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Alphabet R /2

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8. Reprography : The term Reprography is a wide term that covers various processes including small Offset printing machines like Rota Print, Autolith, Multilith etc (Not bigger machines).  Reprography in real sense means duplication of documents. They include written or printed matter, rare books, Engineering drawings, archives, designs etc and duplicated with processes that are based on or aided by photographic reproduction. Therefore Reprography is reproduction process -Reproducing by Photographic means- to convert the images into readable form, by breaking them into minutest dots, lines , pixels or other formats in real time sizes and images.  Which one of the processes are called Reprographic Processes?

  • Microfilm- Conservation of records to Micro reproductions on 35 mm films. Reason for doing so is  for archival or other purposes, as a measure for preservation of records against deterioration from use or loss due to natural aging and fading of inks and further  to save valuable space in keeping duplicate copies. They also help in safe storing of valuable records as a precautionary measure against loss by fire, flood, war and sabotage. The recorded version can not be read by naked eye as they will be in the form of minutest pixels. But the recorded information can be read only with an special enlarger which projects recorded information on a monitor screen. Micro form images are commonly reduced to 5 % of the original document size i.e an A4 size paper will be condensed to nearly 1’’x 3/4’’ frame in the film. For special purposes, greater optical reductions are used.
  • Microfiche or Micro Card : Conservation of records on a 4’’ x 6’’ special cards of films. Reason for doing so is  for archival or other purposes, as a measure for preservation of records against deterioration from use or loss due to natural aging and fading of inks and further  to save valuable space in keeping duplicate copies. They also help in safe storing of valuable records as a precautionary measure against loss by fire, flood, war and sabotage. The recorded version can not be read by naked eye as they will be in the form of minutest pixels. But the recorded information can be read only with an special enlarger which projects recorded information on a monitor screen. An Micro Card or film in 4” x 6” size will hold  100-200 pages of an A3 size paper .
  • Photostat : Several decades ago, till Xerox was introduced, all the photocopies were taken on a thin variety of special, but cheaper variety of Photographic paper called Photostat Paper using Process camera like copying machine. The Photostat paper in roll form used to be loaded on the Camera back and several documents will be loaded in the copy board and exposed through a prism . The exposed Paper will be developed with suitable chemical and washed with water and paper dried through drier cylindrical machines. The images will be white letters on a black background (like negative), but letters in readable form as the exposure will be done through prism for lateral reversal of the image. Both Positive and Negative working photostat papers were made available. All of them produced only black and white images and not colored.
  • Duplicator: Duplicating machines using Stencil paper which are either directly typed or electronically cut Stencils  were used for printing the images on paper. The images are formed by burning process in the the electronically processed stencil cutting machine  to facilitate printing on duplicator.
  • Ammonia or Diazo printing : By this process the architectural and engineering drawings, technical drawings etc drawn on tracing paper are duplicated  on a photo sensitive paper even if the size is very big. The copies will be white lettering on blue background. The only drawback of these prints are that they fade away on constant exposure to light.
  • Digital printing
  • Inkjet printing
  • Electrostatic processes (Xerox)
  • Tabletop small Offset/Thermal printing: On these printing machines only paper plates (not metal plates) acould be used. The latest development by Mitsubishi in this direction is the  Thermal Digi Plate TDP-459 for small offset printing due to be  featured at drupa. This compact table-top system, according to the manufacturer is designed for 2-up printing, images paper offset printing plates without any consumables other than the plate material itself. The TDP system is an environmentally-friendly CTP system which is chemical-free and process less. Read more on this in their site by clicking  :  http://www.mitsubishiimaging.com
9. Re screening: Re screening means, reproducing the halftone image from the already printed book  for reprinting again. Re screening the halftone is not an easy task and it is a highly skilled job. While re screening the halftone images from the already printed material, if the screening is not set properly it may produce Moire effect image i.e the image will have checkered pattern or scratchy look.  How then can the halftone be re printed without moire
Every halftone would have been printed with certain screen angle and screen ruling. When the already printed halftone original is again to copied it is done in few ways as given below:
  • If the printed halftone original is coarse one, the image is enlarged by 1 or 2 % and copied as line work without using a screen. Similarly the size is reduced by 1 or 2 % and processed. The reduction and enlargement is possible only if the  change in the image size is permitted, because for certain technical reason or on account of scaled images, the reduction or enlargement may not be permitted.
  • The second option is to focus the image on the camera back and see which screen angle will reproduce the image with less or no moire effect. If the camera is fitted with a circular screen, then the screen can be rotated to find out which angle can avoid the moire effect and then it can be copied. Generally the turning of the screen by 15º will considerably reduce the moire pattern. For example if the original halftone image has been reproduced with a 45º angle screen, then rotate the angle both sides by 15º to find out which one gives the acceptable image and then copy the image.
  • The third option followed by many printers is, photograph the printed original with a  digital camera, take a print out and then use it as original continuous tone copy for half-toning the image. However the  ultimate goal is to copy as much detail as possible avoiding the problems of overlapping screens.
10. Relief Printing : As the name implies, the relief printing means printing with the print matter using relief plates. The printing areas on the plate will be in relief unlike Offset where the printing and non printing areas are in the same plane. The relief printing includes printing processes like Letterpress Printing, Flexographic printing and Numbering where the number wheels have the numbers in relief.
The Intaglio Printing (not the printing process) is also called relief printing because the printed images are in relief and can be felt by passing the fingers over them.
11. Rotary Press : Rotary printing machines are those that print on the  paper through Cylinder mounted plates pressed by a cylindrical shaped impression Cylinder in contrast to the flat bed machines where the matter to be printed will be mounted on a flat surface and a impression Cylinder rolls over it to cause the print. The Flat bed presses are very slow compared to the Rotary Printing presses. Besides printing on bigger sheets, the Rotary presses are also used for printing on Paper reel. Even though the Flat bed presses also use the  Cylindrical shaped impression cylinder  to cause  impression,  the Plate holding bed  being   flat surface, this is not called Rotary press. Unless both the Plate or image holding bed and the Impression beds are both in cylindrical shape, the press can not be called Rotary Press.
The Rotary printing machines operate with high speed and therefore are used for printing books, pamphlets, newspapers, magazines, labels, posters, and other items, as well as packaging materials whose print orders are high. The Rotary Printing machines also facilitate printing on both sides in one pass which is called perfecting. Sheet-fed rotary machines use stereotype or electrotype plates, flexible plates made of photo polymers, rubber, zinc and Aluminum plates. Printing of continuous Labels on roll paper has become comfortable and easier on Rotary machines. For multi colour printing work, only Rotary machines are more reliable and give accurate register. With multi colour Printing units on the machines, more no of colors in one pass can be easily printed which is not possible on the Flat bed machines. Platen presses or  Flat bed are used for short run and smaller size  work where only relief printing plates can be used.

 

………..Additions to alphabet R to be continued under R/3

About The Author

Jayaraman

Retired Govt of India Official. My hobby is to write articles that range from Printing technologies to Spiritual.

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