JPH11228117A - Re-expanded graphite particle, formed article using the same as raw material and production of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilized the property of a formed article produced using a re- expanded particle by pulverizing a carbon sheet scrap, absorbing a volatile low temp. liquid into the pulverized particle and after that, re-expanding by heating to improve workability. SOLUTION: The carbon sheet scrap is arranged into a fixed particle diameter by a crusher and next, pulverized to adjust to 10-80 mesh particle size and 0.1-0.3 g/cm<3> bulk density by a conical type pulverizer. Next, the incombustible low temp. liquid low in vaporization temp. such as liquefied nitrogen or the like is absorbed in the carbon pulverized particle to increase the specific gravity. Succeedingly, a thermal shock, such as to rapidly expose to a high temp atmosphere is given to the carbon pulverized particle, in which the low temp. liquid is absorbed, to instantly gasify and vaporized the low temp. liquid to re-expand the whole particle. The re-expanded graphite particle becomes an intermediate material or a final material of a raw material of the carbon formed article. When an organic based binder such as phenol resin is added into the re- expanded graphite particle, the formability is improved and the properties or characteristics of the formed body is more improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reexpanded graphite particle made from a carbon sheet left after product removal, a molded article made from the particle, and a method for producing the particle.

[0002]

2. Description of the Related Art A sheet-shaped carbon molded product is obtained by subjecting a scale-like natural graphite to a strong acid treatment with concentrated sulfuric acid, concentrated nitric acid, etc., expanding it by heating and rolling, and then punching or cutting a product having a specific shape. Obtained. The carbon sheet from which the product cannot be removed remains as scrap material or residual material (hereinafter referred to as carbon sheet waste), but conventionally, this was landfilled as industrial waste.

[0003]

However, toxic concentrated sulfuric acid, concentrated nitric acid, and the like remain in these carbon sheet wastes, and when they are buried, they elute and become pollutants. In order to prevent this, it is necessary to perform detoxification treatment, but since this is costly (it is generally difficult to add cost to discarded items), it is necessary to discard toxic items. Become. For this reason, various researches have been made on recycling methods, but they have been found only to be pulverized at most to be a substitute for a pulverized graphite product having a limited use.

[0004] However, since the carbon sheet waste has only an odd shape and is still used, no impurities or the like are attached and no deterioration occurs. In this respect, it is equivalent to a new product, and there is no need to discard it unnecessarily. Thus, the present inventors have conducted intensive studies on these effective utilization methods, and as a result, found that the carbon sheet waste can be used for a new use by being crushed and re-expanded, and provided here.

[0005]

SUMMARY OF THE INVENTION Under the above problems, the present invention provides reexpanded graphite particles obtained by pulverizing carbon sheet waste and reexpanding the pulverized particles. In short, the reexpanded graphite particles according to the present invention may be obtained by pulverizing carbon sheet waste and reexpanding it by some method so that the carbon sheet waste can be formed. Further, the present invention provides reexpanded graphite particles obtained by adding an organic binder to these reexpanded graphite particles in order to improve processability and to improve properties and characteristics of a molded product.

Further, the present invention provides a molded article using the above-mentioned reexpanded graphite particles as a raw material in which the reexpanded graphite particles are formed into a specific shape under a predetermined temperature and pressure. Further, in order to stabilize the properties of the molded article, the present invention provides a molded article made from reexpanded graphite particles obtained by subjecting the molded article to a heat treatment in a reducing atmosphere.

[0007] In addition, the present invention provides a method for producing reexpanded graphite particles which is subjected to the following treatment as the best method for producing the above reexpanded graphite particles. (A) a process of crushing carbon sheet waste remaining after product removal; (b) a process of sucking vaporizable low-temperature liquid into the crushed particles; (c) a process of heating and re-expanding the crushed particles sucked by the low-temperature liquid; The present invention also provides a method for producing reexpanded graphite particles by adding an organic binder to the above reexpanded graphite particles.

[0008]

Embodiments of the present invention will be described below. The present invention relates to re-expanded graphite particles obtained by pulverizing carbon sheet waste and expanding the pulverized particles.There are thought to be various methods for producing the re-expanded graphite particles. The best manufacturing method will be described. FIG. 1 is a block diagram of this manufacturing process, in which the first process is a process of pulverizing carbon sheet waste.

There are various methods for pulverization.
Do it mechanically. That is, first, it is adjusted to a certain particle size by a coarse crusher, and then further finely crushed by a conical crusher, a hammer crusher, or a crusher having a similar function. The size of the pulverized carbon particles obtained by this pulverization is preferably adjusted to about 10 to 80 mesh in consideration of handleability and the like (however, before and after this is also within the use range). When adjusted to this particle size, the bulk specific gravity becomes 0.
It becomes about 1 to 0.3 g / cc.

The next process is a process in which the pulverized carbon pulverized particles are inhaled with the vaporizable low-temperature liquid. This treatment is an important pretreatment of the heat treatment to be performed next, in order to rapidly evaporate the low-temperature liquid sucked by heating and to re-expand the whole particles with the energy. In this sense, the low-temperature liquid is preferably one that evaporates at as low a temperature as possible, and specifically, liquid nitrogen, propane, butane, and others can be considered. Among them, liquid nitrogen is the most preferable because it has a low vaporization temperature and is nonflammable. The operation of sucking the low-temperature liquid into the carbon ground particles may be performed by immersing the particles in the low-temperature liquid. When the particles sufficiently inhale the low-temperature liquid, the specific gravity increases and sinks into the low-temperature liquid.

The subsequent process is a process for re-expanding the pulverized carbon particles into which the low-temperature liquid has been sucked. Specifically, it is to heat the particles, and in this case, it is preferable to apply a so-called thermal shock by rapidly exposing the particles to a high-temperature atmosphere. Thereby, the low-temperature liquid is instantaneously vaporized and evaporated, and the whole particles are re-expanded to become re-expanded graphite particles.

FIG. 2 is an explanatory view of one example of the re-expansion apparatus. In this figure, 10 is a propane hot air burner as a heat source, 12 is a conduit for sending hot air, and 14 is carbon pulverized particles sucked by a low-temperature liquid. A supply device 16 for supplying the inside of the conduit 12, a retention tank for temporarily retaining the carbon pulverized particles to sufficiently react with hot air, a transfer device 18, and a receiving tank 20 are provided.

In the above-described apparatus, the hot air from the propane hot air burner 10 is circulated through the conduit 12 toward the storage tank 16, and the temperature of the hot air is set to at least 200 ° C. . The higher the temperature, the higher the re-expansion rate of the pulverized carbon particles.
If the temperature is higher than 000 ° C., re-oxidation occurs and it is uneconomical, so the maximum temperature can be suppressed to this level. After all, 400-600 ° C. is most efficient. In order to generate hot air having a temperature in this range, 12,500 Kcal is required.
/ H may be supplied by the propane hot air burner 10.

[0014] When the crushed carbon particles in which the low-temperature liquid is completely sucked are supplied into the conduit 12 by the supply device 14, the vaporizable liquid permeated into the crushed carbon particles is instantaneously generated by the hot air atmosphere. It is vaporized and evaporated and is emitted outside the particles, and the pulverized particles are re-expanded by the energy to become re-expanded graphite particles. The reexpanded graphite particles are
The reaction is completed by receiving sufficient heat in the retention tank 16,
It is carried to the receiving layer 20 by the transfer device 18.

The reexpanded graphite particles carried to the receiving layer 20 are cooled here, discharged from the lower part thereof, and collected.
At this time, in order to prevent the reexpanded graphite particles from scattering in the receiving layer 20, a screen 22 is usually installed on the upper part thereof. The reexpanded graphite particles thus produced are expanded to about 2 to 10 times the original particles, and have a bulk specific gravity of 0.02 to 0.05 g / c.
about c

The reexpanded graphite particles that have been subjected to the above treatments are as follows:
It is an intermediate or final product of the raw materials for carbon molded products. That is,
The reexpanded graphite particles are heated at a specified temperature (even at room temperature).
By pressing, it can be formed into a product with a specific shape. Therefore, the reexpanded graphite particles alone have a product value and are to be traded. In this case, if the above-mentioned bulk specific gravity is used, transportation costs and the like can be sufficiently paid. By the way, the expansion of the graphite crystal during the production of the sheet is expanded to a bulk specific gravity of 0.01 g / cc or less.

Further, when an organic binder is added to the above-mentioned reexpanded graphite particles, the formability is improved and the properties of the molded product are improved.
The characteristics are further enhanced. That is, the organic binder is crosslinked between the particles by heating during molding to bind the particles together, thereby improving the flexibility, impact resistance, and strength.
The organic binder used in this case is preferably in the form of powder because of its excellent miscibility. Specifically, a powder of a thermosetting resin such as a phenol resin, a urea resin, a melamine resin, and an alkyd resin is suitable, but polyethylene, polystyrene, polyvinyl chloride, polyester,
Powders of a thermoplastic resin such as nylon can also be used. Among them, the most excellent is an n / phenol resin.

The mixing ratio in this case is within the discretion of a skilled technician, but is generally preferably about 20 to 50% by weight. For example, when n / phenol resin powder is used, re-expansion A ratio of 60% of graphite particles and 40% of resin is ideal. If the proportion of the resin is lower than this, it cannot serve as an additive for improving properties, and if it is too high, the expected effect is not added. The above-mentioned re-expanded graphite particles with an organic binder added thereto are excellent raw materials for carbon molded articles, and, of course, can be traded alone.

When a molded article is formed from reexpanded graphite particles to which a resin is added as a binder, in addition to pressurization, heat is applied in order to further perfect the properties of the resin as the binder. Is a condition. The temperature required at this time depends on the reaction temperature of the resin.
It is about 300 ° C. FIG. 4 shows the relationship between the molding pressure and the bulk density at this time, and is 1 × 10 ⁴ Kg / cm.
^When a pressure of ² or more is applied, the bulk density becomes 1.5 g / cc or more, and a molded article having a sufficient density is obtained.

In addition, a molded article made of reexpanded graphite particles to which n / phenol resin is added as a binder is a material which is more susceptible to high temperatures than a molded article made of reexpanded graphite particles alone. The rate of weight loss over time is suppressed. this is,
This is probably because the binder replenishes the loss of carbon components due to oxidation. FIG. 3 is a graph showing the weight loss rate when the molded article is presented in an air atmosphere at 660 ° C.
It can be seen that in the case where the phenol resin was added at the above ratio, the weight loss rate was suppressed almost twice as compared with the case where the phenol resin was not added.

When the reexpanded graphite particles are used as a raw material for molding, the shape that can be molded is not limited to a sheet. It can be formed into any shape of block and cylinder. Therefore, its use is also made of a heat insulating material, an electrode for a fuel cell, a bipolar plate for a storage electrode by utilizing the properties of carbon, namely, heat resistance, thermal shock resistance, corrosion resistance, conductivity, and anisotropy. A conductive paint, a carbon material containing an alkaline battery electrode, a magnetic shielding plate, an ion absorber, soft graphite, a surface heating element, a sliding material, and the like can be considered.

Further, in the case of a molded article made of re-expanded graphite particles to which a resin is added, a final heat treatment enhances the thermosetting power of the resin, suppresses weight loss, and further enhances product properties. Can be stabilized. This heat treatment is performed at a temperature in the range of 500 to 3000 ° C. in a reducing atmosphere.

[0023]

As described above, according to the present invention, since carbon sheet waste conventionally discarded as having no use value can be regenerated as reusable graphite particles having a use value, a great saving of resources can be achieved. In addition, it is harmless to the global environment because it is toxic but does not need to be discarded.

[Brief description of the drawings]

FIG. 1 is a block diagram of a process for producing reexpanded graphite particles from carbon sheet waste.

FIG. 2 is an explanatory view of a re-expansion device for re-expanding pulverized carbon sheet waste.

FIG. 3 is a graph showing the degree of weight reduction of a carbon molded article in an air atmosphere at 660 ° C.

FIG. 4 is a graph showing the relationship between bulk density and molding pressure when molding a carbon molded article using reexpanded graphite particles.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Heat source 12 Conduit 14 Supply device 16 Detention tank 18 Transfer device 20 Receiving tank 22 Screen

Claims (6)

[Claims] 1. Re-expanded graphite particles obtained by crushing carbon sheet waste and re-expanding the crushed particles. 2. Reexpanded graphite particles obtained by adding an organic binder to the reexpanded graphite particles according to claim 1. 3. A molded article made of the reexpanded graphite particles obtained by molding the reexpanded graphite particles according to claim 1 or 2 at a predetermined temperature and pressure into a specific shape. 4. A molded article made from reexpanded graphite particles obtained by subjecting the molded article according to claim 3 to a heat treatment in a reducing atmosphere. 5. A method for producing reexpanded graphite particles, which is subjected to the following processes (a) to (c). (A) A process for crushing carbon sheet debris left over after product removal. (B) A process for inhaling vaporizable low-temperature liquid into the crushed particles. 6. A method for producing reexpanded graphite particles, comprising adding an organic binder to the reexpanded graphite particles according to claim 5.