JP2918008B2 - Self-fusing carbonaceous powder and high density carbon material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-fusing carbonaceous powder suitable for a raw material for a high-density carbon material and a binder for a carbon composite material, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, many production methods for high-density carbon materials have been known, but these can be roughly divided into the following two methods from the viewpoint of starting materials. Generally done
One method that has were kneaded coke powder, natural graphite, a caking material such as aggregate and coal tar pitch, such as carbon plaques, molded, a method of baking. This method
Since the residual carbon ratio of the binder is very low, the density of the molded body is extremely low in one carbonization, and the density must be increased by repeating the impregnation / carbonization process many times in order to increase the density. In the carbonization process, degassing of volatiles in the binder occurs, and rapid escape of gas not only causes heterogeneous pores to remain inside the molded body, but also causes expansion of the molded body and causes tissue destruction. Therefore, in order to prevent such an adverse effect, the carbonization process involves a very slow temperature rise of 2 to 10 ° C./hr, requiring a production period of 3 to 4 weeks. The molded body after this carbonization step is 2500 ~ 3000 ℃ depending on the application
The carbonization is carried out to produce a graphitic carbon material, and this graphitization step generally requires two to three weeks. As described above, it takes a long time of two to three months to produce a graphitic carbon material from an aggregate such as coke and a binder such as coal tar pitch through a complicated process.

Another method is disclosed in Japanese Patent Application Laid-Open No. Sho.
No.49-23793, No.51-29523
And Japanese Patent Publication No. 60-25364 , in which optically anisotropic small spheres are used as a raw material for a high-density carbon material without using a binder. Optically anisotropic small spheres (mesophase spherulites) generated during the heat treatment of coal tar pitch and petroleum heavy oil at 350-500 ° C are separated from the pitch matrix by solvent fractionation.
This is a method in which a mesophase spherulite obtained by drying is used as a raw material, which is press-molded and then fired, and a high-density and isotropic carbon material can be produced. However, in this method, a large amount of extraction solvent is required in the spherulite / separation step, and the solvent must be separated many times, and it is difficult to completely remove the residual solvent from the obtained spherulite. Therefore, in the subsequent carbonization step, it tends to cause cracks and expansion of the molded body. Moreover, in such a spherulite solvent extraction method, in addition to a low separation yield, it is not easy to control the properties of the generated spherulite, and there are many industrial problems in stably producing a raw material of a constant quality. .

[0004]

As described above, the process of producing a high-density carbon material is extremely complicated and requires a very long production period. It is expensive and is currently severely restricted in its field of use. Therefore, it is one of the major issues in the carbon industry to greatly simplify the production process of the high-density carbon material and shorten the production period. An object of the present invention is to provide a self-fusing carbonaceous powder capable of producing a high-density and high-strength carbon material in a short time and at low cost, and a method for producing the same.

[0005]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have oxidized a specific mesophase pitch in a powder state to thereby obtain an atomic ratio of hydrogen to carbon (H / Prepare an oxidized powder having an atomic ratio of oxygen to oxygen (C) and oxygen (O / C), and use this oxidized powder with an increased carbonization yield and excellent self-fusion properties as a raw material. As a result, the inventors have found that a high-density carbon material can be obtained in a short time and at low cost without adding a binder, and have reached the present invention.

[0006] That is, the present invention relates to a method for producing carbon based on carbon, which is obtained by oxidizing a mesophase pitch having a carbonization yield of 70% by weight or more, a softening point of 170 ° C or more, and an optically anisotropic phase of 70% by volume or more. The atomic ratio of hydrogen is in the range of 0.48 to 0.59, and the atomic ratio of oxygen to carbon is 0.01 to 0.1.
A self-fusing carbonaceous powder having a range of 10 and a method for producing the same.

[0007] The carbon, hydrogen and oxygen contents of the self-fusing carbonaceous powder of the present invention are analyzed using an automatic analyzer to which a technique such as detection by the thermal conductivity of combustion gas is applied. The raw material pitch used in the present invention has a carbonization yield of 70% by weight or more, preferably 80% by weight or more. This carbonization yield is obtained by gradually increasing the temperature of the pitch under an inert atmosphere,
This is the value when the temperature is maintained for about 2 hours after reaching 0 ° C. When a pitch having a low carbonization yield is used as a raw material, voids due to volatile gas are easily generated in the carbonized molded body, resulting in a decrease in the density of the obtained carbon material, its mechanical strength, electric conductivity,
It is important to use a raw material pitch having a high carbonization yield because it has a bad influence on thermal conductivity, corrosion resistance, and the like.

The raw material pitch has a softening point of 170 ° C. or higher by a flow tester and an optically anisotropic phase observed by a polarizing microscope of at least 70 vol%, preferably 80 vol%.
A mesophase pitch of l% or more, more preferably substantially 100 vol%, is used. As long as the mesophase pitch satisfies these conditions, any of coal-based and petroleum-based may be used.In particular, JP-A-1-13621, JP-A-1-254796,
And pitch produced by polymerizing the aromatic hydrocarbons described superacid HF-BF ₃ catalyst in JP-A-3 223 391 is suitably used in terms of high carbonization yield is obtained.

In the production of the self-fusing carbonaceous powder of the present invention, the above-mentioned mesophase pitch is first powdered. The powdering method and powder shape are not particularly limited. Although there is no particular limitation on the particle size distribution, a particle size distribution that maximizes the packing density during molding is preferable. Generally, it is oxidized in a powder state of 200 to 5 μm. Next, this mesophase powder is oxidized under a flow of air or a flow of oxygen. Since the oxidation conditions depend on the properties of the raw material mesophase pitch and the oxidation reactivity, the oxidation treatment conditions should be set so that H / C is in the range of 0.48 to 0.59 and O / C is in the range of 0.01 to 0.10. It is necessary to choose. That is, good moldability can be obtained only by preparing a carbonaceous powder having H / C and O / C within this range , and high density can be achieved without inducing cracking or expansion in the subsequent carbonization step. . The oxidation conditions for this purpose are not particularly limited, but generally 170 to 350 ° C. is preferable for industrial implementation. At 350 ° C or higher, the oxidation reaction proceeds extremely quickly, and it is difficult to control the amount of oxygen absorbed. In addition, there is a possibility that a thermal decomposition reaction of the raw material pitch may be induced. Below 170 ° C., the oxidation reaction is extremely slow and is not practical.

As an example of the difference in reactivity to oxygen,
FIG. 1 shows the weight change at 220 ° C. in the powder state (200 mesh pass) of two types of mesophase pitches AR-I and AR-II produced from naphthalene using HF-BF ₃ as a catalyst. Table 1 summarizes the pitch properties. AR- I with a high softening point shows a gradual weight increase and after 20 hours
The weight increased by 4.5 wt%. On the other hand, the low softening point AR-II shows a rapid oxygen absorption at the initial stage, and 11wt after 20 hours.
%. Although the oxidation reactivity differs in this way, an appropriate oxidation treatment is performed according to the pitch properties, and
By adjusting to H / C and O / C, a mesophase powder that exhibits excellent performance as a raw material for a high-density carbon material can be modified (Examples 1 and 2).

[0011] Excessive oxidation treatment is not preferable because it lowers the fusibility of the mesophase powder and at the same time reduces the carbonization yield and affects the bulk density reduction (Comparative Example 1). On the other hand, if the oxidation treatment is insufficient, the molded product tends to expand or foam due to the volatile gas in the subsequent carbonization step, and a desired carbon material cannot be obtained (Comparative Example 2). Further, depending on the properties of the mesophase pitch, if the oxidation temperature is too high, fusion of the mesophase particles may occur entirely or partially, and the operability may be significantly reduced (Comparative Example 3). In other words, by performing an appropriate oxidation treatment in consideration of the properties of the mesophase pitch and the reactivity to oxygen, excellent self-fusion properties can be imparted, and the carbonization yield can be further increased. Thus, a high-density and high-strength carbon material can be manufactured.

Next, the mesophase powder thus oxidized is molded. In this case, no binder is required. The shape of the molded body can be freely selected depending on the purpose, application, and the like. Molding may be performed at room temperature or in a temperature range where the oxidized powder softens or melts.
It is determined according to the required shape, performance and cost.
According to the present invention, the firing density of the molded body can be controlled not only by the molding pressure but also by the oxidation conditions. In the conventional method, the bulk density of the molded body is mainly adjusted only by the molding pressure. However, if this method is used, any desired bulk density can be controlled by a combination of the molding pressure and the oxidation conditions.

[0013] The mesophase molded body is subsequently fired to produce a desired carbon material. The firing step is performed by heating the molded body to a temperature of 600 to 1500 ° C. in a non-oxidizing atmosphere to carbonize the molded body. If necessary, a step of graphitizing the carbide at a temperature of 2000 to 3000 ° C. may be included.

[0014]

Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by these examples.

Example 1 Mesophase pitch AR- I obtained by polymerizing naphthalene in the presence of superacid HF-BF ₃ (softening point> 300 ° C., carbonization yield 91 wt%, optical anisotropy content 100 vol% , H / C 0.51) was pulverized with a crusher to a size of 74 μm or less. Next, the mesophase powder was heated at a rate of 300 ° C./hr to 220 ° C. in an air stream and treated for 1 hour. H / C of this processed powder is 0.49, O / C
Was 0.021. Next, the oxidized powder thus obtained was molded into a plate at a normal temperature at a molding pressure of 1200 kg / cm ² , and then heated to 600 ° C. at a rate of 60 ° C./hr under a nitrogen flow and held for 2 hours. The carbonization yield was 96 wt%. Then, by baking at 1300 ° C for 2 hours under flowing argon, 50mm x 50mm x
A 10 mm carbonized product was obtained. Further, the obtained carbide is
It was baked at 00 ° C for 2 hours. Table 2 shows the physical properties (bulk density, compressive strength, bending strength) of the obtained product.

Example 2 Mesophase pitch AR- II obtained by polymerizing naphthalene in the presence of superacid HF / BF ₃ (softening point: 207 ° C., carbonization yield)
80 wt%, optical anisotropy content 100 vol%, H / C 0.65) were pulverized with a pulverizer to a size of 74 μm or less. Next, the mesophase powder was heated at a rate of 300 ° C / hr to 220 ° C in an air stream and treated for 2 hours. The H / C of this oxidized powder is 0.51,
O / C was 0.076. This powder was fired at 600 ° C. under the same conditions as in Example 1. The carbonization yield was 91 wt%. afterwards
It was fired at 1300 ° C and 1900 ° C. Table 2 shows the physical properties of the obtained product.

Comparative Example 1 The same mesophase pitch powder as in Example 2 was used, and the temperature was raised to 220 ° C. at a rate of 300 ° C./hr in an air flow and treated for 22 hours. The H / C of this treated powder was 0.41, and the O / C was 0.154. Next, the oxidized powder thus obtained was molded and fired under the same conditions as in Example 1. The carbonization yield after firing at 600 ° C was 79.9 wt%. Then, under the same conditions as in Example 1,
A 1300 ° C fired product and a 1900 ° C fired product were obtained. In this example where both the H / C and O / C of the oxidized powder deviated from the claims, Table 2
As shown in the figure, no high-performance carbon material was obtained.

Comparative Example 2 The same mesophase pitch powder as used in Example 2 was heated at a rate of 300 ° C./hr to 200 ° C. in an air stream and treated for 1 hour. The H / C of this treated powder was 0.60, and the O / C was 0.043. The oxidized powder whose H / C deviated from the claimed range was fired at 600 ° C. under the same conditions as in Example 1, and as a result, the molded product expanded.

Comparative Example 3 The same mesophase pitch powder as used in Example 2 was heated at 300 ° C./hr to 270 ° C. in an air stream and treated for 1 hour. Was observed. H / C of this treated powder is 0.48, O
/ C was 0.12. This powder was fired in the same procedure as in Example 1. In this example, in which the O / C of the oxidized powder was outside the scope of the claims, no high-performance carbon material was obtained as shown in Table 2.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

According to the present invention, a mesophase pitch which is easy to carbonize and graphitize and has a very high carbonization yield is used as a raw material for a high-density carbon material. Sufficient high density and high strength can be obtained only by firing. Furthermore, the fired body structure derived from the mesoface pitch exhibits optical anisotropy, and the carbon bond formed is very strong because of its high density and high purity. The degree of graphitization of this carbon bond is improved by firing at a high temperature, and densification is further promoted by shrinkage, so that the carbon bond is further strengthened. Further, the mesophase pitch used in the present invention is provided with excellent tackiness by moderate oxidation treatment, so that a binder is not particularly required.

In the conventional method using the mesophase spherulite, it is not enough to achieve high density and high strength only by the binder ability of the mesophase spherulite itself. For example, the β component (BI- QS component) was adhered to the surface layer of the mesophase spherulite to control its self-fusing property (JP-B-60-25364). Such a treatment involves the binding component in the 400-600 ° C region, namely β
Controls the meltability of components, promotes adhesion between powder particles, and enables high density and high strength. 600 ° C
The above carbonization promotes higher density and higher strength. However, such a system using mesophase spherulites as a raw material is also substantially a two-component system, and the β component of the spherulite surface layer having a cohesive force and the spherulites themselves have different carbonization behaviors (particularly heat treatment). (Shrinkage characteristics in the process), it must be said that there is a limit to high density and high strength.

Therefore, if a monolithic self-bonding powder consisting of substantially uniform components can be developed instead of a method of attaching such a binder component to the mesophase spherulites, ideal high density and high strength can be attained. I can do it. Since the self-fusing carbonaceous powder in the present invention is characterized by being a substantially one-component system composed of such a homogeneous component,
While maintaining shape stability in the initial stage of carbonization at 0 to 600 ° C., it has appropriate melt fluidity, exhibits excellent binder ability of the particles themselves, and expresses a high bonding force between the particles.
Furthermore, in the latter stage of carbonization, uniform shrinkage is achieved, and high density and high strength are further promoted.

[Brief description of the drawings]

FIG. 1 is a drawing showing the oxidation reactivity of mesophase pitch powder.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-49-17393 (JP, A) JP-A-1-254796 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C10C 3/02-3/04 C01B 31/02

Claims (2)

(57) [Claims] 1. A carbonization yield of 70% by weight or more and a softening point of 170 ° C.
Above, the optically anisotropic phase obtained by oxidizing a mesophase pitch of 70 vol% or more, the atomic ratio of hydrogen to carbon is in the range of 0.48 to 0.59, and the atomic ratio of oxygen to carbon is 0.01. Self-fusing carbonaceous powder in the range of ~ 0.10. 2. A carbonization yield of 70% by weight or more and a softening point of 170 ° C.
As described above, the atomic ratio of hydrogen to carbon is obtained by oxidizing a mesophase pitch having an optically anisotropic phase of 70 vol% or more, and the atomic ratio of oxygen to carbon is 0.01 to 0.59. After molding a self-fusing carbonaceous powder in the range of
High density carbon material obtained by carbonization at a temperature of 00 to 1600 ° C or graphitization at a higher temperature