Plastic Materials

Plastic Materials

Materials under this category can be divided into three sections:

• Transparent plastic

• Vinyl discs

• Optical Storage System

Transparent Plastics

These are flat, transparent acetate or polyester sheets and are available in various thickness commonly ranging from 0.05 mm to 0.25 mm. These are available either as single flat sheets or in rolls. These sheets are used for projection with the help of overhead projectors. The text can be written on them by using special quick-drying ink. In addition, self-adhesive film and letters can be attached to the surface. These plastic sheets can be printed also by photocopiers, laser printers and other standard printing processes.

Vinyl disc

It is composed of a strong plastic material on which audio recordings are made. The discs are marketed in 17.8 cm (7"), 25.4 cm (10"), and 30.5 cm (12") diameter size. The disc has a central hole which fits with the spindle of the turn-table. The inter-table provides for 33 1/3, 45 and 78 revolutions per minute (RPM).

Optical Storage Systems

This technology is most commonly used in producing Compact discs (CD). The disc is made of plastic material. On the plastic surface there is a spiral of pits backed by an aluminised reflective surface. The surface is protected by a strong transparent lacquer. The recording is either an analogue or a digital version of the original. In either case the presence or shape of the pits is 'read' by a laser beam reflected from the mirror-like surface. In this process of reading there is no physical contact with the surface of the lacquer. As such, no damage can occur through using the disc. Different versions of Compact Disks available in the market are: CD Audio, CD-ROM, CD-V, CD-I, CD-R, CD-RW.

The Digital Versatile/Video Disc (DVD) is the new generation of optical disc storage technology. It is replacing laser discs fast as it has the capacity of holding 28 times more data than CDs. DVDs are available in variety of formats: DVD-ROM, DVD-R, DVD- Video, DVD-R/RW, DVD+R/RW, DVD-RAM, DVD-VR, DVD-AR, DVD-SR and DVD-A.

Care and Handling of Plastic Materials

Plastic sheets are not generally used for any long lasting purpose. So long as the document printed or written on them are in need, the sheets are kept flat to avoid wrinkles. These are kept free from moisture to avoid sticking together. If several sheets are kept together one above the other, it is necessary that these are separated by sheets of paper kept in between. On the other hand, the plastic material from which disc is made, is fairly strong. The major care which the disc will need is to protect the groove on it from dust and dirt, and to clean the surface, as well as the stylus of the player before using the disc each time. The pick-up stylus physically vibrates along the groove as the disc is played. As a result, the grooves gradually wear out. This is a natural process of decay. The less number of times a disc is played, the longer it lasts. Use of worn-out stylus quickens the process of decay. So the use of such a stylus should be strictly avoided. Careful handling of discs to avoid their dropping down or scratching on their surface is essential. The discs should be as level as possible on the turn-table, when played. Bending and warping due to exposure to heat and damp are very common. Such damage may also be caused as a result of uneven pressure on the surface. Discs should, therefore, be stored in controlled temperature and humidity. Each individual disc should be placed in the paper sleeve, the opening of which should be against a sealed edge of a cardboard cover in which it is placed. The discs, so covered, are stored vertically, not leaning in either direction. It is not advisable to stack several discs together, stacked one above the other. Though optical storage media can withstand high wear, proper storage condition and handling is essential for their life span. The stability of optical disks mentioned above are in an office environment, but environmental precautions are necessary as oxidation and corrosion may destroy the protective layer and subsequently damage encoded information. 

The potential damage to optical disks can be minimized by carefully implementing the following points: 

• Optical disks require minimum climate control and can be stored in temperature between 5-50 degree Celsius and 10-90 per cent humidity.

• Storage and work area should be regularly cleaned. Disk drives should be cleaned before use.

• If rewritable optical disks are stored, magnets should not be allowed in the storage area.

• Optical disks should be kept in their plastic cartridges. Shelving must be done in a vertical, upright position. Heavy objects should not be kept on the top of optical disks.

• For removing dust from the disks, a soft, lint-free cloth should be used and wiping must be done in a circular motion from the centre to the outer edges. Optical disks should regularly be visually inspected for corrective action. Optical disks containing valuable information meant for long-term storage should be copied from time to time to increase their estimated life span.

• All equipments used for optical disks should be in proper operating conditions. Defective instruments should not be used and be repaired immediately.