WO2024080302A1 - Binder composition for graphite electrode production use, method for producing green electrode for graphite electrode, method for producing baked electrode for graphite electrode, and method for producing graphite electrode - Google Patents

Abstract

The purpose of the present invention is to provide a binder composition for graphite electrode production use, a method for producing a green electrode for a graphite electrode, a method for producing a backed electrode for a graphite electrode, and a method for producing a graphite electrode, whereby it becomes possible to suppress the puffing of a needle coke without spending huge cost for the production of the needle coke and it also becomes possible to improve the production yield and properties of a graphite electrode. Provided is a binder composition for graphite electrode production use, which comprises an inhibitor for graphite electrode production use and a binder pitch. The binder composition for graphite electrode production use is mixed with a needle coke, then the resultant mixture is shaped to produce a green electrode, then the green electrode is burned at 500°C to 1200°C inclusive to produce a baked electrode, and then the baked electrode is graphitized at 2500°C to 3000°C inclusive to produce a graphite electrode.

Description

Binder composition for producing graphite electrodes, method for producing raw electrodes for graphite electrodes, method for producing fired electrodes for graphite electrodes, and method for producing graphite electrodes

The present invention relates to a binder composition for producing a graphite electrode, a method for producing a raw electrode for a graphite electrode, a method for producing a sintered electrode for a graphite electrode, and a method for producing a graphite electrode.
This application claims priority based on Japanese Patent Application No. 2022-163407 filed on October 11, 2022, the contents of which are incorporated herein by reference.

Coal tar, a by-product of coal carbonization, is mostly composed of condensed polycyclic aromatic compounds and has long been used as a raw material for various carbon products. Coal tar products are made up of approximately 30% creosote oil and naphthalene, which are derived from distillate oil components, and the remaining 70% is made up of products derived from coal tar pitch, a heavy component that is a non-distillate. Of these, needle coke made from coal tar pitch occupies an important position as a product with particularly high added value, and is mainly used as aggregate for graphite electrodes for electric steelmaking. In the manufacture of needle coke, pitch from which impurities have been removed in the refining process is coked at a temperature of 400°C or higher using a delayed coker or the like to obtain green coke. Next, the green coke is subjected to a calcination process in which the water and volatile components contained in the green coke are removed to obtain needle coke. In the graphite electrode manufacturing process, needle coke particles are first mixed with binder pitch, which is used to manufacture the compact, in a specified ratio, and then the mixture is heated and kneaded, and then extruded to produce a raw electrode. This raw electrode is then fired and graphitized, and then processed to produce a graphite electrode product.

Since these graphite electrodes are used under harsh high-temperature conditions, they require extremely high thermal shock resistance. To manufacture graphite electrodes with high thermal shock resistance, needle coke with a small thermal expansion coefficient is required. Needle coke made from coal tar pitch (hereinafter sometimes referred to as "pitch-based needle coke") has the smallest thermal expansion coefficient of all cokes, making it the most preferable raw material for graphite electrodes. However, while pitch-based needle coke can produce good-quality graphite electrodes, it has the disadvantage that it is prone to an irreversible expansion phenomenon known as puffing during the graphitization process used to manufacture electrodes, and if graphitized too quickly, cracks will occur in the product, significantly reducing the yield.

As a result, when manufacturing graphite electrodes, it is necessary to raise the temperature for graphitization over a long period of time, resulting in extremely low productivity. This puffing phenomenon is thought to be caused by abnormal expansion due to the rapid desorption and volatilization of nitrogen and sulfur contained in pitch-based needle coke, mainly in the 1500-2100°C and 2500-2800°C ranges during the graphitization process.

For example, Patent Documents 1 and 2 propose a method of reducing puffing by heat-treating pitch coke at 1500° C. or higher to remove nitrogen. Patent Document 3 shows a method of heat-treating raw coke at a normal calcination temperature after pre-treating it with an oxidation treatment or the like. These methods have the problem that the former consumes a large amount of energy due to high-temperature heating, and the latter is more complicated than the conventional methods.
Furthermore, Patent Document 4 proposes that a metal compound used as a puffing inhibitor in a solution state is added only to the surface of lumpy and granular coke before it is kneaded with binder pitch or the like, and then the mixture is heated, thereby increasing the puffing suppression effect while reducing the amount of inhibitor added.

Japanese Patent Application Laid-Open No. 60-33208 Japanese Patent Application Laid-Open No. 60-208392 Japanese Patent Application Laid-Open No. 63-135486 JP 2001-329271 A

However, all of these methods for producing low-puffing needle coke have problems with their economic viability, and they have not been put to practical use, or they do not necessarily achieve sufficient puffing reduction effects.

The present invention has been made in consideration of the above circumstances, and aims to provide a binder composition for producing graphite electrodes that can suppress puffing of needle coke and improve the production yield and characteristics of graphite electrodes without incurring significant costs when producing needle coke, a method for producing raw electrodes for graphite electrodes, a method for producing sintered electrodes for graphite electrodes, and a method for producing graphite electrodes.

An embodiment of the present invention includes the following aspects.
[1] A binder composition for producing graphite electrodes, comprising an inhibitor for producing graphite electrodes and a binder pitch.
[2] The binder composition for producing a graphite electrode according to [1], wherein the inhibitor for producing a graphite electrode contains at least one of a metal consisting of the following element (Mβ) and an oxide having the following element (Mβ).
Element (Mβ): at least one element selected from the group consisting of Group 4 elements, Group 8 elements, Group 9 elements, Group 10 elements, Group 13 elements, Group 14 elements, and Group 15 elements of the long form periodic table.
[3] The binder composition for producing a graphite electrode according to [2], wherein the element (Mβ) is at least one element selected from the group consisting of Si, Ge, Al, B, Ti, Fe and P.
[4] The binder composition for producing a graphite electrode according to [2] or [3], wherein the oxide having the element (Mβ) is a composite oxide having the following element (Mα) and the element (Mβ):
Element (Mα): at least one metal element (excluding element (Mβ)).
[5] The binder composition for producing a graphite electrode according to [4], wherein the element (Mα) is at least one metal element selected from the group consisting of K, Sc, alkaline earth metal elements, and rare earth metal elements.
[6] The binder composition for producing a graphite electrode according to [4], wherein the element (Mα) is at least one metal element selected from the group consisting of alkaline earth metal elements and rare earth metal elements.
[7] The binder composition for producing a graphite electrode according to [4], wherein the element (Mα) is at least one metal element selected from the group consisting of Mg, Ca, Sr, Ba, La, and Ce.
[8] The binder composition for producing a graphite electrode according to [4], wherein the element (Mα) is at least one of Ca and Ce.
[9] The binder composition for producing a graphite electrode according to any one of [4] to [8], wherein the composite oxide has a composition formula represented by the following formula (1):
Mα _3−x Mβ _1−y O _5−z ... (1)
(In the formula, 0≦x<3, 0≦y<1, and 0≦z<5.)
[10] The binder composition for producing a graphite electrode according to any one of [1] to [9], wherein the binder pitch comprises one or more pitches derived from coal tar, FCC decant oil, ethylene heavy ends, petroleum residue, petroleum waste, biomass oil, or biomass tar.
[11] The binder composition for producing a graphite electrode according to any one of [1] to [10], wherein X is a ratio (wt%) of the inhibitor for producing a graphite electrode to a total weight of the binder pitch, and X is 0.02<X<60.
[12] The binder composition for producing a graphite electrode according to any one of [1] to [11], wherein a puffing value _P2800 calculated by the following formula (I) of a test piece prepared in the following evaluation test (i) is 1.20% or less.
P ₂₈₀₀ = (L2 - L1) / L1 × 100 ... (I)
In the formula (I), L1 and L2 have the following meanings.
L1: Thickness of test piece before firing (mm)
L2: Thickness of the test piece after firing to 2800°C (mm)
<Evaluation test (i)>
The binder pitch, the ratio of which to the coal-based needle coke is 30% by weight, and the inhibitor for graphite electrode production, 2% by weight or 5% by weight, are mixed and kneaded for 5 minutes while heating at 165°C, and then the coal-based needle coke is added and kneaded again for 5 minutes while heating at 165°C. This is molded into a disk shape of 20 mmΦ x 3 mm to 15 mm, and calcined in a firing furnace at 1000°C for 3 hours to burn off the binder pitch to obtain a test piece. The test piece is fired at a heating rate of 20°C/min to 2800°C using a heating thermal expansion measuring device, and L1 and L2 of the test piece before and after firing are measured.
[13] The binder composition for producing a graphite electrode according to any one of [1] to [12], wherein a puffing value P _1700-2100 calculated by the following formula (II) of a test piece prepared in the following evaluation test (ii) is 0.7% or less.
P _1700-2100 = (L3-L4) / L5 × 100 ... (II)
In the formula (II), L3, L4 and L5 have the following meanings.
L3: Thickness of the test piece after firing at 2100°C (mm)
L4: Thickness of the test piece after firing at 1700°C (mm)
L5: Thickness of the test piece after firing at 1000°C (mm)
<Evaluation test (ii)>
The binder pitch, the ratio of which to the coal-based needle coke is 30% by weight, and the inhibitor for graphite electrode production, 2% by weight or 5% by weight, are mixed and kneaded for 5 minutes while heating at 165°C, and then the coal-based needle coke is added and kneaded again for 5 minutes while heating at 165°C. This is molded into a disk shape of 20 mmΦ x 3 mm to 15 mm, and calcined in a firing furnace at 1000°C for 3 hours to burn off the binder pitch to obtain a test piece. The test piece is fired at a heating rate of 20°C/min to 2800°C using a heating thermal expansion measuring device, and L3, L4 and L5 of the test piece during firing are measured.
[14] The binder composition for producing a graphite electrode according to any one of [1] to [13], wherein a puffing value _P2800 calculated by the following formula (I) of a test piece prepared in the following evaluation test (iii) is 1.20% or less.
P ₂₈₀₀ = (L2 - L1) / L1 × 100 ... (I)
In the formula (I), L1 and L2 have the following meanings.
L1: Thickness of test piece before firing (mm)
L2: Thickness of the test piece after firing to 2800°C (mm)
<Evaluation test (iii)>
Powdered binder pitch with a ratio of 30% by weight to the coal-based needle coke and 2% by weight of an inhibitor for graphite electrode production are mixed at room temperature for 10 minutes, and then the coal-based needle coke is added and kneaded for 5 minutes while heating at 165°C. This is molded into a disk shape of 20 mmΦ x 3 to 15 mm, and calcined in a firing furnace at 1000°C for 3 hours to burn off the binder pitch to obtain a test piece. The test piece is fired at a heating rate of 20°C/min to 2800°C using a heating thermal expansion measuring device, and L1 and L2 of the test piece before and after firing are measured.
[15] The binder composition for producing a graphite electrode according to any one of [1] to [14], wherein a puffing value P _1700-2100 calculated by the following formula (II) of a test piece prepared in the following evaluation test (iv) is 0.7% or less.
P _1700-2100 = (L3-L4) / L5 × 100 ... (II)
In the formula (II), L3, L4 and L5 have the following meanings.
L3: Thickness of the test piece after firing at 2100°C (mm)
L4: Thickness of the test piece after firing at 1700°C (mm)
L5: Thickness of the test piece after firing at 1000°C (mm)
<Evaluation test (iv)>
Powdered binder pitch with a ratio of 30% by weight to the coal-based needle coke and 2% by weight of an inhibitor for graphite electrode production are mixed at room temperature for 10 minutes, and then the coal-based needle coke is added and kneaded for 5 minutes while heating at 165°C. This is molded into a disk shape of 20 mmΦ x 3 to 15 mm, and calcined in a baking furnace at 1000°C for 3 hours to burn off the binder pitch to obtain a test piece. The test piece is calcined at a heating rate of 20°C/min to 2800°C using a heating thermal expansion measuring device, and L3, L4 and L5 of the test piece during calcination are measured.
[16] The binder composition for producing a graphite electrode according to [12], wherein in the evaluation test (i), a test piece is prepared in the same manner except that the inhibitor for producing a graphite electrode is not used, and when the puffing value (blank) of the test piece calculated by the formula (I) is _P2800b , the ratio of the puffing value calculated by _P2800 / _P2800b is less than 1.
[17] The binder composition for producing a graphite electrode according to [13], wherein in the evaluation test (ii), a test piece is prepared in the same manner except that the inhibitor for producing a graphite electrode is not used, and when the puffing value (blank) of the test piece calculated by the formula (II) is P _1700-2100b , the ratio of the puffing value calculated by P _1700-2100 /P _1700-2100b is less than 1.
[18] Mixing an inhibitor for producing a graphite electrode with a binder pitch to produce a binder composition for producing a graphite electrode;
The binder composition for producing a graphite electrode and needle coke are mixed and molded to obtain a raw electrode.
[19] The method for producing a raw electrode for a graphite electrode according to [18], wherein the inhibitor for producing a graphite electrode contains at least one of a metal consisting of the following element (Mβ) and an oxide having the following element (Mβ).
Element (Mβ): at least one element selected from the group consisting of Group 4 elements, Group 8 elements, Group 9 elements, Group 10 elements, Group 13 elements, Group 14 elements, and Group 15 elements of the long form periodic table.
[20] The method for producing a raw electrode for a graphite electrode according to [19], wherein the element (Mβ) is at least one element selected from the group consisting of Si, Ge, Al, B, Ti, Fe and P.
[21] The method for producing a raw electrode for a graphite electrode according to [19] or [20], wherein the oxide having the element (Mβ) is a composite oxide having the following element (Mα) and the element (Mβ):
Element (Mα): at least one metal element (excluding element (Mβ)).
[22] The method for producing a raw electrode for a graphite electrode according to [21], wherein the element (Mα) is at least one metal element selected from the group consisting of K, Sc, alkaline earth metal elements, and rare earth metal elements.
[23] The method for producing a raw electrode for a graphite electrode according to [21], wherein the element (Mα) is at least one metal element selected from the group consisting of alkaline earth metal elements and rare earth metal elements.
[24] The method for producing a raw electrode for a graphite electrode according to [21], wherein the element (Mα) is at least one metal element selected from the group consisting of Mg, Ca, Sr, Ba, La, and Ce.
[25] The method for producing a raw electrode for a graphite electrode according to [21], wherein the element (Mα) is at least one of Ca and Ce.
[26] The method for producing a raw electrode for a graphite electrode according to any one of [21] to [25], wherein the composition formula of the composite oxide is the following formula (1):
Mα _3−x Mβ _1−y O _5−z ... (1)
(In the formula, 0≦x<3, 0≦y<1, and 0≦z<5.)
[27] The method for producing a raw electrode for a graphite electrode according to any one of [18] to [26], wherein the binder pitch contains one or more pitches derived from coal tar, FCC decant oil, ethylene heavy ends, petroleum residues, petroleum waste, biomass oil, or biomass tar.
[28] The method for producing a raw electrode for a graphite electrode according to any one of [18] to [27], wherein X is a ratio (wt%) of the inhibitor for producing a graphite electrode to a total weight of the binder pitch, and X is 0.02<X<60.
[29] The method for producing a raw electrode for a graphite electrode according to any one of [18] to [28], wherein a puffing value _P2800 of a test piece prepared in the following evaluation test (i) for the binder composition for producing a graphite electrode, as calculated by the following formula (I), is 1.20% or less.
P ₂₈₀₀ = (L2 - L1) / L1 × 100 ... (I)
In the formula (I), L1 and L2 have the following meanings.
L1: Thickness of test piece before firing (mm)
L2: Thickness of the test piece after firing to 2800°C (mm)
<Evaluation test (i)>
The binder pitch, the ratio of which to the coal-based needle coke is 30% by weight, and the inhibitor for graphite electrode production, 2% by weight or 5% by weight, are mixed and kneaded for 5 minutes while heating at 165°C, and then the coal-based needle coke is added and kneaded again for 5 minutes while heating at 165°C. This is molded into a disk shape of 20 mmΦ x 3 mm to 15 mm, and calcined in a firing furnace at 1000°C for 3 hours to burn off the binder pitch to obtain a test piece. The test piece is fired at a heating rate of 20°C/min to 2800°C using a heating thermal expansion measuring device, and L1 and L2 of the test piece before and after firing are measured.
[30] The method for producing a raw electrode for a graphite electrode according to any one of [18] to [29], wherein a puffing value P _1700-2100 calculated by the following formula (II) of a test piece prepared in the following evaluation test (ii) for the binder composition for producing a graphite electrode is 0.7% or less.
P _1700-2100 = (L3-L4) / L5 × 100 ... (II)
In the formula (II), L3, L4 and L5 have the following meanings.
L3: Thickness of the test piece after firing at 2100°C (mm)
L4: Thickness of the test piece after firing at 1700°C (mm)
L5: Thickness of the test piece after firing at 1000°C (mm)
<Evaluation test (ii)>
The binder pitch, the ratio of which to the coal-based needle coke is 30% by weight, and the inhibitor for graphite electrode production, 2% by weight or 5% by weight, are mixed and kneaded for 5 minutes while heating at 165°C, and then the coal-based needle coke is added and kneaded again for 5 minutes while heating at 165°C. This is molded into a disk shape of 20 mmΦ x 3 mm to 15 mm, and calcined in a firing furnace at 1000°C for 3 hours to burn off the binder pitch to obtain a test piece. The test piece is fired at a heating rate of 20°C/min to 2800°C using a heating thermal expansion measuring device, and L3, L4 and L5 of the test piece during firing are measured.
[31] The method for producing a raw electrode for a graphite electrode according to [29], wherein in the evaluation test (i), a test piece is prepared in the same manner except that the inhibitor for the production of a graphite electrode is not used, and when the puffing value (blank) of the test piece calculated by the formula (I) is _P2800b , the ratio of the puffing value calculated by _P2800 / _P2800b is less than 1.
[32] The method for producing a raw electrode for a graphite electrode according to [30], wherein in the evaluation test (ii), a test piece is prepared in the same manner except that the inhibitor for the production of a graphite electrode is not used, and when the puffing value (blank) of the test piece calculated by the formula (II) is P _1700-2100b , the ratio of the puffing value calculated by P _1700-2100 /P _1700-2100b is less than 1.
[33] A method for producing a sintered electrode for a graphite electrode, comprising producing a raw electrode by the method for producing a raw electrode for a graphite electrode according to any one of [18] to [32], and sintering the raw electrode at 500° C. or more and 1,200° C. or less to obtain a sintered electrode.
[34] The method for producing a sintered electrode for a graphite electrode according to [33], wherein Y is a ratio (wt%) of the inhibitor for producing a graphite electrode to the total weight of the sintered electrode, and Y is 0.02<Y<15.
[35] A method for producing a graphite electrode, comprising producing a sintered electrode by the method for producing a sintered electrode for a graphite electrode according to [33] or [34], and graphitizing the sintered electrode at 2500° C. or more and 3000° C. or less to obtain a graphite electrode.
[36] The method for producing a graphite electrode according to [35], wherein the proportion of the graphite electrode production inhibitor remaining in the graphite electrode is 0.01% by weight or less.
[37] A method for producing a graphite electrode, comprising mixing the binder composition for producing a graphite electrode according to any one of [1] to [17] with needle coke and molding the mixture to obtain a raw electrode.
[38] A method for producing a sintered electrode for a graphite electrode, comprising producing a raw electrode by the method for producing a raw electrode for a graphite electrode according to [37], and sintering the raw electrode at 500° C. or more and 1,200° C. or less to obtain a sintered electrode.
[39] The method for producing a sintered electrode for a graphite electrode according to [38], wherein Y is a ratio (weight %) of the inhibitor for producing a graphite electrode to the total weight of the sintered electrode, and 0.02<Y<15.
[40] A method for producing a graphite electrode, comprising producing a sintered electrode by the method for producing a sintered electrode for a graphite electrode according to [38] or [39], and graphitizing the sintered electrode at 2500° C. or more and 3000° C. or less to obtain a graphite electrode.
[41] The method for producing a graphite electrode according to [40], wherein the proportion of the graphite electrode production inhibitor remaining in the graphite electrode is 0.01% by weight or less.

According to the present invention, by using a binder composition containing an inhibitor and binder pitch for producing graphite electrodes, it is possible to suppress puffing of needle coke without incurring significant costs during the production of needle coke, and to improve the production yield and characteristics of graphite electrodes.

FIG. 1 is a diagram showing hot puffing values measured by a thermal dilatometer for Examples 1-1, 1-2, 2-1, 2-2, and 3 and Comparative Examples 1 and 2. FIG. 1 is a diagram showing data obtained by measuring hot puffing in Examples 1-1, 1-2, 2-1, 2-2 and Comparative Example 1 by a differential method. FIG. 1 is a diagram showing hot puffing values measured by a thermal dilatometer in Example 3 and Comparative Examples 1 and 3.

The present invention will be described in detail below, but the present invention is not limited to the following description and can be modified in any manner without departing from the gist of the present invention.
In the following description, "% by weight" is synonymous with "% by mass", and "parts by weight" is synonymous with "parts by mass".
In the present invention, the term "pitch-based" is treated as a synonym for "coal-based."
The "sulfur content of the coke" in the present invention means a value measured in accordance with JIS M8813. The "nitrogen content of the coke" in the present invention means a value measured in accordance with JIS M8819.

1. Binder Composition for Producing Graphite Electrodes One embodiment of the present invention relates to a binder composition for producing graphite electrodes.
The binder composition for producing a graphite electrode according to the embodiment is a composition used for producing a graphite electrode, and contains an inhibitor for producing a graphite electrode (hereinafter, sometimes simply referred to as an "inhibitor") in a binder pitch.
Since the puffing suppression effect can be increased while reducing the amount of inhibitor added, a composition in which the inhibitor is contained in the binder pitch is preferred.

1.1 Inhibitor for Graphite Electrode Production The inhibitor used in the binder composition for graphite electrode production according to the embodiment is intended to suppress puffing of needle coke when the binder composition and needle coke are fired simultaneously to obtain a graphite electrode.

In one embodiment, the inhibitor comprises at least one of a metal consisting of the element (Mβ) and an oxide having the element (Mβ).
Element (Mβ): at least one element selected from the group consisting of Group 4 elements (Ti, Zr, Hf), Group 8 elements (Fe, Ru, Os), Group 9 elements (Co, Rh, Ir), Group 10 elements (Ni, Pr, Pt), Group 13 elements (B, Al, Ga, In), Group 14 elements (Si, Ge, Sn) and Group 15 elements (P, Sb, Bi) of the long form periodic table.

(First embodiment)
The inhibitor of the first embodiment includes a composite oxide having an element (Mα) and an element (Mβ), or a metal or alloy composed of the element (Mβ).
Element (Mα): At least one metal element (excluding element (Mβ)).
Element (Mβ): at least one element selected from the group consisting of Group 4 elements (Ti, Zr, Hf), Group 8 elements (Fe, Ru, Os), Group 9 elements (Co, Rh, Ir), Group 10 elements (Ni, Pr, Pt), Group 13 elements (B, Al, Ga, In), Group 14 elements (Si, Ge, Sn) and Group 15 elements (P, Sb, Bi) of the long form periodic table.

The element (Mα) is preferably at least one metal element selected from the group consisting of K, Sc, alkaline earth metal elements (Mg, Ca, Sr, Ba) and rare earth metal elements (Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) because it is easy to reduce puffing, more preferably at least one metal element selected from the group consisting of alkaline earth metals and rare earth metal elements, even more preferably at least one metal element selected from the group consisting of Mg, Ca, Sr, and Ba, as well as La and Ce, and particularly preferably at least one of Ca and Ce.

The element (Mβ) is preferably at least one element selected from the group consisting of Si, Ge, Al, B, Ti, Fe and P, as this tends to reduce puffing, more preferably at least one element of Si and Ge, and most preferably Si.

The composition formula of the inhibitor of the first embodiment is not particularly limited, but is preferably the following formula (1) because it is easy to reduce puffing.
Mα _3−x Mβ _1−y O _5−z ... (1)
(In the formula, 0≦x<3, 0≦y<1, and 0≦z<5.)

In the formula, x is preferably 0≦x<3, more preferably 0.05≦x≦2.5, and particularly preferably 0.1≦x≦2, since puffing is easily reduced.
In the formula, y is preferably 0≦y<1, more preferably 0.01≦y≦0.8, and particularly preferably 0.1≦y≦0.5, since puffing can be easily reduced.
In the formula, z is preferably 0≦z<5, more preferably 0.05≦z≦4, and particularly preferably 0.1≦z≦3, since puffing can be easily reduced.

_Specific examples of composite oxides having an element (Mα) and an element (Mβ) include, for example, _MgSi3O7 , _{Mg3SiO5 , Mg14Si5O24 , MgO} , _Ca3SiO5 , _{Ca2SiO4 , CaSiO3 ,} Ca8Si5O18, _CaSi2O5 , CaO, _CaCO3 , Ca( _{OH ) 2 , SrSiO3 , Sr3SiO5 , SrSi2O5 , Sr2SiO4 , Ba3SiO5 , Ba2SiO4 , BaSiO3 , BaSi2O5 , Ba2Si3O8 , and Ba5Si8O21 . , Ba3Si5O13 , Ba2SiO4 , BaO , BaCO3 , Ce2SiO5 , Ce2Si2O7 , Ce2Si4O11 , CeSi3O8 , Ce3SiO8 , Ce6Si6O21 , La5Si3O13.5 , La6Si6O21 , La2SiO5 , La2Si4O11 , La2Si6O16 , Pr4.67Si3O13 , Pr2Si2O7 , Pr6Si2 , Pr6Si12O25 , Eu5 ​ ​ ​ ​ ​ ​ ​ Si3O13 , Eu2Si2O7 , Eu2SiO4 , Eu6Si12O33 , CaGe2O5 , Ca3GeO5 , Ca2GeO4 , Ca5Ge3O11 , CaGeO3 , Ca2Ge7O16 , CaAl12O19 , CaAl4O7 , Ca4Al6O13 , Ca5Al6O14 , Ca6Al7O16 , Ca2Al2O5 , Ca3Al2O6 , CaFeO2 , Ca2Fe2O5 ​ ​ ​ ​ ​ ​ ​ ​ ​ , CaFeO3 , CaFe2O4 , CaFe3O5 , CaFe4O6 , CaFe5O7 , CaFe6O8 , CaTi2O4 , CaTi2O5 , Ca3Ti2O7 , Ca4Ti3O10 , CaTiO3 , CaTi5O11 , Mg2Al4O8 , MgAl2O4 , Mg2Al2O5 , MgGe2O4 , Mg2TiO4 , MgTiO3 , MgTi2O4 , MgTi2O5 , MgFe2 O4 , SrAl12O19 , SrAl4O7 , Sr4Al14O25 , Sr12Al14O33 , Sr3Al2O6 , Sr10Al6O19 , Sr3GeO , SrGe4O9 , SrGeO3 , Sr3GeO5 , SrTi11O20 , Sr2Ti6O13 , SrTiO3 , Sr4Ti3O10 , Sr3Ti2O7 , Sr2TiO4 , SrFe12O9 , SrFe2O4 , Sr2Fe3 ​ ​ ​ ​ O6 , SrFeO2 , Sr4Fe6O13 , Sr2Fe2O5 , Sr3Fe2O5 , Sr4Fe4O11 , SrFeO3 , Sr3Fe2O6 , Sr2FeO3 , Sr3Fe2O7 , SrFeO4 , Sr2FeO4 , BaAl12O19 , BaAl4O7 , BaAl2O4 , Ba3Al2O6 , Ba4Al2O7 , Ba7Al2O10 , Ba17Al3O7 , Ba21Ge ​ ​ ​ ​ ​ ​ 2O5 , Ba3GeO , Ba3GeO5 , Ba10Ge7O3 , BaGeO3 , BaGe2O5 , Ba2Ge5O12 , BaGe4O9 , Ba3TiO5 , Ba2TiO4 , Ba4Ti5O10 , Ba4Ti4O11 , BaTiO3 , BaTi2O5 , BaTi4O9 , Ba2Ti9O20 , BaTi5O11 , Ba2Ti13O22 , Ba3FeO5 , Ba2FeO4 ​ ​ ​ ​} , _BaFeO2 , _{Ba2Fe2O5 , Ba8Fe8O21 , Ba5Fe5O14 , BaFeO3 , BaFe2O4 , Ba2Fe6O11 , BaFe4O7 , BaFe7O11 , BaFe12O19 , and BaFe15O23} . The complex oxide contained in the inhibitor of the first embodiment may be one type or _two or _{more types} .

The method for producing the inhibitor of the first embodiment is not particularly limited, and examples thereof include known methods such as measuring and mixing raw material compounds so as to obtain the composition ratio of the target composite oxide, and firing the mixture at a temperature range of 1000° C. to 1500° C. in air or in a reducing atmosphere.
The upper limit of the particle size of the obtained inhibitor is not particularly limited, but is more preferably 10,000 μm or less, particularly preferably 1,000 μm or less, and most preferably 100 μm or less. The lower limit of the particle size is also not particularly limited, but is more preferably 1 nm or more, particularly preferably 10 nm or more, and most preferably 100 nm or more. By controlling the particle size within this range, it is easy to uniformly disperse the inhibitor in the binder pitch, and it is expected that the crystallinity of the obtained inhibitor can be maintained and the puffing effect can be enhanced.
In this specification, the "particle size of the inhibitor" means the mode diameter measured by a method using a laser diffraction type particle size distribution analyzer MT3300EX (manufactured by Microtrac Bell) and ethanol as a dispersion medium.

By using the inhibitor of the first embodiment containing a composite oxide having elements (Mα) and (Mβ), the puffing suppression effect is increased, and the manufacturing yield and characteristics of the graphite electrode are improved. The reason why the inhibitor of the first embodiment exhibits such an effect is not yet clear, but is presumed to be as follows.
It is presumed that the presence of the inhibitor of the first embodiment during the calcination of the needle coke for graphite electrodes causes a complex compound containing nitrogen or a complex compound containing sulfur to be formed at a temperature lower than the temperature at which nitrogen is desorbed from the graphite electrode, and the timing of nitrogen desorption or sulfur desorption is shifted from that of a system without the inhibitor added, thereby suppressing the puffing phenomenon. That is, since the inhibitor of the first embodiment contains a complex oxide having the element (Mα) and the element (Mβ), it reacts with the nitrogen or sulfur in the coke during the temperature rise process during calcination to form a complex compound (nitride, oxynitride, sulfide, oxysulfide, carbonitride), and thus the effect of the first embodiment is achieved.

Second Embodiment
The inhibitor of the second embodiment includes a metal consisting of the element (Mα) or an oxide having the element (Mα), and a metal consisting of the element (Mβ) or an oxide having the element (Mβ). The inhibitor of the second embodiment preferably includes an oxide having the element (Mα) and an oxide having the element (Mβ) because puffing is easily reduced.
Element (Mα): At least one metal element (excluding element (Mβ)).
Element (Mβ): at least one element selected from the group consisting of Group 4 elements, Group 8 elements, Group 9 elements, Group 10 elements, Group 13 elements, Group 14 elements, and Group 15 elements of the long form periodic table.

<Metal consisting of element (Mα) or oxide having element (Mα)>
As the element (Mα), since puffing can be easily reduced, it is preferable that the element (Mα) is at least one metal element selected from the group consisting of K, Sc, alkaline earth metal elements, and rare earth metal elements, it is more preferable that the element (Mα) is at least one metal element selected from the group consisting of Sc, alkaline earth metals, and rare earth metal elements, it is particularly preferable that the element (Mα) is at least one metal element selected from the group consisting of alkaline earth metals and rare earth metal elements, and it is most preferable that the element (Mα) is an alkaline earth metal.

The composition formula of the oxide having the element (Mα) is not particularly limited, but is preferably the following formula (2) because it is easy to reduce puffing.
Mα _3−x1 O _3−z1 ... (2)
(In the formula, Mα is an element (Mα), 0≦x1<3, and 0≦z1<3.)

In the formula, x1 is preferably 0≦x1<3, more preferably 0.05≦x1≦2.5, and particularly preferably 0.1≦x1≦2, because puffing can be easily reduced.
In the formula, z1 is preferably 0≦z1<3, more preferably 0.05≦z1≦2.5, and particularly preferably 0.1≦z1≦2, because puffing can be easily reduced.

Specific examples of the metal consisting of the element (Mα) or the oxide having the element (Mα) include CaO, Ca(OH) ₂ , _CaCO3 , Ca, MgO, _MgCO3 , Mg(OH) ₂ , Mg, SrO, _SrCO3 , _Sr (OH) ₂ , Sr, BaO, _BaCO3 , Ba(OH) ₂ , Ba, _CeO2 , Ce, _Pr6O11 , Pr, _Eu2O3 , and Eu. The oxide having the element ( _Mα ) contained in the inhibitor of the second embodiment may be one type or two or more types.

<Metal consisting of element (Mβ) or oxide having element (Mβ)>
The element (Mβ) is preferably at least one element selected from the group consisting of Si, Ge, Al, B, Ti, Fe and P, more preferably at least one element of Si and Ge, and most preferably Si, because this easily reduces puffing.

The composition formula of the oxide having the element (Mβ) is not particularly limited, but is preferably the following formula (3) because it is easy to reduce puffing.
Mβ _1-y1 O _2-z2 ... (3)
(In the formula, Mβ is an element (Mβ), 0≦y1<1, and 0≦z2<2.)

In the formula, y1 is preferably 0≦y1<1, more preferably 0.01≦y1≦0.8, and particularly preferably 0.1≦y1≦0.5, since puffing can be easily reduced.
In the formula, z2 is preferably 0<z2≦2, more preferably 0.05≦z2≦0.2, and particularly preferably 0.1≦z2≦0.15, since puffing can be easily reduced.

Specific examples of the metal consisting of the element (Mβ) or the oxide having the element (Mβ) include, for example, SiO ₂ , Si, SiO _x , GeO ₂ , Ge, Al ₂ O ₃ , Al, B ₂ O ₃ , and P ₂ O _5. The oxide having the element (Mβ) contained in the inhibitor of the second embodiment may be one type or two or more types.

The method for producing the inhibitor of the second embodiment is not particularly limited, and an example thereof is a method in which the elements (Mα) and (Mβ) are measured and mixed in a desired ratio, and then fired in an air atmosphere and a reducing atmosphere at a temperature range of 1000° C. to 1500° C. to obtain an inhibitor in which an oxide having the element (Mα) and an oxide having the element (Mβ) are composited.
Alternatively, the inhibitor may be prepared by mixing an oxide having an element (Mα) with an oxide having an element (Mβ). The particle size of the composite inhibitor is not particularly limited, but is more preferably 10,000 μm or less, particularly preferably 1000 μm or less, and most preferably 100 μm or less. The lower limit of the particle size is also not particularly limited, but is more preferably 1 nm or more, particularly preferably 10 nm, and most preferably 100 nm or more. By controlling the particle size within this range, it is expected that the inhibitor can be easily uniformly dispersed in the binder pitch, and the puffing effect can be enhanced.

The mixing ratio of the oxide having the element (Mα) and the oxide having the element (Mβ) is not particularly limited, but in order to achieve low puffing, the lower limit of the weight ratio of the oxide having the element (Mβ) to the oxide having the element (Mα) is usually 0.01 or more, preferably 0.05 or more, and more preferably 0.1 or more, while the upper limit is usually 1 or less, preferably 0.7 or less, and more preferably 0.5 or less.

By using the inhibitor of the second embodiment, which contains a metal consisting of the element (Mβ) or an oxide having the element (Mα), and a metal consisting of the element (Mβ) or an oxide having the element (Mβ), the puffing suppression effect is increased, and the manufacturing yield and characteristics of the graphite electrode are improved. The reason why the inhibitor of the second embodiment exhibits such an effect is not yet clear, but is presumed to be as follows.
It is presumed that the presence of the inhibitor of the second embodiment during the calcination of the needle coke for graphite electrodes causes a nitrogen-containing composite compound or a sulfur-containing composite compound to be formed at a temperature lower than the temperature at which nitrogen is desorbed from the graphite electrode, and the timing of nitrogen desorption or sulfur desorption is shifted from that in a system in which the inhibitor is not added, thereby suppressing the puffing phenomenon. That is, since the inhibitor of the second embodiment contains a metal made of element (Mβ) or an oxide having element (Mα) and a metal made of element (Mβ) or an oxide having element (Mβ), it reacts with nitrogen or sulfur in the coke during the temperature rise process during calcination to form a composite compound (nitride, oxynitride, sulfide, oxysulfide, carbonitride), and therefore the effect of the second embodiment is achieved.

1.2. Binder pitch The binder pitch may be the same as the raw material pitch of needle coke. For example, pitch derived from coal tar, FCC decant oil, ethylene heavy ends, petroleum residue, petroleum waste, biomass oil, biomass tar, etc. may be exemplified. The binder pitch may be used alone or in combination of two or more kinds.

When the ratio (wt%) of the inhibitor to the total weight of the binder pitch is X, it is preferable that 0.02<X<60. This makes it easier to obtain a sufficient puffing reduction effect and also makes it easier to reduce adverse effects on electrode products.
The ratio X of the inhibitor is more preferably 0.2<X<50, and further preferably 2<X<40.

1.3. Properties of the Binder Composition for Producing a Graphite Electrode Since the binder composition for producing a graphite electrode according to the embodiment is likely to suppress puffing of needle coke during the production of a graphite electrode, it is preferable that the puffing value _P2800 calculated by the following formula (I) of a test piece prepared in the following evaluation test (i) is 1.20% or less.
P ₂₈₀₀ = (L2 - L1) / L1 × 100 ... (I)
In the formula (I), L1 and L2 have the following meanings.
L1: Thickness of test piece before firing (mm)
L2: Thickness of the test piece after firing to 2800°C (mm)

<Evaluation test (i)>
The binder pitch, the ratio of which to the coal-based needle coke is 30% by weight, and the inhibitor for graphite electrode production, 2% by weight or 5% by weight, are mixed and kneaded for 5 minutes while heating at 165°C, and then the coal-based needle coke is added and kneaded again for 5 minutes while heating at 165°C. This is molded into a disk shape of 20 mmΦ x 3 mm to 15 mm, and calcined in a firing furnace at 1000°C for 3 hours to burn off the binder pitch to obtain a test piece. The test piece is fired at a heating rate of 20°C/min to 2800°C using a heating thermal expansion measuring device, and L1 and L2 of the test piece before and after firing are measured.

The puffing value _P2800 of the test piece prepared in the evaluation test (i) is preferably 1.2% or less, more preferably 1.15% or less, even more preferably 1.1% or less, particularly preferably 1.05% or less, even more preferably 1% or less, and most preferably 0% or less. The lower limit of the puffing value _P2800 of the test piece prepared in the evaluation test (i) is not particularly limited, but is preferably -5% or more, more preferably -2% or more. The lower limit and upper limit of the puffing value _P2800 can be arbitrarily combined, and for example, it is preferably -5% or more and 1.20% or less.

A test piece is prepared in the same manner as in the evaluation test (i) except that no inhibitor is used, and the puffing value (blank) of the test piece calculated by the formula (I) is defined as P _2800b .
In this case, the puffing value ratio calculated by P ₂₈₀₀ /P _2800b for the test piece in evaluation test (i) is preferably less than 1, more preferably 0.95 or less, even more preferably 0.9 or less, and particularly preferably 0.85 or less. The smaller the P ₂₈₀₀ /P _2800b for the test piece in evaluation test (i), the more preferable it is. The lower limit of the P ₂₈₀₀ /P _2800b is not limited, but may be substantially -1.5 or more.

Since the needle coke for graphite electrodes of the embodiment is easy to suppress puffing of the needle coke during the production of graphite electrodes, it is preferable that the puffing value P _1700-2100 calculated by the following formula (II) of the test piece prepared in the following evaluation test (ii) is 0.7% or less.
P _1700-2100 = (L3-L4) / L5 × 100 ... (II)
In the formula (II), L3, L4 and L5 have the following meanings.
L3: Thickness of the test piece after firing at 2100°C (mm)
L4: Thickness of the test piece after firing at 1700°C (mm)
L5: Thickness of the test piece after firing at 1000°C (mm)

<Evaluation test (ii)>
The binder pitch, the ratio of which to the coal-based needle coke is 30% by weight, and the inhibitor for graphite electrode production, 2% by weight or 5% by weight, are mixed and kneaded for 5 minutes while heating at 165°C, and then the coal-based needle coke is added and kneaded again for 5 minutes while heating at 165°C. This is molded into a disk shape of 20 mmΦ x 3 mm to 15 mm, and calcined in a firing furnace at 1000°C for 3 hours to burn off the binder pitch to obtain a test piece. The test piece is fired at a heating rate of 20°C/min to 2800°C using a heating thermal expansion measuring device, and L3, L4 and L5 of the test piece during firing are measured.

The puffing value P _1700-2100 of the test piece prepared in the evaluation test (ii) is preferably 0.7% or less, more preferably 0.6% or less, particularly preferably 0.5% or less, and most preferably 0.4% or less. The lower limit of the puffing value P _1700-2100 of the test piece prepared in the evaluation test (ii) is not particularly limited, but is preferably -5% or more, more preferably -2% or more. The lower limit and upper limit of the puffing value P _1700-2100 can be arbitrarily combined, and for example, it is preferably -5% or more and 0.7% or less.

A test piece is prepared in the same manner as in the evaluation test (ii) except that no inhibitor is used, and the puffing value (blank) of the test piece calculated by the formula (II) is defined as P _1700-2100b .
In this case, the puffing value ratio calculated by P _1700-2100 /P _1700-2100b for the test piece in evaluation test (ii) is preferably less than 1, more preferably 0.9 or less, even more preferably 0.8 or less, and particularly preferably 0.6 or less. The smaller the P _1700-2100 /P _1700-2100b for the test piece in evaluation test (ii), the more preferable it is. The lower limit of the P _1700-2100 /P _1700-2100b is not limited, but may be substantially -1.5 or more.

<Evaluation test (iii)>
Powdered binder pitch with a ratio of 30% by weight to the coal-based needle coke and 2% by weight of an inhibitor for graphite electrode production are mixed at room temperature for 10 minutes, and then the coal-based needle coke is added and kneaded for 5 minutes while heating at 165°C. This is molded into a disk shape of 20 mmΦ x 3 to 15 mm, and calcined in a firing furnace at 1000°C for 3 hours to burn off the binder pitch to obtain a test piece. The test piece is fired at a heating rate of 20°C/min to 2800°C using a thermal expansion measuring device, and L1 and L2 of the test piece before and after firing are measured.

The puffing value P ₂₈₀₀ of the test piece prepared in the evaluation test (iii) is preferably 1.2% or less, more preferably 1.15% or less, even more preferably 1.1% or less, particularly preferably 1.05% or less, even more preferably 1% or less, and most preferably 0% or less. The lower limit of the puffing value P ₂₈₀₀ of the test piece prepared in the evaluation test (iii) is not particularly limited, but is preferably -5% or more, more preferably -2% or more. The lower limit and upper limit of the puffing value P ₂₈₀₀ can be arbitrarily combined, and for example, it is preferably -5% or more and 1.20% or less.

In the evaluation test (iii), a test piece is prepared in the same manner except that no inhibitor is used, and the puffing value (blank) of the test piece calculated by the formula (I) is defined as P _2800b .
In this case, the puffing value ratio calculated by _P2800 / _P2800b for the test piece in evaluation test (iii) is preferably less than 1, more preferably 0.95 or less, even more preferably 0.9 or less, and particularly preferably 0.85 or less. The smaller the _P2800 / _P2800b for the test piece in evaluation test (iii), the more preferable it is. The lower limit of the _P2800 / _P2800b is not limited, but may be substantially -1.5 or more.

Since the needle coke for graphite electrodes of the embodiment is easy to suppress puffing of the needle coke during the production of graphite electrodes, it is preferable that the puffing value P _1700-2100 calculated by the following formula (II) of the test piece prepared in the following evaluation test (iv) is 0.7% or less.
P _1700-2100 = (L3-L4) / L5 × 100 ... (II)
In the formula (II), L3, L4 and L5 have the following meanings.
L3: Thickness of the test piece after firing at 2100°C (mm)
L4: Thickness of the test piece after firing at 1700°C (mm)
L5: Thickness of the test piece after firing at 1000°C (mm)

<Evaluation test (iv)>
Powdered binder pitch with a ratio of 30% by weight to the coal-based needle coke and 2% by weight of an inhibitor for graphite electrode production are mixed at room temperature for 10 minutes, and then the coal-based needle coke is added and kneaded for 5 minutes while heating at 165°C. This is molded into a disk shape of 20 mmΦ x 3 to 15 mm, and calcined in a firing furnace at 1000°C for 3 hours to burn off the binder pitch to obtain a test piece. The test piece is fired at a heating rate of 20°C/min up to 2800°C using a heating thermal expansion measuring device, and L3, L4 and L5 of the test piece during firing are measured.

The puffing value P _1700-2100 of the test piece prepared in the evaluation test (iv) is preferably 0.7% or less, more preferably 0.6% or less, particularly preferably 0.5% or less, and most preferably 0.4% or less. The lower limit of the puffing value P _1700-2100 of the test piece prepared in the evaluation test (iv) is not particularly limited, but is preferably -5% or more, more preferably -2% or more. The lower limit and upper limit of the puffing value P _1700-2100 can be arbitrarily combined, and for example, it is preferably -5% or more and 0.7% or less.

A test piece is prepared in the same manner as in the evaluation test (iv) except that no inhibitor is used, and the puffing value (blank) of the test piece calculated by the formula (II) is defined as P _1700-2100b .
In this case, the ratio of the puffing value calculated by P _1700-2100 /P _1700-2100b for the test piece in evaluation test (iv) is preferably less than 1, more preferably 0.9 or less, even more preferably 0.8 or less, and particularly preferably 0.6 or less. The smaller the P _1700-2100 /P _1700-2100b for the test piece in evaluation test (iv), the more preferable it is. The lower limit of the P _1700-2100 /P _1700-2100b is not limited, but may be substantially -1.5 or more.

The method for producing the binder composition for producing graphite electrodes according to the embodiment is not particularly limited. For example, the inhibitor may be dissolved or dispersed in an organic solvent or heavy oil and added to the binder pitch, so that the inhibitor is applied to the surface of the binder pitch. For example, the inhibitor may be dissolved in a volatile solvent such as alcohol or benzene and then added.

2. Method for Producing a Raw Electrode for a Graphite Electrode Another embodiment of the present invention relates to a method for producing a raw electrode for a graphite electrode.
A method for producing a raw electrode for a graphite electrode according to one embodiment includes mixing an inhibitor and a binder pitch to produce a binder composition for producing a graphite electrode, mixing the binder composition for producing a graphite electrode with needle coke, and molding the mixture to obtain a raw electrode. A method for producing a raw electrode for a graphite electrode according to another embodiment may include mixing a binder composition for producing a graphite electrode that has been produced in advance with needle coke, and molding the mixture to obtain a raw electrode.

The method for producing the binder composition for producing a graphite electrode is as described above.
For example, a method can be exemplified in which the binder composition for producing graphite electrodes is mixed (kneaded) with needle coke, and iron oxide is further added as necessary, and then the mixture is molded. The use of iron oxide may be omitted, but the use of iron oxide can provide a further effect of reducing puffing, so that the amount of iron oxide may be appropriately determined taking into consideration the required quality and economic efficiency.
The molding method is not particularly limited, and may be, for example, extrusion molding.

As needle coke, lump and granular calcined coke, i.e., coarse coke that has not been sized, can be used. The calcined coke may be crushed.
It is preferable to mix fine coke with the coarse coke and adjust the particle size before kneading with the binder pitch. In this case, the amount of the fine coke mixed is preferably 50% by weight or less, more preferably 30% by weight or less, based on the total amount of the needle coke for graphite electrodes. Since the fine coke is not directly related to the puffing reduction effect, the amount of the fine coke to be mixed may be appropriately determined taking into account the electrode quality such as the ash content and the economical efficiency.

Needle coke will be described in more detail below.
As the raw material pitch of the needle coke, pitches that are usually used as raw materials for needle coke for graphite electrodes can be used. For example, pitches derived from coal tar, FCC decant oil, ethylene heavy ends, petroleum residues, petroleum waste, biomass oil, biomass tar, etc. can be exemplified. One type of raw material pitch may be used alone, or two or more types may be used in combination.

The needle coke is not particularly limited, but is preferably a pitch-based needle coke because of its small thermal expansion coefficient. Pitch-based needle coal coke has a high sulfur and nitrogen content and tends to cause high puffing if used as is, but in the present invention, puffing can be sufficiently suppressed even when using pitch-based needle coal coke.
Pitch-based needle coke can be suitably used as an aggregate for graphite electrodes for electric furnace steelmaking.

Although not particularly limited, pitch-based needle coke can be produced by hydrogenating a raw coal tar pitch to obtain hydrogenated coal tar pitch, and then coking the hydrogenated coal tar pitch.
Hydrogenated coal tar pitch is obtained by subjecting a raw coal tar pitch to a hydrogenation reaction (hydrogenation step) and separating light oil from the obtained hydrogenated coal tar pitch (separation step). The light oil separated in the separation step can be recycled by supplying it to the hydrogenation step. The method for hydrogenating the raw coal tar pitch and the method for separating the light oil from the hydrogenated coal tar pitch are not particularly limited, and known methods can be applied.

The raw coal tar pitch is not particularly limited. The manufacturing method (pre-adjustment method) of the raw coal tar pitch is not particularly limited, and for example, a method of substantially removing quinoline insolubles from coal tar heavy oil can be exemplified. As a means for removing quinoline insolubles, a known method can be applied, but a method of treating with an aromatic oil or aliphatic oil solvent, or a method of treating with a mixed solvent of aromatic oil and aliphatic oil is preferable. Specifically, the solvent is mixed with the coal tar heavy oil under appropriate conditions, heated, and then allowed to stand as necessary, and the mixture is distilled to remove low boiling point components, thereby obtaining a raw coal tar pitch that contains almost no quinoline insolubles. As the aliphatic oil, alicyclic compounds such as cyclohexane and cyclopentane, compounds with carbonyl groups such as acetone and ether, light oil, etc. can be used. As the aromatic oil, tar washing oil, anthracene oil, etc. can be used.

In the production of hydrogenated coal tar pitch, petroleum heavy oil may be mixed with the raw coal tar pitch. When petroleum heavy oil is mixed, the coal tar heavy oil and the petroleum heavy oil may be mixed, and then the quinoline insoluble matter may be removed to obtain a mixture of raw coal tar pitch and petroleum heavy oil. Alternatively, the raw coal tar pitch and petroleum heavy oil may be mixed, and the light oil may be separated and used in the hydrogenation process. Furthermore, the light oil-separated coal tar pitch obtained by separating the light oil may be mixed with the petroleum heavy oil and used in the hydrogenation process.

Petroleum-based heavy oils are not particularly limited, and examples include fluid catalytic cracking oil, atmospheric distillation residual oil, vacuum distillation residual oil, shale oil, tar sand bitumen, Orinoco tar, coal liquefaction oil, ethylene bottom oil, and heavy oils obtained by hydrorefining these. In addition to these, the oil may further contain relatively light oils such as straight run diesel, vacuum diesel, desulfurized diesel, and desulfurized vacuum diesel.

The method for converting hydrogenated coal tar pitch into coke is not particularly limited, and examples include the delayed coking method, the visbreaking method, the flexicoking method, and the Eureka process. Among these, the delayed coking method is preferred from the standpoint of productivity and quality stability of needle coke.

In the delayed coking method, hydrogenated coal tar pitch is heated as it passes rapidly through a heating tube and is introduced into a coke drum where coking occurs. There are no particular restrictions on the coking conditions, but the temperature is preferably between 300°C and 600°C, and the coking time is preferably 8 to 72 hours.

The coke thus obtained can be calcined in a rotary kiln, shaft furnace, or the like.
The calcination temperature is preferably from 1000°C to 1700°C, more preferably from 1000°C to 1500°C.
The calcination time is preferably from 1 hour to 6 hours, more preferably from 1.5 hours to 5 hours.

3. Method for Producing a Sintered Electrode for a Graphite Electrode Another embodiment of the present invention relates to a method for producing a sintered electrode for a graphite electrode.
The raw electrode is sintered at 500° C. or more and 1200° C. or less to obtain a sintered electrode for graphite electrode.

The raw electrode may be fired in one step or two steps, for example, by a method of performing primary firing, impregnation, secondary firing, etc.
The firing temperature is from 500° C. to 1200° C., and is preferably from 800° C. to 1100° C. because the binder pitch is easily burned off.

When the ratio (wt%) of the inhibitor to the total weight of the sintered electrode is Y, it is preferable that 0.02<Y<15. However, the inhibitor ratio Y is a value as the amount of ash (metal component or metal oxide). When the inhibitor ratio Y satisfies the above condition, it is easy to obtain a sufficient puffing reduction effect, and it is also easy to reduce the adverse effects of the remaining ash on the electrode product.
The ratio Y of the inhibitor is more preferably 0.1<Y<10, and further preferably 0.5<Y<7.5.

4. Method for Manufacturing Graphite Electrodes Another embodiment of the present invention relates to a method for manufacturing a graphite electrode.
A graphite electrode is obtained by subjecting a sintered electrode obtained by sintering a raw electrode to a graphitization treatment at 2500° C. to 3000° C. In producing a graphite electrode, processing may be performed after graphitization as necessary.

The graphitization temperature is preferably 2500°C or higher and 3000°C or lower, and more preferably 2600°C or higher and 3000°C or lower. If the graphitization temperature is equal to or higher than the lower limit, the inhibitor can be easily burned off sufficiently. If the graphitization temperature is equal to or lower than the upper limit, the graphitization temperature can be easily performed while suppressing deterioration and wear of the electrode due to sublimation and oxidation of graphite. The preferred lower and upper limits of the graphitization temperature can be combined in any way.

The proportion of inhibitors remaining in the graphite electrode is preferably 0.01% by weight or less, more preferably 0.005% by weight or less, and even more preferably 0.001% by weight or less, based on the total weight of the graphite electrode. If the proportion of remaining inhibitors is equal to or less than the upper limit, contamination of the iron during electric furnace steelmaking can be reduced.

As described above, the present invention uses a binder composition for producing graphite electrodes, which contains an inhibitor and binder pitch, and thereby makes it possible to suppress puffing of needle coke without incurring significant costs during the production of needle coke, and to improve the production yield and characteristics of graphite electrodes.
The puffing suppression effect is enhanced by using an inhibitor containing at least one of a metal consisting of the element (Mβ) and an oxide having the element (Mβ). In this case, an inhibitor containing a composite oxide having the element (Mα) and the element (Mβ) is preferred because it further enhances the puffing suppression effect.

In addition, in the present invention, the components in the above embodiment may be replaced with well-known components as appropriate without departing from the spirit of the present invention, and the above-mentioned modifications may be combined as appropriate.

The present invention will be specifically explained below with reference to examples, but the present invention is not limited to the following description.

(1) Method for synthesizing inhibitor _Ca2SiO4 and _Ce2SiO5 were prepared by known methods. The obtained substances were passed through a 100 μm sieve to obtain a particle _size of 100 _μm or less, and used as the inhibitor.

(2) Test piece preparation method-1
In each example, 30% by weight of binder pitch relative to the coal-based needle coke and 2% by weight or 5% by weight of inhibitor were mixed and stirred for 10 minutes, and then kneaded for 5 minutes while heating at 165°C to obtain a mixed powder of binder pitch and inhibitor (binder composition for graphite electrode production). Coal-based needle coke pulverized to a predetermined particle size was added to the obtained binder composition for graphite electrode production, and kneaded for 5 minutes in an oil bath at 165°C. This was molded into a disk shape of 20 mmΦ x 3 mm to 15 mm, and calcined in a baking furnace at 1000°C for 3 hours to burn off the binder pitch and obtain a test piece for puffing measurement.
(3) Test piece preparation method-2
In each example, 30% by weight of binder pitch and 2% by weight of inhibitor were added to coal-based needle coke pulverized to a specified particle size, stirred and mixed for 10 minutes, and then kneaded for 5 minutes in an oil bath at 165° C. This was molded into a disk shape of 20 mmΦ×3 to 15 mm, and calcined in a firing furnace at 1000° C. for 3 hours to burn off the binder pitch and prepare a test piece for puffing measurement.
(4) Test piece preparation method-3
In each example, 30% by weight of binder pitch and 2% by weight of inhibitor were mixed and stirred for 10 minutes to obtain a mixed powder of binder pitch and inhibitor (binder composition for graphite electrode production). Coal-based needle coke pulverized to a predetermined particle size was added to the obtained binder composition for graphite electrode production, and kneaded for 5 minutes in an oil bath at 165°C. This was molded into a disk shape of 20 mmΦ x 3 mm to 15 mm, and calcined in a baking furnace at 1000°C for 3 hours to burn off the binder pitch and obtain a test piece for puffing measurement.
(5) Measurement of cold puffing The obtained test piece was fired at a heating rate of 20°C/min up to 2800°C using a heating expansion measuring device. L1 and L2 were measured before and after firing, and the puffing value _P2800 was calculated using the above formula (I). In addition, L3, L4, and L5 of the test piece during firing were measured, and the puffing value _P1700-2100 was calculated using the above formula (II).

(6) Measurement of hot puffing The obtained test piece was heated to 2800°C at a heating rate of 20°C/min, and the elongation of the length of the test piece during this period was measured using a push rod type thermal dilatometer, and the hot puffing value was calculated by the following formula. The elongation of the length of the test piece (cylinder) corresponds to the elongation in the direction perpendicular to the extrusion direction of the extrusion molding. The lower the hot puffing value, the better.
Hot puffing value (%) = (ΔL / L) x 100
(In the formula, L is the length of the test piece before the test, and ΔL is the elongation in the longitudinal direction of the test piece during the temperature rise to 2800° C.)

[Example 1-1]
Ca ₂ SiO ₄ was used as an inhibitor, and the amount of inhibitor added was 2% by weight based on the coal-based needle coke. Using the test pieces obtained in the above-mentioned "(2) Test piece preparation method-1", P ₂₈₀₀ and P _1700-2100 were calculated by the above-mentioned "(5) Measurement of cold puffing". The results are shown in Table 1. In addition, the hot puffing value was measured by the above-mentioned "(6) Measurement of hot puffing". The results are shown in Figures 1 and 2.

[Example 1-2]
Using the test pieces obtained in the same manner as in Example 1-1, _P2800 and _P1700-2100 were calculated by the method described above in "(5) Measurement of cold puffing". The results are shown in Table 1. In addition, the hot puffing value was measured by the method described above in "(6) Measurement of hot puffing". The results are shown in Figures 1 and 2.

[Example 2-1]
Test pieces were obtained in the same manner as in Example 1-1, except that the amount of inhibitor added was changed to 5% by weight, and _P2800 and _P1700-2100 were calculated by the method described above in "(5) Measurement of cold puffing". The results are shown in Table 1. In addition, the hot puffing value was measured by the method described above in "(6) Measurement of hot puffing". The results are shown in Figures 1 and 2.

[Example 2-2]
Using the test pieces obtained in the same manner as in Example 2-1, _P2800 and _P1700-2100 were calculated by the method described above in "(5) Measurement of cold puffing". The results are shown in Table 1. In addition, the hot puffing value was measured by the method described above in "(6) Measurement of hot puffing". The results are shown in Figures 1 and 2.

[Example 3]
Using _Ca2SiO4 as _an inhibitor and the test pieces obtained in the above-mentioned "(4) Test piece preparation method-3", _P2800 and _P1700-2100 were calculated by the above-mentioned "(5) Measurement of cold puffing". The results are shown in Table 1. In addition, the hot puffing value was measured by the above-mentioned "(6) Measurement of hot puffing". The results are shown in Figure 1.

[Example 4]
Using Ce ₂ SiO ₅ as an inhibitor and the test pieces obtained in the above-mentioned "(4) Test piece preparation method-3", P ₂₈₀₀ and P _1700-2100 were calculated by the above-mentioned method "(5) Measurement of cold puffing". The results are shown in Table 1. In addition, the hot puffing value was measured by the above-mentioned method "(6) Measurement of hot puffing". The results are shown in Figure 3.

[Comparative Example 1]
Test pieces were prepared in the same manner as in Example 2-1, except that binder pitch without inhibitor added was used as a comparison for the mixed powder of binder pitch and inhibitor (binder composition for producing graphite electrodes), and the blank puffing values P _2800b and P _1700-2100b were calculated by the method described above in "(5) Measurement of cold puffing". The results are shown in Table 1. In addition, the hot puffing values were measured by the method described above in "(6) Measurement of hot puffing". The results are shown in Figures 1 and 2.

[Comparative Example 2]
Using _Ca2SiO4 as _an inhibitor and the test pieces obtained in the above-mentioned "(3) Test piece preparation method-2", _P2800 and _P1700-2100 were calculated by the above-mentioned "(5) Measurement of cold puffing". The results are shown in Table 1. In addition, the hot puffing value was measured by the above-mentioned "(6) Measurement of hot puffing". The results are shown in Figure 1.

[Comparative Example 3]
Using _Ce2SiO5 as _an inhibitor and the test pieces obtained in the above-mentioned "(3) Test piece preparation method-2", _P2800 and _P1700-2100 were calculated by the above-mentioned "(5) Measurement of cold puffing". The results are shown in Table 1. In addition, the hot puffing value was measured by the above-mentioned "(6) Measurement of hot puffing". The results are shown in Figure 3.

As shown in Table 1, in Examples 1-1, 1-2, 2-1, 2-2 and 3 in which Ca ₂ SiO ₄ was added as an inhibitor, the P ₂₈₀₀ representing the cold puffing value was smaller than that in Comparative Example 1 in which no inhibitor was added and Comparative Example 2 in which the inhibitor, binder pitch and needle coke were mixed simultaneously. In addition, in Examples 1-1, 1-2, 2-1, 2-2 and 3, the P _1700-2100 representing nitrogen puffing was also low, and the puffing inhibition effect was high.
1, it was confirmed that puffing occurred suddenly from about 1800°C in Comparative Example 1, whereas puffing did not occur in the same temperature range in Examples 1-1, 1-2, 2-1, 2-2, and 3, and the inhibitor suppressed puffing. Also, puffing occurred suddenly at about 2800°C in Comparative Example 2, whereas puffing was suppressed in the same temperature range in Examples 1-1, 1-2, 2-1, 2-2, and 3.
Also, as shown in FIG. 2, in Comparative Example 1, the value increases sharply from around 1800° C., whereas in Examples 1-1, 1-2, 2-1, and 2-2 in which an inhibitor was added, the change in value was small, confirming that the inhibitor suppresses puffing.

As shown in Table 1, in Example 4 in which Ce ₂ SiO ₅ was added as an inhibitor, P 2800, which represents the cold puffing value, _was smaller than in Comparative Example 1 in which no inhibitor was added and Comparative Example 3 in which the inhibitor, binder pitch, and needle coke were mixed simultaneously.
As shown in FIG. 3, it was confirmed that in Comparative Examples 1 and 3, puffing occurred suddenly from about 1800° C. to 2800° C., whereas in Example 4, puffing was suppressed in the same temperature range.

Claims (41)

1. A binder composition for producing graphite electrodes, comprising an inhibitor for producing graphite electrodes and binder pitch.
2. 2. The binder composition for producing graphite electrodes according to claim 1, wherein the inhibitor for producing graphite electrodes comprises at least one of a metal consisting of the following element (Mβ) and an oxide having the following element (Mβ).
   Element (Mβ): at least one element selected from the group consisting of Group 4 elements, Group 8 elements, Group 9 elements, Group 10 elements, Group 13 elements, Group 14 elements, and Group 15 elements of the long form periodic table.
3. The binder composition for producing graphite electrodes according to claim 2, wherein the element (Mβ) is at least one element selected from the group consisting of Si, Ge, Al, B, Ti, Fe and P.
4. 3. The binder composition for producing a graphite electrode according to claim 2, wherein the oxide having the element (Mβ) is a composite oxide having the following element (Mα) and the element (Mβ):
   Element (Mα): at least one metal element (excluding element (Mβ)).
5. The binder composition for producing graphite electrodes according to claim 4, wherein the element (Mα) is at least one metal element selected from the group consisting of K, Sc, alkaline earth metal elements, and rare earth metal elements.
6. The binder composition for producing graphite electrodes according to claim 4, wherein the element (Mα) is at least one metal element selected from the group consisting of alkaline earth metal elements and rare earth metal elements.
7. The binder composition for producing graphite electrodes according to claim 4, wherein the element (Mα) is at least one metal element selected from the group consisting of Mg, Ca, Sr, Ba, La, and Ce.
8. The binder composition for producing graphite electrodes according to claim 4, wherein the element (Mα) is at least one of Ca and Ce.
9. 5. The binder composition for producing a graphite electrode according to claim 4, wherein the composite oxide has a composition formula represented by the following formula (1):
   Mα _3−x Mβ _1−y O _5−z ... (1)
   (In the formula, 0≦x<3, 0≦y<1, and 0≦z<5.)
10. The binder composition for producing graphite electrodes according to claim 1, wherein the binder pitch comprises one or more pitches derived from coal tar, FCC decant oil, ethylene heavy ends, petroleum residues, petroleum waste, biomass oil, or biomass tar.
11. The binder composition for graphite electrode production according to claim 1, wherein the ratio (wt%) of the inhibitor for graphite electrode production to the total weight of the binder pitch is X, and 0.02<X<60.
12. 2. The binder composition for producing a graphite electrode according to claim 1, wherein a puffing value _P2800 calculated by the following formula (I) of a test piece prepared in the following evaluation test (i) is 1.20% or less.
    P ₂₈₀₀ = (L2 - L1) / L1 × 100 ... (I)
    In the formula (I), L1 and L2 have the following meanings.
    L1: Thickness of test piece before firing (mm)
    L2: Thickness of the test piece after firing to 2800°C (mm)
    <Evaluation test (i)>
    The binder pitch, the ratio of which to the coal-based needle coke is 30% by weight, and the inhibitor for graphite electrode production, 2% by weight or 5% by weight, are mixed and kneaded for 5 minutes while heating at 165°C, and then the coal-based needle coke is added and kneaded again for 5 minutes while heating at 165°C. This is molded into a disk shape of 20 mmΦ x 3 mm to 15 mm, and calcined in a firing furnace at 1000°C for 3 hours to burn off the binder pitch to obtain a test piece. The test piece is fired at a heating rate of 20°C/min to 2800°C using a heating thermal expansion measuring device, and L1 and L2 of the test piece before and after firing are measured.
13. The binder composition for producing a graphite electrode according to claim 1, wherein a puffing value P _1700-2100 calculated by the following formula (II) of a test piece prepared in the following evaluation test (ii) is 0.7% or less.
    P _1700-2100 = (L3-L4) / L5 × 100 ... (II)
    In the formula (II), L3, L4 and L5 have the following meanings.
    L3: Thickness of the test piece after firing at 2100°C (mm)
    L4: Thickness of the test piece after firing at 1700°C (mm)
    L5: Thickness of the test piece after firing at 1000°C (mm)
    <Evaluation test (ii)>
    The binder pitch, the ratio of which to the coal-based needle coke is 30% by weight, and the inhibitor for graphite electrode production, 2% by weight or 5% by weight, are mixed and kneaded for 5 minutes while heating at 165°C, and then the coal-based needle coke is added and kneaded again for 5 minutes while heating at 165°C. This is molded into a disk shape of 20 mmΦ x 3 mm to 15 mm, and calcined in a firing furnace at 1000°C for 3 hours to burn off the binder pitch to obtain a test piece. The test piece is fired at a heating rate of 20°C/min to 2800°C using a heating thermal expansion measuring device, and L3, L4 and L5 of the test piece during firing are measured.
14. 2. The binder composition for producing a graphite electrode according to claim 1, wherein a puffing value _P2800 calculated by the following formula (I) of a test piece prepared in the following evaluation test (iii) is 1.20% or less.
    P ₂₈₀₀ = (L2 - L1) / L1 × 100 ... (I)
    In the formula (I), L1 and L2 have the following meanings.
    L1: Thickness of test piece before firing (mm)
    L2: Thickness of the test piece after firing to 2800°C (mm)
    <Evaluation test (iii)>
    Powdered binder pitch with a ratio of 30% by weight to the coal-based needle coke and 2% by weight of an inhibitor for graphite electrode production are mixed at room temperature for 10 minutes, and then the coal-based needle coke is added and kneaded for 5 minutes while heating at 165°C. This is molded into a disk shape of 20 mmΦ x 3 to 15 mm, and calcined in a firing furnace at 1000°C for 3 hours to burn off the binder pitch to obtain a test piece. The test piece is fired at a heating rate of 20°C/min to 2800°C using a heating thermal expansion measuring device, and L1 and L2 of the test piece before and after firing are measured.
15. The binder composition for producing a graphite electrode according to claim 1, wherein a puffing value P _1700-2100 calculated by the following formula (II) of a test piece prepared in the following evaluation test (iv) is 0.7% or less.
    P _1700-2100 = (L3-L4) / L5 × 100 ... (II)
    In the formula (II), L3, L4 and L5 have the following meanings.
    L3: Thickness of the test piece after firing at 2100°C (mm)
    L4: Thickness of the test piece after firing at 1700°C (mm)
    L5: Thickness of the test piece after firing at 1000°C (mm)
    <Evaluation test (iv)>
    Powdered binder pitch with a ratio of 30% by weight to the coal-based needle coke and 2% by weight of an inhibitor for graphite electrode production are mixed at room temperature for 10 minutes, and then the coal-based needle coke is added and kneaded for 5 minutes while heating at 165°C. This is molded into a disk shape of 20 mmΦ x 3 to 15 mm, and calcined in a baking furnace at 1000°C for 3 hours to burn off the binder pitch to obtain a test piece. The test piece is calcined at a heating rate of 20°C/min to 2800°C using a heating thermal expansion measuring device, and L3, L4 and L5 of the test piece during calcination are measured.
16. 13. The binder composition for producing a graphite electrode according to claim 12, wherein in the evaluation test (i), a test piece is prepared in the same manner except that the inhibitor for producing a graphite electrode is not used, and when the puffing value (blank) of the test piece calculated by the formula (I) is _P2800b , the ratio of the puffing value calculated by _P2800 / _P2800b is less than 1.
17. The binder composition for producing graphite electrodes according to claim _{13, wherein in the evaluation test (ii), a test piece is prepared in the same manner except that the inhibitor for producing graphite electrodes is not used, and when the puffing value (blank) of the test piece calculated by the formula (II) is P 1700-2100b} , the ratio of the puffing value calculated by P _1700-2100 /P _1700-2100b is less than 1.
18. Mixing an inhibitor for producing a graphite electrode with a binder pitch to produce a binder composition for producing a graphite electrode;
    The binder composition for producing a graphite electrode and needle coke are mixed and molded to obtain a raw electrode.
19. 19. The method for producing a raw electrode for a graphite electrode according to claim 18, wherein the inhibitor for producing a graphite electrode contains at least one of a metal consisting of the following element (Mβ) and an oxide having the following element (Mβ).
    Element (Mβ): at least one element selected from the group consisting of Group 4 elements, Group 8 elements, Group 9 elements, Group 10 elements, Group 13 elements, Group 14 elements, and Group 15 elements of the long form periodic table.
20. The method for producing a raw electrode for a graphite electrode according to claim 19, wherein the element (Mβ) is at least one element selected from the group consisting of Si, Ge, Al, B, Ti, Fe and P.
21. The method for producing a raw electrode for a graphite electrode according to claim 19, wherein the oxide having the element (Mβ) is a composite oxide having the following element (Mα) and the element (Mβ):
    Element (Mα): at least one metal element (excluding element (Mβ)).
22. The method for producing a raw electrode for a graphite electrode according to claim 21, wherein the element (Mα) is at least one metal element selected from the group consisting of K, Sc, alkaline earth metal elements, and rare earth metal elements.
23. The method for producing a raw electrode for a graphite electrode according to claim 21, wherein the element (Mα) is at least one metal element selected from the group consisting of alkaline earth metal elements and rare earth metal elements.
24. The method for producing a raw electrode for a graphite electrode according to claim 21, wherein the element (Mα) is at least one metal element selected from the group consisting of Mg, Ca, Sr, Ba, La, and Ce.
25. The method for producing a raw electrode for a graphite electrode according to claim 21, wherein the element (Mα) is at least one of Ca and Ce.
26. The method for producing a raw electrode for a graphite electrode according to claim 21, wherein the composite oxide has a composition formula represented by the following formula (1):
    Mα _3−x Mβ _1−y O _5−z ... (1)
    (In the formula, 0≦x<3, 0≦y<1, and 0≦z<5.)
27. The method for producing raw electrodes for graphite electrodes according to claim 18, wherein the binder pitch comprises one or more pitches derived from coal tar, FCC decant oil, ethylene heavy ends, petroleum residues, petroleum waste, biomass oil, or biomass tar.
28. The method for producing raw electrodes for graphite electrodes according to claim 18, wherein the ratio (wt%) of the inhibitor for producing graphite electrodes to the total weight of the binder pitch is X, and 0.02<X<60.
29. 19. The method for producing a raw electrode for a graphite electrode according to claim 18, wherein a puffing value _P2800 calculated by the following formula (I) of a test piece prepared in the following evaluation test (i) for the binder composition for producing a graphite electrode is 1.20% or less.
    P ₂₈₀₀ = (L2 - L1) / L1 × 100 ... (I)
    In the formula (I), L1 and L2 have the following meanings.
    L1: Thickness of test piece before firing (mm)
    L2: Thickness of the test piece after firing to 2800°C (mm)
    <Evaluation test (i)>
    The binder pitch, the ratio of which to the coal-based needle coke is 30% by weight, and the inhibitor for graphite electrode production, 2% by weight or 5% by weight, are mixed and kneaded for 5 minutes while heating at 165°C, and then the coal-based needle coke is added and kneaded again for 5 minutes while heating at 165°C. This is molded into a disk shape of 20 mmΦ x 3 mm to 15 mm, and calcined in a firing furnace at 1000°C for 3 hours to burn off the binder pitch to obtain a test piece. The test piece is fired at a heating rate of 20°C/min to 2800°C using a heating thermal expansion measuring device, and L1 and L2 of the test piece before and after firing are measured.
30. The method for producing a graphite electrode raw electrode according to claim 18, wherein a puffing value P _1700-2100 calculated by the following formula (II) of a test piece prepared in the following evaluation test (ii) for the binder composition for producing a graphite electrode is 0.7% or less.
    P _1700-2100 = (L3-L4) / L5 × 100 ... (II)
    In the formula (II), L3, L4 and L5 have the following meanings.
    L3: Thickness of the test piece after firing at 2100°C (mm)
    L4: Thickness of the test piece after firing at 1700°C (mm)
    L5: Thickness of the test piece after firing at 1000°C (mm)
    <Evaluation test (ii)>
    The binder pitch, the ratio of which to the coal-based needle coke is 30% by weight, and the inhibitor for graphite electrode production, 2% by weight or 5% by weight, are mixed and kneaded for 5 minutes while heating at 165°C, and then the coal-based needle coke is added and kneaded again for 5 minutes while heating at 165°C. This is molded into a disk shape of 20 mmΦ x 3 mm to 15 mm, and calcined in a firing furnace at 1000°C for 3 hours to burn off the binder pitch to obtain a test piece. The test piece is fired at a heating rate of 20°C/min to 2800°C using a heating thermal expansion measuring device, and L3, L4 and L5 of the test piece during firing are measured.
31. 30. The method for producing a raw electrode for graphite electrode according to claim _{29, wherein in the evaluation test (i), a test piece is prepared in the same manner except that the inhibitor for producing a graphite electrode is not used, and when the puffing value (blank) of the test piece calculated by the formula (I) is P2800b} , the ratio of the puffing value calculated by _P2800 / _P2800b is less than 1.
32. The method for producing a raw electrode for graphite electrode according to claim 30, wherein in the evaluation test (ii), a test piece is prepared in the same manner except that the inhibitor for producing graphite electrodes is not used, and when the puffing value (blank) of the test piece calculated by the formula (II) is P _1700-2100b , the ratio of the puffing value calculated by P _1700-2100 /P _1700-2100b is less than 1.
33. A method for producing a sintered electrode for a graphite electrode, comprising producing a raw electrode by the method for producing a raw electrode for a graphite electrode according to any one of claims 18 to 32, and sintering the raw electrode at 500°C or higher and 1200°C or lower to obtain a sintered electrode.
34. The method for producing a sintered electrode for a graphite electrode according to claim 33, wherein the ratio (wt%) of the inhibitor for producing a graphite electrode to the total weight of the sintered electrode is Y, and 0.02<Y<15.
35. A method for producing a graphite electrode, comprising producing a sintered electrode by the method for producing a sintered electrode for graphite electrodes described in claim 33, and graphitizing the sintered electrode at 2500°C or higher and 3000°C or lower to obtain a graphite electrode.
36. The method for producing a graphite electrode according to claim 35, wherein the proportion of the graphite electrode production inhibitor remaining in the graphite electrode is 0.01% by weight or less.
37. A method for producing a graphite electrode comprising mixing the binder composition for producing graphite electrodes according to any one of claims 1 to 17 with needle coke and molding the mixture to obtain a raw electrode.
38. A method for producing a sintered electrode for a graphite electrode, comprising producing a raw electrode by the method for producing a raw electrode for a graphite electrode described in claim 37, and sintering the raw electrode at 500°C or higher and 1200°C or lower to obtain a sintered electrode.
39. The method for producing a sintered electrode for a graphite electrode according to claim 38, wherein the ratio (wt%) of the inhibitor for producing a graphite electrode to the total weight of the sintered electrode is Y, and 0.02<Y<15.
40. A method for producing a graphite electrode, comprising producing a sintered electrode by the method for producing a sintered electrode for graphite electrodes described in claim 38, and graphitizing the sintered electrode at 2500°C or higher and 3000°C or lower to obtain a graphite electrode.
41. The method for producing a graphite electrode according to claim 40, wherein the proportion of the graphite electrode production inhibitor remaining in the graphite electrode is 0.01% by weight or less.

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