Insulated wire

Abstract

The present invention provides 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.　The present invention specifically provides an insulated wire 1 which includes: a conductor 2; and an insulation coating 3 that contains a crosslinked silicone rubber and covers the outer periphery of the conductor 2. When a position at a depth of 10% and a position at a depth of 90% from the outer surface with respect to the thickness of the insulation coating 3 are respectively defined as a shallow position P1 and a deep position P2, the indentation hardness of the insulation coating 3 at the shallow position P1 is not less than 1.1 times that at the deep position P2.

Description

insulated wire

[0001] The present disclosure relates to insulated wire.

[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 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.

[0003] JP 2016-091974 A

[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 method for suppressing self-welding in silicone-coated electric wires is to increase the degree of crosslinking of the silicone rubber, but increasing the degree of crosslinking 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 adhere 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 adheres talc powder to the surface of the silicone-coated electric wire. However, the use of talc can result in unintended slippage of the electric wire, reducing the efficiency of the silicone-coated electric wire manufacturing process, or 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.

[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.

[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.

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

[0011] [Description of 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 insulating coating has a shallow position at a depth of 10% from the outer surface and a deep position at a depth of 90% from the outer surface, 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 it 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, resulting in 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 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 of the indentation hardness of the insulating coating throughout its entire depth direction may be defined as the average hardness, 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 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] 1 shows a cross-sectional structure perpendicular to the axial direction of an insulated wire 1 according to an 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 the material for the conductor 2, including copper and copper alloys, aluminum and aluminum alloys, etc. Copper or copper alloys are particularly preferred due to their high conductivity and flexibility. The conductor 2 may be configured as a single wire, but is preferably made up of multiple wires 21 in order to enhance flexibility during bending. The multiple wires 21 may be bundled together 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, they may all be made up of the same wire, or may include two or more types of wires.

[0021] The insulated wire 1 is 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 The upper limit of the conductor cross-sectional area is not specified, but it is generally 200 mm ２ It is preferable that the thickness of the insulating coating 3 be 0.6 mm or more from the viewpoint of increasing 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 that the thickness be 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 such a powder layer 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 a thermosetting (thermally crosslinked) silicone rubber as the crosslinked silicone rubber that constitutes the insulating coating 3. Among the thermosetting silicone rubbers, it is preferable to use a millable silicone rubber that becomes an elastic body by kneading a crosslinking agent and then heating and crosslinking it. 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 to it 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. From the viewpoint of promoting sufficient crosslinking, particularly near the surface of the insulating coating 3, crosslinking is preferably carried out using a crosslinking agent and a catalyst. From the same viewpoint, 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, from the viewpoint of easily ensuring the flexibility and heat resistance of the insulating coating 3, the content is preferably 3.0 parts by mass or less. From the same viewpoint, 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, from the viewpoint of effectively utilizing the properties of cross-linked silicone rubber, such as heat resistance and flexibility, it is preferable that cross-linked silicone rubber constitutes the main component of the organic polymer that constitutes the insulating coating 3, and more preferably constitutes the entire amount. 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. These additives include cross-linking inhibitors, heat stabilizers, reinforcing fillers, extending fillers, dispersion promoters, lubricants, colorants, acid acceptors (Ca(OH) ２ , Mg(OH) ２ etc.)

[0028] The insulating coating 3 has a uniform composition throughout its entire depth, excluding unavoidable fluctuations, and is continuous throughout. However, the hardness distribution is non-uniform along the depth direction. 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 thickness of the insulating coating 3 from the outer surface, and the deep position (position P2) is 90% of the thickness of the insulating coating 3. 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. The local indentation hardness at specific positions along the depth direction, 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 when the thickness of the insulating coating 3 varies depending on the circumferential position of the insulated wire 1, the depth position for defining the hardness may be determined based on the thickness at each circumferential 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 internal 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 than in the internal region in the insulating coating 3 of the insulated wire 1 according to this embodiment.

[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, which makes the hardness of the insulated wire 1 relatively low. This allows the heat resistance and flexibility of the insulated wire 1 as a whole to be maintained at a high level.

[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, resulting in a high degree of cross-linking near the surface and a low degree of cross-linking in the interior. This allows for suppression of 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 deposition of talc on 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. The upper limit of this factor is not particularly specified, but it should be approximately 2.0 times or less to prevent the hardness from being too low at the shallow position P1 or too high at the deep position P2.

[0033] In the insulating coating 3, the hardnesses at 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. The upper limit of the hardness at the shallow position P1 is not particularly defined, 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. The lower limit of the hardness at the deep position P2 is not particularly defined, 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 is 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 may 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 following embodiment, 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, but 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 description, 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] <Method for Manufacturing Insulated Wire> Next, an example of a method for manufacturing the insulated wire 1 according to this embodiment will be described. When manufacturing 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 successively heated along the longitudinal direction 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 internal 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 internal region, for example, the insulating coating 3 may be heated to a higher temperature, particularly in a shorter time, than the internal region, rather than uniformly heating the entire depth of the insulating coating 3.

[0039] As a means for intensively heating the vicinity of the surface 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 than when infrared rays with a short wavelength 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. After that, if necessary, in the second heating step, the entire insulating coating 3 is heated gently at a temperature lower than that 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 are preferably used. Because short-wavelength infrared rays penetrate deep into the insulating coating 3, it is preferable to heat the insulating coating 3 deep into the interior at a relatively low temperature for a long period of time.

[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] A conductor (conductor cross-sectional area: 51.95 mm) made of a twisted copper alloy wire was used. 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 the composition of each sample.

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

[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 the area near the surface of the molded body to be heated to a high temperature. The first heating furnace was equipped with one unit with a length of 1.0 m, and the second heating furnace was equipped with five units with a length of 1.9 mm arranged 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]

[0046]

[0047] [Evaluation Method] (1) Hardness Each sample insulated wire was cut perpendicular to the axial direction, and the indentation hardness of the insulating coating was measured at each position using a nanoindenter. The hardness measurements were performed at depths of 10% (shallow position), 25%, 50% (middle position), 75%, and 90% (deep position) from the outer surface of the insulating coating. The measured values ​​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 by a tape abrasion test in accordance with ISO 6722. Specifically, a tape-shaped sandpaper was pressed against the outer periphery of each insulated wire with an added mass of 1.9 kg, and the sandpaper was moved at a speed of 1500±75 mm / min. The distance the tape moved until the wire conductor was exposed was measured. The longer the movement distance, the better the abrasion resistance. A movement distance of 1000 mm or more was evaluated as "A," indicating high abrasion resistance. A movement distance of 1500 mm or more was evaluated as "A+," indicating very high abrasion resistance. On the other hand, a movement distance of less than 1000 mm was evaluated as "B," indicating low abrasion resistance.

[0049] (3) Self-fusion resistance The insulated wire of each sample 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 at the portion 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 by a heat life test in accordance with ISO 6722. Specifically, the insulated wire of each sample was held at 175°C for 3,000 hours. After that, a winding test was performed at 1.5 times the diameter, and the insulator 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 by a three-point bending test in accordance with ISO 6722. Specifically, each insulated wire was cut to a length of 220 mm, and the distance between supports was set to 145.6 mm. The maximum bending stress when bending the central portion was measured, and this was taken as the three-point bending force. When the three-point bending force was 45 N or less, the sample was evaluated as "A," indicating high flexibility. On the other hand, when the three-point bending force exceeded 45 N, the sample was evaluated as "B," indicating low flexibility.

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

[0055] First, we will examine the relationship between the manufacturing conditions of 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 furnaces 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 was higher at shallower positions than at deeper positions, with the hardness at the shallower position (10% depth) being at least 1.1 times that at the deeper position (90% depth). The hardness values ​​were 0.80 MPa or greater at the shallower positions and less than 0.80 MPa at the deeper positions. Thus, it was confirmed that by heating at a high temperature for a short time in the first heating furnace, followed by heating at a relatively low temperature for a long time in the second heating furnace, an insulating coating having a higher hardness in the near-surface region 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 constitutes 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 amount of 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 demonstrates 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 regions near the surface of the insulating coating where crosslinking proceeded more significantly than in the interior were formed.

[0058] Sample B3 uses a silicone composition with higher catalyst and crosslinker concentrations than Sample A2 and Samples B1 and B2. However, heating in the first heating furnace was performed at 600°C, the same temperature as heating in the second heating furnace. The linear velocity was also slow, 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 shallower depths was less than 1.1 times that at deeper depths. This suggests that simply increasing the catalyst and / or crosslinker concentration in the silicone rubber composition to accelerate crosslinking is not sufficient to significantly increase the hardness near the surface of the insulating coating compared to the interior. It is therefore necessary to perform crosslinking heating under conditions that allow for concentrated heating of the region near the surface 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, indicating that the cross-linking has sufficiently improved the mechanical strength of the insulation coating as a whole.

[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 crosslinking 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 crosslinking 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 excessively high 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 due to the low hardness of the interior of the insulating coating. However, its self-welding resistance and processability are poor. This is thought to be due to the fact that crosslinking does not progress sufficiently, even in the region near the surface of the insulating coating, resulting in a low hardness. Sample B2 is the same as Sample B1, but with talc powder attached to the outer periphery of the insulated wire. The use of talc powder increases the slipperiness of the insulated wire, improving its self-welding resistance. However, the slipperiness caused by the talc powder makes it difficult to hold the insulated wire accurately during length measurement, resulting in poor processability.

[0062] In sample B3, cross-linking was highly advanced throughout the entire insulating coating, resulting in high hardness, which in turn resulted in very high abrasion resistance and self-welding resistance. The processability was also high. However, the hardness inside the insulating coating was too high, resulting in low heat resistance and flexibility.

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

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

[0065] Here, the silicone rubber composition constituting 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 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 above tests.

[0066]

[0067] According to Table 4, there is a positive correlation between Shore A hardness and elastic modulus. Reference samples 4 and 5, which have a Shore A hardness of 80 or more and an elastic modulus of 3.1 MPa or more, exhibit high abrasion resistance and very high self-welding resistance even without the use of talc. Based on these findings, it is preferable for the insulating coating of silicone-coated electric wires to have a Shore A hardness of 80 or more and an elastic modulus of 3.1 MPa or more in the structure near the surface. Meanwhile, Reference samples 4 and 5 do not exhibit sufficient heat resistance and flexibility, whereas 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. Based on these findings, it is preferable for the insulating coating of silicone-coated electric wires to have a Shore A hardness of approximately 75 or less and an elastic modulus of 2.8 MPa or less in 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.

[0069] 1 insulated wire 2 conductor 21 wire 3 insulating coating P1 shallow position P2 deep position

Claims

1. An insulated electric wire comprising: a conductor; and an insulating coating containing cross-linked silicone rubber and covering the outer periphery of the conductor, wherein a position at a depth of 10% and a position at a depth of 90% from the outer surface of the thickness of the insulating coating are defined as a shallow position and a deep position, respectively, and the indentation hardness of the insulating coating at the shallow position is 1.1 times or more that at the deep position.

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

3. The insulated wire according to claim 1 or 2, wherein the indentation hardness of the insulating coating at the shallow position is 0.80 MPa or more.

4. The insulated wire according to claim 1 or 2, wherein the indentation hardness of the insulating coating at the deep position is less than 0.80 MPa.

5. An insulated electric wire according to claim 1 or 2, wherein the average of the indentation hardnesses of the insulating coating throughout its depth direction is defined as an average hardness, and the indentation hardness of the insulating coating at the shallower position is 1.1 times or more of the average hardness, and the indentation hardness of the insulating coating at the deeper position is 0.90 times or less of the average hardness.

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