Evaluation and analysis of anilox roller (2)
No need for precision instruments during evaluation
As you may have noticed, we have not mentioned any equipment needed to check the anilox rolls. In fact, the evaluation of the anilox roller does not require any inspection equipment at all. You want to understand the relationship between the condition of the anilox roller and the print quality. There is no need to spend nearly $ 10,000 to buy a microscope or $ 60,000 to buy an interferometric instrument. The above high-end equipment is only suitable for laboratory use. In the working environment of the printing workshop, vibration, dust, changes in temperature and humidity, and misoperation by operators may cause errors in instrument test data. In addition, if used improperly, it is easy to damage these precision instruments.
If the anilox roller is clean, using the hole detection mirror or interferometer can also measure the anilox roller mesh opening size, mesh depth and mesh wall thickness and other accurate data. If the anilox roller is clogged with residual ink, the light reflected by the residual ink in the anilox will make the surface of the anilox roller blurred. And the color material in these residual inks will produce visible colors on the surface of the anilox roller, and the haze formed by the magenta residual ink on the surface of the anilox roller can also be found with naked eyes.
Obviously, in the case that the anilox roller cells have been blocked by residual ink, the microscope or interferometer is still used to measure the anilox roller, and the measured data is inaccurate. Because the hole detection mirror is an optical detection instrument, and the dried ink in the hole will produce haze, which will interfere with the focus during measurement. When the ink hole is blocked by residual ink, even using a microscope, the bottom of the hole cannot be clearly seen, and of course, it is impossible to accurately measure the depth of the hole.
The optical interferometer reflects the contour of the cell through an interference pattern composed of changes in the reflected light on the surface of the cell. This method is also called an "echo depth recorder". However, due to the residual ink in the network cavity, the projected light of the instrument will be diffusely reflected, which makes the test result inaccurate and the misleading data is obtained. For example, the instrument may measure that the thickness of the anilox wall is zero, but if there is no mesh wall, the number of anilox rollers should also be zero, which is obviously ridiculous.
Another situation is that the number of anilox rollers measured before cleaning is 715, but after cleaning it becomes 682. Of course, the anilox roller will not change the anilox roll number before and after cleaning. Obviously, the measuring instrument incorrectly interprets the received test data.
A better method for detecting the volume of the anilox roller cell is to measure the solid, mesh tone and highlight parts of the printed matter with a density meter. Optical instruments rely on a calculation formula or an algorithm to confirm the volume of the anilox, and the amount of ink transferred by the anilox roller does not correspond to the volume of the cell, because the amount of ink transferred by the anilox roller is also affected by the PH value and initial , Colorant content, ambient temperature, humidity and other ink rheological characteristics and environmental changes. Therefore, once these conditions change, even if the ink transfer ability does not change, the amount of ink transferred will also change.
We are not saying that the test equipment is worthless for the evaluation of the anilox roll, but that we do not have to rely on these high-end test instruments to determine whether the anilox roll needs cleaning. In fact, if the anilox roller looks dirty with the naked eye, it proves that the anilox roller needs to be cleaned; if it looks clean, it does not need to be cleaned.
Assess the damage of the net hole
Let's take a look at some of the common problems of anilox rollers, so as to understand what work to do to detect the damage of the anilox.
1. Circumferential scratches appear on the surface of the anilox roller
The circumferential scratches on the surface of the anilox roller indicate that there is adhesion in the same cavity, and the anilox wall has been worn or damaged. This is mainly due to the hard particles stuck between the doctor blade and the anilox roller. With the naked eye, scratches can be seen in the circumferential direction of the anilox roller. The typical performance of the printed product is a thin ink line along the direction of the web. Of course, if you use a microscope, you can definitely see the scratches on the anilox roller, but in fact, even without a microscope, you can see the scratches with the naked eye.
2. The surface of the anilox roller is damaged by embedded metal shavings
Metal scratches generally occur when loading and unloading anilox rollers on flexo printing machines. The friction between the anilox roller and the ink fountain, squeegee holder or other metal parts may cause metal chips to be embedded in the mesh, reflecting some highlights on the printed product (that is, some areas on the printed product do not obtain the required ink density ). It may be difficult to see the metal shavings embedded in the net hole with the naked eye, but it can be clearly seen under the magnifying glass.
3. The network wall is damaged
The effect of too much mechanical cleaning on the surface of the anilox roll is well known. There are many factors that cause the erosion of the mesh wall. In an ultrasonic cleaning device, too long a cleaning time or too many cleaning times may cause damage to the mesh wall. The old engraving machine may make the engraved mesh holes uneven and irregular, resulting in uneven erosion of the mesh wall. Once the network wall is eroded, the ink of several network holes will be gathered together, and large pieces of ink will appear on the printed matter. On the surface of the super-polished anilox roller, it can be seen that the contrasting local shadow formed by the ablated area and the surrounding polished cavity area (but it is difficult to see on the surface of the anilox roller that has not been super-polished).
In the medium impact type cleaning device, excessive or repeated cleaning of the anilox roller will cause cumulative damage to the surface of the roller. Some fine holes can be seen on the surface of the anilox roller, and the image on the printed product will be blurred. . Observed under a magnifying glass, it can be seen that the mesh wall has been slightly damaged, and the ink of several mesh holes merged together. Therefore, the use of testing equipment can confirm the problems you have found from the printed matter, that is, the anilox roller no longer provides accurate ink volume to the printing plate.
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