Offset printing plates have undergone the promotion stage of the use of protein plates, gravure plates, and PS plates. With the rapid development of printing technology and the popularity of multicolor high-speed machines, PS plates are popular and are suitable for some large-scale high-end printing products. Good performance, dark tone level, bright tone level reproduction ideal, PS version of the stability is good, not affected by the ambient temperature and humidity, long shelf life, easy to use, printing process is simple, easy to achieve data, standardized control , Has a good rate of India, and dot reproducibility, high resolution, good printability, less water, reducing the paper's flexibility and ink emulsification.
In general, the PS plate production process is: aluminum version of the decontamination process - electrolysis and grinding sand eye - anodizing - sealing hole - coating emulsion - drying - PS version.
1. PS version of the trachoma formation: PS version of the photosensitive resin film is relatively thin, and therefore require the PS version of the trachoma delicate and uniform, the current method of electrolysis more.
2. The purpose of the anodizing of the blank part of the PS plate: to form an oxide film on the aluminum alloy plate of the PS plate, thereby improving the mechanical strength, wear resistance and hydrophilicity of the aluminum alloy plate.
3. The purpose of the PS plate sealing hole is to block the pores of the oxide film and prevent the plate from being contaminated.
4. Surface structure of PS plate
1 positive PS version
Graphic part - diazo compounds
Blank section - Anodized film
2 negative PS version
Graphic part - Lac layer
Blank section - Anodized film
The photo-sensitive film of the positive-type PS plate is decomposed by light, and the photo-sensitive film of the negative PS plate is photo-polymerized. Shaiban process flow: exposure - development - washing - ink and finishing - glue. The PS version is flat from the macro perspective, but it is microscopically inconsistent. The positive version is microscopically speaking: The graphic part is high and the blank part is low. The negative version is microscopically speaking: The graphic part is low, and the blank part is high.
First, PS version of the wetting liquid formula principles and requirements
The formulation of the PS version of the wetting fluid must follow good wetting properties, the emulsification value cannot be less, and the pH of the solution is appropriate. The key is to solve the relationship between the wetting property and the emulsification value. In general, the wetting property is good and the emulsification value is large.
1.PS version wetting fluid must be able to fully wet the layout, in order to achieve the purpose of wetting the PS plate layout, it is necessary to reduce the surface tension, add surfactants, wetting agents, surfactants (carboxymethyl cellulose cmc) . The polar groups in 6501 surfactant, gum arabic and carboxymethyl cellulose (cmc) molecules can be firmly adsorbed on the solid surface, form and complement the colloid layer, and the colloid layer itself has very good water absorption performance. Therefore, the wettability of the printing plate is improved, and the emulsification is also not serious.
2. With cleaning ability.
Can wash the dirty spots on the surface of the PS plate, only add acidic substances such as: phosphoric acid, nitric acid, citric acid, etc. These acidic substances have the cleaning ability. The plate of original offset printing plate gravure plate is zinc alloy, 0.4cm thick. The graphic part of gravure plate is lac, the blank part is the inorganic salt layer, and the inorganic salt layer is added by the acidic substance in the water bucket, added in the clear water. Some electrolytes have an enhanced and stabilizing effect on hydrophilicity and oil resistance, such as phosphoric acid, phosphates, nitrates, and the like.
3 has a very good non-lipid capacity.
Added gum arabic, gum arabic has the role of hydrophilic colloids, the use of the non-lipid capacity of colloids and good water absorption capacity, to consolidate and stabilize the blank part of the four seals, and can reduce the amount of liquid fountain solution. At the same time, gum arabic also has the function of preventing the layout from oxidizing dirt and dirt and restoring the hydrophilicity of the blank part.
4. Can adapt to different climate changes. Add moisture absorbent and moisturizer.
1 Three hydroxyl groups of glycerol molecules can be adsorbed on the surface of the colloidal layer to help absorb the solution.
2 Polyethylene glycol is a good moisturizer. It can absorb moisture when it is shut down, and it is a good wetting agent to reduce the wear of the blank part of the printing plate.
3 The role of ethanol, ethanol (alcohol) (C2H5OH) can not only reduce the surface tension of the solution, but also use its volatility to make the paper absorb minimal moisture.
5. To stabilize the PH value. Adding buffer solvent, the hazard of PH value is too high: the network dot enlarges badly, the blank part is easy to get dirty, and the cleaning ability is poor. The hazard of PH value is too low: acidity is too large, corrosive to the printing plate, the printing plate's resistance to printing force is reduced, drying delays, the ink roller is easy to remove ink. The pH of the wetting fluid is preferably 4 to 5. Stable pH buffers such as: phosphoric acid and sodium dihydrogen phosphate have a buffering effect between them.
H3PO4→H+H2PO-4
NaH2PO4→Na++H2PO4
It generates a homoionic effect between the gates, inhibits hydrogen production, and stabilizes the pH.
In addition, both citric acid and sodium citrate have a cleaning action and a buffering action. [citric acid is a weak acid]
1 Citric acid H3C6H5O7
H3C3H6O7 H2C6H5O7 +H+
H2C6H5O7 HC6H5O7+H+
HC6H5O7
HC6H5O7H+
(The three-step ionization of citrate tribasic acid in solution, "" reversible reaction symbol.)
2 sodium citrate
Na3C6H5O7 Work Na+ +HC6H5O7
As most of the citrate HC6H5O73- changes in acidic medium, it is converted into HC6H5O72-ion, which produces a homoionic effect to maintain the proper pH, which is exactly in line with the acidity of the wetting fluid.
6. The loss of inorganic salt layer can be added. It is necessary to add acidic substances. The blank part of the PVA plate is the inorganic salt layer, and the wetting fluid must enrich the loss of the inorganic salt layer. The PS version does not need to be supplemented with inorganic salt layers. The blank part of the PS plate is an anodic oxide film, which is relatively stable to water and air. During the printing process, the electrolysis of the PS plate will not produce large wear.
Second, wet phenomenon
Wetting refers to an interface phenomenon that occurs when a liquid is in contact with a solid. When the liquid is in contact with a fixed two phases, the free energy of the system decreases to weigh and wet, and vice versa.
1. Internal Causes of Liquid Wetting Solids:
When the liquid and the solid contact with each other, the liquid molecules in the adhesion layer are subjected to the internal force of the liquid, namely, the cohesive force, and on the other hand, the force of the solid molecule, the adhesion force. Therefore, the liquid can wet the solid. Depending on the size of cohesion and adhesion.
2. Wetness assessment
a. Using the contact angle to assess the wetting phenomenon
The interfacial tension between liquid and solid is a physical quantity that cannot be directly and accurately measured. Therefore, the wetting phenomenon is usually judged, and the contact angle θ is often used as a measure of the degree of wetting.
b. The concept of contact angle
The so-called contact angle refers to the point at the junction of the solid, liquid, and gas phases on the normal surface through the center of the droplet as a normal surface and perpendicular to the solid surface. The gas-liquid interface and the solid-liquid interface are tangent to each other. The angle at which the liquid phase is held in the corner.
The relationship between contact angle and wetting
1 When the contact angle θ is 0°, sufficient wetting phenomenon occurs.
2 When the contact angle θ < 90°, it is said to be able to wet.
3 When the contact angle θ>90°, it is called non-wetting.
The contact angle of the liquid to the solid is small, the liquid water beads can spread out, the surface tension is low, and the wetting performance is good. To improve the wetting performance, the gravure must start from the grindstone first, choose the high-quality zinc plate or aluminum alloy, (the PS plate does not use the grind plate, but use the electrolytic method to form the blank part of the anodic oxide film) and adopt advanced processing technology Grinding the dense sand holes on the surface of the printing plate, using the pores of the sand holes to store moisture, forming a basis for the blank part of the printing plate, and thereby expanding the adsorption capacity, to create conditions for resisting the expansion of the ink. The smaller the size of the printing plate is, the better the surface tension of the solution is and the better the wetting performance is.
To improve the wettability of offset printing plates, it is necessary to reduce the contact angle. To reduce the contact angle, it is necessary to add surface active substances, interfacial active substances, and hydrocolloids to reduce the surface tension of the solution. The wettability is good, but be careful not to Excessive, so as not to emulsify seriously, bring other drawbacks.
Ways to improve the stability of the blank part of the printing plate: The first is to select the material with good hydrophilic properties, strong abrasion resistance and stable chemical properties as the basis for the blank part, and start by enhancing the hydrophilicity and oil resistance of the blank part of the printing plate. To achieve the ability of ink and ink to mutually resist the outward expansion of ink, only when this ability is large enough, the blank part of the plate can be fully stabilized. On the other hand, strictly control the proportion of water bucket wetting fluid to enhance the stability of the layout and prevent corrosion. Adding electrolytes to the water not only supplements the consumed hydrophilic base, but also can use the remaining acid to remove the blank of the printing plate. Part of the bonded ink is dirty. ("Chinese Printing")
In general, the PS plate production process is: aluminum version of the decontamination process - electrolysis and grinding sand eye - anodizing - sealing hole - coating emulsion - drying - PS version.
1. PS version of the trachoma formation: PS version of the photosensitive resin film is relatively thin, and therefore require the PS version of the trachoma delicate and uniform, the current method of electrolysis more.
2. The purpose of the anodizing of the blank part of the PS plate: to form an oxide film on the aluminum alloy plate of the PS plate, thereby improving the mechanical strength, wear resistance and hydrophilicity of the aluminum alloy plate.
3. The purpose of the PS plate sealing hole is to block the pores of the oxide film and prevent the plate from being contaminated.
4. Surface structure of PS plate
1 positive PS version
Graphic part - diazo compounds
Blank section - Anodized film
2 negative PS version
Graphic part - Lac layer
Blank section - Anodized film
The photo-sensitive film of the positive-type PS plate is decomposed by light, and the photo-sensitive film of the negative PS plate is photo-polymerized. Shaiban process flow: exposure - development - washing - ink and finishing - glue. The PS version is flat from the macro perspective, but it is microscopically inconsistent. The positive version is microscopically speaking: The graphic part is high and the blank part is low. The negative version is microscopically speaking: The graphic part is low, and the blank part is high.
First, PS version of the wetting liquid formula principles and requirements
The formulation of the PS version of the wetting fluid must follow good wetting properties, the emulsification value cannot be less, and the pH of the solution is appropriate. The key is to solve the relationship between the wetting property and the emulsification value. In general, the wetting property is good and the emulsification value is large.
1.PS version wetting fluid must be able to fully wet the layout, in order to achieve the purpose of wetting the PS plate layout, it is necessary to reduce the surface tension, add surfactants, wetting agents, surfactants (carboxymethyl cellulose cmc) . The polar groups in 6501 surfactant, gum arabic and carboxymethyl cellulose (cmc) molecules can be firmly adsorbed on the solid surface, form and complement the colloid layer, and the colloid layer itself has very good water absorption performance. Therefore, the wettability of the printing plate is improved, and the emulsification is also not serious.
2. With cleaning ability.
Can wash the dirty spots on the surface of the PS plate, only add acidic substances such as: phosphoric acid, nitric acid, citric acid, etc. These acidic substances have the cleaning ability. The plate of original offset printing plate gravure plate is zinc alloy, 0.4cm thick. The graphic part of gravure plate is lac, the blank part is the inorganic salt layer, and the inorganic salt layer is added by the acidic substance in the water bucket, added in the clear water. Some electrolytes have an enhanced and stabilizing effect on hydrophilicity and oil resistance, such as phosphoric acid, phosphates, nitrates, and the like.
3 has a very good non-lipid capacity.
Added gum arabic, gum arabic has the role of hydrophilic colloids, the use of the non-lipid capacity of colloids and good water absorption capacity, to consolidate and stabilize the blank part of the four seals, and can reduce the amount of liquid fountain solution. At the same time, gum arabic also has the function of preventing the layout from oxidizing dirt and dirt and restoring the hydrophilicity of the blank part.
4. Can adapt to different climate changes. Add moisture absorbent and moisturizer.
1 Three hydroxyl groups of glycerol molecules can be adsorbed on the surface of the colloidal layer to help absorb the solution.
2 Polyethylene glycol is a good moisturizer. It can absorb moisture when it is shut down, and it is a good wetting agent to reduce the wear of the blank part of the printing plate.
3 The role of ethanol, ethanol (alcohol) (C2H5OH) can not only reduce the surface tension of the solution, but also use its volatility to make the paper absorb minimal moisture.
5. To stabilize the PH value. Adding buffer solvent, the hazard of PH value is too high: the network dot enlarges badly, the blank part is easy to get dirty, and the cleaning ability is poor. The hazard of PH value is too low: acidity is too large, corrosive to the printing plate, the printing plate's resistance to printing force is reduced, drying delays, the ink roller is easy to remove ink. The pH of the wetting fluid is preferably 4 to 5. Stable pH buffers such as: phosphoric acid and sodium dihydrogen phosphate have a buffering effect between them.
H3PO4→H+H2PO-4
NaH2PO4→Na++H2PO4
It generates a homoionic effect between the gates, inhibits hydrogen production, and stabilizes the pH.
In addition, both citric acid and sodium citrate have a cleaning action and a buffering action. [citric acid is a weak acid]
1 Citric acid H3C6H5O7
H3C3H6O7 H2C6H5O7 +H+
H2C6H5O7 HC6H5O7+H+
HC6H5O7
HC6H5O7H+
(The three-step ionization of citrate tribasic acid in solution, "" reversible reaction symbol.)
2 sodium citrate
Na3C6H5O7 Work Na+ +HC6H5O7
As most of the citrate HC6H5O73- changes in acidic medium, it is converted into HC6H5O72-ion, which produces a homoionic effect to maintain the proper pH, which is exactly in line with the acidity of the wetting fluid.
6. The loss of inorganic salt layer can be added. It is necessary to add acidic substances. The blank part of the PVA plate is the inorganic salt layer, and the wetting fluid must enrich the loss of the inorganic salt layer. The PS version does not need to be supplemented with inorganic salt layers. The blank part of the PS plate is an anodic oxide film, which is relatively stable to water and air. During the printing process, the electrolysis of the PS plate will not produce large wear.
Second, wet phenomenon
Wetting refers to an interface phenomenon that occurs when a liquid is in contact with a solid. When the liquid is in contact with a fixed two phases, the free energy of the system decreases to weigh and wet, and vice versa.
1. Internal Causes of Liquid Wetting Solids:
When the liquid and the solid contact with each other, the liquid molecules in the adhesion layer are subjected to the internal force of the liquid, namely, the cohesive force, and on the other hand, the force of the solid molecule, the adhesion force. Therefore, the liquid can wet the solid. Depending on the size of cohesion and adhesion.
2. Wetness assessment
a. Using the contact angle to assess the wetting phenomenon
The interfacial tension between liquid and solid is a physical quantity that cannot be directly and accurately measured. Therefore, the wetting phenomenon is usually judged, and the contact angle θ is often used as a measure of the degree of wetting.
b. The concept of contact angle
The so-called contact angle refers to the point at the junction of the solid, liquid, and gas phases on the normal surface through the center of the droplet as a normal surface and perpendicular to the solid surface. The gas-liquid interface and the solid-liquid interface are tangent to each other. The angle at which the liquid phase is held in the corner.
The relationship between contact angle and wetting
1 When the contact angle θ is 0°, sufficient wetting phenomenon occurs.
2 When the contact angle θ < 90°, it is said to be able to wet.
3 When the contact angle θ>90°, it is called non-wetting.
The contact angle of the liquid to the solid is small, the liquid water beads can spread out, the surface tension is low, and the wetting performance is good. To improve the wetting performance, the gravure must start from the grindstone first, choose the high-quality zinc plate or aluminum alloy, (the PS plate does not use the grind plate, but use the electrolytic method to form the blank part of the anodic oxide film) and adopt advanced processing technology Grinding the dense sand holes on the surface of the printing plate, using the pores of the sand holes to store moisture, forming a basis for the blank part of the printing plate, and thereby expanding the adsorption capacity, to create conditions for resisting the expansion of the ink. The smaller the size of the printing plate is, the better the surface tension of the solution is and the better the wetting performance is.
To improve the wettability of offset printing plates, it is necessary to reduce the contact angle. To reduce the contact angle, it is necessary to add surface active substances, interfacial active substances, and hydrocolloids to reduce the surface tension of the solution. The wettability is good, but be careful not to Excessive, so as not to emulsify seriously, bring other drawbacks.
Ways to improve the stability of the blank part of the printing plate: The first is to select the material with good hydrophilic properties, strong abrasion resistance and stable chemical properties as the basis for the blank part, and start by enhancing the hydrophilicity and oil resistance of the blank part of the printing plate. To achieve the ability of ink and ink to mutually resist the outward expansion of ink, only when this ability is large enough, the blank part of the plate can be fully stabilized. On the other hand, strictly control the proportion of water bucket wetting fluid to enhance the stability of the layout and prevent corrosion. Adding electrolytes to the water not only supplements the consumed hydrophilic base, but also can use the remaining acid to remove the blank of the printing plate. Part of the bonded ink is dirty. ("Chinese Printing")
Dongxing Aluminum Co., Ltd. , http://www.hljaluminumfoil.com