JPH0791417B2 - Conductive resin composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a conductive resin composition. This conductive resin composition is in the form of compound, paste, molded product, etc., especially in the semiconductor-related form, for preventing electrostatic breakdown,
It is used in a wide range of fields such as materials for storage and transportation, floor materials for preventing static electricity and static electricity, shield materials for preventing electromagnetic interference, wire covering materials for preventing corona discharge deterioration, and synthetic resin thermistors.

2. Description of the Related Art Materials that are added to a resin to give conductivity, that is, fillers, include metals such as silver, copper, aluminum, nickel, palladium, iron, silicon carbide, tin oxide, indium oxide,
Metal compounds such as lead oxide, non-metals such as carbon are crystalline,
It is an amorphous material and is used in the form of flakes, powder, fibers, and the like. In order to obtain a highly stable conductive composition with these fillers, it is important to disperse them uniformly in the resin. For this, the powdery or flake-like ones described above are made into fine particles by pulverization, Thinner and fibrous materials have been required to have a smaller diameter. However, especially in the case of metal fillers, it is often difficult to obtain the desired conductivity even when the oxide film is developed on the surface due to the influence of moisture and oxygen during the above treatment or storage and the dispersion is improved, and other compounds are used. Hydrolysis often has the same adverse effect, and if it is a chemically stable compound or is fibrous, the effect of micronization such as pulverization is small, and a special micronization method is required, and processing cost is high. In view of dispersion in the resin, there is a limit to making fine particles and fine particles, and it is unavoidable to use the particles with relatively large dimensions. Therefore, the resin and the filler are likely to separate from each other after the compounding, resulting in an inhomogeneous dispersed state, and the obtained composition is inferior in moisture resistance, corrosion resistance, and the like, and it is often difficult to maintain conductivity for a long period of time.

DISCLOSURE OF THE INVENTION The present invention uses a novel zinc oxide whisker as a conductive filler, which is different from conventional techniques, that is, atomization of a conductive filler, high dispersion and high conductivity due to miniaturization, and It is an object of the present invention to provide a highly dispersible composition which achieves extremely efficient and stable electrical contact.

Means for Solving the Problems In view of the above problems, the present inventor is a conductive filler that is a stable filler, has good moldability when compounded with a resin, and has a molded article having excellent moisture resistance, corrosion resistance, and conductivity. As a result of various experimental researches and studies, zinc oxide whiskers were extremely stable during kneading and molding with resin and were uniformly dispersed in the resin, with good moldability, and the resulting molded product had extremely stable conductivity. Confirmed to show.

That is, the present invention relates to a conductive resin composition obtained by mixing a resin with a novel tetrapod-shaped zinc oxide whisker as a conductive filler. The novel zinc oxide whisker is composed of a central core portion and a needle-shaped crystal portion extending in four different axial directions from the core portion, and the diameter of the base portion of the needle-shaped crystal portion is 0.7 to 14 μm. In particular, it has a morphological dimensional characteristic such as 1 to 14 μm, and the length from the base to the tip of the needle-shaped crystal portion is 3 to 200 μm, and particularly 10 to 200 μm.

Action Since the zinc oxide whiskers used in the present invention have a tetrapod-like three-dimensional unique structure as described above,
When compounded in a resin, the whisker needle-shaped crystal parts make electrical contact with other whisker needle-shaped crystal parts in a highly efficient manner to enhance conductivity. This has a very high contact probability as compared with a simple linear fiber body which has been conventionally considered advantageous for electrical contact. Furthermore, this zinc oxide whisker achieves extremely high electrical contact compared with the above filler alone system even when mixed and used with other conventionally used granular, flake-like, fibrous, or conductive fillers, and has high conductivity. Make a big contribution. Further, the dispersibility with the resin is also excellent because the above structure contributes to the good wettability due to the inherent properties of zinc oxide. Further, the stability derived from the single crystal property contributes to the reduction of deterioration of the composition over time and the improvement of moisture resistance.

The above tetrapod-shaped zinc oxide whiskers are obtained by heat-treating metallic zinc powder having an oxide film on its surface in an atmosphere containing oxygen. The obtained whiskers have an apparent bulk specific gravity of 0.05 to 0.1 and a yield of 70% or more. The size of the whiskers can be controlled to some extent by the conditions for forming the oxide film.

FIG. 1 is an electron micrograph of the zinc oxide whiskers used in the examples. This whisker was obtained as follows.
That is, powder 1Kg obtained by spraying a 99.99% pure zinc wire in the air by a thermal spraying method using an arc discharge method, adding 500g of ion-exchanged water thereto, stirring for about 20 minutes with a mortar-type crusher, and
Leave in water at ℃ for 72 hours, then dry at 150 ℃ for 30 minutes,
It was obtained by placing it in an alumina magnetic crucible, placing it in a furnace kept at 1000 ° C., and heat treating it for 1 hour.
The apparent bulk specific gravity is 0.09, the thickness of the needle-shaped crystal part is 1 to 14 μm,
The length is 10 to 200 μm. In the figure, the needle-shaped crystal part may be triaxial or biaxial, but it is considered that a part of the tetraaxial one is broken. Plate-like crystals are also recognized. In any case, about 80% is tetrapod-shaped
Occupy FIG. 2 shows an X-ray diffraction pattern of the above whiskers. All showed peaks of zinc oxide, and electron diffraction results showed single crystallinity with few dislocations and lattice defects. Also, the content of impurities is low, and as a result of atomic absorption spectrometry, zinc oxide is 99.9
It was 8%.

Such whiskers also exhibit good dispersibility without being separated from the resin at the time of molding even when blended in a resin having a low viscosity and a high specific gravity. In the present invention, zinc oxide whiskers as a conductive filler to be blended with the resin can impart sufficient conductivity by blending alone, but depending on the purpose of conductivity, other fillers such as silver, copper, aluminum and nickel can be used. , Palladium, iron, tin oxide, indium oxide, lead oxide, silicon carbide, zirconium carbide, titanium carbide, highly conductive carbon, graphite, powders of acetylene black, etc., flakes, and fibers can be used together and mixed.

The resin used in the present invention may be either a thermoplastic resin or a thermosetting resin, which includes polyvinyl chloride, polyethylene, chlorinated polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate,
Polyamide, polysulfone, polyether sulfone, polyphenylene sulfide, polyether ketone, ABS resin, polystyrene, polybutadiene, methyl methacrylate, polyacrylonitrile, polyacetal, polycarbonate, ethylene-vinyl acetate copolymer, polyvinyl acetate, ethylene-tetrafluoroethylene copolymer Polymer, polyphenylene oxide, aromatic polyester,
Examples thereof include polyvinyl fluoride, polyvinylidene fluoride and polyvinylidene chloride. The thermosetting resin includes epoxy resin, unsaturated polyester, silicone resin, melamine-urea resin, phenol resin and the like.

The mixing ratio of the conductive filler with respect to the resin is not particularly limited, but if the mixing amount is too small, the purpose of conductivity is not achieved, and if it is more than necessary, the specific gravity becomes large, and it is disadvantageous in terms of cost. The dispersibility of the filler may be hindered and the filler may protrude to the surface. For this reason, there is a preferable range depending on the purpose of conductivity. That is, 5 to 50% by volume of the resin, preferably 10 to 30%
The capacity is%.

Next, the conductive resin composition of the present invention comprises a resin and zinc oxide whiskers, but additives such as stabilizers, dispersion aids, and fillers may be added alone or in combination depending on the purpose of use. . Further, this composition can be made into a preferable form according to the purpose such as powder, pellets, paste and the like.

The powder can be obtained by blending a resin and whiskers and, if necessary, an additive and mixing them using a rotary type or fixed type mixer. Similarly, the pellets are obtained by kneading with the above mixer, kneading with a kneader or the like, and then cutting into a desired shape with a granulator or the like.

The paste can be obtained by a method in which a resin and whiskers are mixed with at least one solvent or low molecular weight substance and, if necessary, an additive and dispersed and kneaded. Further, as described above, the additives to be added as necessary include antioxidants as stabilizers, for example, monobistriphenol, radical chain inhibitors represented by aromatic amines, mercaptans, peroxide decomposition of monodipolysulfide, etc. Agents, metal deactivators such as acid amides and hydrazides, phenols, sulfides, phosphides and the like and ultraviolet absorbers such as benzophenone-based and benzotriazole-based flame retardants such as bromine-based and phosphorus-based flame retardants , Flame retardant aids such as antimony oxide are included. Examples of the dispersion aid include organic metal salts, and examples of the filler include carbon black, white carbon, calcium carbonate, clay, silicates, talc, alumina hydrate, asbestos, and glass fiber. The compounding amount of these compounding agents is not particularly limited.

The low molecular weight substances used in the paste include carboxylic acids such as diethylene glycol and formic acid, dimerized products such as diethylene glycol, trimerized products such as triethylene glycol, and the like. As the agent, phthalic acid ester, phthalic acid mixed group ester, aliphatic digroup hydrochloric acid ester, glycol ester, fatty acid ester, phosphoric acid ester, epoxy plasticizer, chlorinated paraffin and the like can be used.

Examples The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1 20% by volume of the zinc oxide whiskers, polypropylene resin, and 80% by volume were sampled, mixed for 4 minutes with a V-type rotary mixer, and then kneaded with a bidirectional extruder of different directions to form pellets. Got The pellets were press-molded at 240 ° C to prepare a disc-shaped test piece having a diameter of 50 mm and a thickness of 3.5 mm. With respect to this test piece, the dispersibility was visually evaluated and the specific resistance was measured with a super insulation meter. Thereafter, a humidity resistance test was performed at 40 ° C, 100% RH for 7 days, and the specific resistance was measured in the same manner as above.

The measurement results are shown in Table 1.

Example 2 The same zinc oxide whiskers as in Example 1 were mixed with flake-shaped silver powder (20 to 40 μm particles) at a ratio of 4: 1 (volume ratio). The conductive filler was collected so as to be 15% by volume and the same polypropylene resin as 85% by volume as in Example 1, pellets were prepared in the same manner as in Example 1 to obtain a test piece, and then the same evaluation test was performed. . The results are shown in Table 1.

Examples 3 to 6 are polybutylene terephthalate, ABS resin, and
Polyphenylene sulfide and nylon 66 were selected, whiskers and whisker mixed fillers were mixed in the same manner as in Examples 1 and 2 to obtain pellets, and then test pieces were prepared at the molding temperatures shown in Table 1. An evaluation test was conducted in the same manner. The respective results are shown in Table 1. In Examples 5 and 6, the type and mixing ratio of the whisker mixed filler are different. This is shown in Table 1.

Comparative Examples 1 to 3 After using polypropylene as a resin and metal flakes and powders as a conductive filler in the same manner as in Example 1 to obtain pellets, a test piece was prepared at 240 ° C, and an evaluation test was performed as Example 1. The same method was used. The results are shown in Table 2.

Example 7 Zinc oxide whiskers obtained by the same method as in Example 1
Mixture of 20% by volume and 80% by volume of polymethylmethacrylate
100 g of toluene and 150 g of toluene were collected in a magnetic pot mill and mixed to form a paste, which was cast into a glass plate, left to stand at room temperature for 2.5 hours, and then dried at 150 ° C for 2 hours to form a 30 μm coating film. It was used as a test piece. The evaluation test was conducted in the same manner as in Example 1, and the results are shown in Table 3.

Comparative Example 5 Nickel powder 20% by volume and polymethylmethacrylate 80% by volume were obtained in the same manner as in Example 7 to obtain a paste-like material and a test piece, and the same evaluation method was used. The measurement results are shown in Table 3.

The amount of the mixed filler added in each of Examples 3 to 6 was 15% by volume.

EFFECTS OF THE INVENTION The conductive resin composition of the present invention can be formed into various molded bodies in the form of powder or pellets. This molded body is in a uniformly dispersed state without causing separation of resin and filler during molding, and in particular, due to the effect of zinc oxide whiskers, the addition of a small amount makes it extremely high in conductivity, has little deterioration over time and is resistant to moisture resistance, and has an electrostatic property. It can be suitably used as a material for preventing breakage, a material for preventing static electricity, a material for preventing electromagnetic interference, a material for preventing corona discharge, and the like. In the above-mentioned applications, molding can be performed by a molding method such as compression molding, extrusion molding, injection molding or the like. Moreover, the paste can be used as a material for a conductive film, a conductive adhesive, or the like. In addition, from the point that the effect of adding a small amount of the above is great, the physical properties of the resin are rarely impaired, and there is also a point of discovering physical properties superior to the resin alone.
Its utility value is enormous.

[Brief description of drawings]

FIG. 1 is an electron micrograph showing the structure of a ZnO whisker crystal, and FIG. 2 is an X-ray diffraction pattern.

Claims (1)

[Claims] 1. A resin is blended with zinc oxide whiskers, and said zinc oxide whiskers have a tetrapod-like structure comprising said portion and needle-shaped crystal portions extending in different four-axis directions from this portion, The needle crystal part has a diameter of 0.7 to 14 μm, and the length of the needle crystal part from the base to the tip is 3 to
A conductive resin composition having a thickness of 200 μm.