Coating process of protective adhesive for the hot

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The protective adhesive coating process of optical discs is a well-known process, but this process has been developing for many years, and producers should seek a balance between cost efficiency and process stability

after splashing the reflective layer on the disc, the next process is to spin coat UV protective glue or paint (sometimes involved). The reflective layer is very thin and may be damaged if it is not protected. The metal layer itself cannot be treated, and contact with the metal layer will reduce the reflectivity. Even if there is no physical contact with the reflector, most materials will react with the air quickly, which will inevitably reduce the reflectivity, making it lower than the lower limit of reflectivity by 70%. The protective glue prevents the chemical reaction of the metal layer and also prevents the physical damage of the metal layer

the protective glue process consists of two main steps: spin coating protective glue and UV treatment. The early spin coating machine was very large, and it was fed by parallel conveyor belt, which was different from the current system in many important aspects: the material of the protective layer was not UV treated, but based on solvent, which meant that the disc after spin coating not only needed to be dried, but also the vaporized volatile solvent (generally toxic) needed to be safely transferred out of the work area. This not only increases the complexity of machinery, but also increases the cost. In particular, environmental protection laws in many places require the establishment of solvent recovery systems to strictly control the waste discharged into the air

at present, the protective glue process is considered to be a very mature technology. Compared with early mechanical devices, today's system shows light and efficient characteristics in feeding. The main components of UV rotary coating machine include: blanking bowl slightly larger than the size of the disc, blanking arm, free blanking needle nozzle, feeding groove, feeding pump, and motor that provides disc rotation power

in order to obtain a uniform spin coating effect, a pre quantitative protective glue is fed to the center of the disc. During blanking, the disc speed is very low to ensure that the protective glue dripping on the disc is evenly distributed in strips. Obviously, in order to ensure that the high molecular polymer on the disc has the mechanical properties with the widest range of variability among all known materials, the inherent viscosity of the material, the coating temperature and the disc speed must be strictly controlled. As soon as the protective glue is in place, the disc rotates at a high speed of 2000 ~ 6000rpm, forcing the protective glue to be applied to the outer edge of the disc. The material thrown out of the edge of the disc is returned to the feeding trough to avoid waste

at the outer edge of the disc, there is an area that is not splashed (this area is deliberately covered when plating the reflective layer), so the protective glue will directly adhere to the PC substrate and close the reflective layer to protect the air from erosion of the reflective layer

like other optical disc production process stages, the protective glue process should also avoid defects. The main problems of the protective glue process are the splash spots and uneven thickness when throwing. Because the protective glue is coated on the back of the disc, it doesn't seem to be very important, but it's not. In order to meet the Redbook standard, the disc thickness must be 1.2mm, and the allowable tolerance range is very small. This thickness is the thickness of the entire disc, including PC substrate, protective glue, etc. For CD-R, this problem becomes more important: if the protective glue is too thin, it is not enough to protect the tank and dye layer; If the protective glue is too thick, the total recording times of the disc will be affected

the physical properties of UV glue are also very strict. The impact strength of the central hole is slightly smaller or the notch of the disc box is carried out on the ZBC ⑵ 5B pendulum impact tester according to GB1843 (80); The tensile property is tested on cmt6104 universal electronic testing machine according to gb/t1040 (9) 2 standard. If the sleeve is slightly larger, or the combination of the two will make it difficult for the disc to be removed from the disc box. Users generally take out the disc by bending the disc, so the protective layer should have enough plasticity to resist bending. The protective adhesive also needs to have excellent adhesion characteristics, especially for the very smooth gold reflective layer. The protective adhesive layer is very thin (generally 5 ~ 7 μ m) It should have very tough characteristics to protect the reflector and pits that are vulnerable to erosion. The protective adhesive should also have low shrinkage performance and certain anti stripping performance to prevent the protective layer from falling off during the process of moving the disc

although the main purpose of protective adhesive is to protect the reflective layer, the printing performance of the surface of protective adhesive (whether white printing substrate or final printing label) should also be considered when developing the formula of protective adhesive. Because the disc is printed on the protective layer, the printing medium and the protective layer should have good adhesion characteristics. Most UV protective adhesives look transparent or yellowish, which will slightly affect the color of the substrate and printing ink

the distance between the two lines can be measured when the steel strand is broken. Lo protective adhesive is applied to the surface of the disk reflector in liquid form. After coating, UV curing treatment is required

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