Seven reasons for abnormal drying of printing ink!
Time:2023-09-11
Views:1740
1. The ink layer is too thick
In the process of large-area field printing, because the amount of ink is too large and the ink layer is too thick, the ink layer on the surface of the printing product will appear in the drying process of the surface layer is completely dry and the bottom layer is not completely dry, that is, the phenomenon of false drying. In addition to the ink layer is too thick, the paper speed is too fast, and the UV light irradiation time is insufficient, which will also cause the UV ink to fake dry. Once the ink fake drying phenomenon occurs, it is easy to cause the ink layer on the surface of the printed product to fall off during the post-process processing. This is because the combination fastness of the incompletely dried ink base and the substrate surface is poor, so that the ink layer is scratched off under the action of friction.
Solution
For the live parts printed with spot color UV ink, the color of spot color UV ink should be darker as far as possible when mixing ink, so that the bottom layer of ink can be thoroughly dried by deep ink thin printing during the printing process, and the combination fastness of it and the substrate surface can be increased. At the same time, it is also necessary to ensure the appropriate paper speed and sufficient UV light exposure time, if the paper speed is faster, it is necessary to improve the power of the UV lamp to ensure the drying effect of the ink.
For the live parts printed with spot color UV ink, the color of spot color UV ink should be darker as far as possible when mixing ink, so that the bottom layer of ink can be thoroughly dried by deep ink thin printing during the printing process, and the combination fastness of it and the substrate surface can be increased. At the same time, it is also necessary to ensure the appropriate paper speed and sufficient UV light exposure time, if the paper speed is faster, it is necessary to improve the power of the UV lamp to ensure the drying effect of the ink.
2. UV lamp power is insufficient
The lack of UV lamp power is also one of the reasons for the poor drying of UV ink, which is related to the daily production operation of the enterprise, mainly in the following aspects:
(1) All UV lamps have an effective service life (generally 800 to 1000 hours), when the use of UV lamps more than its service life, although the UV lamp can continue to work, but its power has been greatly reduced.
(2) After replacing the UV lamp, the use timer of the UV lamp is not returned to zero, resulting in the use time of the UV lamp has exceeded the service life but is completely unaware.
(3) Do not pay attention to the surface cleaning of the UV lamp, and the reflector of the UV lamp is too dirty after long-term use, resulting in the loss of reflected energy of the UV lamp (reflected energy can account for about 50% of the power of the UV lamp).
(4) UV lamp power configuration is not reasonable, such as the domestic full rotary self-adhesive label printing machine each group of UV lamp power reasonable configuration is basically more than 3000 watts, foreign equipment due to its printing speed, each group of UV lamp power is basically more than 7000 watts, and some full rotary self-adhesive label printing machine each group of UV lamp power is only 2000 watts.
Solution
First of all, it is necessary to establish a complete and effective UV lamp use management system to ensure that the UV lamp works within the effective service life, timely replacement of the UV lamp that has exceeded the service life, and pay attention to the replacement of the UV lamp unit to zero the use of the UV lamp timer; Secondly, regularly clean the reflector of the UV lamp to reduce the loss of its reflected energy; Furthermore, the power of the UV lamp is reasonably configured according to the structural characteristics of the equipment.
3. Ink over shelf life or excessive additives
Under normal circumstances, if the ink shelf life is exceeded, the ink may be poor drying after printing due to the failure of the photoinitiator in the ink. In addition, in the printing production, in order to improve the performance of the ink, it is often necessary to add additives such as ink mixing oil and adhesives to the ink. If the proportion of additives is too high, it may cause the ink to be too thin and cause poor drying. UV ink itself has thixotropy, that is, it will become thinner and thinner under the action of the shear force of the ink roller. Moreover, after the printing equipment runs for a period of time, there will be friction and heat between the ink rollers, which will reduce the ink viscosity.
Solution
First, ensure that the ink is used within its shelf life; Secondly, pay attention to the amount of ink AIDS and desiccant, it is recommended that the proportion of UV ink additives does not exceed 3% in summer, and does not exceed 8% in winter.
4. Different colors of UV ink drying degree is different
The test shows that the absorption of different colors of UV inks to the spectrum is different, so under the same power of UV lamp, the drying degree of different colors of UV inks is different. Such as white UV ink can directly reflect light, black UV ink will form diffuse reflection of light, magenta UV ink on the absorption of light is better.
According to experience, the difficulty of four-color UV ink drying from difficult to easy is black, cyan, yellow and magenta, while gold and silver UV ink is more difficult to dry than four-color UV ink, white UV ink is also difficult to dry due to the reflection of light.
Solution
According to the drying characteristics of different colors of UV ink, a reasonable printing color order is arranged, and the ink that is difficult to dry is printed first, and then the ink that is easy to dry is printed, which can solve the problem of poor ink drying to a certain extent.
5. Roller density is too low
In actual production, new equipment is more prone to ink drying failure. After careful inspection, it was found that it was because the roller with too low density absorbed the photoinitiator in the UV ink, resulting in poor ink drying.
The drying of UV ink is mainly achieved by the chemical reaction between the photoinitiator and the resin, of which the molecular structure of the resin is larger, and the molecular structure of the photoinitiator is smaller. If the density of the roller is too low, there will be many small holes on the surface, because the diameter of these small holes is larger than the diameter of the photoinitiator, so some of the photoinitiator in the UV ink will be absorbed by the roller, resulting in the drying process of the UV ink, the chemical reaction of the resin and the photoinitiator is insufficient, resulting in poor drying of the ink, and also accompanied by the drying of the ink on the roller surface.
Solution
The simplest way is to replace the roller; If it is too late to replace the roller, the roller can also be removed and soaked in UV ink oil for 12 to 24 hours, at this time the roller will gradually absorb UV ink oil, and when it reaches the saturated state, it is difficult to absorb the photoinitiator in UV ink.
6. Other Reasons
Glossy resin inks for lithography, under normal circumstances, the imprint transferred to paper by rubber cloth can generally dry in a few hours. However, in daily production, it is often encountered that the imprinting is too slow to dry, so the following reasons need to be investigated:
(1) Too much water supply?
(2) Moistening solution pH value is too small?
(3) Printing workshop temperature is too low or humidity is too high?
(4) Poor paper absorption?
Solution
When the above problems occur, it is necessary to strictly control the size of the layout moisture and grasp the pH value of the moistening solution. When the impression is not dry, the printed part should be aired in time for ventilation, so that the air enters the paper to speed up the conjunctiva time.
7. Ink drying too fast
When printing a monochromatic offset press, it often produces the former color blot drying too fast, forming "crystallization", so that the latter color overprint, the main reason is that the dry oil is added too much or the semi-finished product stacking time is too long, and this phenomenon often occurs when printing yellow plate or light background color full plate.
Solution
If this problem occurs, if the number of products that cannot be overprinted is small, a clean soft cloth can be dipped in magnesium carbonate powder, and gently wipe on the surface of each printed matter to coarser its surface; By irradiating infrared rays, the ink layer expands and thickens under heat. If the number is large, humidification treatment can be carried out to make the ink layer hygroscopic expansion and surface coarsening.
After the surface of the ink layer thickens, the latter color ink is easy to adhere, in order to prevent the phenomenon of printing, you can add an appropriate amount of non-dry wax auxiliary agent in yellow ink in advance, so that the ink layer will not crystallize, when printing the light background color full plate, you can mix the oil and diluent, but also to prevent the latter color printing.
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Anna Zhang