Many printers expect RGB input an the printer driver software decides which inks are actually used. You seem to want to skip it and force the printer to use black instead of some cmyk-combination that you call rich black. I have an Epson which also sprays some cyan, magenta and yellow when the color is black and there's nothing visible in my PC to stop it. Epson tells here that stopping colors when printing black is not possible. https://epson.com/faq/SPT_C11CH42201~faq-00004f9-et2720?faq_cat=faq-topFaqs
Your options without getting a new printer nor trying anything risky
- check if the printer driver settings has some advanced user options which allow you to force black prints to happen only with black ink.
- ask manufacturer's support and check their user forums for a workaround
I'm afraid both of these are useless if the printer is a low cost hobby& small office model. The manufacturers do not have any intentions to give professional options to those who maybe could shell out 1000% more money. Without knowing enough of printer technology I cannot decide if there's also a mechanical problem. I mean it may bee too difficult to make a low cost printer where the black ink can cover the paper fully and stays still sharp. Epson claims it tries to keep the color ink channels of the printhead functional by using all of them.
Another approach is to purchase a monochrome laser printer. Two equal copies aligned carefully is dense enough for a good UV exposure. You can, of course, try this also to your current prints.
The risky approach is to print like before, but by filling at first the tanks with black. No guarantee is the printer after trying this any more usable for anything or even for something. It has also another consequence. You will get numerous well visible black dots around your paper in places that you thought to keep white.
An explanation: Governments have persuaded printer makers to spray here and there virtually invisible yellow dots which carry a code: The serial number of the printer and all vital identification information that the printer driver succeeds to extract from the computer. Governments need it because in many western countries newspapers often get printed documents which reveal how politicians try to ensure they stay in power or steal a billion. A trumped raid to the newspaper gives only the printed documents, but the color dots help to find and neutralize the person who leaks documents. The persuading is easy. People know they tend generally to have traffic accidents, to slip when walking at roof edges and to run into randomly flying pieces of lead. And governmental institutions and agencies can suddenly stop to buy anything from a manufacturer who just in yesterday was a prominent supplier.
If you have black in every ink tank the printer identifier dots are no more invisible.
About migrating to Inkscape
Assuming you have the full set of CS6 including Acrobat Pro: Do not scrap CS6 if it's still possible to be used. Inkscape cannot make CMYK print PDFs and it lacks numerous other properties why people wanted to purchase CS6 and still want it.