Title: STUDY MATERIALS - Printed media
Course: Pre-Press Procedure / e-design > Section: Part I – Overview of printing technologies

After the online lectures, the study materials along with the map of new concepts will be uploaded to Moodle.

Printed media

Periodicals

    - Newspapers
    - Magazines

Books

Outdoor Media

- Posters and Billboards

Direct Mail: Letters and Postcards

Product Packaging

Future trends

Future trends of print media

There are several scenarios in history that later proved to be incorrect:

- in the 1902s, radio was to replace printing,
- in the 1950s, television was to replace printing,
- in the 1980s, the use of computers was to replace printing and
- in the 1990s the Internet was to replace printing for good.

However, that is not the case and printing is currently still in the picture, and in some areas, such as the packaging industry, it is even growing.

New media have not destroyed printing. They actually contribute to the production of publications – these media also need advertising. Until now, people are still used to advertising publications and they are even easier and cheaper to produce than ever before. In addition, new media – music, movies and the Internet – are creating new types of publications: TV series books, online auction catalogues and various packaging. Although news and reference works have moved to the Internet or digital media, it is even easier to obtain traditional publications online. Direct mailing advertisements are also still considered to be a much more effective advertising channel than e-mail advertising, as it is common to ignore e-advertising.

However, the digitalisation of communication continues, and therefore changes are already taking place in printing houses. The automation of all production processes continues, which creates an opportunity for faster production with little labour; so-called “one-person printing companies” are established. This has already happened in the field of pre-press, where given increased technological development, equipment has become almost automatic and the amount of time required for this work has decreased from hours to minutes.

The use of digital pre-press makes it possible to complete a printing faster when the materials arrive at the printing house electronically, thus shortening the time of completing the product. Electronic inspections are increasingly being used in the printing process, resulting in higher quality and productivity.

In the future, printing houses are also expected to be more flexible, especially in production using different types of paper, special colours, finishing materials or post-processing methods. The use of additional colours or post-treatment with effect varnish is becoming increasingly common. At the same time, print runs are becoming smaller. As the client has to be constantly offered something new, prints are used for shorter time than before, which means that the life of the print is shorter. Printing houses are increasingly implementing digital printing equipment, which allows production of more personalised prints for the client.

Read more: Põhjamaade paberi- ja tselluloositööstuse särav tulevik; Global printing market to top $821 billion by 2022

Printing technologies

Printing

Over time, various types of printing methods have been invented and tested: the main methods are letterpress, gravure, planography, screen printing and digital printing. All types, both analogue and digital, have one thing in common: an image carrier is prepared for printing and the non-printing parts are covered with ink to transfer the print image to the substrate.

Broadly speaking, printing technologies are divided according to the image carrier in the printing section and the geometry of the pressure surface. Printing sections and image carriers can be flat or round. The very first printing machine consisted of a flat pressure surface which was pressed against a flat image carrier. After some time, it was noticed that when using round carriers it is possible to speed up the printing process. Thus, round pressure cylinders were implemented which rolled over a flat image carrier. Until finally, the combination of a round pressure roller and a round image carrier form was used allowing a maximum printing speed to be achieved.

The use of an image carrier and pressure surface depends on whether the printing process is direct or indirect. In the direct printing process, the image carrier transfers the print image directly to the substrate, and in the indirect printing process, the image is transferred to the material via an intermediate transfer surface. Consequently, in the case of a direct process, the image on the image carrier is a reversed image and in the indirect process it is not reversed.

Direct printing processes are:

  - letterpress;
  - gravure and
  - screen printing, except a special type – pad printing.

Indirect printing processes are:

  - plantography (excluding lithography and dilithography).

Printing methods are mainly distinguished by the cross-section of the image carrier, that is, whether the surfaces carrying the print image are higher, lower, or on the same plane as the surface of the non-image.

The newest type of printing, digital printing, differs from analogue printing methods in that permanent image carriers are no longer used. The image can be deleted from the image carrier and there is no need to make a new image carrier. Some digital printing methods do not even require an image carrier because the ink is sprayed directly onto the paper (for example, an inkjet printer).

It is not possible to rank the methods by means of comparing the different methods. When choosing a printing method, important factors are the type of the product and the size of the print run as well as technical and financial calculations. Metal image carriers allow printing at speeds that cannot be achieved with digital printing, so analogue printing is still the cheapest for large print runs. Classical analogue printing methods are still in use, although digital technology is also used in this field – image carriers for analogue printing are already being created digitally (CTP, computer-to-plate).

With the emergence of digital printing, time consumption has changed the most – prints can now be produced faster. As digital processes make use of automated stages, time consumption is reduced. However, the aim of all different printing methods is to produce high quality printed products. And here, sheet offset printing implementing the analogue method is set as a standard by which the other methods are measured. Digital printing methods are mostly focused on speed and flexibility.

History and principles of printing technology

Traditional printing technologies and principles. History.

Letterpress

Letterpress

Example of letterpress

Letterpress is the oldest printing method. The printing surfaces on the image carrier are higher than the non-printing surface. The first publications date from 200 AD from China. Wood block was used to print on textile and later on paper, and mainly religious church books were reproduced by this method. In Japan, this printing method is called ukiyo-e and is still used today. In Europe, this printing method was called woodcut. To describe artistic woodcuts, the term xylography is also used. In the first letterpress printing machine, a “flat-flat” method was used.

In 1450, Johannes Gutenberg, a German inventor, printer and goldsmith, gathered all the information known so far about printing and, based on this information, designed a printing machine for reproducing books.

Johannes Gutenberg, German inventor, printer and goldsmith

He was the first to use movable and separate types to lay out words, sentences, and finally pages of texts. As he was a goldsmith by profession, he replaced the previous wooden and metal image carriers with tin moulds. The moulds were made of lead, tin and antimony alloy. Gutenberg made the first machine on the bases of a wine press. His first printed publications included leaflets and pamphlets, and later dictionaries, short grammars, indulgence letters, and calendars. Between 1452 and 1454, he printed about 180 copies of the 42-line Latin Bible (Gutenberg Bible, the title 42-line comes from the number of lines on a page).

Gutenberg made the first machine on the bases of a wine press.

The printing revolution began. In a couple of decades, besides one printing house in Europe (in Mainz, Germany), 236 printing houses were established in different cities. By 1480, there were more than 110 printing houses in Germany. And by 1500 in Italy alone, there were 77 printing houses, most of them in Venice.

Before the Gutenberg printing machine, books were copied by hand. Using a printing machine, it was possible to produce books quickly and in large quantities, which led to the rapid spread of books and education. The new type of printing machine allowed about 3,600 sheets to be printed per day. In the first 50 years, 30,000 titles of books with a total print-run of 12 million were printed in Europe. During the century, the number of copies increased tenfold. In this way, book printing went from artisanal to industrial.

The first letterpress printing machine with round image carriers was introduced in 1845, when the American Richard Hoe manufactured a rotary printing machine, which made printing significantly faster. The machine itself was such that there was paper around one cylinder, the text to be printed was attached to the other, and the image was transferred to the paper by rotating both.

American Richard March Hoe (12/09/1812 New York - 07/06/1886 Florence, Italy)

The rotary printing machine made printing significantly faster.

In the 1970s, letterpress was replaced by offset printing. Today, letterpress is used relatively seldom, mostly only for art in small handicraft printing houses. However, old printing machines – such as the Heidelberg Platen – are still used in post-processing after rebuilding. In several printing houses, these machines are used for creasing or to make perforations.

Heidelberg Windmill

Letterpress has a few features that distinguish it from other printing methods.

Due to the high pressure exerted on the image carrier, a shadow of the print image remains visible on the other side of the page. You can also see a dark “halo” at the edges of the image, which is especially visible in coloured letters or as raster dots on a light surface. In addition, letterpress raster dots have very sharp edges. They depend on the substrate and are visible even on a very light-coloured surface.

Flexographic Printing

Flexographic printing

Flexographic printing developed from classical letterpress printing. The first flexographic printing machine was put into operation in 1914. Flexo carriers are made of a flexible soft material – rubber or photopolymer – and their strength and thickness are selected according to the material to be printed. As is characteristic of letterpress printing, the printing surface is higher on the image carrier. But thanks to the flexible carrier, it is possible to print on many different types of surfaces, for example, on an uneven surface or fabric.

Flexo carriers are made of a flexible soft material – rubber or photopolymer

Flexographic printing was earlier used in newspaper printing, but now it is mainly used in the packaging industry. In flexographic printing, up to 10 different colours can be printed in one printing process, and this is especially important when printing packages where special colour tones are important. After the printing process, the result is processed immediately or rewound and processed elsewhere.

The possibility to print on many different materials is a special feature of flexographic printing. Flexographic printing can be used to print on paper, paperboard or cardboard as well as on plastic film or aluminium foil. Thus, in addition to packaging, all kinds of bottle labels and plastic bags can be printed.

The flexo print image also has “halo” edges and is even more noticeable than in the case of book printing letterpress method, but there is no shadow on the other side of the material

Flexographic printing in short:

- The difference from classic letterpress printing – a soft elastic plastic printing carrier is used and the same amount of colour is always applied to it with anilox.
- Flexographic printing ensures a very stable and even thickness of the ink layer.
- Very good result when printing large, even surfaces.
- The thickness and resolution of the ink layer are adjusted by changing the anilox.
- There is no complex ink mechanism characteristic to offset printing machines, and no water is used.

Gravure Printing

Gravure printing

Printing with a carved carrier is called the gravure printing process used to illustrate books as early as in the 15th century. In today's gravure printing, the image is carved onto a round copper image carrier. The carrier is then covered with ink. An ink knife (squeegee) is used to remove excess ink so that ink remains only in the carved grooves. The carvings are also called honeycombs. Initially, the carvings were made by scraping the copper surface and carving with acid, but later engraving by means of diamond drilling was used. Today, the image carrier is cut with lasers. Due to the honeycomb structure of the image carrier, even the full surfaces in the print image appear as rasters and the edge of the image resembles a saw tooth. Today, the honeycombs of laser-engraved letterpress carriers are so fine that the effect is barely noticeable.

A distinction must be made between the use of gravure printing for the arts and the packaging industry. In the latter field, web or rotogravure printing is mostly used and very rarely sheet gravure printing. In gravure printing, in principle, all publications are made in large volumes (100-300,000 copies) or with a large number of pages. The decisive factor is the higher price of the image carrier of the gravure printing compared to others. Typical gravure printing jobs are sleek magazines, catalogues, promotional materials, weekend magazines, and other types of publications with high circulation. In these areas, gravure printing has a great advantage over newspaper printing, as the quality is constant during printing and there are no colour fluctuations. Gravure printing is also used to produce wallpaper, gift wrapping paper, shopping bags, and soft plastic and paper packaging. Gravure printing machines are some of the largest printing machines today. For printing magazines, a paper roll with a width of up to 4.3 meters can be used and in the packaging industry, material with a width of up to 2 meters. For printing packages, it is possible to use 10 to 12 or more different colours.

A recognisable special feature of gravure printing is the serrated edges of the print image. Interrupted transitions and blurred shadowed areas are also typical.

One of the sub-types of gravure printing is pad printing, which can be used to print on three-dimensional objects of any shape. Here the ink is placed in the grooves of the image carrier. In the printing process, the ink is transferred to the object via a rubber pad. This allows printing on a wide variety of objects: pencils, pens, lighters, remote control buttons, or keyboard keys. It is common to use only line elements or contrasting text and only one colour.

Gravure printing in short

- Very high starting price. Normal runs are in the millions, with a paper width of 3 meters or more
- Widely used for printing soft packaging – prints very well on thin film (10-30 micrometres)
- Very good image quality
- Allows you to print at a higher density than other traditional printing methods
- Does not allow printing a full-colour surface – all full surfaces (including text and lines) are in a raster (95-97%), which is often visible to the naked eye.

Lithography

Lithography

Flat printing (planography)

In the flat printing method, the printing and non-printing images are on the same plane.

This printing method is divided into:

    - lithography,
    - offset printing,
    - collotype and
    - dilithography.

Lithography is the forerunner of the most common printing method today – offset printing. Collotyping without halftones, often referred to as phototyping, is used in small-scale reproduction and copying of art. Dilithography was initially used in newspaper printing. The newspapers were then printed on offset printing machines with a wetting section by using letterpress image carriers. This temporary printing method disappeared with the introduction of web offset printing.

 Lithography (lithos “stone” + graph “I write” in Greek) is a flat printing technique based on immiscibility of oil and water, in which case a stone plate is used for printing.

In 1796, playwright Alois Senefelder decided to simplify the process of reproducing text and sheet music for actors, which was at these times done by using letterprint. There was little money – not enough for the printing press or the letters. In 1797, he built the first manual lithographic printing press, the image carrier of which was made of limestone.

The playwright Alois Senefelder built the first lithographic printing press in 1797, the image carrier of which was made of limestone.

Lithographic printing is based on the properties of water and oil and for printing, a limestone plate (or litho stone) was used. The image is drawn on the stone with a wax crayon. The whole surface is then treated with a weak nitric acid solution. In the chemical process, oil combines with the stone and at the same time the pores on the surface of the stone increase in size, making the free surface susceptible to water. When wetting a stone image carrier, only the non-printing surface gets wet due to the mutual repulsion of water and oil. When making a print, ink is applied to the moistened stone; oily ink remains only on the image as the free surface will not be soiled with ink because of water. The image carrier is pressed against the base material with a lithopress and the number of possible prints is unlimited.

In 1826, Alois Senefelder improved his technique and began printing in several colours. In the middle of the 19th century, the first lithographic high-speed printing machine was built in France. At that time this printing method was considered good for advertising materials because the printing process was rather quick. Even at the beginning of the 20th century, maps, posters, advertisements and picture postcards were produced in this way. But given its labour-intensive process, lithography became more and more suitable for artists to reproduce graphics and drawings. All in all, this letterpress method was used for 400 years. Today, however, lithography is already quite rare.

Offset printing

Offset printing

After some initial setbacks, George Mann & Co. opened the first offset printing house in London. In Offenbach, Germany, Faber & Schleicher AG built the first sheetfed offset printing machine, “Roland” in 1910. In 1912, the first “Universal” web offset printing machine, built by the Felix Bottcher Company and the mechanical engineering group Vogtländische Maschinenfabrik AG (VOMAG), was put into operation in Leipzig. Heidelberger Druckmaschinen AG and MAN Roland Druckmaschinen AG, very well known today, were founded in the middle of the 19th century.

Initially, letterpress and offset printing were fairly equal in the printing market, until the share of letterpress began to decline from around the year 1960. The invention of the Euroscale four-colour conversion method gave a major impetus to the development of offset printing and has now become the most widely used printing method.

The patent for the first Heidelberg printing press was registered in 1962 in Germany. In the early 1970s, offset printing began to replace letterpress printing in newspaper printing. With the introduction of phototypesetting and repro cameras, sheet-fed offset printing began to grow in popularity, as production was significantly more efficient compared to letterpress printing.

In offset printing, a round-to-round process scheme is used. As with lithography, the image carrier of offset printing is flat. The properties of the printable and non-printable surface are different on the image carrier. The printing surface is water-repellent, while the rest of the surface is made wet with water. A water layer is applied on the flat image carrier. Water only wets the non-printing surface. Ink is then applied to the printing plate. It only stays on these areas of the printing plate where there is no water layer.

As with lithography, in conventional offset printing the principle of water-to-oil repulsion is used. Ink containing oil adheres only to the dry parts of the moistened printing plate. The printing plate, usually made of aluminium, is covered with a light-sensitive layer (emulsion). By the processes of image projection (exposure) and development, the emulsion is reduced and excess is removed by rinsing. On the printing plate, the printing areas adhere to the ink and the non-printing areas push the ink away. Initially, negative plates were used, where the remaining emulsion was water-binding so that the ink containing oil adhered to the surface from which the emulsion was washed off. Now mostly positive plates are used, where the emulsion remaining on the plate after exposure forms an ink-adhesive print and the ink containing oil remains only where the emulsion has not been washed off. In 1985 a waterless offset printing was also invented, in which a silicone emulsion that repels the ink in combination with special inks allows printing without water.

The print image is first applied to the rubber cover of the rubber cylinder and then from the rubber on the paper. This type of transfer also results in the name of the printing method – offset. The basic principle of offset printing (as well as the basis of colour separation) is that the thickness of the ink layer is the same throughout the printed surface.

Today's offset printing allows the use of printing machines with one to ten colours, although ten-colour printing machines are quite rare. The five-colour printing machine allows printing four process colours and one additional colour without the need to clean the ink sections in between. Some printing machines have a special varnish section added, which adds a protective or decorative varnish layer to the print inside the machine at the end of the printing process. In most cases, the varnish section works on the principle of flexographic printing.

In modern offset printing often CTP technology is used, where the printing plate is made with lasers and without chemicals. With CTP technology, i.e. by drawing an image directly on a plate, it is possible to avoid image deviations and/or shifts that would otherwise occur during copying from the film to the printing plate.

The types of offset printing are sheet-fed offset and web offset. In the case of sheet-fed offset printing, the paper is bent in loose sheets around the printing cylinder. In web offset printing, however, the paper tape is fed into the machine from the rolls. In offset printing, the paper sheet must be turned over after printing the front image to print the back image on the paper sheet. In web offset printing, printing takes place simultaneously on both sides of the paper tape.

In sheet-fed offset printing, anything with a circulation of 1,000 to 50,000 can be printed. It is more efficient to print prints with higher circulations by means of gravure printing. Typical sheet-fed products are business publications, books, brochures and flyers as well as packaging.

Web offset is used when the product has a large circulation and many pages. This includes products such as newspapers and magazines. For these, sheet-fed printing is too slow and at the same time the newspaper has too little circulation for gravure printing. By feeding the paper from the roll, web printing allows printing at speeds that are impossible to achieve in sheet-fed printing. However, unlike gravure printing, web offset printing is produced directly at the end of the printing machine, where there are usually cutting and folding sections.

A distinction is made between high-quality commercial web printing (heatset web offset) and newspaper printing (coldset web offset). Commercial products are usually printed on coated paper that does not absorb ink, which is why these printing machines have a built-in oven to speed up the drying of the ink - hence the name heatset. The paper tape passing through the drying oven ends in a folding machine, where the printed product is processed into the final product. The final printed product can be either saddle stitched or adhesive bound. Stitched binding is not possible due to high speed. Heatset printing products can be recognised by the gloss and smell of the coating added to the printing surface. The ink does not smear when rubbed with a finger. When using papers with small gram-weight, the heatset print does not appear on the other side of the paper and is an important advantage over coldset printing. Typical heatset-printing products are high-volume magazines, catalogues and flyers.

Offset printing is recognised by a proper contrasting print. The absence of halos and the absence of a shadow on the other side of the paper usually refer to offset printing. It is also characteristic that in the case of very light colour tones, raster surface (dot loss) may suddenly disappear and in the case of very dark colours there may be a scattering of the raster dot (dot gain). However, this will not happen if a new type of FM raster is used.

Differences between offset printing and other printing methods:

      - Water is used to distinguish between printable and non-printable surfaces.
      - Ink is transferred from the printing plate to the paper via the rubber cylinder.
      - The thickness of the ink layer on the paper can be changed during printing, as well as by zones.
      - Sophisticated ink and water device.
      - The transfer of ink along the roller of the ink device to the image carrier and from there to the rubber coating paper takes place by ink splitting.
      - The basic principle of offset printing (as well as the basis of ink splitting) is that the thickness of the ink layer is the same throughout the printed surface.

Collotype

Collotype

One special type of offset printing that is quite rare today is the collotype, which allows printing halftones without raster. This method was developed in the middle of the 19th century. The image carrier is a light-sensitive colloid applied to glass. Exposure, development and wetting create a relief surface that hardens differently during subsequent processes. Unlike colloid, the ink adheres to areas with different hardness and this makes it possible to print halftones. Collotypes look like paper photos but are recognisable by their characteristic graininess. Using multiple inks (even up to 20) it is possible to create very true-to-life prints. Although the collotype printing method is suitable for work with a small number of prints, today it has remained only as an original form of art.

Screen Print

Screen printing

Screen printing can also be called serigraphy. Serigraphy derives from the Latin word seri (silk) and the Greek word graphein (write). This is a method in which ink is applied to the print material through a thin mesh tensioned on the frame. This is one of the oldest printing methods. In medieval China and Japan, a pattern was printed on the fabric through a mesh made of hair. Later, fine-mesh silk fabric was used as the mesh, and in modern screen printing a mesh from synthetic polyester or metal wire is used. The first screen printing machine was built in 1924 in the USA.

The mesh surface is coated (or already industrially coated) with a light-sensitive emulsion on which the print image is exposed. In the exposed areas, the emulsion strengthens, but the emulsion in the non-exposed areas is removed during subsequent development and washing. The result is a mesh surface where the image is formed by mesh holes through which the ink can be pressed. The mesh surface is placed against the printing surface, then ink is poured onto the mesh and is rubbed and forced through the open mesh holes with a knife.

In simple screen printing, one matrix and one colour is used, but it is also possible to do multicolour printing. For each colour, a template of the corresponding colour must be placed on the printing surface and one colour after another must be printed. Modern automatic screen-printing machines consist of several colour sections, between which an object is moved (T-shirt, balloon, CD, pen, etc.). When printing on materials with different colours, different base colours are often needed – for example, when printing an image on a dark shirt fabric, a white base colour must be used. The colours for shirt printing are mostly opaque, but for printing on glass also transparent colours are used. In addition, in screen printing it is possible to print with inks that can be scratched off (e.g. lottery), with those that glow in the dark and with metallic inks. Screen printing is also used relatively extensively in ordinary printed products if a certain part of the print is to be highlighted.

Suitable materials are various paper, cardboard, fabric, plastic, sticker materials, aluminium, wood, glass, etc. Packaging, jars and bottles, printed matter and advertising material, art and textile patterns are produced using this method. Electronic CBs are also produced by screen printing.

Screen printing is a printing method with the best colour coverage. The most characteristic feature of screen printing is the printing ink that is higher than the plane of the material – the ink is 10x thicker than in offset printing and thus requires longer drying time. It is also characteristic that the edges of the image are not straight; there is always noticeable jaggedness due to the mesh holes. Due to the relatively high sparsity of the mesh, a dense raster cannot be used for screen printing.

Computer-to-Print

Digital printing

For short runs, digital printing competes very successfully with traditional printing technologies. It is not always clear which technology might be the most appropriate for a particular print job. A number of factors should always be considered in determining which technology to use, such as production economy, print quantity and availability and quality of the substrate. In general, it can be said that the printing technologies based on image carriers are disappearing and digital printing technologies and online media are replacing them. However, there is one area where the traditional printing method not only dominates but also increases its position, and that is the packaging industry.

In the 1990s, there was a lot of talk about digital printing as a new independent way of printing. In fact, the beginning of digital printing dates back to 1938, when the American Chester Carlson invented electrophotography. Carlson generated an electric charge by rubbing the surface of a sulphur-coated metal plate with a woollen cloth. He placed a metal plate against glass, on which he had written some words for testing. After illuminating the plate through the glass, he sprayed a fine powder on the metal plate, which made the words visible. Pressing the metal plate with powder against the wax paper, the words were transferred to the paper. Based on this discovery, the Haloid Company (also known as Xerox since 1961, a big competitor to Kodak at that time) designed the first photocopier in 1949. In order not to resemble traditional processing-based photocopying, this type of copying was soon called xerography, from the Greek words xeros (dry) and graphein (write). The first colour copier came onto the market around 1990, and in the mid-1990s digital colour printers became available. The continuous development of colour printers and the wide use of computers led to the emergence of a new and independent way of printing.

Chester Carlson (in the middle) shows John Dessauer (on the left) and Joseph Wilson (who was Haloid's president) an early xerographic printer. Later, Haloid became the Xerox Corporation. An illustrative image from the Xerox historical archives. © Xerox Corporation

It is usually digital printing when no printing plate is used. Instead, the information is sent to the printing machine directly from the computer, skipping the traditional steps of making a printing film and/or an image carrier. Therefore, such method is called computer-to-print (also abbreviated as Ct-Print). In contrast to the conventional (traditional) printing method, in digital printing the image carrier is dynamic, i.e. the carrier is used repeatedly but the information is deleted from the carrier after each printing.

In new electronic printing methods, there is no physical image carrier. The image to be printed is in virtual form in the memory of the computer. Each subsequent print can be unique. There are dozens of such printing methods. Some are already extinct. There are two common methods.

Laser printers – electronographic method using mostly powder inks, where selenium cylinders are used as image carriers. The image is drawn on the cylinder by means of electric charges. Powder ink adheres to the charged areas, which is transferred from the cylinder to the paper and is fixed by heating.

Inkjet printers – there is no physical intermediate image; the image consists of small dots of ink sprayed onto the paper. Cheap home and office printers use 4 colours. To print photos at least 6 colours are needed. Very good printers have 8 ink cartridges.

Digital printing is divided into:

      - electrophotography (also known as xerography),
      - ionography,
      - magnetography,
      - thermography and
      - inkjet printing.

The most common methods in modern digital printing are electrophotography and the inkjet method. In electrophotography no printing plate is used. The image is applied to the material with a light-sensitive drum. In the case of inkjet technology, the image is created with ink directly on the paper, hence the name computer-to-paper.

Digital printing is also classified as nonimpact printing (NIP) to distinguish it from printing methods where pressure is used, such as loud needle printers or electric typewriters. When printing without pressure, the image is transferred directly to the paper or is created with a laser on an intermittent surface – a drum. A special dye (toner) creates an image on the drum and then it is transferred from the drum to the paper.

Digital printers are used in many different fields. Printers are available in a wide range of sizes, from portable and desktop models to printing production lines.

Digital printing is very often used when traditional printing proves too expensive. Examples of such areas are

      - small colour prints (flyers),
      - test printing (digital proofs),
      - variable data printing (VDP) or also VIP - variable information printing or
      - print on demand (POD).

With POD printing, only as many copies of the book are made as are currently needed or ordered. In principle, books can be printed in a very small circulation. VIP printing is used to print products with variable information. The text part of the publication (for example, name or address) or even the pictorial part can be variable. This allows creating personal publications or different versions. VIP printing can also be combined with traditional printing – for example, custom information from a database of addresses may be added to a business letter or flyer containing general information and printed by means of offset printing.

There is also a difference between digital printing and analogue printing in how the price and profitability of printing are calculated. In digital printing, the price per printed page is usually calculated, but in analogue printing, usually the time spent on printing (i.e. the hourly price) is calculated. Therefore, the price of digital printing is inefficient for large numbers of prints, but when using analogue printing, the price of a copy becomes cheaper the higher is the number of prints. Digital printing is usually still too slow, toner and ink are even more expensive than regular ink, and therefore analogue printing is used for high print runs.

Additional colours are not much used in digital printing. In most cases, only the usual process colours are used - cyan, magenta, yellow and black. Theoretically, any colour ink or toner could be made in digital printing but as only a certain fixed quantity of product can be produced, it is not practical to produce many different additional colours for small quantities of digital printing. However, there are digital printing systems where also a fifth or sixth colour is possible.

Color Laser Printer

Laser printers

The largest type of digital printing technology is xerography (also called dry electrophotography; this must be distinguished from cyanography, a copying method where liquid developer chemicals are used). The name laser printing is also common. This technology is used in most modern copiers, laser printers, and fax machines that use plain paper.

In the first step of the working process, a magnetic charge is applied to the surface of the light-sensitive material applied to the drum. The image is then illuminated on the drum with laser or LED light. When exposed to light, the magnetised state of the drum surface is maintained at the image location and toner (from the soot cartridge) adheres to it. In the next step, the image drawn with the toner is pressed directly onto the paper, fixed with heat and covered with a layer of silicone oil. In the last step, the drum is neutralised and any remaining toner is removed with brushes.

https://youtu.be/WB0HnXcW8qQ

Digital printing with a laser printer can be recognised by the ink layer of the toner being very glossy and cracking when bent or folded. Recently, colour accuracy has also not been an issue, and the print quality of laser printers is quite similar to standard offset printing.

Inkjet Printer

Inkjet printers

Inkjet printing technology is divided into two types:

    - continuous inkjet printers and
    - drop-on-demand inkjet printers.

In inkjet printers, tiny drops of ink are sprayed from the nozzles toward the paper. The flow of ink droplets is guided through a magnetic field before the surface of the paper, where unnecessary droplets are deflected off course and they do not reach the paper but return to the ink tank. The necessary ink droplets reach the paper and form an image. This method does not allow generating normal raster dots of different sizes, and therefore halftones can be generated in a way that equal ink dots are scattered at random locations – this method is called error diffusion. Solvent or alcohol-based inks are often used in inkjet printers, and thanks to the fast drying of the ink, it can be used to print even on plastic. However, the use of such ink in rooms requires a special ventilation system.

In droplet inkjet technology, bubble jet spraying of ink droplets is used. This technology was invented in 1957 by Canon’s engineer Ichiro Endo, making Bubble Jet the brand name for Canon inkjet printers. In a printer with thermal inkjet technology, monochrome or multi-colour printheads are used where the ink is stored in small containers with a heating element. To direct ink onto the paper, ink is heated very quickly so that an air bubble is formed which pushes the ink droplet with a pressure through the nozzle. The ink is mostly water-based and thus the image is not waterproof.

In industrial inkjet printers, heating has been replaced by the use of piezo materials. This technology is used in Epson and Brother printers. Although ink is stored in the same way in the print head container, the pressure in the container is created by a special piezoelectric material. If necessary, the piezoelectric material changes in size when exposed to an electric charge, and the air pressure created by it pushes ink in droplets through the nozzle towards the paper. In this technology, the properties of the ink are no longer a limiting factor – different inks can be used: waterproof, UV-resistant, etc. but the print head (or the piezo material used there) is quite expensive.

    Print of the inject printer

Digiproof

Digital proofing

In today's prepress, colour proofs are digitally printed and analogue proofing methods are obsolete.

Inkjet printers are mostly used to make digital proofs, because as they make use of more inks, a bigger colour gamut can be achieved. The proof system must be characterised by the full achievement of the colour gamut of the simulated printing process. Six or even eight-colour inkjet printers can simulate different output devices on special proof paper. The digital proofer requires pre-calibration to achieve accurate colours. The colour accuracy of a specific output device is guaranteed by the Ugra/Fogra digital print scale attached to the digital proof, from which the spectral values of the colours measured for proofing must exactly match the colours of the simulated printing process. The existence of this digital print scale distinguishes the digital proof from ordinary colour printing.

Plotter

Plotter

Plotter is a digital printer with special functions.

Generally, in plotters either

      - a styles,
      - blade or
      - laser is used to create an image.

Initially plotters were designed to make technical drawings and graphs. Drawing plotters have an ink pen that draws lines or letters on paper of different widths, both from a long roll of paper or as loose sheets. It is mostly used for large drawings and diagrams in architectural bureaus.

A cutting plotter has a special cutting blade (knife) instead of a pen. Letters or other line graphics are cut into the top layer of adhesive material with a cutting blade so that the bottom backing layer is not damaged.

In laser plotters, the cutter is a laser beam instead of a knife. Various colour films are used as material, from which logos, labels and other line graphics can be cut out. It is also possible to cut shapes into paper or engrave on natural leather or thin plywood.

WEP - wide format printer

Wide-format printers

Modern inkjet or laser printers that use wide-width media are called wide-format (WFP) printers. They can print on a fairly wide range of paper, fabric or film material, whereas the material is fed from a roll, which can be several meters long. Wide format printers are used to print on large and very large surfaces, and the print volume is usually very small - only a few copies. The most commonly used surfaces are large signs, shop windows, roadside or house-sized outdoor advertising spaces, stage designs and exhibition backgrounds or art panels. In other words, usually where a large surface is needed but the amount is small.

“Computer-to-” technology

Computer-to technologies

This is the name given to the various technologies by which digital information in a computer is actually transferred to the print material.

This is also the way digital printing is referred to, but only if the information is transferred directly to the printing material – these are computer-to-print and computer-to-paper technologies.

Other computer-to technologies are used in traditional types of printing (such as offset printing) as intermediate processes - computer-to-film, computer-to-plate and computer-to-press.

Computer-to-film

The first technology for producing an image carrier digitally was computer-to-film (CTF for short).

Special films are made in image setters for an analogue image carrier of each colour. The image is illuminated on the film with a laser and the film is developed and fixed. The finished film is then placed on an analogue printing plate and illuminated under UV light, and the printing plate is developed. CTF printers were in use in the 1980s and are now being replaced by new technologies.

Computer-to-plate

CTF technology was replaced by the technology - computer-to-plate (CTP for short). But this is not a method of digital printing. CTP technology is used to make printing plates that are used in traditional printing methods. Unlike CTF technology, in which film is used, the laser illuminates the image directly onto the printing plate, i.e. there is one process less than in CTF. Special printing plates with a light-sensitive surface are used. The light-sensitive surface may be made of silver halide, photopolymer or thermopolymer. Depending on the light-sensitive surface, different colours and different levels of laser thermal power are also used. After the image is drawn, the plates needed to be developed with chemical solutions inside the developing machine and thereafter fixed to be finished. Newer technologies already allow for a chemical-free process. CTP technology significantly increased the quality of the printing plate production: it prevents possible scratches and dust damage when illuminated with a film as well as shadows due to light scattering and obtains a very contrasting raster dot. Compared to CTF, faster working speeds were also achieved – the newest CTP printers produce up to 72 B1 size printing plates per hour.

Computer-to-screen

This technology allows a screen printing matrix to be made by printing an image from a computer to a laser printer that illuminates it directly on a light-sensitive screen.

Computer-to-press

Abbreviated CTP, this means advanced CTP technology where the plate printer is built directly into the printing machine. This technology did not gain much popularity, as the printing machine has to stand idle while the plate was being made. In addition, this technology was more expensive because the plate printer that could fit in the printing machine had to be more compact than a regular plate printer.

Computer-to-print

This is truly the first digital printing method. In digital printing, both the making of the printing film and the image carrier (plate) are sometimes omitted. In most cases, the principle of electrophotography is used, where (instead of a printing plate) the image is transferred on the material by means of a light-sensitive drum.

Computer-to-paper

This is also a true digital printing method. This includes inkjet printers and they do not use a printing plate or a light-sensitive drum. The principle of operation is to spray liquid ink directly onto the paper.