print processes
This section helps the designer to understand the variety of print processes available in the world of commercial print. It looks at which is most appropriate for certain printing jobs and applications, the characteristics of the processes and the disadvantages of each.
screen printing This print process is used for the production of t-shirt designs and designed prints/ posters. Screen printing is most likely used for short print runs but modern high speed technology allows a higher volume of production to happen. It is created using a silk screen which achieves an image on a substrate by forcing ink through a screen, which contains the design wanted, using a squeegee.
Each colour used needs to be separated and a individual screen made which makes the printing a lengthy process but is a flexible process that can be used to print on any substrate. The design for each screen can either be applied straight by hand or through digital image production and exposure of this onto the screen. When looking for a suitable printer for a long run of screen printing check out their previous work to make the highest quality and most appropriate choice.
pad This print process can transfer a 2Dimensional image onto a 3Dimensional object and is used for printing on automotive or electrical objects. It is created using a process similar to gravure an involves the image being transferred and morphed from a metal type plate through a silicone pad onto the substrate. The properties of the silicone pad allow it to pick up the image from a flat plane and transfer it to a variety of surfaces with different shapes, sizes and textures. Their are two main types of pads: round pads, long narrow pads called bar pads and pads made in other shapes called loaf pads.
It is possible to create custom pads from which to print from but this increases the cost for printing. The inks used in PAD printing are solvent based and require mixing with additives before use because other wise they dry too quickly before application is completed. Main disadvantage is cost because the application is onto such a unique shape and to make costs affordable a very high print run would be needed, which is why it is used on packaging because of its high demand.
offset lithography This print process is used for the majority of commercial and modern print projects. A reduction of short run jobs has occurred though with this process as they can be achieved digitally on personal or trade machines, which is cheaper and becoming better for these short runs. It is a process in which the ink sits on the surface of the substrate. The main principle of how this print process works is that ink and water never mix during the process. The image is transferred from the printing plate to a rubber blanket and then to the paper.
When the printing plate is exposed an ink receptive coating is activated at the image area. Then the plate is dampened by the water rollers, which coat the non image areas, and then by the ink rollers, which coat the image area. As the cylinders rotate the image is transferred to the blanket and paper passes through this where the image is transferred to the paper. To achieve a high quality offset look for a printer with a good reputation and one who uses aluminium plates but this will increase printing costs, dramatically in some cases.
letterpress This print process was introduced with the Guttenberg press and was one of the first forms of commercial printing. The finished quality of the printed piece is indented into the substrate as it is achieved through using a raised surface printing plate. This printing plate is often made up of type but photo engraved plates can be used. Letterpress is a form of relief printing as the ink is transferred onto this printing plate straight onto the paper.
Thicker and softer papers will create a deeper impression and carry the design better. A disadvantage of using this printing process is that the impression from the raised surface varies every time it is pressed into a substrate and gives a different visual to the characters. Avoid using metallic inks as when pressed these can look dull on most papers, so look at using foil blocking found in the finishes section of the pack.
flexography This print process is usually used on packaging, such as can labels. It is a form of relief printing that uses a flexible relief plate which can be used on nearly any type of substrate. Flexography is created using a positive mirrored master of the design on a rubber or polymer plate, the image areas are raised above the other areas.
The ink is transferred from the ink roll onto another roll that is textured and holds the ink which then transfers this onto the printing plate in an even coat. Imperfections on the print can occur if the amount of ink is too much or uneven on the plate and can cause the finished printed product to look smudged.
gravure This print process is used for huge print runs for publications such as newspapers, magazines or direct mail catalogs. It is a intaglio printing process which the image is created into the plate surface and the sunken areas of the design holds the ink. It involves engraving the design onto a cylinder plate because similar to offset printing it uses a rotary printing press.
The ink is applied directly to the cylinder plate and then transferred straight to the substrate chosen in a similar way to which the squeegee works in screen printing. A disadvantage of this process is that the substrate must be completely dry before applying the next colour of the design, this could make the process lengthy or more costly with the introduction of a drying process.