Filling CMY cartridges with black ink to get opaque black?

[BlueToBits]

Hi.
I need to print black on transparency as opaquely as possible using a HP7500 E910 printer. It's a back-lit sign with clear letters on a black background 400mm x 300mm. I have worked out how to force the printer to print a composite black using CMYK which works best for the self-adhesive transparency film that offers best compromise between my ideal criteria and print opaqueness, but I would still like more black!
It's possible to see on the attached photo that light from a LED desk light through a frost filter bleeds through the black ink. (sorry, I must get a phone with a better camera) .

I have a spare print head and don't mind dedicating it to this job, so I am considering swapping the C, M and Y cartridges for black cartridges in the spare print head and use the original print-head in the printer for other full colour prints. 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 to do this.

1. Try to source a black HP 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 (Google) any except pigment black only available in Thailand (?!).
2. Refilling empty CMY cartridges with black (dye) ink. This is looking favourite.

As I have invested a lot of time in getting to the point I'm at, I don’t want to unnecessarily risk bricking the printer and having to start over 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, could 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 which uses blue and black boxes still work?
3. Is there a (optical?) sensor that will prevent the wrong colour to be loaded or printed?
4. It took me a day to unblock the spare print head. What’s the best way of keeping the head from drying out when not loaded in the printer?
5. What else have I not considered?

Does anyone have 10 cents worth they can throw in?
Thanks for reading.

 

[The Hat]

Firstly, putting dye black into all your cartridges won’t give you any better black output, and no the printer will not notice any difference, to the printer ink is ink and pigment ink probably won’t stick successfully to the film surface either.

one way to get a better black coverage is to put the film sheet through the printer twice, now I know nothing of the capabilities of HP printers, but I do know that this can be done because I have used this same process on various special print runs.

Registration is critical but it does not have to be 100% for this process to work, you need to print in your normal way, then let the film dry thoroughly then put it back through the printer a second time to apply another coating of ink over the exiting coating.

This is a tried and tested method of applying sufficient enough ink to a print surface to give much deeper colour, you may even try using pigment ink for your second application because this ink won’t be adhering to the actual film surface, more so the previous ink coating...

 

[BlueToBits]

I've not thought about laying pigment ink over dye ink. I do have registration problems using 2 passes, and indeed, 2 passes gets the black I need anyhow. I can get fairly consistent left and right registration (or up and down in landscape) but the pick-up or edge detection on the printer seems not that reliable. Maybe because I'm using transparency and not the 'iron on transfer' paper that I find produces the best black on the transparencies I'm using, and it's looking for a white edge. I can operate the printer with the cover open and notice flashing LEDs under the print head at the start of a print. It all moves very fast so it's difficult to see exactly what's going on. I might try your suggestion but apply a white strip to the leading edge of the sheet.
Cheers

 

[Ink stained Fingers]

if you are running on an Epson printer you may use an ink like this one
http://www.vermontphotoinkjet.com/products/screenprint-inks

I don't know whether other special screenprint inks are available for thermal/bubble printheads - Canon/HP.

 

[PeterBJ]

When in need of some dye black refill ink I have mixed dye cyan, magenta and yellow ink. My result was a dark grey with a colour cast. I couldn't obtain a true black. So I think replacing the Cyan, magenta and yellow inks with dye black will result in a better black. Some HP Photosmart printers use both pigment and dye blacks, so I suggest to use this refill ink for HP photo (dye) black cartridges. It is available from Octoinkjet UK.

I have some old ink jet transparencies. They have a white strip attached to the leading edge, so I think adding one to a transparency would help the printer to position the sheet properly.

 

[BlueToBits]

Thanks for the input folks. It's a all in one HP officejet 7500 which prints A3+ size.

Firstly, putting dye black into all your cartridges won’t give you any better black output,..

Is there a reason for that?
I've read somewhere that the printers create black by using a dot pattern of CMYK at around 40% distribution of each colour with some overlap. So I was hoping that if I changed the CMY for KKK I might get around 160% KKKK? At the moment, using the same print settings I get a purple cast with some transparencies, on most others I get a green cast I'm also using a 2 way mirror-film behind the front sheet and 2nd 'mask' sheet behind that, which is an inkjet frost coated transparency film designed for illuminated advertising signs to be viewed from the non-printed side( the colours are very strange on the printed side) . The frosting's Grrrrreat! (to quote Tony the tiger!) at producing opaque colours (a slight purple cast though) , but it's white rather than clear where unprinted and I need it to be mirrored. The LEDs are only 15mm behind the frosted sheet (120 RGBs) so at the moment the light is passing through the black printed frost, 50% transmissive mirror and the black printed transparency. The transparency black (with a slight green cast) is nowhere near as good as the frost, but I can still see light bleeding through especially in low ambient light levels.
If I can get another half stop in the front sheet black, I'll be laughing chocolate biscuits.

 

[apetitphoto]

Are the LEDs truly white or do they have a bluish cast, as faint as it may be? And is your black truly black?

You may be stuck in the "Paint the wall white, dear" conundrum...

 

[PeterBJ]

....I've read somewhere that the printers create black by using a dot pattern of CMYK at around 40% distribution of each colour with some overlap. So I was hoping that if I changed the CMY for KKK I might get around 160% KKKK?....

That is also what I think. The dye black (photo black) was introduced to improve black and very dark colours. Dye CMYK printers can produce "Darker blacks" than dye CMY printers can.

How about flushing the pigment black cartridge and refill it with dye black and then select plain paper as printing medium to use the pigment black cartridge? Then you would not get the CMY channels in the print head contaminated with black ink that might take some cleaning to get rid of.

 

[The Hat]

I tried printing a couple of 5 cm circles onto Kimolec film using just M,C,Y,BK dye inks, then I let it dry and overprinted with pigment ink, this was a complete failure because the pigment ink wouldn’t dry even using the dye ink as an underlay...
Maybe you should consider using a Laser printer, you’d have better success with that...

http://www.kimoto.ch/products/product-detail/detail/kimolec-pf-90s.html

 

[BlueToBits]

Are the LEDs truly white or do they have a bluish cast, as faint as it may be? And is your black truly black?

You may be stuck in the "Paint the wall white, dear" conundrum...

They flash too fast to be incandescent and seem to be more of a warm white. I would guess around 3000K There seems to be more than one of them but that might be a strobe effect. The only light briefly (~200ms) and when the carriage is moving. It's an HP officejet 7500 printer.