I need to print a cover with black text, on uncoated paper. I want to use one of the Pantone blacks. What is the difference between Pantone black and Pantone process black?
Process black is a more transparent ink, which will give you a grayish look.
If you want a darker black use for example Neutral black 165-1-7c. But it is important than you talk to the printer and tell him that you want the blackest one possible. It is not that important that you specify it on the file. It is more important that you clarify this talking to them.
Some people have special inks for this. Where I live some people call it "night black".
If you want a really black black and your design is on 1 ink you can ask them to pass twice the paper so you have black on black. But it will cost a bit more.
Process black is just black ink and it will print black but not a rich black, which is what we call it in the printing industry where I live. There are 2 ways to achieve rich black: combine it with cyan and/or other 4 color process inks - or use a PMS pantone black that comes ready mixed in a can. I work in commercial printing and which way you go depends on your design and other colors you are using.If you have 4 color process colors in the design already, use process. if you have a PMS palette already or no process - use pantone black.
Actually ther are many PANTONE black swatches and the difference between them is the percentage of the CMYK mix, and the reason for that is to suit a variety of design methods that suits different materials to print on, and different appearence of black color. To be able more to decide what black you need to use I suggest to refere to this nice article about how professional designer use black in design:
Also as Mr. «Rafael» mentioned in his answer, you need really to communicate with your printer because this is the best way to guarantee your results.
From my experience as a (Designer & Printer) at the same time, I found that some times even if you use (100K) process black it will deffers according to the ink manufactorer & the dumping system of the printing machines inspit that common reader or user will not recognize that but expert eye will do.