Guide: In the printing of self-adhesive labels, the problem of poor ink drying often occurs. To solve this problem, we must first find out the reason. Let's take a look at the causes and solutions for the poor drying of self-adhesive label printing inks!
The ink layer is too thick
The ink layer is too thick, the paper feeding speed is too fast or the UV light irradiation time is insufficient. In the large-area solid printing process, since the ink amount is too large and the ink layer is too thick, the ink layer on the surface of the printed product will appear completely in the drying process. Drying and the bottom layer is not dry thoroughly, that is, the phenomenon of dry drying. In addition to the ink layer is too thick, the paper feed speed is too fast, and the UV light irradiation time is insufficient to cause the UV ink to dry. Once the ink dry phenomenon occurs, it is easy to cause the ink layer on the surface of the printed product to fall off during the post-processing. This is because the poorly dried ink underlayer has poor bonding fastness to the surface of the substrate, so that the ink layer is scraped off by the frictional force.
Solution
For the job of printing the spot with the spot color UV ink, try to match the color of the spot color UV ink with the ink, so that the bottom layer of the ink can be thoroughly dried by the deep ink printing method during the printing process, and the The bonding fastness of the substrate surface. At the same time, it is necessary to ensure a proper paper feed speed and sufficient UV light irradiation time. If the paper feed speed is faster, the power of the UV lamp must be increased to ensure the ink drying effect.
Insufficient UV lamp power
Insufficient power of UV lamps is also one of the causes of poor drying of UV inks. This is related to the daily production operations of self-adhesive label printing companies, mainly in the following aspects.
1. All UV lamps have an effective service life (normally 800 to 1000 hours). When the UV lamp is used for more than its service life, although the UV lamp can continue to work, its power has been greatly reduced. For the self-adhesive label printing company, the UV lamp that has exceeded the service life has not been replaced in time due to cost considerations.
2. After replacing the UV lamp, the timer of the UV lamp is not reset to zero, which causes the use time of the UV lamp to exceed the service life but is completely unknown.
3. Do not pay attention to the surface cleaning of the UV lamp. After a long time of use, the UV lamp's reflector is too dirty, causing the reflection energy loss of the UV lamp (reflected energy can account for about 50% of the UV lamp power).
4, UV lamp power configuration is not reasonable, such as some full-rotation self-adhesive label printing machine each group of UV lamps with a power of only 2000 watts, such a configuration is obviously off the bottom. It is understood that at present, the reasonable configuration of each group of UV lamp power in the domestic full-rotation sticker printing press is basically more than 3,000 watts. Because of the faster printing speed of foreign equipment, the power of each group of UV lamps is basically above 7000 watts.
Solution
First of all, self-adhesive label printing companies must establish a complete and effective UV lamp usage management system to ensure that UV lamps work within an effective service life, replace UV lamps that have exceeded their service life in time, and replace the units with UV lamps. Pay attention to zeroing the use timer of the UV lamp. Secondly, periodically clean the reflector of the UV lamp to reduce the loss of reflected energy. Furthermore, the power of the UV lamp can be reasonably configured according to the structural characteristics of the device.
Ink exceeds shelf life or excess ink additive
Under normal circumstances, the shelf life of UV inks is about 1 year. If the shelf life is exceeded, the ink may be poorly dried due to the failure of the photoinitiator in the ink after printing. In addition, in the printing production, in order to improve the performance of the UV ink, it is often necessary to add an additive such as a varnish and an viscous agent to the ink. If the proportion of the additive is too high, the UV ink may be too thin to cause poor drying. In fact, the UV ink itself has thixotropic properties, that is, it becomes thinner and thinner under the action of the ink roller shearing force. Moreover, after the printing equipment is operated for a period of time, frictional heat is generated between the ink rollers, thereby reducing the viscosity of the ink.
Solution
First, ensure that the UV ink is used during its shelf life; secondly, it is recommended that the proportion of UV ink additives not exceed 3% in summer and not more than 8% in winter.
UV inks of different colors have different degrees of drying
Tests have shown that different colors of UV inks have different absorption properties for the spectrum, so under different UV lamps, the UV inks of different colors have different degrees of drying. For example, the white UV ink can directly reflect the light, the black UV ink will form a diffuse reflection of the light, and the magenta UV ink absorbs the light better.
According to experience, the difficulty of drying the four primary color UV inks is black, cyan, yellow and magenta in the order of difficulty, while the gold and silver UV inks are more difficult to dry than the four primary color UV inks. The white UV inks have reflections on the light. The effect is also difficult to dry.
Solution
According to the drying characteristics of UV inks of different colors, the printing color sequence is reasonably arranged, the ink which is difficult to dry is printed first, and the ink which is relatively easy to dry is printed, so that the problem of poor drying of the ink can be solved to some extent.
Rubber roller density is too low
In actual production, new equipment is more prone to poor ink drying failure. After careful inspection, it was found that the rubber roller in the UV ink absorbed the photoinitiator in the UV ink due to the low density, which caused the ink to dry poorly.
The drying of the UV ink is mainly achieved by a chemical reaction between the photoinitiator and the resin, wherein the molecular structure of the resin is large, and the molecular structure of the photoinitiator is small. If the density of the rubber roller is too low, many small holes will appear on the surface. Since the diameter of these small holes is larger than the diameter of the photoinitiator, part of the photoinitiator in the UV ink is absorbed by the rubber roller, causing the UV ink to dry. In the process, the chemical reaction of the resin and the photoinitiator is insufficient, resulting in poor drying of the ink, and accompanied by the phenomenon that the ink is dried on the surface of the rubber roller.
Solution
The easiest way is to replace the rubber roller; if it is too late to replace the rubber roller, you can also remove the rubber roller and soak it in UV varnish for 12 to 24 hours. At this time, the rubber roller will gradually absorb the UV varnish. It is difficult to absorb the photoinitiator in the UV ink after saturation.
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