining benzoic acid and its derivatives was 300 ppm or less. In insulated wire 1-4 of Example 4, the amount of sublimable benzoic acid and its derivatives was also reduced during the VOC reduction treatment, which is thought to contribute to the improvement of smoke generation characteristics.

[0125] Insulated wire 1-5 of Example 5, which had an additional VOC reduction treatment step to reduce the total residual amount of D9 and D10 to 300 ppm or less, emitted smoke at 520 A and 300° C., confirming further improvement in smoke emission characteristics.

[0126] Furthermore, insulated wire 1-6 of Example 6, which had an additional VOC reduction process to reduce the remaining amount of D4 to D10 to about 200 ppm, emitted smoke at 520 A and 300° C., and had the same smoke emission characteristics as insulated wire 1-5 of Example 5. From the above results, it can be said that even if the amount of insulating layer 12 increases with an increase in the cross-sectional area of ​​conductor 10, sufficient smoke generation characteristics can be obtained by reducing the low molecular weight cyclic siloxane so that the remaining amounts of D9 and D10 are 300 ppm or less.

[0127] Although there was a difference in the current value that could be passed before smoking occurred due to the difference in cross-sectional area of ​​the conductor 10, the insulated wire 1-2 of Example 2 and the insulated wire 1-5 of Example 5 had the same smoking temperature. The insulated wire 1-5 of Example 5 had the same smoke temperature as the insulated wire 1-2 of Example 2, despite the increased amount of insulating layer 12. This suggests that by setting the total remaining amount of D9 and D10 to 300 ppm or less, the VOCs do not reach a concentration that is visible as smoke when they volatilize and disperse into the air, and a smoke temperature that is not dependent on the remaining amount of VOCs originally contained in the insulated wire 1 can be obtained.

[0128] Comparing Comparative Example 1 with Examples 1 to 3, an improvement in smoke generation characteristics of approximately 24 to 43% was confirmed. This means that it is possible to improve the safety of the insulated wire 1 against heat generation without increasing the cross-sectional area of ​​the conductor 10, and it can be said that the present invention has made it possible to provide a highly reliable insulated wire 1.

[0129] Furthermore, since Example 1 has a higher smoke-generating temperature than Comparative Example 2, it can be said that the cross-sectional area of ​​conductor 10 was reduced without reducing safety based on the smoke-generating characteristics, and that the present invention has made it possible to achieve both smoke-generating characteristics and a thinner diameter for insulated wire 1.

[0130] The insulated wire 1 of the present invention is provided with various modifications to the configuration and cross-sectional area of ​​the conductor 10 and the thickness and outer diameter of the insulating layer 12 depending on the application and location of use.

[0131] Below is shown an embodiment of the invention having two insulating layers 23, 24.

[0132] [Example 7] A sub-stranded conductor was prepared by twisting together 19 annealed copper wires with a diameter of 0.32 mm. 53 of these sub-stranded conductors were twisted together in a concentric twist structure to form a conductor with a cross-sectional area of ​​95 mm. 2 A conductor 20 having a diameter of 14 mm was formed. Next, using an extrusion molding machine, the outer circumference of the conductor 20 was coated with silicone rubber to form the first insulating layer 23 with a thickness of 1.2 mm, and then heat treatment was performed to cross-link the silicone rubber, resulting in a first insulating layer 23 with an outer diameter of 16.4 mm.

[0133] The conductor 20 coated with the first insulating layer 23 was immersed in acetone at room temperature for 3 hours, thoroughly dried at room temperature, and then heated in a heating furnace at 90°C for 11 hours and 150°C for 11 hours, to evaporate the VOCs in the first insulating layer 23.

[0134] Next, a shield layer 28 is provided on the outer periphery of the first insulating layer 23. The shield layer 28 has a braided structure, and the shield wires used are tin-plated annealed copper wires with an outer diameter of 0.2 mm.

[0135] Next, an aluminum-deposited PET tape was wound around the outer periphery of the shielding layer 28 to form the permeation suppressing layer 26 .

[0136] Next, an extrusion molding machine was used to coat the outer periphery of permeation suppressing layer 26 with silicone rubber to form second insulating layer 24 to a thickness of 1.5 mm, and then heat treatment was performed to crosslink the silicone rubber to form second insulating layer 24, thereby completing insulated wire 5. The outer diameter of insulated wire 5 was finally 20 mm.

[0137] Finally, the insulated wire 5 having the second insulating layer 24 formed thereon is subjected to the same VOC reduction treatment as that for the first insulating layer 23 to reduce the VOCs in the second insulating layer 24, thereby completing the insulated wire 5 of the present invention shown in Figure 5.

[0138] When the amount of VOC remaining in the first insulating layer 23 was measured using the method described below, the total amount of low molecular weight cyclic dimethylsiloxanes D4 to D10 was 316 ppm, of which the total amount of D4 to D8 was 124 ppm and the total amount of D4 to D6 was 39 ppm.

[0139] Similarly, the amount of VOC remaining in the second insulating layer 24 was measured, and the total amount of low molecular weight cyclic dimethylsiloxanes D4 to D10 was 402 ppm, of which the total amount of D4 to D8 was 166 ppm and the total amount of D4 to D6 was 47 ppm.

[0140] That is, the total amount of VOCs remaining in insulated wire 5 was 718 ppm for the low molecular weight cyclic dimethylsiloxanes D4 to D10, of which the total amount of D4 to D8 was 290 ppm and the total amount of D4 to D6 was 86 ppm.

[0141] [Reference Example] An insulated wire of a reference example was prepared by omitting the VOC reduction treatment for the second insulating layer 24 in the insulated wire 5 of Example 7. When the amount of VOC remaining in the second insulating layer 24 of the insulated wire of the reference example was measured, the total amount of low molecular weight cyclic dimethylsiloxanes D4 to D10 was 2185 ppm, of which the total amount of D4 to D8 was 1420 ppm and the total amount of D4 to D6 was 347 ppm.

[0142] Comparative Example 3 An insulated wire of Comparative Example 3 was prepared using the same materials and steps as in Example 7, except that the permeation suppression layer 26 was not provided. The VOCs remaining in the first insulating layer 23 of the insulated wire of Comparative Example 3 were low molecular weight cyclic dimethylsiloxanes D4 to D10 with a total amount of 1403 ppm, of which D4 to D8 was 847 ppm and D4 to D6 was 221 ppm.The VOCs remaining in the second insulating layer 24 were low molecular weight cyclic dimethylsiloxanes D4 to D10 with a total amount of 1300 ppm, of which D4 to D8 was 715 ppm and D4 to D6 was 211 ppm.

[0143] [Reference comparison example] An insulated wire of Comparative Example 3 was prepared by omitting the VOC reduction treatment on the second insulating layer 24, to prepare an insulated wire of Reference Comparative Example. The VOCs remaining in the first insulating layer 23 of the insulated wire of the reference comparative example were low molecular weight cyclic dimethylsiloxanes D4 to D10 with a total amount of 2277 ppm, of which D4 to D8 was 1561 ppm and D4 to D6 was 499 ppm.The VOCs remaining in the second insulating layer 24 were low molecular weight cyclic dimethylsiloxanes D4 to D10 with a total amount of 2434 ppm, of which D4 to D8 was 1660 ppm and D4 to D6 was 507 ppm.

[0144] [Reference example 1] The insulated wire 5 of Example 7, which had been subjected to the VOC reduction treatment of the first insulating layer 23, was used as the insulated wire of Reference Example 1. Of the VOCs remaining in first insulating layer 23 of the insulated wire of Reference Example 1, the total amount of low molecular weight cyclic dimethylsiloxanes D4 to D10 was 359 ppm, of which the total amount of D4 to D8 was 163 ppm and the total amount of D4 to D6 was 25 ppm.

[0145] [Reference example 2] The insulated wire 5 of Example 7, which was processed up to the formation of the first insulating layer 23, that is, the insulated wire of Reference Example 1 from which the VOC reduction treatment was omitted, was used as the insulated wire of Reference Example 2. Of the VOCs remaining in first insulating layer 23 of the insulated wire of Reference Example 2, the total amount of low molecular weight cyclic dimethylsiloxanes D4 to D10 was 2616 ppm, of which the total amount of D4 to D8 was 1732 ppm and the total amount of D4 to D6 was 244 ppm.

[0146] [VOC residual amount measurement method] The amount of VOC (low molecular weight cyclic siloxane) remaining in the insulating layer 22 (first insulating layer 23 or second insulating layer 24) of each insulated wire in each Example, Comparative Example, and Reference Example was measured by gas chromatography using acetone extraction to measure the amount of low molecular weight cyclic dimethylsiloxane D3 to D10. The specific method was the same as the measurement method in Examples 1 to 6 and Comparative Examples 1 and 2 above.

[0147] [Smoke generation characteristics test] The smoke generation characteristics were confirmed with reference to the automotive standard JASO D609. Normally, the smoke generation characteristics are measured by summarizing the relationship between the current value and the time when smoke generation begins at various temperatures. However, in this application, a constant current was passed through the insulated wire 5 at room temperature, and the magnitude of the conductor temperature of the insulated wire 5 when smoke generation occurred was used as an index of the smoke generation characteristics. The specific test method is as follows.

[0148] (1. Sample Preparation) The insulated wire 5 was cut to a length of 1000 mm, and the insulating layer 22 was removed from both ends by a length of 20 mm to prepare a sample. A thermocouple was provided at the center of the sample to measure the conductor temperature.

[0149] (2. Measurement environment) Measurements were taken at room temperature (27±5°C).

[0150] (3. Recording of current application and smoke temperature) A constant voltage / constant current DC power supply was connected to the removed portions of the insulating layer 22 on both ends of the insulated wire 5, and a current of 900 A was passed through it. The conductor temperature when smoke was confirmed to be emitted from the insulating layer 22 was recorded as the smoke emission temperature. The results of each example, comparative example, and reference example are shown in Table 3.

[0151] [Table 3]

[0152] "<5" in Table 3 indicates that the amount was below the detection limit and is not included in the total residual amount.

[0153] The amounts of VOCs remaining in the first insulating layer 23 and the second insulating layer 24 of the insulated wire 5 of Example 7 were both similar to those of Reference Example 1, and the smoke temperature was also equal to or higher than that of Reference Example 1, which is an insulated wire having one insulating layer 22 that had been treated to reduce VOCs. In addition, no smoke was observed in the insulated wire 5 of Example 7 at 280°C. If the temperature were increased any further, the short-term allowable temperature of 300°C would be approached, and smoke would be generated due to thermal decomposition of the insulating layer itself. This smoke could not be clearly distinguished from smoke caused by VOCs, so the smoke generation temperature was set at 280°C or higher.

[0154] Furthermore, when the amount of remaining VOCs in the reference example and example 7 is compared, there is no change in the amount of VOCs remaining in first insulating layer 23 before and after the VOC reduction treatment on second insulating layer 24, and only the amount of VOCs remaining in second insulating layer 24 decreases. From this result, it was confirmed that the presence of permeation suppression layer 26 suppresses the phenomenon in which some of the VOCs desorbed from second insulating layer 24 are re-adsorbed onto first insulating layer 23 during the VOC reduction treatment on second insulating layer 24, and contributes to a reduction in the total amount of VOCs contained in the insulated wire.

[0155] On the other hand, the VOCs remaining in the first insulating layer 23 and the second insulating layer 24 of the insulated wire of Comparative Example 3 both exceeded 1000 ppm, and although the VOCs remaining in each of the first insulating layer 23 and the second insulating layer 24 were less than those in Reference Example 2, the total amount of VOCs remaining in the first insulating layer 23 and the second insulating layer 24 was similar to that in Reference Example 2. The smoke temperature was 220°C, which was not significantly different from that of Reference Example 2, which was an insulated wire having a single insulating layer 22 that had not been treated to reduce VOCs.

[0156] Furthermore, looking at the results of the reference comparative example, even though the first insulating layer 23 had been subjected to a VOC reduction treatment in advance, by the time the second insulating layer 24 was provided, the amount of VOC remaining in the first insulating layer 23 was about the same as that in the second insulating layer 24. From this, it is thought that since the insulated wire of the reference comparative example does not have a permeation suppression layer 26 between the first insulating layer 23 and the second insulating layer 24, during the process of coating and cross-linking the second insulating layer 24, VOCs that have desorbed from the second insulating layer 24 migrate to the first insulating layer 23, thereby increasing the amount of VOCs remaining in the first insulating layer 23.

[0157] Comparing the residual VOC amounts of the Reference Comparative Example and Comparative Example 3, it can be confirmed that the VOC reduction treatment of the insulated wire of the Reference Comparative Example reduced the residual VOC amount of the insulated wire of the Comparative Example, but the reduction was so small that it did not significantly contribute to improving smoke generation characteristics. For this reason, since the insulated wire of the reference comparative example does not have the permeation suppression layer 26 between the first insulating layer 23 and the second insulating layer 24, when the second insulating layer 24 is subjected to VOC reduction treatment to make the insulated wire of the comparative example, a phenomenon occurs in which some of the VOCs that have detached from the second insulating layer 24 are re-adsorbed onto the first insulating layer 23, and it is thought that this limits the effect of reducing the total amount of VOCs contained in the insulated wire.

[0158] The insulated wire of the present invention is provided with various modifications to the configuration and cross-sectional area of ​​the conductor 20, the thickness and outer diameter of the first insulating layer 23 and the second insulating layer 24, and the form of the permeation suppression layer 26 and the shielding layer 28 depending on the application and location of use.

[0159] This application is based on Japanese Patent Application No. 2018-150855 filed on August 9, 2018, and Japanese Patent Application No. 2018-247461 filed on December 28, 2018. The entire specifications, claims, and drawings of Japanese Patent Application No. 2018-150855 and Japanese Patent Application No. 2018-247461 are incorporated herein by reference. [Industrial Applicability]

[0160] The above example is merely one example of the present invention, and it goes without saying that various modifications and applications are possible within the scope of the concept of the present invention, and that the present invention may be provided with appropriate modifications. The present invention is particularly suitable for high-voltage power cables used in automobiles, electrical and electronic equipment, etc., but its applications are not limited to these. In situations where smoke-free properties are required, the present invention may also be applied to low-voltage cables, insulated wires, etc. [Explanation of symbols]

[0161] 1, 2, 3, 4, 5 insulated wire 10, 20 conductors 12, 22 Insulation layer 23 First insulating layer 24 Second insulating layer 26 Transmission suppression layer 28 Shielding Layer

Claims

1. 1. A method for improving the smoke-generating temperature of an insulated electric wire whose smoke-generating temperature is lower than a short-term allowable temperature and whose temperature difference between the short-term allowable temperature and the smoke-generating temperature is greater than 50°C, comprising: The insulated wire has a configuration in which a conductor is covered with an insulating layer containing organopolysiloxane, and after the conductor is covered with the insulating layer, a treatment step is carried out in which the conductor is heated at a temperature of 90°C to 150°C for a total of 22 hours or more; The total amount of low molecular weight cyclic siloxanes D4 to D10 remaining in the insulating layer, which have boiling points in the range of 150°C to 360°C, is reduced to 400 ppm or less, and the total amount of low molecular weight cyclic siloxane D10 remaining in the insulating layer is reduced to 200 ppm or less, The method for improving the smoking temperature of an insulated wire is characterized in that the temperature difference between the short-term allowable temperature and the smoking temperature is set to within 50°C.

2. A method for improving the smoke temperature of an insulated electric wire whose smoke temperature is lower than the short-term allowable temperature and whose temperature difference between the short-term allowable temperature and the smoke temperature is greater than 50°C, comprising: The insulated wire has a configuration in which a conductor is covered with an insulating layer containing organopolysiloxane, and after the insulating layer is covered around the conductor, a treatment step is performed in which the conductor is heated at a predetermined temperature for a predetermined time, The total amount of low molecular weight cyclic siloxanes D4 to D10 remaining in the insulating layer, which have boiling points in the range of 150°C to 360°C, is reduced to 400 ppm or less, and the total amount of low molecular weight cyclic siloxane D10 remaining in the insulating layer is reduced to 200 ppm or less, The temperature difference between the short-term allowable temperature and the smoke temperature is within 50°C, 2. The method for improving the smoking temperature of an insulated wire according to claim 1, wherein the total amount of sublimable substances remaining in the insulating layer is set to 300 ppm or less in the treatment step.

3. 3. The method for improving the smoke temperature of an insulated wire according to claim 1, wherein the insulating layer is made of silicone rubber and is formed by a vulcanization method that does not use organic peroxides, thereby reducing the total amount of sublimable substances remaining in the insulating layer to 300 ppm or less.

4. 4. The method for improving the smoking temperature of an insulated wire according to claim 3, wherein the vulcanization method is addition vulcanization.

5. 5. The method for improving the smoking temperature of an insulated wire according to claim 2, wherein the sublimable substance is benzoic acid or a derivative of benzoic acid.

6. 1. A method for improving the smoke-generating temperature of an insulated electric wire whose smoke-generating temperature is lower than a short-term allowable temperature and whose temperature difference between the short-term allowable temperature and the smoke-generating temperature is greater than 50°C, comprising: The insulated wire has a configuration in which a conductor is covered with at least two insulating layers including a first insulating layer and a second insulating layer, the first insulating layer and the second insulating layer each contain organopolysiloxane; After the first insulating layer is coated around the conductor, a first treatment step is performed in which the conductor is heated at a temperature of 90°C to 150°C for a total of 22 hours or more, and a second treatment step is performed in which the second insulating layer coated around the first insulating layer after the first treatment step is heated at a temperature of 90°C to 150°C for a total of 22 hours or more, The total amount of low molecular weight cyclic siloxanes D4 to D8 having a boiling point in the range of 150°C to 360°C remaining in the first insulating layer and the second insulating layer is set to 500 ppm or less, and a method for improving the smoke temperature of an insulated wire, the method comprising: setting the total amount of low molecular weight cyclic siloxanes D4 to D10 remaining in the first insulating layer and the second insulating layer to 1000 ppm or less, thereby setting the temperature difference between the short-term allowable temperature and the smoke temperature to within 50°C.

7. 7. The method for improving the smoke temperature of an insulated wire according to claim 6, further comprising forming a permeation suppressing layer exhibiting low permeability to the D4 to D8 low molecular weight cyclic siloxanes around the first insulating layer before covering the first insulating layer with the second insulating layer.

8. 8. The method for improving the smoking temperature of an insulated wire according to claim 6, further comprising forming a shielding layer around the first insulating layer before covering the second insulating layer.

9. A method for improving the smoke-generating temperature of an insulated wire as described in claim 7, characterized in that a shielding layer is formed around the permeation-suppressing layer before covering the second insulating layer.

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