Anilox Roll Evaluation

If you are in the business world, you have to make money. You must use limited resources to produce products that satisfy your customers and create revenue. To ensure that you have a competitive advantage, you need to find ways to increase productivity, such as reducing prepress preparation time and costs, reducing consumption, improving print quality, reducing the replacement of anilox rolls and reducing the associated printing costs. But if you want to find a miraculous integrated solution without effort, it is impossible. So where do you go from here? Every step of the production process should be evaluated in a rational and objective manner. The most important one is the evaluation of the anilox Roller.

What is the evaluation of the anilox roll? The traditional definition refers to the use of sophisticated and costly inspection equipment by experienced technicians to perform a comprehensive inspection of the number of anilox roller lines, cell volume, and cell structure and to write a test report, including photomicrographs or Digitally processed network schematics of the contours of the cells. The report includes many figures and charts, but very little practical information is available.

Although it is helpful for the operator to understand the volume of the anilox roller, are you content to check that the anilox roller has only been worn or damaged? Do you want to know the cause of the damage to the anilox roll and how to prevent it from being damaged? The anilox roller is the heart of the flexo press and is also the focus of attention. Traditional inspections cannot tell the operator why the anilox roll is damaged, and it is impossible to suggest improvements to the print quality. So you should ask yourself: what do you hope to get from the evaluation of the anilox roller.

The subject of the assessment

The evaluation of the anilox roll during the printing process is more effective than the occasional anilox roll inspection. The correct assessment includes a rigorous evaluation of the entire process of storage, cleaning, use, and working conditions of the anilox roller, and can provide a series of solutions to improve printing conditions and prevent process failures. The view that the evaluation of the anilox roller should be performed by an outsider (a technician sent by the anilox roller manufacturer) is wrong. In fact, the evaluation of the anilox roller is an important part of improving the printing quality. Obviously, technicians sent by anilox roller makers have been unreasonably evaluating the anilox roll for several weeks in the press room. The appropriately trained press operators can use the anilox roll in their daily work. Condition monitoring.

Assessment Tools

1. Specially designed inspection area

A suitable height fixed bench should be prepared for the operator if it is more ideal near the cleaning device.

2. Support frame for supporting anilox roller journal

The frame can support the anilox roller so that its surface does not come into contact with the table top surface, and it is also conducive to a comprehensive and safe inspection of the surface of the anilox roller. The seat frame should be equipped with bearings so that the anilox roller journal can rotate in it. In addition, grooved wooden brackets may also be used to support the anilox roller journal. However, when using a wooden bracket, it is best to fix it on a heavy and bulky base to prevent accidental tipping of the wooden bracket.

3. Good lighting

Good lighting is extremely important in the evaluation of anilox rolls, but it is often overlooked. In many printing shops, so-called good lighting is to install more fluorescent lamps above the inspection area. It is a good practice to draw a single area separately and use a light source that is comparable to the lighting conditions in the inspection area to illuminate the sheet for comparative inspection.

Other tools that need to be prepared include gear tweezers, a 100x optical magnifier, tape measure, marking labels (used to mark the damaged area), retractable blades (for scraping the dried surface of the anilox roller) and medium coarse teeth锉 (used to remove burrs on the keyway). One-hundredth of an inch micrometer is used to detect the wear of the journal and bearing surfaces. If the anilox roller journal has a thread stop, it is advisable to purchase a set of thread inspection tools (for checking the threaded portion of the journal).

In addition, a set of numbering dies and hammers need to be prepared to mark the anilox roll. Most anilox rolls have been serially printed by the manufacturer at the time of shipment. However, after the anilox roll has been repeatedly cleaned several times, numbers such as numbers will become blurred. In particular, if a side scraper is used, the anilox roller end surface may be excessively worn and the original number and the number of screen lines and the like may be blurred. Therefore, the anilox roll needs to be reprinted after a period of use to ensure that important information is clearly visible.

It is also important to distinguish between anilox rollers by the number of series and screen lines recorded in the logbook. Any damage or blemishes on the surface of the anilox roll should be recorded in the record book, and clearly indicate the damage location and damage degree. The contents recorded in the record book enable the operator to quickly understand the condition of the anilox roller and know which anilox roller needs to be prioritized. If the record shows that more than one mesh roll has suffered the same type of damage, it should cause the operator to be vigilant and should investigate further the cause of the damage to the anilox roll.

No need for precision equipment during assessment

Perhaps you have noticed that we have not mentioned any equipment required for checking anilox rollers so far. In fact, the evaluation of the anilox roll does not require any inspection equipment at all. You want to understand the relationship between the condition of the anilox roller and the printing quality. It is not necessary to spend nearly 10,000 U.S. dollars for microscopes or 60,000 U.S. dollars for interferometric instruments. The above high-end equipment is only suitable for laboratory use. In the working environment of the printing shop, vibration, dust, changes in temperature and humidity, and operator's misoperation may cause the instrument test data to be incorrect. In addition, if used improperly, it is easy to damage these precision instruments.

If the anilox roller is clean, accurate data such as the size of the anilox roller opening, the depth of the cell depth, and the thickness of the network wall can also be measured using a mesh detection mirror or an interferometer. If there is residual ink in the anilox roller network, the light reflected from the residual ink in the network hole will make the surface of the anilox roller unclear. Moreover, the colorant in these residual inks produces a visible color on the surface of the anilox roller, and the naked eye can also find the magenta residual ink formed on the surface of the anilox roller.

Obviously, an anilox roller is still measured by a microscope or an interferometer in the case where the anilox roller cell has been blocked by residual ink, and the measured data is inaccurate. Because the net point detection mirror is an optical detection instrument, the residual ink in the dry point of the net cavity will produce haze, which interferes with the focus of the measurement. When the cell site is blocked by residual ink, it is impossible to clearly see the bottom of the cell site using a microscope. Of course, it is impossible to accurately measure the depth of the cell site.

The optical interferometer reflects the contour of the cell by an interference pattern formed by the change of reflected light on the surface of the cell, and this method is also called an “echo depth recorder”. However, due to the residual ink in the cell site, the diffused reflection of the projected light of the instrument occurs, so that the test result is inaccurate and misleading data is obtained. For example, the instrument may measure the thickness of the mesh wall as zero, but if there is really no mesh wall, the number of mesh lines of the anilox roll should be zero, which is obviously absurd.

In the other case, the number of screen lines of the anilox roll measured before cleaning was 715, and after cleaning it became 682. Before and after the cleaning of the anilox roller, of course, the number of screen lines of the anilox roller will not be changed. Obviously, the measuring instrument incorrectly interprets the received test data.

A better method for detecting the volume of an anilox roller is to use a density meter to measure the field, mesh, and highlight portions of a printed matter. Optical instruments rely on a calculation formula or some algorithm to confirm the volume of the cell, and the amount of ink transferred by the anilox roller does not correspond to the volume of the cell, because the ink volume transferred by the anilox roller is also affected by the PH value of the ink. , pigment content and environmental temperature, humidity and other ink rheological properties and environmental changes. Therefore, once these conditions change, even if the ink transfer ability does not change, the amount of ink delivered will also change.

We are not saying that the test equipment is worthless for evaluation of the anilox roll, but that it is not necessary to rely on these high-end test instruments to determine if the anilox roll needs cleaning. In fact, if the anilox roll had become dirty with the naked eye, it proved that the anilox roll needed cleaning; if it looked quite clean, it would not have to be cleaned.

Assess the damage to the cyberspace

Let's take a look at some of the common problems with anilox rollers to find out what work to do to detect network damage.

1. Abrasion on the surface of the anilox roll

The presence of circumferential scratches on the surface of the anilox roller indicates that adhesion has occurred in the same hole and the mesh wall has been worn or damaged. This is mainly due to the fact that hard particles are caught between the doctor blade and the anilox roller. With the naked eye, it can be seen that the anilox roller has scratches on its circumference, and the typical performance on the printed matter is a fine ink line along the direction of the web transfer paper. Of course, if you use a microscope, you can surely see the scratches on the anilox roller, but in fact, you can see the scratch with the naked eye even without using a microscope.

2. Damaged metal swarf on the surface of the anilox roller

Metallic scratches generally occur when the anilox roller is mounted on a flexo press. The friction of the anilox roller with the ink fountain, squeegee holder or other metal parts may cause the metal chips to be embedded in the cell, reflecting some highlights on the printed matter (that is, some areas on the print product do not obtain the required ink density. ). It may be difficult to see the metal chips embedded in the cells in the naked eye, but it can be clearly seen under a magnifying glass.

3. Walls are damaged

The effect of excessive mechanical cleaning on the surface of the anilox roll is well known. There are many factors that cause erosion of the wall. In an ultrasonic cleaning device, too long a cleaning time or a large number of cleanings may cause the net wall to be damaged. The old engraving machine may make the carved out of the cells uneven and irregular, resulting in uneven erosion of the network wall. Once the web wall is eroded, the inks of several webs will gather together, and large ink packs will appear on the prints. On the surface of the superabrasive anilox roll, a contrasting local shadow formed by the denuded area and the surrounding polished cell area can be seen (but it is difficult to see on the surface of the anilox roll that has not been superabrasively treated).

In the media impact cleaning device, excessive or repeated cleaning of the anilox roller will cause cumulative damage on the surface of the roller. Some fine holes can be seen on the surface of the roller, and the image on the printed material will be blurred. . Observed under a magnifying glass, it can be seen that the mesh wall has been slightly damaged, and the inks of several network points are lumped together. So, using inspection equipment can confirm the problem you have discovered from the printed matter, that is, the anilox roller no longer provides accurate ink to the plate.

4. An anilox roll surface pattern

Due to the different cleaning strengths of the anilox roller during ultrasonic cleaning, a pattern of spotted spots may appear on the surface of the anilox roller, that is, the hot spots formed by the acoustic waves evoked by the cleaning liquid on the surfaces of the cells. This situation will become more and more serious with increasing wear or gradual saturation of the cleaning solution, resulting in uneven degree of cleaning of the anilox roller surface, resulting in different levels of light reflectance between the residual ink at the adhesive and the clean place. Forms a plaque pattern. At this point, it is possible to see the pattern of flower spots on the surface of the anilox roll without the use of high-end inspection equipment. Once the naked eye can be seen on the surface of the anilox roller spot, in print will certainly reflect.

5. Network hole wear

With chrome-plated anilox rollers, wear is a concern. Since the anilox roller base copper is soft, it is still easily worn after chrome plating and the wear is faster. Once the chrome plating layer is damaged, the openings of the cells will become smaller and the network walls will become wider, which will lead to a sharp drop in the ink transmission ability of the cells, that is, the volume of the ink holes in the anilox rolls will become smaller.

Since the ceramic material is a very hard and dense material, and the hardness is second only to diamond, the service life of the ceramic anilox roller is 2 to 5 times longer than that of the chrome-plated roller (refers to normal use, and is carefully protected, stored, cleaned and managed). . In fact, most ceramic anilox rolls that need cleaning have suffered other damage long before the walls have been abraded.

Anilox roll evaluation

Thus, it can be seen through careful and careful inspection when the anilox roller is cleaned. If there is a problem with the print, you should first look for the root cause of the print failure on the anilox roller. Most operators will often identify the anilox roll that has experienced a problem because they are very aware of which anilox roll defect caused print defects such as stains or dirty lines on prints. They even sometimes mark the anilox roll in some way to prevent it from being installed again.