Using black ink in CMY cartridges to get opaque blacker than black?

[BlueToBits]

I realise this is well beyond the design criteria of a printer as it's effectively hacking it, and appreciate anyone committing to reading this tome further! If anyone has any ideas I would love to hear them.

Over time, I need to print 100's of LED back lit signs (not all the same) of clear text against a black background on A3 transparency as opaquely as possible. I've tried many methods and found using my HP 7500 E910 printer offers the best bang for buck within the resources easily available to me. It would be perfect if I could get a slightly blacker black. The image is mostly black so I'm using a lot of ink. I have worked out how to force the printer to print a composite black using CMY laying most ink, and found a self-adhesive transparency film that offers best compromise between my criteria and print opaqueness, but I would still like more black! Overprinting the transparency twice through the printer gives excellent opaqueness but has alignment issues.

I have a spare print head/cartridge holder which I can dedicate to this job, but I would still like to use the printer for other colour prints.

I am considering attempting to swap the C,M and Y cartridges for black cartridges in the spare print head, but before committing to this I would like to ask if anyone can foresee any issues, answer any of my questions or offer any advice or suggestions.

I can see a couple of ways that may do this.

1. Try to source a black cartridge for use in another printer model (?) that is equivalent to the CD972AE, CD973AE and CD973AE possibly needing to swap the chips from used CMY cartridges (I don't mind losing ink level information). I can't find any except CD971AA pigment black, only available in Thailand (?!) which even if I could get in quantity, would probably jam in the head designed for dye ink.
2. Refilling empty CMY cartridges with black (dye) ink.

I have invested a lot of time in getting to the point I'm at, and I don’t want to unnecessarily risk bricking the printer and having to start again if there's something obvious from the outset that will render this a non-starter.

I have identified a few potential contenders:

1. When reverting to the original CMYK print head for occasional colour printing, will anything within the printer's head cleaning, alignment, ink overflow tank, head 'keeper' or other mechanisms contaminate the 'colour' print head, and if so, will flushing the colour head by printing a page of saturated colours restore this?
2. Will the print head alignment function still work?
3. Is there a (optical?) sensor that will prevent the wrong colour to be loaded or printed?
4. What’s the best way of keeping the head from drying out when not loaded in the printer?
5. Is there anything else have I not considered?

Many thanks for reading and for posting any answers, observations comments or ideas.


I've tried cut vinyl, silk screen printing, UV set digital printing, typesetting transparencies, laser printing and laser cut acrylic sheet. All have their own issues and limitations which are mostly time, cost and convenience. Inkjet printing ticks all the boxes except that it's not quite black enough - but a lot better than the laser printing I have tried.
Cheers