Because adhesion and disk flatness must be maintained in varying environmental conditions, the bonding agent plays a critical role in the DVD. Typically, a hot-melt adhesive applied to both halves of the disk, the agent is normally cured by UV light. This process, however, can take hours for the bond to reach final strength.
Imation Corp., Menomonie, Wisconsin, has developed a pressure-sensitive adhesive for DVDs that does not need lengthy curing. The product, called SP-5, is applied to the substrate surfaces as a liquid and when briefly irradiated with UV becomes a high-tack solid glue. Once the disks are mated, no further curing is needed, thus reducing stresses in the substrate which could affect optical properties.
To compare, a DVD has a 0.74-micron track spacing and 0.4-micron minimum pit length against 1.6 microns and 0.83 microns for a CD. In addition, the DVD player's laser can still read the larger pits of a CD, thus giving the desired backwards compatibility.