Reasons for Blackening of Rubber Cable Glue and Copper Wire

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Some manufacturers use ordinary copper in the production of rubber sheathed cables, because copper itself is not oxygen-free copper, and the surface of the copper wire will inevitably be oxidized during processing.


Due to the processing of the copper rod, especially the mastery of the toughening process, and the poor storage conditions of the processed copper wire core, the copper wire core itself is slightly oxidized.

This is also one of the reasons for the blackening of copper.

The insulation of rubber cables is formulated from natural rubber and styrene-butadiene rubber. Since the insulating rubber is in direct contact with the copper wire, sulfur cannot be directly used as a vulcanizing agent, and even a small amount of sulfur will make the copper wire black.

Some compounds that can decompose free sulfur must be used, such as accelerator TMTD, and vulcanizing agent VA-7.

It is also necessary to use some vulcanization accelerators to increase the vulcanization rate and degree of vulcanization, and to ensure the physical, mechanical, and electrical properties of the sulfide.

Insulating rubber

But in terms of elasticity, strength, and permanent deformation of insulating rubber, it is not as good as sulfur-containing rubber.

After decades of practice, it has been confirmed that TMTD cannot solve the problem of the blackening of copper wires. In addition, the insulating rubber should be available in a variety of colors.

Red, blue, yellow, green, and black are the basic colors. The presence of these colors can also make the rubber sticky and blacken the copper wire.

The main fillers in the formula are light calcium carbonate and talc. Due to price reasons, some manufacturers use particularly cheap calcium carbonate and talc in order to reduce costs. These fillers have large particles, large free alkali content, and many impurities.

Therefore, the physical and mechanical properties are relatively poor, and the electrical properties are not good, which may easily cause the copper wire to turn black.

Some factories use activated ultrafine calcium carbonate to improve the physical and mechanical properties of insulating rubber, and most of the activated calcium is treated with stearic acid, which is also the reason for the blackening of copper wires.

The use of vulcanizing agent VA-7 can improve the blackening of copper wires, but due to insufficient vulcanization, the permanent deformation of the rubber is large, which will cause the rubber to become sticky.

Especially after adding accelerator ZDC, the vulcanization speed is accelerated. In order to prevent scorch, the accelerator DM is also added to delay the scorch time.

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