You don't mention which version you are using so my reference to the menu is a little generic but have a look at the setting under Options>Export>Text files.
I think you will find that the option for putting quotes around character value fields (but not numeric) will be set. Change it so you don't get quotes. That should solve your problem.
Let us know if it doesn't.
PS - I was not quite sure if you have an import or and export problem but it reads like an export problem so that is what I answered.