U.S. patent application number 10/621838 was filed with the patent office on 2004-02-05 for conductive antioxidant paint and graphite electrode.
This patent application is currently assigned to Mikuni Color Ltd.. Invention is credited to Fukushima, Tatsuo, Hisashi, Hideyuki, Kawabata, Issei.
Application Number | 20040023021 10/621838 |
Document ID | / |
Family ID | 25202133 |
Filed Date | 2004-02-05 |
United States Patent
Application |
20040023021 |
Kind Code |
A1 |
Hisashi, Hideyuki ; et
al. |
February 5, 2004 |
Conductive antioxidant paint and graphite electrode
Abstract
There are disclosed a conductive antioxidant paint suitably used
as an antioxidant material for a graphite electrode used in arc
furnaces such as electric steel-making furnaces, and a graphite
electrode coated with the conductive antioxidant paint.
Inventors: |
Hisashi, Hideyuki;
(Himeji-shi, JP) ; Kawabata, Issei; (Himeji-shi,
JP) ; Fukushima, Tatsuo; (Himeji-shi, JP) |
Correspondence
Address: |
EDWARDS & ANGELL, LLP
P.O. BOX 9169
BOSTON
MA
02209
US
|
Assignee: |
Mikuni Color Ltd.
|
Family ID: |
25202133 |
Appl. No.: |
10/621838 |
Filed: |
July 16, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10621838 |
Jul 16, 2003 |
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09809749 |
Mar 15, 2001 |
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6645629 |
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Current U.S.
Class: |
428/323 ;
428/408; 428/704 |
Current CPC
Class: |
Y10T 428/25 20150115;
C09K 3/16 20130101; H01B 1/24 20130101; Y10T 428/30 20150115; Y02E
60/10 20130101; H01M 4/366 20130101; H01M 4/583 20130101; H01M
4/624 20130101; C09D 5/24 20130101 |
Class at
Publication: |
428/323 ;
428/704; 428/408 |
International
Class: |
B32B 009/00 |
Claims
What is claimed is:
1. A conductive antioxidant paint comprising a conductive material,
an antioxidant material, a polymer emulsion and an inorganic
colloid as a binder, and a transition metal; and having a pH value
of not more than 9.
2. A conductive antioxidant paint according to claim 1, wherein
said antioxidant material is previously oxidized.
3. A conductive antioxidant paint according to claim 1, wherein
said antioxidant material is a carbide or nitride of an element
selected from the group consisting of B, Si, Ge, Sb, Ti, Sn, Al and
Zr, a boron element or a silicon element.
4. A conductive antioxidant paint according to claim 1, wherein
said inorganic colloid has an average particle size of not more
than 100 nm.
5. A conductive antioxidant paint according to claim 1, wherein
said transition metal is at least one element selected from the
group consisting of Cr, W, Co, Ti and Ni.
6. A conductive antioxidant paint comprising a conductive material,
an antioxidant material, a polymer emulsion and an inorganic
colloid as a binder, and a transition metal, the content of alkali
metal and/or alkali earth metal being not more than 20% by weight
based on the weight of the antioxidant material.
7. A conductive antioxidant paint according to claim 6, wherein
said antioxidant material is previously oxidized.
8. A conductive antioxidant paint according to claim 6, wherein
said antioxidant material is a carbide or nitride of an element
selected from the group consisting of B, Si, Ge, Sb, Ti, Sn, Al and
Zr, a boron element or a silicon element.
9. A conductive antioxidant paint according to claim 6, wherein
said inorganic colloid has an average particle size of not more
than 100 nm.
10. A conductive antioxidant paint according to claim 6, wherein
said transition metal is at least one element selected from the
group consisting of Cr, W, Co, Ti and Ni.
11. A conductive antioxidant paint comprising a conductive
material, an antioxidant material and a binder; and having a total
content of aluminum and silicon elements of not more than 1% by
weight based on the weight of a solid content of the paint.
12. A conductive antioxidant paint according to claim 11, wherein
said antioxidant material is previously oxidized.
13. A conductive antioxidant paint according to claim 11, wherein
said antioxidant material is a carbide or nitride of an element
selected from the group consisting of B, Si, Ge, Sb, Ti, Sn, Al and
Zr, a boron element or a silicon element.
14. A conductive antioxidant paint according to claim 11, further
comprising an inorganic colloid having an average particle size of
not more than 100 nm.
15. A conductive antioxidant paint according to claim 11, further
comprising at least one transition metal selected from the group
consisting of Cr, W, Co, Ti and Ni.
16. A graphite electrode coated with the conductive antioxidant
paint as defined in claims 1, 6 or 11.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a conductive antioxidant
paint and a graphite electrode, and more particularly, to a
conductive antioxidant paint especially suitable as an antioxidant
material for a graphite electrode used in arc furnaces such as
electric steel-making furnaces, and a graphite electrode coated
with such a conductive antioxidant paint.
[0002] Hitherto, artificial graphite electrodes have been used in
conventional arc furnaces such as electric steel-making furnaces.
Upon the use, the graphite electrodes have been exposed to
extremely severe conditions such as large electric current, high
temperature, splashes of molten steel or the like. In particular,
since ultrahigh-temperature arcs are generated at a tip end of the
electrode, the graphite electrode has been exposed to a temperature
as high as about 400 to about 3,000.degree. C. As a result, the
graphite electrode is readily oxidized and consumed by an oxidative
gas entering through openings of the furnace.
[0003] In the electric steel-making furnaces, costs for the
electrode used therein is very high, so that the consumed electrode
leads to large economical loss. Upon the oxidation, 50 to 70% by
weight of a consumed portion of the electrode is due to oxidative
attack from a side surface of the electrode, and the arc itself has
a less influence on the wear-out of the electrode. The wear-out of
the electrode by oxidation becomes more remarkable at the position
closer to the tip end thereof, so that the electrode is tapered
toward the tip end, resulting in accelerated wear-out of the
electrode in the longitudinal direction. Accordingly, if the
oxidative attack from the side surface of the electrode is
sufficiently prevented, the wear-out of the electrode can be
effectively reduced with a large economical merits.
[0004] Conventionally, various methods have been proposed in order
to inhibit the oxidation of the electrode. For example, there are
known a method of applying to the electrode an antioxidant paint
composed of a matrix containing a glazing material (frit) having a
melting point of not more than 1,000.degree. C., and refractory
aggregates (Japanese Patent Application Laid-Open (KOKAI) No.
48-72211); a method of forming a non-conductive antioxidant paint
layer on the surface of graphite electrode (Japanese Patent
Application Laid-Open (KOKAI) No. 59-51499); a method of applying
onto the electrode, a paint prepared by dispersing alumina or
silica fine particles in a colloid solution containing silica
ultrafine particles (Japanese Patent Application Laid-Open (KOKAI)
No. 3-45583); or the like.
[0005] However, since any of these conventional paints is
non-conductive, it is required that a chuck portion of the
electrode is released from being coated therewith in order to
ensure the current flow to the electrode. For this reason, there
arise problems such as complicated coating processes, insufficient
oxidation-resistant property at the uncoated portion of electrode
or the like. In particular, in the method described in Japanese
Patent Application Laid-Open (KOKAT) No. 48-72211, when the frit is
softened at a temperature of not more than 1,000.degree. C., the
coating film undergoes shrinkage, so that film defects such as
peeling-off, penetration or ruptures tend to be caused. In order to
eliminate these film defects, there has been proposed a method of
repeating the coating works until the thickness of the obtained
coating film after melting the frit becomes as large as about 1 mm.
However, in such a case, the working efficiency has been
considerably deteriorated.
[0006] Further, in order to solve the above problems, there have
been proposed conductive antioxidant paints of the type which can
be coated even on the chuck portion of electrode by imparting a
conductivity to the obtained coating film (Japanese Patent
Application Laid-Open (KOKAI) Nos. 7-268248, 7-268249 and
7-268250). More specifically, Japanese Patent Application Laid-Open
(KOKAI) No. 7-268248 describes a conductive antioxidant material
containing a refractory aggregate, a colloidal binder and carbon
black without any glass frits; Japanese Patent Application
Laid-Open (KOKAI) No. 7-268249 describes a conductive antioxidant
material containing a refractory aggregate, a binder and
graphitized carbon black; and Japanese Patent Application Laid-Open
(KOKAI) No. 7-268250 describes a conductive antioxidant material
containing a refractory aggregate, a binder, carbon black and a
polymer emulsion. The refractory aggregate includes oxides such as
silica, alumina, titania or zirconia, and the binder includes
inorganic colloid.
[0007] However, these conventional conductive antioxidant paints
generate a large amount of hydrogen gas during the storage or
transportation, resulting in poor storage stability thereof and
breakage of a container therefor. For this reason, a long-period
storage and a long-distance transportation of these paints are
difficult.
[0008] In addition, in the case where the conventional conductive
antioxidant paints are coated on the electrode, the obtained
coating film suffers from pinholes by the hydrogen gas generated
therefrom, so that the electrode tends to be burned from the
pinholes. Thus, the conventional conductive antioxidant paints are
deteriorated in antioxidant property when exposed to a temperature
as high as not less than 1,000.degree. C. As a result, the
electrode is not only deteriorated in heat resistance and oxidation
resistance, but also more likely to be consumed by the
oxidation.
[0009] Meanwhile, it is known that the temperature within the arc
furnace reaches not less than 1,000.degree. C., thereby causing the
following problems concerning the conventional conductive
antioxidant paints. That is, the oxidation-resistant effect of the
above paints is exhibited by a glass-like coating film formed by
heat-melting film-forming components of the paints at a temperature
of about 800.degree. C. However, when the paints are heated to a
temperature as high as not less than 1,000.degree. C., the obtained
glass-like coating film is unsuitably lowered in viscosity and
fallen off from the surface of the electrode, resulting in a
discontinuous glass-like coating film. Such discontinuous
glass-like coating film fails to prevent the contact between oxygen
and the electrode, thereby causing defects such as burning-in of
the electrode, e.g., cissing thereon.
[0010] As a result of the present inventors' earnest studies to
solve the above problems, it has been found that (1) the generation
of hydrogen gas is caused when the paint has a high pH value, and
is due to by the reaction between a trace amount of alkali
components and impurities of the metal compound; (2) the viscosity
of the glass-like coating film is lowered by melt-penetration of
the alkali components into the coating film; or (3) the generation
of hydrogen gas is caused by the existence of specific elements in
the paint. The present invention has been attained based on the
above finding.
[0011] More specifically, it has been found that the deterioration
in viscosity of the glass-like coating film is due to such a
phenomenon that alkali metals such as sodium and potassium or
compounds thereof such as alkali metal oxides, and alkali earth
metals such as calcium and magnesium or compounds thereof such as
alkali earth metal oxides are melt-penetrated into the glass-like
coating film after burning of carbon, and that the deteriorated
viscosity of the glass-like coating film causes falling-off or
separation of the coating film from the electrode, thereby
adversely affecting the antioxidant effect of the electrode. In
addition, it has been found that the above alkali components tend
to react with the impurities of a metal compound to generate a
hydrogen gas, thereby considerably deteriorating a storage
stability of the paint, and that when hydrogen gas is generated
during drying step of the coating film, pinholes are formed
therein, so that the electrode tends to be burned from the
pinholes.
SUMMARY OF THE INVENTION
[0012] An object of the present invention is to provide an improved
conductive antioxidant paint which is inhibited from generating a
hydrogen gas during the storage or transportation, thereby avoiding
possible breakage of a container therefor and imparting an
excellent storage stability, and which can prevent a graphite
electrode used in arc furnace from being consumed by oxidation; and
a graphite electrode which is coated with the conductive
antioxidant paint.
[0013] Another object of the present invention is to provide a
conductive antioxidant paint which exhibits an excellent
antioxidant effect even when exposed to a temperature as high as
not less than 1,0000.degree. C., and a graphite electrode which is
coated with such a conductive antioxidant paint.
[0014] A further object of the present invention is to provide a
conductive antioxidant paint which has an excellent storage
stability, is free from pinholes when formed into a coating film,
and exhibits an excellent antioxidant effect even when exposed to a
temperature as high as not less than 1,000.degree. C., and a
graphite electrode which is coated with such a conductive
antioxidant paint.
[0015] In a first aspect of the present invention, there is
provided a conductive antioxidant paint comprising a conductive
material, an antioxidant material, a polymer emulsion and an
inorganic colloid as a binder, and a transition metal; and having a
pH value of not more than 9.
[0016] In a second aspect of the present invention, there is
provided a conductive antioxidant-paint comprising a conductive
material, an antioxidant material, a polymer emulsion and an
inorganic colloid as a binder, and a transition metal, an alkali
metal and/or alkali earth metal content being not more than 20% by
weight based on the weight of the antioxidant material.
[0017] In a third aspect of the present invention, there is
provided a conductive antioxidant paint comprising a conductive
material, an antioxidant material and a binder; and having a total
content of aluminum and silicon elements of not more than 1% by
weight based on the weight of the solid content of the paint.
[0018] In a fourth aspect of the present invention, there is
provided a coated graphite electrode comprising a graphite
electrode coated with any of the conductive antioxidant paints
described in the above aspects.
DETAILED DESCRIPTION OF THE INVENTION
[0019] First, the conductive antioxidant paint according to the
present invention will be explained. The conductive antioxidant
paint according to the present invention (hereinafter referred to
merely as "paint") includes a conductive material, an antioxidant
material and a binder, and can form a coating film or layer
exhibiting a good conductivity and antioxidant effect. Therefore,
the paint of the present invention is effective to prevent the
oxidation of a graphite electrode when applied thereon.
[0020] [Conductive Material]
[0021] The conductive material used in the present invention is not
particularly restricted as long as the material can impart a good
conductivity to the resultant coating film. Typical examples of the
conductive materials may include carbon black and graphite. These
conductive materials may be used alone or in the form of a mixture
thereof.
[0022] As the carbon black, there may be used those produced by any
suitable methods such as a furnace method, an acetylene method, a
thermal method and a contact method. Among these carbon blacks,
graphitized carbon black produced by treating carbon black in a
temperature of not less than 2,000.degree. C., preferably 2,500 to
3,000.degree. C. in such an atmosphere containing substantially no
oxygen (e.g., under N.sub.2 gas flow, in vacuum or in carbon
powder) is preferred, and the graphitized carbon black having a
divided value of crystallite thickness Lc (.ANG.) to particle size
(nm) of 1.0 to 3.0 is more preferred.
[0023] The carbon black used in the present invention preferably
contains an alkali metal such as potassium and sodium and/or an
alkali earth metal in an amount of not more than 1% by weight, more
preferably not more than 0.5% by weight. By limiting the alkali
metal and/or alkali earth metal content in carbon black to the
above-specified range, it becomes possible not only to increase the
ignition point of carbon black itself, but also to keep a good
conductivity of the obtained coating film until reaching near
400.degree. C. in which the chuck portion of the electrode is
present.
[0024] As the graphite, there may be used any suitable commercially
available products such as flake graphite, earthy graphite,
artificial graphite, expanded graphite or the like. Among them,
preferred graphites are those having an ash content of not more
than 2% by weight, preferably not more than 1% by weight, more
preferably not more than 0.5% by weight.
[0025] The content of the conductive material is usually in the
range of 0.5 to 50% by weight, preferably 3 to 35% by weight based
on the solid content of the paint.
[0026] When carbon black solely is used as the conductive material,
the content of the carbon black is preferably 2 to 30% by weight,
more preferably 5 to 20% by weight based on the weight of the solid
content of the paint. When the content of the carbon black is less
than 2% by weight, the obtained paint may be deteriorated in
conductivity. When the content of the carbon black is more than 30%
by weight, the viscosity of the obtained paint may tend to become
too high, or the carbon black contained in a coating film may tend
to be burnt, resulting in deteriorated antioxidant performance of
the coating film.
[0027] Also, when graphite solely is used as the conductive
material, the content of the graphite is preferably 0.5 to 20% by
weight, more preferably 3 to 15% by weight based on the weight of
the solid content of the paint. When the content of the graphite is
less than 0.5% by weight, the resultant coating film may tend to be
deteriorated in effect of improving the sliding property. When the
content of the graphite is more than 20% by weight, the viscosity
of the obtained paint may tend to become too high.
[0028] When the combination of carbon black and graphite is used as
the conductive material, the content thereof lies in the
above-specified range.
[0029] When the electrode is consumed during the operation of arc
furnace, a fresh electrode is connected to a top of the old
electrode, and an electrode holder (clamping device) mounted on the
old electrode is moved in the longitudinal direction of the
electrode up to a predetermined position of the fresh electrode.
Upon the replacement step, a coating film formed on the fresh
electrode tends to be damaged by the contact with the electrode
holder. In order to prevent the coating film from being damaged
(peeled) by the contact with the electrode holder, an additional
amount of graphite powder may be contained in the coating film,
thereby improving a sliding resistance thereof and reducing the
damage thereof. The amount of the graphite powder blended is
preferably 10 to 70 parts by weight, more preferably 20 to 60 parts
by weight based on 100 parts by weight of the antioxidant
material.
[0030] [Antioxidant Material]
[0031] The antioxidant material used in the present invention is
not particularly restricted as long as the material can impart a
required antioxidant property to the obtained coating film.
Examples of the antioxidant materials may include oxides such as
silica, alumina, titania and zirconia; carbides such as SiC,
B.sub.4C, CrC, WC, TiC, VC, ZrC and NbC, and carbides of an element
selected from the group consisting of Ge, Sb, Sn and Al; nitrides
such as TiN, VN, NbN and ZrN, and nitrides of an element selected
from the group consisting of B, Si, Ge, Sb, Sn and Al; silicides
such as CrSi.sub.2, TiSi.sub.2 and ZrSi.sub.2; borides such as
ZrB.sub.2, TiB.sub.2 and CrB; or a boron element as a single
substance. The above oxides, carbides, nitrides, suicides and
element may be used alone or in the form of a mixture of any two or
more thereof.
[0032] The antioxidant materials are vitrified when exposed to a
temperature as high as not less than 1,000.degree. C. and,
therefore, can be referred to as "glass-forming substance". More
specifically, the antioxidant materials are gradually converted
into oxides under heated condition, and form a glass-like coating
film while enclosing other components such as inorganic colloid
therein, so that the electrode is shielded and protected from
oxygen by the thus formed film. Among the above antioxidant
materials, ZrB.sub.2, B.sub.4C, TiC, SiC and Si are preferred
because these materials can impart an excellent oxidation-resistant
property to the electrode and an excellent stability to the
glass-like coating film under heated condition. Further, when
carbides are used as the antioxidant material, more excellent
oxidation-resistant effect can be exhibited since the carbides are
oxidized and serve for inhibiting oxygen from penetrating into the
electrode. Among these antioxidant materials, the combination of
B.sub.4C and SiC is especially preferred.
[0033] The antioxidant materials contain impurities such as
aluminum or silicon in the form of a single substance (hereinafter
referred to merely as "aluminum element (metal) or silicon
element"). It is considered that the hydrogen gas is generated by
reacting these impurities with alkali components contained in the
colloidal silica used as a binder. The generation of hydrogen gas
causes remarkable deterioration in storage stability of the paint,
and if the hydrogen gas is generated during drying step of the
coating film, pinholes are formed in the coating film, resulting in
burning of the electrode from the pinholes. Therefore, the
antioxidant materials are preferably pre-treated with acids such as
hydrochloric acid to reduce the contents of aluminum and silicon
elements therein. By reducing the contents of aluminum and silicon
elements in the antioxidant materials, it is possible to inhibit
the generation of hydrogen gas, enhance the keeping property of the
coating solution, and prevent the formation of pinholes upon
coating. The total content of aluminum and silicon elements is
preferably not more than 1% by weight, more preferably not more
than 0.5% by weight based on the weight of the solid content of the
paint.
[0034] The acid treatment of the antioxidant materials is not
particularly restricted as long as the aluminum and silicon
elements can be effectively removed from antioxidant materials by
preliminarily contacting the antioxidant materials with acids. For
example, there may be exemplified a method wherein the acids and
the antioxidant materials are mixed and stirred together. In such a
case, the mixing and stirring time may be appropriately selected
depending upon the amounts of the aluminum and silicon elements
contained in the antioxidant materials, for example, usually not
less than 10 hours, preferably 20 to 50 hours.
[0035] The acids used for the treatment is not particularly
restricted as long as the aluminum and silicon elements can be
reacted therewith. Specific examples of the acids may include
hydrochloric acid, sulfuric acid and phosphoric acid. The acid may
be used in an excess amount higher than the calculated amount based
on amounts of the aluminum and silicon elements contained in the
antioxidant materials.
[0036] The amount of the antioxidant material contained in the
paint is usually in the range of 10 to 90% by weight, preferably 15
to 45% by weight based on the weight of the solid content of the
paint. When the content of the antioxidant material is less than
10% by weight, the obtained coating film may tend to be
deteriorated in stability, thereby causing cissing and, therefore,
promoting the oxidation of the electrode. When the amount of the
antioxidant material is more than 90% by weight, the obtained
coating film may tend to be deteriorated in anchoring property.
Especially, when exposed to a temperature of 400 to 800.degree. C.,
the electrode undergoes oxidation due to deteriorated function of
the coating film.
[0037] [Binder]
[0038] The binder used in the present invention is not particularly
restricted as long as the material ensures a good continuity of the
obtained coating film. Examples of the binders may include polymer
emulsions and inorganic colloids. These binders may be used alone
or in the form of a mixture of any two or more thereof.
[0039] The polymer emulsion acts as a binder capable of enhancing a
continuity of the obtained coating film at a temperature between
room temperature and 400.degree. C., and improving a sliding
property thereof. As such polymer emulsions, there may be
exemplified rubber latexes, resin emulsions or the like. Specific
examples of the polymer emulsions may include emulsions of polymers
produced by emulsion polymerization, or emulsions produced by
re-emulsifying these polymers.
[0040] As the rubber latexes, there may be exemplified natural
rubber latexes and synthetic rubber latexes. Examples of the
synthetic rubber latexes may include butadiene polymers,
styrene-butadiene copolymers, actylonitrile-butadiene copolymers,
methyl methacrylate-butadiene copolymers, acrylate-based latexes or
the like. Examples of the resin emulsions may include emulsions of
polystyrene, styrene-acrylonitrile copolymers, polyvinyl chloride,
ethylene-vinyl acetate copolymers, polymethyl methacrylate,
polyethylene or the like. These synthetic rubber latexes and resin
emulsions may be respectively used alone or in the form of a
mixture of any two or more thereof. Among these polymer emulsions,
styrene-butadiene copolymer latex is preferred, and
carboxyl-containing styrene-butadiene copolymer latex is more
preferred.
[0041] The inorganic colloid also functions as a binder for
strongly anchoring the coating film onto the electrode at a
temperature of about 400 to about 600.degree. C. Examples of such
inorganic colloids may include colloidal silica, colloidal alumina,
colloidal zirconia or the like. Also, inorganic colloid precursors
such as tetraethyl orthosilicate which are capable of forming
inorganic colloid by adding an acid such as HCl thereto, may be
used together with the acid. Among these inorganic colloids,
colloidal silica is preferred. The silica particles used in the
inorganic colloid preferably have an average particle size of not
more than 100 nm. When the average particle size of the silica
particles is more than 100 nm, the inorganic colloid may be
deteriorated in functionality as a binder.
[0042] In general, the colloidal silica is synthesized by desalting
water glass and, therefore, contains residual alkali components
such as sodium and potassium in an amount of 1 to 10% by weight in
the aqueous solution. For this reason, it is considered that when
such a colloidal silica is used, the alkali components derived
therefrom are reacted with the aluminum or silicon elements present
in the antioxidant material to generate a hydrogen gas. As a
result, it is suggested that the paint is considerably deteriorated
in storage stability, and the coating film obtained therefrom
suffers from pinholes due to the hydrogen gas generated upon drying
of the coating film, resulting in burning of the electrode from the
pinholes. Thus, in order to use such a colloidal silica in the
present invention, it is preferred that the colloidal silica is
further subjected to desalting treatment so as to control the
concentration of the alkali components such as sodium and potassium
to not more than 1% by weight, or water contained in the colloidal
silica is replaced with an organic solvent such as methanol and
ethylene glycol. The use of the thus pre-treated colloidal silica
can inhibit the generation of hydrogen gas, enhance the storage
stability of the paint, and prevent the formation of pinholes in
the coating film.
[0043] The amount of the alkali metal and/or alkali earth metal
contained in the inorganic colloid is preferably not more than 1%
by weight, more preferably not more than 0.5% by weight.
[0044] The amount of the binder used is usually 0.05 to 40% by
weight, preferably 1 to 25% by weight (calculated as solid content,
i.e., residual non-volatile components produced when one gram of
the binder is heated in air at 150.degree. C. for one hour) based
on the solid content of the paint.
[0045] The content of the polymer emulsion is preferably 0.05 to
10% by weight (calculated as solid content of the emulsion, i.e.,
residual non-volatile components produced when one gram of the
emulsion is heated in air at 150.degree. C. for one hour) based on
the weight of the paint. When the content of the polymer emulsion
is less than 0.05% by weight, the obtained paint may tend to be
deteriorated in sliding resistance. When the content of the polymer
emulsion is more than 10% by weight, the paint may tend to be
deteriorated in stability with the passage of time.
[0046] The content of the inorganic colloid is preferably 1 to 30%
by weight, more preferably 2 to 15% by weight (calculated as solid
content of the inorganic colloid, i.e., residual non-volatile
components produced when one gram of the inorganic colloid is
heated in air at 150.degree. C. for one hour) based on the weight
of the paint. The content of the inorganic colloid is preferably as
small as possible from the standpoint of a good conductivity.
However, when the content of the inorganic colloid is less than 2%
by weight, the paint exhibits substantially no adhesion force, so
that the coating film obtained therefrom tends to be separated from
the electrode. On the other hand, when the content of the inorganic
colloid is more than 30% by weight, the paint exhibits a good
adhesion force, but is deteriorated in conductivity, resulting in
generation of sparks when applied on the electrode.
[0047] In the case where the combination of the polymer emulsion
and the inorganic colloid is used as the binder, the content
thereof lies in the above-specified range.
[0048] [Other Components]
[0049] The paint of the present invention may further contain a
transition metal in addition to the above-described components. The
transition metal has a function for enhancing a wettability of the
glass-like coating film formed of the antioxidant material,
relative to the electrode. More specifically, the transition metal
shows an effect of increasing a wettability of the glass-like
coating film relative to the surface of the graphite electrode upon
vitrification of silica under a temperature of not less than
1,000.degree. C. That is, the transition metal maintains a
continuity of the glass-like coating film by uniformly wetting the
surface of the graphite electrode and preventing the coating film
from being separated into ball-like pieces, i.e., spheroidized.
[0050] As the transition metals, there may be-used elements
(metals) such as chromium, tungsten, titanium, cobalt or the like.
From the standpoints of safety and inexpensiveness, the use of
chromium, titanium and tungsten elements (metals) is preferred.
[0051] The amount of the transition metal blended in the paint is
not less than 0.1% by weight based on the solid content of the
paint, in order to exhibit an excellent effect thereof. The amount
of the transition metal blended is preferably in the range of 0.1
to 70% by weight, more preferably 2 to 40% by weight, based on the
weight of the solid content of the paint. When the amount of the
transition metal blended is less than 0.1% by weight, the obtained
vitrified coating film may tend to be deteriorated in adhesion to
the graphite electrode, resulting in occurrence of cissing and,
therefore, poor oxidation-resistant property. When the amount of
the transition metal blended is more than 70% by weight, it may be
difficult to maintain a continuity of the coating film obtained by
the vitrification of aggregates or the like.
[0052] Also, the conductive antioxidant paint of the present
invention may further contain antiseptic agents as well as various
other additives such as defoaming agents, leveling agents,
antiprecipitants or the like in order to enhance a keeping property
thereof.
[0053] Next, the process for producing the conductive antioxidant
paint of the present invention will be described below.
[0054] The conductive antioxidant paint of the present invention
may be produced by blending the above-described components together
by the following method. That is, the conductive antioxidant paint
of the present invention is produced by mixing the respective
components with each other in water or an organic solvent, and, if
required, subjecting the obtained mixture to dispersing treatment.
The-amount of water or the organic solvent blended may be
appropriately adjusted before coating depending on coating methods
used. For example, the amount of water or the organic solvent
blended is preferably 20 to 200 parts by weight, more preferably 30
to 80 parts by weight based on 100 parts by weight of the solid
content of the conductive antioxidant paint.
[0055] The organic solvents usable in the present invention are not
particularly restricted as long as the respective components of the
paint can be dispersed therein. Specific examples of the organic
solvents may include alcohol-based solvents such as methanol,
isopropanol, isobutanol, isopentanol, ethylene glycol, ethylene
glycol monopropyl ether, ethylene glycol monomethyl ether, ethylene
glycol monobutyl ether and ethylene glycol monoethyl ether;
hydrocarbon-based solvents such as n-hexane, heptane, xylene,
toluene, cyclohexane, naphtha and styrene; ketone-based solvents
such as acetone, methyl isobutyl ketone, methyl ethyl ketone,
isophorone and acetophenone; amide-based solvents such as
dimethylacetamide and methyl pyrrolidone; and ester-based solvents
such as methyl acetate, ethyl acetate, isobutyl acetate, octyl
acetate, acetic acid ethylene glycol monomethyl ether and acetic
acid diethylene glycol monomethyl ether.
[0056] The dispersing medium used may be appropriately selected
depending on the aims and environments upon use. The conductive
antioxidant paint of the present invention is applied onto the
electrode used under a high temperature condition. Therefore, when
the coating operation is conducted near the position where the
electrode is practically used, the use of less flammable organic
solvents is preferred from the standpoint of inhibiting fire
accidents. In this case, the content of solvents other than water
is preferably controlled to as low a level as possible. For
example, the content of solvents other than water. i.e., volatile
solvents, is preferably not more than 10% by weight, more
preferably not more than 5% by weight.
[0057] Alternatively, volatile solvents may be used to promote
drying of the coating film. In such a case, the volatile solvents
other than water may be contained in an amount of not less than 5%
by weight, if possible, not less than 10% by weight.
[0058] The dispersing method is not particularly restricted as long
as the respective components can be dispersed to a sufficient
extent. For example, the dispersion treatment of a mixture composed
of the above respective components may be conducted using
dissolver, homomixer, ball mill, roll mill, attritor, Dyno-mill,
sand mills such as pico mill, basket mill, easy mill and LMZ-SC
mill, ultrasonic dispersing apparatus, homogenizers such as
altimizer, nanomizer and micro fluidizer, or jet mill.
[0059] Next, properties of the conductive antioxidant paint will be
described below. The conductive antioxidant paint of the present
invention shows any of the following properties.
[0060] [pH Value of Paint]
[0061] The conductive antioxidant paint of the present invention
has a pH value of not more than 9.0. Here, the pH value of the
paint means a pH value measured at ordinary temperature under such
a condition in which the respective components are sufficiently
stirred so as not to precipitate. That is, in the present
invention, the amount of the water-soluble alkali components
contained in the paint is defined by the pH value. When the pH
value of the paint is not more than 9.0, the amount of the
water-soluble alkali components contained in the paint can be
limited to an appropriate range, thereby inhibiting the generation
of hydrogen gas due to the reaction with impurities contained in
the metal compound. As a result, the conductive antioxidant paint
of the present invention shows an excellent storage stability, can
prevent the formation of pinholes when formed into a coating film,
and can exhibit an excellent oxidation-resistant property even when
exposed to as high a temperature as not less than 1,000.degree. C.
In order to further inhibit the generation of hydrogen gas, it is
preferred that the pH value of the paint is not more than 8.5
(lower limit thereof is usually 3).
[0062] As a method of controlling the pH value of the paint to not
more than 9.0, there may be used a method of appropriately
selecting materials used and varying the mixing ratios
therebetween, a method of converting the alkali components into
salts thereof by adding acid substances thereto, a method of
removing the alkali components by ion-exchange treatment, or the
like.
[0063] In particular, in the case of components containing alkali
metals and/or alkali earth metals, such as carbon black, inorganic
colloid, etc., there may be selectively used those having a less
content of these alkali components.
[0064] [Content of Alkali Metals and/or Alkali Earth Metals]
[0065] As to the conductive antioxidant paint of the present
invention, the content of alkali metals and/or alkali earth metals
is not more than 20% by weight based on the weight of the
antioxidant material. By limiting the content of these alkali
components based on the weight of the antioxidant material to the
above range, the glass-like coating film produced from the
antioxidant material at a high temperature is prevented from being
deteriorated in viscosity, thereby maintaining a continuity of the
glass-like coating film. As a result, the coating film produced
from the paint of the present invention can exhibit an excellent
oxidation-resistant property even at a temperature as high as not
less than 1,000.degree. C.
[0066] The content of the alkali metals and/or alkali earth metals
as defined herein is concerned with not individual alkali contents
of the respective components, but a total amount of alkali
components contained in the paint based on the weight of the
antioxidant material. This is because the glass-like coating film
is substantially composed of the antioxidant material solely which
is a residual component only present after exposed to a temperature
of not less than 1,000.degree. C., and as a result, the viscosity
of the glass-like coating film is varied, i.e., influenced by the
amount of alkali components contained in the glass-like coating
film. In order to allow the obtained coating film to exhibit an
excellent oxidation-resistant property, the content of the alkali
metals and/or alkali earth metals contained in the antioxidant
material is preferably not more than 15% by weight, more preferably
not more than 10% by weight based on the weight of the antioxidant
material.
[0067] Accordingly, in the case of components containing alkali
metals and/or alkali earth metals, such as carbon black, inorganic
colloid, etc., there may be selectively used those having a less
content of these alkali components. The amount of the alkali metals
and/or alkali earth metals contained in these components is usually
not more than 1% by weight, preferably not more than 0.5% by
weight.
[0068] In order to control the amount of the alkali metals and/or
alkali earth metals contained in the antioxidant material to not
more than 20% by weight based on the weight of the antioxidant
material, the kind and mixing ratio of the antioxidant material may
be appropriately selected.
[0069] [Content of Aluminum and Silicon]
[0070] As to the conductive antioxidant paint of the present
invention, the content of aluminum and silicon elements contained
in the paint is not more than 1% by weight based on the weight of
the solid content of the paint.
[0071] The amounts of aluminum and silicon elements contained in
the paint can be readily calculated from aluminum and silicon
contents of the respective components blended, if known. Even
though the aluminum and silicon contents of the respective
components are not known, the amounts of aluminum and silicon
elements contained in the paint can be obtained by the following
method.
[0072] That is, 5 g of the paint is heated in air at 150.degree. C.
for 3 hours to measure an amount of combustion residues as the
solid content thereof. In addition, a total amount of aluminum and
silicon elements contained in the solid content of the paint is
measured by X-ray diffraction method to obtain a weight percentage
thereof based on the solid content of the paint.
[0073] By controlling the total amount of aluminum and silicon
elements to not more than 1% by weight based on the solid content
of the paint, it is possible to limit the amount of hydrogen gas
generated from the paint to substantially ignorable level, safely
store and transport the paint, and prevent the formation of
pinholes when formed into a coating film. The total amount of
aluminum and silicon elements contained in the solid content of the
paint is preferably not more than 0.5% by weight, more preferably
not more than 0.1% by weight based on the solid content of the
paint, thereby further inhibiting the generation of hydrogen
gas.
[0074] In order to control the total amount of aluminum and silicon
elements to not more than 1% by weight based on the solid content
of the paint, there may be used a method of preparing a paint by
mixing the above respective components together, and then removing
aluminum and silicon elements from the obtained paint. Preferably,
the total amount of aluminum and silicon elements can be reduced by
the method of previously removing these elements from the
respective components before blending.
[0075] [Formation of Coating Film]
[0076] The conductive antioxidant paint of the present invention is
applied onto the side surface and chuck portion of an electrode
used in arc furnace such that the thickness of the obtained coating
film is usually about 100 to about 500 .mu.m (after drying).
[0077] The conductive antioxidant paint of the present invention
may be applied by an optimum method selected from general coating
methods such as an immersion-coating method, a brush-coating
method, a spray-coating method, an electrostatic coating method or
the like. In this case, the viscosity of the conductive antioxidant
paint may be suitably controlled according to the coating method
used. Also, the coating operation may be repeated a plurality of
times to form an overlapped coating film. Further, different kinds
of paints may be applied two or more times.
[0078] The conductive antioxidant paint of the present invention
shows an excellent storage stability, prevents the formation of
pinholes when formed into a coating film, and exhibits an excellent
oxidation-resistant effect even when exposed to as high a
temperature as not less than 1,000.degree. C., especially not less
than 1,200.degree. C.
[0079] Also, the conductive antioxidant paint of the present
invention can be applied onto s chuck portion of the electrode, and
can exhibit an excellent sliding resistance as well as an excellent
oxidation-resistant effect even when exposed to as high a
temperature as not less than 1,000.degree. C.
[0080] Further, the graphite electrode of the present invention is
prevented from being consumed by oxidation.
EXAMPLES
[0081] The present invention will be described in more detail by
reference to the following examples. However, these examples are
only illustrative and not intended to limit the present invention
thereto.
Examples 1 to 5 and Comparative Examples 1 to 4:
[0082] First, ten pairs of paints (a) and (b) were prepared by
dispersing the respective components shown in (a) and (b) of Tables
1 and 2, for 60 minutes using a sand grinder. Carbon black,
colloidal silica and dispersant used in each composition are shown
in Table 3.
[0083] In Comparative Example 1, an alkali component (MgO) was
positively added to the composition; in Comparative Example 2, no
polymer emulsion (latex emulsion) was added; in Comparative Example
3, no inorganic colloid (colloidal silica) was added; and in
Comparative Example 4, no transition metal (chromium powder) was
added.
[0084] Then, the paint (a) was applied in an amount of 100 to 250
g/m.sup.2 (after drying) onto a whole surface of a test piece
sliced from a graphite electrode by a brush-coating method, and
dried for one hour. Successively, the paint (b) was applied in an
amount of 250 to 500 g/m.sup.2 onto the test piece. The thus
obtained coated test piece was allowed to stand over night for
drying, and then the surface resistivity thereof was measured by a
tester. Thereafter, the test piece was allowed to stand in an
ashing furnace (manufactured by Hayashi Denko Co., Ltd.) at
400.degree. C. for 30 minutes, and the change in surface
resistivity was measured. Then, the test piece was baked at
1,000.degree. C. for 30 minutes, cooled in air to room temperature,
and then observed to examine the condition of the coating film. The
results are shown in Table 4.
[0085] In Examples 1 to 5, although some of the paints after baked
at 1,000.degree. C. were colored slightly green by the oxidation of
chromium, it was confirmed that the paints were free from
occurrence of cissing, were capable-of forming a uniform coating
film, and exhibited a sufficient oxidation-resistant effect.
[0086] In Comparative Example 1, the paint exhibited a very good
condition upon measurement of the surface resistivity at
400.degree. C. However, when baked at 1,000.degree. C., a
non-uniform coating film was formed, and there were observed many
burnt-in portions.
[0087] In Comparative Example 2, upon measurement of the surface
resistivity at 400.degree. C., the obtained coating film was
brittle, and readily fallen off from the electrode. When baked at
1,000.degree. C., a non-uniform coating film was formed, and there
were observed many burnt-in portions.
[0088] In Comparative Example 3, upon measurement of the surface
resistivity at 400.degree. C., the obtained coating film was
brittle, and readily fallen off from the electrode. Further, many
fractures were observed on the coating film. When baked at
1,000.degree. C., it was confirmed that the obtained coating film
was discontinuous, so that clearances were formed between the
coating film and the electrode, and the electrode was severely
damaged. Therefore, the paint failed to show an oxidation-resistant
effect when exposed to a temperature as high as not less than
1,000.degree. C.
[0089] In Comparative Example 4, upon measurement of the surface
resistivity at 400.degree. C., the obtained coating film was kept
in a very good condition. However, when baked at 1,000.degree. C.,
the coating film was discontinuous and suffered from cissing, and
the electrode was damaged.
[0090] As apparent from the above, the graphite electrodes coated
with the paints of the present invention still maintained a good
conductivity at 400.degree. C., and exhibited a good
oxidation-resistant effect even when exposed to 1,000.degree.
C.
Examples 6 to 10 and Comparative Examples 5 to 8:
[0091] First, ten pairs of paints (a) and (b) were prepared by
dispersing the respective components shown in (a) and (b) of Tables
5 and 6, for 60 minutes using a sand grinder. Carbon black,
colloidal silica and dispersant used in each composition are shown
in Table 7.
[0092] In Comparative Example 5, colloidal silica 5 having a high
sodium content was used; in Comparative Example 6, no polymer
emulsion (latex emulsion) was added; in Comparative Example 7, no
inorganic colloid (colloidal silica) was added; and in Comparative
Example 8, no transition metal (chromium powder) was added.
[0093] Then, the paint (a) was applied in an amount of 100 to 250
g/m.sup.2 (after drying) onto a whole surface of a test piece
sliced from a graphite electrode by a brush-coating method, and
then dried for one hour. Successively, the paint (b) was applied in
an amount of 250 to 500 g/m.sup.2 onto the test piece. The thus
obtained coated test piece was allowed to stand over night for
drying, and then the surface resistivity thereof was measured by a
tester. Thereafter, the test piece was allowed to stand in an
ashing furnace (manufactured by Hayashi Denko Co., Ltd.) at
400.degree. C. for 30 minutes, and the change in surface
resistivity was measured. Then, the test piece was baked at
1,000.degree. C. for 30 minutes, cooled in air to room temperature,
and then observed to examine the condition of the coating film. The
results are shown in Table 8.
[0094] In Examples 6 to 10, although some of the paints after being
baked at 1,000.degree. C. were colored slightly green by the
oxidation of chromium, it was confirmed that each paint was able to
produce a uniform glass-like coating film without cissing, and
exhibited a sufficient oxidation-resistant effect.
[0095] In Comparative Example 5, the paint generated a large amount
of hydrogen gas during its storage. After being baked at
1,000.degree. C. for 30 minutes, it was confirmed that the coating
film suffered from pinholes due to the removal of hydrogen gas, and
the electrode was burnt-in from the pinholes.
[0096] In Comparative Example 6, upon measurement of the surface
resistivity at 400.degree. C., the obtained coating film was
brittle, and fallen off from the electrode. When being based at
1,000.degree. C., it was confirmed that the obtained coating film
was non-uniform, and there were observed many burnt-in portions on
the electrode.
[0097] In Comparative Example 7, upon measurement of the surface
resistivity at 400.degree. C., the obtained coating film was
brittle, and readily fallen off from the electrode. Further, many
fractures were observed on the coating film. When being baked at
1,000.degree. C., it was confirmed that the obtained coating film
was discontinuous, so that clearances were formed between the
coating film and the electrode, and the electrode was severely
damaged. Therefore, the paint failed to show an oxidation-resistant
effect when exposed to a temperature as high as not less than
1,000.degree. C.
[0098] In Comparative Example 8, upon measurement of the surface
resistivity at 400.degree. C., the obtained coating film was kept
in a very good condition. However, when being baked at
1,000.degree. C., the coating film was discontinuous and suffered
from cissing, and the electrode was damaged.
Example 11 and Comparative Example 9:
[0099] First, two pairs of paints (a) and (b) were prepared by
dispersing the respective components shown in (a) and (b) of Table
9, for 60 minutes using a sand grinder. Carbon black, colloidal
silica, dispersant and SiC used in each composition were "#4000B"
produced by Mitsubishi Kagaku Co., Ltd., "FINE CATALLOID SBB-120"
(solid content: 20% by weight) produced by Shokubai Kasei Kogyo
Co., Ltd., "DEMOLE N" produced by Kao Co., Ltd., and "DIASIC
CF-12OF" produced by Yakushima Denko Co., Ltd., respectively. The
SiC had a purity of 95%, and contained as impurities, metal
aluminum and silicon element in a total amount of 5% by weight.
[0100] The solid contents of the paints (a) and (b) were 67.1% by
weight and 62.2% by weight, respectively. The contents of the
aluminum and silicon elements were 1.48% by weight for the paint
(a) and 1.33% by weight for the paint (b) based on the weight of
the solid content of each paint.
[0101] In Example 11, treated SiC was used; and in Comparative
Example 9, untreated SiC was used. The SiC was treated as follows.
That is, equivalent amounts of SiC and 0.1N HCl were charged into a
beaker, and the mixture was stirred for 24 hours. Then, the
resultant mixture was stirred by "HOT PLATE & STIRRER"
(tradename) manufactured by Corning Corp., to evaporate water
therefrom.
[0102] The paint containing the thus treated SiC was measured by
X-ray diffraction method to determine the contents of aluminum and
silicon contained in the solid content of the paint. However, the
contents of aluminum and silicon were less than the detection lower
limit and, therefore, undetectable.
[0103] The generation of hydrogen gas from the obtained paint was
continuously observed from the preparation stage thereof. The
results are shown in Table 10.
[0104] Then, the paint (a) was applied in an amount of 100 to 250
g/m.sup.2 (after drying) onto a whole surface of a test piece
sliced from a graphite electrode by a brush-coating method, and
then dried for one hour. Successively, the paint (b) was applied in
an amount of 250 to 500 g/m.sup.2 onto the test piece. The thus
obtained coated test piece was allowed to stand over night for
drying, and then the surface resistivity thereof was measured by a
tester. Thereafter, the test piece was allowed to stand in an
ashing furnace (manufactured by Hayashi Denko Co., Ltd.) at
400.degree. C. for 30 minutes, and the change in surface
resistivity was measured. Then, the test piece was baked at
1,000.degree. C. for 30 minutes, cooled in air to room temperature,
and then observed to examine the condition of the coating film. The
results are shown in Table 11.
[0105] In both of Example 11 and Comparative Example 9, although
some of the paints after being baked at 1,000.degree. C. were
colored slightly green by the oxidation of chromium, it was
confirmed that each paint was able to produce a uniform glass-like
coating film without cissing., and exhibited a sufficient
oxidation-resistant effect.
[0106] However, in Comparative Example 9, the paint suffered from
the generation of hydrogen gas after the elapse of about one month.
On the contrary, the paint obtained in Example 11 was free from the
generation of hydrogen gas even after the elapse of one month.
1 TABLE 1 Example 1 Example 2 Example 3 a b a b a b Carbon black
9.1 10.1 9.0 10.1 9.5 10.1 Graphite powder 3.3 1.3 3.3 15.0 3.3
10.0 SiC powder 19.8 16.6 20.0 15.0 22.0 12.0 B4C powder 2.0 12.5
3.0 15.0 1.5 20.0 Latex emulsion 1.1 1.2 1.1 1.0 1.1 1.0 Colloidal
silica 1 18.0 19.9 -- -- -- -- Colloidal silica 2 -- -- 26.2 29.3
-- -- Colloidal silica 3 -- -- -- -- 26.2 29.4 Colloidal silica 4
-- -- -- -- -- -- Tetraethyl orthosilicate -- -- -- -- -- -- HCl
(0.1N) -- -- -- -- -- -- Silica gel -- -- -- -- -- -- Zirconia sol
-- -- -- -- -- -- Cr powder 29.0 2.4 20.0 2.5 10 1.0 MgO -- -- --
-- -- -- Dispersant 1.0 1.1 1.0 1.1 1.0 1.1 Ion-exchanged water
36.7 43.1 28.3 33.7 26.3 33.6 Alkali/antioxidant (wt. %) 0.56 0.47
0.66 0.56 0.65 0.53 Note: The values in Table represent "part by
weight" unless otherwise specified. Example 4 Example 5 a b a b
Carbon black 9.1 10.1 9.1 10.1 Graphite powder 3.3 1.2 3.3 13.0 SiC
powder 19.8 15.0 15.0 18.0 B4C powder 1.9 13.0 1.8 14.0 Latex
emulsion 1.1 1.0 1.1 1.0 Colloidal silica 1 -- -- -- -- Colloidal
silica 2 -- -- -- -- Colloidal silica 3 -- -- -- -- Colloidal
silica 4 29.2 32.6 -- -- Tetraethyl orthosilicate -- -- 5.5 6.0 HCl
(0.1N) -- -- 10.7 10.7 Silica gel -- -- -- -- Zirconia sol -- -- --
-- Cr powder 29.0 2.4 0.1 0.05 MgO -- -- -- -- Dispersant 1.0 1.1
1.0 1.1 Ion-exchanged water 27.2 30.5 81.0 87.0 Alkali/antioxidant
(wt. %) 0.73 0.59 0.59 0.34
[0107]
2 TABLE 2 Comparative Comparative Example 1 Example 2 a b a b
Carbon black 9.1 10.1 9.1 10.1 Graphite powder 3.3 1.3 3.3 1.3 SiC
powder 19.8 16.6 19.8 16.6 B4C powder 2.0 12.5 2.0 12.5 Latex
emulsion 1.1 1.2 -- -- Colloidal silica 1 18.0 19.9 18.0 19.9
Colloidal silica 2 -- -- -- -- Colloidal silica 3 -- -- -- --
Colloidal silica 4 -- -- -- -- Tetraethyl orthosilicate -- -- -- --
HCl (0.1N) -- -- -- -- Silica gel -- -- -- -- Zirconia sol -- -- --
-- Cr powder 29.0 2.4 29.0 2.4 MgO 9.1 10.1 -- -- Dispersant 1.0
1.1 1.0 1.1 Ion-exchanged water 36.7 43.1 36.7 43.1
Alkali/antioxidant (wt. %) 25.6 20.8 0.56 0.47 Note: The values in
Table represent "part by weight" unless otherwise specified.
Comparative Comparative Example 3 Example 4 a b a b Carbon black
9.1 10.1 9.1 10.1 Graphite powder 3.3 1.3 3.3 1.3 SiC powder 19.8
16.6 19.8 16.6 B4C powder 2.0 12.5 2.0 12.5 Latex emulsion 1.1 1.2
1.1 1.2 Colloidal silica 1 -- -- 18.0 19.9 Colloidal silica 2 -- --
-- -- Colloidal silica 3 -- -- -- -- Colloidal silica 4 -- -- -- --
Tetraethyl orthosilicate -- -- -- -- HCl (0.1N) -- -- -- -- Silica
gel 5.5 6.0 -- -- Zirconia sol -- -- -- -- Cr powder 29.0 2.4 -- --
MgO -- -- -- -- Dispersant 1.0 1.1 1.0 1.1 Ion-exchanged water 36.7
43.1 36.7 43.1 Alkali/antioxidant (wt. %) 0.38 0.38 0.56 0.47
[0108]
3 TABLE 3 Content of alkali metal or Average alkali particle earth
size metal Product and Solvent (nm) (wt. %) maker Carbon black --
-- .gtoreq.0.1 "#4000B" produced by Mitsubishi Chemical Corp.
Colloidal Methanol 10 to 20 0.13 "METHANOL silica 1 SILICA SOL"
produced by Nissan Kagaku Co., Ltd. Colloidal water 10 to 20 0.2
"SNOWTEX O" silica 2 produced by Nissan Kagaku Co., Ltd. Colloidal
water about 50 0.2 "SNOWTEX OL" silica 3 produced by Nissan Kagaku
Co., Ltd. Colloidal water about 100 0.15 to "SPHERICA- silica 4 0.2
SLURRY 120" produced by Shokubai Kasei Kogyo Co., Ltd. Dispersant
(Na -- -- 10 "DEMOLE" salt of produced by Kao formalin Co., Ltd.
condensate of .beta.-naphthalene sulfonic acid
[0109]
4 TABLE 4 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Surface resistivity
(.OMEGA.) 3 4 4 2 3 after coating Surface resistivity (.OMEGA.) 2 2
2 2 3 after treated at 400.degree. C. for 30 min. Condition after
baked at .largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. 1,000.degree. C. for 30 min. Note: The evaluation
results of the condition after baked at 1,000.degree. C. for 30
min. are classified into the following ranks: .largecircle.:
Covered by a continuous coating film without any change; and x:
Damaged by cissing or the like Com. Com. Com. Com. Ex. 1 Ex. 2 Ex.
3 Ex. 4 Surface resistivity (.OMEGA.) 13 3 8 2 after coating
Surface resistivity (.OMEGA.) 12 2 5 2 after treated at 400.degree.
C. for 30 min. Condition after baked at x x x x 1,000.degree. C.
for 30 min.
[0110]
5 TABLE 5 Example 6 Example 7 Example 8 a b a b a b Carbon black
9.1 10.1 9.0 10.1 9.5 10.1 Graphite powder 3.3 1.3 3.3 15.0 3.3
10.0 SiC powder 19.8 16.6 20.0 15.0 22.0 12.0 B4C powder 2.0 12.5
3.0 15.0 1.5 20.0 Latex emulsion 1.1 1.2 1.1 1.0 1.1 1.0 Colloidal
silica 1 18.0 19.9 -- -- -- -- Colloidal silica 2 -- -- 26.2 29.3
-- -- Colloidal silica 3 -- -- -- -- 26.2 29.4 Colloidal silica 4
-- -- -- -- -- -- Colloidal silica 5 -- -- -- -- -- -- Tetraethyl
orthosilicate -- -- -- -- -- -- HCl (0.1N) -- -- -- -- -- -- Silica
gel -- -- -- -- -- -- Zirconia sol -- -- -- -- -- -- Cr powder 29.0
2.4 20.0 2.5 10 1.0 Dispersant 1.0 1.1 1.0 1.1 1.0 1.1
Ion-exchanged water 36.7 43.1 28.3 33.7 26.3 33.6
Alkali/antioxidant (wt. %) 0.56 0.47 0.66 0.56 0.65 0.53 pH value
7.2 7.0 7.3 7.2 7.5 7.3 Note: The values in Table represent "part
by weight" unless otherwise specified. Example 9 Example 10 a b a b
Carbon black 9.1 10.1 9.1 10.1 Graphite powder 3.3 1.2 3.3 13.0 SiC
powder 19.8 15.0 15.0 18.0 B4C powder 1.9 13.0 1.8 14.0 Latex
emulsion 1.1 1.0 1.1 1.0 Colloidal silica 1 -- -- -- -- Colloidal
silica 2 -- -- -- -- Colloidal silica 3 -- -- -- -- Colloidal
silica 4 29.2 32.6 -- -- Colloidal silica 5 -- -- -- -- Tetraethyl
orthosilicate -- -- 5.5 6.0 HCl (0.1N) -- -- -- -- Silica gel -- --
-- -- Zirconia sol -- -- -- -- Cr powder 29.0 2.4 0.1 0.05
Dispersant 1.0 1.1 1.0 1.1 Ion-exchanged water 27.2 30.5 81.0 87.0
Alkali/antioxidant (wt. %) 0.73 0.59 0.59 0.34 pH value 7.5 6.4 6.0
4.8
[0111]
6 TABLE 6 Comparative Comparative Example 5 Example 6 a b a b
Carbon black 9.1 10.1 9.1 10.1 Graphite powder 3.3 1.3 3.3 1.3 SiC
powder 19.8 16.6 19.8 16.6 B4C powder 2.0 12.5 2.0 12.5 Latex
emulsion 1.1 1.2 -- -- Colloidal silica 1 18.0 19.9 18.0 19.9
Colloidal silica 2 -- -- -- -- Colloidal silica 3 -- -- -- --
Colloidal silica 4 -- -- -- -- Colloidal silica 5 25.9 29.0 -- --
Tetraethyl orthosilicate -- -- -- -- HCl (0.1N) -- -- -- -- Silica
gel -- -- -- -- Zirconia sol -- -- -- -- Cr powder 29.0 2.4 29.0
2.4 Dispersant 1.0 1.1 1.0 1.1 Ion-exchanged water 36.7 43.1 36.7
43.1 Alkali/antioxidant (wt. %) 1.65 1.37 0.56 0.47 pH value 9.8
9.7 7.0 6.8 Note: The values in Table represent "part by weight"
unless otherwise specified. Comparative Comparative Example 7
Example 8 a b a b Carbon black 9.1 10.1 9.1 10.1 Graphite powder
3.3 1.3 3.3 1.3 SiC powder 19.8 16.6 19.8 16.6 B4C powder 2.0 12.5
2.0 12.5 Latex emulsion 1.1 1.2 1.1 1.2 Colloidal silica 1 -- --
18.0 19.9 Colloidal silica 2 -- -- -- -- Colloidal silica 3 -- --
-- -- Colloidal silica 4 -- -- -- -- Colloidal silica 5 -- -- -- --
Tetraethyl orthosilicate -- -- -- -- HCl (0.1N) -- -- -- -- Silica
gel 5.5 6.0 -- -- Zirconia sol -- -- -- -- Cr powder 29.0 2.4 -- --
Dispersant 1.0 1.1 1.0 1.1 Ion-exchanged water 36.7 43.1 36.7 43.1
Alkali/antioxidant (wt. %) 0.38 0.38 0.56 0.47 pH value 7.2 7.1 7.2
7.1
[0112]
7 TABLE 7 Content of alkali metal or Average alkali particle earth
size metal Product and Solvent (nm) (wt. %) maker Carbon black --
-- .gtoreq.0.1 "#4000B" produced by Mitsubishi Chemical Corp.
Colloidal Methanol 10 to 20 0.13 "METHANOL silica 1 SILICA SOL"
produced by Nissan Kagaku Co., Ltd. Colloidal water 10 to 20 0.2
"SNOWTEX O" silica 2 produced by Nissan Kagaku Co., Ltd. Colloidal
water about 50 0.2 "SNOWTEX OL" silica 3 produced by Nissan Kagaku
Co., Ltd. Colloidal water about 100 0.15 to "SPHERICA- silica 4 0.2
SLURRY 120" produced by Shokubai Kasei Kogyo Co., Ltd. Colloidal
water .gtoreq.10 1 "CATALLOID 550" silica 5 produced by Shokubai
Kasei Kogyo Co., Ltd. Dispersant (Na -- -- 10 "DEMOLE" salt of
produced by Kao formalin Co., Ltd. condensate of .beta.-naphthalene
sulfonic acid
[0113]
8 TABLE 8 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Surface resistivity
(.OMEGA.) 3 4 4 2 3 after coating Surface resistivity (.OMEGA.) 2 2
2 2 3 after treated at 400.degree. C. for 30 min. Condition after
baked at .largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. 1,000.degree. C. for 30 min. Note: The evaluation
results of the condition after baked at 1,000.degree. C. for 30
min. are classified into the following ranks: .largecircle.:
Covered by a continuous coating film without any change; and x:
Damaged by cissing or the like Com. Com. Com. Com. Ex. 5 Ex. 6 Ex.
7 Ex. 8 Surface resistivity (.OMEGA.) 4 3 8 2 after coating Surface
resistivity (.OMEGA.) 2.5 2 5 2 after treated at 400.degree. C. for
30 min. Condition after baked at x x x x 1,000.degree. C. for 30
min.
[0114]
9 TABLE 9 Comparative Example 11 Example 9 a b a b Carbon black 9.1
10.1 9.1 10.1 Graphite powder 3.3 13.0 3.3 13.0 SiC powder
(treated) 19.8 16.6 -- -- SiC powder (untreated) -- -- 19.8 16.6
B4C powder 1.9 12.5 1.9 12.5 Latex emulsion 1.1 1.2 1.1 1.2
Colloidal silica 23.2 26.0 23.2 26.0 Cr powder 29.3 2.5 29.3 2.5
Dispersant 1.0 1.1 1.0 1.1 Ion-exchanged water 11.3 17.0 11.3 17.0
Note: The values in Table represent "part by weight" unless
otherwise specified.
[0115]
10 TABLE 10 After one day After one week After one month Example 11
.largecircle. .largecircle. .largecircle. Comparative .largecircle.
.largecircle. x Example 9 Note: .largecircle.: No hydrogen gas
generated; and x: Hydrogen gas generated.
[0116]
11 TABLE 11 Comparative Example 11 Example 9 Surface resistivity
(.OMEGA.) 2 3 after coating Surface resistivity (.OMEGA.) 2 3 after
treated at 400.degree. C. for 30 min. Condition after baked at
.largecircle. .largecircle. 1,000.degree. C. for 30 min. Note: The
evaluation results of the condition after baked at 1,000.degree. C.
for 30 min. are classified into the following ranks: .largecircle.:
Covered by a continuous coating film without any change; and x:
Damaged by cissing or the like
* * * * *