How to remove the "sticky" left behind from duct tape/duck tape/gaffer tape stickers?

I have a big plastic banner with metal eyelets in it for hanging, given to me from a shop that no longer used it to hang up outside. I'm working at Glastonbury Festival this year, and want to repaint it to advertise what I'm doing.

It had lots of lettering on it, and it was easy enough to just peel all the lettering off as they consisted of stickers made from something like duct tape. The only problem is that they've left lots of the "sticky" behind, i.e. the glue from the back of the stickers, which means that you can still see the original title of the shop I got it from and their phone number etc.

I want to repaint it using acrylic spray paint, so the difference in texture will really show through and spoil my banner if I can't get it off, but I have no idea how to dissolve the glue and it doesn't scrub off at all with warm soapy water and a scouring pad.

Any suggestions, anyone?