Hi Caroline, just scrub it well and then paint with a paint made especially for plastic offered by several brands, such as Rustoleum, Krylon, and NuKote. These paints last well, even in outside weather on plastic chairs, etc.
Hi Caroline besides prep I would say the type of paint you buy is absolutely the most important thing. Make sure and buy outdoor paint that is specific for plastic. https://www.wikihow.com/Paint-Plastic-Furniture
This information may help:
Use plastic formulated spray paint. It will say that on the can. Clean furniture before painting.
Buy spray paint that is for multi-surfaces. Be sure to clean the furniture well before painting.
Hi Caroline: First, make sure it's clean, no grease or oils and dry. Then, spray paint it with a paint especially made for plastic. Rustoleum and Krylon made good paints. Then, use light sweeping back and forth strokes and let dry between light coats. It may look creepy on the first coat, but the second and/or third coats will make it look good. Don't try to use thick coats as the paint will run and that's a bear to fix. Patience is a virtue in this instance :) Good luck
Scuff with fine steel wool, clean with denatured alcohol or TSP, then prime and paint with a spray paint that is formulated for plastic. I used Krylon.
Always sand first so spray paint can adhere to it. You will want to go to Home Depot or Lowes and pick up some spray paint especially made for plastic.
I do it all the time with Rustoleum or Krylon spray paint.
Use spray paint formulated for plastic
Spray paint made for plastic
Spray paint works best for this.