Problems to be paid attention to when using water-based ink in screen printing
1. In screen printing, we should pay attention to control the parameters of water-based ink, including ink viscosity, fluidity, thixotropy and plasticity.
2. Pay attention to the control index of water-based ink. The control indexes of water-based ink are mainly fineness, viscosity, pH value and drying speed, etc., which play a decisive role in the application effect of the ink.
3. Because the water-based ink is a pure water-based system, it is necessary to pay attention not to mix the water-based ink with alcoholic ink and solvent-based ink or add organic solvents to the ink to avoid printing quality problems.
4. When using water-based ink, stir it evenly, pour it into the ink tank after measuring the appropriate viscosity, if the viscosity is not suitable, you can use thinner or thickener to adjust, and pay attention to control the pH value of the ink, generally in 8.5 ~ 9.5. During the printing process, due to the volatilization of water, the viscosity of the ink will increase and the pH value will decrease. Therefore, you should always observe the use of the ink and find that when the viscosity of the ink increases or the pH exceeds the control range, you should use diluent and pH stabilizer in time. Adjust to ensure the stability of viscosity and pH.
5. In general, ink is very suitable for high-speed printing. If low-speed printing encounters a situation where the drying speed is too fast or the printing effect is not good, a certain proportion of slow-drying agent can be added.
6. After the printing is completed, the remaining ink should be returned to the corresponding original barrel or the cover of the ink tank should be tightly closed for future use. Prevent condensate, thickening or even drying due to ink surface. Water-based ink should be stored in a ventilated and cool room at room temperature controlled at 5 ~ 45 ℃.
7. The ink remaining on the printing equipment after printing can be rinsed with clean water when it is not completely dried, and the ink that cannot be cleaned with clean water can be cleaned with a cleaning agent.
8. The printing suitability of ink is affected by objective conditions such as printing conditions, surface characteristics of the substrate, environmental temperature and humidity, storage time, etc. Therefore, when using it, some additives need to be finely adjusted to obtain the best printing effect. Auxiliaries commonly used in water-based inks include colorants, pH stabilizers, slow-drying agents, defoamers, diluents, etc. In printing, you should be familiar with the characteristics and usage of the additives.
1) The colorant is used to deepen the color, and its dosage should generally be controlled at 0-30%. If it exceeds 30%, the content of the connection material in the ink will be too low, resulting in a decrease in its adhesion and wear resistance.
2) The pH value stabilizer is used to adjust and control the pH value of the water-based ink so that it is stable at 8.0 to 9.5 to ensure the printing state of the water-based ink. At the same time, it can also adjust the viscosity of water-based ink and dilute the ink.
3) Slow drying agent is used to reduce the drying degree of water ink. Slow drying agent can inhibit and slow the drying speed of water-based ink, prevent the ink from drying on the printing plate, and reduce the occurrence of printing failures such as blocking and paste. The amount of slow drying agent should generally be controlled at 0 to 10% of the total ink. If the amount is too much, the ink will not dry completely, and the printed matter will be dirty or produce an odor.
4) The diluent is mainly used to reduce the depth of the color, the amount is not limited. However, the addition of a large amount of diluent may cause the viscosity of the ink to rise slightly. At this time, a small amount of thinner can be added for adjustment.
5) Dilution is mainly used to reduce the viscosity of the ink, the amount should be controlled within 3%, so as not to reduce the color depth of the ink, and keep the pH of the ink unchanged. The thinner should be added slowly while stirring to prevent the viscosity from being too low. If adding more thinner or using high hardness tap water to dilute will produce bubbles, then defoamer should be added.
6) The main cause of foaming problems in the use of water-based inks is that they use water as a diluent. During emulsion polymerization, a certain amount of emulsifier must be used to greatly reduce the surface tension of the emulsion system. The function of the defoaming agent is to suppress and eliminate the generation of air bubbles, to avoid print quality problems such as pinholes, white leakage, and uneven ink color due to the air bubbles, but the general amount of defoaming agent should be controlled at 0.1% to 0.2%.
7) The thickener is mainly used to increase the viscosity of the ink, and at the same time it can give the ink excellent mechanical and physical and chemical stability. It can play a role in controlling the rheology during printing, but the amount should not be too much. More thickeners will thicken the film wall of the bubble and increase its elasticity, making the foam difficult to eliminate. Generally, it is better to control it at 0.5% to 1%.
8) The quick-drying agent is mainly used to speed up the drying speed of the ink, and the dosage is 0-30%.
9) The anti-settling agent can make the pigment particles in the ink suspend and disperse evenly, which is not easy to accumulate and settle, and avoid the phenomenon of floating color.
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