JP2009190957A - Method of manufacturing conductive carbon material and conductive body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a conductive carbon material (charcoal) by carbonizing wood using an iron catalyst capable of obtaining a carbon material (charcoal) exhibiting high conductivity while at the same time recovering iron used for the catalyst to reuse it for carbonizing wood, and a method of manufacturing a conductive body obtaining a conductive molded body from the conductive carbonized material prepared by carbonizing wood. <P>SOLUTION: The method of manufacturing the conductive carbon material includes: impregnating wood with an aqueous solution of iron nitrate; carbonizing the wood impregnated with the aqueous solution of iron nitrate; washing the carbonized material with an aqueous solution of nitric acid; recovering iron from the carbonized material as iron nitrate; and reusing the recovered aqueous solution of iron nitrite. The method of manufacturing conductive body includes: mixing the carbonized material prepared by the method with wood powder; and molding the obtained mixture with heat and pressure to obtain the conductive molded body. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a conductive carbon material and a method for producing a conductor. More specifically, the present invention relates to a method for recovering and reusing iron used as a catalyst in a method for producing a conductive carbon material by carbonizing wood using iron as a catalyst. Furthermore, this invention relates to the manufacturing method of the conductor which obtains an electroconductive molded object from the electroconductive carbon material obtained by carbonizing wood.

  Normally, charcoal produced at a carbonization temperature of 400-500 ° C. has low electrical conductivity, but if formed into a plate shape or the like, electromagnetic shielding (abbreviated as EMS) is imparted. Like Bincho charcoal, it is expected that the conductivity will improve if the processing temperature is increased to nearly 1000 ° C. Actually, several charcoal products with EMS function and conductivity performance have appeared (Non-Patent Document 1 3). However, the low conductivity of charcoal at 400-500 ° C is due to the fact that it consists of amorphous carbon. Even if carbonized at about 1000 ° C, crystallization of wood carbon does not proceed effectively. Therefore, these charcoal products have high conductivity comparable to existing conductive carbon (acetylene black DB (Non-Patent Document 4), Ketjen Black KB (Non-Patent Document 5), artificial graphite LO, etc.) Is hard to think.

  On the other hand, when carbonized at 1500 ° C or higher, the graphite (graphite) structure develops and charcoal becomes a good conductor (Non-patent Document 6), but such high-temperature heat treatment is expensive to operate and has a DB (about 600) in terms of price. Yen / kg) and KB (approximately 2,000 yen / kg) cannot be beaten.

Therefore, nickel-catalyzed carbonization at 900 ℃ (nickel raw material is Ni (CH ₃ COO) ₂ · 4H ₂ O) effectively generates crystalline carbon (T component) and has practical level of EMS performance (30dB) Patent Documents 7 and 8) and the fact that they give highly conductive charcoal comparable to DB (Non-patent Document 9) are noteworthy. However, more interesting from a practical point of view is higher iron-catalyzed carbonization at 800-850 ° C (iron (III) acetate basic, Fe (OH) (CH ₃ COOH) ₂ is used as iron raw material)) It is to provide conductive charcoal (Non-patent Document 9).
Literature
http://www6.ocn.ne.jp/~hagiwara/cont_01.htm http://www.rakuten.co.jp/gardenmate/446722/447883/ http://www.rakuten.co.jp/ho-ei/146902/146903/ http://www.denka.co.jp/cgi-bin/product/showproduct.cgi?id=405 http://www.lion.co.jp/chem/jn/sectop/carbon/k_intro.htm Shigehisa Ishihara: Journal of the Wood Society, 42, 717 (1996), Materials, 48, 473 (1999). T. Suzuki et al: Materials Sci. Res. International, 7, 206 (2001). T. Suzuki et al: J. Wood Sci., 53, 54 (2007). Hokkaido Development Bureau, Ministry of Land, Infrastructure, Transport and Tourism http://www.hkd.mlit.go.jp/topics/tyousa/index.html T. Suzuki et al: Holtzforshung, under submission. http://www.lion.co.jp/chem/jn/sectop/carbon/k_apli.htm

Iron is generally cheaper than nickel, and as mentioned above, good conductive charcoal can be obtained by carbonizing 850 ° C wood containing Fe (OH) (CH ₃ COO) ₂ containing 3% Fe as an aqueous solution. It is done. There are two reasons for using this salt as a raw material: (1) Fe particles are highly dispersed in wood as a result of thermal decomposition at low temperatures, and (2) no harmful gases are generated during decomposition. It is thought to play a major role in increasing the conductivity of charcoal.

  However, in practical production of conductive charcoal, it is desired to recover and reuse iron for cost reduction. Therefore, the present inventors pulverized the obtained iron charcoal and then immersed in 1M acetic acid at room temperature. As a result, the iron removal rate was about 90%, and it was found that most of the iron was recoverable. It was also found that this acetic acid cleaning increased the crystallinity of the iron and charcoal and improved the conductivity by about 10% in terms of volume resistivity.

  However, iron acetate has the following disadvantages. The above iron acetate composition is an approximate value, and it is difficult to prepare a clear and constant composition. Since the composition varies depending on the processing conditions and the like, (3) there is no guarantee that the original composition will be reproduced when washing with the corresponding acid. (4) Since the solubility in water is small (detailed data does not exist), the iron concentration has to be considerably reduced in order to obtain a uniform aqueous solution for impregnation. gFe / 25 ° C water 100g). In other words, it is necessary to remove excess water from wood before carbonization in aqueous solution impregnation, and it is not preferable to use iron acetate in terms of operation and energy, and if the composition is unknown at the time of recovery and reuse, It will interfere with the adjustment of concentration.

  As for the above-mentioned 900 ° C. nickel catalyst carbonized carbon (U-Ni charcoal), it is known that the conductivity performance is improved when washed with dilute nitric acid for nickel recovery (Non-patent Document 9). However, in order to use nickel recovered by acid washing again as a carbonization catalyst, it is presumed that an additional operation such as changing at least the anion from nitric acid to acetic acid is necessary.

  Therefore, the present invention is a method for producing a conductive carbon material (charcoal) by carbonizing wood using an iron catalyst, and at the same time, a carbon material (charcoal) exhibiting high conductivity is obtained and used as a catalyst. An object is to provide a method in which iron can be recovered at a high recovery rate and reused for carbonization of wood. Another object of the present invention is to provide a method for producing a conductor that obtains a conductive molded body from a conductive carbon material obtained by carbonizing wood.

The present inventors can obtain a carbon material (charcoal) exhibiting high conductivity by using iron nitrate (for example, Fe (NO ₃ ) ₃ · 9H ₂ O) as a raw material for an iron catalyst, and The present invention was completed by finding that iron can be recovered from a carbon material (charcoal) using nitric acid at a high recovery rate, and that the recovered iron nitrate can be easily reused as a raw material for an iron catalyst.

Specifically, when Fe (NO ₃ ) ₃ · 9H ₂ O was added to larch wood flour and subjected to iron-catalyzed carbonization at 850 ° C, charcoal exceeding the conductive properties of U-Ni charcoal (U-Fe charcoal) In the dilute nitric acid cleaning performed to recover the iron, the crystallinity of the carbon is improved, and the hot-pressed body of this acid-washed charcoal (A-Fe charcoal) is made of KB, which is the highest grade conductive carbon on the market It has been found that it has very good conductive properties close to the blended molded body.

Ferric nitrate Fe (NO ₃ ) ₃ · 9H ₂ O is easily water-soluble (according to chemical handbooks, 6.25 g Fe / 25 ° C water 100 g) and is regenerated to its original composition by washing with 1M nitric acid. Disadvantages (3) and (4) are overcome. Furthermore, it is presumed that (1) is more advantageous than iron acetate (Tsuzuki Suzuki et al., 1988, Journal of the Wood Society, 34, 537-542). However, regarding (2), there is a concern about the generation of NOx. Therefore, wood carrying a predetermined amount of Fe (NO ₃ ) ₃ · 9H ₂ O was carbonized at around 850 ° C., and the composition of the generated gas was investigated by gas chromatography, but NOx was not detected. The reason for the non-detection of NOx is considered to be that the addition of iron salt promotes the generation of H ₂ and CO at 300 ° C. or less, and the reduction to N ₂ proceeds effectively. The charcoal conductivity of charcoal prepared at 850 ° C is the same for iron acetate and iron nitrate after washing with the corresponding acid, and the combined use of nitric acid is the result of the slightly higher nitric acid in terms of Fe recovery by acid washing. It is concluded that is practically advantageous.

The present invention is as follows.
[1] A method for producing a conductive carbon material,
Impregnating wood with iron nitrate aqueous solution,
Carbonize wood impregnated with iron nitrate aqueous solution,
The carbonized material is washed with an aqueous nitric acid solution, and iron is recovered from the carbonized material as iron nitrate.
Reusing the recovered iron nitrate aqueous solution for impregnation of wood,
The said manufacturing method including this.
[2] The method according to [1], wherein the wood is impregnated with an aqueous iron nitrate solution having a concentration of 1 to 5%.
[3] The production method according to [1] or [2], wherein the carbonization is performed at 800 to 900 ° C.
[4] The production method according to any one of [1] to [3], wherein the washing is performed with an aqueous nitric acid solution having a concentration of 0.1 to 1M.
[5] The production method according to any one of [1] to [4], wherein the washing is performed after pulverizing the carbonized material.
[6] The production method according to any one of [1] to [5], wherein the recovered aqueous iron nitrate solution is reused as it is for impregnation of wood.
[7] The method according to any one of [1] to [5], wherein the recovered aqueous iron nitrate solution is mixed with a newly prepared aqueous iron nitrate solution and then reused for impregnation of wood.
[8] The carbonized material obtained by the production method according to any one of [1] to [7] is mixed with wood flour, and the resulting mixture is hot-press molded to obtain a conductive molded body. A method for producing a conductor.

  According to the present invention, a method of producing a conductive carbon material (charcoal) by carbonizing wood using an iron catalyst, a carbon material (charcoal) exhibiting high conductivity is obtained, and at the same time as a catalyst. It is possible to provide a method capable of recovering iron to be used at a high recovery rate and reusing it for carbonization of wood.

  Although the present invention contributes to the development of the wood industry by expanding the use of wood, the use of raw wood flour as a matrix as a substitute for conventional plastics (polyethylene, epoxy resin, etc.) is significant. ) And 2) may be emphasized. 1) Overcoming the shortcomings of raw wood, which is poor in thermoplasticity and difficult to hot-press, 2) Promoting the utilization of biomass and removing oil, meeting the needs of the times.

The present invention is a method for producing a conductive carbon material,
Impregnating wood with iron nitrate aqueous solution [Iron nitrate aqueous solution impregnation step]
Carbonize wood impregnated with aqueous iron nitrate solution [carbonization process]
The carbonized material is washed with an aqueous nitric acid solution, and iron is recovered from the carbonized material as iron nitrate [washing process]
Reusing the recovered iron nitrate aqueous solution for impregnation of wood [reuse process]
Including that.

  FIG. 1 shows a method for producing a conductive carbon material and a method for producing a conductor from the conductive carbon material of the present invention.

[Iron nitrate aqueous solution impregnation process]
In this step, the wood is impregnated with an iron nitrate [Fe (NO ₃ ) ₃ · 9H ₂ O] aqueous solution.
The wood to be used is not limited to tree species, but, for example, larch, spruce, todomatsu, cedar, white birch, and birch are suitable. The form can be powder, chip or small diameter wood.

  The concentration of the iron nitrate aqueous solution can be appropriately determined in consideration of the tree species and form of the wood used, the optimum amount (concentration) as a carbonization catalyst, etc., and can be, for example, a concentration range of 1 to 5%. However, it is not limited to this range. The optimum amount (concentration) of iron contained in the wood as the carbonization catalyst is, for example, in the concentration range of 0.5-3%.

  Wood is immersed in an iron nitrate aqueous solution and impregnated with iron nitrate. The immersion time and temperature in the iron nitrate aqueous solution can be appropriately determined according to the amount of iron nitrate aqueous solution to be impregnated, and can be, for example, 6 to 24 hours at room temperature (10 to 30 ° C.).

[Carbonization process]
Next, the wood impregnated with the iron nitrate aqueous solution is carbonized.
Carbonization can be performed, for example, by performing a heat treatment at 800 to 900 ° C. in an N ₂ stream for 30 minutes to 2 hours, for example. Instead of the N ₂ air flow, heat treatment can be performed in another inert gas atmosphere.

In general, when dry wood immersed in highly concentrated nitric acid (aqueous solution) is heated, generation of brown gas is observed below 200 ° C. Therefore, when heating wood containing nitric acid, a considerable amount of NO ₂ is expected to be generated together with the nitric acid gas. However, if the amount of nitric acid contained is small, the amount of NO ₂ generated will be small. In the production method of the present invention, Fe charcoal is immersed in dilute nitric acid, recovered as Fe (NO ₃ ) ₃ .9H ₂ O, and then immersed in wood as follows. Since some amount of nitric acid remains in the recovered liquid, it is basically appropriate to vaporize and recover most of the nitric acid while concentrating under reduced pressure. During this concentration process, Fe (NO ₃ ) ₃ · 9H ₂ O is supported on the wood, but at the same time, some amount of nitric acid is also absorbed. Since carbonization is usually performed in an N ₂ gas stream, it is preferable to set the N ₂ flow rate so that NO ₂ (NOx) is below the detection limit.

Even concentration below the detection _{limit, Fe (NO 3) 3 ·} 9H 2 O from NO ₂ (NOx) is not the not generated. However, NO ₂ (NOx) is less likely to be generated from Fe (NO ₃ ) ₃ · 9H ₂ O than nitric acid. Therefore, it is appropriate to set the N ₂ flow rate in consideration of the amount of NO ₂ (NOx) from nitric acid and Fe (NO ₃ ) ₃ · 9H ₂ O. The amount of NO ₂ (NOx) generated from Fe (NO ₃ ) ₃ · 9H ₂ O is measured in Examples.

[Washing process]
The carbonized material is washed with an aqueous nitric acid solution, and iron is recovered from the carbonized material as iron nitrate.
For cleaning the carbonized material with an aqueous nitric acid solution, for example, an aqueous nitric acid solution having a concentration of 0.2 to 4M can be used. Cleaning can be performed by immersing the carbonized material in an aqueous nitric acid solution and stirring at room temperature for 3 hours or more. After washing, the carbonized material from the aqueous nitric acid solution is collected by filtration, washed with water. The aqueous nitric acid solution obtained as the filtrate contains iron eluted from the carbonized material as iron nitrate.

  Cleaning can also be performed after grinding the carbonized material. By recovering the pulverized product, the iron recovery rate can also be raised. The carbonized material after washing can be dried at room temperature or by heating. For the pulverization of the carbonized material, first, if it is a chip material, the particle size is reduced to a few mm (coarse powder) with a general pulverizer, and then ball milling is performed to adjust the particle diameter to 10 μm or less (fine powder). If it is a powder, the first coarse pulverization can be omitted. The fine powder is then kneaded with an adhesive and hot-press molded, but in order to make the molding easier, it can also be performed by wet ball milling with suitable binder particles and solvent added to the coarse powder. .

[Reuse process]
The recovered iron nitrate aqueous solution can be reused for the impregnation of wood. At the time of reuse, the recovered iron nitrate aqueous solution can be used as it is, or the concentration can be adjusted by newly adding iron nitrate or an iron nitrate aqueous solution to the recovered iron nitrate aqueous solution.

In the present invention, iron nitrate is used, but the use of iron nitrate is more advantageous than the case of using (basic) iron acetate Fe (OH) (CH ₃ COO) ₂ in the same amount as iron. This is because regeneration and recovery can be performed more easily.

  Furthermore, since the iron recovery rate is high in the nitric acid cleaning, the effect of improving the crystallinity of carbon is great, and there is an advantage that the conductivity of carbon is further improved.

Furthermore, the regeneration of iron nitrate is easy and quantitative. Moreover, since the solubility with respect to water is high, the impregnation addition operation to the wood after collection | recovery is advantageous compared with iron acetate.
The chemical composition of iron acetate is approximately Fe (OH) (CH ₃ COO) ₂ , and the chemical form of iron in the acetic acid cleaning solution is unclear and it is difficult to have a constant composition. This means that it is difficult to control the iron concentration. Since the solubility in water is low, it is necessary to impregnate the wood with an aqueous solution at a low concentration. In contrast, iron in the nitric acid cleaning solution has a constant composition of Fe (NO ₃ ) ₃ · 9H ₂ O and has high solubility in water, so that it can be impregnated with an aqueous solution at a high concentration. It is preferable to remove some water from the wood after impregnation and before carbonization, from the viewpoint of suppressing the thermal energy required for carbonization, but iron nitrate that can reduce the amount of water removal requires less labor and energy. There is also an advantage that it can be done.

  Furthermore, this invention relates to the manufacturing method of the conductor which mixes the carbonized material obtained with the manufacturing method of the said invention with wood flour, and heat-press-forms the obtained mixture and obtains an electroconductive molded object.

  The carbonized material obtained by the production method of the present invention is mixed with wood flour. The carbonized material is suitably a pulverized product that is pulverized and appropriately classified to have a predetermined particle size. The predetermined particle diameter of the carbonized material is suitably in the range of 0.1 to 5 mm from the viewpoint of moldability.

  The material of the wood powder is not limited to tree species, but for example, larch, spruce, todomatsu, cedar, white birch, and birch are suitable. The particle size of the wood powder is suitably in the range of 0.3 to 0.6 mm from the viewpoint of moldability. Furthermore, it is appropriate that the wood flour is adjusted to a moisture content of 3 to 20%, preferably 5 to 8%, from the viewpoint of moldability.

  The mixing ratio of the pulverized product of the carbonized material and the wood powder can be appropriately determined in consideration of the moldability, the conductivity of the molded body, etc. It is appropriate to be in the range of ~ 1000 parts by mass, preferably 50 to 500 parts by mass.

  Water can be further added to the mixture of the carbonized material and the wood flour. Addition of water is preferable from the viewpoint of obtaining a homogeneous conductive molded body. The amount of water added is suitably in the range of 10 to 50 parts by weight, preferably 20 to 40 parts by weight with respect to 100 parts by weight of the mixture of the pulverized carbonized material and wood flour.

A mixture of the carbonized material and wood powder is hot-press molded to obtain a conductive molded body. Hot pressing can be performed as follows. For example, an appropriate amount of the above mixture is taken in a metal hollow container, sandwiched between a metal base plate and a top plate of the same quality, compressed with a hot press at room temperature for several tens of minutes to 10 kgf / cm ² , and then raised to 120-160 ° C. Warm and hold at 100-300 kgf / cm ² for 10-30 minutes. The preferable conditions for this heat compression (hot pressure) are holding at around 140 ° C. and around 200 kgf / cm ² for about 20 minutes.

1 Addition of nickel salt and iron salt and carbonization Particle size 0.3-2.0mm To larch wood flour (CH ₃ COO) ₂ Ni ・ 4H ₂ O and Fe (NO ₃ ) ₃・ 9H ₂ O as metal respectively 2wt%, 3wt % Was added by impregnation with an aqueous solution, and then U-Ni charcoal was treated at 900 ° C. for 1 h in a N ₂ stream to obtain U-Fe charcoal at 850 ° C. for 1 h. For reference, the additive-free wood powder was carbonized at 900 ° C. for 1 h, and the obtained charcoal was described as None charcoal.

2 Acid cleaning and metal content
U-Ni charcoal and U-Fe charcoal were stirred and immersed in 1M nitric acid at room temperature for 24 hours, washed with distilled water, and dried under reduced pressure at 50 ° C. to obtain A-Ni charcoal and A-Fe charcoal. The contents of Ni and Fe before and after the acid cleaning were determined by dissolving the 800 ° C. combustion residue of each charcoal in aqua regia and measuring each metal concentration by atomic absorption method.

3 X-ray diffraction The above charcoal is irradiated with Cu-Kα rays to measure a diffraction pattern of 3-70 °, and the average crystallite diameter in the thickness direction from the diffraction line near 26 ° derived from crystalline carbon (T component) Lc and its interlayer distance d002 were calculated. As another crystallinity parameter, a value obtained by dividing the intensity of the diffraction line by that of LO (specific intensity, RPI ⁸⁾ ) was also calculated. Moreover, the existence form was identified from the peak of nickel and iron. The same measurement was performed for DB, KB, and RO, and Lc, d002, and RPI were calculated.

4 Mixing ratio and grinding of carbon and wood flour The above-mentioned 5 kinds of charcoal 0.5-2.0g, larch wood flour of 0.3-0.6mm and 0.6-1.0mm particle size (moisture is 6.5% and 7.5% respectively) 3.5-2.0g After adding 0 ml, 1 ml and 2 ml of distilled water and kneading lightly, the mixture was pulverized in a planetary ball mill at 430 rpm for 5-40 minutes. The balls used for grinding were made of agate with a particle size of 15 mm. The particle diameter after grinding by measuring the particle size distribution by a laser refractometer was calculated an average particle diameter D _50.

5 Hot press forming Transfer the crushed contents to a stainless steel container, cool for 10 minutes at 50Kg / cm ² , then heat up to 120-160 ° C for 10-30 minutes and hot press at 100, 200, 300Kg / cm ² for 10-30 minutes did. In addition, it was formed into a solidified disk having a diameter of 20 mm and a thickness of about 2 mm under appropriate hot pressure conditions.

6 Volume resistivity, EMS performance, impedance measurement Volume resistivity (Ω · cm, reciprocal of conductivity) for each molded disk by the four-probe method, 50-800MHz electromagnetic shielding effect (dB) by coaxial cavity tube ^{7) The} Z plot AC impedance was measured at 1-10,000 Hz.

7 Grinding, hot pressing and conductive properties of commercially available conductive carbon
DB, KB, and LO discs were prepared by applying the blending ratio with the wood flour judged appropriate from the results of 6, the grinding conditions, and the hot pressure conditions, and their conductive properties were examined in the same manner as in 6.

[Results and discussion]
Crystal structure of charcoal Figure 2 is an X-ray diffraction pattern of type 5 charcoal. As is clear from this figure, None charcoal is amorphous, but U-Fe charcoal shows a T component diffraction line around 26 °. However, the T component of U-Fe charcoal is not generated as much as U-Ni charcoal, indicating that the carbon crystallization promoting action of Fe is smaller than Ni. The effect of Fe catalyst is small, whereas in U-Ni charcoal, there is metallic nickel, which is an active species, in U-Fe charcoal, iron carbide (cementite, Fe ₃ C) is generated instead of metallic iron. It is convinced from being. However, the peak intensity of A-Fe charcoal exceeded that of U-Fe charcoal, and the dilute nitric acid cleaning increased the crystallinity of carbon as in the case of Ni charcoal. This increase in carbon crystallinity is thought to be due to the removal of metal not only increasing the carbon concentration but also improving the orientation of the crystallites10 ⁾ .

  Table 1 compares the crystal structures of these five types of charcoal with DB, KB, and RO, and the metal content in each charcoal is also noted. Compared to LO, all four types of charcoal composed of T component are greatly inferior in Lc and RPI, but the crystallinity of Ni coal exceeds that of DB, and the crystallinity of A-Fe coal is close to that of DB. As is well known, KB is amorphous carbon in X-ray, and its X-ray diffraction pattern is similar to that of None charcoal. Therefore, the order of crystallinity of carbon is LO >> A-Ni coal> Ni coal> A-Fe coal ≧ DB> Fe coal >> KB = None coal. Assuming that there is no carbon loss due to acid cleaning, the removal rates of Ni and Fe are about 95% and about 80%, respectively. It has something to do with it.

  RPI in Table 2 is an X-ray intensity ratio between the turbostratic carbon (T component) and graphite, and the larger this value, the more crystallization of the carbon progresses. Table 2 shows the crystal structure of carbon after the previous washing with 1M acetic acid and 1M nitric acid. The results show that the crystallinity increases (RPI increases) by acid cleaning, and the effect is greater when pulverized and acid cleaned. It can be seen that nitric acid cleaning is more advantageous than acetic acid cleaning.

2 Hot-press formability and proper hot-press conditions The result of having investigated is illustrated. From these results, the most important factors affecting the formability are the particle size of the wood flour and the amount of water added. If you add 1.0 ml of water to 0.3-0.6 mm wood flour and grind it for 10 minutes or more, it was used. It was found that even if the amount of Fe charcoal was increased to 1.5g regardless of the hot-pressure condition, it could be formed into an apparently uniform and considerably hard disk. In other words, the disks marked with ○ have not been measured for strength, but if they have excellent conductive properties similar to those of DB and KB blends, they can be used in the same applications as ordinary conductive plastics (automobiles, home appliances, etc.) In the electrical system of this system, integrated wiring with plastic cases, three-dimensional wiring boards for electricity, electronic equipment, etc., electronic parts such as switches, connectors, etc.) were sufficiently rigid. The other four charcoal showed the same hot pressing behavior as above, and the presence or absence of metal and acid washing and the difference in catalyst type were not significant. In addition, the ability of wood flour to adjust the size and amount of added water as an appropriate binder, and thus the role as a matrix, is because the carbohydrate components exposed by the decay of wood cells soften and heat flow. Conceivable. Softening and deformation of logs and plates when heated in a water-containing state is a wood processing technology well known as “bending wood”. If this technical principle is understood, it will be useful as a carbon matrix for wet wood flour. Application is easy to come up with, so it is not a specially new technology. Molding is not possible with 2.0g charcoal, which is an anticipated situation indicating that there is a limit to the binder capacity of wet wood flour.

  Table 4 shows the volume resistivity of the disk sample marked with a circle in Table 3. Since this value is a reciprocal of conductivity, a smaller value is given to a higher performance conductor. Although the conductivity is governed by the conductivity of the constituent carbon particles themselves, it is also greatly influenced by the density (density) of the molded body, and from this value, the suitability of the hot press condition can be evaluated and judged. In addition, since it is considered that the added water and the water in the wood flour are almost completely removed during the hot pressing, the carbon concentration on the dry basis is also added for reference.

The volume resistivity drastically decreases as the proportion of charcoal increases, which is evidence that U-Fe charcoal has good electrical conductivity. From the relation ¹¹⁾ , the performance is in the middle of KB and DB. Therefore, it is judged that U-Fe charcoal has sufficient performance as “conductive carbon”. This confirms that the hot-press molding has been performed successfully, with a high-performance conductor with a charcoal / wood powder of 1.5g / 2.5g (charcoal concentration of 39.3%) of less than 1.0Ω · cm in any condition. there were. Therefore, any combination of temperature, time, and pressure of 120-160 ° C, 10-30 minutes, 100-300Kg / cm ² may be used for hot pressing, but somewhat higher than 160 ° C, 200Kg / cm ² It seems to be disadvantageous. Differences in the hot-pressing conditions of the other four charcoal did not have a significant effect on the volume resistivity, and as a whole, 120-140 ° C, 20 minutes, 200-300 Kg / cm ² was judged appropriate. DB, KB, LO even 0.3-0.6mm particle DBH powder 2.5g its 1.5g, when mixed 10 minutes with water 1.0 ml, hot pressing conditions 140 ° C., 20 min, relatively rigid disc at 200 Kg / cm ² was gotten. Therefore, all 5 types of charcoal and 3 types of conductive carbon were mixed and hot-pressed under these conditions and used for evaluation and comparison of the conductive properties of 3.3.

3 Comparison of the effect of acid cleaning with that of commercially available conductive carbon Fig. 4 compares the conductive performance of five charcoal samples. The impedance was given as a value at 1000 Hz, and the electromagnetic shielding performance was given as the minimum value in the measurement range. From this figure, it can be seen that the conductive properties of A-Fe charcoal are better than those of A-Ni charcoal. Moreover, since A-Fe charcoal> U-Fe charcoal in all properties, the effect of improving the crystallinity of carbon by nitric acid cleaning (Fig. 2, Table 1) appears. However, the superiority of U-Fe charcoal over U-Ni charcoal in conductivity and EMS performance means that factors other than the crystal structure of carbon are more importantly involved. The most prominent factor that can explain this is the size of the constituent nanoparticles. That is, according to TEM observation (Fig. 5), U-Ni charcoal is about 50 nm, U-Fe charcoal is about 30 nm, and the latter is considered to be more advantageous than the former in terms of primary particle connection, that is, contact. Since these particle sizes do not change upon acid washing, it is suggested that iron-catalyzed carbonization is essentially superior to nickel-catalyzed carbonization in that it can produce smaller basic unit particles.

  Figure 6 compares DB, KB, and LO. The reason why the performance of A-Fe charcoal does not reach LO is thought to reflect the difference in the crystal structure of carbon, but the conductivity and EMS performance are better than DB, and the former performance is almost equivalent to KB. I know that there is. Overall, A-Ni charcoal is between DB and KB, but A-Fe charcoal is rather highly conductive carbon that is close to KB.

4 Influence of mixing and grinding time Grinding of wood flour and carbon raw material is indispensable for uniform composition of the mixture, but on the other hand, if the treatment becomes severe, excessive particle disintegration or aggregation, carbon crystallinity degradation, etc. This is expected to adversely affect the conductive performance of the molded body. Therefore, this processing needs to be performed under appropriate conditions, and the processing time becomes an important factor as a real problem. Table 5 and Figure 7 is obtained by examining the crystal structure, on the conductive performance of the molded article the influence of the time the respective average particle diameter D ₅₀ and carbon for A-Fe charcoal. From the treatment time of 5 minutes to 10 minutes, it can be interpreted that the pulverization of the particles effectively proceeds and the crystal structure of carbon is destroyed, but as a result of improving the hot press moldability, conductivity and EMS performance are increased. On the other hand, there is no significant difference in D ₅₀ between 10 minutes and 20 minutes, but when the length is increased from 20 minutes to 40 minutes, the particles agglomerate severely, which leads to a deterioration in moldability and a large decrease in conductivity and EMS performance. Can be explained. Therefore, for A-Fe charcoal, mixing and grinding for 10 to 20 minutes is appropriate, and it can be said that it is not necessary to control the treatment time so closely. This process is relatively flexible in time, as was the case with A-Ni charcoal, DB, KB, and LO, with no significant differences in conductivity properties appearing at 10 and 20 minutes. That is, it is reconfirmed that FIG. 6 is accepted as reflecting the intrinsic conductive characteristics of each carbon. In addition, since aggregation of particles can be confirmed more clearly by SEM observation, it is considered better to rely on this visual means to set an appropriate mixing and grinding time.

Measurement of NO + NO2 concentration in reactor outlet gas
10 g of larch wood flour containing 3% Fe (NO ₃ ) ₃ · 9H ₂ O dried under reduced pressure at 50 ° C was placed in a vertical stainless steel reactor and heated to 50 ° C while flowing N ₂ at 130 ml / min. Then, the temperature was raised from 50 ° C. to 850 ° C. at 10 ° C./min, and held at 850 ° C. for 1 hour (this is a process for preparing 850 ° C. Fe charcoal). During this period, (1) 50 ° C to 200 ° C and (2) 200 ° C to 350 ° C reactor outlet gas were collected in 5 L gas bags, respectively, and (1) and (2) nitrogen oxides (NO + NO ₂ ) concentration was measured with a Gastec detector tube (scale range 10-250 ppm, 100 ml aspirated in 1 minute, 2 aspirations, detection limit 2 ppm). As a result, no yellow coloration was observed in both (1) and (2), and the NO + NO ₂ concentration was determined to be 2 ppm or less. By the way, 10 g of larch-added larch wood flour contains 1.0 g of (NO ₃ ) _{3, and} 0.741 g of NO ₂ is present. This total amount is 0.741g / 3900ml = 190ppm be generated as _{NO 2, (1) + (} 2) < a 4 ppm, the incidence of the NO ₂ is <2.1%. Since it was actually below the detection limit, NO + NO ₂ may be regarded as non-occurring. Note that Fe (NO ₃ ) ₃ · 9H ₂ O is completely Fe ₃ O ₄ at 340 ° C. according to the thermogravimetric curve in N ₂ (Suzuki et al., Journal of the Wood Society, 34, 537-542, 1988). . Therefore, it is unlikely that Fe (NO ₃ ) ₃ · 9H ₂ O decomposes while generating NOx at 350 ° C. or higher in the above carbonization.

[Conclusion]
Larch wood powder was added with 3% by weight of Fe (NO ₃ ) ₃ · 9H ₂ O as iron by impregnation with aqueous solution, and then carbonized at 850 ° C-1h. When the obtained charcoal (U-Fe charcoal) was mixed and pulverized with wet wood flour under appropriate conditions, and hot-pressed, it showed better conductive properties than the 900 ° C nickel-added charcoal (U-Ni charcoal) compact. . When U-Fe charcoal was washed with dilute nitric acid at room temperature for iron recovery, the crystallinity of the carbon increased, and the conductive properties of this acid-washed charcoal (A-Fe charcoal) compact were further improved. Its conductivity characteristics exceed those of acid-washed U-Ni charcoal (A-Ni charcoal) molded products and commercially available conductive carbon DB molded products, and it is very close to that of molded products containing KB, the highest grade conductive carbon. It was excellent.

  The present invention is useful in the field relating to the production of conductive carbon.

The manufacturing method of the conductive carbon material of this invention and the manufacturing method of the conductor from a conductive carbon material are shown. FIG. 3 is an X-ray diffraction pattern of the five types of charcoal obtained in the examples. The relationship between the addition amount of a conductive carbon material and volume resistivity is shown. It is the result of comparing the conductive performance of five charcoal samples. It is a TEM observation result of U-Fe charcoal and U-Ni charcoal. It is a comparison result of conductive performance between DB, KB and LO of A-Fe coal and A-Ni coal. It is the result of investigating the influence of mixing and pulverization time on the average particle diameter D50 and the crystal structure of carbon and the conductive performance of the molded body for A-Fe charcoal.

Claims (8)

A method for producing a conductive carbon material, comprising:
Impregnating wood with iron nitrate aqueous solution,
Carbonize wood impregnated with iron nitrate aqueous solution,
The carbonized material is washed with an aqueous nitric acid solution, and iron is recovered from the carbonized material as iron nitrate.
Reusing the recovered iron nitrate aqueous solution for impregnation of wood,
The said manufacturing method including this. 2. The production method according to claim 1, wherein the wood is impregnated with an aqueous iron nitrate solution having a concentration of 1 to 5%. Carbonization is a manufacturing method of Claim 1 or 2 performed at 800-900 degreeC. The production method according to any one of claims 1 to 3, wherein the washing is performed with an aqueous nitric acid solution having a concentration of 0.1 to 1M. The manufacturing method according to any one of claims 1 to 4, wherein the cleaning is performed after pulverizing the carbonized material. 6. The production method according to claim 1, wherein the recovered iron nitrate aqueous solution is reused for impregnation of wood as it is. 6. The method according to claim 1, wherein the recovered iron nitrate aqueous solution is mixed with a newly prepared iron nitrate aqueous solution and then reused for impregnation of wood. A method for producing a conductor, wherein the carbonized material obtained by the production method according to any one of claims 1 to 7 is mixed with wood flour, and the resulting mixture is hot-press molded to obtain a conductive molded body. .