Use of alternatives Alcohol-free fluids

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 the alcohol-based fountain solution was a severe shortage of IPA supplies; the main driving force came from 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." The second generation of advanced formulas is already 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 the measure of fluid 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 glossy alcohol can erode 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. The adhesion ink of the fountain solution to the ink film must be able to adhere a certain amount of fountain solution to form the 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. Conductivity and pH conductance are measures of material conductivity; 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 pH is too high (higher than 5.5), the plate will become dirty; if the pH is too low (below 3.5) the plate will be discolored, the ink will emulsify in the fountain solution, and the ink roll will be deinked. The drying time of the layer is longer. 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. However, paying attention to 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.