Fountain Solution: Half Angel Half Devil

Perhaps the reader is wondering why the angel plus the devil is used to interpret the fountain solution in water offset printing. In actual production, however, it is very important to control the usage of the fountain solution. A slight difference can cause a significant impact on the printing process and printed matter. Impact. For example, the paper that appears during the printing process frequently loses powder, loses its hair, and even “skins” so that it has to shut down the rubber scrubbing phenomenon. This is certainly related to the performance of the paper, but it is also necessary to consider the fountain solution. Whether the dosage is too large or the PH value is too acidic to affect the reduction of paper surface strength. In addition, a very important reason that causes the “back pressure” phenomenon in the printing production process from time to time is the excessive use of the fountain solution or improper proportioning of the fountain solution, and the excessively strong acidity causes the ink to dry too slowly. In many cases, the printed materials are exquisite in color and accurate in overprinting. This is because the back pressure on the parts is dirty, and it cannot properly solve the problem. Only the entire printed matter can be scrapped. Therefore, traditional water-based offset printing can not be separated from fountain solution, but if it is improperly controlled and it has adverse effects, it is indeed a headache.

The fountain solution is mainly composed of water, isopropyl alcohol, or alcohol substitutes and water fountains, and through their respective functions, the fountain solution is commonly used in traditional offset printing. We will briefly introduce them separately.

　　 "clean" water

The main component of fountain solution is water, but it is not our usual tap water. Since tap water contains many calcium and magnesium ions, it will generate saponified calcium after chemical reaction with the ink resin, and has strong adsorption to rubber materials such as a water roller and an ink roller. If they are exposed for a long time, the surfaces of these rollers will crystallize, which will lead to poor water transfer and ink transmission. If they are not handled in time, they will cause the rollers to be scrapped. Because of this, we often see many printing shops installing filters or simply buying bottled water. What needs special emphasis here is that if you use bottled water, you must ensure that the water has filtered calcium and magnesium ions very well. If a filter is used, it must be ensured that the filter has a good ion filtering function, and the filter element should be periodically replaced.

We know that we must use "clean" water in the fountain solution, but what kind of standard can be called "clean"? In fact, the detection indicators of filtered water mainly include conductivity, PH value and solid matter content (PPM) value, and should be detected by a water quality analyzer before adding alcohol and water pipe liquid. The author proposes that the conductivity of water should be less than 400 μs/cm, the PH value should be 6.8-7.1, and the PPM value should be less than 300. In general, the measured values ​​only represent the results at that time, because the quality of the water is changing at any time, so the qualified water quality should be used as soon as possible to avoid changes in its water quality and the use of waste.

Not much alcohol substance

During the printing process, in order to prevent back pressure from appearing, the use of water should be as low as possible under the precondition of ensuring ink supply. The usual measure is to add a certain amount of alcohol in the fountain solution. We can understand this way, the same volume of water, when there is a contact area with the printing plate, but when it contains a certain amount of alcohol, its contact area with the printing plate will increase, thus reducing the number of plate full. The total amount of water needed. The more alcohol content is released, the better the effect of fountain solution will be. This is not the case, under normal circumstances, alcohol consumption accounted for 8% to 10% of the composition of the fountain solution is sufficient, too much will also have an adverse effect on the printing effect. Mainly comes down to the following points.

1. Adding too much alcohol can cause ink emulsification abnormalities, resulting in difficulty in inking the ink roller.

2. Too much alcohol will destroy the adhesive in the ink, dissolve the protective film of the pigment in the metal ink, and reduce the vividness and gloss of the print.

3. Excessive alcoholic substances can damage the paper coating, reduce the surface strength of the paper, cause off-powder and even "peeling."

4. Alcohols are volatile organic compounds that are harmful to the environment and human health.

5. Alcoholic substances are also part of the printing costs. Excessive use is not conducive to reducing production costs.

In addition, the author needs to point out that although isopropyl alcohol (IPA) and industrial alcohols are all alcoholic substances, they have a stronger ability to reduce the surface tension of the solution due to the slow volatilization of isopropyl alcohol. The best choice. As the price of isopropyl alcohol is higher than that of industrial alcohol, it is inevitable that the market will use the commercial alcohol as the purity isopropanol to sell it after blending it with isopropyl alcohol. Here is a simple and convenient detection method for readers to identify. The appearance of isopropanol itself should be clear and pure, which is the first step of the test. Then use a cup to mix clean water and isopropanol in a ratio of 1:1. After standing for 30-45 minutes, observe the clarity of the liquid: Good isopropyl alcohol should continue to maintain a clear and transparent appearance. If it becomes cloudy, it should be Consider its ingredients. Of course, there are also more professional tests, ie, the purity of the product is measured by isopropyl alcohol refractometer. However, the device is not easily available on the market and can be replaced by an alcohol refractometer.

"Harmony" water fountain

The fountain solution is actually a collective name for various fountain solution additives, including acidic electrolytes, buffers, surfactants, hydrocolloids, preservatives, bactericides, defoamers, and the like. Why do you need to add water fountain? Here is a good idea of ​​life. There is oil on the hand and it is very difficult to wash off the oil directly after rinsing with fresh water, but if you use soap, hand soap and other substances, this will become very easy. The reason is that oil and water are mutually exclusive two substances, but they can be indirectly miscible with two immiscible substances through an intermediate medium. The balance of ink and wash in printing is also the same. Ink and water itself are immiscible, because the acid electrolyte in the water fountain provides an acidic environment (PH value is about 4.8-5.5), making the ink and water can be mutually soluble, forming a "water-in-oil" dispersion, that is, the ink Emulsification. When the volume of water accounts for about 15% to 26% of the ink mixture, the ink and fountain solution are in a state of mutual solubility. In addition, other additives in the fountain solution inhibit the volatilization of isopropyl alcohol, control the surface tension and PH value of the fountain solution, as well as the role of cleaning, protection and repair of the printing plate.

Although the fountain solution is also an integral part of the fountain solution, the addition of too much water to the printing process is equally damaging. There are mainly the following points.

1. The excessively acidic dampening solution will destroy the surface strength of the paper and cause the powder to fall off.

2. The excessively acidic dampening solution can also result in off-plate or printing plate degradation.

3. The strong acidity of the fountain solution will make the ink dry and slow, causing the back of the print to become dirty.

"Fit" deployment

With water, alcohol and water, the most important task is to properly deploy it. According to the author's experience, a mixture of 4% water + 1% isopropyl alcohol + 86% filtered water is most suitable. In addition, the tank temperature should be set at about 8 °C, the tank temperature is set at 10 °C ~ 11 °C, you can also slightly increase the temperature according to the actual situation 1 °C ~ 2 °C to reduce the volatilization of isopropyl alcohol.

With the constant breakthrough of technology, alcohol-free fountain solution has been widely used in practical production. We are fully aware of the knowledge and skills of traditional fountain solution, and we are also looking forward to more environmentally-friendly free printing. Alcohol fountain solution brings more surprises.