Same level of printing and non-printing elements is the key feature of Lithography. In this, the non-printing elements are ink-repellent and don’t let ink stick to them while the printing elements are ink-accepting, all thanks to inter-facial surface phenomena.
Lithographic printing has following subdivisions:
- Stone Lithography (prints using a stone and is a straight technique)
- Collotype (another direct method)
- Offset printing (Indirect process for printing), and
- Di-litho (direct process along with printing plate)
Alois Senefelder incepted Lithography in 1796. With the usage of a special ink, the image to be printed was drawn on the stone, and then the stone was moistened. By doing this the non-image zones of the stone surface do not consume ink.
Now, let’s talk about Collotype Lithography. A glass base is exposed to a light sensitive level of gelatin above a negative and thereafter it is developed. Those parts are generated which have diverse swelling characteristics with respect to water. The dampened printing plate is then produced with characteristics of differentiated color shade absorption. Similar to Stone this lithography technique is best suitable for artistic printed products and services.
The greatest Lithographic technology is offset printing. The process is rather indirect in this case as the ink is first transferred to an adaptable intermediate carrier from the printing plate then to a blanket and after all this; onto the substrate.
There are two common technologies that are used to get ink repellent surfaces on the printing plate.
- Conventional Offset printing technology
The printing plate is initially dampened using dampening solution; the solution is put on the printing plate gently by the rollers in a very thin film. The non-image zones are completely hydrophilic, and that means, water receptive. Additionally the ink accepting zones are oleophilic, and they are completely unreceptive to water. The dampening film serves as the transport of ink. Since, offset lithography is popular and the most widespread technology, the dampening solution and result of repellent among the ink are often linked to ‘offset printing’. Inking and dampening units are required for ‘offset printing’ because of this cause.
- Waterless offset printing technology
An appropriate layer of silicone makes the printing surface ink-repellent mainly. A nearly 2 microns thick silicon layer is exposed for deliberate interruption in the ink-receptive base region. The while process is known as ‘Waterless offset’
Different printing plates and special inks need to be used for each technique.
- Di- Litho technology
In Di-Litho offset printing, the printing plates print directly on the substrate which is uniquely created for newspaper printing. The conventional letterpress rotary printing presses can be used in this technology, this serves as a major advantage. The modified printing units have dampening units. The printing is done using conventional plates but a special coating is applied on them, this is because of the very high tension of the direct contact with paper and the high stability it provides when running full print in newspaper printing. This technology was short-lived. Soon, this printing was replaced by ‘web-offset printing’ which was developed due to the new investment made in the Printing industry. Web offset prints on the substrate using blanket cylinders.
Advantages of Lithographic Printing
- Consistent high quality of images
- Quicker and easier production of printing plates.
- Longer life of printing plates as they now come in contact with printing blanket only which is softer and less abrasive than the paper
- Inexpensive production with high quality images in large numbers
Disadvantages of Lithographic Printing
- Expensive for small number of prints
- The image quality is not good enough as rotogravure or photogravure printing, it is good for commercial purpose only.