Galaxy A3 Digitizer Replacement problem?

Hi guys, yesterday I tried to split my broken glass from the lcd and I succeded with it. After this there was an uv loca gel left over the lcd and I used acetone to remove it.

But the problem is that also at the back of the LCD there was specific tape I think white scotch and black but unsure and she also fell off.

I tried to check if the display is still working and it's working. Just wondered about that tape or adhesive I don't know what is it and, is it so important to install a new one, before apply a new uv loca gel over the lcd.

The tape was between LCD and Copper, directly at the back of the lcd when used acetone it was sticky but removable, so I pull all of it, but display still works.

Thanks in advance,

Sorry for my bad English.