Help with PP/PE warping

[Reinier1994]

I have been experimenting with infills, and I'd like to try a brim aswell, since the biggest problem right now is warping in corners. Since the first layer adhesion is fine, and the vacuum table pulls the baseplate straight during the entire print, the corners always want to go inside. This causes huge problems after 5-10 layers, since the radius of the corner goes down by 30-50%. Every next layer falls down and makes the print shrink even more.

Right now I've tried three infills. My conclusion is that infill in the middle and on straights is a bit useless, so I'm focussing most on corner strengthening. Since the PE extruder is a simple on/off device, I cannot work with travel points, so my pattern needs to be continuous in the printing process. Here you can see some of the results:

http://imgur.com/a/JTGEh

I'm pretty sure I want to (for starters) decrease the huge nozzle width of 8mm. I''d also like to see if you guys have an idea which type of infill or outline adjustments could make a bettter result. Thanks for the help!