U.S. patent application number 15/747324 was filed with the patent office on 2018-08-02 for direct-current cable, composition and method of manufacturing direct-current cable.
The applicant listed for this patent is SUMITOMO ELECTRIC INDUSTRIES, LTD.. Invention is credited to Tomohiko KATAYAMA, Yoshinao MURATA, Takanori YAMAZAKI.
Application Number | 20180218804 15/747324 |
Document ID | / |
Family ID | 57983610 |
Filed Date | 2018-08-02 |
United States Patent
Application |
20180218804 |
Kind Code |
A1 |
YAMAZAKI; Takanori ; et
al. |
August 2, 2018 |
DIRECT-CURRENT CABLE, COMPOSITION AND METHOD OF MANUFACTURING
DIRECT-CURRENT CABLE
Abstract
A direct-current cable of an embodiment includes a conductive
portion; and an insulating layer covering an outer periphery of the
conductive portion, the insulating layer containing cross-linked
base resin and inorganic filler, the base resin containing
polyethylene, a BET specific surface area of the inorganic filler
being greater than or equal to 5 m.sup.2/g, and a mean volume
diameter of the inorganic filler being less than or equal to 5
.mu.m, the mass ratio of the inorganic filler with respect to the
base resin being greater than or equal to 0.001 and less than or
equal to 0.05, and the cross-linked base resin being cross-linked
by a cross-linking agent containing organic peroxide.
Inventors: |
YAMAZAKI; Takanori; (Tokyo,
JP) ; MURATA; Yoshinao; (Tokyo, JP) ;
KATAYAMA; Tomohiko; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SUMITOMO ELECTRIC INDUSTRIES, LTD. |
Osaka |
|
JP |
|
|
Family ID: |
57983610 |
Appl. No.: |
15/747324 |
Filed: |
August 10, 2015 |
PCT Filed: |
August 10, 2015 |
PCT NO: |
PCT/JP2015/072676 |
371 Date: |
January 24, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29C 48/78 20190201;
H01B 3/441 20130101; B29C 48/022 20190201; C08K 2201/001 20130101;
B29K 2995/0007 20130101; B29K 2509/02 20130101; H01B 3/006
20130101; C08K 2201/006 20130101; C08K 3/00 20130101; B29L
2031/3462 20130101; C08L 2207/066 20130101; C08L 23/04 20130101;
H01B 7/0275 20130101; B29C 48/154 20190201; C08L 2203/202 20130101;
C08K 3/36 20130101; C08L 2205/02 20130101; H01B 3/307 20130101;
B29K 2096/02 20130101; C08K 3/34 20130101; C08K 2003/222 20130101;
C08L 2312/00 20130101; B29K 2023/0691 20130101; C08K 2003/2227
20130101; B29K 2023/0633 20130101; C08K 3/22 20130101; C08K
2201/003 20130101; B29K 2509/08 20130101; C08K 3/013 20180101; C08K
5/14 20130101; C08L 23/06 20130101; B29K 2507/04 20130101; C08K
3/04 20130101; B29K 2509/00 20130101; C08K 5/375 20130101; C08K
9/06 20130101; H01B 13/14 20130101; C08L 23/04 20130101; C08L 51/06
20130101; C08K 2003/222 20130101; C08L 23/04 20130101; C08L 23/0869
20130101; C08K 3/36 20130101; C08L 23/04 20130101; C08L 51/06
20130101; C08K 3/36 20130101; C08L 23/04 20130101; C08L 23/0869
20130101; C08K 2003/2227 20130101; C08L 23/04 20130101; C08L
23/0869 20130101; C08K 3/04 20130101 |
International
Class: |
H01B 3/44 20060101
H01B003/44; H01B 7/02 20060101 H01B007/02; H01B 13/14 20060101
H01B013/14; B29C 47/00 20060101 B29C047/00; B29C 47/02 20060101
B29C047/02; B29C 47/78 20060101 B29C047/78; C08K 3/22 20060101
C08K003/22; C08L 23/06 20060101 C08L023/06; C08K 3/36 20060101
C08K003/36; C08K 3/04 20060101 C08K003/04 |
Claims
1. A direct-current cable comprising: a conductive portion; and an
insulating layer covering an outer periphery of the conductive
portion, the insulating layer containing cross-linked base resin
and inorganic filler, the base resin containing polyethylene, a BET
specific surface area of the inorganic filler being greater than or
equal to 5 m.sup.2/g, and a mean volume diameter of the inorganic
filler being less than or equal to 5 .mu.m, the mass ratio of the
inorganic filler with respect to the base resin being greater than
or equal to 0.001 and less than or equal to 0.05, and the
cross-linked base resin being cross-linked by a cross-linking agent
containing organic peroxide.
2. The direct-current cable according to claim 1, wherein the
inorganic filler is one or more selected from a group consisting of
magnesium oxide powder, aluminum oxide powder, silica powder,
magnesium silicate powder, aluminum silicate powder and carbon
black.
3. The direct-current cable according to claim 2, wherein a surface
of each of the magnesium oxide powder, the aluminum oxide powder,
the silica powder, the magnesium silicate powder and the aluminum
silicate powder is treated by a silane coupling agent.
4. The direct-current cable according to claim 1, wherein the base
resin further contains copolymer of ethylene and polar monomer or
polyethylene-graft-maleic anhydride, and wherein the mass ratio of
the copolymer of ethylene and polar monomer or the
polyethylene-graft-maleic anhydride with respect to the
polyethylene is less than or equal to 1/9.
5. A composition comprising: base resin, inorganic filler and a
cross-linking agent, the base resin containing polyethylene, a BET
specific surface area of the inorganic filler being greater than or
equal to 5 m.sup.2/g, and a mean volume diameter of the inorganic
filler being less than or equal to 5 .mu.m, the mass ratio of the
inorganic filler with respect to the base resin being greater than
or equal to 0.001 and less than or equal to 0.05, and the
cross-linking agent containing organic peroxide.
6. The composition according to claim 5, wherein the inorganic
filler is one or more selected from a group consisting of magnesium
oxide powder, aluminum oxide powder, silica powder, magnesium
silicate powder, aluminum silicate powder and carbon black.
7. The composition according to claim 6, wherein a surface of each
of the magnesium oxide powder, the aluminum oxide powder, the
silica powder, the magnesium silicate powder and the aluminum
silicate powder is treated by a silane coupling agent.
8. The composition according to claim 5, wherein the base resin
further contains copolymer of ethylene and polar monomer or
polyethylene-graft-maleic anhydride, and wherein the mass ratio of
the copolymer of ethylene and polar monomer or the
polyethylene-graft-maleic anhydride with respect to the
polyethylene is less than or equal to 1/9.
9. A method of manufacturing a direct-current cable in which an
outer periphery of a conductive portion is covered by an insulating
layer, comprising: manufacturing an extrusion molded material by
extrusion molding the composition as claimed in claim 5 to cover an
outer periphery of the conductive portion; and forming the
insulating layer by heating the extrusion molded material at a
predetermined temperature to cross link the base resin.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] An embodiment of the present invention relates to a
direct-current cable, a composition and a method of manufacturing a
direct-current cable.
[0002] Cross-linking polyethylene cables each containing
cross-linking polyethylene in an insulating layer covering an outer
periphery of a conductive portion are widely used as
alternating-current cables.
[0003] When cross-linking polyethylene, organic peroxide such as
dicumyl peroxide is used.
[0004] However, when a cross-linking polyethylene cable is used as
a direct-current cable, volume resistivity of an insulating layer
may be lowered, accumulation of space charges may be increased and
space-charge characteristics may be lowered due to cracked residue
of a cross-linking agent.
[0005] Thus, a method of forming an insulating layer containing
magnesium oxide or carbon black as an inorganic filler is known
(see Patent Documents 1 and 2, for example).
PATENT DOCUMENTS
[Patent Document 1] Japanese Laid-open Patent Publication No.
2014-218617
[Patent Document 2] Japanese Laid-open Patent Publication No.
2015-883
[0006] However, it is desired to improve long-term insulating
performance of an insulating layer against applied direct-current
voltage.
SUMMARY OF THE INVENTION
[0007] The present invention is made in light of the above
problems, and provides a direct-current cable in which long-term
insulating performance of an insulating layer against applied
direct-current voltage and space-charge characteristics of an
insulating layer are good.
[0008] According to an embodiment, there is provided a
direct-current cable including a conductive portion; and an
insulating layer covering an outer periphery of the conductive
portion, the insulating layer containing cross-linked base resin
and inorganic filler, the base resin containing polyethylene, a BET
specific surface area of the inorganic filler being greater than or
equal to 5 m.sup.2/g, and a mean volume diameter of the inorganic
filler being less than or equal to 5 .mu.m, the mass ratio of the
inorganic filler with respect to the base resin being greater than
or equal to 0.001 and less than or equal to 0.05, and the
cross-linked base resin being cross-linked by a cross-linking agent
containing organic peroxide.
[0009] According to an embodiment, there is provided a composition
including: base resin, inorganic filler and a cross-linking agent,
the base resin containing polyethylene, a BET specific surface area
of the inorganic filler being greater than or equal to 5 m.sup.2/g,
and a mean volume diameter of the inorganic filler being less than
or equal to 5 .mu.m, the mass ratio of the inorganic filler with
respect to the base resin being greater than or equal to 0.001 and
less than or equal to 0.05, and the cross-linking agent containing
organic peroxide.
[0010] According to an embodiment, a direct-current cable in which
long-term insulating performance of an insulating layer against
applied direct-current voltage and space-charge characteristics of
an insulating layer are good can be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a cross-sectional view illustrating an example of
a direct-current cable.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0012] Next, embodiments are described with reference to
drawings.
[0013] FIG. 1 illustrates an example of a direct-current cable.
FIG. 1 is a cross-sectional view that is perpendicular to an axial
direction of a direct-current cable 1.
[0014] An outer periphery of a conductive portion 10 is covered by
an insulating layer 20 in the direct-current cable 1. Further, an
inner semi-conducting layer 11 is formed between the conductive
portion 10 and the insulating layer 20 in the direct-current cable
1. Further, an outer periphery of the insulating layer 20 is
covered by a shielding layer 30, and an outer periphery of the
shielding layer 30 is covered by a covering layer 40 in the
direct-current cable 1. Further, an outer semi-conducting layer 21
is formed between the insulating layer 20 and the shielding layer
30 in the direct-current cable 1.
[0015] The conductive portion 10 is formed by twisting a plurality
of conductive core wires.
[0016] As the material constituting the conductive core wire,
although not specifically limited, copper, aluminum, copper alloy,
aluminum alloy or the like may be used.
[0017] As the material constituting the inner semi-conducting layer
11, although not specifically limited, ethylene-vinyl acetate
copolymer, ethylene-ethyl acrylate copolymer, ethylene-butyl
acrylate copolymer or the like may be used.
[0018] The insulating layer 20 contains cross-linked base resin and
inorganic filler.
[0019] The base resin contains polyethylene.
[0020] The polyethylene may be either of low density, intermediate
density and high density. Further, the polyethylene may be either
of straight-chain and branched.
[0021] The cross-linked base resin is cross-linked by a
cross-linking agent containing organic peroxide.
[0022] Although the organic peroxide is not specifically limited,
dicumyl peroxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane,
1,3-bis(t-butylperoxyisopropyl)benzene or the like may be used.
[0023] The base resin may further contain copolymer of ethylene and
polar monomer or polyethylene-graft-maleic anhydride. With this,
the long-term insulating performance of the insulating layer 20
against applied direct-current voltage and the space-charge
characteristics of the insulating layer 20 can be improved.
[0024] As the polar monomer, although not specifically limited,
ethyl acrylate, methacrylate, butyl acrylate, glycidyl methacrylate
or the like may be used, and two or more of them may be used in
combination.
[0025] The mass ratio of the copolymer of ethylene and polar
monomer or the polyethylene-graft-maleic anhydride with respect to
the polyethylene is, generally, less than or equal to 1/9, and
preferably, less than or equal to 5/95. With this, the long-term
insulating performance of the insulating layer 20 against applied
direct-current voltage can be improved. The mass ratio of the
copolymer of ethylene and polar monomer or the
polyethylene-graft-maleic anhydride with respect to the
polyethylene is, generally, greater than or equal to 0.01.
[0026] The BET specific surface area of the inorganic filler is
greater than or equal to 5 m.sup.2/g, and preferably, greater than
or equal to 20 m.sup.2/g. If the BET specific surface area of the
inorganic filler is less than 5 m.sup.2/g, the long-term insulating
performance of the insulating layer 20 against applied
direct-current voltage and the space-charge characteristics of the
insulating layer 20 are lowered. Here, the BET specific surface
area of the inorganic filler is, generally, less than or equal to
100 m.sup.2/g.
[0027] The mean volume diameter of the inorganic filler is less
than or equal to 5 .mu.m, and preferably, less than or equal to 2
.mu.m. If the mean volume diameter of the inorganic filler exceeds
5 .mu.m, the long-term insulating performance of the insulating
layer 20 against applied direct-current and the space-charge
characteristics of the insulating layer 20 are lowered. The mean
volume diameter of the inorganic filler is, generally, greater than
or equal to 0.5 .mu.m.
[0028] The mass ratio of the inorganic filler with respect to the
base resin is 0.001 to 0.05, and preferably, 0.005 to 0.03. If the
mass ratio of the inorganic filler with respect to the base resin
is less than 0.001 or exceeds 0.05, the long-term insulating
performance of the insulating layer 20 against applied
direct-current and the space-charge characteristics of the
insulating layer 20 are lowered.
[0029] As the inorganic filler, although not specifically limited,
magnesium oxide powder, aluminum oxide powder, silica powder,
magnesium silicate powder, aluminum silicate powder, carbon black
or the like may be used, and two or more of them may be used in
combination.
[0030] A surface process by a silane coupling agent may be
performed on each of the magnesium oxide powder, the aluminum oxide
powder, the silica powder, the magnesium silicate powder and the
aluminum silicate powder. With this, the long-term insulating
performance of the insulating layer 20 against applied
direct-current and the space-charge characteristics of the
insulating layer 20 can be improved.
[0031] As the silane coupling agent, although not specifically
limited, Vinyltrimethoxysilane, Vinyltriethoxysilane,
2-(3,4-Epoxycyclohexyl)ethyltrimethoxysilane,
3-Glycidoxypropylmethyldimethoxysilane,
3-Glycidoxypropyltrimethoxysilane,
3-Glycidoxypropylmethyldiethoxysilane,
3-Glycidoxypropyltriethoxysilane,
3-Methacryloxypropylmethyldimethoxysilane,
3-Methacryloxypropyltrimethoxysilane,
3-Methacryloxypropylmethyldiethoxysilane,
3-Methacryloxypropyltriethoxysilane,
3-Acryloxypropyltrimethoxysilane,
N-(2-Aminoethyl)-3-aminopropylmethyldimethoxysilane,
N-(2-Aminoethyl)-3-aminopropyltrimethoxysilane,
N-(2-Aminoethyl)-3-aminopropyltriethoxysilane,
3-Aminopropyltrimethoxysilane, 3-Aminopropyltriethoxysilane,
3-Triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine or the like
may be used, and two or more of them may be used in
combination.
[0032] Here, the inorganic filler whose surface is treated by a
silane coupling agent and the inorganic filler whose surface is not
treated by a silane coupling agent may be used together in
combination.
[0033] A grinding process may be performed on the inorganic filler.
For example, a grinding process by jet grinding may be performed on
the inorganic filler, whose particle size becomes larger as being
adhered with each other when performing the surface treatment using
the silane coupling agent.
[0034] The insulating layer 20 may further contain an
anti-oxidizing agent. With this, thermal aging resistance of the
insulating layer 20 can be improved.
[0035] As the anti-oxidizing agent, although not specifically
limited,
2,2-Thiodiethylene-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate],
[0036]
Pentaerythrityl-tetrakis(3-(3,5-di-t-butyl-4-hydroxyphenyl)propiona-
te), Octadecyl 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate,
2,4-Bis(n-octylthiomethyl)-o-cresol,
2,4-Bis(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-triazine,
Bis[2-methyl-4-{3-n-alkyl (C12 or C14)
thiopropionyloxy}-5-t-butylphenyl]sulfide,
4,4'-Thiobis(3-methyl-6-t-butylphenol) or the like may be used, and
two or more of them may be used in combination.
[0037] The insulating layer 20 may further contain lubricant, a
coloring agent or the like.
[0038] As the material constituting the outer semi-conducting layer
21, although not specifically limited, ethylene-vinyl acetate
copolymer or the like may be used.
[0039] As the material constituting the shielding layer 30,
although not specifically limited, copper or the like may be
used.
[0040] As the material constituting the covering layer 40, although
not specifically limited, polyvinyl chloride or the like may be
used.
[0041] The direct-current cable 1 may be applied for power
transmission of direct-current power or the like.
[0042] Next, an example of a method of manufacturing the
direct-current cable 1 is described.
[0043] The inner semi-conducting layer 11, the insulating layer 20
and the outer semi-conducting layer 21 are formed by extrusion
molding a raw material of the inner semi-conducting layer 11, the
composition containing the base resin, the inorganic filler and the
cross-linking agent as a raw material of the insulating layer 20
and a raw material of the outer semi-conducting layer 21 at the
same time at the outer periphery of the conductive portion 10, and
heating it to a predetermined temperature to cross-link the base
resin. Next, the shielding layer 30 is formed by winding a
conductive wire such as a copper tape, or an annealed copper wire
around the outer periphery of the outer semi-conducting layer 21.
Further, the covering layer 40 is formed at an outer periphery of
the shielding layer 30 by extrusion molding a raw material of the
covering layer 40.
[0044] As the method of manufacturing the composition, although not
specifically limited, a method or the like may be used in which the
base resin, the inorganic filler, if necessary, the anti-oxidizing
agent, the lubricant, the coloring agent and the like are kneaded
to manufacture pellets, and thereafter, the cross-linking agent is
heated and impregnated to the pellets.
[0045] Here, the composition may be extrusion molded by removing
aggregates by using a screen mesh.
[0046] Further, the raw material of the inner semi-conducting layer
11, the above described composition and the raw material of the
outer semi-conducting layer 21 may be extrusion molded at the same
time.
EXAMPLES
[0047] Next, examples of the invention are described. Here, a term
"parts" means "parts by weight".
Example 1
[0048] 100 parts of low density polyethylene (LDPE) with a density
of 0.920 g/mm.sup.3, and MFR (Melt Flow Rate) of 1 g/10 min as the
base resin, 0.1 parts of magnesium oxide powder with a BET specific
surface area of 30 m.sup.2/g, and a mean volume diameter of 0.45
.mu.m as the inorganic filler, and 0.2 parts of
4,4'-thiobis(3-methyl-6-t-butylphenol) as the anti-oxidizing agent
were heated and kneaded at about 180.degree. C. to manufacture
pellets. Next, 2 parts of dicumyl peroxide as the cross-linking
agent was heated and impregnated to the obtained pellets at about
60.degree. C. to obtain composition.
Example 2
[0049] Composition was obtained similarly as Example 1 except that
the amount of the inorganic filler was changed to 1 part.
Example 3
[0050] Composition was obtained similarly as Example 1 except that
the amount of the inorganic filler was changed to 5 parts.
Example 4
[0051] Composition was obtained similarly as Example 2 except that
magnesium oxide powder with a BET specific surface area of 145
m.sup.2/g, and a mean volume diameter of 0.50 .mu.m whose surface
was treated by vinyltrimethoxysilane as the silane coupling agent
was used, as the inorganic filler.
Example 5
[0052] Composition was obtained similarly as Example 4 except that
97 parts of LDPE with a density of 0.920 g/mm.sup.3, and MFR (Melt
Flow Rate) of 1 g/10 min, and 3 parts of polyethylene-graft-maleic
anhydride (MA-g-PE) with a density of 0.920 g/mm.sup.3, and MFR
(Melt Flow Rate) of 1 g/10 min were used, as the base resin.
Example 6
[0053] Composition was obtained similarly as Example 5 except that
1.3 parts of 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane was used, as
the cross-linking agent.
Example 7
[0054] Composition was obtained similarly as Example 6 except that
magnesium oxide powder with a BET specific surface area of 30
m.sup.2/g, and a mean volume diameter of 0.05 .mu.m whose surface
was treated by vinyltrimethoxysilane as the silane coupling agent
was used, as the inorganic filler.
Example 8
[0055] Composition was obtained similarly as Example 6 except that
magnesium oxide powder with a BET specific surface area of 8
m.sup.2/g, and a mean volume diameter of 0.2 .mu.m whose surface
was treated by vinyltrimethoxysilane as the silane coupling agent
was used, as the inorganic filler.
Example 9
[0056] Composition was obtained similarly as Example 6 except that
95 parts of LDPE with a density of 0.920 g/mm.sup.3, and MFR (Melt
Flow Rate) of 1 g/10 min, and 5 parts of ethylene-ethyl acrylate
copolymer (poly(E-co-EA)), in which the content of units originated
from ethyl acrylate was 7 mass %, with a density of 0.930
g/mm.sup.3 and MFR (Melt Flow Rate) of 4 g/10 min were used, as the
base resin, and silica powder with a BET specific surface area of
50 m.sup.2/g, and a mean volume diameter of 0.03 .mu.m was used, as
the inorganic filler.
Example 10
[0057] Composition was obtained similarly as Example 6 except that
silica powder with a BET specific surface area of 90 m.sup.2/g, and
a mean volume diameter of 0.02 .mu.m was used, as the inorganic
filler.
Example 11
[0058] Composition was obtained similarly as Example 6 except that
97 parts of LDPE with a density of 0.920 g/mm.sup.3, and MFR (Melt
Flow Rate) of 1 g/10 min, and 3 parts of poly(E-co-EA), in which
the content of units originated from ethyl acrylate was 7 mass %,
with a density of 0.930 g/mm.sup.3, and MFR (Melt Flow Rate) of 4
g/10 min were used, as the base resin, alumina powder with a BET
specific surface area of 120 m.sup.2/g, and a mean volume diameter
of 0.02 .mu.m was used, as the inorganic filler, and
1,3-bis(t-butylperoxyisopropyl)benzene was used, as the
cross-linking agent.
Example 12
[0059] Composition was obtained similarly as Example 6 3.0 except
that 93 parts of LDPE with a density of 0.920 g/mm.sup.3 and MFR
(Melt Flow Rate) of 1 g/10 min, and 7 parts of poly(E-co-EA) whose
EA concentration was 7% with a density of 0.930 g/mm.sup.3, and MFR
(Melt Flow Rate) of 4 g/10 min were used, as the base resin, and
carbon black with a BET specific surface area of 50 m.sup.2/g, and
a mean volume diameter of 0.05 .mu.m was used, as the inorganic
filler.
Example 13
[0060] Composition was obtained similarly as Example 6 except that
1 part of magnesium oxide powder with a BET specific surface area
of 145 m.sup.2/g, and a mean volume diameter of 0.50 .mu.m whose
surface was treated by vinyltrimethoxysilane as the silane coupling
agent, and 2 parts of silica powder with a BET specific surface
area of 50 m.sup.2/g, and a mean volume diameter of 0.03 .mu.m were
used, as the inorganic filler.
Example 14
[0061] Composition was obtained similarly as Example 6 except that
2 parts of magnesium oxide powder with a BET specific surface area
of 145 m.sup.2/g, and a mean volume diameter of 0.50 .mu.m whose
surface was treated by vinyltrimethoxysilane as the silane coupling
agent, and 3 parts of alumina powder with a BET specific surface
area of 120 m.sup.2/g, and a mean volume diameter of 0.02 .mu.m
were used, as the inorganic filler.
Comparative Example 1
[0062] Composition was obtained similarly as Example 1 except that
the inorganic filler was not used.
Comparative Example 2
[0063] Composition was obtained similarly as Example 1 except that
the amount of the inorganic filler was changed to 10 parts.
Comparative Example 3
[0064] Composition was obtained similarly as Example 1 except that
2 parts of magnesium oxide powder with a BET specific surface area
of 1.4 m.sup.2/g, and a mean volume diameter of 3 .mu.m was used,
as the inorganic filler.
Comparative Example 4
[0065] Composition was obtained similarly as Example 1 except that
2 parts of magnesium oxide powder with a BET specific surface area
of 0.5 m.sup.2/g, and a mean volume diameter of 17 .mu.m was used,
as the inorganic filler.
Comparative Example 5
[0066] Composition was obtained similarly as Example 1 except that
2 parts of alumina powder with a BET specific surface area of 4.1
m.sup.2/g, and a mean volume diameter of 1.5 .mu.m was used, as the
inorganic filler.
[0067] Characteristics of inorganic fillers contained in the
compositions are illustrated in Table 1.
TABLE-US-00001 TABLE 1 BET SPECIFIC MEAN SURFACE VOLUME AREA
DIAMETER SURFACE MATERIAL [m.sup.2/g] [.mu.m] TREATMENT 1 MAGNESIUM
145 0.5 WITH OXIDE 2 MAGNESIUM 30 0.45 WITHOUT OXIDE 3 MAGNESIUM 30
0.05 WITH OXIDE 4 MAGNESIUM 8 0.2 WITH OXIDE 5 SILICA 50 0.03
WITHOUT 6 SILICA 90 0.02 WITHOUT 7 ALUMINA 120 0.02 WITHOUT 8
CARBON 50 0.05 WITHOUT BLACK 9 MAGNESIUM 1.4 3 WITHOUT OXIDE 10
MAGNESIUM 0.5 17 WITHOUT OXIDE 11 ALUMINA 4.1 1.5 WITHOUT
[0068] Characteristics of the compositions are illustrated in Table
2.
TABLE-US-00002 TABLE 2 AMOUNT OF BASE RESIN [PARTS] INORGANIC
FILLER Poly AMOUNT AMOUNT LDPE MA-g-PE (E-co-EA) NO. [PARTS] NO.
[PARTS] EXAMPLE 1 100 0 0 2 0.1 -- -- EXAMPLE 2 100 0 0 2 1 -- --
EXAMPLE 3 100 0 0 2 5 -- -- EXAMPLE 4 100 0 0 1 1 -- -- EXAMPLE 5
97 3 0 1 1 -- -- EXAMPLE 6 97 3 0 1 1 -- -- EXAMPLE 7 97 3 0 3 1 --
-- EXAMPLE 8 97 3 0 4 1 -- -- EXAMPLE 9 95 0 5 5 1 -- -- EXAMPLE 10
97 3 0 6 1 -- -- EXAMPLE 11 97 0 3 7 1 -- -- EXAMPLE 12 93 0 7 8 1
-- -- EXAMPLE 13 97 3 0 1 1 3 2 EXAMPLE 14 97 3 0 1 2 5 3
COMPARATIVE 100 0 0 -- -- -- -- EXAMPLE 1 COMPARATIVE 100 0 0 2 10
-- -- EXAMPLE 2 COMPARATIVE 100 0 0 9 2 -- -- EXAMPLE 3 COMPARATIVE
100 0 0 10 2 -- -- EXAMPLE 4 COMPARATIVE 100 0 0 11 2 -- -- EXAMPLE
5 (Manufacturing of sheet)
[0069] Each of the compositions was press molded to obtain a sheet
with thickness T of 0.15 mm.
[0070] Next, specific volume resistance, long-term insulating
performance against applied direct-current voltage and space-charge
characteristics of each of the sheets were evaluated.
(Specific Volume Resistance)
[0071] Specific volume resistance was measured by soaking the sheet
in silicone oil of 90.degree. C., and applying a direct electric
field of 80 kV/mm to the sheet using a flat plate electrode with a
diameter of 25 mm.
(Long-Term Insulating Performance Against Applied Direct-Current
Voltage)
[0072] Using the sheet, a V-t curve was obtained by soaking the
sheet in silicone oil of 90.degree. C., applying a direct electric
field V.sub.0 [kV/mm] of 10 to 300 kV/mm to the sheet using a flat
plate electrode with a diameter of 25 mm and measuring a period "t"
[h] until dielectric breakdown occurs in the sheet. Next, life
exponent "n" was obtained from the formula
V.sub.0.sup.n.times.t=const.,
[0073] and long-term insulating performance against applied
direct-current voltage was evaluated. Here, when "n" was greater
than or equal to 20, it was determined to be double circle, when
"n" was greater than or equal to 15 and less than 20, it was
determined to be "0" (circle), and when "n" was less than 15, it
was determined to be "x".
(Space-Charge Characteristics)
[0074] Space-charge characteristics of the sheet were evaluated
using a Pulsed Electro Acoustic Non-destructive Test System
(manufactured by Five Lab). Specifically, space-charge
characteristics of the sheet was evaluated by continuously applying
a direct electric field V.sub.0 of 50 kV/mm to the sheet under
atmospheric pressure at 30.degree. C. for an hour, measuring
maximum electric field V.sub.1 in the sheet, and obtaining Field
Enhancement Factor FEF defined by the formula
V.sub.1/(V.sub.0.times.T).
[0075] Here, when the FEF was less than 1.15, it was determined to
be ".smallcircle." (circle) and when the FEF was greater than or
equal to 1.15, it was determined to be "x".
[0076] Evaluated results of the specific volume resistance, the
long-term insulating performance against applied direct-current
current and the space-charge characteristics of each of the sheets
are illustrated in Table 3.
TABLE-US-00003 TABLE 3 LONG-TERM INSULATING SPECIFIC PERFORMANCE
SPACE- VOLUME AGAINST CHARGE RESISTANCE DIRECT- CHARAC- [.OMEGA.
cm] CURRENT TERISTICS EXAMPLE 1 1 .times. 10.sup.15 .largecircle.
.largecircle. EXAMPLE 2 3 .times. 10.sup.15 .largecircle.
.largecircle. EXAMPLE 3 2 .times. 10.sup.15 .largecircle.
.largecircle. EXAMPLE 4 6 .times. 10.sup.15 .circleincircle.
.largecircle. EXAMPLE 5 8 .times. 10.sup.15 .circleincircle.
.largecircle. EXAMPLE 6 4 .times. 10.sup.15 .circleincircle.
.largecircle. EXAMPLE 7 7 .times. 10.sup.15 .circleincircle.
.largecircle. EXAMPLE 8 6 .times. 10.sup.15 .circleincircle.
.largecircle. EXAMPLE 9 5 .times. 10.sup.15 .circleincircle.
.largecircle. EXAMPLE 10 5 .times. 10.sup.15 .circleincircle.
.largecircle. EXAMPLE 11 6 .times. 10.sup.15 .circleincircle.
.largecircle. EXAMPLE 12 4 .times. 10.sup.15 .circleincircle.
.largecircle. EXAMPLE 13 7 .times. 10.sup.15 .circleincircle.
.largecircle. EXAMPLE 14 5 .times. 10.sup.15 .circleincircle.
.largecircle. COMPARATIVE 2 .times. 10.sup.13 X X EXAMPLE 1
COMPARATIVE 1 .times. 10.sup.15 X X EXAMPLE 2 COMPARATIVE 1 .times.
10.sup.14 X X EXAMPLE 3 COMPARATIVE 2 .times. 10.sup.14 X X EXAMPLE
4 COMPARATIVE 9 .times. 10.sup.13 X X EXAMPLE 5
[0077] From Table 3, for each of the sheets manufactured from the
compositions of Examples 1 to 13, respectively, it can be
understood that the specific volume resistance is high, and the
long-term insulating performance against applied direct-current
voltage and the space-charge characteristics are good.
[0078] On the other hand, as the sheet manufactured from the
composition of Comparative example 1 does not contain inorganic
filler, the specific volume resistance, the long-term insulating
performance against applied direct-current voltage and the
space-charge characteristics are lowered.
[0079] For the sheet manufactured from the composition of
Comparative example 2, as the mass ratio of the inorganic filler 2
with respect to the base resin is 0.1, the long-term insulating
performance against applied direct-current voltage and the
space-charge characteristics are lowered.
[0080] For the sheets manufactured from the compositions of
Comparative examples 3 and 5, as the BET specific surface area of
each of the inorganic filler are 1.4 m.sup.2/g and 4.1 m.sup.2/g,
respectively, the specific volume resistance, the long-term
insulating performance against applied direct-current voltage and
the space-charge characteristics are lowered.
[0081] For the sheet manufactured from the composition of
[0082] Comparative example 4, as the BET specific surface area and
the mean volume diameter of the inorganic filler are 0.5 m.sup.2/g
and 17 .mu.m, respectively, the specific volume resistance, the
long-term insulating performance against applied direct-current
voltage and the space-charge characteristics are lowered.
(Manufacturing of Direct-Current Cable 1)
[0083] First, the conductive portion 10 formed by twisting
conductive core wires made of a dilute copper alloy with a diameter
of 14 mm was prepared. Next, the inner semi-conducting layer 11
made of ethylene-ethyl acrylate copolymer, the composition as the
raw material of the insulating layer 20 and the outer
semi-conducting layer 21 made of ethylene-ethyl acrylate copolymer
were extrusion molded at the same time at the outer periphery of
the conductive portion 10 to be the thicknesses of 1 mm, 14 mm and
1 mm, respectively. Then, the product was heated at about
250.degree. C. to cross link the base resin and to form the inner
semi-conducting layer 11, the insulating layer 20 and the outer
semi-conducting layer 21. Next, the shielding layer 30 was formed
by winding a conductive wire such as an annealed copper wire or the
like with the diameter of 1 mm around the outer periphery of the
outer semi-conducting layer 21. Then, the covering layer 40 with
the thickness of 3 mm was formed by extrusion molding polyvinyl
chloride at the outer periphery of the shielding layer 30 to obtain
the direct-current cable 1.
NUMERALS
[0084] 1 direct-current cable [0085] 10 conductive portion [0086]
11 inner semi-conducting layer [0087] 20 insulating layer [0088] 21
outer semi-conducting layer [0089] 30 shielding layer [0090] 40
covering layer
* * * * *