There are several important factors to consider when using Reversacol photochromic dyes, in order to maximise the effectivity of the dyes in a particular application. This section deals with the recommended inclusion levels, suitable solvents, processing temperatures and various situations to avoid which may affect performance and lifetime of the dye.
Due to the high purity profile, only very small inclusion levels are recommended. For best effect, typically from 0.01 to 2.0% is sufficient, depending on application. At higher loadings (depending on the matrix) the dyes saturate out and the photochromic response is reduced.
Reversacol dyes are temperature resistant up to a min of 260°C, with some dyes being stable as high as 300°C.
Reversacol dye powders are most soluble in organic polymers and non-polar aromatic solvents such as toluene, THF, xylene. They are sparingly soluble in acetone and ethyl acetate.
All photochromic dyes are unstable in aqueous systems, and are generally intolerant to free radical attack which causes degradation. Low pH, acidic media should also be avoided.
Depending on the matrix, photochromic dyes can fatigue when subjected to extended periods of strong UV-exposure. Lifetimes can be greatly extended by the correct use of an optimised matrix together with stabiliser packages, e.g. HALS-type, anti-oxidants, UV-absorbers.
Photochromic dyes are unlike conventional permanent dyes (e.g. textiles dyes) in that they do not ‘fix’ onto a substrate. They need to be held in place within a suitable matrix for them to function correctly.