Litho printing, short for lithography printing, is a traditional and widely used printing process in the commercial printing industry. It is known for its ability to produce high-quality, consistent, and sharp images on various materials, making it suitable for a wide range of applications, including brochures, magazines, packaging, posters, and more. Litho printing relies on the principles of oil and water repulsion to create printed images, and it involves several key steps:
1. Plate Preparation:
- Litho printing uses a flat, smooth printing plate typically made of aluminium or a similar material. The plate is coated with a photosensitive emulsion.
- A separate film negative or digital file is created for each colour in the design. These negatives or files contain the image to be printed and are used to create the printing plates.
2. Plate Exposure:
- The prepared plates are exposed to UV light through the film negatives or digital files. The areas that are exposed to light become more receptive to ink, while the unexposed areas remain water-repellent.
3. Plate Development:
- After exposure, the plates go through a chemical development process to remove the unexposed emulsion, leaving behind the image areas that will accept ink.
4. Ink and Water Management:
- Lithography is based on the principle that oil and water do not mix. The ink used in litho printing is oil-based, and the non-image areas on the plate attract water.
- A roller system is used to apply ink to the image areas on the plate while keeping the non-image areas wet with a water-based solution. This ensures that the ink adheres only to the image areas.
5. Printing:
- The plate is mounted on a printing press, which consists of multiple rollers and cylinders. As the plate rotates, it transfers the ink to a rubber blanket cylinder.
- The rubber blanket cylinder then transfers the ink to the paper or other printing material that passes between it and the impression cylinder. This process is called offset printing because the image is offset from the plate to the rubber blanket and finally to the paper.
6. Colour Registration:
- For full-colour printing, multiple printing plates are used, one for each colour (usually cyan, magenta, yellow, and black, or CMYK). These plates must be precisely aligned to ensure accurate colour reproduction and sharpness. This is called colour registration.
7. Drying and Finishing:
- After the ink is applied to the paper, it needs to be dried before further handling. This can be achieved through various drying methods, such as air drying or the use of drying ovens.
- Additional finishing processes, such as cutting, folding, and binding, may follow to complete the printed product.
Litho printing offers several advantages, including high-quality results, excellent colour accuracy, and the ability to print on a wide range of materials, from paper and cardboard to plastics and metal. However, it is a more complex and time-consuming process compared to digital printing, which may be more suitable for short print runs or when variable data is required. Litho printing is often used for large-scale print jobs where quality and consistency are of utmost importance.
