JPH01101343A - Electrically conductive resin composition - Google Patents

Abstract

PURPOSE:To obtain the title composition of stabilized performance, significantly improved in electrical conductivity and processability, by dispersing a synthetic resin matrix with a specific interlaminar compound fiber. CONSTITUTION:The objective composition can be obtained by dispersing (A) 100pts.wt. of a synthetic resin (e.g. polyethylene, silicone rubber) matrix with (B) 5-200pts.wt. of an interlaminar compound fiber with a recurring period in the direction of the crystal c-axis of 21-25Angstrom , prepared by nitric acid treatment of a graphitized product from vapor growth carbon fiber produced by contact between a hydrocarbon compound and ultrafine powdery metal catalyst suspended in a high-temperature zone.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] The present invention relates to a conductive composite material useful for conductive molded products, paints, adhesives, etc.

With the development of electronics technology, there has been a demand for lightweight, highly conductive materials as shielding materials for static electricity and electromagnetic fluids. As such materials, there are resin composite materials in which powders or fibers of metals, carbon, etc. are blended with rubber, plastics, etc. However, materials using metals have the drawback of being heavy and expensive. In addition, carbon-based conductive materials have lower conductivity than metals, and if you try to obtain high conductivity with particulate carbon materials such as carbon black, you will need to increase the amount of the compound, and the processability will be extremely low. In addition, conductivity tends to change due to shear force during kneading or molding, making it difficult to obtain products with stable performance.

On the other hand, when attempting to use graphitized carbon fiber as a conductive material, for example, those obtained by carbonizing polyacrylonitrile fibers or pitch and then graphitizing the fibers have insufficient conductivity and have low processability. On the other hand, a uniform thickness with a diameter of 0.05 to 4 μm, an aspect ratio of 20 to 1000, and almost no branching, obtained by thermally decomposing hydrocarbons using a specific organometallic compound as a catalyst. It has been proposed to improve the electrical conductivity and compounding operability of resin compositions by using carbon fibers in which carbon layers are arranged parallel to the longitudinal axis in the form of tree rings (Japanese Patent Application Laid-Open No. 6-112) -218661)
. However, the electrical resistivity of this product only reaches the level of 104 Ω, and in order to obtain such a value, a large amount of carbon fiber must be added, which deteriorates processability and makes it impossible to put it to practical use. There was a problem.

Accordingly, the present invention provides a carbonaceous fiber-resin-based conductive composition that has superior conductivity and processability and stable performance compared to the compositions of the prior art. It is intended for this purpose.

[Structure of the invention]

The purpose of the present invention, as mentioned above, is to treat graphitized vapor-grown carbon fibers obtained by contacting ultrafine metal catalysts suspended in a high-temperature zone with hydrocarbon compounds and treating them with nitric acid. It is an interlayer compound fiber consisting of a crystal with a repetition period length of 21 in the C-axis direction.
~25 angstroms are achieved with conductive resin compositions dispersed in synthetic resin matrices.

The carbonaceous intercalation compound fiber used as a conductive material in the present invention is obtained by treating a graphitized vapor-grown carbon fiber with nitric acid, which is obtained by contacting a hydrocarbon compound with an ultrafine metal catalyst suspended in a high-temperature zone. obtained by.

Such vapor-grown carbon fibers are produced using hydrocarbon compounds such as aromatic hydrocarbons such as toluene, benzene, and naphthalene, and aliphatic hydrocarbons such as propane, ethane, and ethylene, preferably benzene or naphthalene, as raw materials. 900 with a carrier gas such as hydrogen after gasification.
Contact with a catalyst made of ultrafine metal particles dispersed and suspended in a reaction zone at -1500°C, such as iron, nickel, iron-nickel alloy, etc. with a particle size of 100 to 300 angstroms,
It is obtained by decomposition.

The carbon fibers thus obtained are pulverized using a ball mill, rotor speed mill, cutting mill, or other suitable pulverizer, if necessary. Although such grinding is not required,
This is preferred because it facilitates the formation of intercalation compounds and improves the dispersibility when compounding with other materials.

Furthermore, the carbon fiber thus obtained is heated at 1500 to 3500°C.
, preferably at a temperature of 2500 to 3000°C, 10 to 1
By heat-treating for 20 minutes, preferably 30 to 60 minutes, in an atmosphere of an inert gas such as argon, graphite has a crystal structure in which the carbon hexagonal network planes are substantially parallel to the fiber axis and oriented in the form of annual rings. Compatible fibers are obtained. In this case, if the heat treatment temperature is lower than 1,500°C, the carbon crystal structure will not develop sufficiently, while if it exceeds 3,500°C, the effect will not be particularly enhanced and it is not economical. Furthermore, if the heat treatment time is shorter than 10 minutes, the heat treatment effect will not be sufficient and the degree of development of the crystal structure will vary greatly (on the other hand, if the heat treatment time exceeds 120 minutes, no further improvement will be observed.

When treating the graphitized fiber thus obtained with nitric acid, it is brought into contact with nitric acid at a temperature of 0 to 80°C for no more than 20 hours.

The nitric acid used at this time is b'+? It is preferable to use one with a high J1 degree, preferably one that does not contain water (it is appropriate to use fuming nitric acid with a concentration of 99% or more. Such nitric acid should be in a liquid state when brought into contact with the graphitized fibers. In the case of a liquid, a method such as immersing the graphitized fiber in liquid nitric acid is used, but impurities contained in the nitric acid also come into contact with the graphitized fiber. Therefore, it is desirable to avoid impurities that inhibit nitrate ions from permeating and diffusing between graphite crystal layers, or that impurities themselves enter between graphite crystal layers.

On the other hand, when using nitric acid vapor, the same precautions as above are required, but since non-volatile impurities are naturally eliminated, there are fewer restrictions on the purity and form of the source of nitric acid vapor. There are advantages.

When contacting graphitized fibers with nitric acid, the temperature is between 0 and 80°C.
℃, preferably 5 to 60 ℃, and the contact time does not exceed 20 hours. When the temperature is too low,
Not only does it take a long time for the nitrate ions to diffuse into the graphite crystal layer, but temperature control is also difficult.If the temperature is too high, the fibers are likely to break, and even if they do not break, the mechanical strength will deteriorate. be damaged.

It is necessary that the contact time of the graphitized fibers with nitric acid does not exceed 20 hours, preferably within 15 hours. If the contact is carried out for a longer period of time, the crystal structure of the nitric acid-treated graphitized fibers produced will have a repeating period length in the C-axis direction that is outside the range of 21 to 25 angstroms, resulting in a decrease in conductivity. In addition to this, the stability against heat and humidity also decreases, and even when stored indoors, the properties change significantly over time. Furthermore, if the contact time is too short, the quality will vary greatly, so it is desirable to allow contact for at least 0.1 hour or more. However, if the contact time is less than this, meaningful time control is impossible in operation, and there is almost no economic advantage even if the contact time is shortened, so the preferred contact time is 0.
．． 2 hours or more, and the crystal structure of the nitric acid-treated graphitized fibers produced within this range has a repetition period length of 2 in the C-axis direction.
The thickness is 1 to 25 angstroms. but,
The contact time required to satisfactorily reduce quality variations in such nitric acid-treated graphitized fibers is the shortest when using liquid nitric acid; The lower the concentration, the longer the time required. Therefore, it is preferable to select the shortest necessary contact time depending on the manufacturing conditions such as the concentration and temperature of nitric acid.

The nitric acid-treated graphitized fiber thus obtained is added and dispersed in a synthetic resin matrix to obtain the composition of the present invention.

The synthetic resins used here include, for example, polyethylene, polypropylene, polyvinyl chloride, polystyrene, ethylene/vinyl acetate copolymer resin, ethylene/vinyl acetate copolymer resin,
Thermoplastic plastics such as acrylic ester copolymer resins, thermosetting plastics such as silicone resins, phenolic resins, urea resins, epoxy resins, and urethane resins, and thermosetting plastics such as chlorosulfonated polyethylene, chlorinated polyethylene, ethylene, etc. Rubbers such as propylene rubber, chloroprene rubber, acrylic rubber, silicone rubber, and fluororubber can be used.

There are no particular restrictions on the method of dispersing the nitric acid-treated graphitized fibers in such a synthetic resin, but known kneaders such as a two-roll, Nigoo, Intermix, and Banbury mixer can be used.

There is no particular restriction on the blending ratio of the nitric acid-treated graphitized fibers and the synthetic resin, but from the viewpoint of electrical resistivity and processability, the fiber content should be about 5 to 200 parts by weight per 100 parts by weight of the resin. More preferably, the amount is 10 to 100 parts by weight.

The resin composition of the present invention may contain appropriate additives, compounding agents, or solvents such as fillers, processing aids, plasticizers, antioxidants, and crosslinking agents, depending on the type of resin used. There is no problem if it is contained. Further, the resin composition of the present invention can be formed into articles of a desired shape by selecting an appropriate molding method such as extrusion molding, injection molding, transfer molding, press molding, or the like.

Next 1J0- Metallic iron catalyst particles with a particle size of 100 to 300 angstroms are suspended in a vertical tubular electric furnace whose temperature is adjusted to 1000 to 1100°C while hydrogen is flowing from below, and a mixed gas of benzene and hydrogen is added to this. was introduced from below and decomposed to obtain carbon fibers with a length of 10 to 10,008 m and a diameter of 0.1 to 0.5 μm. Next, the carbon fibers were milled in a planetary ball mill (Fritsch Japan Co., Ltd., P-5 The mixture was ground for 20 minutes using a mold) at a rotational speed of 50 ORPM.

This pulverized carbon fiber was placed in an electric furnace and maintained at 2960-30°C for 30 minutes under an argon atmosphere to graphitize it. X-ray diffraction and electron microscopy revealed that the obtained fibers had a crystal structure in which the carbon hexagonal mesh planes were oriented in the form of growth rings along the fiber axis, and were crushed to a length of 3 to 5 μm. was confirmed.

The graphitized fiber thus obtained was sealed in a container containing fuming nitric acid (concentration 99%) and kept at 23° C. for 3 hours. After a predetermined period of time, the graphitized fibers were separated from the nitric acid by filtration, thoroughly washed with distilled water, and dried in a desiccator for 24 hours.

The length of the repetition period in the C-axis direction of the crystal measured by X-ray diffraction method for the obtained nitric acid-treated graphitized fiber was 24.4.
It was 4 angstroms.

The thus obtained nitric acid-treated graphitized fibers were added to an addition reaction type liquid silicone rubber (TO-μ Silicone Co., Ltd., DY35-05).
5) was added according to the formulation shown in Table 1 and kneaded for 30 minutes with a 6-inch roll mill.
and a crosslinking catalyst (TOμ Silicone Co., Ltd., 5RX-21
2) was added according to the formulation shown in Table 1 and kneaded uniformly to obtain a conductive silicone rubber composition. However, the numbers in the formulation are parts by weight.

For comparison, graphitized fibers obtained as described above without nitric acid treatment, conductive carbon black (Lion Akzo Co., Ltd., Ketchen Black EC), and P
A pulverized product of AN-based carbon fiber (MLD-300, manufactured by Toshisha Co., Ltd.) was mixed in the same manner according to the formulation shown in Table 1 to prepare a silicone rubber composition.

These silicone rubber compositions were heated at 100°C in a mold.
A crosslinked sheet of 100 cranes x 10 mm x 1 fins was prepared by press molding for 20 minutes, and their volume resistivity was measured. The results are shown in Table 1.

Next, the silicone rubber composition was extruded and coated onto a twisted core wire consisting of three aromatic polyamide fibers (Dupont, Kepler) with a diameter of 180 μm, and heated at 200° C. for 30 seconds to form an outer diameter of 0.90 μm. A linear crosslinked product was obtained. In this manner, molding tests were conducted on compositions B, D, F, and H to evaluate moldability. The results are shown in Table 2.

Table 1 A B C” D” E” F “G” H” Silicone rubber 100 100 100 100 100 100
100 100 carbon black
2040PAN carbon fiber
204047 baboon') -0
,ff7 0.07 0.0? 0.0? 0.0
7 0. ff7 0. ff7 0. ff7 crosslinking catalyst 1
ml II i 1 1 From Table 1, it can be seen that the volume resistivity of the composition containing the nitric acid-treated graphitized fiber is extremely small.

Table 2 Results 8 No problems after 5 hours of continuous operation. Appearance is also good D* Same as above F” Continuous operation for 5 hours with no problems, slight cracks on the surface of the crosslinked product.

H” Continuous operation for 5 hours without any problems, however, there is some gelatin on the surface.

From Table 2, it can be seen that the products of the present invention also have very excellent moldability.

The nitric acid-treated graphitized fibers used in Example 1 were added to an epoxy resin (Yuka Shell Epoxy Co., Ltd., Epicoat 828) according to the formulation shown in Table 3, and kneaded with a stirrer for 60 minutes. The roll was passed through five times. After that, an acid anhydride hardener (Yuka Shell Epoxy Co., Ltd., Epicure YH-3)
07) and a curing accelerator (Epicure EM1-24, manufactured by Yuka Shell Epoxy Co., Ltd.) were added, and the mixture was passed through three rolls five times to obtain a conductive epoxy resin composition. Note that, as in Example 1, the numbers in the formulations represent parts by weight.

For comparison, pulverized graphitized fibers and PAN-based carbon fibers that were not treated with nitric acid were used in the same manner as in Example 1, and kneaded in the same manner according to the formulations in Table 3 to prepare epoxy resin compositions. .

Using these epoxy resin compositions, No. 4 dumbbell test pieces according to JIS 6301 were molded by transfer molding at 80° C. for 3 hours. The results of measuring the volume resistivity of these test pieces and the appearance of the molded products are shown in Table 3.

Table 3 I J K"PiM"N1' Epoxy resin 100 100 100 100 10
0 100 PAN
0.10 1.52 0.90 (Ω・- Appearance Good Good Good Good
Zara Nki Defective * is a comparative example.

This result shows that the product of the present invention has good moldability and very good electrical conductivity.

〔Effect of the invention〕

As described above, the conductive resin composition of the present invention has excellent processability and moldability, and also has extremely high conductivity, making it possible to produce electrically sensitive composite materials of significantly higher quality and stability than before. can be easily provided.

Patent applicant: Yazaki Sogyo Co., Ltd.

Claims (1)

[Claims] This is an intercalation compound fiber obtained by treating a graphitized vapor-grown carbon fiber obtained by contacting a hydrocarbon compound with an ultrafine metal catalyst suspended in a high-temperature zone with nitric acid. 1. A conductive resin composition characterized in that a conductive resin composition having a length within a range of 21 to 25 angstroms is dispersed in a synthetic resin matrix.