In the printing process of composite packaging bags, the ink film color of color printing packaging bags mainly depends on the concentration and transfer rate of ink in the printing process.For some specific substrates or specific working inks, the concentration of the working ink is relatively fixed, and the transfer rate depends on factors such as the viscosity of the ink, and is also affected by factors such as printing speed.
1. Changes in temperature and humidity
If the room temperature and the liquid temperature of the ink are greatly changed, the flowing state will change and the color tone will change accordingly.This is because the temperature change affects the ink viscosity.At the same time, the dry weather of high temperature and low humidity will have a significant impact on the ink transfer rate of high-gloss parts.
Therefore, the temperature and humidity of the printing workshop should be controlled in any case when printing high-grade products.In addition, when the ink is used in winter, it should be preheated in advance to reduce the temperature change of the ink itself.
2. Separation of synthetic colors
This kind of scene is easy to occur in light colors and mixed colors such as organic and inorganic pigments with very different specific gravity.In particular, when the ink in the ink tray flows too slowly, precipitation will further promote the separation of synthetic colors, so attention should be paid to smooth ink circulation.
In addition, if mixing is not sufficient during color mixing, the concentration of a certain color tends to increase as printing progresses, so mechanical or other methods such as dissolving machine should be used for sufficient mixing before formal printing.
3. The ink deteriorates to make the color change worse.
Because of long-term printing, ink solvent composition changes, or water in the air mixed with ink causes ink deterioration, making the color change worse.
In order to prevent the temperature drop caused by the heat of vaporization, a slow drying solvent can be used.When the temperature is high and the humidity is high, a certain amount of water may be mixed into the ink, so new ink should be added or replaced completely when abnormalities occur.The residual ink that has been used many times should be filtered or replaced regularly because it has mixed with a lot of dust.
4. The working viscosity and drying speed of the ink change
The change of the working viscosity of the ink can directly affect the color of the color printing packaging bag.When the viscosity is high, the color concentration is relatively high, whereas when the viscosity is low, the color concentration is relatively low.This kind of influence is sometimes very clear and must be paid great attention to.Because of the requirements of the printing process, the working viscosity of the ink should be moderate.When the working viscosity of the ink is too high, it is not conducive to the transfer of the ink, and it is easy to produce a paste version.When the working viscosity of the ink is too small, the color of the printed matter is prone to electrostatic phenomena, which is also not conducive to the control of the ink color.
Changes in viscosity have subtle effects on the flow area caused by ink flow or dot flow methods, especially in multicolor printing.Therefore, when the printing speed is confirmed, the viscosity of the ink is required to be consistent from beginning to end, and an automatic viscosity controller is better used.
When the solvent ratio in the ink changes, the drying speed of the working ink will change, thus affecting the transfer rate of the ink and the printing color.For some inks with less dosage, after being used in the ink tank for a period of time, the natural volatilization of the solvent will not only affect the working viscosity of the ink, but also affect the solvent ratio and volatilization speed, so the solvent should be replenished in time.