Printability adjustment of printed materials II

The influence of temperature The control of the drying temperature is critical, because the fluidity of the ink depends mainly on the temperature and care must be taken to ensure that the temperature is constant. The viscosity of the liquid decreases with increasing temperature. For example, increasing the temperature by a few degrees can convert the syrup from a less mobile liquid to a water-like flow. Based on this fact, it is not difficult to understand that neither the cold ink nor the hot ink can be completed when using a detection system in an attempt to maintain a fixed ink transfer amount. This problem is particularly widespread in some countries in North America and Europe because seasonal temperature changes are likely to cause changes in the printing shop's temperature. It is also necessary to control the amount of diluent to make it consistent, generally the higher the temperature, the lower the required dilution.

The ink's thinness largely affects the density of solid areas. For example, a printer in Southeast Asia obtained an ink temperature of 25°C in the morning. He adjusted the ink to a temperature of 30°C according to the pressure demand, because the temperature of the printing shop has changed in the hot summer, so the viscosity The reduction is so great that as the ink is diluted, the density of the print will be reduced. Therefore, it is very important for the printer to adjust the ink according to the temperature of the printing shop.

Drying and viscosity control Correct drying is the main function of the basic resin and solvent in the ink vehicle, and the resin is insoluble. If you are using a polyamide system that contains more solids, the first step to improving printability is to look at the use of solvents and rosins. Can a solvent system provide a low viscosity carrier and good compatibility? Can the solvent volatilize from the ink?

High-quality inks require good solubility and decomposability so that those inks that are dried on a metal cylinder or plate can be dissolved by the new ink, so that the ink cannot be deposited and dried on the plate or on the metal cylinder. If the drying speed is slow enough or the solvent/water in the ink has the proper dissolving power, the dried ink will dissolve well. Water-based inks are dried by the absorption or evaporation of moisture by the paper. If the ink dries too quickly, it will accumulate quickly and the halftone dots will be destroyed or lost, and the solid part will be uneven or missing. If the drying speed is too slow, dot formation will be a problem. In the case of several kinds of oil and ink overprinting, if the first color ink is imprinted more solidly, the ink layer is thin and as dry as possible, the color overprinting effect after that will be better. This means that the drying speed of successively superimposed inks must be continuous. The first ink must dry fastest and the second slower, but not so slow that it causes the ink to accumulate, the ink to bleed or the back Dirty.

In order to reduce the evaporation of ink on the printer, a closed transfer ink unit is used on modern presses. One of the main requirements for the ink on the press is that it cannot flow and it should remain in a state until after it is transferred to the paper base. Water-based inks want to reduce the diluent to adjust the viscosity of the ink during printing. In most presses, a sink is mounted below the printing unit, and excess ink is drawn into the conduit to maintain the same amount of ink and ink roller position. In this step, the ink in the conduit and on the roller is in contact with the air during the process of waving excess ink. This causes the moisture or solvent in the ink to evaporate, which increases the viscosity of the ink and increases the density of the ink. . Therefore, the amount of diluent added to the ink directly affects the density of the print. As previously discussed, water-based inks are particularly sensitive to the addition of diluents and the viscosity needs to be carefully adjusted. Since the early discussion of water-based inks was very sensitive to thinner, the viscosity adjustment also needed to be careful. The amount of water added to the ink must be strictly controlled, otherwise it will dilute the ink and reduce the viscosity of the ink. It should try to avoid adding new inks in low-viscosity inks in an attempt to increase the viscosity of the inks. According to past experience, the amount of new inks added is quite high. The control of the viscosity of the ink is very important because it determines the properties of the ink and controls the color of the print.

One of the advantages of water-based inks is that less solvent (water) is lost through evaporation, and solvent-based inks will largely evaporate the solvent, causing the viscosity of the ink to change, so more adjustments are needed. Since the main drying method of the water-based ink is accomplished through the penetration of the ink in the ink on the paper or paperboard, and only a small part is completed by evaporation, the printing should be considered when printing with a water-based ink. The quality of the surface of the material. The speed of drying is closely related to the absorbency of the substrate and the type of resin/water used in the ink formulation. This raises a serious problem of finding a balance between the drying speed and the printability of the ink. Especially when using fast-drying inks for high-speed printing, this problem should be paid attention to. This is because the fast-drying ink not only dries faster on the substrate, but also it quickly dries on the printing plate and the metal cylinder. There are many obstacles. The adjustment of the ink drying properties must be related to the printing speed.

Additives Additives are added to the ink to improve the printability of the ink and to give the ink some special properties to meet the final needs. Most of the additives are used in small quantities, but they must fully understand their function, the restrictions they are subject to, and the possible impact of various aspects. The use of surfactants helps spread the toner in the solvent, has a certain effect on gloss, color, and reduces the amount of toner so that they can condense when diluted. Other additives include plasticizers, waxes, accelerators, and the like. There are also special additives in water-based inks, foam eliminators, fungicides, waxes, surfactants, wetting agents, transfer agents, coalescents, anti-caking agents and slip agents, all of these additives. All make the ink have different properties.

In the ink manufacturing and on-machine printing processes, especially in some cases where high-speed circulation is performed, it is inevitable that some foam will appear and it is difficult to remove. The use of excessive foam-removing agent will cause CRATER to make the surface of the print very uneven. Some foam-removing agents contain hydrocarbons and damage the photosensitive resin plate, so care must be taken when choosing foam-removing agents. If it is necessary to add a foam-removing agent, it should be carefully added to the ink in order to be able to squeeze out more foam. How much foam is related to the hardness of the water used, ensure that the amount of foam eliminator used does not exceed 1%, otherwise it will cause more serious expansion of the photosensitive resin plate. Silicone-based foam eliminators need to be diluted with water and added to the ink with regular agitation. If concentrated silicon products are used without dilution, pinholes (small white dots in the image) appear on the final print.

Another important factor in the PH value of a water-based ink is that its pH value remains constant, and changes in the pH value can have a large impact on the ink transfer and printing color. If the pH is too high, the ink will dry too slowly. If the PH value is too low, the viscosity of the ink fluctuates, causing the resin to separate from the solvent and form a precipitate. Only a standard pH meter can easily measure the pH of the finished ink. Usually the water-based ink is alkaline, PH value is greater than 7, the normal pH range is 8-9, but the formula of the ink will have a certain impact on the PH value.

The key to the success of ink films for high-viscosity ink printing is to apply as thin an ink film as possible so that the desired color and ink film properties can be obtained. In order to obtain such an effect, it means that the ink is colored in a lower-viscosity carrier. The powder is present in high concentrations. Another requirement is that the distribution of the toner in the solvent must be uniform or that the toner has good wetting (this is the function of the resin and the toner), regardless of the mechanical method used. In most cases, the wetting of the toner is relatively good, the viscosity is the lowest, the intensity and depth of the color are also good, and the thixotropy is the lowest.

The high viscosity of the ink must be transferred to the substrate with the most effective occurrence. The highly viscous ink is printed with a high viscosity and a fine metal roller. After the squeegee, a thinner ink film thickness can be obtained, so the quality of the print is very good and the cost is low. The ink fountain roller system requires a low viscosity ink and reduces the overall quality. When the transferred ink film is almost the thinnest, the print product can reach the best quality. (to be continued)