Method of manufacturing foamed cross-linked electric wire

Abstract

To provide a manufacturing method of a foamed cross-linked electric wire capable of increasing a foaming degree of an insulating layer.SOLUTION: A method for manufacturing a foamed cross-linked electric wire includes a conductor and an insulating layer covering the conductor, wherein the insulating layer is a foam and is cross-linked. (a) 100 parts by mass of a polyethylene resin, 0.5 parts by mass or more and 3 parts by mass or less of a photoradical generator, 1 part by mass or more and 5 parts by mass or less of a reactive monomer, and 0.5 parts by mass or more and 3 parts by mass or less of a chemical foaming agent, wherein the surface of the conductor is covered with a resin composition extruded at a temperature lower than the decomposition temperature of the chemical foaming agent. (b) After the step (a), the resin composition is cross-linked by light irradiation so that the gel fraction of the resin composition is 5% or more and 50% or less. (c) After the step (b), the resin composition is foamed by heating. (d) After the step (c), the resin composition is further crosslinked by light irradiation.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a foamed cross-linked electric wire. [Background technology]

[0002] Patent Documents 1 and 2 disclose a foamed cross-linked electric wire. The foamed cross-linked electric wire comprises a conductor and an insulating layer. The insulating layer covers the conductor. The insulating layer is a foam. The insulating layer is cross-linked. Because the insulating layer is a foam, it has a low dielectric constant. Because the insulating layer has a low dielectric constant, transmission loss can be suppressed and the time required to transmit a signal can be shortened. Therefore, the foamed cross-linked electric wire is suitable for applications in which large amounts of data are transmitted or transmitted at high speeds.

[0003] The insulating layer is cross-linked, which gives it high heat resistance. This prevents the insulating layer from flowing and deforming due to heat, or from shorting out adjacent wires. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-17257 [Patent Document 2] Japanese Patent Application Publication No. 7-320560 Summary of the Invention [Problem to be solved by the invention]

[0005] One method for forming an insulating layer for a foamed cross-linked electric wire involves coating a conductor with a resin composition containing a chemical foaming agent and then foaming the resin composition. When foaming a resin composition, bubbles tend to break (hereinafter referred to as "cell breakage") or coalesce. The more bubbles break or coalesce, the lower the degree of foaming of the insulating layer. A lower degree of foaming of the insulating layer increases the dielectric constant of the insulating layer.

[0006] In one aspect of the present disclosure, it is preferable to provide a method for producing a foamed cross-linked electric wire that can increase the foaming degree of an insulating layer. [Means for solving the problem]

[0007] One aspect of the present disclosure is a method for producing a foamed cross-linked electric wire comprising a conductor and an insulating layer covering the conductor, the insulating layer being a foam and cross-linked. The method for producing a foamed cross-linked electric wire includes the following steps (a) to (d):

[0008] (a) coating the surface of the conductor with a resin composition containing 100 parts by mass of polyethylene resin, 0.5 parts by mass or more and 3 parts by mass or less of a photoradical generator, 1 part by mass or more and 5 parts by mass or less of a reactive monomer, and 0.5 parts by mass or more and 3 parts by mass or less of a chemical foaming agent, the resin composition being extruded at a temperature lower than the decomposition temperature of the chemical foaming agent; (b) after (a), crosslinking the resin composition by irradiating it with light so that the gel fraction of the resin composition is 5% or more and 50% or less; (c) after (b), the resin composition is expanded by heating; (d) After (c), the resin composition is further crosslinked by irradiating it with light.

[0009] According to the method for producing a foamed cross-linked electric wire that is one aspect of the present disclosure, a foamed cross-linked electric wire having an insulating layer with a high degree of foaming can be produced. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a cross-sectional view showing the configuration of a foamed cross-linked electric wire. [Figure 2] FIG. 2 is a cross-sectional view illustrating the configuration of an electric wire before treatment. [Figure 3] FIG. 1 is an explanatory diagram illustrating the configuration of a manufacturing apparatus for a foamed cross-linked electric wire. [Figure 4] FIG. 2 is an explanatory diagram illustrating the configuration of a molding device. DETAILED DESCRIPTION OF THE INVENTION

[0011] Exemplary embodiments of the present disclosure will now be described with reference to the drawings. First Embodiment 1. Manufacturing method of foamed cross-linked electric wire The foamed cross-linked electric wire 1 shown in FIG. 1 can be manufactured by the manufacturing method of the foamed cross-linked electric wire of the present disclosure. The foamed cross-linked electric wire 1 includes a conductor 3 and an insulating layer 5. The insulating layer 5 covers the conductor 3. The insulating layer 5 is a foam. The insulating layer 5 has a plurality of bubbles 6 therein. The insulating layer 5 is cross-linked.

[0012] The conductor 3 is, for example, a metal conductor. Alternatively, the conductor 3 includes a metal conductor and a coating applied to its surface. The material of the metal conductor is, for example, copper, a copper alloy, aluminum, or an aluminum alloy. The coating is, for example, a plating layer. The plating layer is, for example, a Sn plating layer. The size of the conductor 3 is preferably 36 AWG or more and 50 AWG or less. The conductor 3 may be a single wire or multiple wires twisted together.

[0013] In the method for producing a foamed cross-linked electric wire of the present disclosure, the following steps (a) to (d) are carried out in this order. (a) The surface of the conductor 3 is coated with a resin composition. (b) After (a), the resin composition is crosslinked by irradiating it with light so that the gel fraction of the resin composition is 5% or more and 50% or less. (c) After (b), the resin composition is expanded by heating. (d) After (c), the resin composition is further crosslinked by irradiating it with light.

[0014] The resin composition contains a polyethylene resin. The polyethylene resin is, for example, the main component of the resin composition. The main component is the component that is blended in the largest amount. Examples of polyethylene resins include ultra-high molecular weight polyethylene (UHMW-PE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), and very low-density polyethylene (VLDPE). These may be blended alone or in combination as the polyethylene resin. Furthermore, the polyethylene resin may be partially substituted with other functional groups (i.e., modified).

[0015] The resin composition contains a chemical foaming agent. Examples of the chemical foaming agent include azo compounds, nitroso compounds, hydrazine derivatives, and sodium bicarbonate. Examples of the azo compounds include azodicarbonamide (ADCA). The decomposition temperature of the chemical foaming agent is preferably higher than the melting point of the resin composition.

[0016] Examples of nitroso compounds include N-N'-dinitrosopentamethylenetetramine, etc. Examples of hydrazine derivatives include OBSH (4,4'-oxybis(benzenesulfonylhydrazide)) and HDCA (hydrazodicarbonamide). Chemical foaming agents can be selected depending on the application and purpose.

[0017] The amount of the chemical foaming agent is 0.5 parts by mass or more and 3 parts by mass or less per 100 parts by weight of the polyethylene resin. When the amount of the chemical foaming agent is 0.5 parts by mass or more, the foaming properties of the resin composition are improved. When the amount of the chemical foaming agent is 3 parts by mass or less, abnormal growth of the bubbles 6, coalescence of the bubbles 6, and breakage of the bubbles 6 can be suppressed.

[0018] The resin composition contains a reactive monomer. The reactive monomer functions as a crosslinking aid. The reactive monomer has a functional group that undergoes a crosslinking or polymerization reaction with a radical or cation. Examples of the functional group that undergoes a crosslinking or polymerization reaction with a radical or cation include an acrylic group, a methacrylic group, a vinyl group, a vinyl ether group, an oxetane group, an epoxy group, an alicyclic epoxy group, an amino group, an allyl group, maleic acid, and maleic anhydride. The reactive monomer is, for example, a monofunctional monomer or a polyfunctional monomer. One type of reactive monomer can be blended alone, or multiple types can be blended in combination.

[0019] The amount of reactive monomer blended is 1 part by mass or more and 5 parts by mass or less per 100 parts by weight of polyethylene resin. When the amount of reactive monomer blended is 1 part by mass or more, the crosslinkability of the resin composition is improved. When the amount of reactive monomer blended is 5 parts by mass or less, the occurrence of bleeding can be suppressed.

[0020] The resin composition contains a photoradical generator. The photoradical generator is a photoinitiator that serves as the starting point for a crosslinking reaction. The photoinitiator is, for example, an ultraviolet initiator. The photoradical generator generates radicals when irradiated with light. The ultraviolet initiator generates radicals when irradiated with ultraviolet light. The generated radicals graft the polyethylene resin and the reactive monomer and induce a crosslinking reaction between the grafted monomers.

[0021] Examples of photoradical generators include acetophenone, 4,4'-dimethoxybenzil, diphenylethanedione, 2-hydroxy-2-phenylacetophenone, diphenyl ketone, benzophenone-2-carboxylic acid, 4,4'-bis(diethylamino)benzophenone, 4,4'-bis(dimethylamino)benzophenone, benzoin methyl ether, benzoin isopropyl ether, benzoin isobutyl ether, benzoin ethyl ether, 4-benzoylbenzoic acid, 2,2'-bis(2-chlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole, methyl 2-benzoylbenzoate, and 2-(1,3-benzodioxol-5-yl)-4,6-bis(trichloromethyl)-1,3,5-triazine. , 2-benzyl-2-(dimethylamino)-4'-morpholinobutyrophenone, 2,3-bornanedione, 2-chlorothioxanthone, 4,4'-dichlorobenzophenone, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,4-diethylthioxanthen-9-one, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, 1,4-dibenzoylbenzene, 2-ethylanthraquinone, 1-hydroxycyclohexylphenylketone Examples of suitable anti-oxidizing agents include lithium phenyl(2,4,6-trimethylbenzoyl)phosphinate, 2-methyl-4'-(methylthio)-2-morpholinopropiophenone, 2-isonitrosopropiophenone, 2-phenyl-2-(p-toluenesulfonyloxy)acetophenone, and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide. These may be used alone or in combination.

[0022] The amount of the photoradical generator is 0.5 parts by mass or more and 3 parts by mass or less per 100 parts by mass of polyethylene resin. When the amount of the photoradical generator is 0.5 parts by mass or more, the crosslinking property is improved. Even if the amount of the photoradical generator is more than 3 parts by mass, the crosslinking property is unlikely to be further improved. When the amount of the photoradical generator is 3 parts by mass or less, the mechanical properties such as elongation and tensile strength of the insulating layer 5 are unlikely to decrease, and the manufacturing cost of the foamed crosslinked electric wire 1 can be reduced.

[0023] The resin composition further includes, for example, an additive having a specific function, such as an ultraviolet absorber, a light stabilizer, a process oil, a processing aid, a flame retardant aid, an antioxidant, a lubricant, an inorganic filler, a copper inhibitor, a stabilizer, or a colorant.

[0024] Examples of ultraviolet absorbers include salicylic acid derivatives, benzophenones, benzotriazoles, oxalic acid anilide derivatives, 2-ethylhexyl-2-cyano-3,3-diphenyl acrylate, etc. Examples of salicylic acid derivatives include phenyl salicylate and p-tert-butylphenyl salicylate.

[0025] Examples of benzophenones include 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2,2'dihydroxy-4,4'-dimethoxybenzophenone, 2-hydroxy-4-n-octoxybenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, 4-dodecyloxy-2-hydroxybenzophenone, 3,5-di-tert-butyl-4-hydroxybenzoyl acid, n-hexadecyl ester, bis(5-benzoyl-4-hydroxy-2-methoxyphenyl)methane, 1,4-bis(4-benzoyl-3-hydroxyphenoxy)butane, and 1,6-bis(4-benzoyl-3-hydroxyphenoxy)hexane.

[0026] Benzotriazoles, for example, 2-(2'-hydroxy-5'-methyl-phenyl)benzotriazole, 2-(2'-hydroxy-3',5'-di-tert-butyl-phenyl)benzotriazole, 2-(2'-hydroxy-3'-di-tert-butyl-5'-methyl-phenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3',5'-di-tert-butyl-phenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole, 2-(2'-hydroxy-3',5'-di-tert-amylphenyl)benzotriazole, 2,2'-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol], 2-[2-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]-2H-benzotriazole, other benzotriazole derivatives, etc. These ultraviolet absorbers can be blended alone or in combination.

[0027] Examples of the light stabilizer include hindered amine light stabilizers. Examples of the hindered amine light stabilizer include poly[[6-(1,1,3,3-tetramethylbutyl)imino-1,3,5-triazine-2,4-diyl][(2,2,6,6-tetramethyl-4-piperidyl)imino]hexamethylene[(2,2,6,6-tetramethyl-4-piperidyl)imino]], poly[(6-morpholino-s-triazine-2,4-diyl)[2,2,6,6-tetramethyl-4-piperidyl]imino]-hexamethylene[(2,2,6,6-tetramethyl-4-piperidyl)imino]], Examples include N,N'-bis(3-aminopropyl)ethylenediamine·2,4-bis[N-butyl-N-(1,2,2,6,6-pentamethyl-4-piperidyl)amino]-6-chloro-1,3,5-triazine condensate, and polycondensate of dibutylamine·1,3,5-triazine·N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl-1,6-hexamethylenediamine·N-(2,2,6,6-tetramethyl-4-piperidyl)butylamine. These light stabilizers can be used alone or in combination.

[0028] In (a), as shown in FIG. 2, a pre-processed electric wire 2 is formed, which includes a conductor 3 and a layer 4 of a resin composition. The layer 4 of the resin composition coats the conductor 3. When the surface of the conductor 3 is coated with the resin composition in (a), the temperature of the resin composition is equal to or higher than the melting point of the resin composition and lower than the decomposition temperature of the chemical foaming agent. When the surface of the conductor 3 is coated with the resin composition in (a), the resin composition is extruded at a temperature lower than the decomposition temperature of the chemical foaming agent. When the surface of the conductor 3 is coated with the resin composition in (a), the foaming degree of the resin composition is preferably 10% or less, and more preferably 5% or less.

[0029] The foaming degree is a value measured as follows. The volume and dielectric constant of the resin composition to be measured are each measured. The relative dielectric constant A1 of the resin composition is calculated from the volume and dielectric constant of the resin composition. The foaming degree X (%) of the resin composition is calculated using the following formula (1).

[0030] Formula (1) X=(A1 / A2)×100 In formula (1), A2 is the relative dielectric constant of the polyethylene resin, which is the main component of the resin composition to be measured. A2 is a known value of 2.35.

[0031] By maintaining the temperature of the resin composition at or above the melting point of the resin composition and lower than the decomposition temperature of the chemical foaming agent until the surface of the conductor 3 is coated with the resin composition, the foaming degree of the resin composition when the surface of the conductor 3 is coated with the resin composition can be set to 10% or less. The foaming degree of the resin composition when the surface of the conductor 3 is coated with the resin composition is preferably 5% or less.

[0032] In (b), a light irradiation device can be used. Examples of light irradiation devices include ultraviolet irradiation devices. Examples of light irradiation devices include metal halide lamps, ultraviolet LEDs, high-pressure mercury lamps, xenon lamps, and discharge tube-type devices. Two or more of these light irradiation devices may be used. Discharge tube-type devices may be electrodeless or may have electrodes. In the case of discharge tube-type devices, the peak wavelength of the irradiated light can be adjusted by sealing a specific element between the electrodes.

[0033] The peak wavelength of the light emitted by the light irradiation device is not particularly limited. The peak wavelength of the light emitted by the light irradiation device is preferably close to the reaction wavelength of the photoradical generator. Examples of the reaction wavelength of the photoradical generator include 405 nm, 395 nm, 385 nm, 365 nm, 300 nm, and 285 nm.

[0034] The cumulative amount of ultraviolet light irradiated in (b) is 500 mJ / cm 2 More than 2000mJ / cm 2 It is preferable that:

[0035] By carrying out (b), the resin composition is crosslinked. When crosslinked, the viscosity of the resin composition increases and the gel fraction increases. By carrying out (b), the gel fraction of the resin composition becomes 5% or more and 50% or less. The higher the energy of the ultraviolet light irradiated in (b), the higher the gel fraction. The longer the ultraviolet light irradiation time in (b), the higher the gel fraction.

[0036] The gel fraction is a value measured as follows. An untreated electric wire 2 to be measured is prepared. The length of the untreated electric wire 2 is 10 m. The gel fraction of this untreated electric wire 2 is measured using the xylene extraction method specified in JIS C 3005. The temperature of xylene used for extraction with xylene is 110°C, and the extraction time is 24 hours. When calculating the gel fraction, the weight of the conductor 3 is excluded, and the gel fraction of the resin composition is calculated from the change in weight of the resin composition before and after extraction with xylene.

[0037] In (c), a heating furnace can be used as a heat source. Examples of heating furnaces include electric heaters, microwave heating devices, hot air heaters, infrared heaters, devices that supply steam, and devices that supply superheated steam. Two or more of these heating furnaces may be used. The temperature inside the heating furnace is preferably 300°C or higher and 400°C or lower. The time for heating the resin composition is preferably 5 seconds or higher and 20 seconds or lower.

[0038] In (c), the resin composition foams due to the decomposition of the chemical foaming agent contained in the resin composition. In (c), for example, the temperature of the resin composition is raised above the decomposition temperature of the chemical foaming agent. The higher the temperature of the resin composition in (c), the higher the foaming degree of the resin composition. Furthermore, the longer the heating time of the resin composition in (c), the higher the foaming degree of the resin composition. Since (b) is performed before (c), when (c) is performed, the gel fraction of the resin composition is 5% or more and 50% or less.

[0039] In (d), the same light irradiation device as that used in (b) can be used. The cumulative amount of ultraviolet light irradiated in (d) is 3000 mJ / cm. 2 More than 5000mJ / cm 2 It is preferable that:

[0040] By carrying out (d), the resin composition is further crosslinked. By carrying out (d), the resin composition layer 4 becomes the insulating layer 5. The untreated electric wire 2 becomes the foamed crosslinked electric wire 1.

[0041] 2. Manufacturing equipment for foamed cross-linked electric wire 101 The method for producing a foamed cross-linked electric wire can be carried out, for example, by using a production apparatus 101 shown in Figures 3 and 4. As shown in Figure 3, the production apparatus 101 includes a feeder 103, a molding device 105, a processing unit 107, a cooling device 109, and a winder 111.

[0042] The feeder 103 feeds out the conductor 3. The molding device 105 extrusion-coats the fed-out conductor 3 with a resin composition, thereby forming the untreated electric wire 2. The step of forming the untreated electric wire 2 corresponds to (a).

[0043] The molding device 105 is an extruder. As shown in Fig. 4, the molding device 105 includes a drive device 117, a resin inlet 119, a screw 121, a cylinder 123, and a molding head 125. The drive device 117 drives and rotates the screw 121. The resin composition is introduced into the cylinder 123 from the resin inlet 119. The introduced resin composition advances through the cylinder 123 while being melted and kneaded by the rotating screw 121, and is extruded from the molding head 125 to coat the conductor 3.

[0044] For example, each component of the resin composition can be separately charged into the resin charging port 119. Alternatively, for example, each component of the resin composition can be kneaded in advance with a mixer, blender, roll, or the like, and pelletized, and then charged into the resin charging port 119.

[0045] The treatment unit 107 crosslinks and foams the resin composition layer 4. The treatment unit 107 includes a first light irradiation device 127, a heating device 129, and a second light irradiation device 131. The untreated electric wire 2 passes through the first light irradiation device 127, the heating device 129, and the second light irradiation device 131 in this order.

[0046] The first light irradiation device 127 irradiates the resin composition layer 4 with light. The light irradiation crosslinks the resin composition. As a result, the gel fraction of the resin composition becomes 5% or more and 50% or less. The step of irradiating light by the first light irradiation device 127 corresponds to (b). The first light irradiation device 127 may also have a heating mechanism to prevent the resin composition layer 4 from cooling and hardening. When heating is performed using the heating mechanism, heating is performed under conditions of not less than the melting point of the resin composition and not more than the decomposition temperature of the chemical foaming agent.

[0047] The heating device 129 heats the untreated electric wire 2. The heated resin composition foams. The process of heating the untreated electric wire 2 by the heating device 129 corresponds to (c). The second light irradiation device 131 irradiates the resin composition layer 4 with light. The light irradiation further crosslinks the resin composition. The process of irradiating light by the second light irradiation device 131 corresponds to (d). Through the above process, the resin composition layer 4 becomes an insulating layer 5. The untreated electric wire 2 becomes a foamed crosslinked electric wire 1. The foamed crosslinked electric wire 1 is sent to the cooling device 109.

[0048] The cooling device 109 cools the foamed cross-linked electric wire 1 and solidifies the insulating layer 5. The winder 111 winds the foamed cross-linked electric wire 1 after cooling. The cooling device 109 is, for example, a water-cooled cooling device or an air-cooled cooling device. If there are no manufacturing problems, the manufacturing apparatus 101 does not need to include the cooling device 109.

[0049] 3. Benefits of the manufacturing method for foamed cross-linked electric wire (1A) According to the manufacturing method of the foamed cross-linked electric wire of the present disclosure, it is possible to manufacture a foamed cross-linked electric wire 1 having a high degree of foaming of the insulating layer 5. The reason for this is as follows: By carrying out (b), the gel fraction of the resin composition when carrying out (c) is 5% or more and 50% or less, and the viscosity of the resin composition is appropriately high. Therefore, when carrying out (c), bubbles are less likely to break or the bubbles 6 are less likely to coalesce in the resin composition. As a result, the degree of foaming of the insulating layer 5 is high.

[0050] When (1B)(c) is carried out, the cells are less likely to break or coalesce, and therefore the insulating layer 5 can be made into a foam in which the cells 6 are fine and uniform. In (1C)(b), by adjusting the gel fraction of the resin composition, it is possible to control the bubble diameter and foaming degree in the insulating layer 5. In (b), the higher the gel fraction of the resin composition is within the range of 5% or more and 50% or less, the smaller the bubble diameter and foaming degree in the insulating layer 5 can be made. (1D) The degree of foaming of the insulating layer 5 is stable regardless of the position in the longitudinal direction of the foamed cross-linked electric wire 1.

[0051] <Example> 1. Production of resin composition A pellet-shaped resin composition was produced by blending and kneading the components shown in Table 1. The blend amounts in Table 1 are in parts by mass.

[0052] [Table 1]

[0053] A kneader (TD6-25MDX, manufactured by Doshin Co., Ltd.) was used to knead the components. The components listed in Table 1 are as follows: B028 is low-density polyethylene (Ube Maruzen Polyethylene, MFR 0.4 @ 190°C); 0434N is linear low-density polyethylene (LLDPE) (Prime Polymer, MFR 4.0 @ 190°C); Hizex5305E is high-density polyethylene (HDPE) (Prime Polymer, MFR 0.8 @ 190°C); TAIC is triallyl isocyanurate; TAIC corresponds to the reactive monomer; Irg-TPO corresponds to 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide (BASF); Irg-TPO corresponds to the photoradical generator; ADCA is azo-dicarbonamide (Vinihol AC#3C-K2, Eiwa Chemical Industry Co., Ltd.). ADCA is a chemical foaming agent. Its foaming temperature (i.e., decomposition temperature) is 160-170°C.

[0054] 2. Production of foamed cross-linked electric wire 1 of Examples 1 to 3 Using the manufacturing apparatus 101, foamed crosslinked electric wires 1 of Examples 1 to 3 were manufactured by the method described in the first embodiment. The resin composition used was the one manufactured in the above section "1. Manufacturing of resin composition." Specific manufacturing conditions were as follows:

[0055] The size of the conductor 3 was 44 AWG. The conductor 3 was made by twisting together seven wires with a diameter of 0.02 mm. The thickness of the resin composition layer 4 was 30 to 35 μm in an unfoamed state and approximately 70 μm when 65% foamed. The thickness of the resin composition layer 4 was controlled by adjusting the rotation speed of the screw 121 and the linear speed of the conductor 3. The higher the rotation speed of the screw 121, the thicker the resin composition layer 4. The slower the linear speed of the conductor 3, the thicker the resin composition layer 4.

[0056] The molding device 105 was a 20 mm single screw extruder manufactured by Omiya Seiki. The L / D ratio of the molding device 105 was 20. The first light irradiation device 127 and the second light irradiation device 131 were each ultraviolet irradiation devices (LUV-330-Mix2 manufactured by Oak Manufacturing Co., Ltd.). The heating device 129 was an electric furnace. The inner diameter φ of the electric furnace was 50 mm. The length of the electric furnace in the running direction of the untreated electric wire 2 was 1000 mm. The maximum set temperature of the electric furnace was 500°C.

[0057] In Examples 1 to 3, the temperatures at C1 to C3 of molding apparatus 105 were as shown in the rows "C1" to "C3" in Table 2, respectively. C1 is the portion of cylinder 123 closest to resin inlet 119. C3 is the portion of cylinder 123 closest to molding head 125. C2 is the portion of cylinder 123 midway between resin inlet 119 and molding head 125.

[0058] In Examples 1 to 3, the temperatures at the neck of molding device 105, molding head 125, and die of molding device 105 were as shown in the rows for "Neck," "Head," and "Die" in Table 2. The temperature of the resin composition extruded from molding head 125 and coating the surface of conductor 4 was equal to or lower than the temperature at the die of molding device 105.

[0059] In Examples 1 to 3, the foaming degree of the resin composition at the outlet of the molding head 125 was as shown in the row of "Foaming degree at head outlet" in Table 2. The foaming degree of the resin composition at the outlet of the molding head 125 corresponds to the foaming degree of the resin composition when the surface of the conductor 3 is coated in (a).

[0060] The "Pre-cure" row in Table 2 indicates whether crosslinking was performed in (b). The "Heated" row in Table 1 indicates whether heating was performed in (c). The "Main Crosslinking" row in Table 2 indicates whether crosslinking was performed in (d). In Examples 1 to 3, crosslinking in (b), heating in (c), and crosslinking in (d) were each performed as shown in Table 2. The crosslinking conditions in (b) were as follows:

[0061] Light irradiation device: Metal halide lamp Peak wavelength of ultraviolet rays: around 340 nm UV cumulative light intensity: 1000mJ / cm 2

[0062] The heating conditions in (c) were as follows: Heating temperature: 350℃ Heating time: 15 seconds

[0063] The crosslinking conditions in (d) were as follows: Light irradiation device: Metal halide lamp Peak wavelength of ultraviolet rays: around 340 nm UV cumulative light intensity: 4000mJ / cm 2 The gel fraction of the resin composition immediately after crosslinking in (b) (ie, the gel fraction of the resin composition when (c) is carried out) was as shown in the "Pre-cured gel fraction" row in Table 1.

[0064] 3. Production of foamed cross-linked electric wires of Comparative Examples 1 to 9 The foamed cross-linked electric wires of Comparative Examples 1 to 9 were produced basically in the same manner as in Examples 1 to 3. However, there were differences in the following points.

[0065] In Comparative Examples 1 to 9, the presence or absence of crosslinking in (b) was as shown in the "Pre-cure" row in Tables 2 and 3. In Comparative Examples 1 to 9, the presence or absence of heating in (c) was as shown in the "Heated" row in Tables 2 and 3. In Comparative Examples 1 to 9, the presence or absence of crosslinking in (d) was as shown in the "Main Crosslinking" row in Tables 2 and 3.

[0066] [Table 2]

[0067] [Table 3]

[0068] In Comparative Examples 1 to 9, the temperatures at C1 to C3 of molding apparatus 105 were as shown in the rows "C1" to "C3" in Tables 2 and 3. In Comparative Examples 1 to 9, the temperatures at the neck of molding apparatus 105, molding head 125, and die of molding apparatus 105 were as shown in the rows "Neck," "Head," and "Die" in Tables 2 and 3, respectively.

[0069] In Comparative Examples 1 to 9, the foaming degree of the resin composition at the outlet of the molding head 125 was as shown in the row of "Foaming degree at head outlet" in Tables 2 and 3. In Comparative Examples 1 to 9, the gel fraction of the resin composition immediately after crosslinking in (b) (i.e., the gel fraction of the resin composition when (c) is performed) was as shown in the row of "Pre-cured gel fraction" in Tables 2 and 3.

[0070] 4. Evaluation of foamed cross-linked electric wires of each example and each comparative example For the foamed cross-linked electric wires produced in each of the Examples and Comparative Examples, the foaming degree, gel fraction, and average cell diameter of the insulating layer 5 were measured. The measurement results are shown in Tables 2 and 3.

[0071] The average bubble diameter of the insulating layer 5 was measured as follows. A cross section of the insulating layer 5 was photographed using a Keyence VHX-500 digital microscope to generate a photograph. The photographing magnification was 500x. A measurement area measuring 500 μm × 350 μm was set in the photograph. In that measurement area, the circular equivalent diameter of each of the multiple bubbles 6 was measured using measurement software provided with the VHX-500. The average value of the circular equivalent diameters measured for each of the multiple bubbles 6 was calculated. The calculated average value was used as the average bubble diameter of the insulating layer 5.

[0072] In Examples 1 to 3, the degree of foaming of the insulating layer 5 was high, and the gel fraction of the insulating layer 5 was high. A high gel fraction of the insulating layer 5 indicates that crosslinking of the insulating layer 5 is advanced. In Comparative Examples 1 to 9, the degree of foaming of the insulating layer 5 was low. In Comparative Examples 1 to 3 and 5 to 7, the gel fraction of the insulating layer 5 was also low. A low gel fraction of the insulating layer 5 indicates that crosslinking of the insulating layer 5 is insufficient. In Comparative Examples 1 to 4, 7, and 9, broken cells were observed in the insulating layer 5.

[0073] In Comparative Examples 1 to 4, the temperature of the molding device 105 was higher than in Examples 1 to 3, so foaming of the low-viscosity resin composition proceeded before the crosslinking in (b), causing cell breakage and coalescence of the cells 6. As a result, in Comparative Examples 3 and 4, the degree of foaming was low despite the heating in (c).

[0074] In Comparative Examples 5, 6, and 8, the heating in (c) was not performed, and therefore the degree of foaming was significantly low. In Comparative Examples 7 and 9, the crosslinking in (b) was not performed, and therefore the degree of foaming was low, despite the heating in (c). In Comparative Examples 5 to 7, the crosslinking in (d) was not performed, and therefore the gel fraction was low.

[0075] <Other embodiments> Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments and can be implemented in various modified forms.

[0076] In (1)(d), the resin composition may be crosslinked by irradiating the resin composition with an electron beam. (2) The resin composition may further contain a peroxide, which causes peroxide crosslinking.

[0077] (3) The function of one component in each of the above embodiments may be shared among multiple components, or the functions of multiple components may be performed by one component. Also, part of the configuration of each of the above embodiments may be omitted. Furthermore, at least part of the configuration of each of the above embodiments may be added to or substituted for the configuration of another of the above embodiments.

[0078] (4) In addition to the above-described method for manufacturing a foamed cross-linked electric wire, the present disclosure can also be realized in various forms, such as the foamed cross-linked electric wire 1, a cable including the foamed cross-linked electric wire 1, and a method for manufacturing a cable.

[0079] [Technical idea disclosed in this specification] [Item 1] A conductor and an insulating layer covering the conductor, The insulating layer is a foamed and cross-linked electric wire, (a) coating the surface of the conductor with a resin composition containing 100 parts by mass of polyethylene resin, 0.5 parts by mass or more and 3 parts by mass or less of a photoradical generator, 1 part by mass or more and 5 parts by mass or less of a reactive monomer, and 0.5 parts by mass or more and 3 parts by mass or less of a chemical foaming agent, the resin composition being extruded at a temperature lower than the decomposition temperature of the chemical foaming agent; (b) after (a), crosslinking the resin composition by irradiating it with light so that the gel fraction of the resin composition is 5% or more and 50% or less; (c) after (b), the resin composition is expanded by heating; (d) after (c), the resin composition is further crosslinked by irradiating it with light; Manufacturing method for foamed cross-linked electric wire. [Item 2] A method for producing the foamed cross-linked electric wire according to item 1, In the step (c), the resin composition is heated using one or more heat sources selected from the group consisting of an electric heater, a microwave heater, a hot air heater, an infrared heater, steam, and superheated steam. Manufacturing method for foamed cross-linked electric wire. [Item 3] Item 3. A method for producing a foamed crosslinked electric wire according to item 1 or 2, In the step (b) or (d), the resin composition is crosslinked using one or more of a metal halide lamp, an ultraviolet LED, a high-pressure mercury lamp, and a xenon lamp. Manufacturing method for foamed cross-linked electric wire. [Item 4] A method for producing a foamed crosslinked electric wire according to any one of items 1 to 3, The chemical blowing agent includes one or more of an azo compound, a nitroso compound, a hydrazine derivative, and sodium bicarbonate. Manufacturing method for foamed cross-linked electric wire. [Item 5] A method for producing a foamed crosslinked electric wire according to any one of items 1 to 4, In the step (d), the resin composition is further crosslinked by irradiating it with an electron beam. Manufacturing method for foamed cross-linked electric wire. [Explanation of symbols]

[0080] 1...foamed cross-linked electric wire, 2...electric wire before treatment, 3...conductor, 4...layer of resin composition, 5...insulating layer, 6...air bubbles, 101...manufacturing apparatus, 103...feeder, 105...molding apparatus, 107...treatment unit, 109...cooling device, 111...winder, 117...driving device, 119...resin inlet, 121...screw, 123...cylinder, 125...molding head, 127...first light irradiation device, 129...heating device, 131...second light irradiation device

Claims

1. A conductor and an insulating layer covering the conductor, The insulating layer is a foamed and cross-linked electric wire, (a) coating the surface of the conductor with a resin composition containing 100 parts by mass of polyethylene resin, 0.5 parts by mass or more and 3 parts by mass or less of a photoradical generator, 1 part by mass or more and 5 parts by mass or less of a reactive monomer, and 0.5 parts by mass or more and 3 parts by mass or less of a chemical foaming agent, the resin composition being extruded at a temperature lower than the decomposition temperature of the chemical foaming agent; (b) after (a), the resin composition is crosslinked by irradiating it with light so that the gel fraction of the resin composition is 5% or more and 50% or less; (c) after (b), the resin composition is expanded by heating; (d) after (c), the resin composition is further crosslinked by irradiating it with light; Manufacturing method for foamed cross-linked electric wire.

2. A method for producing the foamed cross-linked electric wire according to claim 1, In the step (c), the resin composition is heated using one or more heat sources selected from the group consisting of an electric heater, a microwave heater, a hot air heater, an infrared heater, steam, and superheated steam. Manufacturing method for foamed cross-linked electric wire.

3. A method for producing the foamed cross-linked electric wire according to claim 1 or 2, In the step (b) or (d), the resin composition is crosslinked using one or more of a metal halide lamp, an ultraviolet LED, a high-pressure mercury lamp, and a xenon lamp. Manufacturing method for foamed cross-linked electric wire.

4. A method for producing the foamed cross-linked electric wire according to claim 1 or 2, the chemical blowing agent comprises one or more of an azo compound, a nitroso compound, a hydrazine derivative, and sodium bicarbonate; Manufacturing method for foamed cross-linked electric wire.

5. A method for producing the foamed cross-linked electric wire according to claim 1 or 2, In the step (d), the resin composition is further crosslinked by irradiating it with an electron beam. Manufacturing method for foamed cross-linked electric wire.

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