Preparation of solar heat absorption coating by vacuum coating

This article introduces the preparation methods and development status of selective solar heat absorption coatings, focusing on the preparation of selective solar heat absorption coatings on metal coils by vacuum coating. The coating is used on flat panel solar collectors, which promotes the transformation of solar collectors from a single vacuum glass tube type to a metal flat panel type.

The use of solar energy in light and heat is the inevitable way for mankind to advance towards scientific and sustainable development. The utilization of solar energy in China is in an application situation where evacuated tube solar collectors and flat-plate solar collectors coexist, and the application fields are developing from domestic hot water to heating, drying, cooling, and steam. With the continuous development of the solar thermal utilization industry, the efficiency of solar collectors has attracted more and more attention and research in the industry.

In order to improve the efficiency of heat collectors, people are constantly exploring heat absorption materials, that is, the preparation of heat absorption coatings and the improvement of heat absorption performance. The research and production of solar selective heat absorption coatings is an effective and feasible method to solve the heat absorption efficiency of materials, so that the optical performance of the coating can absorb its energy to the maximum in the visible and near-infrared regions of the solar spectrum, while ensuring all The absorbed energy will not be lost quickly.

At present, the heat absorption coating prepared by the existing coating technology can be divided into four different process methods:

1) One is electroplating coating. It uses conventional electroplating methods to deposit a layer of black chromium film or black nickel film on the metal surface. This kind of coating has good heat absorption performance, the absorption rate α is 85%～90%, and the emission ratio ε is 15%～25%.

2) The second is electrochemical conversion coating. It uses electrochemical methods to form a black compound film on the metal surface through a chemical reaction. This kind of coating also has good heat absorption performance, the absorption rate α is 82%～88%, and the emission ratio ε is 15%～32%.

vacuum coating machine,pvd coating machine,pvd vacuum machine,vacuum ion coating machine,multi-arc ion coating machine

3) The third is spray coating and sol coating. It uses spraying or sol process to spray the silica gel metal powder mixture onto the metal surface to form a thin film. This coating has good weather resistance, but the coating performance decays quickly. The heat absorption rate α is 90%～93%, and the emission ratio ε is 30%～40%.

The manufacturing cost of the above three coatings is relatively low. Although the heat absorption rate is about 90%, their heat emission ratios are all over 15%. In other words, most of the absorbed solar energy is quickly lost, resulting in low thermal efficiency of the collector. Due to the limitations of the above-mentioned three kinds of coating properties, researchers in related fields have to develop new technologies and processes to obtain high-quality solar heat absorption coatings. So far, the vacuum coating technology has been successfully applied to the solar heat absorption coating. This is the fourth method for preparing the heat absorption coating.

The solar heat absorption coating prepared by vacuum coating technology is under vacuum conditions, using magnetron sputtering and electron beam evaporation processes to coat metal sheets or metal coils with multiple layers of metal nitride, metal oxide, Metal oxynitride forms a multi-layer superimposed heat absorption film system, which has an excellent selective absorption function for solar radiation energy. The advantage of this vacuum coating is that it not only has superior heat absorption optical index, solar heat absorption rate is 95%, thermal radiation emission ratio is 5%, and weather resistance, salt spray resistance, and heat aging resistance are better than Heat-absorbing coating prepared by other processes.

Fujian Xinyue Technology has introduced the world's most advanced metal strip vacuum coating production line in Germany according to the needs of China's flat solar collector market and the development trend of heat absorption coating technology. The following introduces the equipment characteristics, process status and related technical issues of vacuum coating for your reference and discussion.

This equipment mainly obtains solar heat absorption panels (known as blue film cores in the industry) by vacuum coating on the surface of metal panels. Synchronous continuous production of metal belts can run at a speed of 10 m/min. Ultra-high production efficiency is one of the biggest advantages of Xinyue continuous vacuum coating equipment. Applying the multifunctional integrated winding production mode of vacuum coating equipment, the rolled aluminum material is exported from the unwinding equipment, and enters the strip gate part at the front end of the vacuum coating process chamber through the strip buffer device. The sealing roller in the chamber of the strip gate allows the metal strip to enter a range where the vacuum gradient gradually decreases to ensure that the strip reaches the required background and working vacuum before entering the coating process chamber. The equipment is equipped with a plasma sputtering etching pretreatment device to process the surface of the metal strip entering the coating process chamber. On the basis of raising the temperature of the substrate, it removes the water vapor, other impurity gases and the thin oxide layer adsorbed on the surface of the substrate. At the same time, it can also achieve better adhesion of subsequent coatings on the surface of the metal substrate through surface activation. Sex.

Coating process part: use DC magnetron sputtering to prepare infrared high reflection layer of selective solar thermal absorption coating; secondly, use twin rotating target intermediate frequency reactive magnetron sputtering to prepare compound main absorption layer and cermet barrier layer; finally apply double Electron gun rotating crucible evaporation process to prepare SiO2 quartz glass antireflection and antireflection layer. These typical vacuum coating processes belong to the environmentally friendly PVD technology with high deposition rate and are suitable for large-area vacuum coating industrial production.

vacuum coating machine,pvd coating machine,pvd vacuum machine,vacuum ion coating machine,multi-arc ion coating machine

After the metal strip is coated, it will also enter a strip gate cavity to realize the connection between the coating process cavity and the atmosphere. This atmosphere-to-atmosphere continuous vacuum coating technology makes the production efficiency of the blue film coating higher and ensures that the coating has the highest quality and optical indicators. It is the process flow chart of Xinyue solar thermal absorption blue film.

The efficiency of any solar heat sink depends on its ability to convert sunlight energy into thermal energy. The high absorption rate of solar radiation should be the most basic condition, and it is relatively easy to achieve. The most challenging is how to store solar energy in the heat-absorbing plate. Highly selective heat-absorbing coating can store heat energy inside the heat-absorbing body (low emission ratio) while reducing reflection.

vacuum coating machine,pvd coating machine,pvd vacuum machine,vacuum ion coating machine,multi-arc ion coating machine

The condition of the new higher selective solar heat absorption coating is that the solar radiation energy is irradiated on a heat radiation surface in a different wavelength range. The solar radiation energy passes through the anti-reflection and anti-reflection layer, the absorption barrier layer, the main absorption layer and the infrared high reflection layer in turn to reach the aluminum substrate, and finally these energy is absorbed and stored inside the heat sink. High absorption rate (low reflection) in the solar radiation range α=95%, low emission ratio (high reflection) in the infrared light rangeε=5%. These characteristics enable Xingao selective solar heat absorption coating to convert more than 90% of solar radiation energy into heat energy.

The selective solar heat absorption blue film system is composed of multiple thin films with different optical properties, which means it belongs to an optical film system. Therefore, all the techniques for preparing optical thin films can be used to produce this blue film system, such as vacuum deposition, electrochemical reaction, chemical vapor deposition and so on. But the deposition technology that is really widely used is mainly electrochemical method, evaporation and sputtering in vacuum coating deposition technology. In the Shinyue Blue film heat sink, the matrix of the absorption surface is metal. Using evaporation and sputtering in the vacuum coating deposition technology on the metal coil substrate, a multilayer film is sequentially deposited on the surface of the metal substrate to form a selective solar heat absorption coating with certain optical characteristics.

Table 1 describes the comparison of optical index parameters between Xinyue and foreign competitors' blue film products. From the table, we can see that the outstanding optical detection indicators of Xinyue Blue Film have reached the world-class level. The solar spectrum absorption rate before salt spray reached 95.22%, and the emission ratio was 5.60%, both higher than the blue film products of foreign competitors. After 72h salt spray test, the absorption rate of Xinyue blue film only dropped by 1.2%, and the emission ratio only increased by 1.4%. The optical indicators after salt spray were also higher than those of foreign competitors' blue film products. The surface of Xinyue Blue Film is smooth after salt spray, without obvious corrosion points, no pits, and slight discoloration on the surface. Some foreign competitors' blue film products have rough surfaces with obvious corrosion points and pits after salt spray, and the surface has serious discoloration.

vacuum coating machine,pvd coating machine,pvd vacuum machine,vacuum ion coating machine,multi-arc ion coating machine

(1) This article introduces the preparation methods and development status of selective solar heat absorption coatings. It focuses on the application of the world’s most advanced continuous vacuum coating equipment and technology by Fujian Xinyue Technology to prepare high-quality selective solar heat absorption coatings on ordinary aluminum-based strips and plates, which promotes the solar collector to be made of a single vacuum glass Transition from tube type to metal flat type. At the same time, the domestic product market for solar thermal utilization has been expanded, and the level of domestic solar thermal film forming technology has been improved.

(2) The characteristics of the Xinyue selective solar thermal absorption coating process are: the use of DC and intermediate frequency magnetron sputtering process to prepare infrared high reflection layer, main absorption layer and metal ceramic barrier layer, double electron gun rotating crucible evaporation process to prepare SiO2 Quartz glass anti-reflection and anti-reflection layer. These coatings are superimposed to form a film system with selective absorption function for solar radiation energy. The continuous and uninterrupted process operation mode of roll-to-roll and atmosphere to atmosphere greatly improves industrial production efficiency. The prepared coating has high deposition rate and good uniformity.

(3) The aluminum-based blue film products produced by Xinyue have the absorption rate in the solar radiation range (low reflection) α=95%, and the emission ratio in the infrared light range (high reflection)ε=5%, most of the energy It can be absorbed and stored inside the heat sink. The coating has high density, few surface defects, weather resistance, salt spray resistance, and heat aging properties are better than heat absorption coatings prepared by other processes.

(4) From the comparison between Xinyue Blue film and foreign products, we can see that the optical index and heat absorption efficiency of Xinyue Blue film are higher than other foreign products, and the thermal performance changes less. The advancement and stability of the preparation technology of Xinyue solar thermal absorption coating has broken the blockade and monopoly of western developed countries on the Chinese market, and has broken the environmental pollution caused by electroplating and other film-forming technologies. It has a clean, environmentally friendly and sustainable development. The practical significance of.

Founded in 2015,Zunhua Baorui Titanium Equipment Co.,Ltd. is a manufacturer specializing in pvd vacuum ion coating equipment. The company’s products mainly include large plate coating machine, large tube collating machine, tool coating machine and LOW-E glass production line. Mr.Wang baijiang ,general manager of the company ,has been engaged in vacuum coating industry for more than 30 years. He continuously improve production technology, improve product performance and devote himself to provide customers with better product experience and higher production efficiency.