During the long-term storage and use of rubber and its products, due to the effects of heat, oxygen, ozone, metal ions with variable valence, mechanical stress, light, high-energy rays, as well as other chemical substances and molds, it gradually reduces and loses its original properties. The process of physical and mechanical properties is called aging. With the progress and development of the aging process, the properties of rubber and its products will gradually decrease and completely lose their use value. In order to prolong the service life of rubber products, it is necessary to mix some substances that can inhibit the aging process in the rubber, thereby prolonging the storage period and service life of the rubber and its products. These substances are called antioxidants.
There are many types of antioxidants with different effects. According to its main function, it can be divided into anti-thermal oxidation aging agent, anti-ozonant, harmful metal ion inhibitor, anti-fatigue agent, ultraviolet absorber, anti-cracking agent, etc. However, since each protective function is often not dedicated to a certain antioxidant, most antioxidants can act on several aging factors, but to different degrees. The antioxidants commonly used in the wire and cable industry are introduced below. The classification is not clear, only its main protective function is pointed out.
1. Anti-aging agent D: This product is light gray powder, the pure product is a white powder, which is flammable. The specific gravity is 1.18, and the melting point is not lower than 105℃. Soluble in acetone, ethyl acetate, carbon disulfide, chloroform; soluble in ethanol, carbon tetrachloride; insoluble in water and gasoline. It gradually turns gray-black in the air and sunlight but does not affect the protective effect.
Anti-aging agent D is a general-purpose anti-aging agent for natural rubber and synthetic rubber. It has a good protective effect on heat, oxygen, flexural cracking and general aging factors. It has inhibitory effect on harmful metal ions. If used in combination with antioxidant 4010, the anti-heat, oxygen, flexural cracking and anti-ozone effects will be significantly increased. This product is easy to disperse, and the dosage is about 0.5 to 2.0 parts. More than two parts will spray frost.
2. Anti-aging agent RD and anti-aging agent 124: Anti-aging agent RD and anti-aging agent 124 are composed of the same chemical composition, the difference is that anti-aging agent RD is resinous, while anti-aging agent 124 is powdery, and anti-aging agent RD is amber to off-white. Resinous powder, non-toxic. The softening point is not lower than 74°C. Anti-aging agent 124 is off-white powder with a melting point of 114°C. Anti-aging agent RD and anti-aging agent 124 are soluble in acetone, benzene, chloroform, carbon disulfide; slightly soluble in petroleum hydrocarbons, insoluble in water. Contaminating but not significant. It is not easy to spray frost and has no effect on vulcanization. Flammable and non-toxic. It is suitable for natural rubber and synthetic rubber such as styrene-butadiene and eye-fixing. The dosage is generally 0.5 to 3 parts.
3. Anti-aging agent MB: Appearance is white or light yellow crystalline powder, with bitter taste, non-toxic. The specific gravity is 1.42, the melting point is 285℃, soluble in ethanol, acetone, ethyl acetate; insoluble in dichloromethane; insoluble in carbon tetrachloride, benzene, and water. Slightly polluting and easy to disperse. When the dosage exceeds 2 parts, there will be blooming phenomenon. When used alone, the effect is weak, and it should be used in combination with the antioxidant DNP to have a synergistic effect. The antioxidant MB is used as a copper inhibitor, which can weaken the effect of the vulcanizing agent in the rubber on the copper wire, and can significantly improve the blackening of the copper wire and the stickiness of the rubber when the rubber is vulcanized. Anti-aging agent MB can act as a vulcanization retarder. The general dosage of antioxidant MB is 1 to 2.5 parts.
4. Anti-aging agent DNP: This product is light gray powder. The pure product is a light-colored sequin-like crystal with a specific gravity of 1.26 and a melting point of 235°C. Low pollution. It is easy to spray when the dosage exceeds 2 parts. It is a comprehensive antioxidant that resists heat, oxygen and atmospheric aging. It is an excellent copper inhibitor and has an activating effect on thiazole accelerators. Anti-aging agent DNP and MB, DOP and so on have a synergistic effect. It is suitable for natural rubber and synthetic rubber such as neoprene, styrene-butadiene rubber, butadiene rubber and eye-fixing rubber. The general dosage is 0.2 to 1 part.
5. Anti-aging agent NBC: the trade name is anti-aging agent NBC, the appearance is dark gray powder, the melting point is not lower than 83 ℃, it is non-polluting, easy to disperse, and it is an excellent antiozonant. It can be used in rubber that is heat-resistant, resistant to atmospheric aging, and resistant to bending and cracking. It can improve heat resistance and thermal stability in neoprene rubber and chloroether rubber. Suitable for chloroprene, chloroether, chlorinated polyethylene, nitrile rubber, styrene butadiene rubber and other synthetic rubbers, the dosage is 1-2 parts.
Precautions:
Since the protective effect of each antioxidant has limitations, and the aging of rubber products in actual use is the result of a variety of factors, the following points should be paid attention to when choosing an antioxidant:
1) Due to the different characteristics of each antioxidant, and the aging properties of different rubber formulations are different. Therefore, the most effective antioxidant for one rubber material may be ineffective or even harmful to another rubber material. Therefore, the selection of antioxidants must be considered and reasonably selected according to the aging properties of various rubber materials, anti-aging requirements and the characteristics of various antioxidants.
2) When one antioxidant is difficult to meet the requirements, two or more antioxidants should be used together to make it have a coordinated effect and ensure the anti-aging effect.
3) Some antioxidants have a coloring effect and pollution on the rubber. Generally speaking, phenolic antioxidants have poor protective effect, but do not pollute or pollute very little. Amine antioxidants with higher protective effect will cause rubber pollution and serious discoloration. These contradictions should be considered in the selection process.
4) The amount of antioxidant should not exceed the solubility in rubber to prevent frost spray and contaminate the surface quality of rubber
5) Amine antioxidants have adverse effects on rubber scorch; phenolic antioxidants can delay vulcanization and should be paid attention to when selecting them.
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