Polycarbonate discs

Injection molding is employed to stamp out copies of the master discs from polycarbonate. The molded polycarbonate discs are cooled and hardened quickly, within about 4—6 sec, and evenly. The dye layer is then applied. The applied dyes are often proprietary and continually modified in an attempt to get a better dye. The dye must be compatible with the system and adhere to the polycarbonate base. It is applied by spin coating i.e., the disc is spun and the dye is sprayed onto the surface. The dye is then dried and cured. 

A compact disc-based microarray system was developed by Kido et and used for immunoassays. They used a piezoelectric inkjet applicator to deposit the proteins onto a polycarbonate disc. Recently, Clair et al. reported the attachment of small molecules to a polycarbonate compact disc (CD) surface via phosphodiester bonds. Molecular interactions between analytes and some of these molecules can be detected with a conventional CD player. ... 

A second coating of nickel is then electrodeposited onto the mother disc. This nickel layer, the stamper master, is peeled off and used to stamp the data impression onto melted polycarbonate plastic discs. The polycarbonate disc now has all of the pits found on the original glass master disc etched by the laser. Because polycarbonate is clear, it is vacuum coated with a thin aluminum film to produce the reflective layer required by the laser. This delicate aluminum layer is covered with a protective layer of polycarbonate to prevent aluminum oxidation and marring of the data surface. The back of the CD can now be covered with information in the form of art and lettering. 

Hypothesizing Why do you think nickel is used for stamping the polycarbonate discs ... 

The inks used in CID decorating must have no ill effect on the polycarbonate discs and must support fine-detail printing. For these reasons, UV inks are the systems of choice. 

In the CD, digital information is stored on a tran arent polycarbonate disc in the form of microscopic indentations in the surface. The pitted surface is metallized for laser beam reflection and then coated with a protective lacquer. The laser beam enters from below (see Figure 8.24. When the beam hits a pit there is no reflection when it hits a flat element between the pits it is reflected. The no-reflection/reflection sequence delivers a series of zero/one signals to a photodetector which converts the digital information to analogue music signals. 

Fig. 4.23 TEM micrographs of replicas from a polycarbonate disc, made by shadowing from opposite directions normal to the grooves to illustrate the asymmetry of the grooves. In the top photo the shadowing direction is radially inward while for the bottom photo the shadowing direction is radially outward [303]. The inner edge (arrow in top photo) was foimd to have a much steeper slope than the outer edge (arrow in bottom photo). (From Baro et al [303], reproduced with permission.)...

Finally, it must be remembered that discs have to be manufactured at the highest possible speed, so slow moulding cycles are unacceptable. Acrylic discs can be moulded with a 5 s cycle. Polycarbonate discs require a cycle time of 20 s. Some epoxy thermoset substrates require a 1 h cure time It can become difficult to balance the needs for quality against the needs for throughput. 

The growth rate of 4-cumylphenol is expected to parallel the growth rate of polycarbonates, particularly the grades used to produce compact discs (see Table 3). 

In terms of processing there is no need for pre-drying PCHE granules, a standard extruder screw as used for polycarbonate may be used and discs are said to release well from the mould. Question marks remain on the oxidative stability of the polymer and on the quality of adhesion of the reflective layer but Dow claim that metallising is possible. 

For many years vinyl chloride-vinyl acetate copolymers had two main uses, in flooring compositions and for long playing gramophone records. Whereas the former application remains strong, the use in gramophone records has dropped sharply, particularly since the widespread acceptance of polycarbonate-based compact discs. 

PMMA has not been able to compete in the field of compact discs, the market having gone to the polycarbonates (see Chapter 20). It is, however, suitable for optical data storage using large video discs. Large-scale acceptance in the field of optical fibres has been held back by problems of obtaining material of an acceptable level of purity. 

Just as many small-molecule materials, polymers also form glasses [4]. Actually, most polymeric materials of everyday use are made of polymer glasses, polystyrene (PS) cups or compact discs made of polycarbonates, for instance. In many respects polymer glasses are very similar to small-molecule glasses, and there is nothing special about them. However, on the other hand, the special aspects of polymer materials allow specific studies beyond characteristic studies on small-molecule glasses. 

To maximize control in setting tolerances there is usually a minimum and a maximum limit on thickness, based on the process to be used such as those in Tables 3-6 to 3-9. Each plastic has its own range that depends on its chemical structure, composition (additives, etc.), and melt-processing characteristics. Any dimensions and tolerances are theoretically possible, but they could result in requiring special processing equipment, which usually becomes expensive. There are of course products that require and use special equipment such as polycarbonate compact discs (CDs) to meet extremely tight tolerances. 

The pace of development has increased with the commercialization of more engineering plastics and high performance plastics that were developed for load-bearing applications, functional products, and products with tailored property distributions. Polycarbonate compact discs, for example, are molded into a very simple shape, but upon characterization reveal a distribution of highly complex optical properties requiring extremely tight dimension and tolerance controls (3,223). 

Glassy amorphous polymers exhibit excellent dimensional stability and are frequently transparent. Everyday examples include atactic polystyrene, polycarbonate, and polymethylmethacrylate (Plexiglas ), which we encounter in such applications as bus shelters, motorcycle windshields, and compact disc cases. 

The functional groups that typically participate in this type of polymerization are carboxyl, amine, and alcohol groups. Examples of step growth polymers include polyesters and nylons, which are often spun into fibers used to manufacture carpeting and fabrics, and polycarbonates, which are converted into compact discs, jewel cases, and the large bottles used in water coolers. 

The result was the compact disc (CD). Made from 1.2 mm of polycarbonate plastic, the disc is coated with a much thinner aluminum layer that is then protected with a film of lacquer. The lacquer layer (10) can be printed with a label. CDs are typically 120 mm in diameter, and can store about 74 minutes of music. There are also discs that can store 80, 90, 99, and 100 minutes of music, but they are not as compatible with various stereos and computers as the 74—minute size. 

The major uses of BPA are in the production of polycarbonate resins (63%) and epoxy resins (27%). Polycarbonates have major outlets in automotive parts, compact discs, eyeglasses, and sheet and glazing applications, and have caused bisphenol A consumption to more than double during the past decade. Epoxy resins are two-component adhesives for very strong bonding. Miscellaneous uses include flame retardants (mostly tetrabromobisphenol A) and other polymer manufacture. Polycarbonate grade bisphenol A is >99% p,p isomer. The epoxy grade is 95% p,p. The p,p and o,p isomers can be separated by a combination of distillation and crystallization. 

Injection molding requires the barrel temperature to be about 350°C with a barrel pressure in excess of 138 MPa. The mold is maintained at 110°C to ensure uniform flow and high definition, and to discourage an uneven index of refraction, birefringence. The CD is about four one-hundredths of an inch (0.5 mm) thick. For prerecorded CDs, the PC is compression-molded on a stamper imprinted with the recorder information. This takes about 4 sec. Once the clear piece of polycarbonate is formed, a thin, reflective aluminum layer is sputtered onto the disc. Then, a thin acrylic layer is sprayed over the aluminum to protect it. The label is then printed onto the acrylic surface and the CD is complete. This process is described later in greater detail. 

In addition to the construction industry, phenol has many other applications. It is used in pharmaceuticals, in herbicides and pesticides, and as a germicide in paints. It can be used to produce caprolactam, which is the monomer used in the production of nylon 6. Another important industrial compound produced from phenol is bisphenol A, which is made from phenol and acetone. Bisphenol A is used in the manufacture of polycarbonate resins. Polycarbonate resins are manufactured into structural parts used in the manufacture of various products such as automobile parts, electrical products, and consumer appliances. Items such as compact discs, reading glasses, sunglasses, and water bottles are made from polycarbonates. 

Fig. 50. a SFM picture of an indentation of the letter T on PMMA with a nickel tip. Force used for the imaging was 10"6N. b Profile along the line drawn in (a). Reproduced from [416]. c HEUREKA written with the dynamic ploughing technique on a compact disc (CD) of polycarbonate. The holes are information pits in the disc. The letter height is 700 nm, and the indentation depth is 10 nm. Reproduced from [464]... 

Polycarbonate compact discs have also been used as supports for microarray development [112]. The microarray is generated using an inkjet applicator that employs an electric current to dispense monodisperse droplets containing antibodies onto the disk. The sensing reaction is based on competitive inhibition immunoassays using fluorescent antibodies and final readout is accomplished using a fluorescence scanner. 

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