I work next door to K&S signs and I just had a quick word about this.
They showed me the Aluminium diabond (they informed me that it is also referred to as dibond)
It is a rigid aluminium composite sheet with aluminium cover sheets and a centre made of polyethylene.
The diabond can be white on both sides or white on one side and brushed aluminium on the other side.
The white side, which is a polyester lacquered printable material, is perfect for all types of Digital Prints, from signage to fine art imagery.
The sheet is loaded onto a very large flatbed printer and the image is PRINTED DIRECTLY via UV ink onto the diabond sheet and no additional paper is used.
The sheet is then durable and robust for most types of display, including outdoors, bathrooms, terraces, and areas where the images needs to be durable.