Hi,

In my point of view, as long as you have your PhD, you should give a try and submit it by yourself. Actually, as long as it is genuinely your own research work, and that none of the new findings were suggested by your supervisors during a discussion, you don't have to. There is a time when you have to fend for yourself. Obviously you will cite the other papers you have written with your supervisors as references, and that's already a good think.

You will maybe have more difficulties, mainly if you have no affiliations. And yes, having them as coauthors will ease the work as well as the process since they will proofread it and maybe suggest some additions that will improve the paper, but it is not a sufficient reason as that diploma called PhD is entitling you officially as a scientist that is able to conduct researches and publish papers. You have spent 3 years, or maybe more, learning how to do so...

However, if you think that, for a strategic reason, adding them as coauthors will have a benefit in the present or in the future, you should maybe think twice. Planning a career need sometimes few sacrifices. Politics & strategy are not evil, as long as you don't overuse them :-)

As a final word, I just want to remind you that the submission process is almost confidential and there is very few chances that proofreaders will know your supervisors and contact them. Not to be gloomy, but there is a probability that your paper will not be accepted and you can then go back to your supervisors...

Anyway, good luck!!

P.S: Maybe you should think about orienting your next research work on a subject that is far from you PhD one and avoid all this headache ;-)