It depends on what the manufacturer values and which raw material was chosen for the rubber keys. For reasons of cost, natural rubbers are not used for such products. These are probably TPEs (thermoplastic elastomers).
In order to obtain the rubber-like properties, plasticizers must be added to the plastic. Over time, these plasticizers can emerge from the structure of the plastic chains and remain on the surface as an adhesive layer.
TPEs are particularly susceptible to hot water, water vapour, oils, fats, alkalis and alcohol.
In addition, UV stabilizers are added to slow down the glibbing and embrittlement of the keys. As mentioned before, it depends on the quality of the raw materials and additives.
We carry out ageing tests
for our articles and I can say that as a manufacturer of plastic products it is really difficult to guarantee consistent quality over a longer period of time.
We only purchase the raw material with certificate and fill it into the material hopper of the injection moulding machines. But which components the manufacturer of the raw material really mixes with me is difficult for me to understand. We only use simple plastics such as polyamide and know the properties very well.
But with TPEs, the proportion of additives is extremely high and therefore difficult to estimate.