Anilox roller

Roller cup

The anilox roller or anilox roller in the short inking unit - as it is used in the printing industry, for example in flexographic printing , offset newspaper printing or waterless offset printing - is of central importance for the constant and homogeneous dosage of the amount of ink during the printing process. It is the "heart" of the anilox short inking unit and, particularly in the flexographic printing inking unit, the "core element" when the printing ink is transferred to the printing plate surface.

History and Development

A historically based description of the first appearance of the rollers is not possible. Sources from relevant specialist literature say that the English-language expression “anilox roll” comes from the so-called anilox inks, which were already used in the 19th century for printing wallpaper. What is certain is that the first metal rollers were used as early as the late 1930s in order to achieve a homogeneous application of ink on the corresponding substrate.

However, the resulting aniline impression was only able to have a real impact on the production of the anilox rollers towards the end of the Second World War. Further developments in the field of coloring systems can only be traced back in the 1970s.

The introduction of dimensionally stable printing forms made it possible to produce fine screens in flexographic printing. The ink transport via metal rollers was optimized by mechanically engraved anilox rollers made of copper and chrome . Now it was possible to print screen rulings of up to 48 lines per centimeter (L / cm). The halftone printing, which was increasing at this time, required more sensitive inking systems in order to be able to achieve targeted color applications. Anilox rollers were a good solution for this. The paint was supplied by dip roller systems. Excess paint was dosed by nip rollers. The disadvantage of the process was the high dot gain. As an alternative to the squeegee roller, inking systems were used, which were equipped with doctor blades for the exact dosage of the printing inks. The initially rotating squeegee (positive, <90 °) was improved by counter-rotating squeegee (negative,> 90 °) due to the high tone value increases. This type of squeegee applied more efficient ink transfer.

In the 1980s, developments in the area of ink supply by chamber doctor blade units could be advanced. The closed system had the advantage of transferring ink at much higher printing speeds without changes in viscosity.

Developments on the roller surface led to the fact that the chrome roller used up to now, with which screen finenesses of up to 200 L / cm could be produced, was replaced by a ceramic roller. Up until now, the engraving was done mechanically. Due to the higher porosity and surface hardness of the chromium oxide ceramic layer, laser engraving was necessary to create cells. The lasers used for the engraving of cells on the ceramic anilox roller differ in their focal points, which lead to a more or less fine cell engraving. In addition to developments on the surface of the ceramic layer, the introduction of sleeves should enable a quick job change. This often brings about a change in the ink coverage of the printing units and the ink volumes to be dosed from the anilox roller. It was therefore obvious to also design anilox rollers as exchangeable sleeves.

Task and function of the anilox roller

Flexographic printing principle

The anilox roller is part of a printing inking unit. It is the storage medium that is supposed to provide a necessary and defined amount of ink constantly during the printing process. On the surface of the roll, which consists of ceramic or chromium, are tiny and uniform wells or cells (domes), and sometimes also the basis of various lines (Haschur) engraving method to engrave. The non-recessed areas are called webs, the recesses are usually called pans.

The paint is usually applied using a chambered doctor blade system. But also immersion roller systems with two or three rollers and rinsing with color cartridges are in use. With the help of a counter-rotating squeegee (more rarely with squeeze pressure), the anilox roller surface, i.e. the webs, is freed from protruding ink. Thus, a defined and thus controllable amount of color remains only in the depressions. The anilox roller transfers the printing ink to the next roller or, as in flexographic printing, directly to the cliché, in that the depressions are always emptied evenly. However, the emptying is never complete, with every rotation of the roller inside the cells there is a flush of paint. The inking unit is supplied with a defined and reproducible volume of ink due to the rotation of the anilox roller and the associated uniform ink absorption and removal.

The decisive parameters for the amount of ink transferred are the shape of the cells, their geometry , the opening and the material components of the anilox roller itself.

construction

The main body consists of steel , aluminum or fiber-reinforced plastic. According to the type of roller surface, a distinction is made between two rollers, the chrome screen roller and the ceramic screen roller.

Anilox roller types

According to the current status, a distinction is made between two rollers. These are characterized by their respective surface layer. This can be made of chrome or ceramic .

Chrome anilox rollers

The original design of the anilox roller was the chrome anilox roller. The roller blank consists of steel or stainless steel on which a copper layer is galvanized. After the engraving, a protective chrome plating is galvanically applied to increase the wear resistance. The name chrome anilox roller refers to the outermost protective layer.

Chrome anilox rollers have proven themselves for decades in printing units with a 3-roller system for squeezing. In the case of printing units with a doctor blade, on the other hand, wear is quite high and the service life is therefore short. Screen widths of up to 200 lines / cm are possible. When it comes to dosing and transferring, the engraving is an important factor for the chrome roller volume to be produced, so this engraving should be carried out precisely. The roller is then chrome-plated, which serves as wear protection. The production of the cells on the chrome screen roller is done mechanically by means of Molette, electronic hammering with a diamond, or by etching. While the chrome anilox roller achieves a high volume of the cells and is considered to be very wear-resistant in terms of the ink transfer properties, it has a short service life of six months to one year.

Since this design was not optimal, work was done on the roller surface, which led to the fact that in 1980 the first ceramic anilox roller was available, which offered a higher surface hardness and thus a longer service life. The disadvantage is the higher price compared to the chrome roller.

Ceramic anilox rollers

The chrome oxide ceramic layer is applied to the roller surface in a thermal coating process, the plasma coating. A high-speed plasma jet melts metallic and non-metallic materials. The cells are produced on the ceramic anilox roller using a laser process. The lasers used are [[CO ₂ laser]], YAG lasers and fiber lasers.

Due to the homogeneous layer structure of the roller, exact engraving is possible, which in turn has advantages for the emptying and refilling behavior of the rollers. Initially, a Co ₂ laser was used to produce cells. The mode of operation of the laser leads to the melting of the ceramic layer when the laser beam arrives. A crater rim is created, which becomes higher and higher when the process is repeated, thus creating a ridge.

The advantages of the CO ₂ laser are the creation of a closed surface, low pollution and homogeneous coloring. The disadvantage is the production of coarse, unclean cells. In order to be able to produce even finer engravings for controlled color applications, a YAG laser has been used since the late 1990s, which makes it possible to engrave screen finenesses of up to 500 L / cm. The cup is engraved by evaporating the material. The advantages of the YAG laser are the creation of clear contours, capillary surfaces and stable color transfer.

Since the YAG technology has some disadvantages, such as rapid contamination and wide webs, resulting from the remelting of the ceramic layer, the fiber laser has also been used since 2002, another solid-state laser that through its high intensity at the focal point can produce particularly fine cells. The laser beams correspond to a Gaussian-shaped energy distribution, have a high beam quality and therefore lead to the highest grid fineness. The advantages of the fiber laser compared to the YAG laser are a geometrical and uniform aesthetics of the cells, smooth bowl walls that lead to improved wear behavior, low energy consumption, a compact design and high efficiency. The disadvantage is the four times higher price compared to the CO ₂ laser and the limitation that not all materials can be removed. The appropriate laser process is selected depending on how the engraving is produced.

The use of the ceramic anilox roller is 99.99% for printing UV inks, solvent inks and water-based inks in the flexographic printing process, whereas the chrome anilox roller is mainly to be found in coating plants, as it can achieve a higher volume due to the smaller number of cells. Ceramic anilox rollers are highly wear-resistant and are used wherever precise ink transfer is required over a long period of time. The roller blank is usually made of steel or, in a lightweight construction, aluminum or carbon fiber (see also sleeve technology in flexographic printing) .

The ceramic based on chromium oxide (Cr ₂ O ₃ ) is applied to the surface using a plasma coating process. Due to the high particle speed, there is no need for an adhesive layer between the base body and the chromium oxide ceramic, and the density and adhesive strength are very high. However, some manufacturers use a Ni-Chromium carrier layer when the longevity and temperature of the ceramic anilox roller are high. After the plasma coating, fine processing is carried out by grinding or lapping, then the desired grid is engraved using laser engraving. The surface energy of the ceramic is also decisive for the color release behavior. The color release is positively influenced by certain manufacturers through certain surface finishing processes.

High screen rulings of up to 600 lines / cm can be achieved.

Engraving specifications

Types of engraving

Ruling - screen width

In addition to the shape and depth, the number of cells determines the volume. These are counted in a row on a certain route. The reference distance is 1 cm, so that the dimensions are given in lines per cm (lines / cm). Lines per inch (L / inch) is the measurement in the Anglo-Saxon system of measurements, which can be converted to L / cm. This corresponds to the ruling or grid width .

The conversion is: 100 L / cm = 254 L / inch or 1 L / cm = 2.54 L / inch. In addition to the number, the distance between the cells can also be determined. The grid width provides information about the distance between the depressions. The number and spacing of the cells thus result in the ruling. Counting is in the angular position. In addition to the number, the ruling can also be used to specify the width of the cells, thus determining the fineness of the ruling. The usual screen fineness of the chrome anilox roller is a maximum of 200 L / cm and can achieve a higher volume than ceramic anilox rollers. The screen fineness of the ceramic anilox roller is 500 to 600 L / cm. The development tends towards higher screen rulings, but they have so far been of no use in practical application.

Cup

As already described, cells of the same shape and depth are engraved into the roller surface. You determine how much paint can be absorbed and released again.

Engraving depth

The engraving depth is measured in micrometers ( µm ). The engraving depth determines the size of the possible cup volume. An engraving can be deep, but due to the shape and size of the cup it can still have the same theoretical volume as a flat engraving.

Flank angle

The flank angle is specified in degrees ( ° ). The flank angle is the angle between the legs of a pyramid. The flatter the engraving, the larger the flank angle. A steep flank angle results in better emptying and can therefore offer a higher volume. By varying the flank angle with the same grid width and engraving depth, the volume is specifically influenced.

angle

Engraving angle

The engraving angle is given in degrees ( ° ).

The engraving angle is calculated as the angular position to the roller axis, the angular position is recognized when viewed from above. There are four engraving angles in use, because only square or hexagonal geometries can be accommodated closed on an anilox roller. Usually you can

Square shapes: 90 ° and 45 ° angles
Hexagonal shapes: 30 ° and 60 ° angles can be distinguished.

When using a doctor blade, angles of 45 ° and 60 ° have a clear advantage, because the point is to the roller axis. The squeegee is continuously supported and the tip position allows the cells to be gently filled and emptied during rotation.

The angular position of the cells is another important indicator of the volume of the cells to be produced. It is indicated facing the roller axis and shows either square (orthogonal 0 ° / 45 ° angle) or hexagonal shapes (hexagonal 30 ° / 60 °) without spaces. Due to the high packing density at the 60 ° angled position, a homogeneous paint application and high paint application can take place. Hence, it is most widely used. However, this knowledge creates a need for discussion in the area of the anilox roller. The 45 ° angle results in a higher paint application and the 60 ° angle results in a more constant color transfer. When transferring paint, glue and glue, on the other hand, the 45 ° angle is more likely to be used. Investigations have shown that after finishing (polishing of the surface) the emptying behavior of the cups is constant at the 60 ° angle. In contrast, the 45 ° angular position has a reduced volume from 40% to 29%. This can be explained by the fact that the finish makes the bar surfaces smoother and the bar portions larger.

web

The necessary squeegee support when wiping off the paint is ensured by the web. It therefore has a wide range of influences on ink transfer and squeegee behavior. The web width and the opening width of the cells together give the cell width. The web can be present at the crossing points of the cells (pointed web) or sag by a percentage. It can also be broken up (communicating cells). Ultimately, it was recognized that a hundred percent delimitation of the cup and squeegee support ensures the best paint application.

Cell opening

The opening of the cells represents the contact surface of the cells with the cliché. The larger this is, the more homogeneously the cliché can be colored. The web width and the opening width are in relation to one another, the cup / web ratio. An engraving that contains 200 L / cm has a cell width of 200 micrometers. If the web width is 100 micrometers wide and the opening width is also 100 micrometers, the ratio is 1: 1. It becomes clear that the broad web is not responsible for the coloring. The color must be distributed to the right and left from the 100 micrometer wide opening on the cliché over a non-colored web width of 100 micrometers. The printed image is consequently porous and unsteady. Therefore, it can be seen that a minimum web width is optimal for calm coloring. In addition to the web width / opening width, the depth [μ] is a further indication of the emptying behavior of the cells.

In the Anglo-Saxon language area, there is a relationship between the shape of the depth / opening of the cups, but this information is contained in the ruling, cup / web ratio and depth.

Relationship cliché

Based on the knowledge that the anilox roller rulings were two to three times finer than the cliché in earlier times, inadequate coloring of the finest printing elements was accepted. Discoveries, driven by the DFTA, that even the smallest element finds a supporting web when the anilox roll is rolled over, led to the size of the smallest element being set equal to the size of a cell with a web. This led to the assumption that the number of lines on the anilox roller must be 5-6.5 times greater than the cliché. The smallest grid point of the cliché should always be larger than the grid cell on the roller. Otherwise, the raster point dips into the cell, absorbs too much ink and over-coloring of the raster point leads to printing difficulties, e.g. B. a moiré formation. For example, with a screen width of 48 L / cm of the cliché, the screen roller should have at least a 240 L / cm screen width.

Accordingly, high print quality is achieved through conformal transfer of color between the cliché and anilox roller. Depending on the area of application (flexible packaging, corrugated cardboard printing, label printing, etc.), the selection of the anilox roller should be carefully discussed with the supplier in order to adapt parameters such as printing ink, printing material and machine technology.

volume

Volume anilox roller

The volume is given in cubic centimeters per square meter ( cm³ / m² ) (corresponds to 1 μ), which is the most common. Further dimensions are called g / m², ml / m² and BCM = Bilion-Cubic-Micron (1 BCM = 1.55 cm³ / m²). If the anilox roller has more cells, a specific amount of ink can be transferred, which corresponds to a smaller scoop volume.

The volume describes the volume of the cells below the bridge. The volume specification is nevertheless a theoretical quantity and not identical to the actual emptying behavior of the cells. With different cell shapes, varying emptying can take place with the same grid width and volume. In addition, factors such as the rheological properties of the ink, surface tension, printing provision, speed, substrate, etc. have an influence on the actual volume of the anilox roller. Due to their geometry and distribution, the cells on the roller surface represent the scoop volume. They control how much liquid can be absorbed by the roller, transported to the cliché and released onto the surface again.

Cup shapes

The process of cell production for chrome and ceramic anilox rollers are different, due to different surface properties. Shapes with different properties in terms of volume and emptying behavior are created.

The chrome screen roller is made of shapes such as pointed pyramids, truncated pyramids and truncated pyramids with a steep flank and a wide base. While the pointed pyramid tends to be poorly emptied and to a higher risk of contamination, the truncated pyramid leads to an improved emptying. The truncated pyramid with a steep flank shows the best emptying and achieves the highest volume.

The cup shapes created on the ceramic roller are called pointed dome, dome and U-shape. The pointed dome has the worst emptying. It is also most prone to pollution. The cup-shaped dome shows better emptying behavior, so U-shape ensures optimal emptying. A high volume and an optimal contact between color and cliché are further advantages of this cup shape.

In summary, the parameters enable

Ruling [L / cm]
Depth [μ]
Angle [°]
Bar / cup ratio [1: x]
Volume [cm³ / m²]

to be able to make a description of the performance of the anilox roller.

Engraving process

Electronic / mechanical engraving

The conventional engraving methods relate exclusively to chrome rollers .

Moletting: With a Moulette - a knurling tool - on whose surface the engraving is prefabricated as a die, the engraving is embossed into the copper layer or directly into the steel. This is followed by the protective chrome plating.
Electronically carved engraving: With a diamond stylus, corresponding to the desired pyramid shape, cells are carved in very specifically via an electronic control. The engraving depth and the cup / web ratio can be precisely influenced. Due to its high mechanical strength, the diamond enables steep flank angles to be generated.

Other processes that are also used in gravure printing and are rather rare with anilox rollers.

Etching of the copper surface after applying the mask:
Engraving via Heliostat: The Heliostat also works with a diamond stylus, but this performs a swinging movement and the cells are cut out of the surface.
The general roughening of the roll surface is usually done by sandblasting

Laser engraving

Ceramic rollers are engraved with a CO ₂ or YAG laser . Compared to chrome anilox rollers, they are much harder, but also more brittle and therefore cannot be mechanically engraved.

The ceramic layer is melted with a controlled CO ₂ laser and partially vaporized or vaporized directly with the YAG laser. When it cools, a particularly hard ceramic layer, a few micrometers thick, is formed, also known as a “recast”. This recast corresponds to the web portion of the roller. The finer the web portion, the higher the wear.

The contactless laser engraving enables optimal and targeted design of the bowl geometry and the scoop volumes. The color release behavior and the refilling of the cells are improved. Different cell volumes are possible with the same screen fineness. The same theoretical transmission volume can also be achieved with different screen rulings.

A multi-pulse process is used to increase the cell volume. For physical reasons, the engraving depth is limited, as otherwise there will be no more color splitting, among other things.

Areas of application

In various printing processes, anilox rollers are an important element for transferring liquids such as paint, varnish, glue or glue. The appropriate printing method must be selected depending on the transmission medium used and the desired print product.

Mostly used in high-quality flexographic printing, when printing on paper, cardboard, gift and tissue paper, the anilox roller serves as a transfer element for low-viscosity inks such as solvent inks, water colors and UV inks. It is transferred directly to the cliché and from there to the printing material. The ink is supplied via immersion roller systems, which wipe off excess ink using a doctor blade. Newer systems work with chambered doctor blades, in which the viscosity of the ink is kept constant by the closed system. The high quality of flexographic printing to date is due to the ceramic anilox roller used, which makes it indispensable for the flexographic printing process. In offset printing in so-called (anilox) inking units for newspaper printing, it has the task of absorbing color on its surface, storing it and transferring it to the cliché. The inking units consist of a chamber doctor blade, a screen (anilox) roller and a rubberized applicator roller. Compared to conventional offset printing, it has fewer rollers, which is the reason for the lower viscosity of the ink. Since chrome rollers, due to their hydrophilic ceramic, favor accumulation and transport into the ink fountain, they are not particularly suitable for offset printing, but ceramic anilox rollers are predominantly used.

The focus of this technology is the elimination of the zone screw technology, which results in minimal set-up effort and shorter set-up times. In coating plants in gravure printing, the anilox roller is mainly used for the transfer of various resin, silicone and glue solutions. Since liquids of high viscosity are used here, chrome rollers are most suitable because they can offer a higher volume. Due to the longer service life due to the higher surface hardness and porosity, squeeze rollers whose surface is made of ceramic are still used.

Flexographic printing

Due to the direct letterpress printing process , there is only one intermediate step in the transfer of ink onto the printing material. The anilox roller transfers the printing ink to the cliché, the printing plate. The cliché colored in this way then prints directly on the substrate. Therefore, the demands on the anilox roller are very high in terms of accuracy and reproducibility of the ink output.

The ink volume of the anilox roller must be matched to the respective print motif. The total amount of coloration of the anilox roller is changed by replacing it with a differently structured anilox roller with the desired volume. "There is no such thing as an anilox roller that is equally suitable for all production processes and printing materials."

Another cause of moiré formation can be an unfavorable ratio of the angular position of the engraving to the angular position of the reprofilm . Excessive printing provision and assembly errors can also be identified as reasons. The usual ruling of the anilox roller in flexographic printing is 260 L / cm and a hexagonal cell shape at a 60 ° angle is preferred in many cases. However, for the reasons mentioned, this cannot generally apply.

Anilox roller sleeves are a more recent development, that is, a pneumatically tensioned sleeve system. A faster change, greater flexibility and fewer operating personnel are the advantages of this technology. Anilox roller sleeves are mainly used in the area of central cylinder machines, they are coated with ceramic and are therefore laser-engraved.

In flexographic printing, anilox rollers of 120 to 600 lines / cm are usually used.

Web offset newspaper printing

Anilox short inking unit

In the offset printing sector, anilox short inking units are sometimes used for newspaper printing, which has lower requirements on the inking quality. The requirement on the service life of the anilox roller is very high. It has to guarantee several hundred million cylinder revolutions because - in contrast to flexographic printing - it is an integral part of the inking unit. It is precisely adapted to the specific machine type and always doses the same amount of paint. Many printing machine manufacturers produce these anilox rollers themselves. Laser-engraved ceramic rollers with a cup or hash structure are mostly used. Often, small, flat pans are also engraved in the depths of the hash. The exact nature is often a company secret or has been patented.

The screen width of such anilox rollers is around 60 L / cm.

Waterless offset printing

In waterless offset printing, it is necessary to influence the ink release of the anilox roller and thus the layer thickness in the printed product through very precise temperature regulation (the warmer the anilox roller is on the surface, the higher the ink layer thickness in the printed product). This made it necessary to temper the anilox roller. This is guaranteed by very efficient heat dissipation - thin wall layers and high water flows. Laser-engraved ceramic rollers are used, the ceramic layer being very thin (up to 0.1 mm) and a plastic segment underneath. The exact nature is also rarely published in full. This applies in particular to the temperature control of the anilox roller.

With waterless offset printing, a coarser screen fineness (approx. 40 lines / cm) is used due to the higher viscosity of the inks (more viscous).

Finishing

Coating units are used to refine printed products and are always connected to a dryer system. In sheet-fed offset printing in particular, finishing with varnishes or metallic inks in inline postpress - the varnishing unit is located inside the printing machine after the actual printing process - is very common. There are two different systems. One of them is a chambered doctor blade lacquer unit and therefore basically a flexographic printing unit. The lacquer is applied to the anilox roller with a chamber doctor blade and metered. The amount of paint applied depends on the scoop volume of the anilox roller. The anilox roller must be replaced according to the requirements of the print job. Two to three anilox rollers with different scoop volumes in exchange are usually sufficient.

Ceramic anilox rollers with a hexagonal engraving at a 60 ° angle are standard. The Haschur engraving type has been introduced for a few years , with the advantage that the endless groove at a 45 ° angle means that fewer ridges influence the transfer behavior. This means that there is a higher supply of lacquer on the surface, which enables a lower engraving depth. An additional, flatter counter-engraving at a 70 ° angle enables a more even paint distribution.

Anilox rollers in coating plants use screen finenesses of 10 L / cm to 180 L / cm.

For metallic colors, scented varnishes or matt effects, coarse pigment particles , even platelets or capsules, are used, which can be very different from one another with regard to their size. This should be taken into account when choosing anilox roller, because the pigment grain to be transferred must always be smaller than the cell opening. Otherwise, pigment agglomerates that are too large float on top of the engraving and grind (there is no transfer) or they stick in the cells and stick there (the scoop volume is reduced).

Cleaning the anilox roller

Dirt particles or dried paint on anilox rollers have a negative effect on the print quality. The rollers are usually cleaned immediately after each print run. If cleaning is delayed or interrupted, the anilox roller cups will no longer be properly emptied, as the transfer of defined amounts of ink or coating from the flexographic printing forme to the substrate can no longer be guaranteed. Investigations have shown that impurities are deposited on the bottom of the wells and on the edge of the bridge. This influences the emptying behavior of the wells and results in a widening of the webs, which can also be mistaken for wear. Daily cleaning is essential for the longest possible service life of the anilox roller without wear and tear and soiling. The volume share decreases from 20% to 50% after new condition. For the removal of paint residues, a distinction is made between chemical cleaning, mechanical cleaning and physical cleaning. However, the degree of soiling and the type of roller used (different screen finenesses on the roller surface) must be adapted to the cleaning process. Heavy soiling therefore requires chemical cleaning at screen finenesses of 400 to 600 L / cm. However, due to the high corrosion resistance and low porosity of the ceramic layer, these highly aggressive agents have no effect on the roller.

If the cleaning is no longer successful, additional cleaning methods are used, depending on the degree of contamination.

Ultrasonic method
High pressure cleaning systems with dry ice, sodium carbonate or the finest plastic granulate.
Deep cleaning with laser (laser cleaning)

The color combination, the condition of the color, pH value , temperature, mechanical movement and time determine the cleaning time.

Chemical cleaning

Corrosive liquids are used here, with the help of which the paint / varnish deposits are chemically softened and then removed under high pressure with water. This method is most commonly used for rollers with high screen finenesses (400 L / cm and more). After the anilox roller has been placed in the closed system, the slowly rotating roller surface is wetted with a heated chemical liquid, which is removed and filtered after exposure. The final cleaning is carried out with a spray device that uses water to remove residues of the cleaning fluid and the loosened dirt particles.

Physical cleaning

Ultrasonic cleaning

Ultrasonic cleaning is based on the principle of "sound waves" caused by cavitation. This creates microscopic air bubbles that explode as a result of the pressure acting on the roller surface at the moment of impact.

Laser cleaning

The gentle laser cleaning (LaserEcoClean) is based on the thermomechanical effect. The absorption of laser radiation leads to the instantaneous expansion of the dirt in the cells. This changes the thermodynamic properties of the material. A shock wave forms which destroys the adhesion between the paint and the ceramic. The laser beam is focused on a spot size that corresponds to several cells in terms of area.

defects

Sometimes it happens that cleaning the roller is no longer worthwhile because the wear has progressed too far. Rollers with higher screen fineness especially show this phenomenon - the roll suddenly shows an unexpected increase in its transfer volume. This is triggered by breaking webs. The roller is about to "off". Cleaning can no longer save anything.

Measurements

Age-related and user-related changes in the shape of the cells occur due to wear and soiling, and the proportion of webs increases. A from then on poorer emptying of the paint leads to a moderate coloring with less volume. For this purpose, parameters such as the scoop volume, number of grids, proportion of bars, cell depth, bar width / opening and bar / opening ratio should be checked with suitable measuring devices. Particularly important in this context are the volume and the bridge portion. Due to the dominance of the ceramic anilox roller on the market, the measuring devices have established themselves for this. Devices to be used are:

Confocal microscope (information about the cell topology, as well as an optical image with the structure with infinite depth of field)
Interferometer (information on cell topology, WYKO)
Optical roller microscopes
Pipetting method (Armi, Urmi 1, Volugraph, Ravol-Tester)
Fluorescence (Urmi 2)
Laser Scanning Microscope (Lasertec, Leica)
Capacitive measurement (microspace)
Capatch (Steinhardt)
Stylus, volume formula with microscope

Interferometric measurement

The image acquisition takes place with a white light interferometer, which evaluates image data and generates information on volume and depth in 3D representation. Similar devices are called confocal microscopes, optical microscopes, and interferometers.

Confocal microscope

It is a 3-dimensional elevation model that shows the surface of the anilox roller. The detailed topography of the surface can be seen in close connection with the evaluation. The automatic detection of the ridge portion and cell depth is therefore of great importance.

Optical roller microscopes

Devices such as cameras, monitors and measuring devices with the associated software supply the number of raster, bar / opening width and the bar portion.

Volugraph

The color imprint on the anilox roller is measured using a planimeter. A squeegee distributes ink in the roller surface in order to then make an impression on paper. A planimeter measures the area of the transferred amount of paint on the roller surface and the area of paint on the paper. Both values give the current scoop volume. The time required for the measuring process is 20 minutes for three measuring points. The measurement accuracy is ± 5%.

Capatch

The capatch is another way of determining the volume of anilox and gravure rollers. For the measurement it is glued to the anilox roller surface. It contains a capsule with a liquid that presses the liquid out of the capsule by wiping it over with a doctor blade. The length of the distance covered defines the volume. The time required for the measurement is only 3 to 4 minutes and has a measurement accuracy of ± 5%.

Urmi

Urmi is a roller measuring device for the quick and precise determination of the scoop volume on laser-engraved ceramic anilox rollers. It was developed to reduce the time required to optimize the print quality, as well as to increase the measurement accuracy for the scoop volume. A fluorescent liquid is distributed in the visible area by a doctor blade and measured in the structure of the roller surface. The proportion determines the amount of liquid in the structure and thus also the scoop volume. The measurement should be made on a dry and clean part of the surface of the roller, otherwise the illuminating light will be reflected. The light would travel through the fluorescent liquid again and produce an increased proportion. To prevent this, the indicator liquid should be removed with a cleaning agent based on naphthalene after each measurement. The duration of the measurement is faster than with the Volugraph and has an accuracy of ± 5%.

Demarcation

Sometimes the printing form cylinder is incorrectly referred to as an anilox roller in industrial gravure printing . There are historical reasons for this. The starting point for a rotary high-pressure process were simply blasted or roughened roller surfaces. However, the color transfer was not sufficiently homogeneous and uncontrollable. Therefore, the experience from gravure printing, which works with well-engraved chrome rollers in the industrial sector, was used. For this reason, the original type of roller, the engraving process and, above all, the principle of the rotary continuous cell emptying are quite similar. In gravure printing, however, the raster on the printing forme cylinder results in the print image.

In contrast to the gravure printing plate cylinder, the anilox roller does not have the task of transferring a print image directly onto the substrate.

Web links

Flexographic printing process. Retrieved April 21, 2016

literature

Helmut Kipphan: Handbook of the print media. Springer Verlag, Berlin 2000.
Helmut Teschner: Print & Media Technology. 11th edition. Fachschriften Verlag, Fellbach 2003.
KH Meyer (ed.): Technique of flexographic printing. 5th expanded edition. Rek & Thomas Medien AG, DFTA (German-speaking flexographic printing specialist group) St. Gallen 2006.

Individual evidence

↑ KH Meyer (Ed.): Technique of flexo printing . 5th expanded edition. Rek & Thomas Medien AG, DFTA (German-speaking flexographic printing specialist group) St. Gallen 2006, p. 70.

↑ ^a ^b ^c Helmut Kipphan: Handbuch der Printmedien . Springer Verlag, Berlin 2000, pp. 415f.

↑ flexographic and gravure printing, journal, special edition, DFTA- anniversary of September 2004, pp 62-65.

↑ KH Meyer (Ed.): Technique of flexo printing . 5th expanded edition. Rek & Thomas Medien AG, DFTA (German-speaking flexographic printing specialist group) St. Gallen 2006.

↑ ^a ^b Helmut Teschner: Print & Media Technology. 11th edition. Fachschriften Verlag, Fellbach 2003, p. 10.22

^ Helmut Teschner: Print & Media Technology. 11th edition. Fachschriften Verlag, Fellbach 2003, p. 664.

↑ , trade journal. In: flexographic and gravure printing. Issue 2-2005, pp. 4–9.

↑ Flexo and gravure: 'Issue 2-2005, pp. 4-11.

↑ KH Meyer (Ed.): Technique of flexo printing . 5th expanded edition. Rek & Thomas Medien AG, DFTA (German-speaking flexographic printing group) St. Gallen 2006, p. 72.

↑ KH Meyer (Ed.): Technique of flexo printing . 5th expanded edition. Rek & Thomas Medien AG, DFTA (German-speaking flexographic printing specialist group) St. Gallen 2006, p. 65.

↑ Trade journal for packaging printing : Flexoprint . February 1992 edition, pp. 19-21.

↑ Ink dosing scooping (anilox offset) TU Darmstadt: Construction of offset inking units . Design principles in printing machine construction at TU Darmstadt

↑ NIIR Board: Handbook on Printing Technology (offset, gravure, flexo, screen) . National Institute Of Industrial Research, 2002, ISBN 978-81-7833-087-7 ( page 18 ). Page 18 ( Memento of the original from April 23, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2
↑ KH Meyer (Ed.): Technique of flexo printing . 5th expanded edition. Rek & Thomas Medien AG, DFTA (German-speaking flexographic printing specialist group) St. Gallen 2006, p. 73.
↑ ^a ^b Helmut Kipphan: Handbuch der Printmedien . Springer Verlag, Berlin 2000, p. 265.
↑ the other is a simple roller system
↑ ^a ^b ^c Dortschy (Ed.): Guide - Anilox roller in the coating unit. P. 9/10, online as PDF ( memento of the original from January 3, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved July 8, 2001. @1@ 2

[1] KH Meyer (Ed.): Technique of flexo printing . 5th expanded edition. Rek & Thomas Medien AG, DFTA (German-speaking flexographic printing specialist group) St. Gallen 2006, p. 70.

[kipphahn-2] Helmut Kipphan: Handbuch der Printmedien . Springer Verlag, Berlin 2000, pp. 415f.

[3] xographic and gravure printing, journal, special edition, DFTA- anniversary of September 2004, pp 62-65.

[4] KH Meyer (Ed.): Technique of flexo printing . 5th expanded edition. Rek & Thomas Medien AG, DFTA (German-speaking flexographic printing specialist group) St. Gallen 2006.

[teschner-5] Helmut Teschner: Print & Media Technology. 11th edition. Fachschriften Verlag, Fellbach 2003, p. 10.22

[6] Helmut Teschner: Print & Media Technology. 11th edition. Fachschriften Verlag, Fellbach 2003, p. 664.

[7] , trade journal. In: flexographic and gravure printing. Issue 2-2005, pp. 4–9.

[Fachzeitschrift-8] Flexo and gravure: 'Issue 2-2005, pp. 4-11.

[9] KH Meyer (Ed.): Technique of flexo printing . 5th expanded edition. Rek & Thomas Medien AG, DFTA (German-speaking flexographic printing group) St. Gallen 2006, p. 72.

[10] KH Meyer (Ed.): Technique of flexo printing . 5th expanded edition. Rek & Thomas Medien AG, DFTA (German-speaking flexographic printing specialist group) St. Gallen 2006, p. 65.