GR3770 print density

[Guest]

Hello,

I just bought a riso gr3770... I'm making some print tests with it and everything seems to work fine BUT when I try to print solid color without any image, there's two problem:
- the density at the border of the print is higher than at the center of it (see first image below)
- there are some horizontal "waves" that never disappear (see second image below)

I washed the color drum, checked the pressure of the impression roller but the problems are still here.

Since this is my first experience with a riso, I really don't know how to correct those problems. Any advice would be very welcome!

img-004.jpg

img-005.jpg

[jermyth]

Re: GR3770 print density

The uneven density can be from the impression roller needing replaced. Over time it gets warpped by paper and the drum.
The waves I feel are a RISO thing. Some drums do it, some don't. I think it has to do with the manufacturing of the rollers inside the drum.
Most customers understand large solid colors are not going to have perfect consistency, espcially with an OLD RISO.

Please explain your drum washing process too please, you may need to ink up the drum more to help with the fill. OR adjust the squeege doctor gap and squeege pressure.
Also what is the copy count on the RISO?

Good luck.

[psykolio]

Re: GR3770 print density

Thank you jermyth!
The copy count is 1305000... I washed the blue drum (the one that produces the results above) by rubbing some benzine ("essence f" in french) both on the outer and inner screens of the drum. I heard that maybe the ink I use is a little bit too old and shaking the cardridge before printing could help to remove the waves...
But I have the same problems with all drums, black, green, blue, washed or not.
I will check the squeegee doctor gap when i get some new ink... And if nothing changes, I'll replace the impression roller.

Thanks again for your help!