Insulating glass is a film product composed of one or more layers of metal and other compounds coated on the glass surface. Its coating layer has the characteristics of high transmission of visible light and high reflection of infrared rays, which makes it have very low far infrared rays The emissivity plays the role of both thermal insulation and thermal insulation, which is in line with the effect of environmental protection and low carbon.
There are many types of thermal insulation glass, which can be roughly divided into LOW-E glass, ITO glass, AZO glass and so on.
Performance and process comparison
⑴LOW-E glass is mainly divided into offline and online
①On-line LOW-E glass refers to the use of high temperature pyrolysis and other chemical methods on the float glass production line to decompose metal halides or organometallic compounds and plate a metal oxide semiconductor film, such as tin oxide film, on the glass surface.
Its biggest advantages are: simple production process, convenient processing, relatively low cost, and certain heat insulation performance. But its biggest disadvantage is that the film thickness cannot be accurately controlled, the optical performance index is difficult to stabilize, and the continuity and repeatability in the production process have certain difficulties, so there is still a certain distance from the high-performance thermal insulation function.
② Offline LOW-E glass is currently widely used in the world by vacuum magnetron sputtering coating technology, using magnetron sputtering and other methods to deposit multiple layers of metal and dielectric films on the glass. The film adopts a silver film as a functional layer. The pure silver film is between the two metal oxide films. The metal oxide film provides protection for the pure silver film, and acts as an intermediate layer between the film layers to increase color purity and light. Transmittance.
Its advantages are: good thermal insulation performance, high degree of process automation, easy film control, stable product quality, excellent optical performance and other characteristics. Thin film materials include: titanium oxide, zinc oxide, tin oxide, silicon oxide, silver, stainless steel, as well as silicon nitride and silicon oxynitride, which have been used in some new processes. The use of the silver layer is crucial, and the existing offline LOW-E glass is also divided according to the standards of single silver, double silver, triple silver, and multiple silver. Its thermal insulation performance is mainly determined by the optical characteristics of silver metal and is irreplaceable.
Therefore, the silver layer plays a decisive role in the offline LOW-E glass. It is precisely because of the use of silver, which brings certain troubles to the subsequent production and processing of LOW-E glass. The silver layer is very easy to oxidize, so single silver, double silver, triple silver and even more silver require many metal films and The dielectric film layer protects the silver layer. Therefore, it requires a longer coating production line and more coating target settings, so the energy consumption is very large, and the price of the equipment is very expensive (of which foreign import equipment requires hundreds of millions of yuan, domestic equipment also needs tens of millions of yuan), the disadvantages of coating products are: The storage period is relatively short, the moisture resistance is not ideal, and the oxidation resistance is low. It cannot be used in a single piece exposed to the air. It must be processed into a composite product such as a hollow interlayer to use the film.
These characteristics determine that the application of LOW-E glass is restricted to a certain extent. Due to various problems, it can be used in most high-end office buildings and buildings. It is also difficult to expand to other areas on a large scale. Low-E glass is rarely used in the field of home appliance panels.
⑵Insulation glass principle of ITO and AZO
AZO and ITO thin films are transparent and are both TCO heat-insulating glass. They are materials with conductive properties. This material has a wide energy gap n-type semiconductor material. The space occupied by electrons and the energy level occupy a certain amount of energy. The gap (forbidden band), so a beam of energy incident will cause energy reflection, the outer electrons are excited, and a shock of the same frequency as the incident energy is generated, and this shock emits energy of the same frequency as the original energy, reflecting this incident energy Go back, so as to release energy into the air for the second time, so that as the air flows, the energy is absorbed and taken away, resulting in thermal insulation. This is the principle of conductive and thermal insulation of ITO and AZO films.
①Performance of ITO glass
ITO is short for IndiumTinOxide. The ITO film is an n-type semiconductor material with a band gap of 3.5-4.3 ev. The excitation absorption threshold for the forbidden band in the ultraviolet region is 3.75 ev, which is equivalent to a wavelength of 330 nm. Therefore, the light transmittance of the ITO film in the ultraviolet region Very low. At the same time, the near-infrared region is reflected by the carrier's plasma vibration phenomenon, so the light transmittance of the ITO film in the near-infrared region is also very low. At the same time, it has high conductivity, high visible light transmittance, high mechanical hardness and good chemical stability. Therefore, it is the most commonly used thin film material for the transparent electrodes of liquid crystal displays (LCD), plasma displays (PDP), electroluminescent displays (EL/OLED), touch panels (TouchPanel), solar cells and other electronic instruments.
However, as the main material of ITO, indium is a rare metal and is known as "industrial monosodium glutamate". The distribution of indium in the earth's crust is relatively small and scattered. Its rich minerals have not been discovered. Although the amount of mineral deposits is small, it is indispensable. At the same time, indium is toxic. It is more toxic than lead. It is harmful to the environment during its mining and production processes and can cause pollution to water bodies. It is for this reason that ITO targets are relatively expensive. Therefore, the use price of ITO glass is pushed up, and the application field of ITO glass is limited. If it is applied to the field of thermal insulation glass, its price is difficult to be accepted by the market and has no price advantage.
②AZO glass performance
AZO, also known as zinc aluminum oxide, is considered to be one of the most promising materials. It is also a cheap, reliable, and environmentally friendly transparent conductive film material. It is the best substitute for ITO film. AZO materials are stable, raw materials are rich and non-toxic, easy to dope and prepare, so that it has a wide range of applications. In the field of flat panel displays such as electroluminescent displays (ELD), electrochromic displays (ECD), and plasma displays (PD), AZO thin films with low resistivity and high transmittance will also play a huge role. The AZO transparent conductive film generates heat when energized. Using this, it can be used for the anti-fog and anti-frost of cars, aircraft windshields, camera lenses and ski glasses.
The advantages of AZO glass are: it has high chemical stability, is easy to manufacture, and the film layer is also more rigid. The AZO film does not have a long crystal structure chain, which can greatly reduce the manufacturing cost; the surface is smooth, the oxidation resistance is strong, the thermal insulation performance is excellent, the high temperature resistance, the high temperature stability is strong, the radiation protection performance is good, suitable for large-scale production. At the same time, the AZO film has high transmittance in the visible light region, high reflectivity to infrared light, plays a heat shielding role, and saves energy consumption. The above characteristics of AZO film also determine its ideal material for heat insulation glass.
With the rapid development of industrial modernization, thermal insulation glass is widely used in various fields. However, due to the different thermal insulation requirements of various industries, how to choose thermal insulation glass in a reasonable application field can achieve high performance and reasonable Cost-effective. The current status quo is that most of the construction industry is still represented by LOW-E glass, and TCO glass in the fields of home appliances, automobiles, and solar energy is the dominant. It is hoped that the application field of thermal insulation glass can be expanded more widely in the near future.