It all depends on the employee contract you signed. At the company I work for the contract states that everything we make and do not disclose is company owned. This is because our work hours are so flexible that it can be hard to say what is "outside office hours".

But as long as I disclose my side projects they are mine and the company fully supports us in our side projects.

My advice: Read your employee contract and then talk to HR - make sure everything is legit before you make your move. That way there will be no surprises.