Introduction to popular printing processes
It is important to understand how printing works. You don't need to be a printing expert, but knowing basic techniques and terminology can help you sharpen your skills if you want to create a successful project—from design concept to final print product. Of course, if you have any questions related to the printing industry, you can also contact us, and we will answer you for free.
Creating a fantastic design is only the first step. It is equally important to understand what happens to the file once it is sent to the print shop and how to choose the right printing method for the job. The main difference between printing technologies is between those that require a master (traditional printing) and those that do not require a printing plate, also known as non-imprinting (NIP). In this article, we will focus on traditional printing techniques. These methods use a printing plate (or image carrier) to transfer ink to a printing substrate such as paper, plastic, metal, etc.
1. Letterpress printing
Letterpress printing is when the printing elements of the printing plate are higher than the non-printing elements. Printed elements are coated with a layer of ink (directly or indirectly), which is then transferred to the substrate, while non-printed areas are recessed and remain ink-free. Letterpress printing is used with the following printing systems: book printing, flexographic printing, and letterpress printing. The technology can be used for printed products such as small format jobs, business cards, labels, carriers and bags.
2. Book printing
Book printing is the oldest letterpress printing technique, which uses printing plates made of lead alloys or synthetic materials. Letterpress printing is suitable for the reproduction of text and images, and prints are characterized by sharp edges.
In practice, letterpress also included other forms, such as woodblock prints, photolithographic zinc "cuts" (boards), and linoleum blocks, which could be used with metal or woodblocks. Gutenberg's discovery of individual, movable typefaces in the 15th century made it possible to replicate typeface elements economically and quickly. Removable fonts are metal blocks that each contain only one character: letters, numbers, and punctuation marks. These blocks can then be rearranged to create any type of text.
3. Flexographic printing
Flexo printing is a form of direct letterpress printing characterized by the use of flexographic printing plates. First introduced in the early 1900s, it can be used on absorbent and non-absorbent substrates in packaging, label and newspaper printing due to its soft plate and low viscosity inks.
4. Movable type printing
Movable type printing is a form of indirect printing, meaning that the image from the printing plate is transferred to the paper via an intermediate carrier (cylinder). It is called dry offset printing and is mainly used for cardboard packaging.
5. Gravure printing
Gravure printing is the opposite of letterpress printing. The printing elements are recessed below the surface of the plate, while the non-image areas are at a constant level. Designs are cut, scratched or etched onto printed boards. The grooves are filled with ink, and the raised (non-printing) portion of the plate or cylinder is wiped or scraped off the ink, leaving only the ink in the grooves.
Ink is transferred from the unit to the printed substrate by high printing pressure and the adhesion between the ink and the substrate. Typical features of intaglio printing are jagged edges on letters and lines.
Gravure printing is often used for high-volume printing of packaging, wallpaper and gift wrap with fast-drying inks, and various printing technologies based on the gravure printing principle are used to produce special prints such as stamps and banknotes.
6. Photolithography
Lithography was invented by Alois Senefelder in 1796. The image to be printed is drawn on the stone with special ink. The stone needs to be wetted before inking, after which non-image areas of the stone surface will not be inked. Due to very short print runs, lithography was used only for fine art prints.
7. Offset printing
Offset printing is the main lithographic printing technique and falls under the category of indirect printing, where the ink is first transferred from the printing plate to a flexible intermediate carrier or blanket and then onto the substrate. It is called offset because the image does not go directly from the plate to the paper.
In traditional offset printing, the printing plate is wetted with a fountain solution consisting of water and additives before the ink is applied. Non-image areas are hydrophilic, which means they absorb water, while image areas are oleophilic or ink-absorbent. In other words, the ink sticks to the image areas and the water sticks to the non-image areas because the film of fountain solution prevents ink transfer.
In waterless offset printing, the printing plate is not wetted with fountain solution and the surface is ink-repellent because the non-image areas of the printing plate consist of a layer of ink-repelling silicon. Ink-receiving areas are exposed due to interruptions in the silicone layer. Images printed using offsets are separated into basic colors. Prepare one plate for each color used, or four in the case of 4-color (CMYK) printing. Each roller has its own assigned ink, which, as they pass over the page, transfers the ink and builds the layers of color, resulting in a full-color page. Offset printing can also add special colors called Pantones or PMS colors if specific colors are required. Offset printing is typically used for larger print jobs of 1,000 pieces and up. Screens are usually made of fine fabrics, such as silk, plastic or metal fibers and threads, which are then stretched over wooden or aluminum frames. It is placed on top of a fixed substrate (fabric, paper, etc.). Place the ink on top of the screen and use a squeegee (rubber blade) to push the ink evenly into the screen opening and onto the substrate. The ink penetrates the open spaces in the screen onto the substrate. Then lift the frame up and push the scraper back across the screen. The scraper transfers the ink through the open mesh.
8. Screen printing
Printing elements are the areas where ink is forced through the printing master – in this case the screen. The non-image areas are rendered ink impermeable by blocking the stencil.
Understanding the printing process, costs, and constraints can help you not only create stunning designs, but also answer any questions and guide your customers to the best solutions that are affordable and effective.
