It's not Alps, it uses Acer switches, although they're Alps mount.
Acer used an unknown printing method on ABS, not PBT. I've done extensive testing on these and this method has characteristics of dye-subbing, rimless pad printing, and lasering all in one. Even detailed analysis hasn't ruled out any of these methods. At the moment we're referring to this as "dyesub ABS" for lack of better understanding. See my thread of high-magnification scanning electron microscopy photographs of these keycaps for more info.
