Water is a polar molecule, oil is a non-polar molecule, and water oil is two incompatible substances. When the two insoluble liquids become an emulsion under the action of an emulsifier, they are called emulsified.
The use of water for offset printing is unique because of the possibility of emulsification between the use of water, fountain liquid and ink. The emulsification between water and ink is formed under the influence of emulsifiers. Emulsifiers are generally amphiphilic molecules, ie they have lipophilicity and hydrophilicity. The soaps and washing powders used in daily life are emulsifiers and have amphiphilic molecules that are lipophilic and hydrophilic in order to wash off the oil stains and dust on clothes. The water in the fountain liquid used for offset printing is not pure water. It contains many lipophilic substances and emulsifiers. Offset resin inks are not completely non-polar. Some additives in the inks are polar, hydrophilic, and some have both hydrophilic and lipophilic properties. At the same time, there are surface active substances, paper, and PH value on the paper. In fact, the emulsification phenomenon existing in the offset printing process is unavoidable. It is important to control the amount of emulsification that does not exceed 30%.
Types of emulsification during offset printing In general, emulsification during offset printing can be divided into two types:
1 oil dispersed in water. The oil-in-water emulsion is indicated by the symbol O/W.
2 Water is dispersed in oil. The water-in-oil emulsion is expressed in terms of W/O compliance.
(In the formula, O: indicates oil; W: indicates water)
The emulsification of O/W type is known as the phenomenon of water in printing, and it rarely occurs, but this type of emulsification must absolutely be avoided.
The emulsification of W/O type is more common, and it should be controlled within a certain range during printing, generally within 30%.
Emulsification Hazards 1. When the emulsification is severe, the color of the ink blotting is lost, and the color error of the printed sample is large.
2. Emulsification in the offset printing process will cause the ink to be diluted and the tinting strength of the ink to decrease.
3. Ink cohesion is reduced, resulting in floating and other phenomena.
4. The ink roller will have the possibility of deinking due to emulsification.
5. The drying speed of the printed product slows down.
6. The increase in water consumption during offset printing is the prerequisite for ink emulsification. Water is large, and the water absorbed by the paper also increases, causing the paper to expand and contract, and it also affects the accuracy of overprinting.
Offset emulsification is the emulsification caused by emulsifiers that cause similar miscibility between water and oil. Therefore, we analyze the type of emulsifier below.
1 The surface active material ink consists of colorants, binders and auxiliary materials. The free fatty acids and oleic acid in the ink vehicle are surfactants. Surfactant commonly used in fountain solution is 6501 (cmc) surfactant, which is a condensate of lauric acid diethanolamide, can effectively reduce the surface tension and interfacial tension of the aqueous solution, and has a certain emulsification effect on the ink.
2 The natural high-molecular polymer water canal is inseparable from the natural high-molecular polymer gum arabic, which is a surface active material and can effectively reduce the surface tension of aqueous solutions. When the printing is used, the sealant can avoid the contact between the PS plate and the air and water molecules and prevent the plate from oxidizing. The off-line offset printing also uses it.
3 Curing powder aluminum hydroxide ink dilute agent Weili oil is a light yellow-brown transparent paste oil made of aluminum hydroxide AL (OH) 2 and linseed oil or resin varnish. Aluminum hydroxide is also Factors that affect ink emulsification.
Factors affecting emulsification 1. Influence of paper Offset and offset papers and relief papers used in off-set printing have surface active substances in the compounds. These surface active substances fall off into the fountain solution and reduce the surface tension of the water fountain solution. , thereby promoting the emulsification of the ink.
2.Influence of ink 1 The acid value of the ink is large, the content of free fatty acid in the continuous material is more, the polarity in the ink is strong, the emulsification phenomenon is serious, and the emulsification is small;
2 ink color material is a coloring agent, pigment can be divided into organic colorants and inorganic color materials, if the ink color material contains surface active substances will affect the emulsification of the ink, compared to black ink emulsification smaller;
3 The viscosity of the ink is large, the corresponding cohesive force is large, the water resistance is good, and the emulsification is small;
4 offset printing ink used in the preparation of diluting agent, dilute the white ink, white oil, Weili oil, dilute the main component of the oil is aluminum hydroxide AL (OH) 2, with hydrophilicity.
3. Influence of the hopper solution The wetting powder used in the offset printing fountain liquid has a principle in the preparation and requires good wetting performance. However, the emulsification should not be too large and the pH value should be appropriate. However, under normal conditions, the wetting property is good and the emulsification value will be large. The key to solving the problem is to deal with the relation between the wetting property and the ink emulsification value. According to the external factors such as ink and paper properties, the surface tension of the solution should be reduced within the allowable range of the emulsification value, and the wetting property should be improved. When the fountain solution is used, it must be dissolved in fresh water in strict accordance with the instructions for wetting the powder.
In addition, the acidity of the strong water fountain liquid will often cause ink emulsification, because in the solution there are many anions such as: phosphate ions, nitrate ions are all excellent surface active substances, will make the water fountain liquid surface tension coefficient is reduced much Under severe mechanical roller compaction, the fountain solution will disperse into the ink to cause the ink to emulsify, and the ink will lose its proper adhesion. In severe cases, some of the pigments in the ink are soluble in water or acid. The separation of the pigment and the binder causes the pigment to disperse on the plate and the blank part floats.
4. Influence of the size of the offset printing surface water The amount of water used in the offset printing process is large and the emulsification phenomenon will be serious. When the water consumption is small, the emulsification will decrease. In order to reduce the occurrence of emulsification, it is necessary to use the minimum amount of moisture without preserving the plate or paste.
Offset emulsification precautions Emulsification cannot be avoided in the actual work of offset printing. The key is that the emulsification of the ink cannot exceed the allowable range. In summary, the prevention of ink emulsification should be started in the following aspects.
1. Control the amount of surfactants, emulsifiers, and wetting agents in the offset fountain solution.
2. Strictly control the surface moisture of the offset printing plate to reduce the emulsification of the ink due to the loss of the surface active material of the paper.
3. Control the acid value of the ink, increase the viscosity, and reduce the ink flowability.
4. Reduce the amount of dilute agent, white ink, Weili oil and driers, red dry oil, white dry oil.
5. Stabilize the PH value of the fountain solution, and use the minimum amount of water on the premise of not contaminating the plate or pasting, and strive to print high-quality printing products. (Wen / Wang Xincheng) ("China Packaging News")
The use of water for offset printing is unique because of the possibility of emulsification between the use of water, fountain liquid and ink. The emulsification between water and ink is formed under the influence of emulsifiers. Emulsifiers are generally amphiphilic molecules, ie they have lipophilicity and hydrophilicity. The soaps and washing powders used in daily life are emulsifiers and have amphiphilic molecules that are lipophilic and hydrophilic in order to wash off the oil stains and dust on clothes. The water in the fountain liquid used for offset printing is not pure water. It contains many lipophilic substances and emulsifiers. Offset resin inks are not completely non-polar. Some additives in the inks are polar, hydrophilic, and some have both hydrophilic and lipophilic properties. At the same time, there are surface active substances, paper, and PH value on the paper. In fact, the emulsification phenomenon existing in the offset printing process is unavoidable. It is important to control the amount of emulsification that does not exceed 30%.
Types of emulsification during offset printing In general, emulsification during offset printing can be divided into two types:
1 oil dispersed in water. The oil-in-water emulsion is indicated by the symbol O/W.
2 Water is dispersed in oil. The water-in-oil emulsion is expressed in terms of W/O compliance.
(In the formula, O: indicates oil; W: indicates water)
The emulsification of O/W type is known as the phenomenon of water in printing, and it rarely occurs, but this type of emulsification must absolutely be avoided.
The emulsification of W/O type is more common, and it should be controlled within a certain range during printing, generally within 30%.
Emulsification Hazards 1. When the emulsification is severe, the color of the ink blotting is lost, and the color error of the printed sample is large.
2. Emulsification in the offset printing process will cause the ink to be diluted and the tinting strength of the ink to decrease.
3. Ink cohesion is reduced, resulting in floating and other phenomena.
4. The ink roller will have the possibility of deinking due to emulsification.
5. The drying speed of the printed product slows down.
6. The increase in water consumption during offset printing is the prerequisite for ink emulsification. Water is large, and the water absorbed by the paper also increases, causing the paper to expand and contract, and it also affects the accuracy of overprinting.
Offset emulsification is the emulsification caused by emulsifiers that cause similar miscibility between water and oil. Therefore, we analyze the type of emulsifier below.
1 The surface active material ink consists of colorants, binders and auxiliary materials. The free fatty acids and oleic acid in the ink vehicle are surfactants. Surfactant commonly used in fountain solution is 6501 (cmc) surfactant, which is a condensate of lauric acid diethanolamide, can effectively reduce the surface tension and interfacial tension of the aqueous solution, and has a certain emulsification effect on the ink.
2 The natural high-molecular polymer water canal is inseparable from the natural high-molecular polymer gum arabic, which is a surface active material and can effectively reduce the surface tension of aqueous solutions. When the printing is used, the sealant can avoid the contact between the PS plate and the air and water molecules and prevent the plate from oxidizing. The off-line offset printing also uses it.
3 Curing powder aluminum hydroxide ink dilute agent Weili oil is a light yellow-brown transparent paste oil made of aluminum hydroxide AL (OH) 2 and linseed oil or resin varnish. Aluminum hydroxide is also Factors that affect ink emulsification.
Factors affecting emulsification 1. Influence of paper Offset and offset papers and relief papers used in off-set printing have surface active substances in the compounds. These surface active substances fall off into the fountain solution and reduce the surface tension of the water fountain solution. , thereby promoting the emulsification of the ink.
2.Influence of ink 1 The acid value of the ink is large, the content of free fatty acid in the continuous material is more, the polarity in the ink is strong, the emulsification phenomenon is serious, and the emulsification is small;
2 ink color material is a coloring agent, pigment can be divided into organic colorants and inorganic color materials, if the ink color material contains surface active substances will affect the emulsification of the ink, compared to black ink emulsification smaller;
3 The viscosity of the ink is large, the corresponding cohesive force is large, the water resistance is good, and the emulsification is small;
4 offset printing ink used in the preparation of diluting agent, dilute the white ink, white oil, Weili oil, dilute the main component of the oil is aluminum hydroxide AL (OH) 2, with hydrophilicity.
3. Influence of the hopper solution The wetting powder used in the offset printing fountain liquid has a principle in the preparation and requires good wetting performance. However, the emulsification should not be too large and the pH value should be appropriate. However, under normal conditions, the wetting property is good and the emulsification value will be large. The key to solving the problem is to deal with the relation between the wetting property and the ink emulsification value. According to the external factors such as ink and paper properties, the surface tension of the solution should be reduced within the allowable range of the emulsification value, and the wetting property should be improved. When the fountain solution is used, it must be dissolved in fresh water in strict accordance with the instructions for wetting the powder.
In addition, the acidity of the strong water fountain liquid will often cause ink emulsification, because in the solution there are many anions such as: phosphate ions, nitrate ions are all excellent surface active substances, will make the water fountain liquid surface tension coefficient is reduced much Under severe mechanical roller compaction, the fountain solution will disperse into the ink to cause the ink to emulsify, and the ink will lose its proper adhesion. In severe cases, some of the pigments in the ink are soluble in water or acid. The separation of the pigment and the binder causes the pigment to disperse on the plate and the blank part floats.
4. Influence of the size of the offset printing surface water The amount of water used in the offset printing process is large and the emulsification phenomenon will be serious. When the water consumption is small, the emulsification will decrease. In order to reduce the occurrence of emulsification, it is necessary to use the minimum amount of moisture without preserving the plate or paste.
Offset emulsification precautions Emulsification cannot be avoided in the actual work of offset printing. The key is that the emulsification of the ink cannot exceed the allowable range. In summary, the prevention of ink emulsification should be started in the following aspects.
1. Control the amount of surfactants, emulsifiers, and wetting agents in the offset fountain solution.
2. Strictly control the surface moisture of the offset printing plate to reduce the emulsification of the ink due to the loss of the surface active material of the paper.
3. Control the acid value of the ink, increase the viscosity, and reduce the ink flowability.
4. Reduce the amount of dilute agent, white ink, Weili oil and driers, red dry oil, white dry oil.
5. Stabilize the PH value of the fountain solution, and use the minimum amount of water on the premise of not contaminating the plate or pasting, and strive to print high-quality printing products. (Wen / Wang Xincheng) ("China Packaging News")
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