How much isopropanol is effective but safe for viny?

I make my own cleaning fluid using isopropanol and distilled water but am aware that some think IPA is not good for vinyl. Since  the contact time is quite limited I think that it is probably OK to use a small amount as a solvent for greasy contaminants. What do you thing know is a safe level? 25  percent, 10 per Cent , or some other level??