A BRIEF HISTORY OF PRINTING

A very simple form of printing was practiced in China and Korea around 175AD. Reverse images in wood, and later bronze were made. These were inked, then paper was placed over the image and gently rubbed with a bamboo stick.
 
 The big breakthrough came around 1440 by Johann Guttenberg of Mainz, Germany. Guttenberg devised a method of casting separate type pieces in an alloy of mainly lead. These could be hand set into pages of text for printing. This method of setting type was to last for around 500 years!

His next task was to invent a printing press. Guttenberg got his idea from observing a wooden wine press. This method of printing is called “Letterpress”. The typeface was inked, the paper was then put over the type and the handle of the press pulled to make the impression.

There were no major improvements until around 1800 when Earl Stanhope made the first iron press. The method of printing was the same as the earlier wooden presses, but a larger sheet could be printed due to the rigidity of the iron.

Various iron presses were made, probably the most well known being the Columbian invented by George Clymer. Clymer took out a patent on his press lasting fourteen years. After this time various manufacturers made similar presses. All of these printing presses were hand inked and therefore relatively slow.

Things speeded up with the next generation of presses - the “platen”. Earlier platens were treadled and hand fed, but achieved a much greater speed than the earlier hand presses. One reason for this was the rollers which automatically applied the ink. Later platens such as the Thompson Auto and the more famous Heidelberg had auto feeders and drive motors. The Heidelberg achieving a top speed of 5,500 impressions per hour. Nowadays the design and typesetting is all originated on computers but most printing is done Offset Litho from single sheet fed presses, printing from one to ten colours, or Web Offset colour presses (reel fed). Digital printing is also a growing market for colour printing for smaller runs. Hot Metal press still retains a small letterpress department for the occasional work needing a visible impression.

INDUSTRY STANDARD PRINT FORMATS

Dry Lithography

Identical to offset lithography but without the use of water, the non-printing areas of a special plate being silicon and non-receptive to the special inks that are used.

Flexography

Printing from a relief image with a rubber or plastic plate using liquid ink, either solvent or water based, plus pigment dyes, and is used mainly for packaging products.

Gravure
(Photogravure)
Printing from an intaglio copper plate or cylinder (Rotagravure) where the image is formed by the same size small squares, but of varying depth, the deeper cells producing the greater print density, or as more common today by using an invert halftone when the print density range is produced by both the depth and size of dots. The ink is of low viscosity, mainly solvent with pigment, dyes and binder. For good quality printing it requires a smooth paper.

Inkjet
on-impact printing process where the image is formed by a continuous stream of ink droplets of the same size and frequency. The position of the dot on the substrate is determined by an electrostatic charge. The unwanted droplets are diverted to a waste tray.

Laser
Describes the process where digital information from computer is used to generate pulses of light to form images on a light sensitive drum. Thereafter the actual non-impact printing process is xerographic.

Letterpress
Printing from a relief printing image of metal, rubber or plastic with a viscous ink direct to the paper.

Letterset
Uses a shallow-depth relief letterpress printing plate which transfers the printing image first to an offset blanket then to the paper.

LIithography
Printing from a planographic metal plate, the printing and on-printing areas being on the same plane, with the non-printing areas only accepting water, and the printing areas only accepting a greasy ink. When the inked image is directly transferred to the paper it is known as “direct lithography”, but when, as in most cases, the ink is first transferred to a rubber offset blanket and then to the paper, permitting good quality printing on the less smooth papers, it is termed “offset lithography”.

Non-Impact Printing

A term used to describe modern printing processes such as Laser and Ink Jet printing. These processes are described as non-impact as there is no direct physical contact between the printing mechanism and the paper.

Screen
The printing image is produced through a mesh made by a cut or photographic stencil, the ink being forced through the mesh by a squeegee. The ink film thickness of the printed image is significantly greater than that produced by other printing processes. Can print on a wide range of material.

Thermal
An impact printing process where the image is formed by an electrically heated printing head contacting a special paper, coated or surface treated, containing a concealed colour dye and an activator which becomes coloured when touched by a heated element, forming a letter or number. Used for recording information on charts and supermarket instant weight and price labels.

Thermography
A method of imitating the more expensive die stamping, as used for stationery. The printing is as normal for letterpress or lithography, but the wet printed image is dusted with coloured resin and immediately fused by heat, producing a similar relief image to die stamping but without the embossing on the reverse sides of the sheet.

Xerography

Non-impact printing using an electrostatic charge to produce a printing image on a drum which then attracts a resinous powder and is transferred to the paper and fused to give the finished print. Now able to produce colour printing.

TYPES OF PRINTING

Digital - very cost effective for short run printing, it works directly from electronic data and infuses on the paper. The quality is not quite on a par with lithography and you cannot use spot Pantones® or metallic inks.

Litho - by far the most popular print process, a metal plate is treated so that the image area attracts the oil-based inks, while the wet non-image areas resist them. The process is more expensive than digital though and only starts to pay for itself on larger runs.

Screen - is historically the oldest form of printing. Ink is applied to a porous silk screen and passes through a stencil or template to leave an impression. Normally used for banners, POS material and textile printing.

Thernal - is the process of creating an image using a heated print head. The print does not smear and is water resistant. Normally used for sell by dates on packaging, eggs and also plastic mailing envelopes for personalisation.

Thermal Paper - Thermal papers are high technology products. The base paper is first pre-coated and then treated with a special emulsion containing heat-sensitive modifiers, co-reactants, pigments and colour formers. The heat from a thermal head (eg in a fax machine) melts the modifier, which in turn dissolves the co-reactant which allows the colour formers and pigments to mix, producing a high-contrast image on the paper.



Web - a method of printing which uses a continuous roll of paper. They are very fast presses and are only suitable for large print runs. Used for long run high quality work which is not suitable for gravure and also for continuous forms for the IT industry.

Gravure Printing - Process in which recesses on a printing cylinder are filled with ink and the surplus removed by a blade. The paper contacts the cylinder and ' lifts' the ink from the recesses before depositing it on the paper. Generally used for long-run printing such as magazines and catalogues.

Inkjet Printing - A printer that sprays drops of ink onto the substrate to form an image this is now extensively used for large format printing due to the quality of print and flexibility to print on different materials. MICR - Magnetic Ink Character Recognition Paper - usually a high quality bond paper with good surface characteristics and dimensional stability for printing with magnetic inks for computer sorting. Used mainly by the banking industry to facilitate the processing of cheques and also the examining bodies for multiple choice papers.