Ink thixotropy is one of the properties of the printing process and it has a great influence on the quality of the printed product. The so-called thixotropy refers to the ink under the influence of external forces and external environmental factors and effects, the ink thinning or thickening, a phenomenon of fluidity changes. For the printing process, stable product printing quality requires the ink to maintain a moderate and stable flow. However, due to the inherent factors of the ink and the printing conditions, the ink will inevitably appear “thixotropic†during the printing process, which affects the stability of the product quality. Therefore, a correct understanding of the thixotropy of ink, from the process, technology to take some measures to overcome and make up, reduce the degree of thixotropic ink printing, in order to better ensure product quality.
Understanding the thixotropy of ink In the production process practice, we have found that the general ink has a certain thixotropy, and the main performance is that the ink becomes lean after being agitated and rubbed to increase the fluidity, and it is put to rest. After a while, the ink will return to its original thicker state. If the viscosity of the larger ink, under the stirring of the external force, its solidification state is destroyed, it has a certain degree of fluidity. In the static state, as the time increases, the solidification state gradually increases. When the power is turned on again, it will affect the normal flow of the ink in the ink fountain, and even the phenomenon of non-transmission. On the other hand, the ink on the ink fountain and the rubber roller of the printing press undergoes a rotational friction, and its temperature increases, so that the fluidity and the ductility also increase. After the ink is transferred to the printed sheet, the external force disappears and the fluidity thereof Reduced ductility, followed by thinning and thickening, to ensure the clarity of the printed ink. In addition, when the temperature is low, the ink becomes thick; on the contrary, the ink becomes thin and the fluidity increases. When the machine is stopped for a long time, the ink in the ink fountain will gradually return to its original shape by thinning and thickening. These are the normal phenomenon of ink thixotropy.
Generally in the printing process, the vast majority of ink will be thick and thin, the reason is the temperature change factors, such as the machine temperature, ink roller temperature, plate heating and so on. When the ink has a certain thixotropy, it is advantageous for the smooth and even transfer and printing of the ink. Influencing the thixotropy of ink, in addition to the above-mentioned factors, is mainly determined by the ink composition characteristics, such as the use of inks made of pigments with strong surface adsorption, the thixotropy is large; the ink in the ink is pin and plate The thixotropy of the spherical particles is larger than that of the spherical particles, and the thixotropy of the pigments is large. This is due to the fact that the pigment molecules attract each other to flocculate; the wettability of the pigment and the binder is poor, and the thixotropy of the ink is also Large; resin molecules than the major ones, ink thixotropy is also large. In addition, the thixotropy of the pigment ink is also relatively large, the reason is that the pigment content in the ink is too much and the quality of the pigment is poor, such as poor wetting, relative density is low, and the tinting power of the ink is low. There are also problems such as when there are too few binders in the ink and the viscosity is too small. The effect of ink thixotropy on print quality can be said that ink thixotropic discomfort has a great influence on print quality. In the production practice, we found that in the printing process, especially in the case of low temperature and slow machine speed, the ink in the ink fountain is often not smoothly conveyed, the ink supply is not normal, and the ink of the printing product is getting lighter and lighter. Affects the stability of printing ink color, which is the main performance of ink thixotropy. In this regard, it should be noted that the ink in the ink fountain is often stirred to maintain a continuous, uniform flow and ensure the quality of the ink. Some inks in the transmission process, due to thixotropy is too large, before its thixotropic phenomenon, its viscosity is higher, it is easy to cause ink blocking, paste plate failure during printing. Therefore, some presses are equipped with a stirrer in the ink fountain, which stirs the ink to make it “thixotropy†to improve the flow of the ink and reduce the viscosity of the ink so as to prevent the occurrence of blockage and stencil of the ink. The thixotropy of the ink is too large, the ink in the printing process is more and more dilute, the ink of the printing ink is printed and faded, and it is almost impossible to adjust. This ink is not suitable for printing full-version printing on the field, and printing should pay attention. this problem.
Technical measures for controlling the thixotropy of inks Printing requires the ink to have an appropriate thixotropy. If the ink thixotropy is too large or too small, it will have a bad influence on printing. The thixotropy of the ink is mainly determined by its material properties, but as previously mentioned, the printing conditions also affect the thixotropy of the ink to a certain extent. Therefore, when the inherent thixotropy of the ink cannot achieve normal printing, corresponding control can be performed through technological measures. Such as printing in accordance with the characteristics of the printer and the temperature level, adjust the moderate ink flow. When the printing speed is low and the temperature is low, since the thixotropy of the ink is small, its fluidity is also small, which is not conducive to uniform ink transfer and ink deposition. At this time, the ink can be appropriately thinned to meet the requirements of the printing process. In order to prevent the excessive “thixotropic change†of the ink and the adverse effect on printing, it is necessary to control the printing process conditions so that the thixotropy of the ink is controlled within the printability range. The first is to try to do it in a constant temperature and humidity environment. Printing, installation of air-conditioning equipment in the workshop. If the conditions are limited, when the climate is dry and the wind is large, the doors and windows of the workshop can be closed to prevent the ink from thickening and becoming sticky. Secondly, in the case where the thixotropy of the ink itself is too large, the printing speed should be controlled as much as possible. In the lowest range, to reduce the friction coefficient of the machine, so that the ink temperature increases, so that the ink thinning; Third, under the condition that does not affect the uniform layout, full ink, to minimize the use of the ink roller on the machine Branch number to reduce the friction coefficient during printing; Fourth, adjust the position of the ink roller and water roller on the machine to prevent the contact between the ink roller and the ink roller, between the ink roller and the plate, or between the water roller and the plate, and the friction coefficient. A large cause of abnormal temperature rise makes the ink thinning; Fifth, control the ink fountain roller rotation stroke, if the ink fountain roller rotation stroke is large, the temperature will be high, the ink is also easy to thin. Therefore, in the case of high printing speed, the rotation stroke of the ink fountain roller should be adjusted as small as possible, and the gap between the ink fountain roller and the ink fountain roller should be adjusted slightly to meet the printing and ink supply requirements. ) In the case of a large printing plate, the printing speed must be controlled to a lower level to reduce frictional heating. Seventh, a reasonable selection of printing inks is required. The printed cable version requires a slightly larger thixotropy of the ink, and printing of a large area of ​​the ink on the ground The thixotropy is slightly smaller so that the printing quality can be improved.
In summary, the thixotropy of ink has a certain influence on printing, and the factors influencing the thixotropy of ink are various. Therefore, the correct understanding of the thixotropy of ink and its related factors, in the printing process to take appropriate technical measures to properly control the ink in the printing process to maintain a relatively stable state, to effectively avoid this or that print quality defects The production of printing quality and printing quality is of great significance.