JP2017188248A - Insulated wire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an insulated wire excellent in flame retardancy and direct-current stability.SOLUTION: An insulated wire has a conductor, and an insulating layer which is arranged on the outer periphery of the conductor and has an inner layer and an outer layer, where the inner layer is formed from a first resin composition containing a base polymer containing a polyolefin-based resin, the outer layer is formed from a second resin composition containing a base polymer containing a polyolefin-based resin and a flame retardant, a thickness of the inner layer is 0.215 mm or more, a thickness of the outer layer is 1.41 or more with respect to a thickness of the inner layer of 1, and the insulated wire has such flamer retardancy that a distance between an upper fixed portion and an upper end of a carbonization portion is 50 mm or more and a distance between the upper fixed portion and a lower end of the carbonization portion is less than 540 mm, after extinction, in a vertical flame test according to EN45545-2, and has such direct current stability as to prevent dielectric breakdown when immersed in salt water and charged for 240 hours in a direct current stability test according to EN50305.6.7.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an insulated wire.

  Insulated wires used as wiring for railway vehicles and automobiles are required not only to have electrical characteristics but also to be flame retardant so as not to burn in the event of a fire. Therefore, a flame retardant is mix | blended with the insulating layer of an insulated wire. For example, as a material for forming an insulating layer, a flame-retardant resin composition in which a polyolefin-based resin that is a base polymer is blended with a metal hydroxide that is a flame retardant has been proposed (see, for example, Patent Document 1).

JP 2013-18932 A

  By the way, an insulated wire is required to have high electrical characteristics such as insulation, withstand voltage, and direct current stability.

  However, with conventional insulated wires, it is difficult to ensure sufficient DC stability even if the insulation and withstand voltage can be increased. The direct current stability means that, for example, when a predetermined voltage is applied by immersing an insulated wire in salt water, dielectric breakdown does not occur even if a predetermined time elapses. In the insulating layer, the direct current stability tends to decrease due to the blending of the flame retardant, and this tendency becomes more prominent as the blending amount of the flame retardant increases. Although it is conceivable to reduce the blending amount of the flame retardant in order to improve the direct current stability, the high flame retardancy required for the insulating layer cannot be maintained. Thus, with conventional insulated wires, it is difficult to obtain a good balance between flame retardancy and DC stability at a high level.

  This invention is made | formed in view of the said subject, and aims at providing the insulated wire excellent in a flame retardance and DC stability.

According to one aspect of the invention,
Conductors,
An insulating layer disposed on the outer periphery of the conductor and having an inner layer and an outer layer;
The inner layer is formed from a first resin composition containing a base polymer containing a polyolefin resin,
The outer layer is formed from a second resin composition containing a base polymer containing a polyolefin-based resin and a flame retardant,
The inner layer has a thickness of 0.215 mm or more;
The thickness of the inner layer is 1 and the thickness of the outer layer is 1.41 or more,
In the vertical combustion test in accordance with EN45545-2, after extinguishing the flame, the distance between the upper fixed part and the carbonized part upper end is 50 mm or more, and the distance between the upper fixed part and the carbonized part lower end is less than 540 mm; ,
In the DC stability test according to EN50305.6.7, an insulated wire having DC stability that does not cause dielectric breakdown when immersed in salt water and applied for 240 hours is provided.

  According to the present invention, an insulated wire excellent in flame retardancy and DC stability can be obtained.

It is sectional drawing perpendicular | vertical to the length direction of the insulated wire which concerns on one Embodiment of this invention.

When the present inventors examined the said subject, it turned out that coexistence with a flame retardance and DC stability is difficult for the following reasons in an insulating layer.
Although a flame retardant is mix | blended with an insulating layer in order to improve a flame retardance, generally a flame retardant tends to have low adhesiveness with the base polymer which forms an insulating layer. Therefore, when a flame retardant is blended in the insulating layer, a minute gap is formed between the flame retardant and the base polymer. If there are minute gaps in the insulating layer, water will easily penetrate into the insulating layer when the insulated wire is immersed in water in the DC stability test. The penetration of water causes the insulating layer to conduct and eventually breaks down. That is, when a flame retardant is blended in the insulating layer, the insulating layer easily takes in water, so that the time until dielectric breakdown is shortened and the DC stability is lowered.

  Thus, while it is necessary to increase the blending amount of the flame retardant from the viewpoint of flame retardancy, it is necessary to suppress water penetration by reducing the blending amount of the flame retardant from the viewpoint of direct current stability. It is difficult to achieve both of these by simply adjusting the blending amount of the flame retardant.

  Therefore, the present inventors have studied paying attention to configuring the insulating layer not as a single layer structure but as a laminated structure including an inner layer and an outer layer. As a result, the inner layer is configured to have high direct current stability without the addition of a flame retardant, and the outer layer is configured to have a high flame resistance by adding a flame retardant. It was found that DC stability and flame retardancy can be achieved at a high level by setting the ratio within a predetermined range. The present invention has been made based on such knowledge.

[One Embodiment of the Present Invention]
Hereinafter, an embodiment of the present invention will be described.

<Configuration of insulated wire>
First, the structure of the insulated wire which concerns on one Embodiment of this invention is demonstrated, referring drawings. FIG. 1 is a cross-sectional view perpendicular to the length direction of an insulated wire according to an embodiment of the present invention. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

  As shown in FIG. 1, the insulated wire 1 according to this embodiment includes a conductor 11 and an insulating layer 12 having an inner layer 13 and an outer layer 14.

(conductor)
As the conductor 11, a commonly used metal wire, for example, a copper wire, a copper alloy wire, an aluminum wire, a gold wire, a silver wire, or the like can be used. Moreover, you may use what gave metal plating, such as tin and nickel, to the outer periphery of a metal wire. Further, a collective stranded conductor obtained by twisting metal wires can be used. The outer diameter of the conductor 11 is preferably 1.23 mm to 5.5 mm.

(Insulating layer)
An insulating layer 12 is provided on the outer periphery of the conductor 11. The insulating layer 12 has an inner layer 13 that covers the outer periphery of the conductor 11 and an outer layer 14 that covers the outer periphery of the inner layer 13.

  An inner layer 13 is disposed on the outer periphery of the conductor 11. As will be described later, the inner layer 13 is formed of a first resin composition that substantially does not contain a flame retardant, and is configured to have high DC stability. The inner layer 13 is formed, for example, by extruding and crosslinking the first resin composition on the outer periphery of the conductor 11.

  An outer layer 14 is disposed on the outer periphery of the inner layer 13. As will be described later, the outer layer 14 is formed of a second resin composition containing a flame retardant, and is configured to have high flame retardancy. The outer layer 14 is formed, for example, by extruding and crosslinking the second resin composition on the outer periphery of the inner layer 13.

In the present embodiment, the insulating layer 12 is configured such that the inner layer 13 having excellent DC stability and the outer layer 14 having excellent flame retardance have a predetermined thickness from the viewpoint of achieving both DC stability and flame retardancy. ing. Specifically, the thickness of the inner layer 13 is 0.215 mm or more, the thickness of the inner layer is 1, and the thickness of the outer layer is 1.41 or more. By setting the thickness of the inner layer 13 to at least 0.215 mm, the DC stability required for the insulated wire 1 can be obtained. On the other hand, since the inner layer 13 does not contain a flame retardant, the flame retardancy is low, and there is a risk of reducing the flame retardance of the entire insulating layer 12, but the outer layer 14 having excellent flame retardancy is provided on the outer periphery of the inner layer 13. By setting the thickness of the outer layer 14 to a ratio of 1.41 or more with respect to the thickness of the inner layer 13, the flame retardance can be increased while maintaining the DC stability of the entire insulating layer 12 high.
Thereby, in the vertical combustion test based on EN455545-2, the insulating layer 12 has a distance between the upper fixed portion and the carbonized portion upper end of 50 mm or more and a distance between the upper fixed portion and the carbonized portion lower end is less than 540 mm after the extinction. In the direct current stability test according to EN50305.6.7, the direct current stability is such that it does not break down when it is immersed in salt water and applied for 240 hours. .

  The thickness of the insulating layer 12, that is, the total thickness of the inner layer 13 and the outer layer 14, is not particularly limited, and may be appropriately changed according to the outer diameter of the conductor 11 to be used. For example, when the outer diameter of the conductor 11 is 1.23 mm to 5.5 mm, the thickness of the insulating layer 12 is preferably 0.7 mm to 0.8 mm. At this time, the thickness of the inner layer 13 is preferably 0.215 mm to 0.3 mm, and the thickness of the outer layer 14 is preferably 0.4 mm to 0.5 mm. Further, it is preferable that the thickness of the inner layer 13 is 1 and the thickness of the outer layer 14 is 1.41 or more and 3 or less. By configuring the insulating layer 12 in this way, it becomes possible to achieve both flame retardancy and DC stability at a higher level. In addition, the thickness of the outer layer 14 should just be 1.41 or more when the thickness of the inner layer 13 is 1, and the upper limit is not specifically limited. From the viewpoint of flame retardancy, the thicker outer layer 14 is better, but in order to reduce the diameter of the insulated wire 1 by reducing the outer layer 14 while maintaining the desired high flame retardancy, the thickness of the outer layer 14 is changed to the inner layer 13. The thickness is preferably 3 or less with respect to the thickness.

(First resin composition)
Then, the 1st resin composition which forms the inner layer 13 is demonstrated.
The first resin composition contains a base polymer containing a polyolefin-based resin and substantially does not contain a flame retardant. By not blending a flame retardant, it is possible to suppress a decrease in direct current stability due to blending of the flame retardant.

  As the base polymer of the inner layer 13, a polyolefin resin can be used. As the polyolefin resin, a polyethylene resin, a polypropylene resin, or the like can be used, and a polyethylene resin is particularly preferable. Examples of the polyethylene resin include low density polyethylene (LDPE), linear low density polyethylene (LLDPE), ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer. A polymer, an ethylene-glycidyl methacrylate copolymer, or the like can be used. These polyolefin resin may be used individually by 1 type, and may use 2 or more types together.

(Second resin composition)
Then, the 2nd resin composition which forms the outer layer 14 is demonstrated.
The second resin composition constituting the outer layer 14 contains a base polymer containing a polyolefin resin and a flame retardant.

  As the base polymer of the outer layer 14, the same components as the polyolefin resin of the inner layer 13 described above can be used. From the viewpoint of improving the flame retardancy of the outer layer 14, it is preferable to use an ethylene-vinyl acetate copolymer (hereinafter also referred to as EVA) as the polyolefin resin. EVA has vinyl acetate (hereinafter also referred to as VA) in its molecular skeleton, and when the outer layer 14 burns, it can suppress combustion by desorbing acetic acid and causing an endothermic reaction.

  Among EVAs, EVA having a melting point (Tm) measured by a differential scanning calorimetry (DSC method) of 70 ° C. or more is more preferable. EVA has a tendency to increase the amount of VA and increase the flame retardancy as Tm decreases. However, when the amount of VA increases, it tends to deteriorate due to an increase in acetic acid desorbed at the time of heating. May be low. If EVA has a Tm of 70 ° C. or higher, the amount of VA is 28% by mass or less and is in an appropriate range, so that desired flame retardancy can be obtained without impairing heat resistance. On the other hand, the upper limit value of Tm of EVA is not particularly limited, but is preferably 100 ° C. or less, more preferably 95 ° C. or less, and 90 ° C. or less from the viewpoint of obtaining desired flame retardancy. Is more preferable. According to EVA having a Tm of 100 ° C. or less, the VA amount is 6% by mass or more, and a desired flame retardancy can be obtained. That is, according to EVA having a Tm of 70 ° C. to 100 ° C., the heat resistance as well as the flame retardancy of the outer layer 14 can be maintained high.

  The base polymer of the outer layer 14 may contain two or more types of EVA having different Tm. For example, two or more types of EVA having a Tm of 70 ° C. or higher may be included, and EVA having a Tm of less than 70 ° C. may be included. EVA having a Tm of less than 70 ° C. has a larger VA amount than that of EVA having a Tm of 70 ° C. or more, and is 28% by mass or more. By using EVA having a Tm of less than 70 ° C. together with EVA having a Tm of 70 ° C. or more, the VA content in the base polymer constituting the outer layer 14 is adjusted to a range of 25% by mass or more and 50% by mass or less as described later. It becomes easy to do.

  EVA having a Tm of 70 ° C. or higher preferably has a melt mass flow rate (MFR) of 6 g / 10 min or higher. By using such EVA, the fluidity when the second resin composition is melted can be increased, and the productivity when forming the outer layer 14 by extrusion can be improved. In addition, when using 2 or more types of EVA, it is good that at least 1 type of MFR of these is 6 g / 10min or more.

  The base polymer constituting the outer layer 14 is preferably used in combination with the above-described EVA having a Tm of 70 ° C. or higher and an acid-modified polyolefin resin. The acid-modified polyolefin resin is obtained by modifying a polyolefin resin with an unsaturated carboxylic acid or a derivative thereof. The acid-modified polyolefin-based resin increases the adhesion between EVA and the flame retardant, and suppresses the formation of a gap at the interface between the EVA and the flame retardant. Thereby, the water absorption in the outer layer 14 can be reduced, and the direct current | flow stability fall by the mixing | blending of a flame retardant can be suppressed.

  In the acid-modified polyolefin-based resin, examples of the polyolefin-based resin include those described above. Examples of the acid component to be modified include maleic acid, maleic anhydride, and fumaric acid. These acid-modified polyolefin resins may be used alone or in combination of two or more.

  The acid-modified polyolefin resin preferably has a glass transition point (Tg) of −55 ° C. or lower. According to the acid-modified polyolefin resin having a Tg of −55 ° C. or lower, the Tg of the base polymer can be lowered, and cracking when the outer layer 14 is exposed to a low temperature environment can be suppressed. That is, the cold resistance of the outer layer 14 can be improved.

（式（１）中、Ｘ_ｋは、ある種類ｋのＥＶＡのＶＡ量（質量％）を、Ｙ_ｋは、ある種類ｋのＥＶＡがベースポリマ全体に占める割合を、そしてｋは自然数を、それぞれ示す。） In the second resin composition forming the outer layer 14, the VA content in the base polymer calculated by the following formula (1) is preferably 25% by mass to 50% by mass, and 25% by mass to 46% by mass. More preferably, it is more preferably 25% by mass to 35% by mass. When the amount of VA in the base polymer is less than 25% by mass, the flame retardancy of the outer layer 14 may be insufficient. On the other hand, if the amount of VA exceeds 50% by mass, the amount of acetic acid desorbed from EVA when the base polymer is heated to a high temperature increases, so that the EVA contained in the base polymer tends to deteriorate and the outer layer 14 Heat resistance may be reduced.

(In Formula (1), X _k is the VA amount (mass%) of EVA of a certain type k, Y _k is the ratio of the EVA of a certain type k to the entire base polymer, and k is a natural number, respectively. Show.)

  The amount of VA in the base polymer can be appropriately changed depending on the ratio (mass ratio) between EVA having VA and the acid-modified polyolefin resin. The ratio should just be a ratio from which the VA amount in a base polymer will be 25 to 50 mass%. Preferably, the ratio of EVA to the acid-modified polyolefin resin is 70:30 to 99: 1. That is, the EVA content is 70% by mass or more and 99% by mass or less, and the acid-modified polyolefin resin content is 1% by mass or more and 30% by mass or less with respect to the base polymer.

  The base polymer preferably contains EVA and an acid-modified polyolefin resin, but contains other polymers than EVA and the acid-modified polyolefin resin as long as the properties of the second resin assembly are not impaired. May be. In this case, the total content of EVA and acid-modified polyolefin-based resin is preferably 90% by mass or more, more preferably 95% by mass or more, and still more preferably 100% by mass with respect to the base polymer.

  A flame retardant is blended in the second resin composition forming the outer layer 14. As the flame retardant, a non-halogen flame retardant is preferable because it does not generate a toxic gas. For example, a metal hydroxide can be used. When the outer layer 14 is heated and burned, the metal hydroxide decomposes and dehydrates, lowers the temperature of the outer layer 14 with the released moisture, and suppresses the combustion. Examples of the metal hydroxide that can be used include magnesium hydroxide, aluminum hydroxide, calcium hydroxide, and metal hydroxides in which nickel is dissolved. These flame retardants may be used alone or in combination of two or more.

  From the viewpoint of controlling the mechanical properties (balance between tensile strength and elongation) of the outer layer 14, the flame retardant is a silane coupling agent, a titanate coupling agent, a fatty acid such as stearic acid, a fatty acid salt such as stearate, and a steer. It is preferable that the surface is treated with a fatty acid metal such as calcium phosphate.

  The blending amount of the flame retardant is preferably 100 parts by mass or more and 250 parts by mass or less with respect to 100 parts by mass of the base polymer. If the blending amount is less than 100 parts by mass, the flame retardancy of the outer layer 14 is lowered, and the desired high flame retardancy may not be obtained in the insulating layer 12. If the blending amount exceeds 250 parts by mass, the mechanical properties of the outer layer 14 are lowered, and the elongation rate may be lowered.

  The first resin composition and the second resin composition may contain other additives as necessary. For example, when the inner layer 13 or the outer layer 14 is cross-linked, a cross-linking agent or a cross-linking aid may be included. Examples of the crosslinking method include an irradiation crosslinking method in which crosslinking is performed by irradiation with an electron beam or radiation, and a chemical crosslinking method in which crosslinking is performed by heating. In the case of the irradiation crosslinking method, a crosslinking assistant may be contained in the first resin composition or the second resin composition. As the crosslinking aid, for example, trimethylolpropane triacrylate (TMPT), triallyl isocyanurate (TAIC: registered trademark), or the like can be used. In the case of the chemical cross-linking method, a cross-linking agent may be contained in the first resin composition or the second resin composition. As the crosslinking agent, for example, organic peroxides such as 1,3-bis (2-t-butylperoxyisopropyl) benzene and dicumyl peroxide (DCP) can be used.

  In addition to crosslinking agents, other additives include flame retardant aids, antioxidants, lubricants, softeners, plasticizers, inorganic fillers, compatibilizers, stabilizers, carbon black, colorants, etc. May be. These can be contained in the range which does not impair the characteristics of the first resin composition and the second resin composition.

  The first resin composition and the second resin composition can be obtained by mixing predetermined components and kneading while heating. The kneading conditions and the order of adding each component are not particularly limited. The kneading can be performed using a mixing roll, a Banbury mixer, a single-screw or twin-screw extruder, and the like.

<Insulated wire manufacturing method>
Next, the manufacturing method of the insulated wire 1 mentioned above is demonstrated.

  First, a first resin composition for forming the inner layer 13 is prepared by kneading, for example, low density polyethylene and a crosslinking agent as a base polymer. As the method, known means can be used. 1 resin composition is obtained.

  Moreover, the 2nd resin composition which forms the outer layer 14 is prepared similarly to the 1st resin composition. For example, a second resin composition for forming the outer layer 14 is prepared by kneading a base polymer containing EVA and an acid-modified polyolefin resin, a metal hydroxide, and a crosslinking agent.

  Subsequently, the inner layer 13 is formed by extruding the first resin composition with a predetermined thickness on the outer periphery of the conductor 11 using an extruder. Furthermore, the second resin composition is extruded at a predetermined thickness on the outer periphery of the inner layer 13 to form the outer layer 14. Then, the insulated wire 1 of this embodiment is obtained by bridge | crosslinking the inner layer 13 and the outer layer 14, for example. The inner layer 13 and the outer layer 14 may be formed by simultaneously extruding the first and second non-halogen resin compositions.

[Effects of the embodiment of the present invention]
According to the present embodiment, the following one or more effects are achieved.

The insulated wire 1 of this embodiment includes an inner layer 13 formed from a first resin composition that does not substantially contain a flame retardant and an outer layer 14 formed from a second resin composition that includes a flame retardant. 12, the thickness of the inner layer 13 is 0.215 mm or more, and the thickness of the outer layer 14 is 1.41 or more when the thickness of the inner layer 13 is 1. Since the inner layer 13 does not contain a flame retardant, the flame retardance is low, but there is no decrease in DC stability due to the inclusion of the flame retardant, and the DC stability is excellent. On the other hand, since the outer layer 14 includes a flame retardant, the direct current stability is lower than that of the inner layer 13 not including the flame retardant, but is excellent in flame retardancy. In the present embodiment, by setting the inner layer 13 and the outer layer 14 to a predetermined thickness, the insulating layer 12 can have high flame retardance while maintaining high DC stability.
Specifically, the insulation layer 12 has a distance of 50 mm or more between the upper fixed portion and the carbonized portion upper end after the extinction in the vertical combustion test in accordance with EN455545-2, and the distance between the upper fixed portion and the carbonized portion lower end. It has flame retardancy such that it is less than 540 mm, and DC stability that does not cause dielectric breakdown when immersed in salt water for 240 hours in a DC stability test according to EN 50305.6.7. become.

  According to this embodiment, for example, on the outer periphery of the conductor 11 having an outer diameter of 1.23 mm to 5.5 mm, the inner layer 13 having a thickness of 0.215 mm to 0.3 mm and the thickness of 0.4 mm to 0.5 mm. When the thickness of the inner layer 13 is 1, the outer layer 14 has a thickness of 1.41 to 3, and the insulating layer 12 has a thickness of 0.7 to 0.8 mm. By laminating so that the direct current stability and the flame retardance can be achieved at a higher level in the insulated wire 1.

In the present embodiment, the second resin composition forming the outer layer 14 includes an ethylene-vinyl acetate copolymer (EVA) having a melting point of 70 ° C. or higher by the DSC method and an acid-modified polyolefin resin, and is derived from EVA. It is preferable to contain a base polymer having a vinyl acetate content (VA amount) of 25% by mass or more and 50% by mass or less and a flame retardant.
EVA is a polymer containing vinyl acetate (VA) and excellent in flame retardancy, but if the amount of VA is excessively large, the heat resistance of the outer layer 14 may be reduced. In this respect, in the present embodiment, the use of EVA having a melting point of 70 ° C. or more and an appropriate amount of VA makes it possible to achieve both flame retardancy and heat resistance.
The acid-modified polyolefin resin increases the adhesion between EVA and the flame retardant, suppresses the formation of gaps at the interface between EVA and the flame retardant, reduces the water absorption in the outer layer 14, and the direct current due to the incorporation of the flame retardant. A decrease in stability can be suppressed.
Thus, in the 2nd resin composition which forms the outer layer 14, by using predetermined EVA and acid-modified polyolefin-type resin so that VA amount may be 25 mass%-50 mass%, in the insulating layer 12 Both DC stability and flame retardancy can be achieved at a high level, and heat resistance can be maintained high.

  EXAMPLES Next, although this invention is demonstrated in detail based on an Example, this invention is not limited to these Examples.

In this example, the following components were used as raw materials for forming the inner layer and the outer layer.
・ Linear low density polyethylene (LLDPE) (“Evolue SP1510” manufactured by Prime Polymer Co., Ltd.)
EVA (1) (TM: 89 ° C., MFR: 15 g / 10 min, VA amount: 14% by mass): Mitsui DuPont Polychemical Co., Ltd. “Evaflex EV550X”
EVA (2) (TM: less than 70 ° C., MFR: 100 g / 10 min, VA amount: 46 mass%): “Evaflex EV45X” manufactured by Mitsui DuPont Polychemical Co., Ltd.
Acid-modified polyolefin (TM: 70 ° C., Tgi-55 ° C. or lower): “Tuffmer MA8510” manufactured by Mitsui Chemicals, Inc.
Magnesium hydroxide: “Mag sheath S4” manufactured by Kamishima Chemical Co., Ltd.
Trimethylol propantoacrylate (crosslinking aid): “TMPT” manufactured by Shin-Nakamura Chemical Co., Ltd.

<Production of insulated wires>
First, a resin composition for forming an inner layer and an outer layer was prepared.
In this example, LLDPE was used as the inner layer forming material (first resin composition).
Further, 20 parts by mass of EVA (1), 50 parts by mass of EVA (2), 30 parts by mass of acid-modified polyolefin, 100 parts by mass of magnesium hydroxide, and 4 parts by mass of a crosslinking aid. By mixing and kneading, a second resin composition as a material for forming the outer layer was prepared. In the second resin composition, the VA content in the base polymer was 25.8% by mass.

Subsequently, the prepared first resin composition and second resin composition were extruded on the outer periphery of the conductor to form an inner layer and an outer layer, and an insulated wire was produced.
Specifically, a twisted conductor having an outer diameter of 1.23 mm was prepared by twisting 37 strands having an outer diameter of 0.18 mm. Subsequently, an inner layer and an outer layer were formed on the outer periphery by simultaneously extruding the first resin composition and the second resin composition with a predetermined thickness, respectively, and irradiating them with an electron beam to crosslink them. . In Examples 1 to 16 and Comparative Examples 1 to 4, the thickness of the inner layer and the outer layer, and the ratio of the thicknesses were appropriately changed as shown in Tables 1 and 2 below, to produce insulated wires. In Tables 1 and 2, the thicknesses of the inner layer and the outer layer are the minimum values in the length direction of the insulated wire.

<Evaluation of insulated wires>
The produced insulated wire was evaluated by the following method.

(DC stability)
The DC stability of the insulated wire was evaluated by a DC stability test in accordance with EN50305.6.7. Specifically, as the manufactured insulated wire, three samples were prepared, these three samples were immersed in salt water, + 1500V and -1500V were applied as DC voltages, and all three samples were passed even after 10 days or more. When the dielectric breakdown did not occur, the test was evaluated as “good” as being excellent in direct current stability, and “failed” as “low” as the DC stability was low when even one of the insulation breakdown was less than 10 days.

(Flame retardance)
The flame retardancy was evaluated by a flame retardancy test in accordance with EN45554-2. Specifically, after the burned flame was applied to the manufactured insulated electric wire having a length of about 60 cm at a position of 475 mm from the upper fixing portion at an angle of 45 ° for 1 minute, the distance between the upper fixing portion and the carbonized upper end was If it is 50 mm or more and the distance between the upper fixed part and the lower end of the carbonized part is less than 540 mm, it will be accepted as “good” as being excellent in flame retardancy, otherwise it will be rejected as being inferior in flame resistance. evaluated.

<Evaluation results>
In each of Examples 1 to 16, the thickness of the inner layer having excellent DC stability is 0.215 mm or more, the thickness of the outer layer having excellent flame retardancy is set to 1, and the thickness of the outer layer is 1. Therefore, it was confirmed that DC stability and flame retardancy can be achieved at a high level in the insulating layer composed of the inner layer and the outer layer.
On the other hand, in Comparative Examples 1 to 4, although high flame retardancy can be obtained by setting the outer layer to a predetermined thickness, the thickness of the inner layer is smaller than 0.215 mm, so the desired DC stability cannot be obtained, It was confirmed that DC stability and flame retardancy cannot be achieved at a high level. For example, in Comparative Examples 1 and 3, it was confirmed on the 9th day that one of the three samples breaks down. In Comparative Example 2, it was confirmed that dielectric breakdown occurred one by one on the 6th, 7th, and 8th days, and that all 3 samples breakdown. In Comparative Example 4, it was confirmed that dielectric breakdown occurred on the 6th and 9th days, and that all 3 breakdowns.

<Preferred embodiment of the present invention>
Hereinafter, preferred embodiments of the present invention will be additionally described.

[Appendix 1]
According to one aspect of the invention,
Conductors,
An insulating layer disposed on the outer periphery of the conductor and having an inner layer and an outer layer;
The inner layer is formed from a first resin composition containing a base polymer containing a polyolefin resin,
The outer layer is formed from a second resin composition containing a base polymer containing a polyolefin-based resin and a flame retardant,
The inner layer has a thickness of 0.215 mm or more;
The thickness of the inner layer is 1 and the thickness of the outer layer is 1.41 or more,
In the vertical combustion test in accordance with EN45545-2, after extinguishing the flame, the distance between the upper fixed part and the carbonized part upper end is 50 mm or more, and the distance between the upper fixed part and the carbonized part lower end is less than 540 mm; ,
In the DC stability test according to EN50305.6.7, an insulated wire having DC stability that does not break down when immersed in water and applied for 240 hours is provided.

[Appendix 2]
In the insulated wire of appendix 1, preferably,
The inner layer has a thickness of 0.215 mm to 0.3 mm.

[Appendix 3]
In the insulated wire of appendix 1 or 2,
The outer diameter of the conductor is 1.23 mm or more and 5.5 mm or less.

[Appendix 4]
In the insulated wires of appendices 1 to 3, preferably,
The insulating layer has a thickness of 0.7 mm or more and 0.8 mm or less.

[Appendix 5]
In the insulated wires according to appendices 1 to 4, preferably,
The flame retardant is a metal hydroxide.

[Appendix 6]
In the insulated wires according to appendices 1 to 5,
The second resin composition forming the outer layer contains the flame retardant in an amount of 100 parts by mass to 150 parts by mass with respect to 100 parts by mass of the base polymer.

[Appendix 7]
In the insulated wires of appendices 1 to 6, preferably,
The second resin composition forming the outer layer contains an ethylene-vinyl acetate copolymer and an acid-modified polyolefin resin having a melting point of 70 ° C. or higher by DSC, and is derived from the ethylene-vinyl acetate copolymer. A base polymer having a vinyl acetate content of 25% by mass to 50% by mass and a flame retardant are contained.

[Appendix 8]
In the insulated wire of appendix 7, preferably,
The acid-modified polyolefin resin has a glass transition point (Tg) of −55 ° C. or lower.

[Appendix 9]
In the insulated wire of appendix 7 or 8,
The second resin composition forming the outer layer includes the ethylene-vinyl acetate copolymer and the acid-modified polyolefin resin in a ratio of 70:30 to 99: 1.

1 Insulated wire 11 Conductor 12 Insulating layer 13 Inner layer 14 Outer layer

Claims (5)

Conductors,
An insulating layer disposed on the outer periphery of the conductor and having an inner layer and an outer layer;
The inner layer is formed from a first resin composition containing a base polymer containing a polyolefin resin,
The outer layer is formed from a second resin composition containing a base polymer containing a polyolefin-based resin and a flame retardant,
The inner layer has a thickness of 0.215 mm or more;
The thickness of the inner layer is 1 and the thickness of the outer layer is 1.41 or more,
In the vertical combustion test in accordance with EN45545-2, after extinguishing the flame, the distance between the upper fixed part and the carbonized part upper end is 50 mm or more, and the distance between the upper fixed part and the carbonized part lower end is less than 540 mm; ,
An insulated wire having a DC stability that does not cause dielectric breakdown when immersed in salt water for 240 hours in a DC stability test according to EN50305.6.7.   The insulated wire according to claim 1 whose thickness of said inner layer is 0.215 mm or more and 0.3 mm or less.   The insulated wire according to claim 1 or 2, wherein an outer diameter of the conductor is 1.23 mm or more and 5.5 mm or less.   The insulated wire in any one of Claims 1-3 whose thickness of the said insulating layer is 0.7 mm or more and 0.8 mm or less.   The insulated wire according to any one of claims 1 to 4, wherein the flame retardant is a metal hydroxide.

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