1 Introduction The ideal offset ink should have the dual characteristics of high viscosity and low viscosity. As we all know, the basic performance of ink is mainly determined by the binder. In the production process, different resin binders are used, and the quality and performance of the ink are also completely different. At present, rosin-modified phenolic resins are mostly used for lithographic offset printing inks. There are many varieties of this type of resin, the main difference is the use of different phenols, such as phenol, bisphenol A, tert-butyl phenol, octyl phenol, nonyl phenol, dodecyl phenol and so on. With the gradual increase of phenolic molecular weight, the performance of the resin will be significantly improved and improved. In this regard, many people have done research. Some researches have been conducted on rheological properties and printing suitability (1), and some have conducted detailed discussions on the constituent raw materials, synthetic processes, and ink applications of rosin-modified phenolic resin binders (2, 3). Various kinds of information in recent years indicate that there are not many domestic manufacturers that have mastered the production technology of high-grade alkylphenol phenolic resins. However, the earlier rosin phenolic resins, such as phenol, bisphenol A, tert-butylphenol and other modified rosin phenolic resins, have always had a conflict of increasing viscosity and solving solubility problem. It is difficult to ensure high viscosity and low viscosity at the same time when producing inks using such low molecular weight resin binders. Of course, using low molecular weight resins can also increase ink viscosity. For example, increase the viscosity of the resin or increase the amount of resin in the binder. However, both of these conditions are bound to result in high viscosity and insufficient fluidity of the ink. In fact, it is a "high-viscosity, high-viscosity" product; the molecular weight of the resin can also be made lower, but such a resin is difficult to ensure high viscosity. The usual practice is to mix them and get some performance trade-offs. This is often very passive and often overlooks others. The author starts with the analysis of the influence of the viscosity and fluidity of ordinary low viscosity (low molecular weight) resin binder inks on printing, and focuses on the excellent performance of high viscosity and low viscosity inks. 2 Effect of ink stickiness and fluidity on printing Inks produced with low molecular weight resin binders, whether they are sticky or fluid, can only be selected within a certain range. Therefore, there is a problem that the stickiness is high or low, the fluidity is too large or too small, and thus the printing is directly affected. (1) If the viscosity is high and the fluidity is large, the ink appears thin and sticky. When printing, there will be flying ink and pulling paper hair, aAB, referred to as flying ink area. (2) If the viscosity is high and the fluidity is small, the ink becomes thick and sticky. When printing, there will be more severe paper pulling and poor transfer. bBC, referred to as the paper pull area. (3) If the viscosity is low and the fluidity is high, the ink appears thin and soft. There will be dirty prints and dot gains when printing. dAD, referred to as dirty area. (4) If the viscosity is low and the fluidity is too small, the ink will appear soft and weak. When the printing occurs, there will be a situation that the ink piles and the dots are not clean, cCD, or the ink accumulation area. Among them, the most important is the O point. This is a theoretical pole value that does not exist in practice. However, the diamond ABCD area can be considered as an acceptable product area. The four corner areas a, b, c, and d are the most problematic areas. 3 High Viscosity and Low Viscosity Ink Properties The above analysis refers to those ordinary low viscosity low molecular weight resin binder inks. At present, most of the high-quality lithographic four-color inks used in the link material, mostly by high-level alkyl phenol (octyl phenol, nonyl phenol, dodecyl phenol, etc.) phenolic resin production. The ink produced with such a resin binder has the characteristics of high viscosity and low viscosity. The excellent properties of high viscosity and low viscosity inks are closely related to the structure of the resin. Mainly have the following characteristics: The resin has a large molecular weight, a high softening point and a high viscosity. The high viscosity of the resin is the premise of the high viscosity of the ink, and it is also the guarantee that the ink can achieve low viscosity. Rosin-modified phenolic resins are complex macromolecular compounds obtained by the addition of rosin (polymerized rosin) and a phenolic phenolic resin, followed by esterification with a polyol. The macromolecule high-viscosity rosin modified phenolic resin has high structural characteristics, good gelability and strong cohesion. Therefore, when the ink is produced, even if the viscosity is made lower, it can maintain sufficient high viscosity, good rubber elasticity and cohesion. Essentially speaking, high viscosity and low viscosity are a relative concept and they are two contradictory aspects. The higher the viscosity, the better, and the lower the viscosity, the better. If we do not talk about uniformity, we can use ordinary low-viscosity resins, can also produce very high viscosity inks (open sticky) and very low viscosity inks (open sticky). However, such inks are not easy to use, and they have no use value. The real meaning of the so-called high viscosity and low viscosity should be "to maintain a sufficiently high viscosity in the case of low viscosity." The ink with this dual characteristic can be called good ink. Second, the use of such resin long-chain alkyl phenols (octyl phenol, nonyl phenol, dodecyl phenol, etc.) helps to improve the solubility of the resin. Therefore, although the higher alkylphenol phenolic resin has a large molecular weight and a relatively high softening point, it has good solubility in vegetable oils and a certain range of mineral oil solubility. Good oil solubility helps make the ink less viscous and also helps improve the flow of the ink. Therefore, inks with high viscosity, strong cohesion, good elasticity, low viscosity, and good fluidity have good printability. In addition, such high-viscosity resins contain hydrophilic carboxyl groups, polyols, and other polar groups, which is conducive to improving the wettability of the pigment; at the same time, it also contains a long-chain alkyl group that is lipophilic (hydrophobic), and therefore very Good oil-water balance, which is very beneficial to ensure the ink's good rheological properties and water resistance. In short, high viscosity and low viscosity ink has many excellent properties, including two aspects: First, the ink itself has the inherent characteristics, such as high adhesion, high gloss, fast fixation, strong water resistance; second, good printability , such as good ink transferability, transferability, dot reproducibility and so on. 4 High Viscosity and Low Viscosity Ink with Broader Adaptability High-viscosity and low-viscosity inks are excellent in performance, and the requirements for viscosity and fluidity are very loose, and the quality is also guaranteed. (1) The overall shift of the graph indicates that the viscosity of the ink can be greatly reduced. Due to high resin viscosity, good elasticity, and strong cohesion, even if the viscosity is significantly reduced, the ink can still maintain sufficient high viscosity and good flow properties. Therefore, there will be no problems such as poor delivery, no ink, and piles of ink. (2) The overall expansion of the graphic EFGH shows that the control range of the viscosity and fluidity of the ink can be relaxed. The higher alkylphenol phenolic resin has a sufficiently high viscosity and good dissolution properties. Therefore, even if the viscosity of the ink is made much lower than that of the ordinary low viscosity resin binder ink, the ink can maintain sufficient viscosity. On the other hand, because the viscosity of the ink is low, even if the viscosity is made a little higher, the ink can still be thick and sticky, flow without soft, thick and loose. Similarly, since such inks have sufficient viscosity and elasticity, even if the fluidity is made a little larger, the ink will not appear soft and there will still be a good body bone; on the other hand, due to the low viscosity of the ink, even With less fluidity, the ink will not stick. (3) The EFGH rectangles are all within the safety zone, not just the diamond ABCD. In the area of ​​the rectangular EFGH (which has been enlarged), the viscosity of the ink is higher and lower; the fluidity is larger and smaller; and both the ink performance and the use effect can be maintained. 5 High Viscosity and Low Viscosity Ink Technology High-viscosity, low-viscosity ink is a product of rapid development in the printing industry. People should see that high-speed printing of lithographic offset sheet requires high-viscosity, low-viscosity ink. The rapid development of rotary offset printing technology also requires high-viscosity and low-viscosity offset offset printing inks. This fact is also proved by this fact. Since 2000, the company started to research and develop a new generation of rotary offset ink formulations that completely use rosin-modified phenolic resin binders and achieved success. After years of production and use, it has matured. This kind of high viscosity and low viscosity web offset printing ink has obvious performance advantages. There are some characteristics of lithographic offset printing sheet-fed ink. Some technical indicators are similar or similar to lithographic offset printing sheet-fed ink.
Adapts to both sheetfed and offset inks
Source: Northeast Printing Network
Talking about the Performance of High Viscosity and Low Viscosity Offset Printing Inks