Comic book shop owners across Iowa hope today’s opening of the “X-Men” sequel in theatres will translate to new customers.Some theatres started showing “X2: X-Men United” early this morning, just after midnight. The comic book, on which the film is based, first appeared in 1963. Matt Johnson is co-owner of Cup O’ Kryptonite, a Des Moines comic store/coffee house and Internet cafe. Johnson says comic books are mislabeled and underestimated as being just for boys.Johnson says they’re far from just kids-stuff — they’re for an intelligent reader. “Comic books are just another form of literature, just another art form. Some of the best stuff that’s ever been done in comic books is being done right now.” Johnson says “X2” is going to be huge and he trusts fans of the film will venture back to the movie’s roots — the comic book.Johnson and many other store owners will be in theatres this weekend, not watching the movie, but handing out free comic books to people coming out of the theatres, hoping they’ll be hungry for more of the story from the page, not the screen. Many comic shops across Iowa are taking part in “Free Comic Book Day,” which is tomorrow (Saturday).