Comparison of Technical Craft and Product Properties of Reflective Glass

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Reflective glass is made by using techniques like vacuum method or chemical coating method to coat the glass with metals such as gold, silver, chrome, titanium, nickel, stainless steel and so on or oxide thin films or nonmetal oxide thin film, or it can also be made through the plasma exchange method. First, infiltrate metal ion into glass surface to replace its original ions. In this way, reflective film can be formed to produce reflective glass. It has a great variety of colors: gray, gold, blue, green, brown, and so forth. The performance principle of reflective glass is predominantly thin film optical theory. It makes use of the infrared reflection property of some thin film materials, while taking advantage of interference effect of thin film over the visible wavelength range. By adjusting the thickness of the films, heat reflection can be realized and the desired color of reflection can be made.

The manufacturing techniques of reflective glass are: evaporation coating, sol gel coating, online spraying thermolysis coating, cathodic vacuum magnetron sputtering coating, etc. However, presently, the most notably techniques in producing reflective glass of large commercial areas are cathodic vacuum magnetron sputtering coating and online spraying thermolysis coating. Currently, among them, heat reflective coated glass produced by cathodic vacuum magnetron sputtering coating technique is the most advanced techniques for large-area reflective glass production internationally.

Online spraying thermolysis coating happens in the annealing prozone of the float glass. In online heat reflection coating, organometallic compound is sprayed onto the upper surface of glass. The high temperature of glass makes the organometal compound break up into metallic oxides to form thin films. Multilayer film is allowed, but it is difficult to control the optical performances. The products belong to hard mould series, and the surface of the film can be used inwardly or outwardly. They can be used by single piece, cut, edging, drill hole, and heat treatment are also available, but the optical performance is bad and the product categories are very few. In online low-e coating, liquid metal powder is directly sprayed onto the surface of hot glass, and as the glass cools down, the metal film becomes a part of glass. So, this film belongs to hard mould series. The products can be hot bended, tempered, and long-term storage. Its weakness is bad thermal property. Unless the film is thick, or its “U” value can be only half of sputtering low-e coated glass. The transparency will become very weak if film thickness is increased to improve its thermal property.

Cathodic vacuum magnetron sputtering coating, also named off-line coating, is the most advanced technique for large-area reflective glass production internationally up until now. Compared with traditional coating method, it has significant improvement in the aspects of functions, labor productivity, cost, etc. Cathodic vacuum magnetron sputtering coating is classified into heat reflecting coating and low-e coating. In heat reflecting coating, first, put the glass into the vacuum chamber, let in the reactant gas, and when the cathode sputtering is charged with electricity, under the effect of electric field, electricity ion will drive out the metal particles to form the charge particles. The accumulation of charge particles on the glass then becomes a thin layer. By this way, multilayer production is available and numerous materials can be produced. Off-line heat reflecting coating has solid and even film, stable chemical property, have access to many ideal optical properties, and rich reflective colors. Off-line low-e coating needs to plate a layer of pure silver as a functional film. The pure silver film is between the two metal oxide films so that it can be protected by the metal oxide films. As the in-between layer of the films, it can increase the color purity and light transmission. There are many metal target materials to choose from and many combinations of metal targets, so, the off-line low-e coatings produced by sputtering method can afford many configurations. Sputtering coating liquid is better than thermal spraying in both color and purity. Off-line method is also more flexible in the aspect of new product development. The uppermost advantage is that the “U” value of the off-line low-e coated hollow glass produced by sputtering is better than pyrolysis method, but the film is comparatively fragile.