I think it's definitely un-ethic and probably illegal.

I am not expert on this, just some experiences.

Normally if you work for a company, all your inventions in your work related area should belong to your company. You shouldn't do side business that directly compete with your company's interest. If you still want to stay in your current position, the answer is big NO, NO, NO, NO, NO!

If you want to quit your job, you can consider to patent it after a long enough waiting period. Long enough to proove that your invention is not inspired by your current job.