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FLEXO PRINTING TECHNIQUE
 
Flexography  (flexo for short)  Printing is a printing technique made with a flexible printing plate. Flexo printing, like letterpress printing, is a high-pressure technique. In this press, the work to be printed is at a certain height from the body of the mold. Since the mold (cliché) is flexible, it can be bent easily. In this printing technique, the mold is mounted on the mold cylinder (with double-sided tape). The ink reservoir delivers the ink to the Anilox roller. The anilox roller contacts the high parts and the high parts receive ink. The image is transferred onto the printing substrate passing between the mold cylinder and the printing cylinder.

In Flexo Printing, printing is done directly on the substrate material with flexible printing molds. Therefore, 'Flexo Printing' is a direct printing technique.
Flexo printing, like letterpress printing, is a branch of the high-pressure system.
Flexo printing, which is an improved version of letterpress printing, is the most widely used printing technique in packaging printing.
Flexo printing machines are (mostly) 'ROTATIVE' and they print on plastic film in coil form. It is also preferred for printing on uneven surfaces such as cardboard, kraft, corrugated cardboard (box).

1.1. INKS USED IN FLEXO PRINTING
The inks used in flexo printing are analine type or rotogravure inks with low viscosity and are volatile and quick-drying due to the solvents added.
Alcohol-based inks have better color intensity and faster drying speed. Its disadvantage is that it is harmful to the health of employees due to the smell it emits and the employees breathing the solvent.
If water-based inks are used, drying ovens must be included in the printing. However, there is a decrease in color intensity of such printing inks. It is easier to clean from the hoppers.
In flexo printing, foam is formed as the anilox roller constantly rotates in the ink chamber. To prevent this problem, 'FOAM BREAKER' should be added to flexo inks.

1.2. SUBSTRATE MATERIALS USED IN FLEXO PRINTING
With flexo printing, it can be applied to uneven surfaces such as cardboard, kraft, corrugated cardboard, and flexible plastic films such as CPP, MOPP, BOPP, PET (Polyester), PE (Polyethylene) (LDPE -HDPE), PVC (Polyvinyl Chloride), which form flexible packages, and special Printing is done on aluminum foil using inks.
It is important to ensure that plastic films are corona treated before printing. In cases where corona is absent or insufficient, corona application must be made to ensure that the ink adheres.

1.3. ANILOX ROLLER
Anilox roller, whose main feature is the adjustment of the thickness (amount) of the ink layer, is a ceramic-coated roller in plasma state that is engraved with a laser. Because ceramics are very strong against wear.
Anilox rollers are not mandatory for flexo printing, but in the absence of anilox, there should be 2-3 rollers that will perform the function of anilox. In other words, anilox alone performs the work of 2-3 rollers. Therefore, in addition to flexo printing, anilox is also used in the varnishing unit of offset machines.

1.4. SCREEN ANGLES IN FLEXO PRINTING
Since the texture on anilox rollers is generally 60°, the angles to be used in flexo printing are therefore used by turning 7.5°. Since the yellow color is a light tone, its color cannot be perceived by the eye.

1.5. VISCOSITY OF FLEXO INK
Since flexo inks contain solvents, the ink film dries quickly as the solvents evaporate. If flexo inks lose solvent, the inks become less permanent and their viscosity increases. If the viscosity changes, there will be a difference in the amount of ink transferred to the plate. As the viscosity increases, the amount of ink transferred also increases. Excess ink overfills the cells in the anilox rollers.

The same situation, that is, the increase in the amount of transferred ink, also occurs as the printing speed of the machine increases. In this regard, ink viscosity must be balanced with printing speed. If the printing speed is to be increased, the ink viscosity must be reduced accordingly. Ink viscosity should be balanced according to printing speed.

Viscosity value according to ford cup4;

For corrugations: 20″ – 25″(seconds)
On other cartons: 30″ – 45″(seconds)
These values ​​vary depending on machine conditions.
Viscosity in case of alcohol-based ink: 14″ – 18″
Viscosity in case of water-based ink: 16″ – 24″

CONTROL IN FLEXO PRINTING
In flexo printing, Print Control is carried out via the monitor.

FEATURES THAT DISTINGUISH THE FLEXO PRINTING SYSTEM FROM OTHER PRINTING SYSTEMS
The features that distinguish flexo printing from other high-pressure printing systems are the use of very low viscosity, water and solvent-based inks suitable for rapid drying depending on the material to be printed, and the ability to make the first and last prints at the same quality between 1 and 5 million times thanks to rubber and photopolymer plates. Because only a soft surface plate can produce results on rough surface printing materials.

The most important advantages of the system compared to other systems are that it provides problem-free printing on a wide variety of surfaces thanks to water- and solvent-based, quickly evaporating inks. Another advantage is that the thin-structured fluid ink does not need to be crushed or softened. In flexo printing, transitional intermediate tones are obtained by changing the size and size of the dot.

COMPARISON OF FLEXO AND LETTER PRINTING SYSTEMS
Flexo printing, like letterpress printing, is a high-pressure technique. Flexo printing has differences from letterpress printing:

 The materials used in flexo printing technique are rubber (polymer) and rubber based.
Flexo printing plates can produce several million prints.
Flexo printing technique is generally preferred for packaging printing (on plastic film).
Flexo printing inks are water or solvent based, high fluidity, and dry by absorption or evaporation.
Flexo printing is done from roll to roll.
Flexo printing is high speed.

ADVANTAGES OF FLEXO PRINTING
Flexo gives good printing color consistency.
 Flexo prints generally require fewer operators than offset or gravure prints.
Good water-based inks can be prepared.
Flexo printing is good on rough surfaces.
 Flexo printing offers a wide range of substrates, including low weight papers.
If the molded cylinder is ready, the preparation can be done very quickly.
There is less waste in flexo.
Water-based and UV-curable flexo inks greatly reduce environmental problems.
In flexo printing, large surfaces are obtained without gaps.
Flexo technology continues to increase quality and efficiency.
Flexo printing is faster than sheet offset printing.
Flexo printing machines are much cheaper than sheet offset.
Since flexo printing machines are multi-colored (6-8-10), they allow the use of more extra colors.
It is especially preferred in packaging printing.

DISADVANTAGES OF FLEXO PRINTING
Can be easily installed on low relief moldings, dusty or dirty.
Required press pressure control is essential.
 Highlights tend to disappear and shadows tend to fill in.
Point size edges in easing are troublesome, especially 1% and 2% points.
Flexo speeds are generally less than gravure or web offset.
Preparing the molds is a long procedure.

FLEXO PRINTING TERMS
Anilox Roller :  Screen  roller Photopolymer
: Main  material  of  plastic  plate​  ​General name for melts (liquid fluid) such as UVC Exposure:  The light source with the lowest wavelength used for plate exposure in flexo printing.

Source: Istanbul University – Printing Techniques