I have been asked by a journal to provide my affiliated university. The assumption is that I am a professor or researcher. I work in industry and spend my non-working hours doing research. What is a common way to handle this problem?
It depends upon your specific company. At one extreme, your company might not want you publishing anything, even if your research has nothing to do with their work (as an example, read about the story of Gosset who used the pseudonym "student"). At the other extreme, your company might be happy with you publishing and listing their company as your affiliation. Or, your company might be somewhere in between and be okay with you publishing, but not listing them as your affiliation. I would ask around or see what other people do at your company in a similar situation.
Also, you say you did the research on your own time, however, your company may still be able to prohibit you from doing any research, even on your own time. You would need to read the fine print on your contract or employee handbook to answer the specific question: "May I publish while working for company X?".
Last, I have seen authors that simply list their home address either because they are retired, unemployed, or in a situation similar to yours. See these similar posts: