Third, the printing process
1. The pH of the wetting fluid: When the pH is low, a displacement reaction occurs with the metal salt in the dry oil, thereby inhibiting the drying of the ink. The pH of dampening in printing is strictly controlled (between 4.0 and 5.6).
Table 2 shows the effect of a different set of pH values ​​on the ink drying time at room temperature:
Table II
2. Layout Moisture: In the printing process, if the plate surface is too watery, not only will the paper absorb too much water and deform, the water droplets dispersed in the ink will affect the drying speed of the ink, and it will form oil-in-water emulsified ink, which will affect Imprinted dry.
3. Excessive stacking of printed sheets: The area of ​​printed sheets is large, the surface of the sheet is smooth, the stack of sheets is high, and air is difficult to enter.
4. The printing speed is too fast: After the ink is transferred to the substrate, it cannot be dried in time, and then it enters the next color printing or piles up on the delivery table. Practice has proved that if the printing speed exceeds 10,000 in the printing of sheet-fed paper, common domestic inks are prone to produce problems such as dirty backing, mixed colors, and back sticking.
<This is also related to the quality of the ink itself. If the thixotropy of the ink itself is good, it can be printed at a very high speed. Sometimes the printing speed can be up to 14,000 and it will not appear during the printing process. Sticky and mixed colors. The author uses two inks at the factory for comparison. One is the Japanese butterfly ink and the other is the crystal ink produced in Tianjin. As a result, it was found that the drying speed of Nissan butterfly ink was significantly stronger than that of crystal ink. >
5. Influence of temperature and humidity on the environment: The internal energy of the temperature-increasing molecules increases and the speed of the movement increases. This promotes the formation of more peroxides in the dry vegetable oil and accelerates the oxidative polymerization reaction. This oxidative polymerization reaction is added. The heat reacts and the heat released will promote drying. The opposite is true when the temperature is lowered.
The experimental data of the influence of the temperature and humidity of a group of environments and the change of the pH of the paper on the drying time of the ink are given below:
Table 3
Through the above table, we will find that the environmental temperature, humidity, and the paper's PH value are the three effects of ink drying on the paper surface. Therefore, it is even more important to ensure the constant temperature and humidity of the printing environment in actual printing.
<The ambient temperature and humidity of the workshop is preferably controlled at 20±2°C, and the relative humidity is 50 to 65%>
Finally, we must note that the relative humidity of 70% when the manganese lead drying capacity is not enough, we must use cobalt catalyst.
Fourth, ink film is too thick
Too much ink film will reduce the contact between the ink layer and the air, especially the conjunctiva on the surface of the ink layer will hinder the oxygen in the air, and the middle part will dry slowly.
Therefore, we must strictly prevent the following situations during printing:
(a) Imprints due to other causes are not robust and increase the thickness of the prints incorrectly.
(b) The ink on the layout caused by excessive moisture is light, but the ink color is increased by increasing the ink supply.
(c) Over-emphasizing the vividness and thickness of the print. Inappropriate increase in ink supply.
(4) The coloring power of printing ink is too low but it is necessary to increase the thickness of the ink layer to remedy it.
(In the deployment of light-colored spot color ink, pay attention to the saturation of the color to be slightly higher, so that when the printing can make the substrate thinner on the ink film, is conducive to drying. In addition to the type of ink used in the deployment of ink more Less, the smaller the emulsification of the ink during printing, the better it is for drying.
The thickness of the ink layer on the surface of the substrate and the distribution of the graphic.
Uniform distribution of large areas of the graphics and text because the wetting liquid is also consumed in the same place, the ink emulsification is consistent, but both sides of the graphic area due to direct contact with the blank part of the excess moisture, so that both sides of the ink emulsification than the middle More serious, drying also becomes slow. Similarly, when the area on the lithography is smaller, especially for a small-area solid field or a small-area dark tone network, the emulsification value of the ink will also be very large, and the problem of ink layer dripping will occur more easily. In addition to the amount of desiccant to increase the amount of use, but also strictly control the layout of the amount of water.
Some solutions to the problem of non-printing of printing products in printing
In fact, in the modern multi-color offset printing, even with good printing conditions and reasonable processes, it is difficult for the ink to be dried in time during the printing process or before the printing is completed. Therefore, we are in production. The following three methods are often used to accelerate the drying of the ink film or to prevent the back of the print from picking up.
Dusting powder: dusting is a common method used in printing. It is an effective means for back-scratching caused by slow drying of the ink film. When the ink layer is thick, the amount of dusting powder can be appropriately increased, especially for substrates. When the surface has a small area of ​​dark tone or solid ink, more attention should be paid to increasing the amount of dusting. Generally, the amount of powder to be sprayed should be as small as possible in the effective range. Otherwise, the ink color of the printed matter will be affected. In particular, it is necessary to pay attention to controlling the amount of dusting on products that require hot stamping and lamination.
Drying rack: In the printing machine's delivery section adopts the method of layered delivery, that is, every 5 ~ 20cm (the thickness of the separated layer of paper can be adjusted according to the density of the substrate and the thickness of the surface ink layer, the density of the substrate When the thickness of the layer is large, the separated layer height should be appropriately reduced. The layered delivery is to prevent the unbleached ink film from being damaged under the weight of the paper, or the back surface felting.
Shaking air: Printed products with poor surface absorption and thick ink film are generally dry slowly. Since the stacking of paper and oxygen in the air less interfere with the process of oxidation and drying, the paper is gently shaken to make it breathable at intervals. Increasing the contact between ink and air can effectively accelerate ink drying.
Finally, let's review the key to the slow drying of the ink film on the surface of the control printed matter mentioned in this article, as well as some processing methods for the slow-drying printing of inks:
1. Select the appropriate ink, 2. Use as few additives and additives as possible in the printing process, 3. Use the appropriate amount of drying oil, 4. Control the amount of water in the layout and the pH of the fountain solution in the printing, 5. Ensure the environment Constant temperature and humidity is very important, 6. To control the thickness of the ink film graphic, 7. Spraying, drying rack, shake dry.
So far we have analyzed some reasons for the slow drying of the ink film on the printed matter and some solutions when the ink is drying slowly. I hope to have some help for everyone.
1. The pH of the wetting fluid: When the pH is low, a displacement reaction occurs with the metal salt in the dry oil, thereby inhibiting the drying of the ink. The pH of dampening in printing is strictly controlled (between 4.0 and 5.6).
Table 2 shows the effect of a different set of pH values ​​on the ink drying time at room temperature:
Table II
Paper
Drying time
PH=7.0
PH=3.8
PH=3.6
PH=3.0
PH=2.0
Offset paper front
12
16
17
22.5
70
Security paper front
15
twenty one
twenty two
32
84
2. Layout Moisture: In the printing process, if the plate surface is too watery, not only will the paper absorb too much water and deform, the water droplets dispersed in the ink will affect the drying speed of the ink, and it will form oil-in-water emulsified ink, which will affect Imprinted dry.
3. Excessive stacking of printed sheets: The area of ​​printed sheets is large, the surface of the sheet is smooth, the stack of sheets is high, and air is difficult to enter.
4. The printing speed is too fast: After the ink is transferred to the substrate, it cannot be dried in time, and then it enters the next color printing or piles up on the delivery table. Practice has proved that if the printing speed exceeds 10,000 in the printing of sheet-fed paper, common domestic inks are prone to produce problems such as dirty backing, mixed colors, and back sticking.
<This is also related to the quality of the ink itself. If the thixotropy of the ink itself is good, it can be printed at a very high speed. Sometimes the printing speed can be up to 14,000 and it will not appear during the printing process. Sticky and mixed colors. The author uses two inks at the factory for comparison. One is the Japanese butterfly ink and the other is the crystal ink produced in Tianjin. As a result, it was found that the drying speed of Nissan butterfly ink was significantly stronger than that of crystal ink. >
5. Influence of temperature and humidity on the environment: The internal energy of the temperature-increasing molecules increases and the speed of the movement increases. This promotes the formation of more peroxides in the dry vegetable oil and accelerates the oxidative polymerization reaction. This oxidative polymerization reaction is added. The heat reacts and the heat released will promote drying. The opposite is true when the temperature is lowered.
The experimental data of the influence of the temperature and humidity of a group of environments and the change of the pH of the paper on the drying time of the ink are given below:
Table 3
Production environment conditions
Effects of Different Conditions of Temperature and Humidity on the Drying of Oil Types and Oxidation Polymerized Drying Inks
Offset paper PH
(RH)65% , 18°C
(RH)75%, 20°C
6.9
6.1
12.4
5.9
6.6
14.1
5.5
6.7
23.3
5.4
7.0
30.1
4.9
7.3
38.0
4.7
7.6
60.0
4.4
7.6
80.0
Through the above table, we will find that the environmental temperature, humidity, and the paper's PH value are the three effects of ink drying on the paper surface. Therefore, it is even more important to ensure the constant temperature and humidity of the printing environment in actual printing.
<The ambient temperature and humidity of the workshop is preferably controlled at 20±2°C, and the relative humidity is 50 to 65%>
Finally, we must note that the relative humidity of 70% when the manganese lead drying capacity is not enough, we must use cobalt catalyst.
Fourth, ink film is too thick
Too much ink film will reduce the contact between the ink layer and the air, especially the conjunctiva on the surface of the ink layer will hinder the oxygen in the air, and the middle part will dry slowly.
Therefore, we must strictly prevent the following situations during printing:
(a) Imprints due to other causes are not robust and increase the thickness of the prints incorrectly.
(b) The ink on the layout caused by excessive moisture is light, but the ink color is increased by increasing the ink supply.
(c) Over-emphasizing the vividness and thickness of the print. Inappropriate increase in ink supply.
(4) The coloring power of printing ink is too low but it is necessary to increase the thickness of the ink layer to remedy it.
(In the deployment of light-colored spot color ink, pay attention to the saturation of the color to be slightly higher, so that when the printing can make the substrate thinner on the ink film, is conducive to drying. In addition to the type of ink used in the deployment of ink more Less, the smaller the emulsification of the ink during printing, the better it is for drying.
The thickness of the ink layer on the surface of the substrate and the distribution of the graphic.
Uniform distribution of large areas of the graphics and text because the wetting liquid is also consumed in the same place, the ink emulsification is consistent, but both sides of the graphic area due to direct contact with the blank part of the excess moisture, so that both sides of the ink emulsification than the middle More serious, drying also becomes slow. Similarly, when the area on the lithography is smaller, especially for a small-area solid field or a small-area dark tone network, the emulsification value of the ink will also be very large, and the problem of ink layer dripping will occur more easily. In addition to the amount of desiccant to increase the amount of use, but also strictly control the layout of the amount of water.
Some solutions to the problem of non-printing of printing products in printing
In fact, in the modern multi-color offset printing, even with good printing conditions and reasonable processes, it is difficult for the ink to be dried in time during the printing process or before the printing is completed. Therefore, we are in production. The following three methods are often used to accelerate the drying of the ink film or to prevent the back of the print from picking up.
Dusting powder: dusting is a common method used in printing. It is an effective means for back-scratching caused by slow drying of the ink film. When the ink layer is thick, the amount of dusting powder can be appropriately increased, especially for substrates. When the surface has a small area of ​​dark tone or solid ink, more attention should be paid to increasing the amount of dusting. Generally, the amount of powder to be sprayed should be as small as possible in the effective range. Otherwise, the ink color of the printed matter will be affected. In particular, it is necessary to pay attention to controlling the amount of dusting on products that require hot stamping and lamination.
Drying rack: In the printing machine's delivery section adopts the method of layered delivery, that is, every 5 ~ 20cm (the thickness of the separated layer of paper can be adjusted according to the density of the substrate and the thickness of the surface ink layer, the density of the substrate When the thickness of the layer is large, the separated layer height should be appropriately reduced. The layered delivery is to prevent the unbleached ink film from being damaged under the weight of the paper, or the back surface felting.
Shaking air: Printed products with poor surface absorption and thick ink film are generally dry slowly. Since the stacking of paper and oxygen in the air less interfere with the process of oxidation and drying, the paper is gently shaken to make it breathable at intervals. Increasing the contact between ink and air can effectively accelerate ink drying.
Finally, let's review the key to the slow drying of the ink film on the surface of the control printed matter mentioned in this article, as well as some processing methods for the slow-drying printing of inks:
1. Select the appropriate ink, 2. Use as few additives and additives as possible in the printing process, 3. Use the appropriate amount of drying oil, 4. Control the amount of water in the layout and the pH of the fountain solution in the printing, 5. Ensure the environment Constant temperature and humidity is very important, 6. To control the thickness of the ink film graphic, 7. Spraying, drying rack, shake dry.
So far we have analyzed some reasons for the slow drying of the ink film on the printed matter and some solutions when the ink is drying slowly. I hope to have some help for everyone.
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