JP2001123123A - Electroconductive antioxidative coating material and graphite electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electroconductive antioxidative coating material having an excellent antioxidative effect at a high temperature of >=1,800 deg.C. SOLUTION: This electroconductive antioxidative coating material is characterized in that the coating material comprises an electroconductive material, an antioxidizing material, a polymer emulsion as a binder, an inorganic colloid and a transition metal in an aqueous medium and the content of the alkali metal and/or an alkaline earth metal is <=20 wt.% based on the amount of the antioxidant. The antioxidizing material is a carbide or a nitride of a simple substance selected from the group consisting of B, Si, Ge, Sb, Ti, Sn, Al and Zr or a simple substance of B or Si.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive antioxidant paint and a graphite electrode, and more particularly to a conductive antioxidant which can be suitably used as an antioxidant for a graphite electrode used in an electric furnace such as an electric steelmaking furnace. The present invention relates to an antioxidant paint and a graphite electrode formed by applying the paint.

[0002]

2. Description of the Related Art Conventionally, artificial graphite electrodes have been used in electric steel furnaces and other arc furnaces. This graphite electrode is used under very severe conditions, such as being affected by a large current, a high temperature, and scattering of a melt. In particular, an ultra-high temperature arc is generated at the tip of the electrode, and the
Since it is exposed to a high temperature of about 3,000 ° C., it is easily oxidized and consumed by an oxidizing gas entering from an opening in a furnace.

[0003] In a steelmaking furnace, the cost of the electrode accounts for a high proportion, so that the consumption of the electrode is a great economic loss. Oxidative depletion of the electrode occurs 50-70% by weight from the side,
There is little wear by the arc itself. Further, the electrode is tapered by oxidative wear toward the tip, so that oxidative wear in the longitudinal direction is accelerated. Therefore, if the oxidation from the side of the electrode is sufficiently prevented, the consumption of the electrode is reduced and the economic merit is great.

[0004] For example, Japanese Patent Application Laid-Open No. 7-268250 discloses a conductive antioxidant of a type that can be coated on an electrode chuck portion by applying conductivity to a coating medium, and is used as a fire-resistant antioxidant in an aqueous medium. aggregate,
Conductive antioxidants comprising a binder, carbon black and a polymer emulsion have been proposed. The refractory aggregate contains an oxide such as silica, alumina, titania, and zirconia, and the binder contains an inorganic colloid.

[0005] Actually, it is known that the temperature in an arc furnace rises to 1000 ° C or higher, and the above-mentioned conductive antioxidant (paint) has the following problems.
That is, the above-mentioned paint exhibits an antioxidant effect by melting a coating component by heat at about 800 ° C. to form a glassy coating film. If the temperature drops too much, the vitreous coating falls off and the continuity of the vitreous coating is interrupted. As a result, oxygen cannot be cut off, and burning of the electrode such as cissing occurs.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to further improve the above-mentioned conductive antioxidant, particularly to prevent oxidation at a high temperature of 1000 ° C. or higher. An object of the present invention is to provide a conductive antioxidant paint excellent in effect and a graphite electrode formed by applying the paint.

[0007]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that a decrease in the viscosity of a glassy coating film at a high temperature is caused by dissolution of an alkali component into the coating film. I got That is, an alkali metal compound such as an alkali metal such as sodium or potassium or an oxide thereof, and an alkaline earth metal compound such as an alkali earth metal such as calcium or magnesium or an oxide thereof are mixed with a glassy coating after burning of carbon. Dissolves in the membrane and reduces its viscosity. As a result, the glassy coating film falls off and the antioxidant effect is impaired.

[0008] Moreover, the above-mentioned alkali component easily reacts with impurities of the metal compound to generate hydrogen gas. Therefore, not only is the storage property remarkably inferior, but when hydrogen gas is generated during drying of the coating film, a pinhole is formed, and the electrode may burn from the pinhole.

The present invention has been completed based on the above findings, and a first gist of the present invention is to provide an aqueous medium containing a conductive material,
A conductive paint containing an antioxidant, a polymer emulsion as a binder, an inorganic colloid, and a transition metal, wherein the content of alkali metal and / or alkaline earth metal is 20% by weight of the antioxidant. % Or less, and a second aspect of the present invention resides in a graphite electrode characterized by being coated with the above-mentioned conductive antioxidant paint.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the conductive antioxidant paint of the present invention will be described. The conductive antioxidant paint of the present invention (hereinafter simply referred to as “paint”) is a conductive material, an oxidation-resistant material,
A polymer emulsion and an inorganic colloid as a binder,
It contains a transition metal.

[0011] Examples of the conductive material include carbon black and graphite. As the carbon black, those obtained by any production method such as a furnace method, an acetylene method, a thermal method, and a contact method can be used. In particular, under an atmosphere in which oxygen is substantially absent (for example, in an N ₂ stream,
Graphitized carbon black treated in a vacuum or in carbon powder) at a temperature of 2000 ° C. or higher, preferably 2500 to 3000 ° C. is suitably used. Further, as the graphitized carbon black, the thickness Lc (Å) of the crystallite is determined by the particle diameter (n).
Those having a value divided by m) in the range of 1.0 to 3.0 are preferably used.

As the graphite, any commercially available graphite such as scale-like graphite, earthy graphite, artificial graphite and expanded graphite can be used. Graphite having an ash content of 2% by weight or less, preferably 1% by weight or less, more preferably 0.5% by weight or less is suitably used.

When the electrode is consumed by the operation of the arc furnace, a new electrode is connected to the upper part, and an electrode holder (gripping machine) is used.
Is moved in the longitudinal direction of the electrode and re-gripped. At this time, the coating film comes into contact with the electrode holder, and the coating film may be damaged. In such a case, by incorporating graphite powder in the coating to prevent damage (peeling) of the coating upon contact, the sliding property of the coating is improved and the damage of the coating is reduced. .

As the oxidation resistant material, for example, B, Si, G
e, selected from the group consisting of Sb, Ti, Sn, Al and Zr
Of carbide or nitride of B or Si
Can be used. These are higher than 1000 ° C
It has the property of vitrifying under temperature and is called a vitreous forming substance.
You can also jump. That is, the above-mentioned oxidation resistant material is hot
It gradually changes to oxides and other components (inorganic colloids)
Etc.) to form a glassy coating film,
Protect from oxygen. B_FourC, SiC and Si are
Electrode oxidation prevention and hot stability aspects of glassy coatings.
Is preferred. When carbide is used as oxidation resistant material
Is the penetration of oxygen into the electrode by oxidation of the carbide
Is prevented, so a more excellent antioxidant effect is exhibited.
You. In particular, B _FourAcid resistant consisting of a combination of C and SiC
A chemical material is preferably used.

The polymer emulsion functions as a binder for forming a uniform continuous coating film at room temperature and improving the slidability. Examples of such a polymer emulsion include a rubber latex and a resin emulsion.
There are also emulsions of polymers obtained by emulsion polymerization and emulsions obtained by re-emulsification of polymers.

Examples of the rubber latex include natural rubber latex and synthetic rubber latex. Examples of the synthetic rubber latex include a butadiene polymer, a styrene-butadiene copolymer, an acrylonitrile-butadiene copolymer, a methyl methacrylate-butadiene copolymer, and an acrylate latex.

Examples of the above resin emulsion include emulsions of polystyrene, styrene-acrylonitrile copolymer, polyvinyl chloride, ethylene-vinyl acetate copolymer, polymethyl methacrylate, polyethylene and the like. In these polymer emulsions, a styrene-butadiene copolymer latex, particularly a styrene-butadiene copolymer latex containing a carboxyl group, is preferably used.

The inorganic colloid functions as a binder for adhering the coating film on the electrode at a temperature of about 400 ° C. to 600 ° C. Examples of such an inorganic colloid include colloidal silica, colloidal alumina, and colloidal zirconia. In addition, an inorganic colloid precursor such as tetraethyl orthosilicate, which forms an inorganic colloid by adding an acid such as HCl, can be used together with the acid. Among these, colloidal silica is preferably used. The size of the silica particles is preferably 100 nm or less in average particle size. If it is larger than this, the function as the binder described above will be inferior.

The transition metal has a function of improving the wettability of the glassy coating film formed from the oxidation-resistant material to the electrode. That is, when the transition metal is not present, the glassy coating repels on the graphite electrode in a ball-like manner, thereby hindering the continuity of the coating. The resulting vitreous coating is maintained. As the transition metal, a simple substance (metal) such as chromium, tungsten, titanium, and cobalt is used. From the viewpoint of safety and cost, chromium, titanium or tungsten is preferably used.

The paint of the present invention contains the above-mentioned components, and is characterized in that the content of alkali metal and / or alkaline earth metal is 20% by weight or less of the amount of the oxidation-resistant material. That is, in the present invention, by specifying the amount of the alkali component with respect to the oxidation-resistant material as described above,
Prevents a decrease in viscosity of a glassy coating film formed from an oxidation resistant material at a high temperature and maintains continuity of the glassy coating film. As a result, in the present invention, an excellent antioxidant effect is exhibited even at a high temperature of 1000 ° C. or higher.

In the present invention, the problem is not the individual alkali content of the components of the paint, but the amount of the total alkali component in the paint specified for the oxidation-resistant material. This is because the main component remaining at a high temperature of 1000 ° C. or more is only a glassy coating formed from an oxidation-resistant material, and in the present invention, the amount of the alkali component contained in the glassy coating is This is because the change in the viscosity of the glassy coating film that occurs depending on the problem is considered. The content of the alkali metal and / or the alkaline earth metal is preferably 15% by weight or less, more preferably 10% by weight or less of the amount of the antioxidant.

Therefore, in the present invention, in the case of a component accompanied by an alkali metal and / or an alkaline earth metal such as carbon black and inorganic colloid, a type having a small content of these components is selected and used. Each of the above components having an alkali metal and / or alkaline earth metal content of usually 1% by weight or less, preferably 0.5% by weight or less is used.

In particular, by setting the content of potassium or sodium in carbon black to 0.5% by weight or less, the ignition point of carbon black itself can be increased, and the temperature around 400 ° C. at which the electrode chuck is present can be obtained. The conductivity of the paint can be maintained up to this point.

An inorganic colloid, for example, colloidal silica, is usually synthesized by desalting from water glass, and 1 to 10% by weight of an alkali component such as sodium or potassium remains in an aqueous solution. Therefore, in the present invention, as the colloidal silica whose alkali concentration is adjusted to 1% by weight or less, colloidal silica in which water is replaced with an organic solvent such as methanol or ethylene glycol or desalted colloidal silica is used.

Therefore, the amount of each of the above components in the present invention varies depending on the type of the component used. That is, it is necessary to adjust the material so that the content of the alkali metal and / or the alkaline earth metal is 20% by weight or less of the amount of the oxidation resistant material. However, the proportion of each of the above components in the paint is generally as follows.

The amount of carbon black is usually 2 to 30% by weight, preferably 5 to 20% by weight. If the content of carbon black is less than 2% by weight, sufficient conductivity cannot be obtained, and if it exceeds 30% by weight, the viscosity of the paint becomes too high, or the carbon black in the coating film burns and becomes acid resistant. Performance tends to decrease.

The amount of graphite is usually 0.5 to 20% by weight, preferably 3 to 15% by weight. If the graphite content is less than 0.5% by weight, the effect of improving the sliding property of the coating film is not sufficient, and
If it exceeds 0% by weight, the viscosity of the paint tends to be too high.

The amount of the oxidation resistant material is usually 10 to 90% by weight, preferably 15 to 45% by weight. 1 content of anti-oxidant
If the amount is less than 0% by weight, the stability of the coating film is deteriorated, and cissing occurs, and the electrode is easily oxidized. If the amount is more than 90% by weight, the binding property of the coating film is deteriorated.
The electrode tends to be oxidized in the range described above and not function as a coating film in the subsequent temperature range.

The polymer emulsion (solid content) is usually 0.05 to 5% by weight, preferably 0.1 to 3% by weight. When the content of the polymer emulsion is less than 0.05% by weight, the effect of improving the sliding property of the glassy coating film is not sufficient,
If the amount exceeds 5% by weight, the temporal stability of the coating tends to decrease.

The inorganic colloid (solid content) is usually from 1 to 30.
% By weight, preferably 2 to 15% by weight. When the content of the inorganic colloid is less than 2% by weight, the adhesion of the paint to the electrode is low and the coating is easily peeled off. When the content is more than 30% by weight, a problem occurs in terms of conductivity and sparks are caused.

The transition metal is usually 0.1 to 70% by weight, preferably 2 to 40% by weight. When the content of the transition metal is less than 0.1% by weight, the glass formed by the oxidation resistant material is used. The adhesiveness between the glassy coating and the electrode is deteriorated, so that cissing is likely to occur and the antioxidant effect is reduced. If it exceeds 70% by weight, the glassy coating becomes difficult to be continuous.

The coating material of the present invention is prepared by mixing the above components with water at a predetermined weight ratio and subjecting the mixture to a dispersion treatment. The proportion of water can be adjusted depending on the form of application before the application, and may be 20 to 200% by weight based on the solid content of the conductive antioxidant composition component. For the above dispersion treatment, a dissolver, a homomixer, a ball mill, a roll mill, an attritor, a dyno mill, a pico mill, a basket mill, an EG mill and the like are used. In addition, a preservative, various additives (antifoaming agent, leveling agent, anti-settling agent) and the like may be added to the paint of the present invention in order to enhance the preservability of the paint.

Next, the graphite electrode of the present invention will be described. The graphite electrode of the present invention is obtained by applying the above-mentioned paint on at least the side surface. As the graphite electrode, an electrode for an arc furnace is preferably used. Usually, it can be applied with a thickness of about 100 to 500 μm (after drying) including the chuck portion. For application, the most suitable method can be selected from general coating film forming methods such as a dipping method, a brush coating method, a spray (spraying) method, and an electrostatic coating method. At this time, it is necessary to adjust the paint to a working viscosity suitable for each construction method. Paints having different compositions can be applied two or more times.

[0034]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention.

Examples 1 to 5 and Comparative Examples 1 to 4 First, according to the compositions (a) and (b) shown in Tables 1 and 2 below, the mixture was dispersed for 60 minutes by a sand grinder. (B) was used as a set to obtain 10 kinds of paints. Table 3 shows the carbon black, colloidal silica and dispersant used.

In Comparative Example 1, the alkali component (Mg
This is an example in which O) is added. Comparative Example 2 omits the polymer emulsion (latex emulsion), Comparative Example 3 omits the inorganic colloid (colloidal silica), and Comparative Example 4 omits the transition metal (Cr powder).

Next, 100% of the paint (a) was applied to the entire surface of the test piece obtained by slicing the graphite electrode by a brush coating method.
It was coated to a thickness of to 250 g / m ² (after drying), after 1 hour drying was applied paint (b) to a thickness of 250~500g / m ^2. This was left overnight and dried, and the surface resistance was measured with a tester. Then, it was left in an incinerator (manufactured by Hayashi Denko) at 400 ° C. for 30 minutes, and the change in resistance was examined. Then 1
After baking at 000 ° C. for 30 minutes and cooling to room temperature, the state of the coating film was judged. Table 4 shows the results.

[0038]

[Table 1]

[0039]

[Table 2]

[0040]

[Table 3]

[0041]

[Table 4]

In the case of Examples 1 to 5, even after baking at 1000 ° C., some chromium was slightly oxidized and the greenish color became strong. However, a uniform glassy coating film was formed without causing cissing. As a result, a sufficient effect as an antioxidant was confirmed.

In the case of Comparative Example 1, the resistance was very good in the resistance measurement at 400 ° C., but at 1000 ° C., the coating film became uneven and many burn-in portions occurred.

In the case of Comparative Example 2, the coating film was brittle and dropped off even at a resistance measurement at 400 ° C., and at 1000 ° C., the coating film became uneven and many burn-in portions occurred.

In the case of Comparative Example 3, the coating film was brittle and easily peeled off, and cracks and the like were observed in the resistance measurement at 400 ° C. This is considered to be due to this effect.
It was confirmed that the continuity of the coating film was poor, a gap was formed between the coating film and the electrode, and the electrode was damaged, and the effect of preventing oxidation at 1000 ° C. or higher was not exhibited.

In the case of Comparative Example 4, the condition was very good at 400 ° C., but at 1000 ° C., the continuity of the coating film was interrupted and cissing occurred, and the electrode was damaged.

As described above, it can be seen that the graphite electrode coated with the coating material of the present invention does not lose conductivity at 400 ° C. and has a good antioxidant effect at 1000 ° C.

[0048]

According to the present invention, application to the electrode chuck portion is possible, and the sliding resistance and 1000 ° C.
A conductive antioxidant paint and a graphite electrode having an excellent antioxidant effect at high temperatures as described above are provided.

Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court II (Reference) H01B 1/04 H01B 1/04 1/24 1/24 A (72) Inventor Kazuma Kawabata Kokubunji, Okuninocho, Himeji-shi, Hyogo 138-1 F-term in Gokoku Shigyo Co., Ltd. (Reference) 4J038 CA011 CA021 CA041 CA061 CA071 CB021 CB051 CC021 CC051 CD021 CG141 GA06 HA026 HA036 HA076 HA156 HA216 HA316 HA436 HA446 HA476 KA02 KA12 KA20 MA08 MA10 DA02 PC10 DA02 PC DA18 DA19 DA24 DA32 DA42 DD02

Claims (5)

[Claims] An aqueous medium containing a conductive material, an antioxidant, a polymer emulsion as a binder, an inorganic colloid, and a transition metal, wherein the content of an alkali metal and / or an alkaline earth metal is reduced. A conductive antioxidant paint, wherein the amount of the antioxidant material is 20% by weight or less. 2. The oxidation resistant material is B, Si, Ge, Sb, T.
2. A single carbide or nitride selected from the group consisting of i, Sn, Al, and Zr, or a single body of B or Si.
3. The conductive antioxidant paint according to claim 1. 3. The conductive antioxidant coating according to claim 1, wherein the average particle diameter of the inorganic colloid is 100 nm or less. 4. The transition metal is Cr, W, Co, Ti, Ni.
4. One or two or more selected from the group of
The conductive antioxidant paint according to any one of the above. 5. A graphite electrode formed by applying the conductive antioxidant paint according to claim 1. Description: