The development of a high performance low emissivity (Low-e) window film has been a challenge as well as a great opportunity. Retrofit versions have been around for years, in spite of their typical performance that is lower compared with coated glass. The challenge has been the abrasion and corrosion protection of the infra-red reflecting coating. Low emissivity and visible light transmission are typically achieved by very thin, highly IR reflective metal layers, e.g. silver or multilayer stacks that are typically very soft. Unlike sealed glass windows, retrofit film coatings have to be able to withstand household cleaning chemicals and abrasion from cleaning tools. Polymeric protection coatings are normally used; however, they absorb radiation in the thermal IR range thereby greatly reducing the benefits of the IR reflective coating. In this paper we will discuss the development of retro-fit window films that have overcome the common issues with these products. These films have significant performance improvements, with emissivity below 0.1 and in the same order of coated glass. They are also corrosion resistant, compatible with common window cleaning chemicals and can withstand abrasion from typical cleaning tools.
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