The anilox roller is a key component in the anilox roller glazing device. Its function is to absorb the required amount of varnish and apply it to the glazing plate. The engraved part and absorption of the roller must be compatible with the varnish and substrate used. Specific cleaning procedures must be followed to ensure the best performance and reliability of the anilox roller.
The anilox roller is a product of the flexographic printing process. The word anilox itself indicates its origin (anil is aniline) because it was originally used to apply aniline-based flexo inks. During the transition period, the anilox rolls developed into highly technically complex components. KBA ’s long-standing expertise in short-ink ink delivery means KBA is the only printing press manufacturer in the world with the technical know-how needed to manufacture anilox rolls within the company. Anilox rolls manufactured in KBA Division Boyle are mainly used for short ink paths without ink keys and water. The anilox rollers used in KBA's online glazing unit were provided by two professional manufacturers, Praxair Surface Technologies and Zecher.
Types of carved nets
The entire surface of an anilox roller is engraved. The classic carved mesh is composed of net holes. The previous concave parts were pyramidal and arranged like a chessboard. Later, a hexagonal shape having spherical concave portions arranged in a honeycomb pattern was adopted.
Although people currently choose closed structures such as hexagons to apply metallic pigment varnishes, in other applications, they have gradually turned to open structures. Today, years of experience have shown that hatching, or hatching like thread or line screens, is the most efficient structure. Although hatching has the advantage of preventing foam formation, problems can occur when the varnish pattern is more complicated, because centrifugal force drives the varnish to the edge of the roller along the groove. This shift in the application of varnish may cause ghosting. Of course, this may also be caused by improper wetting or insufficient varnish in the blade cavity. On the other hand, ghosting caused by irregular glazing can be eliminated by making the diameter of the anilox roller and the glazed plate cylinder 1: 1.5.
The latest type of engraved part of the pattern to be developed is cross-hatching. The pattern it generates is like a negative picture screen, but it is not composed of net holes or grooves, but is made of what can be called "grooved products" Composed of ingredients. Zecher uses the engraved part of the 90 ° cross to create a breakthrough in the shadow groove wall, leaving only long and slender traces. It has been found that the amount of varnish applied by this type of structure is not more than that of other structures, but the degree of dispersion of varnish is small, the centrifugal force is no longer a problem, and the varnish can be released more efficiently at high speed .
Praxair has further developed the cross-hatching by trimming the groove walls to form pyramidal "islands" or "pillars" under the name of the acronym ART (Reticulated Reverse Technology). Here, the two sets of hatched carved parts are also made at right angles to each other. If the angle of the cross-hatching is reduced to 75 °, the structure is twisted in one direction. Stretching the pillars will flatten them so that the entire surface of the roller is actually covered with varnish. Therefore, when transferred to the substrate, the varnish can be spread out in a shorter time. Although the engraved part is too flat and the varnish on the anilox roller is shallow, the varnish has been more or less pre-dispersed when the varnish is applied. Thin, so it can maintain its maximum thickness. This type of cross hatch is called the ART-TIF engraved part (thin ink film). It is used on an anilox rolls with high gloss varnish, which produces gloss levels that are 5 points higher than ART.
key parameter
On the anilox roller, the reproduction resolution of the anilox corresponds to the number of lines per cm or lines per inch (100 lines? Cm = 250 lines? Inches, 100 lines? Inches = 40 lines? Cm). The fineness is determined by the difference between the width of the mesh wall and the width of the opening (the diameter of the cell or trench in microns). This is referred to as the ratio of mesh holes to mesh walls, and usually varies from 1: 8 (fine) to 1:25 (rough). In the engraving part of ART and TIF, the interval of the pyramid and the side length of the pyramid are measured.
The angle of the best reticulated pattern formed with the axis of the drum is 60 ° for hexagonal and hatched reticulated patterns. The angle is 45 ° for ART and TIF, and TIF has an additional twist of 75 °.
The finer the texture, the shallower the depth of the engraved part (in microns), so the absorption (in cubic centimeters? Square meters, or BCM; 1 cubic centimeter? Square meters = 0.645BCM; 1BCM = 1.55 cubic centimeters Square meters). Absorption cannot be calculated for ART and ART-TIF textures. The smaller the amount of absorption, the smaller the amount of wet varnish (in cubic centimeters? Square meters) actually applied. The degree to which the glazing oil is emptied by each structure depends partly on the shape of the structure and the roughness of the mesh wall, and partly on the surface tension of the material used to make the glazing plate. The actual amount applied to the substrate also depends on how the glazing oil film splits on the glazing plate. It is estimated from experience that about one-quarter to one-third of the varnish (and thus the absorption) on the roller will be transferred to the substrate.
Because the density of the low-viscosity varnish (about 1 gram? Cubic centimeter) is similar to the density of water, the amount (volume) applied in the wet state is the same as the quantity applied in the wet state (unit: grams? Therefore, in practice, the anilox roller is often referred to as "6 g" roller, "12 g" roller, etc.
If the amount of varnish applied to the substrate is small, it can be concluded that the varnish layer will be thinner. This is called the layer thickness index. It is based on the depth of the engraving (in microns) divided by the absorption (in cubic centimeters? Square meters). The conflict caused by the unit of measurement is solved by deleting the unit of measurement in the index. As the name implies, the engraved part of the thin ink film has the lowest index value (1.3), followed by ART (1.8). Other textures are between 2.5 and 3.5, depending on the laser used.
Choose the correct type of anilox roller
The amount of varnish transferred by the anilox roller is constant and it is uniform across the width of the web. The total amount applied can only be changed by replacing the rollers, and it is not possible to measure the zones. Therefore, when production requires the application of different varnishes, it is essential that the anilox roller selected has the anilox and absorption capacity that is most suitable for the varnish and substrate used by the job.
It is not just the amount of varnish delivered that is affected by the texture structure: where pigment varnish is used, the mesh holes, grooves, or columnar voids must also be large enough to accommodate the pigment particles. The size of metallic pigments is between 7-17 microns, interference pigments (such as Merkel's single flake-shaped or encapsulated pearl-shaped Iriodin (pearl pigment)) and scented capsules can be between 5 and 200 microns in size, The exact size depends on its specifications. By comparison, the pigments in standard printing inks are only 1-3 microns. Even if the mesh holes and grooves are large enough, not all pigment particles can disappear in them: the remaining particles will be pressed against the mesh wall by the scraper, thereby accelerating the surface wear. This is one reason why pearlescent varnishes should be applied with ART rollers.
Most printing plants usually use multiple anilox rollers. To avoid confusion, the anilox data must be easily identifiable. Therefore, anilox rolls should be stored in containers or on shelves along with their technical specifications. If in doubt, it is best to check the roller with a volume meter.
Unfortunately, many anilox rolls are still using non-standard markings made on the steel end faces by stamping or vibration etching. When the roller is mounted on a printing press, this mark has the disadvantage of being difficult to read. For some time, Praxair's standard and custom anilox rollers have an ID (identification) bar, so that even if the roller is installed on the glazing device, you can read the roller information at a glance. The ID bar is different according to the size of the roller and the customer's requirements, and is engraved on the outside of the net structure on the edge of the cylindrical surface. These data are computer generated and sculpted on the ceramic surface together with the net structure. The identification strip is as wear-resistant as the engraved surface.
Quality of surface and engraved parts
The surface of the anilox roll includes a ceramic layer in which the anilox structure is laser-engraved. Ceramics are particularly hard and wear-resistant. The ceramic layer should also be firmly bonded to the metal roller body to protect the roller body from corrosion. The layer should be free of foreign particles and can be engraved with high quality by laser. But its most important quality is low porosity, so the surface must be completely smooth and sealed. The smoother the surface, the lower its interfacial tension relative to the varnish. The lower the interfacial tension, the easier it is to clear the varnish in the mesh during the transmission and cleaning of the varnish. Praxair guarantees that the surface micropores (pinholes) of the company's rollers do not exceed 3%. Even with ART and TIF reticulation, the effects of these pinholes are negligible.
Clean up
The anilox engraved on advanced anilox rollers has very smooth anilox walls, so it is less prone to contamination than their predecessors. ART and TIF rollers are especially easy to clean. Nevertheless, it is still important to clean them immediately after use and to clean them thoroughly through regular maintenance. After the printing is completed, the anilox roller is cleaned online with a varnish supply system, so that the anilox roller can be kept in the scraper cavity. When performing maintenance, it must be removed from the device. One of KBA ’s competitors ’roll libraries related to the anilox rolls of the varnishing device does not comply with KBA ’s principle of easy maintenance (and identification) of rolls.
A variety of processing methods can be used to clean the rollers outside the printing press, and care should be taken when using these methods. The manufacturer's instructions should be strictly followed!
Chemical cleaners are more or less aggressive. Now also provides biodegradable products. The greater the aggressiveness of the cleaning agent, the greater its aggressiveness to the roller surface, and the greater the risk of corrosion. Many printers conduct aggressive deep cleaning once a week, with proper compliance with health and safety related precautions.
Traditional mechanical cleaning uses steel brushes. The disadvantage of this method is that all net holes cannot be cleaned 100% effectively, and the wall of the net may be damaged.
Media jetting is a more effective method. Sodium bicarbonate and plastic beads are relatively mild, and solid carbon dioxide (dry ice) is more effective, but may also be more aggressive.
Ultrasound is another method, although it is more expensive than medium jetting. KBA can provide an ultrasound system, or as an alternative you can rent CleanMobil hourly from Zecher. If used properly, the device is very effective, but if it is out of control, its strength may damage the ceramic. The laser cleaning method uses a relatively weak laser beam to evaporate the varnish residue. The thoroughness of cleaning depends on the length of time the laser acts on the roller.
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