What is rotary printing?

Ejemplo de impresión rotativa.

A rotary printing machine is a printing machine in which the images to be printed are curved around a cylinder.

Printing can be done on various substrates, such as paper, cardboard and plastic just like offset printing.

Substrates can be fed in sheets or unwound in a continuous roll through the press to be printed and modified if necessary (e.g. die-cut, varnished in overprint, embossed).

Rotary printing presses that use continuous rolls are sometimes referred to as web presses.

In its simplest form, a rotary press consists of two cylinders rotating in opposite directions: the plate cylinder has curved printing plates attached to its surface and the impression cylinder works to press the paper against the inked plates as the paper passes between the cylinders.

Note: Currently many of the parts on rotary machinery are made with a 3D metal printing technique that can make metal parts.

This is the opposite of silk-screen printing because in this case the plates are fixed to the surface and it is all automatic. In the case of textile printing screen printing or sublimation the process uses plates, but it is very manual.

How does it work?

In ancient times, when there was no rotary machinery, the typographic technique was used, embossed plates were made with the text to be printed on the communiqués for society.

A simple two-colour rotary printing press uses two successive plate cylinders, each with a different typographic shape and each with its own inking system. The same side of the same sheet of paper receives two successive impressions of two different colours as it passes through the press.

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Printing on both sides of a sheet of paper and printing in three, four or even five colours can be achieved on a rotary printing press using different combinations and successions of printing plates and cylinders.

Very large, highly automated rotary presses can achieve extremely high production rates.

These machines have cylinders with a circumference large enough to accommodate two or more plates, so that with each revolution the cylinder prints two or more copies of the same page.

Similar arrangements allow a cylinder to print eight copies of the same page in a single revolution.

Quality control is very important in colour printing, as the different colour prints on a page must be in perfect register with each other.

This control is achieved on the presses by means of photoelectric cells that selectively pick up the guide marks printed on each colour as they pass and react to any irregularities in the distance between these guide marks.

Any errors are automatically corrected by modifying the speed of a group of cylinders or the pressure of the rollers that control the paper tension between one group of cylinders and the next.

Rotary printing machine types

Rotary printing machine

Today, there are three main types of presses: offset (including web offset), gravure and flexo (short for flexography). Although all three types use cylinders to print, they vary in their method.

In offset lithography, the image is chemically applied to a plate, usually by exposing photosensitive layers on the plate material.

Lithography relies on the fact that water and oil do not mix, which allows the planographic process to work.

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In the context of a printing plate, a wettable surface (the non-image area) can also be called hydrophilic and a non-wettable surface (the image area) hydrophobic.

hotogravure is a process in which small cells or holes are etched into a copper cylinder, which can be filled with ink.

All the colours are etched at different angles, so that when printing each colour is placed in the right position to give the appropriate image.

Flexography is a relief system in which a relief image is created on a typically polymeric plate.

There are many types of printing that are completely opposite in technique, process and result, such as holographic printing or lenticular. Rotary printing sticks to volume, speed and basic colour or black and white printing.

For other materials such as wood it is better to use other engraving techniques such as xilography. And for special finishes with hot stamping or selective varnish, other types of machinery are also used, and for other types of advertising needs.

What is rotary printing used for?

What is rotary printing used for?

Newspaper web press printing.
Newspaper web press printing

Press printing is especially used for large print runs of the same product, whether it is a newspaper, brochures, catalogues and similar items and of course all copies are the same.

Thanks to the printing speed and quality, large print runs of the same product can be obtained in a short period of time.

If any details need to be personalised one by one, this is normally done by each kiosk or point of sale that receives the magazine or newspaper to sell. With print pad printing you can easily stamp like a stamp on the finished product.

+  Laser Printing

Many companies choose to carry out their own pad printing operations in-house, as the installation costs are quite low. In addition, the pad printing equipment does not take up much space and the process is fairly easy to learn.

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