Some summaries on the development of oil-resistant nitrile rubber seals
Nitrile-butadiene rubber (NBR) is a copolymer of acrylonitrile and butadiene monomers. It is mainly produced by low-temperature emulsion polymerization. It has excellent oil resistance, high wear resistance, good heat
resistance and viscosity Relay is strong. The disadvantages are poor low temperature resistance, poor ozone resistance, poor insulation performance and slightly lower elasticity.
Nitrile rubber is mainly used in the manufacture of oil-resistant rubber products. There are five kinds of acrylonitrile content (%) in nitrile rubber, such as 42-46, 36-41, 31-35, 25-30, 18-24. The higher the acrylonitrile content,
the better the oil resistance, but the corresponding decrease in the cold resistance. It is widely used in the manufacture of various oil-resistant rubber products, various oil-resistant gaskets, gaskets, casings, flexible packaging,
soft rubber hoses, printing and dyeing rubber rollers, cable rubber materials, etc. elastic material.
In the actual formulation development, our formulation engineers are often distressed and need to meet two contradictory requirements at the same time. For example, the sealing ring used in some high and cold regions
needs to consider its oil resistance and low temperature performance. In fact, these two requirements are requirements in two opposite directions. For example, increasing the content of acrylonitrile increases the oil
resistance, which will lead to resistance Low temperature performance decreases. The following is a summary of some of the oil-resistant nitrile rubber formulations collected:
1. The choice of nitrile rubber: the oil resistance and strength of the high acrylonitrile content will be better, but the processing performance will be poor, and the cold resistance will also be poor, so the nitrile rubber with
high acrylonitrile content cannot be selected blindly. Appropriately select nitrile rubber with medium acrylonitrile content.
2. The effect of reinforcing agent on the oil resistance of nitrile rubber: Since carbon black can be adsorbed on the surface of rubber molecules to form an adsorption layer, this adsorption layer can form quasi-crosslinking
with rubber molecules. When the vulcanizate is soaked in oil, it is mainly The volume of rubber expands, and the carbon black particles can neither be extracted nor swelled. With the increase of the amount of carbon black,
the rubber content will decrease, so that the swelling volume of the vulcanizate in oil becomes smaller, and the more oil-resistant the vulcanizate is. However, the amount of carbon black should also be adjusted according
to the physical properties of the compound.
3. The effect of plasticizer on oil resistance: the plasticizer itself does not participate in the reaction. When the vulcanizate is soaked in oil, the plasticizer will be drawn out, making the volume smaller, and the oil entering
from the rubber surface will increase the volume. Large, overall, the volume of the vulcanizate does not change much, increasing its oil resistance. With the increase of plasticizer, the oil resistance becomes better. When it
exceeds a certain level, if the plasticizer is added again, the oil resistance does not change significantly. High molecular weight plasticizers are relatively more difficult to extract than low molecular weight plasticizers.
Controlling the balance of extraction and swelling improves the volume change rate of the rubber compound, but the oil will also destroy the network structure of the rubber, resulting in a decrease in performance.
4. Influence of vulcanizing agent: sulfur is generally used as vulcanizing agent, and the oil resistance becomes better with the increase of the amount of sulfur, but when the amount of sulfur exceeds 3 parts, the change of
oil resistance will not be obvious. The reason is that the increase of sulfur will increase the number of cross-linking bonds in the vulcanizate, the overall bond energy will increase, and reduce the oil entering into the vulcanizate.
When the amount of sulfur exceeds 3 parts, the number of cross-linking bonds will be saturated, and then increase the amount of sulfur and cross-linking bonds. The increase in the number is not obvious, and the oil resistance
will change little accordingly.
The above is some experience in the formulation of oil-resistant nitrile rubber, I hope it can help you in the development of the formula.