Due to its ability to effectively connect inorganic fillers and organic matrix resins, coupling agents form active organic monolayers at the interface between inorganic and organic materials. One end binds to the surface of the inorganic material, while the other end undergoes chemical or physical entanglement with the organic material, forming an organic cohesive whole. So the use of coupling agents can promote the uniform dispersion of conductive fillers, improve the leveling and wetting properties of the slurry. The content of coupling agent in conductive polymers should have an optimal value.
When the coupling agent content is around 4.0%, the volume resistivity of the conductive polymer is the smallest. Coupling agent content<At 4%, the coupling agent does not completely cover the conductive filler, causing uneven dispersion of silver powder in the resin and resulting in a higher volume resistivity of the coating film; content>At 4%, the silver particles are evenly dispersed, but the coupling agent thickens the coating layer on the surface of the silver particles, and the distance between the conductive particles is large, exceeding the critical values of electron emission and tunneling effect, thereby increasing the volume resistivity; When the content of coupling agent is around 4%, not only are the silver powder particles evenly dispersed, but also the coupling agent coating thickness is appropriate, and the volume resistivity of the coating film is minimized at this time.
Conductive silver paste refers to silver paste printed on conductive substrates, which 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. There are a wide range of printing methods, such as screen printing, relief printing, flexographic printing, gravure printing, and flatbed printing, which can all be used. Different printing methods can be selected according to the requirements of film thickness, and the resistance, solder resistance, and friction resistance also vary depending on the film thickness. This silver paste comes in two types: thick film color paste and resin type. The former is a high-temperature sintering process using glass material as a binder, while the latter is a low-temperature drying or radiation (UV, EB) curing type of wire mesh silver paste using synthetic resin as a binder. Conductive silver paste is composed of conductive fillers, adhesives, solvents, and additives. Conductive fillers use silver powder and copper powder with the best conductivity, and sometimes gold powder, graphite, carbon black (there are now specialized conductive carbon black), carbon fiber, nickel powder, etc. Synthetic resins used as adhesives include epoxy resin, alkyd resin, acrylic resin, polyurethane resin, melamine formaldehyde resin, phenolic resin, vinyl chloride vinyl acetate copolymer resin, etc. The volume is the medium boiling point (120-230 ℃) solvent used to dissolve the wire mesh silver paste of these resins. In addition, additives such as dispersants, lubricants, coupling agents, etc. can be added as needed. The characteristics required for conductive silver paste include conductivity (anti-static), adhesion, printability, and solvent resistance.
Thick film color paste is used for ICs (integrated circuits), capacitors, electrodes, etc. Resin type silver paste is used for printed circuits, membrane switches, anti-static packaging, etc.
