Since the coupling agent can better connect the inorganic filler and the organic binder resin, it forms an active organic monolayer between the inorganic and organic interfaces, one end is combined with the surface of the inorganic substance, and the other end is chemically or physically interacted with the organic substance. intertwined to form an organically combined whole. Therefore, the use of coupling agent can promote the uniform dispersion of conductive fillers and improve the leveling and wettability of the slurry. The content of the coupling agent in the conductive polymer should have a maximum value.
When the coupling agent content is about 4.0%, the volume resistivity of the conductive polymer is small. When the content of the coupling agent is less than 4%, the coating of the conductive filler by the coupling agent is incomplete, so that the silver powder is not uniformly dispersed in the resin, resulting in a large volume resistivity of the coating film; when the content is more than 4%, the silver particles are uniformly dispersed , but the coating layer of the coupling agent on the surface of the silver particles is thicker, and the distance between the conductive particles is larger, which exceeds the critical value of electron emission and tunneling effect, so that the volume resistivity becomes larger; when the content of the coupling agent is about 4% At this time, not only the silver powder particles are uniformly dispersed, but also the coating thickness of the coupling agent is appropriate, and the volume resistivity of the coating film is small at this time.
[Conductive silver paste] refers to the silver paste that is printed on conductive substrates so that it has the ability to conduct current and eliminate accumulated static charges. It is generally printed on non-conductive substrates such as plastic, glass, ceramics or cardboard. Printing methods are very wide, such as screen printing, letterpress printing, flexographic printing, gravure printing and lithographic printing, etc. can be used. Different printing methods can be selected according to the requirements of film thickness, and the resistance, solder resistance and friction resistance of different film thicknesses are also different. This kind of silver paste has two kinds of thick film color paste and resin type. The former is a high-temperature sintering type with glass frit as a binder, and the latter is a low-temperature drying or radiation (UV, EB) curing screen silver paste with synthetic resin as a binder. The conductive silver paste is composed of conductive fillers, binders, solvents and additives. The conductive fillers use silver powder and copper powder with high conductivity, and sometimes gold powder, graphite, carbon black (now there is a special conductive carbon black), carbon fiber, nickel powder, etc. Synthetic resins used as adhesives include epoxy resins, alkyd resins, acrylic resins, polyurethane resins, melamine formaldehyde resins, phenolic resins, vinyl chloride-vinyl acetate copolymer resins, and the like. The volume is the medium boiling point (120-230°C) solvent for the screen silver paste to dissolve these resins. Moreover, additives, such as a dispersing agent, a slip agent, and a coupling agent, are added as needed. The properties required for conductive silver paste are: conductivity (antistatic), adhesion, printability and solvent resistance.
Thick film color paste is used for IC (integrated circuit), capacitors, electrodes, etc., resin type silver paste is used for printed circuit, membrane switch, anti-static packaging, etc.
