Why are the UV map edges of this simple curved pane not straight when flattened

[Zolly]

Hi , I would like to be able to create a UV map for this object and have the UV map edges be straight. Can this be done with Zbrush? I have been using the UVmaster plugin and I always get the curved edges. How can I get straight edges that reflect the straight edges of my object. Either with ZBrush or some other app.
Thanks for any help!!

I also need to do this same shape with rounds in the corner

[Zolly]

Well I can say that Blender did this quite easily, still wondering if and why not ZBrush maybe can not?

Thanks