One of the key tasks when printing with a flexo machine is performed by anilox - shaft, due to which the ink is distributed according to the target form of printing. Despite the outwardly simple device, this element is characterized by a complex principle of operation, the nuances of which are determined by the properties of its surface. Today, the anilox shaft is available in different versions, improving not only in structural, but also in functional qualities.
Anilox Functions
The purpose of the shaft is one thing - to evenly transfer the paint layer in the right volume with a calibrated dosage. An important characteristic of this process is the exposure of the parameters of the layer so that the paint does not stick together at the junction points and does not spread out due to redundancy. In modern printing equipment, the sufficiency of the volume used when applying to the form of ink is determined by the optical density, which is calculated by standard measurement methods. The optimal ratio is 1.55, which allows for high-quality reproduction of the full tone range with the necessary contrast.
Construction and materials
As the name implies, the part has a cylindrical shape, which can be hollow or monolithic. A feature of the shaft is a cellular coating with honeycombs with a diameter of 2 to 25 microns on average. Today, special coatings are sometimes used to create anilox working surfaces, sometimes performed using the laser engraving technique. As for the materials of manufacture, the first aniloxes were rubber, after which they were replaced by metal analogues with a chrome coating. Some modifications also use copper plating, and a thin layer of nickel is used to protect chrome surfaces. In any case, the presence of a porous structure on the surface is an important condition for the construction of the anilox shaft.
To prevent rapid cell wear, many manufacturers are experimenting with spraying compounds. In the competition, technologists from different companies strive to meet two requirements - the minimum layer thickness and high dynamic wear resistance, which implies protection against corrosion and accidental mechanical damage.
Varieties of anilox
The main differences between different types of modern anilox shaft are in the method of engraving the surface. At the basic level, one can distinguish the mechanical method of forming tetrahedral cells (clichograph) and laser models of the formation of hexagonal cells.
The use of tetrahedral pores due to the characteristic shape of the cells does not allow for an increased ink transfer. In turn, hexagonal cells not only provide bulk ink transfer, but also allow you to maintain a higher process speed. In many ways, this difference is caused by the coatings of the raster shaft of two types. The same chrome is more often used in creating tetrahedral honeycombs, while ceramic aniloxes are formed using laser engraving. At the same time, it cannot be said that the hexagonal configuration is definitely more profitable in all cases. Depending on the characteristics of a particular model, the properties of absorbency, hardness and tension on the surface may change, which also affects the quality of the final print result.
Anilox lineature
The number of cells per square inch (12 lines, i.e. 2.54 cm) depends on this indicator. Usually it is calculated taking into account the angle of inclination of the cells relative to the axis of the cylinder. On average, it varies from 30 ° to 60 °. Designs with a low index of lineature are more often used for varnishing and working with die printing. The average range of lineature ranging from 165 to 300 lpi, as a rule, is used in shafts with coatings, the cell volume of which is about 12 cm 3 / m 2 . For combined flexographic printing, it is appropriate to use a high lineature of up to 1200 lpi, at which the cell volume will be 3 cm 3 / m 2 . As this indicator builds up, the uniformity of the paint coating also increases. The more honeycombs, the better the ink transfer will be, although this rule is only observed if the shaft area corresponds to the print form, and the correct calculation of the cell parameters on the working area was initially performed.
Anilox cell volume
This value will depend on the useful capacity per unit area of the working surface of the shaft. Usually for numerical representations, the cm 3 / m 2 ratio is used, although specialists often use BCM specification markings. It is important to consider that the cell volume can increase not only due to expansion, but also by deepening. The higher the honeycomb capacity, the richer the color and the thicker the varnish layer - the die density also increases proportionally. On the other hand, a decrease in volume leads to an increase in the efficiency of printing and an improvement in its quality. During operation of the flexographic machine, the cell volume will be reduced. This is a natural process due to wear of the coating, clogging of the cells with dirt, the appearance of defects, etc. To date, the following standardized cell sizes are used:
- 5.4 cm 3 / m 2 - used to work in vector design.
- 3.4 cm 3 / m 2 - used in combination printing.
- 2.3 cm 3 / m 2 is the most advantageous format for process printing.
Many experts believe that it is better for the user to calculate the anilox precisely by the volume of cells, since it affects the result of the printing process to a greater extent. Despite the relationship between print quality and the lineature, it does not always give an accurate idea of the optimal ink transfer formats, requiring consideration of many indirect parameters. Actually, the manufacturers themselves are guided by the principle of evaluating a suitable anilox shaft for a flexo machine by the capacity of the coating cells, trying to diversify the size ranges of honeycombs on the working surface.
Printing defects using anilox
The improper use of the shafts of moisturizing and colorful machines often leads to the formation of imprint defects. The most common defects of this kind include:
- Frying. The appearance of pronounced areas where the ink is perceived in the same way as printed fragments. This defect indicates an insufficiently effective operation of humidification. Problem areas are found in the center or along the edges of the form.
- Shadowing. Weak background regarding uniform distribution of ink over the entire print area. Among the reasons for the formation of shadows, there are violations in the shaft settings.
- Rinsing. Leaving dark or light streaks, which may be due to excessive contamination of the shaft surface or irregularities in the adjustment of the ink supply.
- Paint transfer defects. Improper ink distribution during flexographic printing can cause gloss, barrel-forming, or even surface damage.
- Patterning. This defect is known as ghosting. Rollers that are not adjusted correctly may cause duplication when printing.
Anilox shaft care
Since the flexo machine’s workflow involves many consumables in the form of moisturizing liquids, dyes, solvents, and other chemicals, the functional surfaces become clogged over time and require cleaning. Surface cleaning can not only reduce the risk of print defects, but also extend the life of the shaft. The simplest care products include washing procedures using soft non-abrasive brushes and chemical solutions.
Specialized Anilox Cleaning Methods
In professional operation, cleaning of anilox rolls is regularly performed using ultrasonic and laser methods. The first method involves the supply of ultrasonic waves in order to achieve the effect of cavitation, in which the smallest gas bubbles destroy foreign particles on the surface, but use this method with extreme caution, since excessive power of the wave supply can damage the cell structure. Laser cleaning is carried out with the help of special optical devices that provide sharp heating with strong fluctuations on the shaft cover. In this way, even shafts with a high lineature on a ceramic coating can be cleaned without risk of damage.
New technologies
New trends in the industry of anilox production are associated with their structural optimization and increase of technical and operational parameters. In particular, lightweight modifications of rollers with plastic high-strength bases appear, spraying techniques with engraving are improved, and the resistance of surfaces to typical contaminants is increased. The use of laser technology in the manufacture of printing equipment expands its functionality. Already today, combined devices appear on the market that provide printing of dies and rasters with a high shutter speed when applying consumables.
Conclusion
Choosing the right anilox is not an easy task and requires a multilateral analysis of the planned workflow. It is necessary to take into account not only the printing characteristics as such, but also the working conditions, as this will reduce the cost of maintaining the device in the future. In selecting a design for its protective properties, the working temperature of the anilox shaft is calculated in advance, which can vary from +50 ° to +150 ° on average. The composition of chemical consumables is also taken into account, among which there may be alcohol-containing solutions, varnishes, flushing liquids with caustic soda, etc. All these data together make it possible to understand which type of anilox with its coating will be the most profitable acquisition in terms of operational and economic indicators.