JPS5935011A - Molded article of porous carbon and its preparation - Google Patents

Abstract

PURPOSE:To mold the titled molded article having a high porosity, sharp pore diameter distribution and improved mechanical strength, by molding a mixture of short carbon fiber, binder resin, and soluble particulate substance under heating and pressure, eluting the soluble paticulate substance, calcining the resultant substance. CONSTITUTION:A mixed mass of (A) 100pts.wt. short carbon fiber having about 3-30 diameter of fiber and <= about 2mm. length of fiber and (B) 20-100pts.wt. bnder resin (e.g., phenol resin) is crushed. 100pts.wt. prepared crushed material is blended with (C) 20-100pts.wt. soluble particulate substance having a given particle diameter and prticle size distribution, the blend is pressed under heating and molded into the desired shape. The prepared molded article is immersed in (D) a solvent and the soluble particulate substance is dissolved and removed. The resultant substance is dried, calcined at about 800-1,200 deg.C, and carbonized. For example, polystyrene and benzene, starch and water, etc. may be used as a combination of the soluble particulate substance and the solvent.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides carbon edge HD. The present invention relates to a porous carbon molding machine using as a base material and a method for producing the same. More specifically, the present invention relates to a porous carbon molded product having a large porosity, a sharp pore size distribution, and excellent mechanical strength, and a method for producing the same.

In recent years, porous carbon molded products based on carbon fibers have become increasingly popular in fields such as filter materials and electrode substrates for fuel cells. In particular, the latter requires a porous carbon molded product with excellent conductivity, chemical stability and mechanical strength, high porosity and a sharp open pore size distribution.

Porous carbon fiber molded products based on carbon fibers are manufactured by various methods as described below.

One method is to coat a web of carbon fibers with pyrolytic carbon due to its chemical stability (U.S. Patent No. 11
3, 829, 327). The carbon fiber paper obtained by this method has excellent chemical stability, aroma, and conductivity, but it is not economical because it involves an expensive vapor deposition process, and it is necessary to increase the porosity. This has the disadvantage that mechanical strength decreases.

Another method for producing a porous 'pL carbon sheet-like molded product is as follows:
An alcohol with a boiling point of 150° C. or higher is used as a preliminary binder to form the pitch fiber mat;
This method then heat-treats the Tonogitsuchi weft fiber mat in a non-oxidizing atmosphere (US Pat. No. 3,991,169). According to this method,
Only porous carbon sheet-like molded products with high porosity and good conductivity but not necessarily excellent mechanical strength can be obtained.

Furthermore, as another method, a carbon fibrous web obtained by infusible and carbonized webs made of pitch fibers produced by blow spinning is disclosed (US Pat. No. 3,966).
No. 0,601). According to this method, a porous carbon sheet with excellent electrical conductivity can be obtained, but it has the disadvantage that mechanical strength decreases if the porosity is significantly reduced.

In addition to the above-mentioned drawbacks, a common drawback of the above methods is that it is difficult to narrowly control the pore size distribution; , unevenness tends to occur on the substrate surface with respect to gas diffusion, which may reduce efficiency.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of conventional carbon molded products, and to create a porous product that has a large porosity and a sharp pore size distribution compared to that of W products, and has excellent electrical conductivity and mechanical strength. Our goal is to provide carbon molded products. A further object of the present invention is to provide a method for producing such a porous carbon molded article.

The porous carbon molded product obtained by the present invention has continuous pores, the porosity is 50-85%, the mechanical strength is
In particular, the crushing strength is 50Kg/lyn" or more.The pore radius is 3 to 30% depending on the purpose of the desired carbon molded product.
The diameter can be arbitrarily selected within the range of 150μ, and in the pores (・
¥] distribution is extremely narrow. That is, in the pore radius 1'' [- number distribution histogram shown in the attached Figures 1 and 3, more than 60% of the pores have a difference between the lower limit pore radius and the upper limit pore radius. It has a pore radius distributed within a range of 20μ. Such a distribution covers pore radii in which more than 60% of the pores fall within a narrow range, such as IO~30/7, 30-50μ, and especially 5-10μ when the average pore radius is small. This is the distribution. These properties provide extremely superior secondary properties compared to conventional porous carbon molded articles.

A porous carbon molded article having the above characteristics can be obtained by the manufacturing method according to the present invention. That is, a soluble particulate material is mixed into a mixture of smoked carbonaceous fibers and a binder resin, and after heating and pressure molding, the soluble particulate material is eluted and further fired.

The smoked carbonaceous fiber used in the present invention is obtained by cutting carbonaceous fiber with a fiber diameter of 3 to 30 μ into pieces of 2 to 1III+ or less.
What is the fiber length? If it exceeds the throat, it will become entangled and pill-like during the process leading to molding, making it impossible to obtain the desired porosity and pore size distribution. txt as a carbonaceous fiber precursor.

Any material such as pitch, polyacrylonitrile or rayon can be used.

The binder resin used in the present invention is a phenol resin, furfuryl alcohol resin, or the like, which serves as a bonding material after carbonization and is useful for bonding between carbon fibers. The mixing amount of the binder resin is 20 to 1 part by weight of the short flame fiber.
00 polydispersion part. If the amount of the binder resin mixed is less than 20 overlapping parts, the binder resin will be too small to completely fix the fibers during molding. Furthermore, if more than 100 parts by weight of the binder resin is mixed, the surface rfii of the soluble particulate matter is coated with the binder resin, resulting in incomplete elution of the soluble particulate matter and a predetermined continuous pore diameter and porosity. I won't be able to do it.

The pores of the coal car molded article of the present invention are substantially determined by soluble particulate matter traps, and in the production method of the present invention, a predetermined particle size is used in order to adjust the porosity and pore size. A soluble particulate material having a distribution is added to the smoked carbonaceous fiber and binder resin mixture described above.

The distribution is within μ.

The soluble particulate material may be either organic or inorganic as long as it is solid at the temperature during molding and is soluble in a suitable solvent. Table 1 shows soluble particulate matter that can be used in the present invention. As the solvent for dissolving and removing the soluble particulate matter after molding, any solvent can be used as long as it can dissolve the particulate matter. Select and use an appropriate solvent from those listed below.

(Own) Table 1 (Note) DMF...dimethylformamide, THF...
・TetrahyP Lofuran, MPK...The particle size of the methyl ethyl ketone soluble particulate material can be arbitrarily determined depending on the pore size of the desired carbon molded product, but the particle size distribution is as shown in Table 2 as an example. You must choose accordingly. But 2
However, it is of course not limited to this.

Table 2 For example, using organic soluble particulate matter, 60% of the pores
When manufacturing a charcoal molded product having a pore radius within the range of 5 to 10μ, the particle radius of the organic soluble particulate material used is 10 to 50μ as shown in the top row of Table 2.
is within the grain radius range and more than 70% of the excretion
Select organic particulate materials within the 40 micron particle radius range.

The amount of soluble particulate matter to be added is in the range of 20 to 100 parts by weight based on 100 parts by weight of the mixture of short carbon fiber and binder resin, depending on the desired porosity and pore radius of the carbon molded product. selected from.

Hereinafter, the method for preparing a porous carbon molded article of the present invention will be described in more detail. In the following description, the case where the pitch is used as an all-carbon fiber precursor will be particularly described.

Oxidized pitch fibers obtained by infusibility treatment of raw material pitch fibers are heat-treated at 400 to 800° C. in an inert gas atmosphere in order to maintain strength so as not to break or break during molding. Heat-treated nine carbon fibers (hereinafter simply referred to as carbon fibers) are cut into lengths of two fins or less.

A binder resin such as a phenol resin is mixed with a solvent such as methane or alcohol, and cut carbon fibers are immersed in a solution in which the resin is completely dissolved for 30 minutes to 2 hours, so that the carbon fiber surface is almost uniformly coated. Coat the bonding material resin. If the dipping time is too short, too little binder resin will adhere to the surface of the carbonaceous fibers, making it impossible to completely fix fiber #4 during molding. Further, if the heating time is longer than 2 hours, there is no particular problem, but it is not preferable in terms of productivity.

After soaking for a specified period of time, pass through a filter for 4 to 50 minutes.
Heat and dry at an appropriate temperature of ~70°C for 30 minutes to 2 hours. If the drying temperature is too high, the binder resin will melt and solidify at this point, so the temperature must be selected appropriately. For the same reason, the drying time should also be selected appropriately.

After the drying is completed, the produced lumps are crushed, and soluble granular substances having a predetermined particle size distribution are added to and mixed with the crushed pieces. At this time, if the particulate matter and the carbonaceous fibers are not mixed uniformly, uneven density will occur in the pores in the molded product.

The homogeneous mixture thus obtained is processed using a mold Sores or a roller at an appropriately set temperature and pressure depending on the type of binder resin and the desired size, thickness and shape of the molded product. Press-formed using methods such as continuous pressing. If the temperature during molding is too high, depending on the type of granular material added, it may change in quality and later be eluted into the solvent and become separated. If the temperature is too low, it will take a long time to cure, which is unfavorable in terms of productivity. Furthermore, if the pressure is too high, the carbonaceous fibers will break and the soluble particulate matter will be deformed, making it difficult to obtain the desired porosity and pore diameter. If the pressure is too low, there will be areas where the bonding by the binder resin is incomplete, and layered cracks will likely occur in the molded product.

After molding, 30% per 1mm thickness depending on the thickness of the molded product.
Post-cure at a suitable temperature for minutes to 1 hour.

After post-curing, a suitable solution I capable of dissolving the soluble particulate material
The molded product is immersed in J1 for 30 minutes to 4 hours to elute particulate matter. At this time, in the case of organic particulate matter, even if the particulate matter is not completely eluted, it will be carbonized during the subsequent high-temperature firing, so there is no risk of contamination of impurities into the carbon molded product. Regardless of whether it is organic, inorganic, or gold,
If the elution is incomplete, the shape of the pores after firing becomes complicated and the diffusion ability is reduced, so a sufficiently long elution time will yield a better molded product. However, if it is too long, it will lead to a decrease in productivity.

0.0 to prevent distortion of the molded product from which the particulate matter has been eluted.
Dry while applying a load of about 05 to I K17 cm.

After drying, it is fired and carbonized at a temperature of 800 to 1200°C.

At this time, the carbonaceous fibers having surface activity and the binder resin adhere to each other with good affinity (1), and as a result, the carbonaceous fibers are firmly bonded to each other by using the binder (7).

-1, and bake at 1800 to 2400°C as necessary.

The present invention will be explained below with reference to Examples.

Example 1 Carbonaceous fibers heat-treated at 600°C and having an average diameter of 1271 and used as a pitch raw material are cut to a size of 2 or less] 7, methanol 1
00 tons of phenolic resin 45 layers were immersed in a binder resin solution for 1 hour, filtered, and further heated at 60 to 70°C.
Dry smoked for about 3 hours. The amount of 7χ phenol resin attached to the surface of the carbonaceous fiber was 30 parts by weight per 100 parts by weight of the carbonaceous fiber.

This dry mixture is crushed, and the particle radius is 10 to 50μ (about 70% of which is 2
67 parts of polyvinyl alcohol particles previously sieved to a particle size of 0 to 40μ) were added and mixed uniformly.

The homogeneous mixture thus obtained was put into a mold, and
Pressure molding was carried out under the conditions of 140°C and 140°C.

Furthermore, the phenol resin was left to stand still in a 140°C oven for 4 hours to fully harden the fc.

The molded product obtained by KL7 in this way was immersed in hot water at 70°C for about 4 hours.
Soaked in oil for an hour. At this time, 150% or more of the polyvinyl alcohol f1 in the molded body was eluted into the warm water.

1) The molded body fK: 140'C10 was dried under a load of 1 Kg/c-. Then 1000℃ and then 2000℃
Calcined at ℃.

In this way, 1! ) The carbon molded product has a porosity of 68
%, compressive breaking strength 100 to 9/cm”, volume resistivity (
(in-plane) 9×10-”Ω sub.

! Fig. 1 shows the number of pore radius nutograms in carbon molded articles of t, 9, and l.

As shown in Figure 1, more than 75% of the pores are 5~10μ
This allows the pore radius to be within the range of , and shows a sharp pore radius distribution that was previously unobtainable.

Although conventional porous carbon molded articles having a porosity of about 70% had low compressive fracture strength, the porous carbon molded article obtained by the present invention is far superior.

In addition, for comparison fiC, a carbon molded article was obtained which was made of carbon fiber prepared in the same manner as in this example and only a phenol resin (that is, a system that did not contain polyvinyl alcohol, which is an organic particulate material).

The frequency distribution histogram of the pore radius of the carbon molded product is 1@
Shown in Figure 2. The carbon molded product contains about 40% of the pore radius within the range of 5 to 1()μ, and has a more eroded distribution compared to the carbon molded product of the present invention.

Moreover, the calculated porosity was about 25%, and the material was not porous, which is the object of the present invention.

Furthermore, the ratio of carbon fiber and binder phenol is changed without using polyvinyl alcohol, and the porosity is approximately 70%.
A porous carbon molded article was manufactured, but the compressive fracture strength was so brittle that it could not be measured.

Crushed dry mixture io obtained in the same manner as in Example 1
o Add 60 parts by weight of sugar particles, which have been sieved to a grain radius of 30 to 70 μm, to the heavy press section and mix uniformly.

The homogeneous mixture thus obtained was put into a mold, and
Pressure molding was carried out under the conditions of k(q/(J) and 140°C.

Furthermore, the phenol resin was left to stand still in a 140° C. oven for 4 hours to fully cure the phenol resin. The molded body thus obtained was
It was immersed in warm water at ℃ for about 4 hours.

Figure 1 Approximately 60% of the sugar in the molded body was dissolved into the hot water.

Furthermore, the molded body was heated at 140°C with a load γ of 0.1 Kf/crn2.
Dry under. Thereafter, it was fired at 1000°C and then at 2000°C. The thus obtained carbon molded product had a porosity of 65%, a compressive breaking strength of 110 Kg/cmt, and a volume resistivity of 9×10-”Ωcfn (in-plane).

Further, a frequency distribution histogram of the pore radius in this carbon molded product is shown in FIG. As shown in Figure 3, 70
More than % of the pores had a pore radius within the range of 10 to 30/7, showing a sharp pore size distribution.

[Brief explanation of the drawing]

Figure 1 shows the shape of the porous carbon molded product of the present invention (Example 1).
The frequency distribution histogram of one hole radius, Figure 2 is for comparison of soluble particulate matter f! - Histogram of the frequency distribution of the pore radius of the molded product obtained without using carbon fibers. FIG. 3 is the histogram of the frequency distribution of the pore radius of the porous carbon molded product of the present invention (Example 2). mJL half-sex (JJ) 1000 yen (, u) Fig. 3 2000 yen (JJ)

Claims (1)

[Scope of Claims] (1) A porous carbon fiber-based material having a porosity of 50 to 85%, a pore size distribution of a chassis, and a compressive breaking strength of 50 kg/♂ or more. ^ Carbon molded product. A porous carbon molded article according to claim 1, characterized in that: (3) More than 60% of the pores are fine (1
, a porous carbon molded article according to claim 1, having a radius of . (4) Claim 1, characterized in that 60% or more of the pores have a pore radius within the range of 10 to 30μ.
The porous carbon molded product described in . 67- (5) The porous carbon molded product according to claim 1, wherein 60% or more of the pores have a pore radius in the range 11 to 59μ. (6) A mixture mass consisting of 100 parts of short fiber and 20 to 100 parts of binder resin is obtained, the mixture mass is crushed, and soluble granular material having a predetermined particle size distribution is added to 100 parts of the mixture. It is characterized by adding and mixing 20 to 1 ooxi parts to the fishtail, molding under heat and pressure, removing the soluble particulate material from the molded product by immersing it in a solvent that can dissolve the soluble particulate material, and then firing. A method for manufacturing a porous carbon molded product using carbon fiber as a base material. (7) The 70-weight LX of the soluble particulate material is
The manufacturing method according to item 6. (8) The manufacturing method according to claim 6 or f47, wherein the smoked carbonaceous fiber has a fiber diameter of 3 to 30 μm and a fiber length of 2 mm or less. (9) Claim 6, wherein the smoked carbonaceous fiber is a carbonaceous fiber obtained by heat-treating oxidized pitch fiber at a temperature of 400 to 800°C in an inert gas atmosphere.
9. The manufacturing method according to any one of Items 1 to 8. 0+) The binder resin is a phenolic resin or a furfuryl alcohol resin. 'F
1. The manufacturing method according to any one of items 6 to 9. θ1) The soluble particulate material is polyvinyl alcohol,
νJ? The manufacturing method described in any of the patents is characterized in that the organic 7Q-soluble particulate material is selected from vinyl chloride, polystyrene, polymethyl methacrylate, sugar and starch. 02 The particle radius of the organic soluble particulate material is 10 to 5
12. The manufacturing method according to claim 11, wherein the particle radius of at least 70% by weight of the particulate material is in the range of 20 to 40 microns. 0 [Yes] The particle radius of the organic soluble particulate material is 30~
within the range of 70μ, of which at least 70% by weight
12. The manufacturing method according to claim 11, wherein the particle radius of the granular material is within a range of 40 to 60 microns. 0 荀 The organic soluble particulate material has a particle radius of 40 to 10
12. The manufacturing method according to claim 11, wherein the particle radius of at least 70% of the particulate material is within the range of 60 to 80 microns.