Principle of light stabilizer
As beautification and protection of substrate coating itself is in need of protection, in particular for hazardous substances in the environment such as heat energy, oxygen, water, and light. Although most of the polymers do not absorb ultraviolet light directly, but all the paint more or less contains materials that absorb UV light, causing resin peroxide substance.
Ultraviolet radiation (which comes from the Sun) will make the coating’s performance and to make it worse. Artificial light will produce the same effect. Ultraviolet rays harmful to the damage the polymer’s chemical bonds. This makes resin degradation leading to changes such as loss of gloss paint, powder, discoloration, yellowing, loss, loss of physical performance and protection. This chemical process called photo-oxidation.
UV-LED light oxidation process
Photo-oxidation are two important processes. First is the photodissociation process, the complex processes that exist in multiple steps, including UV, and then open the molecules key to the formation of free radicals. The second process is the oxidation process, formed in the photolysis of radicals react with oxygen to produce superoxide free radicals.
In the photo-oxidation process has 5 steps. In the following description, the r stands for paint resins easily oxybenzone in parts.
Paint absorbs UV radiation. UV-absorbing substances (such as resin or impurities) will be absorbed into high energy excitation energy of the excited state (R*). These excited molecules are very active, and goes through a variety of processes. Process or make two of the same excited state back to normal, or key is split.
If the molecule cannot become the norm, the key cracking formation of free radicals (R ·).
Formed in the photolysis of radicals react easily, such as oxygen to produce superoxide free radicals. This process is called oxidation.
Peroxy radicals by hydrogen bonds pull attacks the polymer backbone (R’H), formation of peroxides and free radicals. These free radicals can react with the oxygen in the third generate additional oxidative free radicals.
Peroxides, neither heat nor ultraviolet stability, decomposition and the formation of additional free radicals. As the process continued, more and more molecular bonds were opened, performance degradation of the coatings.
Types of light stabilizer
Light stabilizer has two main groups of products. The first category, UV absorbers, as the name suggests is to absorb harmful UV rays in order to protect the paint. Second, hindered amine light stabilizer, by capturing free radicals to prevent degradation of the coating.
• UV absorbers are the chromophore and polymer backbone competition, prior to its absorption of ultraviolet rays to prevent degradation. UV-absorbers are colorless or nearly colorless, additive, which in the UV region of the spectrum has a strong absorption power. Ultraviolet light absorber absorbs light energy can be converted into heat.
Hindered amine light stabilizers (HALS) is in front of the degradation reaction captures free radicals, so as to avoid degradation. Hindered amine can also impede thermal oxidation. Hindered amine light stabilizers for polymers, or even hindered amine light stabilizer depletion after the degradation resistance has remained light. Explanation of this phenomenon is the product of the oxidation of hindered amine light stabilizers such as hydroxylamine Hydroxyl-Amine and ether, also inhibits photolysis. Hindered hydroxyl and hydroxylamine ethers were able to capture the peroxide radical.