A DVD is combined by two single sheets using an adhesive process.

Bonding is the main process of DVD production. A variety of DVD discs, regardless of their format or storage capacity, are formed by a combination of two 0.6mm monolithic adhesive processes. DVD-5 is a single sheet with a recording surface and sputtered with a reflective layer and a single blank sheet. DVD-9, DVD-10, DVD-14, and DVD-18 have metallized pit recording surfaces on both monoliths. For adhesive systems that are suitable for all DVD formats, the adhesive material must be universal. The bonding process must form a strong bond at the two different material levels. These materials may be aluminum, polycarbonate, gold, silicon, silver.

The bonding process is not introduced from the DVD. Magneto-optical discs and compact discs are all bonded together. The technique used to bond these discs is called hot melt bonding. The adhesive is heated to a temperature between 120° C. and 180° C. (typically 165° C.) and is applied to the surface of both halves using a roller. The thickness of the adhesive layer per disc is very thin (about 30 μm). In the second stage, two monoliths are combined under the effect of light. In the final stage, uniform pressure acts on the disc to complete the bonding process.

Hot melt bonding is a widely used and proven technology with the advantages of lower material costs and cheaper equipment. However, DVD bonding does not use this technology. Because DVD-9 is unique among various DVD formats, the two monoliths that make up DVD-9 have a recording surface with a pit structure. The DVD-9 can only be read from a single side, the laser must go through the adhesive layer to read the second monolithic information layer (L1 layer). That is, the adhesive layer must be similar to the material specification of the polycarbonate.

Layer thickness, uniformity, low levels of physical defects, and all optical properties are all critical parameters. Instead of hot melt bonding, UV bonding is used instead. UV adhesion is more complicated because not only is the material used under very constrained conditions, but eventually a curing process is also required. The DVD adhesive layer is very thin and the thickness specification should be 55±15 μm.

Although one or two manufacturers have also provided adhesive film technology as an alternative to the DVD bonding process, most production line manufacturers have chosen a UV bonding process that is suitable for all types of DVD discs. Because most production line manufacturers prefer to develop their own UV adhesive systems, they do not want to integrate adhesive systems from professional providers.

Although it is always possible to provide different optical grades of polycarbonate for different injection moulding machines, it is not always possible to provide the respective optical grade adhesive materials and connectors for different bonding machines. To obtain reliable, constant performance, the resins and processes used in the bonding process must be closely matched.

Originally, there are two types of UV-bonding resins: free radicals and cations. The free-radical esters are based on acrylic components and the cationic resin-based epoxy or vinyl ether materials. Both resins have advantages and disadvantages. The treatment of epoxy adhesives is not affected by the oxygen in the air (acrylic acid maintains tackiness under aerobic conditions), but on the other hand epoxy-type adhesives often contain toxic components, some of which can be processed in the process Produces highly corrosive by-products. This means that the metalized substrate must be coated with a protective glue before bonding. Another difference is that the epoxy resin sometimes needs to be continuously treated for 30 minutes while the UV lamp is exposed. Acrylic materials require continuous exposure of the UV lamp until processing is completed. Although both types of resins are used for DVD bonding, acrylic systems are more commonly used.

The biggest problem with adhesive systems is avoiding bubbles. If there are bubbles, waste sheets will be produced and the two molded sheets will be discarded. Feeding technology, rotational speed, and the viscosity of the material are all very important factors that affect bubble generation. Although UV-adhesive protective coatings are applied using spin coating, this is not the only technology available.

For example, gap dispersion techniques use the capillary principle. The adhesive material is injected into the center of the program area by a fine probe. The capillary action causes the adhesive between two adjacent DVDs to flow toward the center and outer edge of the disk. Surprisingly, most adhesive systems do not actually bond the center of the disc. In most cases, the isolation ring near the center of the disk acts as a barrier.

Regardless of how the adhesive material is used, if the final disc is disc-shaped, it must be removed. The shrinkage of the substrate temperature and the adhesion of the disc adhesion layer (up to 8% of the UV adhesive shrinkage) is a major factor that system designers need to be concerned about.

After the screening of the optical properties and the prevention of the formation of air bubbles, after obtaining a completely flat disk, the concern is whether the two substrates are completely bonded together.

The intensity of DVD adhesion is another parameter of interest. Two parameters are important: peel strength and impact resistance. Under normal circumstances, users cannot easily separate two single films. If a single piece falls off, the disc becomes obsolete. The stripping strength can be tested using a screwdriver to open a single piece, which is the standard test method for early DVDs.