Types of Printing Processes Explained

The types of printing processes today are many. However here are explained the main processes used today:

• Gravure printing
• Offset Printing - offset web and sheetfed lithography
• Flexography
• Screen printing
• Digital printing
• Letterpress

Here is each type of process explained:

1. Gravure Printing

How does it work?

The process of gravure printing, or rotogravure printing, utilizes an engraved cylinder.  The engraving is accomplished by means of an acid reaction to the metal.  

During the printing process, the following takes place as shown in the illustration below:

1. The indentations in the cylinder are filled by dipping the cylinder in an ink fountain.  
2. A doctor blade then scrapes off the excess ink on the cylinder, leaving the ink inside the engraved depressions, also known as an image carrier.  
3. The cylinder is then squeezed onto the substrate, usually paper. The impression cylinder ensures that the substrate pushes into the image carrier to absorb the ink.

Gravure printing.

What is it used for?

Gravure printing is still widely used today. It produces very consistent quality, is difficult to duplicate and one of the most expensive. Therefore it is often used to print money. This form of printing is utilized when a customer requires very detailed or fine images on a high quantity job.  The cylinders do not wear out for a long time and can be run at very high speed.

Gravure printing is also used for other big ticket items like stock certificates, passports and stamps.

2. Offset Printing

How does it work?

With offset printing, the process involves more chemistry.  Here are the steps as illustrated in the picture below:

1. A coating on water is applied to an aluminum plate cylinder. An aluminum plate is mounted to it. Aluminum is hydrophyllic (loves water) and so the water will stick to it.  However image areas are burned (usually by a laser) onto the plate so that not all areas will retain water.  
2. Then an ink roller rolls over the printing plate.  Because the ink is oil based, it will not stick to the watered areas of the plate. However areas that do not have water will accept the ink. 
3. The ink then transfers the image to the offset cylinder which has a rubber blanket on it.  The rubber blanket will not accept most of the water, but the ink will stick to it.  
4. Then the offset cylinder will roll and transfer that image to the paper.

Offset printing.

What is it used for?

Offset printing is generally used for print runs over 1000 copies.  It is ideal for printing that doesn't require any changes, but can have identical information from copy to copy.  It is by far the most common form of printing today and is used for newspapers, magazines, business cards, flyers etc.

3. Flexography

How does it work?  

This process of printing has it's distinction in the materials used to transfer the ink.  Here are the steps as illustrated below.

1. A fountain cylinder rotates into an ink tray and draws ink up to the anilox cylinder.  
2. A doctor blade will scrape off excess as per the thickness required by the press operator.
3. The ink is then transferred to a plate cylinder which is usually made of rubber.  
4. The ink is then transferred to a substrate, usually cardboard or a plastic. The transfer is ensured by means of an impression cylinder which will squeeze the substrate onto the plate cylinder.

Flexography explained.

What is it used for?

Because the process involves a rubber plate, the substrate can be almost anything.  For example, this process can print on things like metal and plastic in addition to paper. The quality is not as high as other processes, but can be much more versatile when it comes to printing on various substrates.

4. Digital Printing

How does it work?

When anything printed originates from a digital based media onto a print media, that's digital printing.  People utilize this almost every day when they use their desktop computer.  Nowadays however, much larger format printers that utilize ink-jet and laser technology are used.

What is it used for?

The process is being controlled by a computer which allows for great flexibility from copy to copy. Since it can be so easily customized, this process is suitable for those requiring more personalized products.  The downside is that it is more expensive when printing longer runs.  Therefore this type of printing process is utilized mostly for shorter runs or jobs that required custom printing from sheet to sheet.

5. Screen Printing

How does it work?

While screen printing is generally a craft, it is used in high production commercial environments. 

This process of screen printing, or silkscreen printing has it's distinction in the process used to transfer the ink.  Here are the steps as illustrated below.

1. A substrate, whether a piece of paper or a t-shirt is laid down flat.
2. An image or stencil is laid down which defines the image that will be transferred.
3. A screen or mesh is laid overtop.
4. Ink is laid on the mesh and a squeegee is used to flood the screen with ink.
5. The screen momentarily pushes down onto the stencil and onto the substrate and the printed image is produced.

Screen printing.

What is it used for?

The most common application of screen printing is on t-shirts.  However it is used in other applications such as on metal, ceramic, wood and circuit boards. The advantages of screen printing are that what it prints is long-lasting and produces sharp images.

6. Letterpress Printing

How does it work?

Letterpress is one of the oldest forms of printing.  In it's very simplest form, it uses raised type to press ink onto paper.  Perhaps one of the oldest form of letterpress was carried out by Johannes Gutenberg.  The process works like this as per the diagram below:

1. Ink is applied to a raised surface.  This can be performed by hand or in a rotary press automatically.
2. Paper or another substrate is pressed down onto the raised surface.
3. The paper is removed and dried.

What is it used for?

Today, almost nothing.  Modern printing methods have replaced this older form of printing, and so has remained as a craft only.

Conclusion

There are many other types of printing processes that could be explained here, many of which are antiquated. They include the following:

Woodblock printing

Etching

Mezzotint

Chromolithography

Hot metal typesetting

Dot matrix printing

Inkjet printing

Laser printing

Thermal printing