Previously we have covered the brief history of flexographic printing in our blog. Now, let us take a look at what flexographic printing is actually and how and where we use it.

Briefly summarized: flexographic printing is a letterpress printing technology where we print from a rotation, that is from a roll. In this case, the plate is flexible (that is where the term ‘flexographic’ comes from); it is either rubber or plastic. Since fast-drying ink is used for this type of printing, and since it is ideal for a large number of copies, the main field of use of flexographic printing is packaging.

Characteristics of flexographic printing

During flexographic printing, the surface of the plate protrudes out of the plane of the plate cylinder, but unlike in letterpress printing, an anilox roller containing ink cells is used to apply the ink to the plate, which is different from other printing methods. While the ink consumption within sheets is controlled by zone screws in letterpress- and offset printing, it is not required on flexographic printing presses because the amount of ink needed to evenly ink the plate is continuously supplied by the anilox roller, and the unused ink does not accumulate on the anilox roller.

The plate in flexographic printing (cliché) is a flexible plate, which is glued onto a cylinder or a sleeve with specific systems of washers or it is a flexible endless plate on a sleeve. This can be rubber or photopolymer. (In the past, only rubber plates were used.) Some of the advantages of photopolymer plates are that the plate can be created quickly and simply, they can be used for a large number of copies and they can be used multiple times. It is important to note that – depending on the print media – a wide variety of ink can be used during production.

Flexographic printing has become a crucial sector of packaging industry, and it can be used especially in case of materials that cannot be printed on or to a limited extent. Such materials are flexible stretch films, fibrous materials, paperboard, corrugated sheets, various types of plastic or aluminum. Typical products of high quality prepared with flexographic printing are corrugated cardboard boxes, plastic shopping bags, self-adhesive labels, napkins but also envelopes, gift wrapping papers and wallpapers.

The scope of printable materials is also diverse as it can be paper, cardboard, corrugated sheet, plastic or aluminum foil.

One of the most common joining technologies is gluing, which is almost as old as humankind itself. We have records from the dawn of history of egg white used as glue, but for example sealing wax was used to seal documents. However, with the emergence of synthetic materials, usage on an industrial scale also became possible.

The most important questions of adhesive technology:

What makes and why do adhesives stick? What are the conditions to be able to use a material as an adhesive? What are the properties of an adhesive that can be used to glue a pair of materials?

The adhesive creates a bridge between components made from identical or different materials. Adhesive joints can be used between metals, materials of metallic and non-metallic structure of identical or different quality and in case of other materials (e.g. plastics, textiles, etc.). The bonding mechanism depends on adhesion, that is the adhesion of the adhesive to the work piece, and on the internal strength and cohesion of the adhesive. There is no efficient gluing without an appropriate adhesive.

The fundamental condition for a good bonding strength to form is the wetting of the material to be glued by the adhesive (which assumes the liquid state of the adhesive), and the fixing of interactions as a result of the wetting, that is the solidification of bonds. Adhesives join the surfaces of solid materials with adhesion and with their own solidity without significantly changing the structures and original properties of materials joined. If materials are joined in three dimensions (e.g. plywood), we talk about binding agents.

The process of gluing can be divided into several steps. First step is the appropriate preparation of surfaces to be joined and the application of adhesive. The second sub-process is joining, which is the connection of the surfaces of materials intended to be joined, according to the instruction manual or to process specifications. The last step is solidification, during which the adhesive becomes solid. The strength of adhesive joints is determined by the internal solidity of materials to be glued (cohesion), by the internal strength of the adhesive layer and by forces on the adhesive side (adhesion). In a good adhesive joint, these forces are identical.

In case of adhesives, adhesive technology makes a distinction between natural (modified) materials, such as adhesives of vegetable, animal (that is adhesives made from their building materials or products) or mineral origin and synthetic adhesives. It is worth noting sealants that are identical with adhesives from a chemical aspect, and the field of adhesive technology also includes adhesion primers.

Rarely happens that a very technical topic, such as adhesive technology gets the attention of filmmakers and moviegoers. This is exactly what happened in 1997, when the American comedy Romy and Michele’s High School Reunion was presented to the public.

The story revolves around the white lie of two friends, Romy (Mira Sorvino) and Michele (Lisa Kudrow) from the title, who are unsuccessful since their high school years: the two blondes come up with the idea to pose at the high school reunion as the inventors of Post-it Notes. But really, who invented the product in real life?

Two colleagues of 3M take the credit: Arthur Fry wanted to paste a church hymn on a wall in a way so that the paper containing the hymn would not be damaged after removing the gluing but would not even fall to the ground until then. His co-inventor, Spencer Silver, engineer, was developing adhesives at the company. In 1968, they combined the two ideas (a piece of paper + sticking), and the world got to know the typically yellow-colored notes in 1979. The solution was considered to be revolutionary in its field because the adhesion did not leave a mark and Post-it Notes proved to be reusable.

It is interesting to note that the product could have been world-famous in 1977, however, consumers did not get hooked, but two years later, during its re-introduction, 3M supported the journey of the whole new adhesive paper with a massive advertising campaign.

Since then, Post-it Notes have become one of the symbols of office life, while the 1997 movie has become iconic in the last two decades. The immortality of 3M’s product is proven by the fact that the use of virtual Post-it Notes in the digital world, on computers has also become widespread.

Flanker has become the partner of flexographic printing companies and enterprises since the beginning. But where does this process come from historically? In order to get to know the answer, we have to jump back to the beginning of the story, to the 19^th century.

The name of flexographic printing , which is one of the types of letterpress printing, comes from the flexible printing form, where the flexible printing plate needed for printing is fixed to cylinder walls of various circumference. Due to this, it is possible to print on several types of surface, such as paper, plastic, metal.

Due to the flexibility, everything started with rubber printing forms, the patent of which was registered in 1853, and the first press with this method was put into operation by Bibby, Baron & Sons, an American enterprise producing paper bags, in 1890.

In 1905,  a French company, C. A. Holweg presented a new technological innovation: they used synthetic aniline dye for flexographic printing, which proved to be more efficient than the previously used substance of dye and sugar. Due to the paint that dried very quickly, the continuous operation of printing houses and the use of rotary presses started to spread.

The so-called “do it yourself!” movement lasted from the turn of the century to around 1935, when printers experimented with the assembly of their flexographic presses – however, the ink dispensing mechanism was not yet perfect, and the splattering of ink caused uneven quality and dangerous situations. There was no instrument to check ink circulation and printing presses did not have protection against splatter at all.

New papers of various characteristics emerged: grease-, water- and alkali-proof papers. These made it possible to pack products that were not possible to pack before, such as meat and soap, and it increased the surfaces available to flexographic printing.

In the 1920s, Germany and France invested into research and started to use new materials for the printing forms, such as phenolic plastic and natural rubber, while synthetic rubber was introduced in 1932, when the majority of flexographic printing presses manufactured was sold in Germany. The process was called “gummidruck” and this name is still used today.

Cellophane has been introduced in this period by DuPont and it was the first non-absorbent package on the market. Printers ended the use of water-based inks because aniline dyes better adhered to surfaces, thus improving printing quality. Aniline inks still raised a huge problem: aniline is a toxic substance and gummidruck was mainly used for printing on food packaging. In the 1940s, the American FDA (Food and Drugs Administration) prohibited the use of aniline ink for food packaging. This step caused a huge downturn in the market demand.

Flexographic printing has continuously kept losing popularity until 1949, when a safe and non-toxic ink was permitted to use for printing. However, the new permission by FDA did not help flexographic printing to become popular again. Printers realized that customers need a new name instead of gummidruck so that it does not remind people of the inks previously considered to be toxic. After the public opinion polling in 1951 by Franklin Moss, president of Mosstype Corporation, the process received several possible names, and “flexographic” was the most popular of all. Eventually, at an industry consultation in 1952, it was decided to use the name “flexography”.

By the way, by the 1950s, aniline colorants were replaced by pigments and other more advanced colorants, while the quality of printing forms also improved. In 1953, the first flexographic printing press with central cylinder was introduced. Within a few years, the quality of flexographic printing further improved due to the use of new dyes completely replacing aniline and suitable to use with plastic print media.

In the 1990s, the quality of flexographic printing further improved due to the use of photopolymer printing plates, up-do-date drying methods and more innovative inks of various types. The use of digital plates has also increased the quality of the final printed image.