What Are The Stabilizers For PVC Edge Banding Formulations?

PVC is processed at high temperatures, which easily emits HCL and forms an unstable polyene structure. At the same time, HCL has an autocatalytic effect, which will further degrade PVC. In addition, the presence of oxygen or ions such as iron, aluminum, zinc, tin, copper and cadmium will catalyze the degradation of PVC and accelerate its aging. Therefore, plastics will have various undesirable phenomena, such as discoloration, deformation, cracking, mechanical strength decline, electrical insulation performance decline, brittleness, etc. In order to solve these problems, stabilizers, especially heat stabilizers, must be added to the formulation. Stabilizers for PVC include heat stabilizers, antioxidants, UV absorbers and chelating agents. When the formula is designed, different varieties and different quantities of stabilizers are selected according to the requirements of product use and processing technology.

(1) Heat stabilizer The heat stabilizer must be able to capture the HCL with autocatalytic effect emitted by PVC resin, or be able to react with the unstable polyene structure produced by PVC resin to prevent or mitigate the decomposition of PVC resin. Generally, the characteristics and functions of the heat stabilizer selected in the formula are considered with the requirements of the product. For example:

Lead salt stabilizers are mainly used in hard products. Lead salt stabilizer has the characteristics of good thermal stabilizer, excellent electrical performance and low price. However, it is highly toxic and easy to pollute products, so it can only produce opaque products. In recent years, a large number of compound stabilizers have appeared, and one-component stabilizers have been in danger of being replaced. The composite stabilizer is characterized by strong specificity, low pollution, and simple batching in processing enterprises. However, due to the lack of a unified standard, the compound stabilizers of each company vary greatly.

Barium-cadmium stabilizer is a class of heat stabilizer with good performance. It is widely used in PVC agricultural film. It is usually used in combination with barium, cadmium, zinc and organophosphite and antioxidants.

Calcium and zinc stabilizers can be used as non-toxic stabilizers in food packaging, medical devices and pharmaceutical packaging, but their stability is relatively low, and the transparency is poor when the calcium stabilizer is used in large amounts, and it is easy to spray frost. Calcium-zinc stabilizers generally use polyols and antioxidants to improve their performance, and calcium-zinc composite stabilizers for rigid pipes have appeared in China recently.

Organotin heat stabilizer has good performance and is a good variety for PVC hard products and transparent products, especially octyltin has almost become an indispensable stabilizer for non-toxic packaging products, but its price is more expensive.

Epoxy stabilizers are often used as secondary stabilizers. This kind of stabilizer can improve the stability of light and heat when used in combination with barium-cadmium-calcium-zinc stabilizers, but its disadvantage is that it is easy to exude. There are also polyols and organophosphites as auxiliary stabilizers.

In recent years, rare earth stabilizers and hydrotalcite stabilizers have also appeared, rare earth stabilizers are mainly characterized by excellent processing performance, while hydrotalcite is a non-toxic stabilizer.

(2) Antioxidant PVC products are oxidized due to heat and ultraviolet rays in the process of processing and use, and their oxidative degradation is related to the production of free radicals. The main antioxidant is a chain break terminator or free radical eliminator. Its main function is to combine with free radicals to form stable compounds, so that the chain reaction is terminated, and the main antioxidant for PVC is generally bisphenol A. There are also auxiliary antioxidants or hydrogen peroxide decomposers, and the PVC auxiliary antioxidants are triphenyl phosphite and benzene diethylhexyl phosphite. The combination of main and auxiliary antioxidants can exert a synergistic effect.

(3) Ultraviolet absorber PVC products used outdoors, due to ultraviolet radiation in its sensitive wavelength range, PVC molecules into an excited state, or its chemical bonds are destroyed, causing free radical chain reaction, promoting PVC degradation and aging. In order to improve the ability to resist ultraviolet rays, ultraviolet absorbers are often added. The commonly used ultraviolet absorbers for PVC are triazine-5, UV-9, UV-326, TBS, BAD, OBS. Triazine-5 has a good effect, but the film is slightly yellow because of its yellow color, and it can be improved by adding a small amount of phthalocyanine blue. UV-9 is commonly used in PVC agricultural film, and the general dosage is 0.2~0.5 parts. The salicylic acid type of TBS, BAD and OBS have a mild effect, and when used in combination with antioxidants, they will get a good anti-aging effect. For non-transparent products, the weather resistance is generally improved by adding lutile titanium dioxide with shading, and if ultraviolet absorbers are added, a large amount is required and is not very cost-effective.

(4) Chelating agent In the PVC plastic stabilization system, the phosphite that is often added is not only an auxiliary antioxidant, but also plays the role of a chelating agent. It can form metal complexes with harmful metal ions that promote the de-HCL removal of PVC. Commonly used phosphite esters are triphenyl phosphite, benzodiethylhexyl phosphite and diphenyloctyl phosphite. In PVC agricultural film, the general dosage is 0.5~1 parts, which is easy to color at the initial stage when used alone, and the thermal stability is not good, so it is generally used in conjunction with metal soaps.