JP2013125632A - Method for manufacturing electric wire coated with silane crosslinked polyethylene, and method for manufacturing cable coated with silane crosslinked polyethylene - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric wire/cable manufacturing method capable of reducing a time of a crosslinking operation, and restraining manufacturing costs from increasing due to capital investment as much as possible, the electric wire/cable having a high degree of crosslinking and a smooth appearance after extrusion molding.SOLUTION: A conductor 10 is crosslinked with polyethylene graft-copolymerized with a silane compound by a free radical generation agent on the conductor to obtain silane crosslinked polyethylene. The polyethylene graft-copolymerized with the silane compound by the free radical generation agent has a melt index of 5 g/10 minutes or less under test conditions of 190°C and 21.18 N. The silane compound in an amount of 1.5 weight portion or more is contained in 100 weight portion of polyethylene. The silane crosslinked polyethylene in which a ratio of an addition amount of the silane compound to an addition amount of the free radical generation agent is 35 or more is extrusion-coated to form an insulation coating layer, and the extrusion-coated insulation coating layer is crosslinked on the conductor through a heating pipe 12 supplied with overheated steam.

Description

  The present invention relates to a method for producing an electric wire coated with silane-crosslinked polyethylene and a method for producing a cable coated with silane-crosslinked polyethylene.

  Polyethylene is used as a coating material for electric wires and a coating material for cables because of its excellent electrical insulation. In particular, cross-linked polyethylene obtained by introducing a cross-linked structure into polyethylene can add heat resistance to the coating material, and is therefore widely used as a coating material for power cables and the like. Examples of methods for crosslinking polyethylene include organic peroxide crosslinking, electron beam irradiation crosslinking, and silane crosslinking. Here, in the silane crosslinking, after the polyethylene is molded, the crosslinking proceeds by simply leaving the polyethylene copolymerized with the silane compound in the atmosphere containing moisture or in a high humidity environment. Therefore, there is a merit that the initial capital investment can be relatively reduced, and it is utilized as a method for manufacturing a low voltage power cable of about 600V.

  Conventionally, an electric wire / cable using a silane-crosslinked polyolefin having an insulating layer composed of a silane-crosslinked polyolefin containing no fluorine-based lubricant around the conductor, and the surface of the insulating layer is made of polyethylene having a melting point of 130 ° C. or higher. There is known an electric wire / cable using a silane-crosslinked polyolefin having a skin layer and an insulating layer and a skin layer formed by solid extrusion molding (for example, see Patent Document 1).

  According to the electric wire / cable using the silane cross-linked polyolefin described in Patent Document 1, the insulating layer of the silane cross-linked polyolefin provided around the conductor has a sufficient degree of cross-linking, and has heat deformation characteristics and extrusion appearance. Can provide good electric wires and cables.

JP 2008-181754 A

  Electric wires and cables using silane-crosslinked polyethylene are generally produced as follows. That is, first, in order to graft copolymerize a silane compound with polyethylene, polyethylene, a silane compound, and a free radical generator are mixed, kneaded and reacted. Next, after adding a silanol condensation catalyst here, the conductor which consists of copper, or a cable core is extrusion-coated. In the extrusion coating process, a polyethylene obtained by graft copolymerization of a silane compound is prepared once, and in a separate process, the silanol condensation catalyst and the polyethylene are mixed and kneaded and extrusion coated. The entire kneading process is carried out with one extruder. In addition, there are methods such as extrusion coating. The wire / cable obtained in this way is allowed to stand in the atmosphere or in a high humidity environment, so that the coating material is cross-linked.

  And with the globalization of the market in recent years, there is an active movement to align domestic standards with international standards. In the field of low-voltage power cables, a JIS standard that conforms to the IEC standard is established, and in particular, a crosslinked polyethylene used as an insulator is required to pass a hot set test at an air temperature of 200 ° C. The hot set test measures the ease of deformation of an insulating material at a high temperature, and polyethylene having a low degree of cross-linking, which could be used in the conventional standards, is greatly rejected and rejected. For this reason, development of the silane crosslinked polyethylene with a higher degree of crosslinking is calculated | required.

  However, increasing the addition amount of the silane compound and the addition amount of the free radical generator for the purpose of increasing the degree of crosslinking of the silane-crosslinked polyethylene will result in rough surface and extrusion-like projections during extrusion molding. May occur. Therefore, it may be difficult to improve the degree of crosslinking of the silane-crosslinked polyethylene used for the wire / cable coating material.

  In addition, the method of leaving the wires and cables obtained by extrusion coating in the atmosphere and crosslinking as in the prior art takes about one week in order to obtain a higher degree of crosslinking than the conventional method. It takes a long time to get In addition, the method of leaving and crosslinking in the air has a problem that the required number of days fluctuates due to seasonal factors such as temperature and humidity, making it difficult to manage quality.

  In order to solve this problem, there is a method in which an electric wire / cable wound around a drum is placed in a crosslinking facility adjusted to a high temperature and a high humidity to be crosslinked. A desired degree of crosslinking can be obtained by leaving it in the environment for about 1 day, and the workability of quality control can be improved.

  However, with this method, considering the mass production of electric wires and cables, it is necessary to specially prepare extremely large capacity bridging equipment, which leads to an increase in capital investment and, in turn, increases the production cost of electric wires and cables. End up.

  Therefore, in obtaining wires / cables using silane-crosslinked polyethylene having a desired high degree of crosslinking, a method for producing wires / cables that can minimize the time required for crosslinking work and suppress the increase in production costs due to capital investment. Development is required.

  Accordingly, the object of the present invention is to produce electric wires and cables that have a high degree of cross-linking, have a smooth appearance after extrusion, and can minimize the time required for cross-linking operations and increase in manufacturing costs due to capital investment. It is to provide a method.

  (1) In order to achieve the above object, the present invention is a silane-crosslinked polyethylene obtained by crosslinking a conductor and polyethylene obtained by graft copolymerization of a silane compound with a free radical generator on the conductor, the silane Polyethylene obtained by graft copolymerization of the compound with the free radical generator has a melt index of 5 g / 10 min or less at 190 ° C. and 21.18 N, and the silane compound is 1. An insulating coating layer is formed by extrusion coating silane-crosslinked polyethylene which is contained in an amount of 5 parts by weight or more and the ratio of the addition amount of the silane compound is 35 or more with respect to the addition amount of the free radical generator. A silane cross-linked poly-Si film characterized by cross-linking an insulating coating layer formed by extrusion coating through a heating tube supplied with superheated steam. Method for producing a coated comprising insulated wire of styrene are provided.

  (2) In order to achieve the above object, the present invention provides a silane obtained by crosslinking polyethylene obtained by graft copolymerization of a silane compound with a free radical generator on the outside of an electric wire having an insulating coating layer formed on a conductor. Crosslinked polyethylene, which is a polyethylene obtained by graft copolymerization of the silane compound with the free radical generator, has a melt index of 5 g / 10 min or less under 190 ° C. and 21.18 N test conditions, A sheath layer is formed by extrusion-coating silane-crosslinked polyethylene which is contained in an amount of 1.5 parts by weight or more with respect to 100 parts by weight of polyethylene and the ratio of the addition amount of the silane compound is 35 or more with respect to the addition amount of the free radical generator. The sheath layer extrusion-coated on the insulating coating layer was cross-linked by passing it through a heating tube supplied with superheated steam. Method for producing a cable is provided which is formed by coating the silane cross-linked polyethylene, characterized in.

  According to the method for producing an electric wire and cable coated with the silane-crosslinked polyethylene according to the present invention, the degree of crosslinking is high, the appearance after extrusion is smooth, the production time is shortened and the equipment is invested. It is possible to provide a method of manufacturing an electric wire or cable that can suppress an increase in cost as much as possible.

It is a side view of the manufacturing apparatus for demonstrating the manufacturing method of the electric wire or cable which coat | covers the silane crosslinked polyethylene which concerns on embodiment of this invention. It is drawing for demonstrating the extruder in the manufacturing method of the electric wire or cable which coat | covers the silane crosslinked polyethylene which concerns on embodiment of this invention. It is sectional drawing of an electric wire provided with the insulator which consists of silane crosslinked polyethylene concerning embodiment of this invention. It is sectional drawing of a cable provided with the sheath layer which consists of silane crosslinked polyethylene concerning embodiment of this invention.

[Embodiment]
The silane-crosslinked polyethylene used in the method for producing an electric wire or cable coated with the silane-crosslinked polyethylene according to the embodiment of the present invention is a silanol condensation catalyst obtained by graft-copolymerizing a silane compound with a free radical generator, and Silane-crosslinked polyethylene crosslinked in the presence of moisture. Specifically, in the silane-crosslinked polyethylene, the silane compound is contained in an amount of 1.5 parts by weight or more with respect to 100 parts by weight of polyethylene, the ratio of the addition amount of the silane compound to the addition amount of the free radical generator is 35 or more, The melt index of polyethylene obtained by graft copolymerization of the compound with a free radical generator at 190 ° C. and 21.18 N is 5 g / 10 min or less.

  The amounts of the silane compound and the free radical generator added to the polyethylene are based on the following results that have been intensively studied by the present inventors.

  That is, first, in a reaction in which a silane compound is graft copolymerized with polyethylene, a free radical generator is decomposed by heat to generate free radicals. The generated free radicals extract hydrogen from the polyethylene, thereby generating polymer radicals. When a silane compound is added to the generated polymer radical, polyethylene obtained by graft copolymerization of the silane compound is obtained.

  However, actually, in addition to the above reaction, bonds between polymer radicals occur simultaneously. When this reaction proceeds too much, the molecular weight of polyethylene increases, and further, a three-dimensional bridge structure is formed and crosslinked. As a result, the fluidity at the time of extrusion is reduced, resulting in a problem of poor appearance due to surface roughness, protrusions and the like. When a silanol condensation catalyst is added at the time of extrusion coating, reaction between polyethylenes obtained by graft copolymerization of a silane compound due to the influence of moisture in the polymer also occurs, so these problems appear more remarkably.

  On the other hand, the present inventor added 1.5 parts by weight or more of silane compound to 100 parts by weight of polyethylene, and the ratio of the addition amount of the silane compound to the addition amount of the free radical generator (ie, weight). Ratio) is 35 or more, and the melt index under the test conditions of 190 ° C. and 21.18 N of polyethylene obtained by graft copolymerization of the silane compound with a free radical generator is 5 g / 10 min or less. The inventor has obtained knowledge that can prevent the occurrence of surface roughness and protrusions. Furthermore, the present inventor obtained knowledge that a silane-crosslinked polyethylene having a high degree of crosslinking can be obtained after promoting crosslinking under appropriate conditions, and the electric wire formed by coating the silane-crosslinked polyethylene according to the present embodiment or It came to the manufacturing method of a cable.

  This is because the polymer radical generated by the free radical generator reacts preferentially with the excessively added silane compound, so that the high molecular weight and cross-linking of polyethylene can be suppressed, so that the deterioration of extrudability can be suppressed. At the same time, it is considered that a high degree of crosslinking can be realized by increasing the graft amount of the silane compound.

  Next, the manufacturing process of the manufacturing method of the electric wire or cable which coat | covers silane crosslinked polyethylene was examined. In a resin or rubber material, it is a common technique to increase the temperature in order to accelerate the crosslinking reaction with an organic peroxide or sulfur. However, in silane crosslinking, a sufficient crosslinking rate cannot be obtained even if the temperature is raised to 100 ° C. or higher with hot air, hot air, or the like in an environment with little moisture. This is thought to be due to the lack of water necessary for the reaction. There is also a problem that polyethylene is oxidized when the temperature is too high.

  Therefore, the inventors decided to study the promotion of crosslinking in the presence of high-temperature steam. In general, high-temperature steam at 100 ° C. or higher refers to high-pressure saturated steam. In high-pressure saturated water vapor, the temperature and pressure are uniquely determined. For example, a pressure of about 1.6 MPa is required to achieve 200 ° C. For this reason, when applied to the promotion of cross-linking of electric wires / cables, the apparatus becomes large, and there is a problem that the extrusion-coated polyethylene is deformed by pressure.

  Then, the inventors further studied the evaporated steam by paying attention to the superheated steam that was heated to a high temperature of 100 ° C. or higher while maintaining the normal pressure. As a result, it was found that the silane crosslinking speed was dramatically improved by heating in high-temperature superheated steam for a short time, and the present invention was obtained. This is considered to be due to the simultaneous supply of temperature (energy) and moisture necessary for the reaction. Furthermore, since the apparatus for generating superheated steam is simple, the deformation of the polyethylene is suppressed due to normal pressure, and since there is hardly any oxygen, the oxidative deterioration of the polyethylene does not occur. It was confirmed that the process is suitable for the method of manufacturing electric wires and cables coated with.

  The silane compound used in this embodiment has both a group capable of reacting with a polymer and an alkoxy group that forms a crosslink by silanol condensation. Specifically, the silane compound may be vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane or the like, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β. Aminosilane compounds such as-(aminoethyl) γ-aminopropyltrimethoxysilane, β- (aminoethyl) γ-aminopropylmethyldimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, β- (3,4- Epoxycyclohexyl) ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, epoxysilane compounds such as γ-glycidoxypropylmethyldiethoxysilane, acrylic silane compounds such as γ-methacryloxypropyltrimethoxysilane, bis ( -(Triethoxysilyl) propyl) disulfide, polysulfide silane compounds such as bis (3- (triethoxysilyl) propyl) tetrasulfide, mercaptosilane compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, etc. Can be used.

  Examples of the free radical generator include dicumyl peroxide, benzoyl peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, t-butylperoxyisopropyl carbonate, t- Thermal decomposition of butyl peroxybenzoate, 2,5-dimethyl-2,5-bis (benzoylperoxy) hexane, methyl ethyl ketone peroxide, 2,2-bis (t-butylperoxy) butane, cumene hydroperoxide, etc. However, organic peroxides that generate free radicals can be mainly used.

  In the present embodiment, 1.5 parts by weight or more of the silane compound is added to 100 parts by weight of polyethylene. That is, the silane compound is added in an amount of 1.5 parts by weight or more for the purpose of increasing the degree of crosslinking of the silane-crosslinked polyethylene obtained by increasing the amount of the silane compound graft-copolymerized to polyethylene. If the silane compound is less than 1.5 parts by weight, the degree of crosslinking is low and the hot set test cannot be passed. Moreover, it is preferable to add 5 parts by weight or less of the silane compound in order to suppress the generation of foreign matters due to an increase in the reaction between the silane compounds and the deterioration of the appearance and characteristics of the molded product.

  Further, the weight ratio of the addition amount of the silane compound to the addition amount of the free radical generator is set to 35 or more. Here, the weight ratio can be calculated by (a) / (b) where the addition amount of the silane compound is (a) and the addition amount of the free radical generator is (b). (A) / (b) is set to 35 or more in order to suppress the rough appearance and the formation of protrusions due to the increase in the molecular weight of polyethylene. When (a) / (b) is less than 35, a good extruded appearance cannot be obtained. Moreover, it is preferable to set (a) / (b) to 150 or less in order to suppress the generation of foreign matters due to an increase in the reaction between silane compounds and the deterioration of the appearance and characteristics of the molded product.

  Examples of the polyethylene used in the present embodiment include high-density polyethylene, linear low-density polyethylene, low-density polyethylene, or ultra-low-density polyethylene, or a mixture of two or more of these.

  Furthermore, the melt index under the test conditions of 190 ° C. and 21.18 N of polyethylene obtained by graft copolymerization of the silane compound according to the present embodiment with a free radical generator is 5 g / 10 min or less. When the melt index exceeds 5 g / 10 min, the molecular weight of polyethylene tends to be low, and the degree of crosslinking tends to be difficult to increase, and the hot set test cannot be passed.

  A silanol condensation catalyst can be further added to the silane-crosslinked polyethylene according to the present embodiment. Examples of the silanol condensation catalyst used include dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, dioctyltin diacetate, dibutyltin dioctate, dioctyltin dioctate, stannous acetate, stannous caprylate, tin bisneodecanoate, capryl Zinc acid, zinc naphthenate, cobalt naphthenate and the like can be mentioned. In order to increase the condensation efficiency, acids such as carboxylic acid compounds and sulfonic acid compounds and alkalis such as amine compounds may be used, or they may be used in combination with the above-described tin and zinc compounds. The amount of addition depends on the type of catalyst, but is set to 0.001 to 1.0 parts by weight per 100 parts by weight of polyethylene. As an addition method, in addition to the method of adding the reagent as it is, a method of using a master batch previously mixed with a crystalline polyolefin resin such as polyethylene can also be adopted.

  Further, the silane-crosslinked polyethylene according to the present embodiment includes a process oil, a processing aid, a flame retardant, a flame retardant aid, a crosslinking agent, a crosslinking aid, an antioxidant, an ultraviolet absorber, a copper damage inhibitor, and a lubricant. In addition, compounding agents such as inorganic fillers, compatibilizers, stabilizers, carbon black, and colorants can be appropriately added.

  In order to generate superheated steam, it is necessary to further heat 100 ° C. saturated steam, and methods such as heating with a burner, electric heater, electromagnetic induction, etc. are known. In the present invention, a known heating method is adopted. May be.

  The generated superheated steam is supplied into a heating pipe installed after the extruder. The supply port to the heating tube may be provided at one place or a plurality of places according to the length of the heating pipe. The degree of cross-linking of the polyethylene after passing through the heating tube depends on the temperature of the superheated steam and the residence time in the heating tube. Since these conditions vary depending on the blend of the silane-crosslinked polyethylene, they can be set as appropriate. However, if the temperature of the superheated steam is too low or if the residence time in the heating tube is too short, there is a concern that the crosslinking reaction will not be sufficiently promoted, so the temperature of the superheated steam is preferably in the range of 150 to 600 ° C. The residence time in the heating tube is preferably 10 seconds or longer. Since the residence time in the heating tube is determined by the length of the heating tube and the conveyance speed of the electric wire / cable, it can be adjusted by the conveyance speed when the length of the heating tube is constant.

  In order to prevent the temperature drop of the superheated steam in the pipe and the heating pipe from the superheated steam generator to the heating bowl, a method of heating the circumference of the pipe and the heating pipe with a heater or the like can be taken. In addition, polyethylene may foam due to moisture in the interior during heating. In that case, it is also possible to pressurize the inside of the heating tube by a general method as long as the covering material is not deformed.

  As a method for extruding silane-crosslinked polyethylene, a known production method can be applied. An example will be described with reference to FIG. Polyethylene is charged from the raw material hopper 16 of the extruder 11, and then a mixed liquid of the silane compound and the free radical generator is charged from the liquid inlet 17 on the downstream side, and the silane compound is graft copolymerized with the polyethylene. Further, a silanol condensation catalyst is introduced from the downstream supply port 18, kneaded, and extrusion coated onto the conductor.

  In addition, a method in which the raw material hopper is charged all at once, a polyethylene having a silane compound graft-copolymerized in advance is prepared, this is charged from the raw material hopper, and a silanol condensation catalyst is charged from the raw material hopper or the supply port 18 There are ways to do this.

  The extrusion temperature at this time is selected to be a temperature higher than the melting point of polyethylene, and is generally 80 to 200 ° C. Further, when the silane compound is graft-copolymerized, it is necessary to select a temperature at which the free radical generator is sufficiently decomposed to generate free radicals within the residence time of the extruder. When the extrusion temperature is lower than 100 ° C., a phenomenon occurs in which superheated steam is condensed in the heating tube and water droplets are generated on the surface. Since this takes away latent heat when it re-evaporates, there is a problem that the material temperature stagnates around 100 ° C. For this reason, it is desirable that the extrusion temperature be 100 ° C. or higher.

  FIG. 3: shows the outline | summary of the cross section of an electric wire provided with the insulator which consists of silane bridge | crosslinking polyethylene concerning embodiment of this invention. FIG. 4 shows an outline of a cross section of a cable including a sheath layer made of silane-crosslinked polyethylene according to the embodiment of the present invention. One structural example of an apparatus for carrying out the manufacturing method of the present invention will be described with reference to FIG.

  The electric wire 1 includes a conductor 10 made of a metal material such as copper, and an insulator 20 as an insulating coating layer that covers the outer periphery of the conductor 10. The cable 2 includes a sheath 30 as a sheath layer that covers the outer periphery of the electric wire 1. The insulator 20 and the sheath 30 are mainly composed of silane-crosslinked polyethylene according to the present embodiment. Each of the insulator 20 and the sheath 30 covers the conductor 10 or the electric wire 1 by extrusion molding of silane-crosslinked polyethylene.

  The conductor 10 is supplied from the feeder 21. The polyethylene obtained by graft copolymerization of the silane compound passes through the crosshead portion of the extruder 11 and is coated on the conductor 10. Subsequently, superheated steam is supplied from the superheated steam generator 13 to the installed heating pipe 12, and the electric wire 1 covered with polyethylene continuously passes through this. At this time, silane crosslinking proceeds. Subsequently, it is cooled in the cooling water tank 14 and taken up by the winder 15. Here, although the manufacturing method of the electric wire provided with the insulator which consists of silane bridge | crosslinking polyethylene was demonstrated, this manufacturing method is made to pass through the heating pipe 12 installed continuously, after extrusion-coating the insulation coating layer as a sheath layer. By carrying out silane crosslinking by this, it can be used also about the manufacturing method of a cable provided with the sheath layer which consists of silane crosslinked polyethylene.

(Effect of embodiment)
The silane-crosslinked polyethylene used in the method for producing an electric wire or cable coated with the silane-crosslinked polyethylene according to the present embodiment includes 1.5 parts by weight or more of silane compound with respect to 100 parts by weight of polyethylene. The ratio of the added amount to the added amount of the free radical generator is 35 or more, and the melt index of polyethylene obtained by graft copolymerization of the silane compound with the free radical generator at 190 ° C. and 21.18 N is 5 g / 10 Since it is less than or equal to minutes, the degree of crosslinking can be increased, and the extruded appearance can be smoothed. In addition, in the method of manufacturing an electric wire or cable coated with the silane-crosslinked polyethylene according to the present embodiment, a high degree of crosslinking can be realized, the time required for the crosslinking work can be shortened, and the capital investment compared to the conventional method. It is possible to suppress the increase in manufacturing cost due to the above. Moreover, according to the method of manufacturing an electric wire or cable coated with the silane-crosslinked polyethylene according to the present embodiment, the electric wire or cable is installed after the extruder, and is passed through a heating tube supplied with superheated steam. It can be continuously heated and crosslinked. Such electric wires / cables coated with silane-crosslinked polyethylene can be used as electric wires and cables such as low-voltage power cables.

  The electric wire provided with the coating | covering material which consists of silane crosslinked polyethylene which concerns on Examples 1-5 and the electric wire which concerns on Comparative Examples 1-8 were produced.

  First, polyethylene obtained by graft copolymerization with a silane compound was prepared. Using a single screw extruder with a screw diameter of 100 mm, in accordance with the composition shown in Table 1, polyethylene is introduced from the raw material hopper, and then a mixed liquid of vinyltrimethoxysilane and dicumyl peroxide is introduced from the downstream liquid injection port. A silane compound was graft copolymerized. The cylinder temperature was set to 200 ° C., and extrusion was performed so that the residence time in the extruder was 1 to 2 minutes.

Subsequently, using a single screw extruder having a screw diameter of 130 mm, a masterbatch containing polyethylene and a silanol condensation catalyst graft-copolymerized with the silane compound was introduced from a hopper according to the composition shown in Table 1, kneaded, and then on a copper conductor. Coated. The cylinder temperature was set to 190 ° C. and extrusion was performed so that the residence time in the extruder was 2 to 3 minutes. The conductor size was 100 sq, the insulating coating thickness was 2.0 mm, and the take-up speed was 30 m / min.

  The extruded electric wire was passed through a heating pipe having a length of 15 m installed after the extruder. Superheated steam at 150 ° C., 200 ° C., and 400 ° C. was supplied to the heating tube. As the superheated steam generator, an apparatus for generating superheated steam by electromagnetic induction was used. The residence time in the heating tube is 30 seconds. Thereafter, the cooled and wound electric wire was used as an evaluation sample.

  For comparison, an electric wire manufactured under the same temperature condition using a continuous atmospheric hot-air vulcanizer was also evaluated. The normal-pressure hot air vulcanizing device is a device that uses hot air heated by electric heat to accelerate the crosslinking, and is a known device that is often used for vulcanizing silicone rubber.

  In addition, an electric wire that is cooled and wound without passing through a heating tube after extrusion is manufactured, and thereafter, the crosslinking is promoted for 24 hours in a thermostatic chamber at 80 ° C. and a relative humidity of 95%, and 23 ° C., A cross-linked product for 7 days in a room adjusted to a relative humidity of 50% was also evaluated. Each evaluation was performed by the following method.

(Melt index)
Regarding polyethylene obtained by graft copolymerization with a silane compound, a melt index (melt mass flow rate) based on JIS K 7210 was measured. The temperature was 190 ° C. and the load was 21.18N. The thing of 5 g / 10min or less was set as the pass.

(Extruded appearance)
The smoothness of the surface of the covering material and the presence or absence of protrusions were evaluated visually and by hand. An electric wire judged to be sufficiently smooth was accepted (good).

(Gel fraction)
The copper conductor was removed and extraction was performed in hot xylene at 130 ° C. for 24 hours. The gel fraction was defined as (residual gel weight after extraction) / (silane cross-linked polyethylene weight before extraction) × 100 (%). 70% or more was accepted.

(Hot set test)
The copper conductor was removed, the inside of the coating material was ground smoothly, and a hot set test based on 9 of JIS C 3660-2-1 was performed. A dumbbell-shaped sample was suspended in a thermostat having an air temperature of 200 ° C., a load of 20 N / cm ² was applied for 15 minutes, and the elongation under load was measured. Thereafter, the load was removed, and after 5 minutes, the sample was taken out and sufficiently cooled, and then the permanent elongation was measured. A sample having an elongation under load of 175% or less and a permanent elongation after cooling of 15% or less was regarded as acceptable.

  As shown in Table 2, in Examples 1 to 5 according to the present invention, a high degree of crosslinking was obtained by high-temperature and short-time heating with superheated steam, and passed the hot set test. On the other hand, as shown in Table 3, in Comparative Example 1, since the amount of the silane compound added is less than specified, the degree of crosslinking is low and the hot set test is not passed. In Comparative Example 2, since the ratio of the addition amount of the silane compound and the addition amount of the free radical generator is less than specified, a good extruded appearance cannot be obtained. In Comparative Example 3, since the melt index of polyethylene obtained by graft copolymerization of the silane compound is larger than the specified value, the degree of crosslinking is low and the hot set test is not passed. As shown in Comparative Examples 4 to 6, it can be seen that those produced by continuous heating with normal hot air cannot obtain a sufficient degree of crosslinking. Further, in Comparative Example 7 in which crosslinking is accelerated in a constant temperature and humidity chamber of 80 ° C. and 85% relative humidity for one day, a high degree of crosslinking can be obtained. This is a manufacturing method not very suitable for processing. In Comparative Example 8 left at room temperature, a sufficient degree of crosslinking cannot be obtained even after 7 days.

  As described above, by using the production method of the present invention, an electric wire / cable coated with silane-crosslinked polyethylene having a high degree of crosslinking and a smooth extrusion appearance can be obtained in a short time and at a low cost, and its industrial utility is extremely high. it is conceivable that.

  While the embodiments and examples of the present invention have been described above, the embodiments and examples described above do not limit the invention according to the claims. It should be noted that not all combinations of features described in the embodiments and examples are necessarily essential to the means for solving the problems of the invention.

DESCRIPTION OF SYMBOLS 1 Electric wire 2 Cable 10 Conductor 20 Insulator 30 Sheath 21 Feeder 11 Extruder 12 Heating pipe 13 Superheated steam generator 14 Cooling water tank 15 Winder 16 Raw material hopper 17 Liquid injection port 18 Supply port

Claims (2)

Conductors,
A silane-crosslinked polyethylene obtained by crosslinking polyethylene obtained by graft copolymerization of a silane compound with a free radical generator on the conductor, wherein the polyethylene obtained by graft copolymerization of the silane compound with the free radical generator is 190 ° C. The melt index under the test condition of 21.18 N is 5 g / 10 min or less, the silane compound is contained in an amount of 1.5 parts by weight or more with respect to 100 parts by weight of polyethylene, and the ratio of the added amount of the silane compound is free. An insulating coating layer is formed by extrusion-coating a silane-crosslinked polyethylene that is 35 or more based on the amount of radical generator added;
A method for producing an electric wire obtained by coating silane-crosslinked polyethylene, wherein an insulating coating layer formed by extrusion coating on the conductor is passed through a heating tube supplied with superheated steam and crosslinked. On the outside of the electric wire with an insulating coating layer formed on the conductor,
A silane cross-linked polyethylene obtained by cross-linking polyethylene obtained by graft copolymerization of a silane compound with a free radical generator, wherein the polyethylene obtained by graft copolymerization of the silane compound with the free radical generator is 190 ° C. and 21.18 N The melt index under the conditions is 5 g / 10 min or less, the silane compound is contained in an amount of 1.5 parts by weight or more with respect to 100 parts by weight of polyethylene, and the ratio of the addition amount of the silane compound is the addition amount of the free radical generator The sheath layer is formed by extrusion coating with silane-crosslinked polyethylene that is 35 or more against
A method for producing a cable obtained by coating a silane-crosslinked polyethylene, wherein a sheath layer formed by extrusion coating on the insulating coating layer is crosslinked by passing through a heating tube supplied with superheated steam.

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