There are various methods of printing or printing processes. In this unit, we shall take a look at the five most common types. These include the following:
(i) Lithography (ii) Offset (iii) Gravure
(iv) Screen process (otherwise known as silk-screen printing)
(v) Laser printing
Generally, printing may be done manually (hand-printing) or through the use of machines (machine-printing). In hand printing, when types are selected they are arranged the way they are to be printed and the appropriate type of ink is put on them. Thereafter, they are impressed on paper. This process is slow, tedious and cannot be used for commercial purposes. Most of the printing jobs in which this method is used are small scale productions. The method takes more time and human effort, and extra care is taken to avoid errors that could mar the work.
After the printing, the types can be rearranged in the preferred order for future use or taken to the galley.
Machine printing, on the other hand, is the more efficient, faster and cost-effective method of printing involving the use of machines. This method involves the preparation of plates. It is from the plates that the impressions are produced. The process requires much skill and it is generally more complex than hand printing.
Comparing hand printing with machine printing is like comparing manual farming as used on many Nigerian farms with mechanised farming. Manual farming is more labour-intensive and time consuming.
At the end of the day, the output is smaller, while mechanised farming is less labour intensive and faster, with higher output at the end of the day.
Many people have discovered that mechanised agriculture is better and more profitable, and if they can afford it, they switch from manual to mechanised agriculture. The same scenario applies in printing. As soon as people in the printing business have sufficient funds to acquire the required facilities, they transit from manual to mechanised printing because of the accruing benefits and advantages.
However, hand printing has not completely disappeared. Many small scale printers still utilise manual printing techniques for various reasons.
Some of the reasons often proffered for the resilience of manual printing in Nigeria include low funds, epileptic power supply, need to take advantage of cheap labour and the need to accommodate small scale productions, among others.
The five methods of printing discussed below involve machine printing, because generally machine printing is more popular and more advisable than hand printing. The difference among the five methods lies in the processes involved. This is why these methods are more often referred to as printing processes rather than methods of printing.
3.1.1 Lithography
This involves printing from a smooth surface of a metal plate which has been treated such that the ink used sticks to the design being printed.
The first lithographic press (which was then hand – operated) was used in 1798 by Alloys Senefelder. By 1869, R. Hoe and Co had developed a power-driven lithographic press.
The lithographic press operates a photomechanical process involving the transfer of images. Its speed is high and it is relatively cheap to set up. It is generally cost – effective and the quality of work produced is good.
However, the machine requires constant maintenance, and the lithographer needs proper training to be able to handle the machine. The types must be properly arranged before plates are made since it is very expensive, if not outrightly impossible, to consider effecting corrections on the plates.
3.1.2 Offset
This is an indirect process of printing as opposed to the direct (letterpress) method. It involves taking a photograph of the page to be printed and placing the negative, over a plate. The light – sensitive plate is exposed to some ray of light through spaces on the negative, thereby hardening the letters. The non-printing surface is washed away and the printed plate is soaked in water and later in ink. The inked letters are impressed on a rubber blanket which then prints on paper.
3.1.3 Gravure
This is a printing process in which images are transferred from ink-filled depressions in a surface to the printing paper. It is often used in the printing of photographs and artistic works because of its ability to reproduce excellently. It has a high degree of fidelity, and can thicken or
coarsen as the need may be. However, the cost of initial plates may be high, while the printing cylinders require a longer preparation time.
It must be noted, however, that it can produce up to 25,000 copies per hour, but the minimum number of runs is usually 5,500. Since it is usually used for photography and artistic work, it is also most commonly known as photogravure. It is also known as “intaglio”.
3.1.4 Screen Process (or Silk Screen Printing)
This involves the use of a stencil. The stencil itself is a light (thin) sheet (or layer) of cardboard (or metal) in which holes are cut in a shape such that a designed pattern (figure, letter, etc.) is produced when a brush, with pigment, is run over. Through an embedded mesh screen, ink is forced to the surface of whatever object on which printing is to be done.
The screen is usually silk, nylon, metal mesh or dracon. If the printing involves different colours, a separate stencil is produced for the different colours.
3.1.5 Electrostatic Printing
In this process, the web, without touching, is passed over devices that put an electric charge on the areas to be printed on the paper. It then passes through a chamber with ink dust floating in it. The dust is given an opposite electric charge so that it is attracted to the printing areas.
The web is then heated in a giant microwave oven to bake the dust onto the paper. If more than one colour is used, the web is passed through other chambers containing the appropriately coloured ink dust.
3.1.6 Laser Printing
This is a more advanced and more modern version of electrostatic printing. It is a process aided by a computer joined to the photocopier.
The photocopier itself is the most universal form of electrostatic printing. The computer translates digital instructions from DTP (Desktop Publishing) computers into graphical information. Instead of using a strong light to etch the graphical information onto the electrostatic drum (or rotary press), the information is etched more accurately by a laser beam driven by its own computer.
The laser itself, according to Oxford Advanced Learners’ Dictionary is a device that produces a narrow, intense and highly controlled beam.
Laser beam, over the years, has been deployed to solve many problems, including health problems, warfare, and several others. The utilisation of laser beams in printing is a highly welcome development because it has
greatly improved the quality of printing jobs and advanced the frontiers of printing technology.
Self Assessment Exercise 4.1 Write short notes on the following:
a. Lithography, b. Offset, c. Gravure,
d. Screen Process.
4.0 CONCLUSION
Printing technology has passed through various phases, giving rise to various methods or processes. Interestingly, new phases do not automatically wipe away the practices and methods associated with earlier phases. Therefore, the processes and methods of various phases thrive simultaneously. For example, although laser technology is now in use in printing, the earlier methods still exist side by side. Each printing organisation evaluates its needs Vis-a-vis the challenges of the jobs it has to execute and the resources available to it. Thereafter, it decides on which printing method or process to utilise. It is no surprise, therefore, that some printing organisations utilise a particular method for certain categories of jobs while using another process or method for other categories of jobs. This is allowed, provided the client that commissioned the job or the reader gets value and is satisfied.
5.0 SUMMARY
From the initial time-consuming and less efficient manual approach to printing called hand printing, printing has developed through various machine-aided processes. Each process has tried to improve on the preceding processes, but older processes or methods of printing have not been completely obliterated. The older methods are still in use because of the varying needs of printing organisations and their clients as well as the resources available to them.
6.0 TUTOR MARKED ASSIGNMENT (TMA)