Discussion on the bonding process in the hottest D

2022-08-15
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Discussion on the bonding process in DVD printing

a DVD is combined by two single chips using the bonding process

bonding is the main process of DVD production. The pollution caused by various DV plastic granulator processes is often an important source of environmental pollution in China. D discs, regardless of their format or storage capacity, are formed by the combination of two 0.6mm single sheets through the bonding process. DVD-5 is a single chip with recording surface and splashed reflection layer bonded with a blank single chip. The recording surfaces of DVD-9, dvd-10, dvd-14 and DVD-18 have metallized pits on both single sheets. For the bonding system applicable to all DVD formats, the bonding material must be universal. The bonding process must form a solid bond on the level of two different materials, which may be aluminum, polycarbonate, gold, silicon and silver

the bonding process was not introduced from DVD. Both magneto-optical disc and laser disc are bonded. The technology used to bond these discs is called hot melt bonding. The adhesive is heated to 120 ℃ ~ 180 ℃ (typical value is 165 ℃), and it is coated on the surface of the two halves with a roller. The thickness of adhesive layer of each disc is very thin (about 30 μ m)。 In the second stage, the two monolithic plates are combined under the action of light. At the last stage, the uniform pressure acts on the disc, which can reduce the friction between the spring plates and complete the bonding process

hot melt bonding is a widely used and proven technology, which has the advantages of low material cost and cheap equipment. However, DVD bonding does not use this technology. Because DVD-9 is relatively unique in various DVD formats, the two single chips that make up DVD-9 have pit structure recording surfaces. DVD-9 can only be read from one side, and the laser must pass through the adhesive layer to read the second monolithic information layer (L1 layer). That is to say, the adhesive layer must be similar to the material specification of polycarbonate

layer thickness, uniformity, low physical defect level, and all optical properties are very key parameters. Therefore, instead of hot-melt bonding, UV bonding is used. UV bonding is more complex because not only the material is applied under very constrained conditions, but also a curing process is ultimately required. DVD adhesive layer is very thin, and the thickness specification should be 55 ± 15 μ m。

although oneortwo manufacturers have also provided adhesive film technology as an alternative to DVD bonding process, most production line manufacturers still choose UV bonding process suitable for all types of DVD discs. Because most production line manufacturers prefer to develop their own UV bonding systems rather than integrate bonding systems from professional providers

although it is always possible to provide polycarbonate of corresponding optical level for different injection molding machines, it is not always possible to provide bonding materials and connectors of corresponding optical level for different bonding machines. In order to obtain reliable and constant performance, the resin used in the bonding process must be strictly matched with the process

originally, there are two types of UV bonded tree esters: free radicals and cations. Free radical tree esters are based on acrylic components, and cationic tree esters are based on epoxy or vinyl ether materials. Both tree esters have advantages and disadvantages. The treatment of epoxy adhesives is not affected by oxygen in the air (acrylic acid can maintain viscosity in an aerobic environment), but on the other hand, epoxy adhesives often contain toxic components, some of which can produce strong corrosive by-products in the treatment process. This means that the metallized substrate must be coated with protective adhesive before bonding. Another difference is that epoxy resin sometimes needs to be treated for 30 minutes when exposed to UV light. Acrylic material requires continuous exposure with UV lamp until the treatment is completed. Although both types of resin are used for DVD bonding, acrylic systems are more commonly used

the biggest problem of the bonding system is to avoid bubbles. If there are bubbles, waste sheets will be produced, and the two molded single sheets will be discarded. Cutting technology, rotation speed and material viscosity are all very important factors that affect the generation of bubbles. Although UV adhesive protective paint is applied by spin coating method, this is not the only technology available

for example, the gap dispersion technique uses the principle of capillarity. Stick with the real fiber of wood flour to fill, mix with PE, PVC and other resins, and inject the material into the center of the program area through a fine probe. Capillary action makes the adhesive between two adjacent DVD sheets flow to the center and outer edge of the disc. Strangely, most bonding systems do not actually have the center of the bonded disc. In most cases, the isolation ring near the center of the disc acts as a barrier

regardless of the use of bonding materials, if the final disc is dished, it must be removed at the same time. The substrate temperature and the shrinkage of the disk adhesive layer (the shrinkage of UV glue can reach 8% at most) are the main factors that the system designer needs to care about

after screening the optical properties and preventing the formation of bubbles, we need to care whether the two substrates are completely bonded together

dvd bonding strength is another parameter that needs to be concerned. Two parameters are important: peel strength and impact resistance. In general, users cannot easily separate two monolithic devices. If a single piece falls off, the disc is discarded. Using a screwdriver to pry open a single piece can test the peel strength, which is the standard test method of early DVDs

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