Please do not use 70% alcohol, as it has too much water content. The encoder is made of graphics film, which is processed in water based chemistry. The amount of water in 70% alcohol is enough to soften the emulsion on the encoder and can result in damage to it. I had a customer repeatedly clean his encoder with 70% alcohol and eventually stripped the emulsion completely off the encoder.
My tried and true method for hundreds of encoder strips I have cleaned on many brands of printers is a microfiber cloth and acetone, with 100% success and not one damaged. In addition, acetone is much better at removing ink from encoders than even 100% alcohol.
Regards,
Jim Hancock