Лако-красочные материалы — производство

Adhesives used to temporarily fixture glass elements to allow processing are required to cure within seconds, without shrinking. After processing, they are required to debond quickly, without harming the surfaces. Whilst conventional adhesives are not suited to this task, hot melts do meet the requirements of this application, provided that no strains are produced in the optical elements when the adhesive cools to room temperature after having been heated for the bonding process.

For optical cementing, the adhesive must have optical clarity and a matching refractive index, without causing any strains. Optical cements are used to bond the majority of devices used for optical observing, in optical measuring instruments and in space research, in medical devices required to be designated ‘sterile’, and in sensor technology. According to the relevant application, the requirements for optical clarity and resistance to aging may differ considerably. In optical compo­nents, the cement must compensate for the different coefficients of thermal expansion of the optical glasses, and the cement layer will differ depending on the refractive index and thickness of the adhesive. Black or dark adhesives are well suited for the bonding of optical elements into mechanical mounts because they reduce light scatter. Flexibility is crucial for these adhesives in order to prevent strains from being induced in the optical elements in as wide a temperature range as possible. The elements to be bonded generally have differences in thermal expansion. When the correct adhesive is chosen, its flexibility — as well as a predefined thickness of the bond-line — can help to minimize the strains induced. Bubble-free application is necessary to provide for imperviousness and resistance to moisture-induced aging. In order to ensure correct adhesion of the cement to the glass surface, the surface must be cleaned prior to bonding. The mounting adhesives must be resistant to fungal attack and also exhibit low outgassing figures. Thus, the cements used for mounting optical elements include epoxy, polysulfide,

polyurethane and urethane-modified acrylic, as well as silicone-based adhesives. Currently, the use of UV-cured adhesives is still increasing.

8.8.2