Printing Errors or Lights & Stuck Print Jobs

I would like to print transparencies for use as screen printing positives. I do so now, and wonder if I can manipulate the print settings to make the black more opaque. I print from Adobe Photoshop and Illustrator. I use HP ink, HP transparency film, and I choose settings in the Adobe products which then seem to be overridden by my decision to set the print characteristics in the HP printer driver software. My printer is a 6940, the driver software is HPF6940T.GPD 6.11.2009. The the printer is no longer actively supported but the question is general and I'd be happy to get some knowledge regarding currently supported printers. So far the most opaque black I get on HP transparency film is to choose a paper type of HP premium photo plus paper. I do not choose the 'print from black cartidge only' option. I choose 'best' quality. The results are such that I need to print two copies and sandwich them together to block UV light effectively for screen exposure. I've read a lot of various (other) forum posts about manipulating the type of black or color gamut settings in the Adobe Software, and then messing around with the Epson printer driver settings, but I don't have an Epson. I've seen some forum questions on here that are similar to this, but they've been archived, and weren't answered well. So I thought I'd ask again. Using HP products, drivers, ink, supplies, using an HP laptop and wearing an HP T-shirt;  how do I print the darkest most UV blockingest transparencies. Note I don't care about any color than black, nor do I care about finest resolution or most minute detail. I want opaque black. I'd be thankful for any feedback.