Glass substrates are used for a variety of purposes, from automotive to architectural applications. Generally, glass manufacturers produce standard size glass sheets in large quantities and then cut the glass to size based on the customer requirements. Some of the glass will have to be bent into various shapes. Typically, glass is shaped using a bending process which requires heating the glass. In addition to bending, glass may be subjected to a heating operation for tempering or heat strengthening, as is well known in the art. The most efficient bending, tempering and heat strengthening processes take place at temperatures ranging between 1150° F. (621° C.) and 1450° F. (788° C.).
Depending on the end use of the glass substrate, the glass will need to exhibit various performance properties such as emissivity, visible light reflectance, color, etc. The glass substrates can be coated with a functional coating so that the substrate can achieve the desired performance properties. Functional coatings such as photocatalytic coatings, solar management coatings, low emissivity coatings, conductive coatings, etc. are well known in the art.
As can be gleaned from the above, customers often require a glass substrate that will be both coated and heat treated. In many instances, it is desirable to form a heat treated, coated substrate by first coating the substrate and then heat treating it. If the heating step is being performed to bend the glass, for example, it is simpler to apply a coating composition to a flat glass substrate and then bend the substrate than vice versa.
For a given project, such as a commercial construction project, a customer will need coated glass that has been heat treated and coated glass that has not been heat treated. Ideally, the heat treated, coated glass and the non-heat treated, coated glass will exhibit the same appearance and provide similar functional characteristics. This would be the simplest solution for both the glass manufacturer and the customer.
It has been difficult to design coating compositions for glass substrates that allow the coated substrate to have the same appearance after it has been exposed to a heating operation such as bending, tempering or heat strengthening as it did before the heating operation. It would be desirable to have a durable coating composition that can be applied to a glass substrate to provide a coated substrate having the same appearance regardless of whether or not the coated substrate has undergone a heating operation. The present invention provides such a coating composition.