In the process of label flexo printing, UV inks do more with less!
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UV ink has been widely used in label flexo printing because of its fast curing speed, high printing color density and good stability. It does not dry in the ink fountain without contact with ultraviolet light. It has low odor and is basically free of VOC. . However, in actual printing, it is inevitable that some problems will be encountered, such as incomplete curing, poor adhesion, appearance of line-like color points, and inability to withstand sunlight. The following will analyze the causes of these printing problems and summarize the corresponding solutions. Method.
Remember to take a small copy and make a record!
01. ink curing is not complete
Problem Description
There is ink on the paper guide roller between the printing units, and it is transferred to the printing material; the back of the printed product is dirty after winding.
Cause analysis and solution
To solve the problem of incomplete UV ink curing, it is necessary to find the cause from the three aspects of curing device, printing operation and ink itself, and then solve the problem.
First check the surface of the UV lamp and the reflector to see if there is any dirt that hinders the UV light from illuminating the printed product. If it is, clean it and develop the habit of regularly cleaning the UV lamp, lampshade and reflector with anhydrous alcohol. At the same time, check the use time of the UV lamp. If it has exceeded the service life, replace it to ensure that the UV lamp has sufficient power; or open several sets of UV lamps to increase the UV radiation energy.
If the printing speed is too fast, the UV radiation energy received by the UV ink is insufficient, and the curing time is too short, so that the UV ink is not cured completely, and the printing speed can be solved. If the ink layer is too thick, only the surface layer of the UV ink will be cured and the internal curing will be incomplete. At this time, the anilox roller needs to be replaced, and the amount of ink is appropriately reduced to reduce the thickness of the ink layer.
The above is an external cause of incomplete UV ink curing, and the internal cause is that the UV ink itself has a narrow range of absorption spectrum of UV light and the emission spectrum of the UV lamp. At this time, a suitable photosensitizer can be added to the ink. The addition ratio is 1% to 3%, and the curing efficiency is improved by enlarging the absorption spectrum range of the ink, thereby improving the curing effect.
02. ink layer adhesion is poor
Problem Description
When the adhesion of the ink layer was tested with 3M-600 tape, the ink peeled off from the surface of the printing material, or the ink after printing was peeled off from the ink layer.
Cause analysis and solution
Improper selection of printing materials or low surface tension is the most common cause of poor ink adhesion. If the printing material does not match the ink, it needs to be replaced. For plastic film materials, the surface tension can be increased by corona treatment, or the coating can be increased. Layers to improve adhesion, in addition to ensure that its surface tension reaches more than 38 dynes.
In some cases, the poor adhesion of the ink is also related to the ink formulation. If there is a problem in comparing different batches of ink, a primer can be pre-printed before printing the ink.
When the hot stamping process is used, if the adhesion of the ink on the surface of the hot stamping foil is poor and it is easy to fall off, the varnish can be coated for protection.
The adhesion between the ink layers is poor, and the ink of the former color is often over-cured, and the curing power of the UV lamp of the previous color group can be appropriately reduced.
Incomplete curing of the ink is also one of the reasons for the poor adhesion of the ink layer. Find the cause and take corresponding measures.
03. appears irregular line color point
Problem Description
The same layout, the same color appears irregular line-like color points, like a meteor.
Cause analysis and solution
The various problems of the scraper are the most common cause of this phenomenon. If the scraper is damaged, the scraper needs to be replaced; if the scraper is thin or the material is soft, the back knife can be added, or the scraper blade with a thickness of 0.15 mm to 0.3 mm can be used. The wrong contact angle can also cause this problem. It is recommended that the blade angle be 20° to 35°. In addition, the blade pressure is also one of the reasons. The lightest blade pressure should be used.
To solve this problem, we can also start with the anilox roller, and the anilox roller that is replaced with a higher number of lines can also be improved under the premise of ensuring the amount of ink transferred.
If the viscosity of the ink is too high, the ink transfer effect is not good, and problems may occur. The diluent may be appropriately added to reduce the viscosity of the ink; in order not to change the color density, it may be heated, especially in the northern part of winter.
04. prints are not resistant to the sun
Problem Description
The label fades after exposure for a while in daylight.
Cause analysis and solution
Different inks have different lightfastness levels. To achieve the desired lightfastness, you must choose a ink with a higher lightfastness. Also note that when spot color inks are formulated, the lightfastness level of the spot color inks depends on the lightfastness level of each of the primary color inks used. If a sufficient level of fast-fast ink is selected, but the desired light-resistant time is still not achieved, the thickness of the ink layer can be appropriately increased.