Insulated wire

Abstract

To provide an insulated wire which contains a crosslinked silicone rubber in an insulation coating, and which is capable of suppressing self-fusion while maintaining high heat resistance and flexibility by means of the characteristics of the insulation coating itself.SOLUTION: An insulated wire 1 includes a conductor 2, and an insulation coating 3 that contains a crosslinked silicone rubber and covers the outer periphery of the conductor 2. With respect to the thickness of the insulation coating 3, a position at a depth of 10% from the outer surface and a position at a depth of 90% from the outer surface are defined as a shallow position P1 and a deep position P2, respectively, and the indentation hardness of the insulation coating 3 at the shallow position P1 is at least 1.1 times that at the deep position P2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to insulated wire. [Background technology]

[0002] In the field of automobiles and the like, silicone-coated electric wires having an insulating coating made of a material containing cross-linked silicone rubber are sometimes used as insulated electric wires. Taking advantage of the high flexibility of cross-linked silicone rubber, silicone-coated electric wires are particularly suitable for use as thick electric wires to which high voltages are applied. Such thick electric wires are becoming increasingly important in applications such as electric wires connecting batteries and drivetrain devices in electric vehicles and hybrid vehicles. Such silicone-coated electric wires suitable for use in automobiles are disclosed, for example, in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2016-091974 Summary of the Invention [Problem to be solved by the invention]

[0004] When manufacturing a silicone-coated electric wire, the steps of forming a layer of uncrosslinked silicone rubber composition around the outer periphery of a conductor and crosslinking the silicone rubber composition by heating are carried out consecutively. The crosslinked silicone-coated electric wire is then wound up. Because crosslinked silicone rubber has a tendency to self-weld, fusion is likely to occur between the wound layers in the silicone-coated electric wire wound up in this manufacturing process, which reduces the productivity of the silicone-coated electric wire.

[0005] One way to prevent self-welding in silicone-coated electric wires is to increase the degree of cross-linking of the silicone rubber, but increasing the degree of cross-linking in silicone-coated electric wires can impair the properties of the silicone rubber, such as heat resistance and flexibility.

[0006] Therefore, another method for suppressing self-fusion of a silicone-coated electric wire is to apply talc to the surface of the silicone coating layer. The use of an inorganic compound powder such as talc imparts lubricity to the surface of the silicone-coated electric wire, making it less likely to self-fusion even when the silicone-coated electric wire is wound. Patent Document 1 also applies talc powder to the surface of the silicone-coated electric wire. However, the use of talc can lead to unintended slippage of the electric wire, reducing the efficiency of the silicone-coated electric wire manufacturing process, and scattering of the talc. Therefore, it would be desirable to be able to suppress self-fusion of a silicone-coated electric wire by utilizing the properties of the insulating coating itself, without using a powder material such as talc.

[0007] In view of the above, an object of the present invention is to provide an insulated wire having an insulating coating containing cross-linked silicone rubber, which can suppress self-welding while maintaining high heat resistance and flexibility due to the properties of the insulating coating itself. [Means for solving the problem]

[0008] The insulated wire of the present disclosure has a conductor and an insulating coating that includes cross-linked silicone rubber and covers the outer periphery of the conductor. The positions at a depth of 10% and a depth of 90% from the outer surface of the insulating coating are defined as shallow and deep positions, respectively, with the indentation hardness of the insulating coating at the shallow position being 1.1 times or more that at the deep position. [Effects of the Invention]

[0009] The insulated wire of the present disclosure is an insulated wire containing cross-linked silicone rubber in an insulating coating, and is an insulated wire that can suppress self-welding while maintaining high heat resistance and flexibility due to the properties of the insulating coating itself. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view showing an insulated wire according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Description of the embodiments of the present disclosure] First, an embodiment of the present disclosure will be described. An insulated wire according to an embodiment of the present disclosure has the following configuration.

[0012] [1] An insulated wire according to an embodiment of the present disclosure includes a conductor and an insulating coating containing cross-linked silicone rubber and covering the outer periphery of the conductor. The positions at a depth of 10% and a depth of 90% from the outer surface of the insulating coating are defined as shallow and deep positions, respectively, with the indentation hardness of the insulating coating at the shallow position being 1.1 times or more that at the deep position.

[0013] In the insulated wire, the insulating coating containing cross-linked silicone rubber has a higher hardness in shallower regions near the surface than in deeper regions near the conductor. In cross-linked silicone rubber, a higher hardness indicates a higher degree of cross-linking. In other words, in the insulated wire, the degree of cross-linking of the silicone rubber is higher in the region near the surface of the insulating coating, making it less likely for self-welding to occur at the surface of the insulating coating when the wire is wound during the manufacturing process. Meanwhile, the interior of the insulating coating maintains a lower degree of cross-linking than the region near the surface, maintaining high heat resistance and flexibility. By providing a predetermined hardness distribution in the depth direction of the insulating coating, it is possible to simultaneously suppress self-welding and maintain heat resistance and flexibility through the properties of the insulating coating itself, without relying on external substances such as talc.

[0014] [2] In the aspect [1] above, the insulated wire may not have a layer of inorganic compound powder attached to the outside of the insulating coating. As described above, the insulated wire according to the embodiment of the present disclosure has a high hardness of the structure near the surface of the insulating coating, which allows the insulating coating itself to effectively suppress self-fusion. Therefore, there is no need to attach inorganic compound powder, such as talc, to the surface in order to suppress self-fusion. By avoiding the use of powder such as talc, contamination of equipment and the surrounding environment due to scattering of powder during the insulated wire manufacturing process and reduced manufacturing efficiency due to slippage of the insulated wire can be prevented. Furthermore, the impact of powder on the appearance of the insulated wire can be avoided.

[0015] [3] In the above-mentioned aspect [1] or [2], the indentation hardness of the insulating coating at the shallow portion may be 0.80 MPa or more. Such a sufficiently high hardness of the insulating coating at the shallow portion can particularly effectively suppress self-welding of the insulated wire.

[0016] [4] In any one of the above aspects [1] to [3], the indentation hardness of the insulating coating at the deep position may be less than 0.80 MPa. Such a sufficiently low hardness of the insulating coating at the deep position can effectively maintain high heat resistance and flexibility of the insulated wire.

[0017] [5] In any one of the above aspects [1] to [4], the average hardness is the average of the indentation hardnesses throughout the entire depth direction of the insulating coating, and the indentation hardness of the insulating coating at the shallower position may be 1.1 times or more the average hardness, and the indentation hardness of the insulating coating at the deeper position may be 0.90 times or less the average hardness. In this way, the hardness at the shallower position is sufficiently higher than the average hardness, and the hardness at the deeper position is sufficiently lower than the average hardness, thereby achieving a high level of both suppression of self-welding due to the contribution of the structure near the surface of the insulating coating and maintenance of heat resistance and flexibility due to the contribution of the internal structure.

[0018] [Details of the embodiments of the present disclosure] An insulated wire according to an embodiment of the present disclosure will be described in detail below with reference to the drawings. Hereinafter, various properties are values ​​measured at room temperature in the atmosphere unless otherwise specified.

[0019] <Insulated wire structure> 1 shows a cross-sectional structure perpendicular to the axial direction of an insulated wire 1 according to one embodiment of the present disclosure. The insulated wire 1 has a conductor 2 and an insulating coating 3 that covers the outer periphery of the conductor 2.

[0020] Various metal materials can be used as materials for the conductor 2, including copper and copper alloys, aluminum and aluminum alloys, etc. In particular, copper or copper alloys are preferable because of their high conductivity and flexibility. The conductor 2 may be configured as a single wire, but is preferably made up of multiple wires 21 from the viewpoint of increasing flexibility when bent. The multiple wires 21 may be bundled to form the conductor 2, or may be twisted together to form a twisted wire. The conductor 2 may be compression molded. When the conductor 2 includes multiple wires 21, the wires may all be made of the same wire, or may include two or more types of wires.

[0021] The insulated wire 1 is configured as a silicone-coated wire, and the insulating coating 3 is made of a material containing cross-linked silicone rubber. The insulating coating 3 has a non-uniform hardness distribution along its thickness. The component composition and physical properties of the insulating coating 3 will be described in detail later.

[0022] The specific dimensions of the insulated wire 1 are not particularly limited, but from the viewpoint of effectively utilizing the properties imparted by the insulating coating 3 containing cross-linked silicone rubber, such as flexibility and heat resistance, the conductor cross-sectional area is set to approximately 20 mm 2 It is preferable to use a large diameter wire such as the above. There is no particular upper limit for the conductor cross-sectional area, but it is generally 200 mm 2It is preferable to set the thickness of the insulating coating 3 to 0.6 mm or more in order to enhance the effect of providing a hardness distribution in the depth direction of the insulating coating 3. There is no particular upper limit to the thickness of the insulating coating 3, but it is preferable to set it to approximately 2.5 mm or less.

[0023] The insulated wire 1 may be used in the form of a simple coated wire having an insulating coating 3 provided around the conductor 2, or may have another component disposed outside the insulating coating 3. Examples of the other component disposed outside the insulating coating 3 include an outer conductor made of a metal braid or metal foil, and an insulating sheath disposed around the outer conductor. Furthermore, applying a layer of inorganic powder such as talc to the outside of the insulating coating 3 provides lubricity to the insulated wire 1 and is highly effective in preventing self-fusion. However, as will be described later, the insulated wire 1 according to this embodiment does not need such a powder layer because the insulating coating 3 itself has a high self-fusion suppression effect. Rather, from the viewpoints of avoiding contamination of the equipment and surrounding environment due to scattering of powder during the manufacture and use of the insulated wire 1, reducing manufacturing efficiency due to slippage of the insulated wire 1, and affecting the appearance due to the powder, it is preferable that the insulated wire 1 not have a layer of such powder attached outside the insulating coating 3. In the insulated wire 1, the insulating coating 3 is preferably composed of a single layer containing silicone rubber and having a predetermined hardness distribution, but this does not prevent the insulating coating 3 from having multiple different layers, and in that case, it is preferable that the layer containing silicone rubber and having a predetermined hardness distribution constitutes the outermost layer of the insulating coating 3.

[0024] <Insulating coating> Here, a detailed description will be given of the insulating coating 3 that constitutes the insulated wire 1. As described above, the insulating coating 3 is made of a material containing cross-linked silicone rubber.

[0025] It is preferable to use thermosetting (thermally crosslinked) silicone rubber as the crosslinked silicone rubber that constitutes the insulating coating 3. Among thermosetting silicone rubbers, it is preferable to use millable silicone rubber, which becomes an elastic body when heated and crosslinked after kneading with a crosslinking agent. Crosslinked silicone rubber has a structure in which a polymer chain with an organopolysiloxane main chain and organic groups such as methyl groups, ethyl groups, vinyl groups, and phenyl groups are bonded is crosslinked.

[0026] The crosslinking of thermosetting silicone rubber can be promoted by heating, but if necessary, crosslinking may be promoted using a crosslinking agent such as an organic peroxide and / or a catalyst such as a platinum catalyst. To promote sufficient crosslinking, particularly near the surface of the insulating coating 3, crosslinking using a crosslinking agent and catalyst is preferred. From a similar perspective, the content of the crosslinking agent in the silicone rubber composition is preferably 1.0 part by mass or more, and even 1.7 parts by mass or more, per 100 parts by mass of silicone rubber. On the other hand, to ensure the flexibility and heat resistance of the insulating coating 3, the content should be 3.0 parts by mass or less. From a similar perspective, the content of the catalyst is preferably 0.5 parts by mass or more, and even 1.2 parts by mass or more, per 100 parts by mass of silicone rubber, and is preferably 2.5 parts by mass or less.

[0027] The constituent material of the insulating coating 3 may contain organic polymers other than cross-linked silicone rubber. However, in order to effectively utilize the heat resistance, flexibility, and other properties of cross-linked silicone rubber, it is preferable that cross-linked silicone rubber be the main component, or even the entire component, of the organic polymers that constitute the insulating coating 3. Furthermore, the constituent material of the insulating coating 3 may contain additives in addition to the above-mentioned cross-linking agent and catalyst, as appropriate. Examples of such additives include cross-linking inhibitors, heat stabilizers, reinforcing fillers, extending fillers, dispersion promoters, lubricants, colorants, and acid acceptors (e.g., Ca(OH)2, Mg(OH)2).

[0028] The insulating coating 3 has a uniform composition throughout its entire depth, excluding unavoidable fluctuations in the components, and is continuous throughout. However, the hardness varies unevenly along the depth. Specifically, the insulated wire 1 has a region near the surface that is harder than the inner region. Specifically, the shallow position (position P1) is 10% of the depth from the outer surface of the insulating coating 3, and the deep position (position P2) is 90% of the depth. The hardness of the insulating coating 3 at the shallow position P1 is 1.1 times or more that at the deep position P2. In this embodiment, indentation hardness is preferably used as the hardness. Furthermore, the local indentation hardness at specific positions along the depth, such as the shallow position P1 and the deep position P2, can be measured using, for example, a nanoindenter on a cross section of the insulated wire 1 cut perpendicular to the axial direction. Even if the thickness of the insulating coating 3 varies depending on the position, the positions for determining the hardness can be determined based on the thickness at each position.

[0029] The shallow position P1 represents the region near the surface of the insulating coating 3 (including the region on the surface), and the deep position P2 represents the region inside the insulating coating 3. The relationship between the hardness at the shallow position P1 and the deep position P2 indicates that the region near the surface of the insulating coating 3 is harder than the inner region. In cross-linked silicone rubber, the higher the degree of cross-linking, the higher the hardness tends to be. In other words, the relationship between the hardness indicates that the degree of cross-linking of the silicone rubber is higher in the region near the surface of the insulating coating 3 of the insulated wire 1 according to this embodiment than in the inner region.

[0030] Generally, cross-linked silicone rubber has self-adhesive properties, but increasing the degree of cross-linking reduces the likelihood of self-adhesive bonding. In the insulated wire 1 according to this embodiment, the region near the surface of the insulating coating 3 has a high degree of cross-linking, which increases the hardness of the region, making it less susceptible to self-adhesive bonding. In the manufacturing process of the insulated wire 1, a silicone rubber composition is applied to the outer periphery of the conductor 2, cross-linked by heating, and then the resulting insulated wire 1 is wound. If the insulating coating 3 has high self-adhesive properties, self-adhesive bonding between the wound layers would reduce the productivity of the insulated wire. However, in the insulated wire 1 according to this embodiment, self-adhesive bonding on the surface is suppressed, making self-adhesive bonding between the wound layers less likely to occur. Note that self-adhesive bonding occurs on the surface of the insulated wire 1, and the degree of cross-linking of the silicone rubber inside the insulating coating 3 is essentially irrelevant.

[0031] On the other hand, cross-linked silicone rubber is a material with high heat resistance and flexibility, but if the degree of cross-linking becomes too high, these high heat resistance and flexibility may be lost. However, in the insulated wire 1 according to this embodiment, the inner region of the insulating coating 3 is maintained in a state with a relatively low degree of cross-linking, where the hardness is relatively low. This allows the insulated wire 1 as a whole to maintain high heat resistance and flexibility.

[0032] As described above, in the insulated wire 1 according to this embodiment, the hardness of the insulating coating 3 at the shallow position P1 is at least 1.1 times that at the deep position P2. This results in a high degree of cross-linking near the surface and a low degree of cross-linking in the interior, thereby suppressing self-fusion while maintaining high heat resistance and flexibility. As described above, maintaining heat resistance and flexibility and suppressing self-fusion are achieved as a characteristic of the insulating coating 3 itself by controlling the degree of cross-linking and the hardness correlated therewith. This does not require the contribution of an external substance, such as the application of talc to the outer periphery of the insulating coating 3. From the viewpoint of maintaining heat resistance and flexibility and further enhancing the effects of suppressing self-fusion, it is more preferable that the hardness of the insulating coating 3 at the shallow position P1 be at least 1.2 times, or even 1.4 times, that at the deep position P2. While the upper limit of this ratio is not particularly specified, it should be approximately 2.0 times or less to prevent the hardness from becoming too low at the shallow position P1 or too high at the deep position P2.

[0033] In the insulating coating 3, the hardnesses of the shallow position P1 and the deep position P2 are not particularly limited as long as they satisfy the above relationship. However, in order to sufficiently enhance the effect of suppressing self-welding at the shallow position P1, the hardness should be 0.80 MPa or more, further 0.85 MPa or more, or 0.90 MPa or more. There is no particular upper limit to the hardness at the shallow position P1, but it is preferably approximately less than 1.0 MPa. On the other hand, in order to sufficiently enhance the effect of maintaining heat resistance and flexibility at the deep position P2, the hardness should be less than 0.80 MPa, further less than 0.75 MPa. There is no particular lower limit to the hardness at the deep position P2, but it is preferably approximately 0.50 MPa or more.

[0034] As described above, the hardness of the insulating coating 3 may vary in any distribution throughout the thickness of the insulating coating 3, as long as the value at the shallow position P1 is at least 1.1 times the value at the deep position P2. However, it is preferable that the hardness decreases as the position (inner position) becomes deeper. This makes it easier to suppress self-welding of the insulating coating 3 while maintaining high levels of heat resistance and flexibility. From the same perspective, the average hardness of the insulating coating 3 throughout the depth direction should be defined as the average hardness, and the hardness at the shallow position P1 should be at least 1.1 times, or even 1.2 times, the average hardness. The hardness at the deep position P2 should be no more than 0.90 times, or even no more than 0.85 times the average hardness. Here, the average hardness can be determined, for example, by measuring the hardness at representative points in each of five equal regions of the insulating coating 3 in the thickness direction and averaging the results. As an example, as in the embodiment described later, the representative points may be set at positions corresponding to 10%, 25%, 50%, 75%, and 90% of the thickness of the insulating coating 3.

[0035] As described above, the presence of a highly cross-linked region near the surface of the insulating coating 3, which has a high hardness, is highly effective in suppressing self-fusion. However, if the highly cross-linked region is distributed too deep, the effect of suppressing self-fusion saturates, and the heat resistance and flexibility of the insulated wire 1 as a whole may actually be reduced. Therefore, it is preferable that the region with significantly higher hardness than the interior remain in a thin region near the surface of the insulating coating 3. For example, assuming a depth position that is 50% of the thickness of the insulating coating 3 as the intermediate position, it is desirable that the hardness at the intermediate position be kept to 90% or less, or even 85% or less, of the hardness at the shallow position P1.

[0036] In the above, the hardness of each portion of the insulating coating 3 is defined by the indentation hardness in MPa. The Shore hardness at the shallow position P1 can be in the range of A80 to A90. At the deep position P2, the Shore hardness can be in the range of A60 to A75. In cross-linked silicone rubber, the higher the degree of cross-linking and the higher the hardness, the higher the modulus of elasticity tends to be. In the insulated wire 1 according to this embodiment, the modulus of elasticity of the insulating coating 3 is not particularly limited, but the flexural modulus can be in the range of 3.1 MPa to 3.9 MPa at the shallow position P1. At the deep position P2, the flexural modulus can be in the range of 1.7 MPa to 2.8 MPa.

[0037] <Insulated wire manufacturing method> Next, an example of a method for producing the insulated wire 1 according to this embodiment will be described. When producing the insulated wire 1, first, an uncrosslinked silicone rubber composition is placed around the conductor 2. At this time, predetermined components constituting the silicone rubber composition are kneaded, and the resulting composition is extrusion-molded around the conductor 2. If necessary, the conductor 2 may be preheated before extrusion molding. Thereafter, the obtained coating is sequentially heated to crosslink the silicone rubber, thereby obtaining the insulated wire 1 according to this embodiment.

[0038] When cross-linking the silicone rubber by heating, the degree of cross-linking is higher near the surface of the insulating coating 3 than in the inner region, thereby forming an insulating coating 3 that is harder at shallow position P1 than at deep position P2. To increase the degree of cross-linking of the silicone rubber near the surface compared to the inner region, for example, instead of uniformly heating the entire depth direction of the insulating coating 3, the region near the surface can be heated to a higher temperature and for a shorter time than the inner region.

[0039] As a means for intensively heating the surface vicinity of the insulating coating 3, it is preferable to use an infrared heating furnace. In an infrared heating furnace, infrared rays are irradiated onto the surface of the insulating coating 3, heating the constituent materials of the insulating coating 3 through molecular vibration. In particular, when infrared rays with a relatively long wavelength are used for heating, the infrared rays are reflected from the surface and are less likely to penetrate deep into the insulating coating 3 compared to when short-wavelength infrared rays are used, and heating occurs intensively in the region near the surface due to absorption of the infrared rays. In the first heating step, crosslinking is caused by heating to a high temperature intensively near the surface of the insulating coating 3. If necessary, in the second heating step, the entire insulating coating 3 can be heated more slowly at a lower temperature than in the first heating step to promote crosslinking within the interior of the insulating coating 3 to the required degree. In the second heating step, infrared rays with a shorter wavelength than those in the first heating step can be used. Because short-wavelength infrared rays penetrate deep into the insulating coating 3, it is preferable to heat the insulating coating 3 deep within at a relatively low temperature for a long period of time. [Example]

[0040] Examples are shown below. Here, the relationship between the hardness distribution in the insulating coating and the properties of a silicone-coated electric wire was evaluated. In these examples, the properties were evaluated at room temperature in the air unless otherwise specified.

[0041] [Sample preparation] Conductor constructed as a twisted copper alloy wire (conductor cross-sectional area: 51.95 mm 2 ) was preheated to 100°C, and a silicone rubber composition was extruded to a thickness of 1.0 mm around the conductor. Table 1 below shows the component compositions of the silicone rubber compositions for Samples A1, A2, and B1 to B3 (unit: parts by mass). Table 1 also shows the crosslinking rate (Tc80; measurement temperature 120°C) and maximum torque measured for each sample composition.

[0042] The materials used in preparing the silicone rubber composition are as follows: Silicone rubber: Wacker Asahi Kasei Silicone "ELASTOSIL R401-70" Catalyst: Platinum catalyst "ELASTOSIL AUX BATCH PT 1" manufactured by Asahi Kasei Wacker Silicone Co., Ltd. Crosslinking agent: Wacker Asahi Kasei Silicone "ELASTOSIL R CL101" Crosslinking inhibitor: Wacker Asahi Kasei Silicone "ELASTOSIL AUX 4K-I" Heat stabilizer: Wacker Asahi Kasei Silicone "ELASTOSIL AUX STABILIZER H0"

[0043] The molded body obtained by the above extrusion molding was heated in an infrared heating furnace to crosslink the silicone rubber. Two infrared heating furnaces, a first heating furnace and a second heating furnace, were used, and the molded body was heated by passing it continuously through the first heating furnace and then the second heating furnace. The first heating furnace uses infrared rays with a longer wavelength than the second heating furnace, allowing it to heat the area near the surface of the molded body to a high temperature. The first heating furnace was equipped with one unit measuring 1.0 m in length, and the second heating furnace was equipped with five units measuring 1.9 mm in length in series. Table 2 below shows the heating conditions applied to Samples A1, A2, and Samples B1-B3, i.e., the heating temperatures and linear speeds in the two heating furnaces. The heating temperatures were measured inside the heating furnaces.

[0044] The crosslinked insulated wires were used as samples for subsequent evaluation, except for sample B2, which had talc powder attached to the outer periphery of the insulated wire.

[0045] [Table 1]

[0046] [Table 2]

[0047] [Evaluation method] (1) Hardness Each sample of insulated wire was cut perpendicular to the axial direction, and the indentation hardness of the insulating coating was measured at various positions using a nanoindenter. Hardness measurements were taken at depths of 10% (shallow position), 25%, 50% (middle position), 75%, and 90% (deep position) from the outer surface of the insulating coating. The measurements at each position were then averaged to calculate the average hardness.

[0048] (2) Abrasion resistance The abrasion resistance of each sample insulated wire was evaluated using a tape abrasion test in accordance with ISO 6722. Specifically, a 1.9 kg weight of sandpaper tape was pressed against the outer circumference of each insulated wire, and the sandpaper was moved at a speed of 1500 ± 75 mm / min. The distance the tape traveled until the wire conductor was exposed was measured. The longer the travel distance, the better the abrasion resistance. A travel distance of 1000 mm or more was rated "A," indicating high abrasion resistance. A travel distance of 1500 mm or more was rated "A+," indicating very high abrasion resistance. A travel distance of less than 1000 mm was rated "B," indicating low abrasion resistance.

[0049] (3) Self-fusion resistance Each sample of insulated wire manufactured as described above was wound on a reel. The insulated wire was pulled out from the reel, and the pulled-out portion was visually inspected to confirm the presence or absence of fusion. When no fusion marks that would be problematic in practical use were visually observed on the surface of the insulating coating of the insulated wire where the layers were in contact with each other when wound on the reel, the sample was judged to have high self-fusion resistance, "A." Furthermore, when no fusion marks were visually observed, the sample was judged to have very high self-fusion resistance, "A+." On the other hand, when fusion marks that would be problematic in practical use were visually observed, the sample was judged to have low self-fusion resistance, "B."

[0050] (4) Heat resistance The heat resistance of the insulating coating was evaluated using a heat life test in accordance with ISO 6722. Specifically, each sample of insulated wire was held at 175°C for 3,000 hours. After that, a winding test was performed at 1.5 times the diameter, and the insulation was visually inspected for cracks. Samples without cracks were rated "A" for high heat resistance. On the other hand, samples with cracks were rated "B" for low heat resistance.

[0051] (5)Flexibility The flexibility of each sample insulated wire was evaluated using a three-point bending test in accordance with ISO 6722. Specifically, each insulated wire was cut to a length of 220 mm, and the center was bent with a support distance of 145.6 mm. The maximum bending stress was measured and used as the three-point bending force. If the three-point bending force was 45 N or less, the sample was rated as "A," indicating high flexibility. On the other hand, if the three-point bending force exceeded 45 N, the sample was rated as "B," indicating low flexibility.

[0052] (6) Processability The workability of each sample of insulated wire was evaluated based on measurement error. Specifically, each manufactured insulated wire was measured to a length of 1 m and cut out. The length of the cut insulated wire was then precisely measured. If the error in the length of the cut insulated wire was within 1%, that is, if the length of the insulated wire was within the range of 1 m ± 10 mm, the workability was rated as "A," indicating high workability. On the other hand, if the error in the length of the insulated wire was outside that range, the workability was rated as "B," indicating low workability. If the surface of the insulated wire is not very smooth, or conversely, if it is too smooth, the insulated wire cannot be held securely when measuring the length during cutting, which increases the likelihood of errors in the measured and cut length of the insulated wire.

[0053] [Evaluation results] Table 3 shows the results of each evaluation for Samples A1, A2 and Samples B1 to B3, along with whether or not talc powder was used.

[0054] [Table 3]

[0055] First, we examine the relationship between the manufacturing conditions for the insulating coating and the hardness distribution. As shown in Table 2, for both Samples A1 and A2, the insulating coating was crosslinked by heating at a high temperature of 800°C in a first heating furnace, followed by heating at a lower temperature of 600°C in a second heating furnace. The compacts were passed through the heating furnace at a relatively high linear speed of 30 m / min. As shown in Table 3, for both Samples A1 and A2, the hardness of the insulating coating at shallower positions was higher than that at deeper positions, with the hardness at the shallower position (10% depth) being more than 1.1 times that at the deeper position (90% depth). The hardness values ​​at the shallower positions were greater than 0.80 MPa and less than 0.80 MPa at the deeper positions. Thus, it was confirmed that by performing high-temperature, short-time heating in the first heating furnace followed by long-time heating at a relatively low temperature in the second heating furnace, an insulating coating with a higher hardness near the surface than in the inner region could be formed. It is believed that the heating in the first heating furnace caused crosslinking of the silicone rubber to proceed intensively in the region near the surface, resulting in an increase in hardness.

[0056] Comparing Sample A1 and Sample A2, as shown in Table 1, Sample A2 has a higher concentration of catalyst and crosslinker in the composition that makes up the insulating coating. Therefore, Sample A2 is more likely to undergo rapid crosslinking of the silicone rubber. Correspondingly, Sample A2 has a higher hardness than Sample A1 throughout the entire depth of the insulating coating. The change in hardness between depths is also greater for Sample A2, with the hardness at the shallower position (10% depth) being 1.5 times that at the deeper position (90% depth). This indicates that increasing the concentration of catalyst and / or crosslinker in the silicone rubber composition and accelerating crosslinking can effectively increase the hardness near the surface of the insulating coating.

[0057] On the other hand, samples B1 and B2 were formed with an insulating coating using the same silicone rubber composition as sample A2, but were heated in the first heating furnace at 600°C, the same temperature as the second heating furnace. Furthermore, the heating linear speed was relatively slow at 20 m / min. Similar to samples A1 and A2, samples B1 and B2 also exhibited a distribution in the hardness of the insulating coating, with the hardness at shallower positions being higher than that at deeper positions. However, the change in hardness with depth was smaller than that of samples A1 and A2, with the hardness at shallower positions not reaching 1.1 times the hardness at deeper positions. Thus, by heating the silicone rubber slowly at a relatively low temperature, crosslinking proceeded uniformly throughout the insulating coating, and no areas near the surface of the insulating coating where crosslinking progressed more significantly than in the interior were formed.

[0058] Sample B3 uses a silicone composition with higher catalyst and crosslinker concentrations than Samples A2, B1, and B2. However, heating in the first heating furnace was performed at 600°C, the same temperature as in the second heating furnace. The linear speed was also slower, at 15 m / min. Sample B3 exhibited higher hardness throughout the entire depth of the insulating coating than any of the other samples. However, the hardness uniformity was high, and like Samples B1 and B2, the hardness at the shallower portion was less than 1.1 times that at the deeper portion. This suggests that simply increasing the catalyst and / or crosslinker concentration in the silicone rubber composition to accelerate crosslinking is not enough to significantly increase the hardness near the surface of the insulating coating compared to the interior. Therefore, it is necessary to conduct crosslinking under conditions that allow for concentrated heating of the near-surface region of the insulating coating.

[0059] Next, we will examine the relationship between the hardness distribution in the insulation coating and the properties of the insulated wire. All samples showed high abrasion resistance, which suggests that the mechanical strength of the insulation coating as a whole was sufficiently improved by cross-linking.

[0060] Furthermore, samples A1 and A2 exhibited sufficiently high properties in terms of self-welding resistance, heat resistance, flexibility, and processability. The high self-welding resistance corresponds to the fact that cross-linking is sufficiently advanced in the region near the surface of the insulating coating, resulting in high hardness. The high heat resistance and flexibility correspond to the fact that cross-linking does not progress excessively inside the insulating coating, maintaining a relatively low hardness. The high processability is thought to be the result of not only suppressing self-welding, but also the fact that talc is not attached to the periphery, preventing excessive lubricity. In particular, sample A2 exhibited particularly high wear resistance and self-welding resistance, corresponding to the particularly high hardness near the surface.

[0061] Sample B1 exhibits high heat resistance and flexibility, corresponding to the low hardness of the interior of the insulating coating. However, its self-adhesion resistance and processability are low. This is thought to be because cross-linking does not progress sufficiently, even in the region near the surface of the insulating coating, resulting in a low hardness. Sample B2 is an insulated wire of sample B1 with talc powder attached to the outer periphery. The use of talc powder increases the slipperiness of the insulated wire, improving its self-adhesion resistance. However, the slipperiness caused by the talc powder makes it difficult to hold the insulated wire accurately during length measurement, resulting in low processability.

[0062] In sample B3, cross-linking is highly advanced throughout the entire insulating coating, resulting in high hardness and correspondingly very high abrasion resistance and self-welding resistance. Processability is also high. However, the hardness inside the insulating coating is too high, resulting in low heat resistance and flexibility.

[0063] The above test results confirmed that by appropriately setting the conditions for cross-linking the silicone rubber in a silicone-coated electric wire, and creating a distribution in the hardness of the insulating coating such that the hardness at the shallower positions is at least 1.1 times that at the deeper positions, it is possible to obtain an insulated electric wire that has excellent self-fusing resistance and processability, as well as excellent heat resistance and flexibility, even without using talc powder.

[0064] [Reference test - Shore hardness, elastic modulus and properties of insulating coating] So far, we have evaluated the relationship between the distribution of indentation hardness in the insulating coating and various properties of silicone-coated electric wires. For reference, we will now briefly show the relationship between the Shore hardness and elastic modulus of the insulating coating and various properties.

[0065] Here, the silicone rubber composition that constitutes the insulating coating of Sample A1 was uniformly cured throughout to prepare a reference sample. Five samples with different hardness levels were prepared by adjusting the heating conditions during curing. Table 4 below shows the results of Shore A hardness and flexural modulus measurements for each sample, as well as the results of various evaluations performed in the same manner as the tests described above.

[0066] [Table 4]

[0067] Table 4 shows that Shore A hardness and elastic modulus are positively correlated. Reference samples 4 and 5, which have a Shore A hardness of 80 or greater and an elastic modulus of 3.1 MPa or greater, exhibit high abrasion resistance and very high self-welding resistance even without the use of talc. These findings suggest that it is preferable for the insulating coating of silicone-insulated electric wires to have a Shore A hardness of 80 or greater and an elastic modulus of 3.1 MPa or greater for the structure near the surface. While Reference samples 4 and 5 do not exhibit sufficient heat resistance and flexibility, Reference samples 1 to 3, which have a Shore A hardness of less than 80 and an elastic modulus of less than 3.1 MPa, exhibit high heat resistance and flexibility. These findings suggest that it is preferable for the insulating coating of silicone-insulated electric wires to have a Shore A hardness of approximately 75 or less and an elastic modulus of 2.8 MPa or less for the internal structure.

[0068] Although the embodiments of the present disclosure have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0069] 1. Insulated wire 2 conductors 21 Wire 3. Insulation coating P1 shallow position P2 deep position

Claims

1. A conductor; an insulating coating including a cross-linked silicone rubber and covering the outer periphery of the conductor; With respect to the thickness of the insulating coating, a position at a depth of 10% and a position at a depth of 90% from the outer surface are defined as a shallow position and a deep position, respectively. The insulated wire has an indentation hardness of the insulating coating at the shallow portion that is 1.1 times or more that at the deep portion.

2. 2. The insulated wire according to claim 1, wherein the insulating coating does not have a layer on the outside thereof to which inorganic compound powder is attached.

3. 3. The insulated wire according to claim 1, wherein the insulating coating has an indentation hardness of 0.80 MPa or more at the shallow position.

4. 3. The insulated wire according to claim 1, wherein the insulating coating has an indentation hardness of less than 0.80 MPa at the deep position.

5. The average of the indentation hardness in the entire depth direction of the insulating coating is defined as the average hardness. The indentation hardness of the insulating coating at the shallow position is 1.1 times or more the average hardness, and 3. The insulated wire according to claim 1, wherein the indentation hardness of the insulating coating at the deep position is 0.90 times or less the average hardness.

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