The film-forming process of water-based paint is a phenomenon of molecular chain cohesion, which can be generally divided into three steps: water volatilization, particle deformation, and particle merging.
After the construction, the first step is water volatilization. When the latex particles of water-based coatings account for 74% (volume) of the adhesive layer, the particles approach each other and reach a dense filling state; secondly, the water continues to volatilize and the polymer particles are deformed. The capillary pressure is higher than the deformation resistance of polymer particles. The more volatile the medium is, the higher the pressure is. Then, the polymer particles coalesce and fuse to form a continuous coating; finally, the water continues to evaporate. When the pressure reaches the point where the molecular chains in each particle diffuse into the molecular chains of the other particle, the polymer molecular chains gradually diffuse into each other, resulting in a uniform coating film and the completion of the curing and drying process.
Graphite is a simple substance of carbon. It is soft, gray-black, with a relative density of 2.25 and a melting point of 3,527°C. It has stable chemical properties and can conduct electricity.
The properties of graphite depend on its structure. In graphite crystals, carbon atoms form covalent single bonds with three adjacent carbon atoms via sp² hybrid orbitals, and are arranged in a hexagonal plane network structure. In graphite crystals, the carbon-carbon bond distance in the plane is 1.415×10-m, and the distance between the lamellae is 3.35×10-10m. It is now believed that the easy sliding between graphite sheets is due to the relatively free p-electrons that have not participated in the hybridization, which is equivalent to the free electrons in metal crystals. Therefore, graphite has electrical and thermal conductivity properties, and the resistivity of graphite is 0.0ln·cm. Graphite has high electrical conductivity and can be used alone or in combination with carbon black in conductive coatings.
Composite conductive agent
In order to reduce the formation of conductive fillers and improve conductivity, composite conductive agents are often used. Composite conductive agents can be divided into composite powder and composite fiber according to their shape.
According to the definition of the International Organization for Standardization (ISO 3252), composite powder is a powder in which each particle is composed of two or more different materials, and its particle size must be large (usually greater than 0.5 pm) to show various macroscopic properties. The metal-coated composite powder is a composite powder formed by plating metal on each core particle, which has the excellent properties of both the coated metal and the core. According to the different core materials, metal-coated composite powders are roughly divided into three types: metal-metal, metal-nonmetal, and metal-ceramic, such as glass beads, copper powder and mica powder coated with silver powder and carbon black coated Nickel powder, etc. In addition, there are also composite conductive powders with metal oxide as the outer shell and silicon or silicon compound, TiO, etc. as the inner shell, such as the light-colored Sn Oz coated on the surface of ZnO by Xia Hua et al. Conductive fillers have good conductivity and good application prospects.
There are many kinds of composite fibers, such as nylon, glass fiber, carbon fiber coated metal or metal oxide. The polyacrylonitrile fiber is coated with Cu and Ni, and Ni is plated on the outside of Cu, wax emulsion technique which can keep the inner copper layer from being oxidized and make it have stable electrical conductivity. Another example is the use of electroless plating to deposit a metal coating on the glass fiber to prepare a metal-plated conductive glass fiber, which is used as a composite conductive agent for antistatic coatings.
Leave a message
We’ll get back to you soon