I have been trying to use Verbatim BVOH soluble interface for my prints but my parts have poor layer to layer adhesion on any layer which also required use of BVOH. My base material is Verbatim PLA. I have tried a range of temperature settings for both materials from 210 to 218 degrees. After adjusting bridge flow rate to 1.0, problems I had with both materials bridging over sparse infill on the purge tower or part went away. The part now prints cleanly and the BVOH easily and cleanly separates from the part leaving a near perfect part surface.
I suspect there are trace amounts of BVOH left in the print head that are contaminating the PLA causing weak adhesion of PLA between layers. I tried increasing the purge tower drastically- 35mm X 60mm, with no improvement. I tried replacing the BVOH with gray PLA (the part is printed in white) and then printed using the identical settings to see if I could see the gray blending with the white in the part itself. The two colors stayed completely separate between what would have been soluble interface and regular support or the part itself. This seems to confirm that it is the BVOH itself that is not being completely purged from the nozzle and then mixes with the PLA while that material is printing.
The test part I am using is a small panel with a raised frame around it. Because of the shape, I can print the part in one position so that no support material is needed. If I flip it, then support IS needed. If printed so support is not needed, using the same settings, the layers adhere to each other extremely well. If I flip the part over and print with support, then the part layers easily separate.
Any suggestions would be appreciated.