There are many kinds of colours of polyurethane caster overlay products, mainly according to customer demand. It often appears yellowing phenomenon in the process of use, which is caused by the influence of external oxidation factors, greatly affecting the aesthetics of the product, and yellow rubber-coated products are also very difficult to find this problem, so we have to solve and prevent from the root cause.
1, the control of hot pressing temperature, to prevent thermal aging.
2, add accelerator for the ammonia ester caster overmoulding. Accelerator can be used DM and M to achieve yellowing level 4, but the whole system needs to be adjusted. The use of yellowing-resistant accelerators such as dithiocarbamates has a beneficial effect on yellowing, but at the expense of great physical properties and operation. The faster the vulcanisation, the less chain breakage occurs and the ageing is suppressed. At the same time, however, the overall physical properties are sacrificed. This is because the cross-linking bonds generated by fast and slow vulcanisation are different. For example, tensile strength and tearing are greatly affected. But the elastic brittleness will increase.
3, should be slightly undersulfurised, the more to the positive vulcanisation point, the more serious the chain breakage, causing yellowing.
4, the use of oil, to add less, especially the chain alkyl more can not be added to the polyurethane overlay in the use, because of poor compatibility, oil penetration out of the surface at the same time also dissolved in the oil inside the additives and so on also to the surface.
5, the control of heavy metals, for example, zinc oxide, light calcium, oil more or less contain heavy metals. If the heavy metal content is high, the heavy metal will produce oxidation and discolouration, yellowing is very easy to occur.
6, the adjustment of acidity and alkalinity. Urethane caster wrapping rubber is weakly acidic, there will be a slight inhibition of the vulcanisation reaction, and the same is to control the intensification of chain breaking.
In summary, many aspects of urethane caster wrapping rubber processing and production will produce yellowing phenomenon, we can be based on the above method of multifaceted processing process quality control, so that its physical and mechanical properties tend to stabilise, so as to obtain the right improvement.