Trucos de diseño para diseñar como locos

Printing systems: offset printing

All those graphic designers whose work is not oriented only to digital media playback, you’ll have to deal, at some point in your professional lives, with different printers and printing systemsprevailing.

The most widely used printing method, given that I mean in this publication to reproduce a digital document in a physical medium, due to its ability to produce a large number of copies in short time, is the system offset.

Offset printing inherits techniques invented in lithographic printing

The term offset, or indirect, comes from the technique used to apply ink to the physical medium, ink is not transferred directly from the plate to paper. In this publication you should assume that this support it’s paper but it could be as well fabric or other support. This type of printing, more commonly known as rotary printing press, use a rubber roller as a carrier to transfer the ink from the engraved sheet with the document image to the final stand. The lower image shows the schematic design of the offset process, for a two-sided printing.

It is important to note that the block is multiplied by each of the inks used, ie, have a mechanical assembly, mounted in sequence one after anotherfor each color used for printing.

The block is formed by drippers, water rollers, ink rollers, plate roller, rubber roller and paper. The drippers determine the amount of ink to be applied to ink roller, in this way it is manually controlled the amount of each color being applied to the sheet. The ink roller and the water one cover the anodized aluminum plate where the water-repellent areas retain the grease ink while the hydrophilic maintain the aqueous solution. The amount of ink that drippers transfer to the ink rollers is controlled by the driver, which adjusts the emitters until the color percentages are optimal for each of the plates.

At present the photosensitive anodized aluminum plate is first treated with a laser, which can be also thermal or light violet, in a process known as CTP, or computer to plate, which causes areas recorded with the image and text to become hydrophobic, while the rest of the plate remains hydrophilic. Once recorded the iron does not acquire any type of relief, ie, remains completely flat, unlike other systems such as rotary printing flexography or gravure printing. In offset printing it’s only altered the properties of the iron. Each plate is tested before it is mounted on the roller. It is also possible to use polyester plates instead of anodized aluminum, but usually printers prefer the latter because of their higher quality and durability.

Computer to plate has virtually eliminated all the problems arising from the use of photoliths, or films

Iron roll transfers ink to the rubber roller and this in turn makes the same on the paper. In a one side offset printer on the other side of the paper is a counterpressure roller, also known as pressure roller or printing roller, which facilitates the ink to be properly transferred to the paper.The two-sided offset printing instead of counterpressure roller have another printing unit, therefore the rubber rollers of both blocks also facilitate the application of the ink of the printing block opposite.

Once printed the ink on paper should be dried, either by means of absorption of ink, either by passing the paper through a drying unit. Which determines what kind of paper you can use and also the type of printing.

Advantages of offset printing:

  • Offset printing is currently the most economical printing system, when dealing with very large print runs in a short space of time with a good quality level. In digital printing, which discuss in a future publication, you can get a better picture quality, but can not compete over print volume per hour, thanks in large measure also to the implementation of the CTP, nor for costs.
  • The use of rubber roll as intermediary in the transfer, extends the life of the iron to about two million copies, as long as we talk anodized aluminum plates, in an optimal state of storage.
  • You get a great image quality and consistency.
  • From the economic point of view it is more advantageous the more copies are printed.



About mimoriarty

Diseñador gráfico multidisciplinar; me gustaría trabajar y compartir experiencias con diseñadores de todo el mundo

One comment on “Printing systems: offset printing

  1. Pingback: Printing systems: gravure « MiMoriarty's Blog

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This entry was posted on April 20, 2012 by in Conocimientos, multilanguaje and tagged , .

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