1. Production process
Online Low-E glass is produced after the process of float glass by spraying a chemical solution with Tin compounds as the main component on the hot glass surface to form a single layer of Tin Oxide (SnO2) compound film with a certain low emissivity function.
Offline Low-E glass is made in a large area glass coating line, using a vacuum magnetic sputtering method to uniformly sputter silver (Ag) and other metals and metal compounds on the glass surface. It consists of at least four-layer films with a pure silver film between two metal oxide films. The metal oxide film provides protection for the silver layer and acts as an intermediate layer to adjust the color appearance and light transmittance.
2. Variety and appearance
The online Low-E glass has not many choices of colors & performance. The parameters such as transmittance and reflectance are not adjustable.
Offline Low-E glass has a variety of options, such as high, medium, and low transmissions according to different climate characteristics. Offline Low-E glass has rich and varied colors, parameters such as transmittance and reflectivity can be adjusted according to design requirements, the Offline Low-E glass film layer is more uniform, the color is more natural, and it presents different visual effects when reflected against the sun by different weathers.
3. Performance parameters
The spectrum of online Low-E glass shows the characteristics of tin oxide conductive film, while the spectrum of offline Low-E glass shows the characteristics of both silver and tin oxide composite film, both of which have a good transmission for visible light and near-infrared light.
Offline Low-E glass has much higher reflection and has less absorption & higher reflection of far infrared than the former. Therefore, compared with online Low-E glass, offline Low-E glass has an extremely low shading coefficient and extremely low U-value.
4. Technique and cost
The production technology of online Low-E glass belongs to chemical coating, the equipment and process are relatively simple, the production cost of the glass product is relatively low.
The production technology of offline Low-E glass belongs to high vacuum magnetic sputtering coating, and the equipment and process require experienced operations and technique support. The production cost is relatively high.
5. Product applications
In many countries, online Low-E glass is mainly used for low rise buildings. This is because online Low-E glass can be used in a single panel, and the price is relatively cheaper. The offline Low-E glass mostly will be adopted as insulated glass or other compound products with excellent performance and relatively high price, which is used in high-end buildings such as commercial buildings.
6. Product stability
Some people are still worrying that the offline Low-E glass coating will have the problem of silver oxidation. As a matter of fact, research and experimental data results show that the silver layer inside of the insulated glass with a dry gas environment will not oxidize at all. Over the past 20 years of offline Low-E application, experience shows us that offline Low-E glass insulating glass is a long-term stable product.
Online Low-e glass has good processability, It requires only simple production equipment, good for the tempering process, not easy to cause a scratch. It can be bent and tempered. The offline Low-e glass has higher requirements on the glass processing plant, such as a higher requirement of tempering machine and operation experience of the operators, high requirement of the water purity, etc. For the insulating glass process, the quality of the desiccant, aluminum spacer, butyl sealant (first sealant), and silicone sealant (second sealant) must also be very high! Otherwise, the offline Low-e glass might oxidize and color will change as well.
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