In a survey conducted by a large printing company in Shenzhen, it was seen that the company was promoting non-alcoholic printing and achieved very good results. Using alcohol-free printing can not only reduce the cost of printing, it is not only more environmentally friendly, but also can reduce a series of environmental problems caused by the volatilization of alcohol, so compile this article without alcohol printing, in order to make everyone better Understand and apply alcohol-free printing.
I. Alcohol substitutes
Alcohol replacements differ from IPA (isopropyl alcohol) in several key properties, including their viscosity, surface tension, pH, and conductivity of the fountain solution. Non-alcoholic products cannot be freely applied to different printing presses. This requires close communication with the printing operators and seeks the best fountain solution formulation from suppliers.
In fact, there are many alternatives to alcohol that can be used. They all consist of one or more chemicals extracted from the chemical groups of glycols and glycol ethers, and some other additives like IPA are also added. And these formulas all try to completely replace the IPA in the fountain solution and provide some unique properties. More importantly, the concentration of alcohol substitutes we use is much lower than the concentration of IPA. Under the same printing conditions, a small amount of alcohol substitutes can achieve 10 to 20 times the effect of containing IPA fountain solution.
Second, fountain solution viscosity
Adding IPA to the fountain solution greatly increases its viscosity, but many alcohol substitutes have little or no effect on viscosity. Due to the lower viscosity of alcohol substitutes, less fountain solution is measured by extrusion or using a measuring roll on a continuous contact dampening roller. This necessitates an increase in the dampening roller speed, causing many printing operators to mistakenly determine More water must be used when printing with an alcohol substitute fountain solution. In fact, the solution to increase the viscosity to a certain extent is to cool the fountain solution.
Third, the surface tension
The ability to wet the plate quickly and form a thin film of water is the two key requirements for offset printing on the fountain solution, which is primarily determined by the surface tension of the fountain solution. It is generally believed that the fountain solution with low surface tension can be used in high-speed printing, but there is also the opposite report in Europe. According to related knowledge, current alcohol substitutes can achieve the low surface tension of IPAs that printing operators are accustomed to.
The surface tension of pure water is 72×10-3N/m. In fountain solution, the concentration of alcohol is 10%-25%, and the surface tension is reduced to (35-45)×10-3N/m. The fountain solution rapidly forms a continuous film covering the entire printing plate. Alcohol-free fountain solutions use surfactants and solvents to reduce surface tension.
Surfactants or surface active additives are all organic chemicals, because of their polar molecular structure, they all tend to concentrate on the interface. Under normal conditions, they are at the interface between fountain solution and air and ink and air. In the case of high-speed printing, these interfaces change rapidly, so the surfactant must disperse quickly to replenish the new interface. A large amount of surfactant in the fountain solution is very important in the printing process, but too much addition will exacerbate ink emulsification.
Fourth, printing brightness and luster
Alcohol is a diluent that actively attacks the ink. It delustens the ink and affects the color. To achieve acceptable color, a thicker ink film is required on the impression cylinder.
The most common method for checking the quality of printing during the printing operation when looking at the sample. Whether it is monochrome printing or color printing, operators must often use their eyes to repeatedly compare the prints and proofs to find out the difference between prints and proofs, correct them in time, and ensure the quality of printed products. The following two issues are worth our attention when printing samples:
A: There is a difference between seeing light and seeing under sunlight
In production practice, most of them work under the illumination of a power source, and each light source has a certain color. This brings certain difficulties to the correct judgment of the original or product color. Under the colored light, the color change is generally the same color becomes lighter and the complementary color becomes darker. For example, the red color is lower, the red color is lighter, the yellow color is orange, and the green color is changed. Dark, dark green, white red.
Under the green light, the green becomes lighter, the green becomes lighter, the yellow turns greenish yellow, the red turns black, and the white turns green.
Under the yellow light, the yellow lightens, the magenta turns red, the green turns green, the blue turns black, and the white turns yellow.
Under the blue light, the blue lightens, the green lightens, the green darkens, the yellow turns black, and the white turns blue.
In the printing shop, generally choose a fluorescent lamp with a higher color temperature (3500~4100K) and better color rendering coefficient as a sample light source, but be aware that the fluorescent lamp is slightly blue-purple.
Two: The strength of light directly affects the judgment of the color of printing samples
The strength of light not only affects the color of light, but also changes the appearance of color.
We usually observe a light-receiving cylinder. The light-on side is the tone, and the back-light surface is the dark tone. The combination of light and dark is the midtone.
The same object, under the standard light source, is a positive color. If the light gradually becomes stronger, its hue will also change to a bright hue, and the light will be enhanced to a certain degree, and any color may turn white. Black porcelain also has a white point of reflection because of the concentration of light at the point of reflection and its strong reflection. In the same way, the light gradually decreases, and the various colors change to a hue with low lightness, and the light weakens to a certain degree, and any color will turn black, because the object does not reflect any light or black. Table 1 shows the effect of light intensity on color.
The sample stand in the printing shop must meet the requirements. Generally, the illuminance must reach about 100LX in order to correctly identify the color.
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