On the characteristics and application technology

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Talking about the characteristics and application technology of metal nano ink

nanotechnology is a far-reaching high-tech in this century. Its emergence gave birth to a large number of new disciplines. Such as nano physics, nano chemistry, nano biology, nano materials science and so on. 20 ⑶ 5 the research object of nanotechnology is the material or structure with the scale of 1~100nm, including the manufacturing and processing technology of nano materials, characteristics and application technology, characterization and measurement technology, etc. The so-called nanometer is actually a unit of measurement of length, but this unit is very small. 1nm = 10-9m, i.e. 1 billionth of a meter. It has been found that due to the small size effect, surface and interface effects, and quantum effects of substances in the nano scale, they (nanoparticles, nanowires, nano films) show a series of unique properties in many aspects, such as sound, light, electricity, magnetism and mechanics. For example, ordinary metals are mostly solid at room temperature, like gold, silver, copper and iron, which have high melting points. The case of metals in nano state is not the case. If we put gold nanoparticles in the palm of our hand, we can find that the particles will melt into a paste like ice. Moreover, some metal nanoparticles will spontaneously ignite due to strong oxidation even in normal air

as we all know, ordinary ink is a complex polymer composition, which has specific viscosity and excellent printability. The main ingredients are pigments (dyes), polymer binders, solvents and a small amount of additives. When inking, people put the above components in a certain proportion into special equipment, and after full dispersion, a uniform printing ink with a certain viscosity and thixotropy is prepared. The composition and manufacturing method of nano ink are no different from ordinary ink. If there is any difference, it is only the pigment particles used in the two inks, which are very different in particle size. The pigment particle size of ordinary ink is micron (m), while that of nano ink is nanometer. The difference between the two is about 1000 times. It is understandable that the introduction of nano pigments with specific properties will bring modest changes in some aspects of its ink manufacturing process. Although both nano ink and ordinary ink are used for the printing of products, the former mainly focuses on the application of special functions, while the latter is often used for the printing of monochrome or color printing materials

Recently, although nano ink has just emerged, it has initially shown excellent performance and great attraction in the fields of processing and installation of electronic components, decoration and decoration of high-end products, sterilization and testing in medicine, and anti-counterfeiting printing of special products. This paper focuses on the metal nano ink and its application in the electronic field in my haydale company. In addition, the relevant theoretical issues are also briefly discussed

as mentioned above, nanoparticles are the core component of nano ink. The nanoparticles used in ink can be organic or inorganic according to their properties; It can be metallic or non-metallic; Or their oxides. According to the different application fields of ink, people can choose freely. The particle size of nanoparticles used in nano ink should be several nanometers. It should be noted that the particle size of nanoparticles often refers to the average value. Even for products of the same production batch number, it is difficult to achieve complete consistency in the particle size of each particle, but only aggregates with different size distribution. It should be emphasized here that not all nanoparticles can be used as pigments of nano ink. The reason is very simple: ordinary nanoparticles have large surface activity and high energy, and particles are very easy to agglomerate in groups. Once there is agglomeration between particles, it is difficult to disperse them with general methods. Nano particles used in nano ink have special requirements, that is, each particle should have monodispersity, which is the technical key to the success of nano ink manufacturing

1. Monodisperse nanoparticles

nanoparticles have the typical characteristics of extremely small particle size and very large surface area. With the sharp increase of particle surface energy, the melting point decreases significantly. For example, under normal conditions, the melting point of gold is 1063 ℃. However, when solid gold turns into gold nanoparticles with a diameter of 2nm, the melting point changes significantly, and it has decreased from 1063 ℃ to a level close to room temperature. Using this property, people can easily sinter it into a metal conductor even at a very low temperature

the fundamental difference between monodisperse nanoparticles and ordinary nanoparticles is that the surface of the former has been coated with a thin layer of special coating agent, so that the surface activity of particles and the decline of their melting point are temporarily suppressed in a moderate range. Even in solvent or resin solution, it can always maintain the characteristics of uniform dispersion. In other words, the monodisperse stability of the particle is excellent. This is what nano inks are eagerly looking forward to in their manufacture or storage. However, ordinary nanoparticles are completely different. Their surface is not protected by any protective film, but directly exposed to the outside world. The original excessive surface activity and high surface can make the particles always in an unstable state, and particles are easy to agglomerate with each other

the manufacturing methods of metal nanoparticles generally include physical methods and chemical methods. As one of the physical methods, evaporation method is to add the metal to the molten state in a container full of inert gas, so that the vaporized metal can solidify rapidly into metal nanoparticles. The advantage of this method is the high purity of the product, but the disadvantage is the poor continuous production of nanoparticles. The production of metal nanoparticles by chemical methods can be divided into dry method and wet method. No matter the former or the latter, their respective product purity is not too high, often containing a small amount of impurities such as alkali or sulfide. In this regard, we have to add a complex purification process in order to purify the metal nanoparticles just produced. Although chemical methods can be produced continuously in batches, there is still room for price increase, but the total cost of their products after purification is too high. In short, in order to obtain high-purity metal nanoparticles, it is necessary to carefully compare and carefully select the most reasonable process methods

2. composition and characteristics of metal nano ink

as mentioned above, metal nano ink is composed of metal nanoparticles (monodisperse particles), resins, solvents, additives, etc., which are uniformly dispersed in a certain proportion

metal nanoparticles are one of the most important components in ink, and it is the only source of making printed graphics conductive. Its conductivity mainly depends on the metal properties of nanoparticles, that is, the smaller the inherent resistance of metal, the better the conductivity, and vice versa. Such as silver, copper, gold and so on have good conductivity. Theoretically, their nanoparticles can be used as nano ink raw materials. However, this is not always the case in practical inking applications, because we have to consider the chemical reactivity of the metals used. The chemical activity of metals such as copper is relatively large, and its particles, especially nanoparticles, are easy to be oxidized in the air and lose the characteristics of metals. At present, it is still difficult to solve this problem from a technical point of view. Therefore, the actual example of copper nanoparticles used in nano ink has not been reported yet. On the contrary, gold and silver have stable chemical properties and good conductivity, so their nanoparticles have become the main raw materials for today's metal nano inks

as another important component of metal nano ink, thermosetting resin has two functions: first, monodisperse metal nanoparticles are incorporated into the resin system to become a uniform resin component with certain viscosity and printability; The second is to give the ink some bonding function, so that the printing ink can be firmly attached to the printed substrate. Therefore, the chemical structure and molecular weight of the resin are very critical and cannot be neglected. Commonly used resins include acrylate resin, phenolic resin and epoxy resin. It is necessary for people to choose polymer resins with corresponding chemical structures according to different printing substrates. The main functions of solvent in ink: first, it is used to dissolve solid resin and make it a resin solution for ink matching; Second, it is used as diluent to adjust the viscosity of ink to meet the requirements of printing. When the resin is selected, what solvent is appropriate? Here we need to look at the solubility parameters of resin and solvent. If these two parameters are close, it means that the solvent is a good solvent for this resin, that is, it has good solubility. On the contrary, it cannot be used as the solvent of the resin. Commonly used organic solvents include toluene, xylene, cyclohexanone, butanone, diacetone alcohol, ethylene glycol ether and some higher alkanes. Nowadays, all countries attach great importance to the relationship between environment and people, 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 some properties of ink and improve the quality of ink, a small amount of additives are often used. Such as surfactants, leveling agents, plasticizers and defoamers. Although both silver nano ink and ordinary conductive silver ink are used for conductive printing, the performance and application of the two inks are also significantly different due to the different conductive particles used

3. mixed silver ink (silver powder + silver nanoparticles)

ordinary conductive silver ink is often used for conductive printing of thin-film switches and thin-film circuits. However, when facing the printing of electronic products with faster transmission speed and higher performance requirements, ordinary silver ink has great defects in both conductivity and reliability, which can not meet the higher requirements of this kind of electronic products for ink. It is true that we can choose not to use silver nano ink to complete this task. However, if the products do not have ultra-fine printing requirements, we rush to use silver nano ink for printing, It is inappropriate from the perspective of operation and management. The reason is that this means that the performance of the selected raw materials is excessive, that is, people often say that a big horse pulls a small car, which is an unnecessary waste. In this regard, people have developed a new product called mixed silver ink, which uses a small amount of silver nanoparticles to modify metal silver powder (sheet or spherical). This product is very suitable for the printing processing of electronic products with high conductivity, high reliability and no special fine requirements. Table 3 lists the composition and characteristics of the ink

in the mixed silver ink, the total content of silver has a great influence on the conductivity of the ink. The experiment shows that the silver content accounts for 80% - 95% of the solid components of the ink. The silver content is too small, and the conductivity of the ink is insufficient; On the contrary, too much silver will also damage the conductivity of the ink for other reasons. When the silver content is 85%, the volume resistance of the ink is within 1010-6cm. When the silver content rises to 90%, the volume resistance decreases to the minimum value, that is, 610-6cm. After that, as the amount of silver in the ink increases, its volume resistance does not decrease, on the contrary, it gradually increases. The reason here can be explained as follows: when the amount of silver in the ink increases to the maximum, in other words, the percentage content of resin adhesive (binder) has reached the minimum. At this time, the resin content is further reduced (silver content

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