Alcohol-free fountain solution

The function of the offset printing wetting system is to transfer the water-based solution to the printing plate so that the non-graphical part of the printing plate resists ink. Isopropyl alcohol (IPA) is the most commonly used additive in fountain solutions. IPA can reduce the surface tension of the fountain solution and increase the viscosity of the fountain solution; IPA evaporation can also play a "cooling" effect. The alcohol-based fountain solution also has the advantage of making the operation of the offset printing process more "loose," and can compensate for various problems caused by factors such as old printing equipment, poor maintenance, and lack of operator skills.

The initial reason for the elimination of alcohol-based fountain solutions was a severe shortage of IPA supplies; today's main driving force comes from aspects such as environmental protection, health and safety. The use of non-alcohol (precisely should be no IPA) printing, ink adjustment is simple, printing quality, clear dots, and little ink emulsification. At the beginning of the non-alcohol printing process, the printing factory has been looking for products with IPA characteristics that can replace IPA. They can be called first-generation "alternatives of alcohol." Today, the second generation has become a state-of-the-art formula that is a well-deserved "no-leaf" formula. Herein, "alcohol free" may refer to an alternative formulation of unleavened (IPA) formulation and alcohol (IPA).

In terms of the viscosity, surface tension, pH, and conductivity of the fountain solution, alcohol substitutes were asked about IPA. The commonly used alcohol substitutes are mainly composed of one or more ethylene glycol and glycol ether family chemicals and other additives. Initially, these products can only reduce the amount of IPA; now it has been able to completely replace the IPA in the fountain solution, and has better operating performance. Unleavened products are not universal, so printers must contact the supplier closely to obtain the best fountain solution.

It is said that web printing manufacturers tend to use one-component non-alcoholic products, while sheet-fed printers prefer to use composite non-alcoholic products. In comparison, compound alcohol-free products are more flexible. Under the influence of the "integrated system" thinking, generic fountain solution products often add all the substances that need to be added. This fountain solution is generally considered to be the most reliable. It is worthwhile to note that the concentration of alcohol substitutes in fountain solution is much lower than that of IPA. Study the performance of the fountain solution, generally starting from the following aspects:

1. Viscosity

Viscosity is a measure of the fluid's resistance to flow. The concentration of the alcohol substitute in the fountain solution is much lower than the IPA, so the alcohol substitute has little effect on the viscosity of the fountain solution. Due to the lower viscosity of the fountain solution using the alcohol substitute, in the continuous flow contact type wetting system, there is little dampening fluid on the water transfer roller or the metering roller, and it is necessary to increase the speed of the wetting roller to ensure the The amount of liquid supply. One way to compensate for the loss of viscosity is to cool the fountain solution, but excessive cooling of the fountain solution can also have a negative effect.

2. Surface tension

The rapid wetting of the plate and the formation of a water film are two key requirements for the offset fountain solution, which is mainly determined by the surface tension of the fountain solution. The apparent tension of pure water is 72 dyne/cm. In the fountain solution, a concentration of (10-25)% of the alcohol can reduce the surface tension of the fountain solution to (35-45) dyne/cm so that the fountain solution can quickly form a continuous film. Printing plate on the auxiliary exhibition opened. The non-alcoholic fountain solution uses surface active agents and solvents to reduce the surface tension. Due to its polar molecular orange structure, surfactants will accumulate at the interface. When the press is running at high speed, the interface changes rapidly and the surfactant must also be quickly transferred to compensate for the new interface. The content of surfactant in the fountain solution is very important in the printing process, and if the content is too high, it will cause the ink to emulsify.

It is generally believed that a dampening solution with a low surface tension is more suitable for high-speed printing, but the opposite is also reported. Today's alcohol alternatives have the same low surface tension as IPA.

3. Printing brightness and gloss

Alcohol will attack the ink and cause the ink to lose its luster and affect the color. In the same process, the ink in the printing press must maintain a relatively thick ink layer to achieve acceptable color. When alcohol substitutes are used, they do not dilute the ink at the correct concentration, so the amount of ink used and the amount of water used are less. The observation is that the dot gain is smaller and the dots are also clearer.

4. Adhesion of fountain solution to ink film

The ink must be able to adhere to a certain amount of fountain solution to form an emulsion. Under ideal conditions, the fountain solution quickly adheres to the ink and reaches equilibrium operating conditions. Under balanced operating conditions, small dampening droplets diffuse into the ink, forming a "water-in-oil" emulsion locally. The pressure between the plate and the blanket helps the emulsification to occur. The amount of fountain solution in the emulsion can affect the density, drying, viscosity, viscosity, and ink transfer properties of the ink. Excessive emulsification can destroy the balance of ink and ink, resulting in thinning of the ink layer and incomplete images, resulting in "snowflakes" on the prints.

5. Conductance and pH

Conductance is a measure of the conductivity of a material; pH is the amount of hydrogen ion concentration in water. It is very important for the fountain solution to keep the conductance and pH constant.

The conductivity of pure water is close to 0 microm, which is a good conductor of electricity. The conductance of water is proportional to the amount of ions in the water, so conductivity is also used as an approximate measure of water quality. Before the printer is used, the conductivity of the fountain solution needs to be measured. The abnormal conductance of the conductance is caused by any impurity. In the printing process, due to the contamination of the ink and the material in the paper, it is normal that the dampening wave conductance increases. According to GATF's practice, every four hours of the printing process requires one side of the belt and each batch of new fountain solution also needs to measure the conductance. When water is replenished, the change in conductance after filling in water should be less than 50 microhms. If the conductance changes by 200 microhms, it must be processed before being used.

When measuring conductance, the pH is generally measured at the same time. The pH of the fountain solution should generally be 4.4 to 5.0. If the p H value is too high (higher than 5.5), the printing plate will be dirty; if the pH is too low (below 3.5), the printing plate will be dispelled, the ink will emulsify in the fountain solution, and the ink roller will be deinked. The ink drying time lengthens. For high-quality printing, the pH of the fountain solution used has to be kept optimally, otherwise there will be a series of problems, paste (ink emulsified in the fountain solution), printing plate printing (text on the plate Part of the ink is not inked), the win is (the ink is attached to the graphic part of the plate), the ink roller is de-inked (the ink roller is not attached with ink), or the ink is not dried safely on the paper.

To ensure the stability of the pH, buffers are added to all dampening waves. When the concentration of the fountain solution changes, the pH may not change much, but its conductance continues to increase. Therefore, the conductance is more suitable than the pH for determining the change of the solid content in the solution. Once, note that small changes in pH can help avoid many printing problems.

6. The use of an alcohol-free fountain solution for alcohol replacement serves two purposes:

One is to use safe materials to make high-quality products, and the other is to choose and use good-quality, unleavened fountain solutions. Printing is an interactive process. The industry cannot expect to change one of the links (such as removing alcohol) without making a full adjustment.

When using a new fountain solution (or any other new material), the operator can test it before applying it. The printing unit itself is the best laboratory. Under controlled conditions (that is, other conditions than the test article remain stable), testing on the printing unit can provide the entire information needed to solve the actual problems of the printing process. When testing, it is best to follow the manufacturer's specifications. Within the tolerances of technical specifications, generally begin at the low end, and all the original data of the test process should be preserved.

7. Mechanical adjustment

The structure, control system, wetting system, configuration, etc. of different printing presses are not necessarily the same, and adjustment methods are also difficult to unify. The use of non-alcoholic fountain solution requires more stringent equipment than when using IPA fountain solution, so some of the problems that can be masked when using IPA fountain solutions are apparent. It is recommended that the use of alcohol be reduced to around 8%. If there are still problems, it shows that the IPA has indeed masked some issues that are worth noting.

The key to ensuring the success of the unleavened printing is the correct selection of the hardness of the water roller of the wetting device and the adjustment of the nip. When printing with alcohol-free printing, the hardness of the metering roller is slightly lower than when the alcohol fountain solution is used. The hardness of a typical metering roller is (25 to 30) Shore, and it becomes harder after use. When using non-alcoholic fountain solution, it is recommended to reduce the hardness of the metering roller to (8 to 22) Shore because the soft roller is easy to absorb water and the gap between the metering roller and the chrome roller can be increased without increasing the printing pressure. Make the operator's adjustment more relaxed. Another problem encountered when using standard hardness metering rolls is the formation of streaks (or ridged water lines) on the hall rolls and metering rolls of the water, and the resulting print streaks in the week. Using a soft metering roller to increase the nip, it is often possible to flatten the water film on the chrome roller. Another reason for the formation of ridged water lines is the speed difference between the two rollers.

The use of an alcohol fountain solution also requires adjustment of the gap between the roller and the dampening roller. With an IPA dampening solution, this gap is generally (8 to 10) mm wide, whereas when using an alcohol-free fountain solution, the nip is reduced to (3 to 5) mm. In a typical IPA wetting device, the metering roller and the chrome roller are geared by a separate motor, and the plate roller is driven by the printer. If the plate roller starts to drive the chrome roller, the speed of the chrome roller increases and the wetting control is lost. When the wetting system's roller accelerates beyond normal conditions, water tends to collect at both ends of the roller, causing splashing; the roller's excessively fast speed also causes the wetting system's motor to be unduly stressed, resulting in open circuit and motor failure.

The adjustment of the metering roller speed is also a key issue. In order to measure the non-alcoholic fountain solution, a higher rotational speed of the dampening roller is often required, and up to the conditions will result in an inaccurate projection and inaccurate control range.

Some printers' metering rollers are designed to be spindle type in order to evenly distribute the fountain solution over the plate. Some of the non-enzymatic fountain solution preferably uses a spindle pair metering roller. If the middle part of the plate roller is too wet and both ends are too dry, the metering roller must usually be deflected; if there is not enough dampening fluid in the center of the plate roller, the metering roller should be parallel to the chrome roller. The optimum angle of deviation varies with the alcohol substitute used and should be determined experimentally. By observing the dirty lines formed in the creases of the printing plate, it can be determined whether the ink balance is good or not. After the printing press enters a stable state, the printer shut-down well is used to evaluate the dirty lines. When the ink balance is ideal, a fine and uniform dirt line will be produced on the pass width of the printing plate. If the printing plate is too dry at a certain position, the width of the dirty line increases, and if it is too wet, the dirty line is eliminated.

8. Problems that may be encountered

Switching to the non-alcoholic fountain solution is likely to encounter some of the unprecedented problems. The problems caused may include:

Metering roller sucks ink

Alcohol replacements make metering rollers sensitive to ink. The ink is first attached to the chrome plate and then passed to the metering roller. The solution is to contact the printer manufacturer or use a specially formulated mixture to corrode the rollers. The hydrophilicity of the metering roller is maintained by coating with a gum or coating. Some agencies believe that the metering roll sensitivity is due to the contamination of the fountain solution, as only a 1% blanket cleaner can be used to break a satisfactory fountain solution.

Ridged watermark

As mentioned earlier, with the use of alcohol substitutes, if the hardness of the metering roll is (25 to 30) Shore, ridged watermarks may occur and thus affect print quality. The solution is to use a soft measure. There are also some manufacturers that have long-fiber surface metering rolls that are more hydrophilic. Maintaining the correct concentration It is important to determine the correct concentration of the fountain solution, especially when initially formulated. Most alcohol substitutes will slowly burst from the liquor. Because there is no method that can be used to determine the concentration of alcohol substitutes, the use of an unleavened fountain solution needs to be replaced at least once a week. Cooling the fountain solution too much. When increasing the speed of the printer, cooling is important, but the operator sometimes overcools the fountain solution. This increases the viscosity of the ink and causes problems with paper picking and stacking. The correct temperature pair first depends on the conditions of the printing year workshop, while the dampening fluid refrigeration unit should be adjusted to (10 ~ 13) °C. Or as recommended by the supplier.

Organic growth

If organic growth occurs in the fountain solution circulatory system, the circulatory system should be cleaned at least once a week, including a discharge hopper. Can be washed with normal water; mold remover is also used to prevent the growth of organic matter; also can be used to bleach (1 ~ 5)%