How a photocopier works (using xerography)

There are two main types of copy machines, xerographic and electrostatic. Both use the same process to make a copy but they each do it in a slightly different way.

1. Charging: The surface of a cylindrical drum is electrostatically charged by either a high voltage wire called a corona wire or a charge roller. The drum has a coating of a photoconductive material. A photoconductor is a semiconductor that becomes conductive when exposed to light[1].

2. Exposure: A bright lamp illuminates the original document, and the white areas of the original document reflect the light onto the surface of the photoconductive drum. The areas of the drum that are exposed to light (those areas that correspond to white areas of the original document) become conductive and therefore discharge to ground. The area of the drum not exposed to light (those areas that correspond to black portions of the original document) remain negatively charged. The result is a latent electrical image on the surface of the drum. (In digital machines, the original document is scanned and digitized and a laser is employed to discharge the drum in a similar fashion)

3. Developing: The toner is positively charged. When it is applied to the drum to develop the image, it is attracted and sticks to the areas that are negatively charged (black areas), just as paper sticks to a toy balloon with a static charge.

4. Transfer: The resulting toner image on the surface of the drum is transferred from the drum onto a piece of paper with a higher negative charge than the drum.

5. Fusing: The toner is melted and bonded to the paper by heat and pressure rollers.

6. Cleaning: The drum is wiped clean with a rubber blade and completely discharged by light.

This example is of a negatively charged drum and paper, and positively charged toner as is common in today's digital copiers. Some copiers, mostly older analog copiers, employ a positively charged drum and paper, and negatively charged toner.

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The Process Of Offset Printing

Offset printing refers to the printing technique where ink is applied to a metal plate that is etched with images, then transferred to a rubber plate and finally imprinted on the substrate. That is just a small part of the entire offset printing process. The entire process involves the pre-press production, the actual press run and the bindery.

Creating The Artwork

The creative process can involve any number of people from graphic artists, cartoonists, copywriters, and creative directors to illustrators and editors. It is very important to proofread the entire artwork before sending for final printing. The artwork is generally sent in a digital format either on CD, floppy or via the Internet.

The Printing Process

Offset printing is something almost every commercial printer is involved in. However the quality of offset printing often depends on the experience of the printer and the equipment used. There are three main steps in the printing process.

• Pre-press Production: Once the artwork has been approved it needs to be converted to film and plates for printing. The film negatives are created from the digital files. The images from the negatives are then transferred onto the printing plates much like developing photographs. Different materials from paper to aluminum are used to produce plates. Each of the four colors – C, M, Y and K has a separate plate.
• The Press Run: Offset printing works on the principle that oil and water do not mix. The press run or offset printing process or offset press is made of the feeding system, the printing system or three cylinders, the inking system and the delivery system. There are different types of offset presses as well that are used for the press run. The press run starts with a blank substrate and ends with a printed substrate.
• Bindery: The bindery is the stage when the printed substrate is given the final treatment before it is declared ready for use. If the substrate is in the form of a large roll, it is cut into required size sheets. It is glued, bound, stapled and collated before being shipped to the final destination.

Thus, the offset printing process involves a number of stages and the hard work of many professionals. It is no wonder that offset printing is a large industry in itself and the applications of offset printing are increasing day by day.

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Applications Of Offset Printing

It would be difficult to create a complete list of the applications of offset printing. If something needs to be printed, offset printing can do it. Here are some examples of the applications of offset printing to get you thinking on the entire scope of offset printing.

• Newspapers are probably the most visible example of offset printing that is a part of everyone’s life. Every morning you are greeted with an application of offset printing. It is to the credit of the speed of offset printing that such high volumes can be generated every single day.

• Books are another application of offset printing without which life would simply not be the same. Whether for education or entertainment, books are the life source of many a people and they have offset printing to thank for making books affordable.

• The law too has to thank offset printing for making the legal process more streamlined. Large volumes of legal forms and documents are printed using offset printing.

• Businessmen would be lost without offset printing. Important financial data is at their fingertips thanks to offset printing.

• The marketing and advertising industry would regress by centuries if it weren’t for offset printing. The entire direct marketing industry would perish. Offset printing is used for printing flyers, brochures, PR material and a host of other marketing applications.

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