Showing posts with label Print Media. Show all posts
Showing posts with label Print Media. Show all posts

Tuesday, 28 March 2017

Printing Process - Relief Print, Platen Press, Flatbed, Cylinder Rotary, Offset, Screen Printing

INTRODUCTION

The art and science of making a large number of duplicate reproductions of an original copy is termed as printing. It may also be defined as the art of preserving all other arts. Printing is the medium tor printed communication.
We start our days with newspapers, then we buy milk packets, every day we come across many books, currency notes and so many printed items. So, we can say that printing is a part and parcel of our life. Three major printing processes basically are used to print printed materials. These are Relief Printing Process, Planographic Printing Process, and Screen-Printing Process. In addition, there are many minor or highly specialized printing processes. These include Die Stamping, Thermo Printing, etc.
We shall discuss only the major printing processes in detail. In order to understand these processes, we must understand the following two terms clearly:
Image Area: It is that area on the printing surface that receives ink. For example: raised portions of a rubber stamp.
Non-Image Area: It is that area on the printing surface, which does not receive ink. For example: depressed portions of a rubber stamp.

PRESENTATION OF CONTENT

There are three major printing processes. In this article we shall discuss about these three processes in detail. The content of the lesson shall be presented as follows:
Relief Printing Press
Planographic Printing Process and
Screen-Printing Process

RELIEF PRINTING PROCESS

It is the oldest printing process and came into being with the invention of movable types in the fifteenth century by Johan Gutenberg. The matter, which is to be printed is a mirror image (reverse) or is backward reading (right to left).
The image to be printed is raised and the non-image area is depressed.
The basic principle behind this process is that there is a physical separation between the image areas and the non-image areas. Image areas are raised, and catch ink to produce impression on paper while non-image areas are lowered and do not catch ink.

STEPS INVOLVED IN RELIEF PRINTING

First of all, relief printing plates are prepared i.e. the master is prepared with a combination of metal or wooden types are assembled together. This is known as typesetting or composing. Also used are illustrations prepared by photomechanical methods called blocks. All the composed matter are combined and locked together in a frame. In this the image areas are raised while non-image areas are depressed on the master/printing surface.
Ink rollers on the master apply ink, image areas receive ink and non-image areas do not.
The printing surface or master is then pressed against the substrate to obtain the impression. Ink is transferred from image areas on the substrate. The non-image areas, which are depressed, don’t come in contact with the inking rollers or the paper and so give no impression. Examples for this process are:
  • Letterpress
  • Flexography

LETTER PRESS PRINTING PROCESS

Letterpress Printing Process- Platen Press Flatbed Cylinder Rotary
Platen Press Flatbed Cylinder Rotary
Printing originated with the letterpress. -The nomenclature "letterpress" brings to mind the images of raised letters pressing against a surface, on which their shape of ink is transferred. Actually letterpress printing is not just meant for printing only letters but also borders, rules, illustrations, etc. Letterpress is a relief printing process. On the basis of printing surface or master and the surface on which paper is placed, the letterpress printing machines can be classified in three main groups. These are:
  1. Platen Press
  2. Flatbed Cylinder
  3. Rotary

PLATEN PRESS:

The surface on which the paper (to‘ be printed) is placed for printing is flat and is called platen, and the forms or master or printing surface is also placed on a flat surface known as the flatbed. Since the paper is put on the platen (flat surface), therefore this group of machines is also known as platen press or platen machine or treadle machine.

Process Platen Press

First of all a forms or printing surface is prepared for printing each letter and image is cast separately using wood (engraving/carving) or alloys made up of tin, antimony, lead etc. Then these letters and images are arranged together and locked in a frame firmly. This is technically known as the forms or chase. It acts as the printing surface.
The master frame is fixed in a plane surface and inking is done by inking rollers which pick up the ink from a revolving ink disc fixed above the ‘machine and then pass it across the forme.
Paper is fed by inserting in between the two flat surfaces. The plane surface on which paper is placed for printing is known as platen.
Bringing the flat surfaces in contact with each other does printing. The whole composed matter comes under the pressure at the same time where a controlled pressure is required to transfer the ink from the matter to the paper clearly and correctly.

Types of Jobs Suitable for Platen Machines:
These types of machines are best suited for printing letter heads, cards, bill forms, leaflets, pamphlets, inserts, visiting cards, office files, serial numbering, etc. Platen presses can also do embossing, die cutting, creasing and foil stamping, numbering, etc. which other printing presses just cannot.

Advantages of Platen Press

  • Flat to flat type of machines are available in different sizes to suit different jobs. The printing work can be stopped in between and any correction can be carried out.
  • Small works in less numbers can be printed at very cheap rates.

Disadvantages of Platen Press

  • The speed of printing of flat-to-flat type of machines is very slow. The average speed is 1200 impressions per hour.
  • Since the paper used for printing by these machines is in the form of sheets, a lot of time is wasted in changing the sheets of papers repeatedly. So printing becomes a very time consuming process.
  • In flat-to-flat type of machines printing is possible only in one colour during one impression.

FLAT BED CYLINDER PRESS:

This group of letterpress machines is also known as flat bed cylinder presses. The surface of the printing surface remains flat while the surface carrying paper is cylindrical. Earlier these presses were operated by steam power, but now days they are operated by electrical power.

Process of Flat Bed Cylinder Press:

  • The average speed is 1200 impressions per hour.
  • At first a matter is prepared in the same way as in the platen press and is placed on a plane surface called flat bed.
  • This bed travels to and fro from one end to the other end of the machine. Inking is done by the ink rollers, which are rolled over the bed.
  • The impression cylinder is a part of these machines, which is used to grip the paper and to apply the pressure. It revolves about its own axis.
  • Due to the to and fro motion of the flat bed and the pressure applied by revolving impression cylinder, the image areas are printed on the substrates.
Examples of Fiat Bed Cylinder Press
  • Stop cylinder machines.
  • Swing cylinder machines
  • Single-revolution-cylinder machine
  • Two-revolution-cylinder machine
Types of Jobs Suitable for Flat Bed Cylinder Machines:
  • These machines are efficient enough to print considerably longer run jobs i.e. in larger numbers and for much bigger paper sizes.

Advantages of Flat Bed Cylinder Press

  • Flat to cylinder type of machines are cheaper and flexible in printing.
  • Since there is a revolving impression cylinder and is power driven the printing speed quite high. The average speed of these machines is 4000 impressions per hour.