Metal Nano Ink and Application Technology in the Electronics Industry (II)

March 14, 2019

2. Composition and Characteristics of Metal Nano Ink

As described above, metal nano inks are uniformly dispersed by a certain proportion of metal nanoparticles (monodisperse particles), resins, solvents, additives, and the like. Table 1 lists the composition and properties of metallic nano inks.

Metal nanoparticles are one of the most important components in inks, and they are the only source of conductivity for printed graphics. The good or bad of its conductivity mainly depends on the metal properties of the nanoparticles, that is, the smaller the intrinsic resistance of the metal, the better the conductivity, and vice versa. For example, the conductivity of silver, copper, gold, etc. are all good. In theory, their nano-particles can be used as nano-ink materials. However, it is not always true in actual ink application because we also have to consider the chemical reactivity of the metal used. The chemical reactivity of metals such as copper is relatively large, and the particles, especially nanoparticles, are easily oxidized in the air and lose their metal properties. At present, to solve this problem, from a technical point of view, there are still some difficulties. Therefore, practical examples of copper nanoparticles for nano inks have not been reported so far. In contrast, gold and silver have stable chemical properties and good electrical conductivity, so their nanoparticles have become the primary raw material for metal nanoinks today.

As another important component of the metal nano ink, the thermosetting resin has two functions. First, the monodisperse metal nanoparticles are incorporated into the resin system to become a uniform resin composition having a certain viscosity and printability; The ink is given a certain adhesive function so that the ink can be firmly attached to the printed substrate. Therefore, the chemical structure and molecular weight of the resin are critical and cannot be ignored. Commonly used resins include acrylate resins, phenolic resins, and epoxy resins. It is very necessary for people to select the appropriate chemical structure of the polymer resin according to different printing substrates.

The main role of the solvent in the ink: First, it is used to dissolve the solid resin, making it a resin solution, so as to match the ink; second, it is used as a diluent to adjust the ink viscosity to meet the printing requirements. When the resin is selected, what kind of solvent is appropriate? Here depends on the solubility parameters of the resin and solvent. If these two parameters are relatively close to each other, it indicates that the solvent is a good solvent for this resin, ie, the solubility is good. On the contrary, it cannot be used as a solvent for the resin. The most commonly used organic solvents are toluene, xylene, cyclohexanone, butanone, diacetone alcohol, glycol ethers and certain higher alkanes. Today, all countries attach great importance to the interrelationship between the environment and people, the environment and society. The toxicity of solvents and their impact on the surrounding environment are major issues that must be considered.

In order to improve certain properties of the ink and improve the quality of the ink, a small amount of additives are often used. Such as surfactants, leveling agents, plasticizers and defoamers.

Silver nano inks and common conductive silver inks are used for conductive printing, but due to the different conductive particles used, the performance and application of these two inks are also significantly different. Table 2 is a comparison of the characteristics of silver nano inks and ordinary conductive silver inks.

From Table 2, it can be seen that metal nano inks have similarities with common conductive silver inks, and there are also different places. When using them, they should be appropriately selected according to the purpose and object.

(to be continued)

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