As a graphic designer, understanding how printing works is important. You don’t need to be a print expert, but knowing the basic technologies and terminology can help you improve your skills if you want to create a successful project – from design conception to the final printed product.
Creating a fantastic design is only the first step. Knowing what happens after you send your files to the printer and how to choose the appropriate printing method for a job is just as important. The main distinction in printing technologies is between those that require a master (conventional printing) and those that do not require a printing plate, otherwise known as non-impact printing (NIP).
In this article, we’ll be focusing on conventional printing technologies. These methods use printing plates – or image carriers – to transfer ink to printing substrates such as paper, plastic, metal etc. We’ll break them up further by defining them by 3 main characteristics:
- Surface relief
- Differences in wetting (surface tension)
- Openings in the printing master
Let’s get started…
1. Surface relief
Letterpress means the printing elements of the printing plate are raised above the non-printing elements. The printing elements are coated with a layer of ink (directly or indirectly) followed by the transfer of ink to the substrate whereas the non- printing elements are recessed and remain ink free.
Letterpress is used with the following printing systems: book printing, flexographic printing and letterset. The technique is useful for printed products such as small-format jobs, business cards, labels, carriers and bags.
Book printing is the oldest letterpress printing technology, which uses a printing plate made of lead alloys or synthetic materials. Letterpress is suited for the reproduction of text and images, and the printed product is characterized by sharp edges.
In practice, letterpress also includes other forms such as wood engravings, photo-etched zinc “cuts” (plates) and linoleum blocks, which can be used alongside metal or wood type. Gutenberg’s discovery of individual, moveable type in the 15th century made it possible to reproduce type elements economically and quickly.
Moveable type refers to metal blocks that each only contained one character: letters, numbers, and punctuation. These blocks could then be rearranged to create any type of text.
Flexographic printing is a form of direct relief printing, characterized by the use of flexible printing plates. It was first introduced in the early 1900’s and can be used on absorbent and non – absorbent substrates in packaging, label and newspaper printing due to the soft plate and low viscosity ink.
Letterset printing is a form of indirect printing meaning the image of the plate is transferred to paper via an intermediate carrier (cylinder). It is referred to as dry offset printing and is mainly used on cardboard packaging.
Gravure printing, or intaglio, is the opposite of letterpress. The printing elements are recessed, below the surface of the plate, whilst the non-image areas are at a constant level.
The design is cut, scratched, or etched into the printing plate. The recesses are filled with ink and the raised (non-printing) portions of the plate or cylinder are wiped or scraped free of ink leaving the ink only in the recesses.
The ink is transferred from the cells to the printing substrate by high printing pressure and adhesive forces between the ink and substrate. The typical features of gravure printing are serrated edges on the letters and lines.
Gravure printing is often used for high-volume printing of packaging, wallpaper, and gift wrap using fast-drying inks, and various printing technologies based on the principles of gravure printing are used to produce speciality printed items such as stamps and bank notes.
2. Differences in wetting (surface tensions)
This means that the printing and non- printing areas are on the same level – planographic printing. Lithography and offset lithography are planographic processes that utilize the property that water will not mix with oil.
The printing areas are oleophilic or ink accepting, whereas the non-printing areas are oleophobic meaning they repel ink.
Lithography was invented by Alois Senefelder in 1796. The image that needed to be printed was drawn on stone with a special ink. The stone needed to be dampened before applying ink, after which non-image areas of the stone surface did not take on ink. Stone lithography is only used for artistic printed products, due to very short print runs.
Offset printing is the major lithographic technology, which falls under the category of indirect printing meaning ink is firs transferred from the printing plate onto a flexible intermediate carrier or blanket and then onto the substrate. It’s called offset because the image does not go directly to the paper from the plates.
Two types of systems are used to create an ink repellent effect on the printing plate:
Conventional offset printing
In conventional offset printing, the printing plate water is dampened with a dampening solution made up of water and additives, before applying ink. The non-image areas are hydrophilic, meaning they are water receptive and the image areas are oleophilic, or ink receptive.
In other words, the ink adheres to the image area, the water to the non-image area, as the film of the dampening solution prevents the transfer of ink.
Waterless offset printing
In waterless offset printing the printing plate is not dampened with a dampening solution, the surface is ink repellent as the plate’s non-image areas consist of a layer of silicon that repels ink. Areas that are ink receptive are exposed by an interruption of the silicone layer.
An image that is printed using offset is separated into basic colors. A plate is prepared for each color used, or four plates in the case of 4-color (CMYK) process printing. Each roller has its own specified ink and as they pass over the page, transfer ink and build layers of colors, resulting in a full color page.
Offset printing can also add specialized colors called Pantones or PMS colors if specific colors are needed. Offset printing is generally used for larger print jobs of 1,000 pieces and up.
3. Openings in the printing master
The printing elements are the areas where ink is forced through the printing master – in this case a screen. The non-image areas are made impermeable to ink by a blocking stencil.
The screen is generally made of fine fabric such as silk, plastic or metal fibers and threads which is then stretched over a wooden or aluminum frame.
It is placed on top of the substrate (fabric, paper etc.) that is held in place. Ink is placed on top of the screen, and a squeegee (rubber blade) is used to push the ink evenly into the screen openings and onto the substrate. The ink penetrates the open spaces in the screen onto the substrate. The frame is then lifted away and then the squeegee is pushed back across the screen.
As a graphic designer you will come across a client in need of a design for print. Knowing the printing process, the costs, and limitations can help you as a designer to not only create amazing designs, but also answer any questions and guide your client to give them the best possible solutions that are affordable and effective.