The protective performance of rubber protection wax is affected by many factors, among which the main influencing factors are carbon number distribution of rubber protection wax, proportion of n-isomeric hydrocarbons, use temperature, degree of crosslinking, compounding agent, type of rubber compound, load, filler and softeners, etc.
Among them, the distribution of carbon atom number and the proportion of n-isomeric hydrocarbons are the key factors, which have a decisive influence on the protective performance of rubber protection wax.
1. Carbon number distribution of rubber protection wax
The alkane with low carbon number has small relative molecular mass, low melting point and low branching degree, and is easy to migrate from the rubber to the surface of the rubber, but the low carbon number alkane will dissolve in the rubber after the temperature rises.
When the number of carbon atoms is higher, the migration speed is slower, the resulting protection wax film is very thin, cannot form a protective layer, and has almost no protective effect on the rubber.
2. The chemical composition of rubber protection wax
Rubber protection wax is mainly composed of n-alkanes, iso-alkanes and cyclic hydrocarbons. When the relative molecular weight is the same, the migration speed of n-alkanes is faster than that of iso-alkanes. The more branches of iso-alkanes, the slower the migration speed. Cyclic hydrocarbons with long side chains migrate more slowly.
The n-alkane crystals are large flakes and loose, and ozone in the atmosphere easily penetrates the protection wax film to erode the rubber surface.
After adding a certain amount of isoparaffins to n-paraffins, since the regularity of crystalline molecules is destroyed, a wax film with fine, amorphous and dense crystals can be obtained, thereby enhancing its ability to resist ozone erosion.
3. Use temperature of rubber protection wax
When the operating temperature of the rubber is -5~55℃, ozone has an aging effect on the rubber; when the operating temperature is lower than -5℃, due to the scarcity of activated molecules, the two cannot chemically react, that is, the rubber will not be affected by ozone. produce aging phenomenon;
When the operating temperature is above 55°C, ozone will decompose to generate harmless oxygen, so the rubber will not be aged due to ozone.
Therefore, the composition of the appropriate number of carbon atoms of the rubber protection wax should be controlled. Otherwise, at any temperature point in the range of 0 to 55 °C, the protection wax cannot be guaranteed to play its due protective role.
4. Rubber protection wax compound
Different sizing materials have different adaptability to the protective effect of protection wax. For example, in the NR/SBR/BR system, the ozone test shows that the protective effect of microcrystalline wax is significantly better than that of ordinary paraffin.
Different sizing materials, the exposure results are sometimes opposite. The test results of the NR/SBR/BR system show that the microcrystalline wax is significantly better than the ordinary paraffin wax.
5. Rubber protection wax filler
After adding fillers, some fillers will promote the migration of protection wax, such as channel carbon black, white carbon black, lamp smoke carbon black, etc.; some fillers will inhibit or slow down the migration of protection wax.
If calcium carbonate filler is added, the ejection speed will be reduced below that of a compound without filler. The higher the activity of the filler, the more wax will be ejected.
6. Rubber protection wax softener
Some softeners will delay the migration and ejection of paraffin wax, while some softeners will accelerate the migration and ejection of paraffin wax.
Migration and spraying are related to temperature: increasing the temperature (such as 40 °C), because the protection wax is more dissolved in the n-paraffin oil, the amount of frost spray is reduced; lowering the temperature, the n-paraffin oil will enhance the migration of the protection wax.
7. The amount of protection wax added
A small amount of protection wax is added to the rubber. After mixing, the two are completely miscible with each other, and the protection wax has no blooming phenomenon. Generally speaking, the larger the amount of protection wax added, the faster the migration speed, the faster the wax film formation speed, and the thicker the wax film.
However, after the addition amount reaches a saturated state, due to the poor compatibility between the protection wax and the rubber, the protection wax will generate local stress in the rubber product and reduce the dynamic flexural performance of the rubber.
8. Modified rubber protection wax
After the ordinary unmodified rubber protection wax migrates to the rubber surface, the formed wax film tends to agglomerate and has poor adhesion to the rubber surface.
Therefore, necessary technical measures should be taken to improve the physical properties of the rubber protection wax and improve its adhesion to the rubber surface. The modification of the rubber protection wax is one of the main technical measures taken.
Compared with ordinary rubber protection wax, modified rubber protection wax has a variety of beneficial functional groups such as carboxyl and hydroxyl groups in its molecular structure. The use of modified rubber protection wax can reduce the amount of chemical antiozonants, or even do not use chemical antiozonants.