The adhesive is prone to aging in the process of use, and it is necessary to add a protective system to delay aging and avoid rapid decline in performance. Physical antioxidants are generally light screening agents or wax, chemical antioxidants include amines, phenols, esters and other compounds. A small amount of antioxidant should be added to synthetic rubber during the synthesis process, and a larger amount of antioxidant should be added during the post-processing process.
1. Antioxidant for synthetic rubber
The antioxidant added to synthetic rubber during the synthesis process should be selected according to the synthesis process and product color. Soluble polyrubber needs to choose an antioxidant that is easily soluble in the solvent used for rubber synthesis, and emulsion polyrubber should choose an antioxidant that can form a stable emulsion with the emulsifier used for rubber synthesis, and choose a polluting or non-polluting antioxidant according to the color of the product. Polybutadiene rubber (BR), styrene thermoplastic elastomer, isoamyl rubber (IR) and other dissolved polyrubber previously used antioxidant BHT (264), and sometimes used phosphite ester antioxidant TNP (TNPP). The antioxidant TNP is easily hydrolyzed, and its use is prohibited because the nonylphenol produced affects the reproductive health of organisms. Antioxidant BHT is relatively small in molecular weight and volatile, and foreign studies believe that more of its volatile substances are harmful to the environment, so other phenolic antioxidants are mostly used to replace it, and the more common antioxidants are 1076 and 1520, or auxiliary antioxidants are used to produce synergistic effects. Light colored latex rubber mostly uses phenolic antioxidant styrene to turn phenol, dark rubber mostly uses polluting amine antioxidant. Synthetic rubber antioxidants are developing in the direction of environmental protection, large relative molecular weight, compounding and multi-function. The oxidation induction period or oxidation induction temperature of raw rubber can be detected by DSC, and the properties of antioxidant can also be investigated by heat-resistant oxygen aging properties. Light-colored rubber products also need to investigate the heat and oxygen aging properties and yellowing resistance.
Two. Antioxidant
1. Physical antioxidants
The synthetic rubber compound mostly uses paraffin wax as a physical antioxidant resistant to ozone and weather aging. When rubber is vulcanized, the paraffin dissolved in it gradually migrates to the rubber surface after cooling, forming a dense and flexible wax film, thereby isolating ozone in the air and playing a protective role. Compared with the common protective wax, the modified protective wax has a variety of functional groups (such as carboxyl group, hydroxyl group, etc.) in its molecular structure. The protective capacity of modified protective wax is 1.5~3 times higher than that of ordinary protective wax. The use of modified protective wax can reduce the amount of anti-ozone agent.
2. Chemical antioxidants
The main antioxidants used in the processing of synthetic rubber are amines and quinolines. Common varieties are antioxidant 4020,4010 NA and RD. The dosage of these three kinds of antioxidant accounts for more than 80% of the current dosage of antioxidant in China.
There are many naphthylamine antioxidants, such as phenyl-alpha-naphthylamine (antioxidant A), 1-phenyl-beta-naphthylamine (antioxidant D). However, due to its toxicity and carcinogenicity, countries began to greatly reduce its production in the 1970s until the current ban.
China's antioxidant RD has become one of the main antioxidant of radial tire compound, the effective ingredient in the product is 2, 2, 4-trimethyl-1, 2-dihydroquinoline two, three, tetramer, especially the dimer anti-aging performance is excellent, so the content of dimer should be increased as far as possible. Antioxidant RD has excellent heat resistance to oxygen aging, has a strong inhibition effect on metal ions such as copper, but has poor ozone resistance and flex resistance, and needs to be used in combination with antioxidant AW or p-phenylenediamine antioxidant (antioxidant 4020). Antioxidant AW can prevent the cracking of rubber products caused by ozone, especially suitable for rubber products used under dynamic conditions, and the use of antioxidant H, D and 4010, can enhance its effectiveness.
