JPH01101372A - Electrically conductive composite resin composition - Google Patents

Abstract

PURPOSE:To obtain an electrically conductive composite resin composition having excellent electrical conductivity and moldability and stabilized quality, by treating a graphite fiber having a specific crystal structure with nitric acid and dispersing the obtained interlaminar compound fiber in a synthetic resin matrix. CONSTITUTION:Milled carbon fiber is heat-treated at 1,500-3,500 deg.C, preferably 2,500-3,000 deg.C for 20-120min, preferably 30-60min in an inert gas atmosphere (e.g. argon) to obtain graphite fiber having crystal structure characterized by a hexagonal carbon network plane concentrically oriented parallel to the fiber axis. The graphite fiber is made to contact with nitric acid (preferably fuming nitric acid having a concentration of >=99%) at 0-80 deg.c, preferably 5-60 deg.C for <=20hr. The obtained interlaminar compound fiber having the recurring period of the crystal of 21-25Angstrom in the direction of C axis is dispersed in a synthetic resin matrix. The amount of the interlaminar compound fiber is 5-200 pts.wt. per 100pts.wt. of the synthetic resin matrix.

Description

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

Conventional ■Takanobu 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 electric sensitivity than metals, so if you try to obtain a high 4-electrode material using a particulate carbon material such as carbon black, it is necessary to increase the blending amount, which significantly reduces processability. Not only is it low (conductivity easily changes due to shear force during kneading or molding), but it also has the disadvantage that it is 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 electrical sensitivity and are also low in processability. On the other hand, those obtained by thermally decomposing hydrocarbons using a specific organometallic compound as a catalyst have a diameter of 0.05 to 4 μm, an aspect ratio of 20 to 1000, and a uniform thickness with almost no branching. It has been proposed to improve the 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. 6l-218661)
. However, the electrical resistivity of this material only reaches a level of 10-2 Ω, and in order to obtain such a value, a large amount of carbon fiber must be added, resulting in poor processability and impractical use. The problem was that there was no.

try to do it. Therefore, it is an object of the present invention to provide a carbonaceous fiber-resin-based conductive composition that has better conductivity and processability than the compositions of the prior art and has stable performance. It is.

[Structure of the invention]

. The purpose of the present invention as described above is to treat graphite fibers having a crystal structure in which the carbon hexagonal network planes are substantially parallel to the fiber axis and oriented in the form of tree rings by treating them with nitric acid. A glabellar compound fiber having a repetition period length in the C-axis direction of the crystal within a range of 21 to 25 angstroms is achieved by a tetraelectric composite resin composition dispersed in a synthetic resin matrix. Ru.

The carbonaceous compound fiber used as a conductive material in the present invention is obtained by treating graphite fiber with nitric acid, which has a crystal structure in which the carbon hexagonal network plane is substantially parallel to the fiber axis and oriented in the form of annual rings. It will be done.

The carbon fiber that is the material of the graphite fiber in the present invention is made from a hydrocarbon compound such as an aromatic hydrocarbon such as toluene, benzene, or naphthalene, or an aliphatic hydrocarbon such as propane, ethane, or ethylene, preferably benzene or naphthalene. The raw material is gasified and heated at 900 to 1500°C with a carrier gas such as hydrogen to a catalyst made of ultrafine metal, such as iron, nickel, or iron-nickel alloy with a particle size of 100 to 300 angstroms, made of ceramics or graphite. It is obtained by contacting and decomposing something coated on a substrate.

The carbon fibers thus obtained are pulverized using a ball mill, rotor speed mill, or other suitable pulverizer, if necessary. Although such pulverization is not essential, it is effective in improving dispersibility when used in composite materials and the like.

Furthermore, the carbon fiber thus obtained is heated at 1500 to 3500°C.
, preferably at a temperature of 2500 to 3000°C, 20 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. Fiber is 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. Further, when the heat treatment time is shorter than 20 minutes, the heat treatment effect is not sufficient and the degree of development of the crystal structure varies greatly, while on the other hand, when the heat treatment time exceeds 120 minutes, no further improvement is observed.

When treating the graphite fibers thus obtained with nitric acid, the fibers are 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 preferably one with as high a concentration as possible, preferably one that does not contain water.
It is appropriate to use 9% or more fuming nitric acid. Such nitric acid may be in a liquid state or in a vapor state when brought into contact with the graphite fibers. In the case of liquid, methods such as immersing graphite fibers in liquid nitric acid are used, but since impurities contained in nitric acid also come into contact with graphite fibers, nitrate ions can penetrate and diffuse between graphite crystal layers. It is desirable to avoid impurities that would inhibit the graphite crystals or would themselves enter between the 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 is.

When contacting graphite fibers with nitric acid, the temperature is between 0 and 80°C.
, preferably 5 to 60°C, and the contact time should not exceed 20 hours. If the temperature is too low, it not only takes a long time for the nitrate sulfur to diffuse into the graphite crystal layer, but it also has the disadvantage of making temperature control difficult. Even if it does not, the mechanical strength will be impaired.

The contact time of the graphite fibers with nitric acid must 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 resulting nitric acid-treated graphite fibers will have a repeating period length in the C-axis direction that is outside the range of 21 to 25 angstroms, resulting in conductivity. Not only does this lead to a decrease in the temperature, but also the stability against heat and humidity 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 shorter than this, it is impossible to achieve operationally meaningful time control, and there is almost no economic advantage even if the contact time is shortened, so the preferred contact time is 0.2 hours. The crystal structure of the nitric acid-treated graphite fiber produced within this range has a repetition period length of 21 to 25 angstroms in the C-axis direction. However, the contact time required to satisfactorily reduce the quality variation of such nitric acid-treated graphite fibers is
The shortest time is required when using liquid nitric acid, and when using vaporized nitric acid, the longer time is required as the concentration of the vapor decreases. 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 graphite fibers thus obtained are added and dispersed in a synthetic resin matrix to obtain the composition of the present invention.

Examples of synthetic resins used here include thermoplastics such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, ethylene/vinyl acetate copolymer resin, ethylene/acrylate copolymer resin, silicone resin, phenol resin, Thermosetting plastics such as urea resins, epoxy resins, and urethane resins, as well as chlorosulfonated polyethylene,
Rubbers such as chlorinated polyethylene, ethylene/propylene rubber, chloroprene rubber, acrylic rubber, silicone rubber, and fluororubber can be used.

There are no particular restrictions on the method of dispersing nitric acid-treated graphite fibers in such synthetic resins, but for example, two rolls,
Known kneading machines such as Nigoo, Intermix, and Banbury mixer can be used.

In addition, there is no particular restriction on the blending ratio of nitric acid-treated graphite fiber and synthetic resin, but from the viewpoint of electrical resistivity and processability,
It is preferable that the fiber content is about 5 to 200 parts by weight, more preferably 10 to 100 parts by weight, based on 100 parts by weight of the resin.

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.

! A: A mullite ceramic plate coated with a metal iron catalyst with a particle size of 100 to 300 angstroms is placed in a horizontal tubular electric furnace, the temperature is adjusted to 1000 to 1100°C, and a mixed gas of benzene and hydrogen is introduced. length 2
Carbon fibers with a diameter of ~101-1 ~5-0 μm were obtained. Next, this carbon fiber was processed using a planetary ball mill (Flisochu Japan Co., Ltd., P-5 type) at a rotational speed of 50 ORP.
The mixture was ground with M for 5 minutes.

This pulverized carbon fiber was placed in an electric furnace and maintained at 2960 to 3000°C for 30 minutes in an argon atmosphere to graphitize it.

The obtained fibers were analyzed by X-ray diffraction and electron microscopy.
It was confirmed that the carbon hexagonal mesh plane had a crystal structure parallel to the fiber axis and oriented in the shape of annual rings, and was crushed to a length of 70 to 100 μm.

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 graphite 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 of the obtained nitric acid-treated graphite fiber was 24.6 angstroms.

The nitric acid-treated graphite fibers obtained in this way were coated with an addition reaction type liquid silicone rubber (TOμ Silicone Co., Ltd., DY35-055).
) according to the formulation shown in Table 1 and kneaded for 30 minutes with a 6-inch roll mill. Next, an inhibitor for controlling the crosslinking rate (To-μ Silicone Co., Ltd., MR-23)
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, graphite fibers obtained as described above without nitric acid treatment, conductive carbon blanks (Lion Akzo Co., Ltd., Ketchen Black EC), and PA
Crushed products of N-based carbon fiber (MLD-300, Toshisha Co., Ltd.) were kneaded in the same manner according to the formulations in Table 1 to prepare silicone rubber compositions.

These silicone rubber compositions were heated at 100°C in a mold.
, press molded for 20 minutes to obtain 100 dragons x IQ am
Crosslinked sheets of l++n were prepared and their volume resistivity was measured. The results are shown in Table 1.

Next, the silicone rubber composition described above was extruded and coated on a twisted core wire consisting of three aromatic polyamide fibers (DuPont, Gebler) 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")I" Silicone rubber 100 100 100 100 100 1
00 100 100 carbon black
2040PAN carbon fiber IS
20 40 inhibitor o, o70.07 o, o'r
o, o'7o, rfIo, ff7o, m o, o'y
Crosslinking catalyst 11111111 1.130.0247.10.36
31.4 5.943.99.63 (Ω・− From Table 1, it can be seen that the volume resistivity of the product containing nitric acid-treated graphite fiber is extremely small.

Table 2 Results 8 Continuous operation for 5 hours, no problems, appearance is good D1 Same as above F'' Continuous operation for 5 hours, no problems. There are slight cracks on the surface of the crosslinked product.

H” Continuous operation for 5 hours without any problems.However, there is some roughness 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 graphite fibers used in Example 1 were added to chlorosulfonated polyethylene (DuPont, Hypalon 45) according to the formulation in Table 3, and an antioxidant (Ciba Geigy, Irganox 1035) was added. In addition, after thoroughly kneading with two rolls, transfer to a stirrer, add toluene, and mix thoroughly.
After kneading for 8 hours, a conductive paint with a solid content of 25% was prepared.

For comparison, ground graphite fibers and PAN-based carbon fibers that were not treated with nitric acid were used in the same manner as in Example 1, and were kneaded in the same manner according to the formulations shown in Table 3 to prepare conductive paints.

These paints were applied onto a polyester film using an applicator and dried to form a coating film with a thickness of about 400 μm. The results of measuring the volume resistivity of each coating film are shown in Table 3.

Table 3 I J” K” Chlorosulfonated polyethylene 100 100
100 Antioxidant 2.5 2.5 2.5 Nitric acid treated graphite fiber Group untreated graphite fiber Group PAN type carbon carbon fiber Group Toluene
458 458 458* is a comparative example.

This result shows that the product of the present invention exhibits extremely high conductivity.

〔Effect of the invention〕

As described above, the conductive composite resin composition of the present invention has excellent processability and moldability, as well as extremely high conductivity, making it easier to produce conductive composite materials of much higher quality and stability than before. can be provided to

Claims (1)

[Claims] An interlayer compound fiber obtained by treating graphite fiber with nitric acid with a crystal structure in which the carbon hexagonal mesh plane is substantially parallel to the fiber axis and oriented in the form of annual rings, and the length of the repetition period in the c-axis direction of the crystal. 1. An electrically conductive composite resin composition, characterized in that a conductive composite resin composition having a diameter in the range of 21 to 25 angstroms is dispersed in a synthetic resin matrix.