UV ink has been widely used in label flexographic printing due to its advantages such as fast curing speed, high printing color density and good stability, as long as it is not exposed to ultraviolet rays, it will not dry in the ink fountain, has a small odor, and basically does not contain VOC. . However, in actual printing, some problems will inevitably be encountered, such as incomplete curing, poor adhesion, line-shaped color spots, and light resistance. The following will analyze the causes of these printing problems and summarize the corresponding solutions. Method.
Ink curing is not complete
Problem Description
There is ink on the paper guide roller between the printing units, and it will be transferred to the printing material; the back of the printed product will be dirty after winding.
Cause analysis and solution
To solve the problem of incomplete UV ink curing, we need to find the reason from the curing device, printing operation, and the ink itself, and then solve the symptom.
First check whether there are dirt on the surface of the UV lamp and the reflector that hinders the UV light from irradiating the printed matter, clean it if there is, and develop the habit of regularly cleaning the UV lamp, lampshade and reflector with absolute alcohol. At the same time, check the use time of the UV lamp. If it has exceeded the period of use, replace it to ensure that the UV lamp has sufficient power; or turn on 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, which leads to incomplete curing of the UV ink. Reducing the printing speed can be solved. If the ink layer is too thick, only the surface layer of the UV ink is cured and the internal curing is not complete. At this time, the anilox roller needs to be replaced to appropriately reduce the amount of ink applied and reduce the thickness of the ink layer.
The above are the external reasons for the incomplete curing of the UV ink, and the internal reason is that the UV ink absorption spectrum of the UV light and the emission spectrum of the UV lamp are relatively narrow. At this time, a suitable photosensitizer can be selected to add to the ink The addition ratio is 1% to 3%, and the curing efficiency is improved by expanding the absorption spectrum range of the ink, thereby improving the curing effect.
Poor adhesion of ink layer
Problem Description
When using 3M-600 tape to test the adhesion of the ink layer, the ink fell off the surface of the printing material, or the post-printing ink fell off the first ink layer.
Cause analysis and solution
Improper selection of printing material or low surface tension is the most common reason for 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. Layer to improve its adhesion, in short to ensure that its surface tension reaches 38 dynes or more.
In some cases, the poor adhesion of the ink is also related to the ink formula. If this problem exists in different batches of ink, it can be pre-printed with a primer layer before printing the ink.
When the hot stamping first printing process is adopted, if the ink has poor adhesion on the hot stamping foil surface and is easy to fall off, it can be coated with varnish for protection.
The poor adhesion between the ink layers is often due to excessive curing of the previous color ink, which can appropriately reduce the curing power of the UV lamp of the previous color group.
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.
Irregular line-shaped color points appear
Problem Description
Irregular line-shaped color points appear on the same layout and in the same color, like a meteor.
Cause analysis and solution
The various problems of the doctor blade are the most common reasons for this phenomenon. If the doctor blade is damaged, the doctor blade needs to be replaced; if the doctor blade is thin or soft, the back knife can be added, or the doctor blade with a thickness of 0.15mm to 0.3mm can be used. ; Incorrect contact angle will also cause this problem, it is recommended that the blade angle is 20 ° ~ 35 °; In addition, the pressure of the blade is also one of the reasons, the lightest blade pressure should be used.
To solve this problem, you can also start with the anilox roller. On the premise of ensuring the amount of ink transfer, it can also be improved by replacing it with a higher number of anilox rollers.
If the ink viscosity is too high, the ink transfer effect is not good, and there will be problems. You can add a thinner to reduce the viscosity of the ink; in order not to change the color density, it can also be heated and used, especially in the northern regions in winter.
Prints are not lightfast
Problem Description
The label fades after being exposed to sunlight for a period of time.
Cause analysis and solution
Different inks have different lightfastness levels. To obtain the ideal lightfastness effect, inks with higher lightfastness levels must be selected. Pay attention to the preparation of spot color inks. The light fastness of spot color inks depends on the light fastness of each primary color ink used. If you have selected a sufficient level of light fast ink, but still can not achieve the required light fast time, you can increase the thickness of the ink layer.
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