If you're keen to persue the method you're using then just skip what I've placed here.
If however all you want to do is show two scroll ends opening up to reveal it's contents then this is how I'd go about it...
Rather than use nodes and thence, forced to use Blender's internal renderer, (fantastic as it certainly is) I usually opt for the OpenGL render for most of my videos because of it's speed and also because
what I see in the 3D window is what I (usually) get in the output video. At my age one can't sit around waiting!
The scrolled rolls or 'ends' are simply cylinders. You can add handles or whatever. I've knocked this up as a quickie.
The parchment is a textured 2D plane laid flat underneath, complete.
Two (what I call and explain below) 'Inviso Masks' conceal the left and right exposed sections that stick out from the scrolls.
That's pretty much it.
The scrolls and masks are moved sideways and in unison. The scrolls rotate so you can't parent the masks to them.
With the above in place all you need is a few keyframes. Two for each mask and another two for the scrolls, and you have it!
"Inviso Masks" are pretty much like chroma key green or crimson panels but without all the fuss from nodes and their settings. They can be made to "cloak" selectively, anything that is behind them! This makes them extremely useful for hiding bits and pieces that could otherwise ruin an effect.
You'll note the background masonary hasn't been affected at all and yet the parchment's outer sections have been completely concealed!
The masks themselves are only 2D planes with a common material channel and with a transparency setting of just 0.008.
This ensures they're invisible to the eye and yet by virtue I guess of Blender's coding, treat it's semmi-transparent material as it would a solid colour and blocking what's behind it. (given certain other settings)
It took me an hour to work out with any degree of predictability exactly what it took to make them conceal 3D objects and what it also took to get them immune again.
The details - To cloak an object that is to end up behind one of these planes, simply parent it to the plane. That's all it takes.
You can un-parent it again immediately after and the cloaking will still hold.
To remove the cloaking effect from an object, join it with the plane first up, and MAKE SURE YOU SELECT THE OBJECT FIRST, THE PLANE SECOND!!
Once joined, part them again by selecting the object, goto Edit Mode,
select all the object's faces and MAKE SURE NOTHING IN THE PLANE HAS BEEN SELECTED AS WELL - then press 'P', and select "Part by Selection".
Once you deselect everything, that object should be visible through the panel. (uncloaked)