JP2006291022A - Insulating composition, wire/cable, and method for producing insulating composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an insulating composition having a higher effect that can be obtained by adding an inorganic filler than conventional compositions, and to provide a wire/cable using the same and a method for producing the same. <P>SOLUTION: The insulating composition of the present invention uses a low-density polyethylene as a material for a polyolefin resin and magnesium oxide which is surface-treated with a vinylsilane and then milled by jet milling. These components are kneaded through a twin-screw extruder so that the filler in the insulating composition has an average particle size of 200 nm or less to prepare an insulating composition. The resulting insulating composition has a higher volume resistivity and direct current breakdown strength than conventional insulating compositions. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to an insulating composition, an electric wire / cable, and a method for producing the insulating composition, in particular, an insulating composition having improved insulating performance as compared with the conventional one, The present invention relates to a method for producing an insulating composition.

  Conventionally, an insulating composition in which magnesium oxide (MgO) is added as an inorganic filler to a crosslinked polyethylene (hereinafter referred to as XLPE) obtained by crosslinking low density polyethylene (hereinafter referred to as LDPE) is used for the insulating layer of the cable. Therefore, it is found that the direct current characteristics are improved as compared with the case where XLPE not added with MgO is used for the insulating layer. The cable using the insulating composition of this MgO added XLPE as an insulator is a direct current cable. It has been confirmed that it can be put into practical use (for example, see Patent Document 1).

  By the way, the inorganic filler such as MgO may cause re-aggregation when added to the insulator, thereby generating coarse particles having a large diameter (hereinafter referred to as a re-aggregation component) in the insulator. The re-aggregation component may cause clogging of the screen mesh in the cable insulator extrusion process. Further, if a re-aggregation component is present in the cable insulator, this becomes a defect, which deteriorates the impulse destruction performance of the cable. As a countermeasure for suppressing this re-aggregation, it is effective to perform compound treatment with MgPE that has been subjected to surface treatment using vinylsilane and then subjected to pulverization treatment by jet pulverization (see, for example, Patent Document 2).

The XLPE insulator to which MgO is added using the above-mentioned method has effects such as an increase in volume resistivity, a decrease in space charge accumulation, and an improvement in DC breakdown strength as compared with an XLPE insulator without addition of MgO. Therefore, it is effective as an insulator for a DC cable.
Japanese Patent No. 3428388 Japanese Patent No. 3430875

  However, when the dispersion state of MgO in the XLPE insulator manufactured by the above method was confirmed by observation through transmission electron microscope photography (hereinafter referred to as TEM photography), the average particle diameter of MgO dispersed in XLPE was confirmed. The diameter was found to exceed 200 nm.

  In other words, the reaggregation component that affects the Imp performance has been considered to be on the order of several μm, and has been evaluated with an optical microscope. In order to confirm the above, it was evaluated by TEM photography that has a higher resolution than the optical microscope that is the conventional observation technique. Even with this method, it was clarified that a re-aggregation component was still generated and present in the XLPE insulator. Despite the fact that the average particle diameter of the raw material MgO is about 100 nm, in the above compound adjustment method, the average particle diameter of MgO dispersed in the insulator is still larger than the particle diameter of the raw material MgO. Became clear.

  The effect of adding this inorganic filler, especially as a DC cable (improvement of volume resistivity, reduction of space charge accumulation, improvement of DC breakdown strength) is due to the average particle size of the filler dispersed in the insulator. It is considered that the effect obtained by the addition of the inorganic filler can be further enhanced by making the size smaller.

  The present invention has been made in view of the above-mentioned problems, and its object is to provide an insulating composition that is further improved by the addition of an inorganic filler as compared with conventional insulating compositions, electric wires and cables using the same, and insulation. It is in providing the manufacturing method of a composition.

  In order to achieve the above object, the present invention provides an insulating composition in which an inorganic filler is dispersed in a polyolefin resin, wherein the dispersed inorganic filler has a diameter of 200 nm or less. It provides things.

  Examples of the polyolefin resin mainly include polyethylene resins, and it is desirable to use low density polyethylene.

  The inorganic filler is preferably magnesium oxide that has been subjected to surface treatment and pulverization treatment. The surface treatment is preferably performed using vinylsilane as the surface treatment agent, and the pulverization treatment is preferably performed by jet pulverization.

  In order to achieve the above object, the present invention provides an electric wire / cable characterized in that the insulating composition of the present invention is an insulating layer.

  Furthermore, in order to achieve the above object, the present invention provides an inorganic filler having an average particle diameter of 200 nm or less when dispersed in a polyolefin resin when an insulating composition is prepared by mixing a polyolefin resin and an inorganic filler. The present invention provides a method for producing an insulating composition, which is characterized by being controlled so as to become.

  According to the present invention, it is possible to obtain an insulator composition whose volume resistivity and DC breakdown strength are further improved as compared with the conventional insulating composition, and an electric wire / cable using the insulator composition as an insulating layer.

  Hereinafter, preferred embodiments of the insulating composition and electric wires / cables according to the present invention will be described.

[Configuration of insulating composition]
The insulating composition according to the embodiment of the present invention is such that an inorganic filler is added to a polyolefin resin material so that the inorganic filler is uniformly dispersed, and the average particle diameter of the inorganic filler is 200 nm or less. Features.

  As a material for the polyolefin resin, low density polyethylene (LDPE) is used. At this time, the LDPE may be crosslinked (XLPE). In the present invention, the polyolefin resin material may be high-density polyethylene, medium-density polyethylene, ultra-low-density polyethylene, linear low-density polyethylene, or the like in addition to LDPE, and these may be cross-linked. It may be a thing.

  Further, magnesium oxide (MgO) is used as the inorganic filler. Since re-agglomeration may occur when the inorganic filler is added to the insulator, it is desirable to subject the inorganic filler to a surface treatment with vinylsilane and then to a pulverization process by jet pulverization. In the present invention, the inorganic filler may be titanium oxide, calcium carbonate, magnesium hydroxide, silica or the like in addition to MgO.

  The effects obtained by adding a filler to the insulator (improved volume resistivity, reduced space charge accumulation, and improved DC breakdown strength) are due to the specific surface area of the filler dispersed in the insulator. Since the effect increases as the particle size of the filler is smaller, the average particle size of MgO added to the LDPE is adjusted to 200 nm or less.

  When the average particle diameter of the added MgO is 200 nm or less, as will be described later, the volume resistivity and DC breakdown strength of the insulating composition are further improved.

[Insulating composition manufacturing method]
The method for producing an insulating composition according to an embodiment of the present invention uses a twin screw extruder for kneading an insulator and an inorganic filler so that the average particle diameter of the inorganic filler is 200 nm or less. .

  The twin screw extruder can arrange two screws in parallel and apply high shear stress to the extruded resin between the screws. Therefore, when the inorganic filler is kneaded into the polyolefin resin material, the dispersibility of the inorganic filler is further improved by kneading under a high shear stress.

  Furthermore, since the inorganic filler particles are less likely to re-agglomerate due to improved dispersibility of the inorganic filler and high shear stress, the average particle size of the inorganic filler added to the insulator is controlled to be small. It becomes possible to do.

  By producing an insulating composition by the above method, an insulating composition with further improved volume resistivity and direct current breakdown strength can be obtained.

  The method for kneading the inorganic filler into the polyolefin resin is not particularly limited as long as it can be controlled so that the average particle diameter of the inorganic filler is 200 nm or less. In addition to the above method, for example, the same dispersion effect can be obtained even when a twin-screw extruder and a roll machine are used in combination. That is, the same effect can be acquired by diluting the polyolefin resin material which added the inorganic filler in high concentration to low concentration with a roll machine using a twin screw extruder.

[Cable configuration and manufacturing method]
The cable which concerns on embodiment of this invention is obtained by coat | covering a conductor outer periphery with the said insulating composition.

  FIG. 1 is a schematic cross-sectional view of a cable according to an embodiment of the present invention. The cable 1 has an internal semiconductive layer 3 formed so as to directly cover the outer periphery of the conductor 2 having a substantially circular cross section. An insulator 4 is coated on the outer periphery of the inner semiconductive layer 3, and an outer semiconductive layer 5, a shielding layer 6, and a sheath 7 are sequentially formed on the outer periphery.

  Next, the cable 1 is formed by extruding the inner semiconductive layer 3 on the outer periphery of the conductor 2. Subsequently, by forming the insulator 4 made of the above-described insulating composition, the outer semiconductive layer 5, the shielding layer 6, and the sheath 7 in order, the cable 1 having a cross-sectional shape as shown in FIG. can get.

  Since the cable 1 thus obtained is coated with an insulating composition having further improved volume resistivity and DC breakdown strength, the volume resistivity and DC breakdown strength are further improved as compared with conventional DC cables.

  Examples of the present invention are shown below.

[Example of insulating composition]
Using a twin screw extruder with a screw diameter of 15 mm and L / D = 60 (L: screw length, D: screw diameter), LDPE and MgO were controlled so that the average particle diameter of MgO was 200 nm or less. The insulating composition of MgO-dispersed LDPE was prepared by kneading. The LDPE having a density of 0.920 g / mm ³ and MI (melt index) = 1 was used. MgO having an average particle diameter of 50 nm was subjected to surface treatment with vinylsilane and then pulverized by jet pulverization.

  As an example using such a preparation method, Sample 1 with 1 part by weight of MgO added to 100 parts by weight of LDPE, Sample 2 with sample added with 5 parts by weight, and Sample 3 with 10 parts by weight added. As shown in Table 1.

  In addition, as a comparative example, those kneaded only by a roll machine using the same LDPE and MgO as those of Samples 1 to 3 are shown in Table 1. Here, Sample 4 is obtained by adding 1 part by weight of MgO to 100 parts by weight of LDPE, Sample 5 by adding 5 parts by weight, and Sample 6 by adding 10 parts by weight. Further, LDPE without addition of MgO is also shown in Table 1 as a comparative example. This is designated as Sample 7.

(Average particle diameter of MgO after kneading)
Next, a sheet having a thickness of 6 mm was prepared by press molding using each of the above samples, and the average particle diameter of MgO dispersed in LDPE was determined by observing a photograph of the slice piece by TEM photography. The results are as shown in Table 1.

  As is clear from the results in Table 1, for Samples 1 to 3 which are examples of the present invention, the average particle diameter of MgO is about 100 nm, while MgO in Samples 4 to 6 which are comparative examples. When the same amount of MgO was added, the average particle diameter of MgO in LDPE was smaller when kneaded with a twin screw extruder than when kneaded with a roll machine. .

(Volume resistivity)
Further, a sheet sample having a thickness of 0.15 mm was formed by press molding using each of the above samples, and the volume resistivity at a temperature = 90 ° C. and a DC applied electric field = 80 kV / mm was evaluated. The results are as shown in Table 1.

  As is clear from the results in Table 1, the samples 1 to 3 as examples of the present invention have a volume resistivity significantly higher than those of samples 4 to 6 as comparative examples to which the same amount of MgO is added. Improved. Moreover, it turns out that the difference of the volume resistivity of an Example and a comparative example becomes large as the addition amount of MgO is increased.

(DC breakdown strength)
Next, using a material kneaded with 1 part by weight of MgO, using a sample 1 as an example and a sample 4 as a comparative example, a sheet sample having a thickness of 0.15 mm is formed by press molding, The DC breakdown strength at a temperature = 90 ° C. was evaluated. The results are as shown in Table 1.

  As is clear from the results in Table 1, when the same amount of MgO was added, the DC breaking strength was higher when kneaded with a twin screw extruder than with roll kneading.

  Table 1 shows the volume resistivity and DC breakdown strength of LDPE not added with MgO as Sample 7 of Comparative Example. Compared with the LDPE not added with MgO, the sample added with MgO has higher volume resistivity and DC breakdown strength.

  From the above results, by adding MgO to LDPE, further effects such as improvement of volume resistivity and improvement of DC breakdown strength can be obtained, but this effect reduces the average particle diameter of MgO dispersed in LDPE. It is clear that it becomes more prominent.

[Example of cable]
As an example, as the conductor 2 in FIG. 1 on conductor outer periphery of the conductor cross-sectional area 100 mm ^2, and extruded to a thickness of 0.7mm the inner semiconducting layer 3, and then on the inner semiconducting layer 3 The insulating composition consisting of Sample 1 in Table 1 was extruded as an insulator 4 to a thickness of 3 mm, the outer semiconductive layer 5 was 1 mm thick, the shielding layer 6 was 0.3 mm thick, and the sheath 7 was The cable 1 was manufactured by sequentially forming a thickness of 3 mm. At this time, using this as the sample 8, the characteristics were evaluated, and the results are shown in Table 2. Further, as a comparative example, a cable using an insulating composition consisting of the sample 4 of Table 1 as the insulator 4 was also manufactured, and this was used as a sample 9 to evaluate the characteristics. The results are shown in Table 2.

  As is apparent from the results in Table 2, it can be seen that the effect of the characteristics by the insulating composition of the present invention is also exhibited in the cable using the insulating composition. That is, when an insulating composition prepared by adding and kneading MgO to LDPE is used as an insulator, the volume resistivity is improved by reducing the average particle diameter of MgO dispersed in LDPE. DC breakdown strength is improved.

  From the above examination results, it has been clarified that when the average particle size of the inorganic filler after being dispersed in the polyolefin resin is 200 nm or less, a more remarkable effect of adding the inorganic filler is obtained. If the insulating composition of the present invention is applied to a cable as an insulating layer, a further effect of the above characteristics can be expected particularly in a DC cable. Of course, the effect of the characteristics can be obtained even when it is used in an AC cable.

It is a section schematic diagram of a cable concerning an embodiment of the invention.

Explanation of symbols

1 Cable 2 Conductor 3 Internal Semiconductive Layer 4 Insulator 5 External Semiconductive Layer 6 Shielding Layer 7 Sheath

Claims (9)

An insulating composition in which an inorganic filler is dispersed in a polyolefin resin,
An insulating composition, wherein an average particle size of the dispersed inorganic filler is 200 nm or less.   The insulating composition according to claim 1, wherein the polyolefin resin is crosslinked.   The insulating composition according to claim 1, wherein the polyolefin resin is low-density polyethylene.   The insulating composition according to any one of claims 1 to 3, wherein the inorganic filler is magnesium oxide subjected to a surface treatment and a pulverization treatment.   5. The insulating composition according to claim 4, wherein the surface treatment uses vinyl silane as a surface treatment agent.   The insulating composition according to claim 4 or 5, wherein the pulverization is performed by jet pulverization.   An electric wire / cable comprising the insulating composition according to any one of claims 1 to 6 as an insulating layer.   When preparing an insulating composition by mixing a polyolefin resin and an inorganic filler, the average particle diameter of the inorganic filler dispersed in the polyolefin resin is controlled to be 200 nm or less in diameter. A method for manufacturing an insulating composition.   The method for producing an insulating composition according to claim 8, wherein the preparation for controlling the average particle size of the inorganic filler to be 200 nm or less is performed by a twin screw extruder.

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