Why should food packaging be kept out of direct sunlight? -- Reinterpretation of photoinitiator

If you look at the food packages around you, some of them say "Store in a cool, dry place. Avoid direct sunlight ".

One reason is that the packaged food contains water. Food goes bad easily after being heated by direct sunlight.

In food packaging, on the other hand, an additive called photoinitiator is often used, which is an important component of the ink printed on the packaging material. Under the light, the photoinitiator may decompose to produce free radicals, resulting in polymer cross-linking and degradation, affecting the physical and mechanical properties and service life of the product; There may also be by-products (such as aldehydes) that pose a risk of chemical migration.

For now widely used UV inks, because the photoinitiator in the printing process can not be completely transformed or removed clean, low molecular weight photoinitiator applied to the surface of packaging materials is still likely to migrate to food. In addition to generating free radicals, photoinitiator may produce byproducts (such as aldehydes, etc.) in the process of illumination, and these byproducts also migrate to food or release odor.

In addition, photoinitiators are generally added in excess to the photocuring system. In addition to the normal reaction photoinitiator, the remaining photoinitiator will gradually decompose and produce free radicals under the action of sunlight, leading to the cross-linking and degradation of polymer macromolecules, making the coating yellow and brittle, affecting the physical and mechanical properties and service life of products.