Problems needing attention in the successful appli

Problems needing attention in the successful application of alcohol free printing

alcohol free printing with alcohol substitutes is easier to achieve the balance of water and ink. Printing with a specific thickness of ink film that is not diluted by alcohol can obtain higher quality prints with a little fine and less emulsification

when investigating a large printing enterprise in Shenzhen, we saw that the enterprise is promoting alcohol free printing and achieved good results. The use of alcohol-free printing can not only reduce the printing cost, but also be more environmentally friendly, and can reduce a series of environmental problems caused by alcohol volatilization. Therefore, this article on alcohol-free printing is compiled in order to let everyone better understand and apply alcohol-free printing

alcohol free printing with alcohol substitutes is easier to achieve water ink balance. Printing with an ink film of a specific thickness that is not diluted by alcohol can obtain higher quality printing with a little fine and less emulsification

1. Alcohol substitute

alcohol substitute is different from IPA (isopropanol) in several key properties, including its viscosity, surface tension, pH value and the conductivity of fountain solution. Alcohol free products cannot be applied to different printing machines at will, which requires close communication with printing operators to seek the best formula of fountain solution from suppliers

in fact, there are many alcohol substitutes that can be used. They are all composed of one or more chemicals extracted from the chemical family of glycol and glycol ether, and some other additives similar to IPA are also added. And these formulas try to completely replace IPA in fountain solution, and provide some unique properties. More importantly, the concentration of alcohol substitutes we use is far lower than that of IPA. Under the same printing conditions, a small amount of alcohol can replace Panasonic exchange servo electromechanical products to achieve the effect of containing IPA fountain solution 10 ~ 20 times

2. Viscosity of fountain solution

adding IPA to fountain solution will greatly increase its viscosity, but many alcohol substitutes have little or no effect on viscosity. Due to the decrease of viscosity of alcohol substitutes, less fountain solution is measured by extrusion or by using measuring rollers on continuous contact fountain rollers, so the speed of fountain rollers must be increased, resulting in many printing operators mistakenly concluding that more water must be used when printing with alcohol substitutes. In fact, the solution to improve the viscosity to a certain extent is to cool the fountain solution

3. Surface tension

the ability to quickly wet the printing plate and form a thin water film is the two key requirements of offset printing on the fountain solution, which is mainly determined by the surface tension of the fountain solution. It is generally believed that the fountain solution with low surface tension can be better used in high-speed printing, but there are also reports on the contrary in Europe. It is understood that the current alcohol substitutes can achieve the low surface tension of IPA that printing operators are accustomed to and adopt hydraulic clamping

the surface tension of pure water is 72 n/m. In the fountain solution, the concentration of alcohol is 10% ~ 25%. Reducing the surface tension to reach (35 ~ 45) n/m can make the fountain solution quickly form a continuous film to cover the whole printing plate. Alcohol free fountain solution uses surfactants and solvents to reduce surface tension

surfactants or surfactant additives are organic chemicals, which tend to concentrate on the interface because of their polar molecular structure. Under normal circumstances, they are on the interface between fountain solution and air and between ink and air. In the case of high-speed printing, these interfaces change rapidly, so the surfactant must be quickly dispersed to replenish the new interface. A large amount of surfactants in fountain solution is very important in the printing process, but adding too much will also aggravate ink emulsification

4. Printing brightness and gloss

alcohol is a diluent that actively invades the ink. It makes the ink lose luster and affects the color. In order to achieve an acceptable color, it is required to coat a thicker ink film on the embossing cylinder. When used at a suitable concentration, alcohol substitutes have no dilution effect on the ink, and only a small amount of ink and water are needed to obtain an acceptable color. In this way, the point will be more accurate, and the trend of point increase will also decrease

5. Conductivity and pH value

in printing, it is very important to maintain the consistency and stability of conductivity and pH value. Before printing, the conductivity of fountain solution should be measured first. Any impurity may lead to abnormal conductivity. At this time, the conductivity of water should be re inspected. In the printing process, ink and paper [encyclopedia] may pollute the fountain solution, and the increase of its conductivity is normal

pH value can be measured simultaneously with conductivity. The pH value of acid fountain solution should generally be 4.0 ~ 5.0. For high-quality printing, it is important to maintain the optimal pH value of the fountain solution used. All acidic fountain solutions have a buffer effect to some extent. If the concentration increases, the conductivity will continue to increase at a linear speed, while the pH value begins to decline, and then tends to be flat. Therefore, conductivity can determine the concentration of fountain solution more than pH value

if the pH value is too high (higher than 5.5), the printing plate may be dirty. In order to keep the printing plate clean, it is necessary to increase the amount of water, which may cause serious emulsification of the ink. If the pH value is too low (below 3.5), the printing plate may be scratched, the ink will emulsify, the drum will peel off, and the ink drying time will be extended

6. Practical application of alcohol substitutes

there are two goals for using alcohol-free fountain solution. The first is to use safety materials to produce high-quality products; The second is to choose and use alcohol-free products to achieve better results. According to the different fountain equipment, water, ink, substrate and even live parts, these choices will also be different

7. Pre test alcohol substitutes

if the printing machine is replaced with a new fountain solution, it must be inspected and tested in advance. The actual test of a printing unit may sometimes be better than a laboratory equipped with various measuring equipment. When testing, it should be carried out within the range of measurable tolerance. The best way is to carry out according to the instructions of the equipment. If the tolerance has a certain range, the setting and operating performance of the printing process can be recorded in the document starting from the lower limit

when using alcohol substitutes, it is important to establish the best ink and water balance through printing experiments. The test shows that the use of alcohol-free materials may need to adjust the production conditions in the past. However, in order to measure this accurately, the production conditions of the enterprise must be quantified

8. Mechanical adjustment

special attention should be paid to that when printing with alcohol-free fountain solution, the requirements for various parameter tolerances are more strict, and any problems masked by the use of IPA may occur. Therefore, if you want to use alcohol-free printing, it is recommended to reduce the alcohol consumption by about 8% first. If this adjustment will cause problems, then once you use alcohol-free printing, the problems are likely to be exposed

(1) the key to the success of alcohol free printing is the relationship between the hardness of the test roll and the imprint line

the main consideration should be the measurement roll, which is slightly lower than the hardness used when using alcohol fountain. The measuring roller usually has a hardness of 25 ~ 30, and sometimes hardens after printing. It is suggested that when alcohol substitutes are used, the hardness of the measuring roll should be reduced to 18 ~ 22. Because the softer roller is often easier to accept more water, its softness increases the width of the imprint line between the measuring roller and the chrome roller without increasing the pressure, which makes it easier for the printing operator to adjust the width

(2) through adjustment, reduce the imprint line width between the roller and the wetting roller to meet the needs of precise direct extrusion of plastic products.

when using alcohol fountain, the imprint line stripe width is usually 5/16 ~ 3/8 inch (8 ~ 10mm), which depends on the diameter of the drum. By increasing the width of the imprint line between the chromium alloy roller and the plate cylinder, a thin water film can be produced, and sliding can be caused between them. When alcohol substitutes are used, the width of the imprint line may be reduced to 1/8 ~ 3/16 inch (3 ~ 5mm). If there is not enough sliding, the plate cylinder will drive the chrome roller

in a typical alcohol wetting system, the metering roller and chromium alloy roller are driven by the wetting system, and the plate cylinder is driven by the printing machine. If the plate cylinder starts to drive the chrome roller, the cylinder speed increases and the control of the wetting system will be lost. If the ink roller has abnormal wetting, the water volume at the end of the ink roller will increase, which will lead to splashing or spray. Too high speed of the ink roller will also exert excessive pressure on the wetting device, which may lead to circuit disconnection and motor damage. Ideally, when using alcohol-free fountain solution, the wetting system should be able to operate at the same speed (or slightly higher speed). L3 - total length 150; L2 - initial distance between clamps 115 ± 5; L1 - length of parallel part 60 ± 0.5; L0 - distance between markings 50 ± 0.55

(3) adjustment of measuring roller speed

the measurement of alcohol free fountain solution often needs to be carried out on the fountain roller with high speed (when running at high speed, it can lead to slip and improper tolerance control)

(4) considering the deflection or bulge of the water roll

the bulge of the water roll often occurs in some printing equipment. At this time, the middle diameter of the measuring roll is larger than the edge diameter

some alcohol-free fountain solutions work well on skewed measuring rollers, while other machines need to be equipped with measuring rollers similar to chrome rollers to reduce the pressure in the center of the roller

when the printing plate runs to a place where the middle is wet or the edge is dry, the measuring roller must be skewed. If sufficient water cannot be received in the middle of the printing plate, a measuring roller similar to the chrome roller should be configured. The most appropriate skew angle should be determined experimentally, as it may vary depending on the alcohol substitutes used

the formation of curved foam lines on the edge of the printing plate is a good performance of ink balance. After the printing machine is stable, stop the machine to check the foam line. Ideally, the ink balance will produce very shallow and uniform foam lines in the width direction of the printing plate. If the printing plate is too dry, the foam line width increases; If it is too wet, the foam line will disappear