Offset printing is based on the principle of ink incompatibility, so controlling the ink balance on the printing plate is the key to ensuring the quality of offset printing.
1. Balance of ink and water In order to achieve ink-water balance, printing companies should do the following: 1 Adjust the amount of water, ink and printing pressure of the printing equipment, and bring it into balance. At the same time, under the premise of achieving printing effects, it is necessary to use the minimum The amount of water and ink are printed, and the speed is kept constant during the printing process, which is the so-called "three flat two small one constant." 2 Strictly control the pH of the fountain solution at about 5.0, the alcohol concentration at about 13%, and the temperature of the tank is controlled at about 10°C. 3 pay attention to the nature of raw and auxiliary materials, a reasonable mix of use. The inks that match the nature of the paper should be used, and since the ink additives can adjust the printability of the ink, it is necessary to add it in an appropriate amount according to the specific situation. 4 Use water-retentive and ink-absorbing printing plates to promote ink-water balance. 5 strictly control the temperature and humidity of the workshop, the temperature should be controlled at 22 ~ 25 °C, humidity should be controlled at 55% ~ 65%.
2. Fountain solution (water)
How to judge the size of water? The simplest and most direct method of determination is to measure the reflection of the layout visually. If it is gray, it means that the amount of water is moderate. In addition, if the ink fountain roller deinking, the ink droplets can be seen in the ink bucket shows that the amount of water is too large; if the soft goods printing software, due to the corners of the tilt caused by the uneven delivery, then the amount of water is too large; careful observation If there are obvious traces of graying in the mouth of the printed product, the amount of water is too large; if there is a noticeable drop of water at the tip of the printing plate clamp and the rubber blanket after shutting down, the ink color changes very much before and after it is turned on again. Large, then the amount of water is too large.
3. Ink and additives control the water, let's look at the ink. The trouble seems to be a large amount of water on the surface, but actually the problem lies in the ink. Due to the phenomenon of gluing, the operator has increased the amount of water, and water has drastically reduced the ink color. In order to achieve the printing effect, the amount of ink is increased, resulting in a large water and ink situation and the formation of ink emulsification.
The main component of black ink is carbon black, which is poor in water resistance, the moisture on the plate surface is absorbed by the ink, the layout is dark, and it is easy to paste the plate. At this time, it is necessary to adjust the ink by adding proper amounts of additives to the ink. Printability. Such as adding detackifier can improve the wettability of the ink, reduce the viscosity, improve the ink transfer performance, but does not increase the fluidity, can ensure the emulsification rate of the ink is about 25%, thus eliminating the ink over emulsification and stacking ink failure. But pay attention to the amount of additives should be controlled at 5% or less, if you add too much, it will cause the ink viscosity is too small, fluidity is too large, and thus easier to cause ink emulsification and paste.
In winter, the temperature is low and the viscosity of the ink is high. In addition to adding a detackifier to the ink, printing companies can also add No. 6 varnish (with dosage less than 5%) or aviation kerosene (with 1% to 2%). Both of them can reduce the viscosity of the ink and increase the fluidity. In summer, the temperature is high, and the ink viscosity is small. A printing company can add No. 0 varnish to the ink (the amount is controlled below 5%) to increase the viscosity of the ink, increase the transfer rate, and reduce the degree of emulsification.
Offset printing is a complex process. The operator must first adjust the printing equipment, control the pH, alcohol concentration, and ambient temperature and humidity of the fountain solution. Then, the amount of water and ink should be strictly controlled so as to achieve a good ink-water balance. Improve the printability of the ink. With proper control of all aspects, stable and high-quality products can be printed.