UV ink has been widely used in label flexographic printing because of its advantages of fast curing speed, high printing color concentration and good stability, as long as it does not touch ultraviolet rays, it will not be dry and fixed in ink bucket, small smell and basically no VOC. But in the actual printing, it is inevitable to encounter some problems, such as incomplete curing, poor adhesion, the appearance of line color points, sun resistance and so on, the following will be on these printing problems cause analysis, and summed up the corresponding solutions.
Remember to take the small book, do the record o!
01 Ink curing is incomplete
Problem description
There is ink on the guide roll between the printing units and it will be transferred to the printing material.
Cause analysis and solutions
solve the UV ink curing incomplete problem need from the curing device, printing operation, ink itself three aspects to find the cause, and then to solve the disease.
To check whether there is dirt on the surface of the UV lamp tube and the reflector cover that prevents the UV light from irradiating the print, if any, clean, and develop the habit of cleaning UV lamp tube, lampshade and reflector cover regularly with anhydrous alcohol. Meanwhile, check the service time of the UV lamp tube, if it has exceeded the service life, it should be replaced to ensure that the UV lamp has enough power; or turn on several sets of UV lights to increase the UV radiation energy.
Printing speed too fast will cause UV ink to accept UV radiation energy is not enough, curing time is too short, resulting in UV ink curing is not thorough, reduce printing speed can be easily solved. Ink layer too thick will cause only UV ink surface curing and internal curing is not complete, this time need to replace the roller, appropriate reduction of ink, reduce the thickness of ink layer.
The above are UV ink curing incomplete external cause, and the internal cause is UV ink itself to the absorption spectrum of UV light and the emission spectrum of the lamp matching a narrow range, at this time can choose the appropriate photosensitizer added to the ink, adding a ratio of 1%~3%, by expanding the absorption spectrum of ink to improve the curing efficiency, thereby improving the curing effect.
02 Poor adhesion of ink
Problem description
3 M-600 tape for ink coating adhesion test, ink from the substrate surface off, or after printing ink from the first printing ink layer off.
Cause analysis and solutions
Improper selection of printing materials or low surface tension is the most common reason for poor ink adhesion, if the printing material and ink do not match, it needs to be replaced; for plastic film materials, the surface tension can be improved by corona treatment, or the coating can be increased to improve its adhesion, in short, to ensure that its surface tension up to 38 dyne.
In some cases, poor ink adhesion is also related to ink formulation, if the contrast test of different batches of ink have this problem, you can preprint the ink before printing a layer of bottom paint.
When using the first hot and then printing process, if the ink on the surface of hot stamping foil adhesion is poor, easy to fall off, can be coated with smooth oil for protection.
poor adhesion between ink layers, often the former color ink curing excessive, can appropriately reduce the previous color group UV lamp curing power.
Ink curing is not complete is also one of the causes of poor adhesion of ink layer, find its cause, take appropriate measures can.
03 Irregular Line Point
Problem description
The same layout, the same color appears irregular line color points, like a meteor.
Cause analysis and solutions
The problem of spatula is the most common cause of this phenomenon. If the scraper is damaged, it is necessary to replace the scraper; if the scraper is thin or soft, it can increase the back knife, or replace the 0.15 mm~0.3 mm thickness scraper blade; the wrong contact angle will also cause this problem, it is recommended that the scraper angle is 20°mm~35°; in addition, the scraper pressure is also one of the reasons, the lightest scraper pressure should be used.
This problem can also be solved from the roller, in the premise of ensuring the amount of ink transfer, the replacement of a higher number of wire roller also has the effect of improvement.
Ink viscosity is too high to lead to poor ink transfer effect, there will also be problems, can be appropriate to add diluents, reduce ink viscosity; in order not to change the concentration of discoloration, can also be heated to use, especially in the northern winter area.
04 Printing is not sun-resistant
Problem description
The label faded after exposure to sunlight for some time.
Cause analysis and solutions
Different levels of ink sun resistance, to achieve the ideal sun resistance effect, must choose a higher level of ink. In the spot ink blending should also pay attention to, spot ink sun resistance level depends on the use of each primary ink. If you have selected enough grade of sun-resistant ink, but still can not achieve the required sun-resistant time, you can appropriately increase the thickness of the ink layer.
