Checkout my post on UV Film. In this forum.. I think It answers many of your problems. Note, that film is for Epson injets, which use 'Dye-Based' Inks. The HP printer maybe using 'Pigment' based Inks?? which is a no-no, especially for us PCB'ers. This maybe the source of your problems.
Setting printer for 'Transparency' produces naff output, always see-through. Try setting it to PhotoGlossy, this setting works best.
Note: Inkjets can't print to tracing paper, the reason it runs is because it doesn't have the 'resin' coating which absorbs and sets the ink.
My Epson R200 injet produces really dense black, and sticks to this New film very easy... Plus its cheap, and as a bonus, prints on my CDR/DVD-r's.
Normal transparencies are less than useless, especially for fine tracking & pads. I used to use 3M inkjet film, this produces slightly grey-ish blacks, and often needed touching-up. Since finding this super-res film, which I output @5760 dpi, I've had no probs.
Epsons are almost made for UV artwork
If you can't get the desired results with your HP? you may need to buy an epson, note: not the R800 as this uses wierd gloss optimizers. The R200 is the kiddie, plus has separate ink carts for all the colours.
Hope this helps
Steve