Ordinary wetting fluid is added to some of the chemical components in water, formulated as a higher concentration of the original liquid, diluted with water or made into a solid powder when used, dissolved in water when used. The water film in the blank part of the lithographic printing plate must always maintain a certain thickness, ie it must not be too thin nor too thick, and it must be very uniform. Excessive water content, printed products appear white, the field part of the so-called "watermarks", so that the imprint is false, the ink is dark and uneven; water is too small, first in the blank part of the printing ink appears, causing dirty version, with As the time went by, the ink gradually blocked the non-inked parts and appeared "burning paste." Therefore, the amount of wetting fluid must be moderate. General requirements, the use of the least amount of water, to achieve the balance of the amount of water and ink, without causing the layout from the dirty.
First, the preparation of common dampening fluid
1, can fully wet the printing plate blank part of the layout. To have better wetting properties, it is necessary to reduce the surface tension of the wetting fluid. The substance that can significantly reduce the surface tension of the solvent is a surfactant. Therefore, we must add emulsifiers, wetting agents, surfactants.
2. It has the ability to clean the blank part of the layout. To be able to wash away the dirt on the plate, you need to add phosphoric acid, nitric acid, citric acid and other acidic substances, only the acidic material has a good cleaning ability.
3, has a very good sense of fat. You need to put gum arabic. It can supplement the hydrocolloid layer that is lost on the printing plate layout and improve the hydrophilicity and oil resistance of the blank part, especially in the summer when the weather is hot and oily ink printing is more significant, but the amount used should not be too much, otherwise it is easy Deinking of the ink roller occurs.
4, can adapt to different climate changes by adding moisture absorbent.
5, Bucket wetting liquid can stabilize PH value, add buffering solvent.
6, can add loss of inorganic salt layer, you need to add acid.
Second, the use of ordinary dampening fluid
It is generally believed that the PS version is less resistant to acids and bases and the wetting cranial PH is preferably between 5-6. The pH value of the wetting liquid is related to the amount of the wetting fluid stock solution, the amount of the stock solution is large, the pH value of the wetting liquid is low, and the acidity is enhanced. In the printing process, the actual printing conditions should be combined to control the pH of the wetting fluid and to increase or decrease the amount of the wetting fluid.
1, the hazard of PH value greater than 7 is too high
a, printing plate easy to "glue"
In the printing process, under the rolling force with directional friction, the ink layer expands to the periphery of the graphic and text, and the blank part of the graphic image is eroded by the ink layer. The weak acidity leads to insufficient oil resistance of the water film on the printing plate. , And to make the hydrophilicity of the blank part weaken, so that the network points to expand hair, hair paste, can cause severe paste.
b, the printing plate is easy to float dirty and dirty
In the case where the acidity is too weak, since the inorganic salt layer of the printing plate cannot be continuously replenished at the time of printing, the hydrophilicity of the blank portion is weakened and gradually oleophilic, resulting in hanging dirt. Therefore, the increase of the amount of raw liquid added, so that a slight drop in the pH of the wetting fluid, to prevent hanging dirty. When the PH value is less than or equal to 6, the surface tension coefficient of the water bucket syrup does not change. When the pH value continues to increase, the surface tension coefficient decreases significantly, so that the water bucket solution is dispersed into the ink to form a water-in-oil state, causing the layout. Dirty phenomenon.
2, the PH value is too low (strong acid) hazard
a. The corrosiveness of the printing plate is strong, and the printing plate printing rate is reduced.
When the acidity is too strong, the inorganic salt layer of the plate begins to dissolve and the graphic part is corroded and damaged. In severe cases, the grain of the plate will also be damaged. Due to the strong acidity of the bucket, the sand is damaged. , The amount of water in the Tibetan Plateau is also reduced. The blank part is susceptible to sebum and dirt. The graphic and textual basis is eroded by strong acid, weakening the sense of fat, causing the net point to become smaller or incomplete.
b. Ink emulsification occurs.
Too strong acidity of the water bucket solution will often cause the emulsification of the ink. This is because there are many anions such as nitrate ions in the water bucket solution. It is an excellent surface active material that will lower the surface tension of the water bucket solution and the ink will lose its proper value. Viscous force, ink pigments and binders are separated, causing the pigments to disperse on the plate, and the blanks cause floating.
C, ink roller deinking
The metal ink roller easily reacts with the overly strong acid solution, causing the metal ink roller to be easily deinked.
d, hinder printing dry
Strong acidity, acidity and chemical reaction of the salt, when the acid has reached enough to react with metal salts in the driers, the ink drying will be destroyed, and play a role in inhibiting drying. The strong acidity will cause the printing ink to dry slowly, and will affect the normal production constantly. At the same time, the back of the product is easy to get dirty and hinder the product quality. When the PH value is less than 3.8, it will inhibit the ink drying.
e, dark gray ink
Normal wetting fluid is acidic, it will play a role in destroying the structure of the ink and make the ink emulsified. At the same time, when the acidity is too strong, the color of the ink will be destroyed, and the ink color will appear dark and dull.
(Text / Wang Xincheng)
First, the preparation of common dampening fluid
1, can fully wet the printing plate blank part of the layout. To have better wetting properties, it is necessary to reduce the surface tension of the wetting fluid. The substance that can significantly reduce the surface tension of the solvent is a surfactant. Therefore, we must add emulsifiers, wetting agents, surfactants.
2. It has the ability to clean the blank part of the layout. To be able to wash away the dirt on the plate, you need to add phosphoric acid, nitric acid, citric acid and other acidic substances, only the acidic material has a good cleaning ability.
3, has a very good sense of fat. You need to put gum arabic. It can supplement the hydrocolloid layer that is lost on the printing plate layout and improve the hydrophilicity and oil resistance of the blank part, especially in the summer when the weather is hot and oily ink printing is more significant, but the amount used should not be too much, otherwise it is easy Deinking of the ink roller occurs.
4, can adapt to different climate changes by adding moisture absorbent.
5, Bucket wetting liquid can stabilize PH value, add buffering solvent.
6, can add loss of inorganic salt layer, you need to add acid.
Second, the use of ordinary dampening fluid
It is generally believed that the PS version is less resistant to acids and bases and the wetting cranial PH is preferably between 5-6. The pH value of the wetting liquid is related to the amount of the wetting fluid stock solution, the amount of the stock solution is large, the pH value of the wetting liquid is low, and the acidity is enhanced. In the printing process, the actual printing conditions should be combined to control the pH of the wetting fluid and to increase or decrease the amount of the wetting fluid.
1, the hazard of PH value greater than 7 is too high
a, printing plate easy to "glue"
In the printing process, under the rolling force with directional friction, the ink layer expands to the periphery of the graphic and text, and the blank part of the graphic image is eroded by the ink layer. The weak acidity leads to insufficient oil resistance of the water film on the printing plate. , And to make the hydrophilicity of the blank part weaken, so that the network points to expand hair, hair paste, can cause severe paste.
b, the printing plate is easy to float dirty and dirty
In the case where the acidity is too weak, since the inorganic salt layer of the printing plate cannot be continuously replenished at the time of printing, the hydrophilicity of the blank portion is weakened and gradually oleophilic, resulting in hanging dirt. Therefore, the increase of the amount of raw liquid added, so that a slight drop in the pH of the wetting fluid, to prevent hanging dirty. When the PH value is less than or equal to 6, the surface tension coefficient of the water bucket syrup does not change. When the pH value continues to increase, the surface tension coefficient decreases significantly, so that the water bucket solution is dispersed into the ink to form a water-in-oil state, causing the layout. Dirty phenomenon.
2, the PH value is too low (strong acid) hazard
a. The corrosiveness of the printing plate is strong, and the printing plate printing rate is reduced.
When the acidity is too strong, the inorganic salt layer of the plate begins to dissolve and the graphic part is corroded and damaged. In severe cases, the grain of the plate will also be damaged. Due to the strong acidity of the bucket, the sand is damaged. , The amount of water in the Tibetan Plateau is also reduced. The blank part is susceptible to sebum and dirt. The graphic and textual basis is eroded by strong acid, weakening the sense of fat, causing the net point to become smaller or incomplete.
b. Ink emulsification occurs.
Too strong acidity of the water bucket solution will often cause the emulsification of the ink. This is because there are many anions such as nitrate ions in the water bucket solution. It is an excellent surface active material that will lower the surface tension of the water bucket solution and the ink will lose its proper value. Viscous force, ink pigments and binders are separated, causing the pigments to disperse on the plate, and the blanks cause floating.
C, ink roller deinking
The metal ink roller easily reacts with the overly strong acid solution, causing the metal ink roller to be easily deinked.
d, hinder printing dry
Strong acidity, acidity and chemical reaction of the salt, when the acid has reached enough to react with metal salts in the driers, the ink drying will be destroyed, and play a role in inhibiting drying. The strong acidity will cause the printing ink to dry slowly, and will affect the normal production constantly. At the same time, the back of the product is easy to get dirty and hinder the product quality. When the PH value is less than 3.8, it will inhibit the ink drying.
e, dark gray ink
Normal wetting fluid is acidic, it will play a role in destroying the structure of the ink and make the ink emulsified. At the same time, when the acidity is too strong, the color of the ink will be destroyed, and the ink color will appear dark and dull.
(Text / Wang Xincheng)