The influence of the auxiliary materials required

  • Detail

The influence of the auxiliary materials required by the printing machine on the printed matter (I)

I. ink balance control

due to the high-speed operation of the printing machine, once the ink loses balance in the printing process, it will enter the vicious cycle of imbalance. When the problem is solved, many bad prints have been printed, causing serious waste. Therefore, it is necessary to correctly know that the ink balance is an important factor that determines the printing quality of the pointer back to zero

ink and water balance is a dynamic process. To analyze various factors affecting ink and water balance and their interactions, we must clarify the principle of "ink and water separation". The printing layout is simply divided into inking area (ink friendly and water repellent area) and inking area (hydrophilic and water repellent area). The so-called ink and water balance is to achieve the water volume and ink volume required for printing respectively in these two areas to complete picture transfer. During printing, water floats into the ink in the form of uniform and fine particles in the proportion of 20% and 25% to form a stable emulsion, that is, in the printing process, because the water film is sheared during transmission between the printing plate and the ink roller to the plate, some of it is split and brought to the ink system, so the process of water ink balance is the process of rapidly forming a stable emulsion in the system. We often say that we should use [minimum water consumption] printing to prevent the layout from getting dirty. In fact, this is the amount of water to ensure the formation of a stable emulsion. If the amount of water is increased, there will be [inverted emulsion], that is, the ink floats in the water, which is an unstable emulsion. At this time, the ink is in an unstable state. The formation of stable emulsion is affected by many factors, including fountain solution (water quality in the water tank of printing machine), paper and ink

1 effect of the plate solution on the balance of water and ink

the fountain solution reaches the paper through the water roller, ink roller, printing plate and adhesive tape. At the same time, the paper scraps return to the fountain solution through the adhesive tape and printing plate. Therefore, the chemical composition of the fountain solution is affected by these factors in the process of its transmission, especially for papers that are not acidic or alkaline, because the calcium often used in the manufacture of alkaline paper will combine with other ions in the fountain solution, change the chemical properties of the fountain solution, and produce particles adsorbed on the plate, roll and adhesive tape. During the operation of the machine, this particle will form sediment, causing excessive wetting and other problems. When the fountain solution acts on the offset printing process, it is also affected by physics and machinery, which changes its own performance. The change of the performance of the fountain solution directly affects the balance of ink and water. Therefore, it is very important to check, measure and adjust the composition of fountain solution regularly to ensure the balance of ink and water

1. Water quality problems

the content of water in fountain solution often exceeds 98%, so it is very important to control the chemical properties of water, and the inspection proportion will be greatly reduced. Tap water is the main component of fountain solution, but before it becomes our drinking water, it has been treated with chlorine or acid in the water plant, so the quality of tap water is an unknown factor, which varies with time and place. After long-term use of water containing impurities, impurities will corrupt the water quality and cause the printing plate to get dirty. In offset printing, we are most afraid of hard water containing more minerals in the water. The hardness of water is determined by various alkaline substances dissolved in it, such as lime and magnesium carbonate. In long plate printing, this substance will not only accumulate on the printing plate and in the water tank, but also combine with the acids in the water and ink to form dirty soap like substances. These substances are neither hydrophilic nor ink friendly, but stick to the printing plate, so that the non graphic area on the printing plate loses its hydrophilic layer and becomes dirty, resulting in the phenomenon of half printing; Empty pages are stuck on the ink roller; Sticking to the water roller will cause inaccurate measurement, and at the same time, it will destroy the viscosity of the ink and produce unstable emulsion

2. The hardness of water

eliminates obstacles in the printing process. The quality of water is very important. The quality of water used as wet water depends on its type or quantity of salinity. Therefore, tap water is generally suitable because it is purified

the measurement of water hardness is based on the dissolution of alkaline earth metals by salt: its expression is based on "German hardness" (° DH), and 1 ° DH is equal to 10 mg of calcium oxide equivalent in one liter of water

from the following table, we can know the hardness of water:

° DH is very soft ° DH is slightly hard

° DH is soft ° DH is hard

° DH is medium soft 30 ° DH is very hard

1 ° dh=1.25eh (British Standard)

=1.79fh (French Standard)

the hardness of water is absolutely affected by geology and can change in a short time. The manufacturer can analyze the water quality by adding moisture

on offset printing, the hardness of water should not be higher than 10 ° DH; If this number is exceeded, calcium and magnesium salts will stay on the printing plate, blanket and ink roller and interfere with the operation of the ink. Moreover, the chemical reaction of calcium salt and the fatty acid on the ink will produce lime phenomenon, which will have a negative effect on printing. To prevent this problem, water softeners can be added to avoid it value

5 pH value reflects the content of hydrogen ions in water. The reasonable acidity of the fountain solution can prevent the ink from drying on the printing plate, but too strong acidity will excessively corrode the plate, resulting in excessive inking. Therefore, for high-quality printing, it is very important to control the pH value of fountain solution

6 the content of hydrogen ions in water or liquid can cause water to become acidic or alkaline. This reaction is displayed by pH value, and then expressed in logarithmic grade

the value of neutral water is 7. Below this number, the liquid will gradually become acidic, and conversely, it will gradually become alkaline. The true science of pH value shows that offset printing practitioners can assume that their more detailed introduction to the properties of new composite materials can be measured by referring to the research paper published in the journal "advanced materials" on May 29

0 12 3 4 5 6 7 if the spring installed on the car has not been strictly tested 891011213 14

acidic neutral alkaline

but remember that the increase or decrease of the value of one degree is essentially a change of ten times the original acid or alkali concentration

in practice, the pH value of 4.8 to 5.5 is the degree suitable for offset printing wetting, and a little acid

is added, thus increasing the water receiving and surface tension on the printing plate

the pH value can be measured with the display paper (test paper), and the color of the display paper after being wet in water can be displayed by comparing it with the pre printed danger level. Improper pH value will lead to adverse printing consequences. For example, adding some buffer to the wetting agent can reach 4.8 to 5.5, which is the most suitable for offset printing

acidic bucket liquid below 5 degrees can cause:

a ink drying difficulties

b dry oxidation (discoloration) of metal

c the service life of the printing plate is shortened

alkaline bucket liquid above 7 degrees can cause:

b the surface tension between ink and water is reduced, and the ink is easy to emulsify

c printing plates are prone to floating

Copyright © 2011 JIN SHI