MAM CD-R Manufacturing Process





Molding

    
Injection molding is used to stamp a polycarbonate disc.
Polycarbonate was chosen because of its transparency, stability,impact resistance. Furthermore, it is free from impurities.
Polycarbonate, in the form of pellets, is heated to 350 degrees and injected into a mold cavity. A metal stamper is used to form the pregroove - spiral track during injection.
The polycarbonate needed for manufacturing the disc is stored in a silo as pellets. Before use, it is dried for two hours at 120°C.

The injection machine has a variety of sections. There is a polycarbonate reservoir. Below is an endless screw powered by an engine which conveys the polycarbonate to the mold.

Resistance heaters melt the plastic by raising it to a temperature of 320°C. The mold has two sections, one fixed, and one movable so that the part can be ejected. The mold is cooled by pressurised circulating water with a temperature of 120°C.

In the fixed section, there is a stamper with the task of creating the spiral on the disc. When the plastic has been injected into the mold, a circular recorder 0.8 mm thick removes the unwanted part from the disc, which is then ejected mechanically from the mold.

Molding is an extremely important and delicate operation. There may be defects such as incorrect proportions to the spiral, bluring on the edge if the two sections of the mould were incorrectly positioned, or the disc may be eccentric if the stamper was incorrectly positioned.

Controls carried out during the molding phase :

 Visual inspection:  
« Orange peel ».
Uneven surface where the stamper was not perfectly flat.
Bluring at the centre (knife) or edge of the disc (due to a gap between the two mold sections).
Scratches (damaged mold).
Flow marks due to incorrect polycarbonate injection.
 Spiral geometry:
Pitch.
Depth.
Spacing.
Radius.
 Birefringence:
A tendency of certain surfaces to split a ray of light crossing them. Polycarbonate is birefringent because its molecules are aligned, and there are internal constraints caused by the molding. The laser beam splits and the wavelength is different (difference between the two: 60 nm). If birefringence is too significant, the CD-R will be unusable.
 Mechanical characteristics:
 Rigidity is tested by flexing.

Dye Coating

The dye is applied by spin coating.
The thickness and evenness of the dye are important for the quality of the disc.
Drying : The dye must be dried and cured to ensure adequate adhesion to the polycarbonate.


                               
Information on the dye used by MAM, its preparation and its application onto the CD-R cannot be disclosed at present.

Silver or gold coatings (Sputtering)
The gold (or silver) layer is applied in a vacuum chamber (sputter, Balzus equipment) by magnetic bombardment of a piece of gold. Argon injected into the chamber attacks the gold, and the gold atoms are thrown and fixed onto the disc by the magnetic field.

The CD-R is masked to limit the application of gold to the usable areas. The deposit should not go over the edge of the disc since the lacquer will cover the entire disc. Thus the position of the mask must be checked carefully.

Checks are made on light transmission (5%), eccentricity and the deposit at the edges of the disc.


Sputtering

  In order for the disc to be readable by laser, it must reflect the laser light. Silver or gold is used. Silver has a better reflectivity than gold.

The silver or gold is layered in a chamber, using vacuum - sputter. Argon inside the chamber attacks the metal, and this metal is projected using an electromagnetic field.


Lacquer Coating

Same process as for the dye, but in this case the nozzle dispenser is fixed.
Afterwards, the disc passes under an ultraviolet light to cure the lacquer coating.

 
The lacquer is deposited using a fixed nozzle.

It is then exposed to UV light for several seconds for perfect heat treatment.

When the process is stable, it is checked once a day.
The heat treatment must last long enough for the lacquer to be neither sticky nor overbaked. Since the gold layer and dye tends to peel, it needs to be properly covered, and the lacquer is applied all the way to the edge of the disc.

Marking and batches

Discs are separated according to which injection press they come out of and are marked with an inkjet printer. The barcode printed during pressing is read and the discs are sorted and marked. The batch number changes if the stamper or dye is changed, when maximum capacity is reached or whenever there is a significant change in the production process.

Marking means the CD-R will be traceable all the way to the source.

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