engleski

Photo-oxidation stability of microcapsules in thermochromic prints

In this paper, photochemical stability of two thermochromic prints was investigated: vegetable oil based offset and UV curing screen printing ink. The obtained preliminary results can be used for further detailed examination of prints stability. It is well known that thermochromic printing inks are very unstabile when exsposed to UV irradiance and this is why they are mainly used for applications that are not directly exposed to sunlight. The results of the study show the heterogeneous nature of photo-oxidative degradation of thermochromic prints, and the opposite behaviour of photo-oxidation can be noticed comparing examined prints. Microcapsules in the UV curable screen print by fixation with polar polymer binder can create a new product stable to photo-oxidation. For this reason, the areas where the microcapsules and binder are bonded together are stable. Degraded only areas where binder is not related to microcapsules. Microcapsules in offset print do not have the ability to create new stabile forms due to smaller polarity and different chemical omposition of the offset oxidized binder. In the offset print, the microcapsules are the least photo-oxidative stable and also cause lower photo-oxidative stability of the binder in contact with them. Cavities are formed in the areas where microcapsules are in contact with the binder, while the areas in which the binder is not in contact with microcapsules are not degraded.

photo-oxidation, thermochromic, print, offset print, UV curable screen print

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