I was taking apart my HP laserjet color printer today because it started to print this blank white spot in the center of my pages. What I found a sizable tear in this plastic sheet/film. What is this part called, so I can explain it to HP's warranty department?
That is the transfer belt, it maintains a positive static charge and the paper sticks to it as it passes under the toner cartridges that have a negative charge. Hence without a positive charge in that area of the page it will not pick up any toner.