I know what you mean - depending on the silk, I find that some of my ties do have a tendency to stay wrinkled, whereas others smooth out much more quickly. My printed ties tend to lose their wrinkles very quickly, whereas grenadines and woven ties tend to hold wrinkles a bit more, in my experience.
As others have said, giving the tie time between wearings (say, a week or more) helps. Instead of hanging, I roll most of my ties and store them in a set of drawers and I think that rolling helps to get rid of wrinkles, too.
You know. I used to roll all my ties. And then I read somewhere about hanging ties being better for wrinkles... .
That was before I owned any vandas though. So maybe I should go back to that option.