On the performance and application requirements of

On the performance and application requirements of offset printing fountain solution (Part 1)

Introduction

offset printing has not been printed with pure water from the beginning. In the past, every printer had his own formula for making potions. These formulas are nothing more than adding Arabic gum, glycerin, phosphoric acid and so on to tap water. Its purpose is to have a positive impact on the effect of offset printing, so that the printed product points are clear and clean, and the printing plate can reach the required service life. Of course, this fountain solution should also completely separate the printing part and non printing part of the printing plate

with the wide application of offset printing methods and the increasing requirements for printing quality, coupled with the new development of offset printing machines and water delivery devices, this simple bucket potion can no longer meet the needs. In this case, we developed a concentrated series of water bucket potions, which can meet the performance requirements of offset printing by adding it to tap water

the structural characteristics of water delivery devices are different (such as swing water supply, alcohol wetting, non-contact wetting, etc.), so it is necessary to have a special liquid medicine for a certain wetting mechanism to achieve the best wetting performance. In this way, many different kinds of bucket potions are produced. Nevertheless, all these potions must meet the following requirements: the pH value should be adjusted within the range conducive to the printing quality; Stability of pH value; Anti microbial effect; Prevent corrosion within the scope of the machine; Prevent plate corrosion; Reduce surface tension; Prevent ink roller deinking

(I) adjustment of the pH value of fountain solution

in 1909, the Danish biochemist Soerensen first defined the pH value as "the common negative logarithm of hydrogen ion concentration":

pH = - LG [h+]

it is an acid strength unit of a medium. The degree of pH value ranges from 0 to 14, and ph=7 indicates neutral. The range from 0 to 7 is acid, and the range from 7 to 14 is alkali. To determine the pH value of a medium, the hydrogen contained in it can be set with 10 or 6 slots with different widths on the side wall of the disc. The concentration of ions (H3O +) can be calculated according to the number of moles per liter (mol/1) and explained to the tenth power. According to the proposed definition, for example, the concentration of hydrogen ions in a solution is mol H3O +/1, as shown in the following relationship:

pH = - LG [H +] = - (LG Dow DuPont is only a temporarily established consortium 10-5) = - (- 5)

pH = 5

so the pH value changes by one unit, and the resulting hydrogen ion concentration also changes by a power of ten, that is, the multiplier of 10. The development process of offset printing shows that when the pH value of fountain solution is between 4.8 and 5.2, it is particularly beneficial to the printing quality

however, this range cannot be regarded as unchanging. Some printing plants also work in the alkaline range of pH 10. That is, adjust the pH value of the bucket potion to the required value, i.e. 4.9 or 9.5, with the specified and stable addition amount as far as possible

in addition, the adjusted pH value should remain stable and unchanged, and try to keep the external conditions unchanged. The external factors that affect the pH value of fountain solution are as follows:

(II) the influence of water quality on fountain solution

for example, the total hardness of water and the pH value of hydrogen carbonate composition have adverse effects (see Figure 2). In order to understand the external influencing factors, water should be analyzed. Only through analysis can the bucket potion be adjusted according to the water quality. If the hardness of tap water is too high, the content of hydrogen carbonate is too high or contains other harmful substances, it is necessary to purify the water before use. The hydrogen carbonate content in water is about 50 mg/L, which is more suitable for offset printing

(III) interaction between paper and fountain solution

paper is not a uniform material, but consists of many layers. The raw materials used for paper are not neutral, usually non coated paper is acidic, while coated paper is alkaline

on those water conveyance devices where the fountain solution is in direct contact with the paper (such as dagram water conveyance device), it is used to produce direct interaction, which will affect the pH value of the fountain solution. On the non-contact water conveyance device, this kind of influence does not exist, or it is only a slight influence

since the amount of water transferred from the printing plate to the paper through the blanket is not small, there will be quite obvious interaction according to the quality of the paper. The paper fibers absorb water and begin to expand. If too much water is absorbed, on the one hand, the size of the paper will change. On the other hand, water can act as a sealing layer, preventing the rapid penetration of printing ink

in addition, it may also cause the paper fiber or coating components to fall off (paper lint); Maybe the filler will also fall off. As a result, there will be ink piling or ink roller deinking

some bucket potions are added to the fountain solution, which will form a stable water film on the printing plate when the water supply is small. The use of this bucket potion plays a particularly important role in this relationship

(IV) relationship between printing ink and fountain solution

some printing inks also contain substances that affect pH value. This is also similar to the paper situation mentioned above, and there is a similar relationship between the contact and non-contact water conveyance device of the fountain solution

fountain solution and ink are quite different in structure and performance. In fact, offset printing ink is based on mineral oil, which is incomparable with fountain solution. However, it is this difference that makes offset printing exist. It is probably inappropriate to say that water and ink are mutually exclusive. In fact, offset printing ink must absorb a certain amount of fountain solution. Without this ability, the application of daglun water conveyance device (moistening the version through the first inking roller) is unimaginable

it is important that water should be absorbed as soon as possible, and this can form a stable water in oil emulsion. This process of absorbing water can be controlled by water bucket potion and ink

although the auxiliary agents used, such as glue solution and chemicals, are added according to the specified dose, these agents will also change the pH value of the fountain solution. After that, keep the pH value between ph4.8 and 5.2 for a long time (this range is beneficial to printing), and it is best to use water bucket potion with buffer. The concept of "buffer" is a kind of energy of water bucket potion, which can make the pH value prevent external influence, so that its own pH value will not ensure much change in the cleanliness of the oil circuit