What causes whitening agent to turn yellow? How can we avoid it?

I don't know if you have found any problems. All sewing agents that change color and turn yellow are light-colored sewing agents, and dark-colored sewing agents will not change color and turn yellow no matter how long they are used. Light-colored sewing agents are as follows: China white sewing agent, matte white sewing agent, ivory white sewing agent, moonlight silver sewing agent, flash silver sewing agent, silvery white sewing agent, etc. Before analyzing and explaining why the light-colored sewing agent turns yellow, it should first be explained that most of the sewing agent manufacturers in the market do not have a good solution to the problem of yellowing resistance of "white sewing agent". Although I heard that only a few manufacturers claimed to have developed "anti-yellow and white sewing agent", they didn't use it, and they didn't know whether it was true or not.

The use of nonylphenol can also lead to discoloration and yellowing. Due to the influence of external environmental factors, long-term exposure to high temperature leads to discoloration and yellowing of sealant. "65438+3BAC anti-yellowing raw material" was not added to the beautiful sewing thread, which led to the discoloration and yellowing of the beautiful sewing thread. Nonylphenol is an important fine chemical raw material and intermediate. Its appearance is colorless or yellowish liquid at room temperature, slightly phenolic, insoluble in water and soluble in acetone; Mainly used in the production of surfactants, antioxidants, textile printing and dyeing auxiliaries, lubricating oil additives, pesticide emulsifiers, resin modifiers and so on. Promote colloid curing reaction and shorten curing time. Increase the luster and elasticity of the colloid surface. Improve the moisture resistance of colloid and enhance water permeability. Softening system paint film. Improve amine whitening and improve the anti-whitening ability of the system. As the mainstream sewing agent, epoxy resin belongs to thermosetting resin and needs to be combined with curing agent to be applied in practice. Most curing agents are cycloaliphatic amines and polyether amines. Its biggest disadvantage is that the curing at low temperature is very slow, and it needs to be heated to "above 30℃" or a large number of accelerators to complete the curing.

Although nonylphenol can improve the amine whitening and anti-whitening properties of the system, the short-term construction effect of cosmetics is similar to that of conventional cosmetics. But inferior quality is inferior quality, and this effect can only last for 2-3 months. Half a year at most, the sewing agent will change color and turn yellow. The more corrosive the curing agent is, the worse the yellowing resistance is, and the faster the caulking agent becomes discolored and faded. Nonylphenol is a chemical raw material, which is colorless or yellowish liquid at room temperature and is often used as antioxidant and activator. It can shorten the curing time, enhance the gloss of the colloid surface, enhance the toughness of the colloid, and also enhance the whitening resistance of the colloid. However, the stability of this substance is not strong, and the beauty sewing material added with nonylphenol will turn yellow in about half a year. In addition, the anti-yellowing effect of cosmetic sewing agent will be worse and worse, especially the reaction of light-colored cosmetic sewing agent.

Exposed to the sun for a long time, all products will turn yellow and discolor, and so will the sewing agent. Especially in the external high temperature environment, the anti-oxidation performance of the sealant will be affected, and the sunlight will accelerate the oxidation of the sealant, leading to the direct yellowing of the light-colored sealant and even the fading of the dark-colored sealant. Many materials need to be added to sewing thread, among which curing agent 1, 3- cyclohexyldimethylamine is one of the commonly used curing agents for epoxy resin, which has strong yellowing resistance, stable color and fast curing time. Domestic sewing agent brands do not use epoxy curing agent. Choosing this composition can prolong the anti-yellowing ability for many years.