General knowledge of coatings: Research Progress of conductive coatings

Core tip: 0 Preface Conductive coating is a kind of functional material with the rapid development of coating industry and modern industry in recent years It refers to the coating applied on non-conductive substrate, which has a certain ability of conducting current and dissipating static charge Most of its film-forming materials are insulated In order to make the coating have conductivity, the common treatment method is to add conductive particles At present, some developed countries are developing conductive coatings, among which Japan and the United States started earlier in this field Most of the products developed are conductive coatings filled with nickel powder, copper powder, silver powder and carbon black Conductive coating as conductive Application scope and advantages of roller ceramic coating Recommended introduction: the surface of ceramic rubber plate used for roller ceramic coating is cast into durable rubber plate by hundreds of independent small ceramic pieces Each ceramic piece has raised characteristics Under general conveyor belt pressure, thousands of unique cast bumps can produce positive traction, prevent slipping and extend the service life of conveyor belt roller At the same time, the bottom layer adopts high-quality rubber, which has strong elasticity and can play a good impact resistance role The scope of application of roller ceramic coating is one three six 83857180 (the same as V) 1 Roller coating in extremely harsh working environment 2 The belt joint is not suitable for fixing with iron buckle; 3 It is suitable for leather The conductive coating is a kind of functional material with the rapid development of coating industry and modern industry in recent years It refers to the coating applied on the non-conductive substrate, which has the ability of conducting current and dissipating static charge Most of the film-forming materials are insulating In order to make the coating have conductivity, the common treatment method is to add conductive particles At present, some developed countries are developing conductive coatings, among which Japan and the United States started earlier in this field Most of the products developed are conductive coatings filled with nickel powder, copper powder, silver powder and carbon black As a conductive coating, conductive coating has important practical value in electronic industry, construction industry and aviation technology In this paper, the research progress of intrinsic conductive coatings and dopant conductive coatings is reviewed The development of intrinsic conductive coating the intrinsic conductive coating is a kind of conductive coating which takes the intrinsic conductive polymer as the film-forming material At present, most of the preparation methods of conducting polymer used in conducting coating are focused on the direct use of conducting polymer as film-forming resin, the mixed use of conducting polymer and other resins, and the use of conducting polymer materials as conductive fillers, among which polyaniline, polypyrrole, polythiophene and Polyquinoline are the most typical research fields, Polyaniline and polypyrrole are more studied Polypyrrole (PPy) is a kind of conductive polymer material with wide application prospect In the presence of oxidant, pyrrole (py) monomer can be oxidized and polymerized into PPy rapidly, but pure PPy has poor conductivity without doping Good conductivity can only be obtained after doping with appropriate dopant The two doping structures of conductive polypyrrole are shown in Figure 1 Shangxiuli [1] et al Synthesized polypyrrole (PPy) in cellulose acetate (CA) matrix by phase separation in situ polymerization can make even PPy / Ca conductive composite film After the film is formed, the film surface (reverse side) towards the glass is insulated, while the film surface (front side) towards the solution is conductive When the ratio of pyrrole to cellulose acetate is 0.091, the surface resistance of the conductive composite film is about 20 Ω / cm Among many conductive polymer materials, polyaniline is considered to be the most promising conductive polymer material because of its low cost, simple synthesis, high conductivity, high temperature resistance, good oxidation resistance and environmental stability The intrinsic polyaniline is non-conductive, and only after doping with proton acid can it have conductivity, while polyaniline doped with macromolecular proton acid has more excellent conductivity, because on the one hand, macromolecular proton acid has surface activation, which is equivalent to surfactant, and doping into polyaniline can improve its solubility; on the other hand, macromolecular proton acid is doped into polyaniline, The conformation within and between polyaniline molecules is more favorable to the charge delocalization on the molecular chain, and the conductivity is greatly improved Li Hongmin et al [2] prepared polyaniline / acrylate copolymer (AA) conductive film by solution blending method with polyaniline (PANI) doped with dodecylbenzenesulfonic acid (DBSA) as conductive component and chloroform as solvent The results show that polyaniline particles are uniformly distributed in the matrix to form a better conductive network, which makes the blends have good conductivity Liu Yijun et al [3] prepared a kind of conductive polyaniline with low cost and high conductivity doped with inorganic acid by oxidative polycondensation method Using the polyaniline as conductive filler and epoxy resin as film-forming material, a new conductive coating with conductivity in the range of 10-8 ~ 10-5s / M was prepared Ningxiaohui et al [4] synthesized polyaniline with nanometer size by chemical oxidation polymerization Using polyaniline as conductive filler and acrylate as film-forming material, a new anticorrosive conductive coating with conductivity in the range of 10-8-10-4s / M was prepared 2 the research progress of dopant conductive coating dopant conductive coating is based on the polymer added conductive materials, using the conductive effect of conductive materials, to achieve the coating conductivity of more than 10-12S/m It not only has the conductive function, but also has many excellent properties of polymer It can adjust the electrical and mechanical properties of the coating according to the needs of use in a large range, and has low cost, simple and easy operation, so it has been widely used The dopant type conductive coating is composed of polymer, conductive filler, solvent and assistant The commonly used conductive fillers include metal system fillers, carbon system fillers, metal oxide system fillers, composite fillers, new nano conductive fillers, etc 2.1 carbon system conductive coating carbon system conductive coating is a functional coating with large amount at present, which has the advantages of low cost, light weight, high structure, non-toxic and harmless The conductive fillers used as carbon conductive coatings mainly include graphite, graphite fiber, carbon fiber, high temperature calcined petroleum coke, various carbon black and silicon carbide, etc In particular, the conductive polymer filled with carbon black has been widely used, because the conductive carbon black has the advantages of low price, small density, not easy to settle and strong corrosion resistance, but the conductivity is relatively poor; at the same time, because the surface contains a large number of polar groups, it is difficult to disperse and easy to flocculate, One of the most simple and effective solutions is to add dispersants to reduce the attraction and cohesion of carbon black particles, so that they can be evenly and stably dispersed in the matrix Carbon based conductive coatings are usually composed of conductive fillers, matrix resins, auxiliaries and solvents After mechanical mixing, they are coated on the surface of non-conductive substrate to form a special curing film, which produces conductive effect According to the existing carbon conductive coating samples and research reports, we can see that the basic method is to increase the content of conductive filler to improve the conductivity of the coating Huang Pengbo et al [5] studied the influence of three titanate coupling agents ntc-401, ct-136, JSC and two silane coupling agents KH-550, KH-570 on the conductivity of carbon black conductive coating The results show that the resistance of the system increases with the addition of ntc-401, ct-136 and JSC, while KH-550 and KH-570 reduce the resistance of the system, among which KH-550 with the mass fraction of 2.5% is the best Yu Dongxiu et al [6] developed a kind of modified carbon fiber system conductive coating based on acrylate resin The influence of the modified carbon fiber / resin mass ratio, the type and amount of coupling agent, the way of adding and the curing process of the coating on the electrical energy of the coating was determined by single factor method, The optimum technological conditions for the preparation of the conductive coating of carbon fiber system were determined as follows: the mass ratio of modified carbon fiber to resin was 0.7, the amount of tmc-102 pretreated with 1% (mass fraction) and the amount of tmc-102 added directly with 1.5% (mass fraction), the comprehensive properties of the conductive coating were better; the curing temperature was 50 ℃, the curing time was 20 minutes, and the film thickness was 150 μ M, Its surface resistivity reaches 1.02 Ω / sq Gan Yusheng [7] studied the substitution of non-metallic conductive coating for metallic conductive coating, and selected silica sol as the carrier, ultrafine graphite and high structure carbon black to prepare the coating according to different proportions; and tested the coating thickness and surface resistance of the coating, and screened out the ratio suitable for shell making; verified by different steel processes, This kind of coating can be used in investment casting shell making of various iron and steel castings It has a wide range of raw materials and low price 2.2 graphite conductive coating graphite is a kind of high conductive layered material, which can be used as conductive filler and compounded with conductive polymer to prepare polymer matrix composite with excellent conductivity Graphite coating, with its good conductivity, low price and simple operation, has an irreplaceable position in the inner and outer coating of the color tube glass shell In order to make the coating have good conductivity, it is necessary to prepare high-purity ultra-fine graphite through deep processing to meet the needs The crystal structure of natural graphite can be divided into two kinds: crystalline (scale) and aphanitic (earth) Under high power microscope, the coating made of flake graphite has good conductivity due to the overlapping of graphite particles and no gap between particles Although the earth like graphite particles are closely arranged, the particle shape is very irregular and the surface is rough Compared with flake graphite, the conductivity is slightly poor, but it can still meet the requirements of low resistance internal conductive graphite coating In recent years, with the development of nanotechnology, the conductive polymer materials made by the composite of graphite nano materials and matrix are rising day by day; as a new type of conductive filler, expanded graphite has the advantages of good conductivity, small friction loss, small pollution, etc., and the addition of expanded graphite can greatly improve the conductivity of polymer materials, reduce its conductive percolation field filter value, Therefore, it has an important application value in antistatic coatings and conductive polymer composites The shape of the conductive filler has a great influence on the conductivity of the material It is generally considered that the conductive particles are better in sheet shape and worse in ball shape Because the sheet particles have more surface contact, the probability of forming a conductive channel is greater, while the spherical particles are point contact, the probability of forming a conductive channel is much smaller Wang Hengfei and other [8] developed water-based coatings with graphite as conductive filler and styrene acrylic emulsion as the base material The relationship between the amount of graphite and water, curing temperature and volume resistivity, and the relationship between coating resistance and temperature were analyzed The results show that when the graphite content is 14% ~ 20%, the water content is 55% ~ 65%, and the curing temperature is 70 ℃, the conductivity of the coating is the best, and the resistivity is 0.25 Ω· cm Zhang Lulu et al [9] modified the traditional solventless epoxy glass flake coating with self-made chemical silver plated flake graphite, and prepared the glass flake conductive coating The resistance, surface dry / dry time, thickness, hardness, corrosion resistance and BSE photos of glass flake conductive coating with different mass fraction of electroless silver flake graphite were studied The results show that the surface dry / dry time is shortened, the thickness is increased, and the hardness and corrosion resistance of the coating are improved The optimum mass fraction of the scale graphite in the coating is 30% Yang Chao et al [10] prepared a waterborne tertiary fluorine / expanded graphite composite conductive coating with water based tertiary fluorine emulsion as base material, expanded graphite as filler and adding other fillers and auxiliaries The effects of the mass fraction of expanded graphite, dispersant and temperature on the conductivity were investigated The results show that the 26% mass fraction is better