Click here to see a photographic comparison between offset versus screen printed white ink.
Once the lenticular effect has been printed (seen from the front), the sheets are run through the press twice more to print an all-over flood coat white backing. This offset white ink is translucent and usually suffices to hide a clear adhesive for when the intention is to stick the prints to a white backing e.g. report covers.
Screen printing a pass of opaque white ink over the two previous passes of offset white ink, provides much higher opacity and boosts the colour saturation of the front side lenticular print. It’s effectively like a thick coat of white paint on the back, suitable for then overprinting a backside design -in the case of 2-sided pieces. If one holds the print up to a bright light, then there’s still show through of the other side print, so it’s not claimed to be a block out.