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Accurately mastering the drying speed of an ink is extremely important because it involves the quality and productivity of printed matter. At present, there are many kinds of inks. Take offset printing ink as an example. If the ink is dried too fast, the surface of the ink film will often become vitrified. The next black ink will not be overprinted. Severely, it will cause a lot of products to be scrapped; otherwise, if the ink is dry The speed is too slow, the penetration time is too long, the next ink color can not be overprinted in time, will affect the production efficiency, the ink film is dull, the network is not clear, distortion. If you print a large-area field version on a paper with a high degree of smoothness, there will also be problems such as a dirty back surface of the paper. The normal ink drying speed not only enables the ink film to be firmly adsorbed on the substrate, but also ensures the improvement of product quality.
First, the dry form of offset printing ink
The dry form of offset printing inks is penetration, oxidative conjunctiva drying. The ink is made of dried vegetable oil that has been refined and used as a binder. After the ink is printed on the paper, it penetrates through the paper on the one hand. On the other hand, under the catalysis of the desiccant, it slowly absorbs oxygen in the air and gradually polymerizes it. Conjunctiva can take hours or dozens of hours to fully dry. Ink is usually dried at room temperature.
Second, the catalytic properties of various desiccants
In order to accurately grasp the amount of desiccant, the catalytic properties of various desiccants must be understood. There are two kinds of desiccants: white and red dry oil. The main raw material of white dry oil is metal lead and manganese, which is in the form of a creamy white paste. It does not affect the discoloration of light-colored inks. Its dry form is mainly oxidized conjunctiva. The ink surface and the bottom layer are simultaneously dried, and in general, the temperature At 14-18°C, it is sufficient to add 5-10% white dry oil for drying. Excessive stickiness may occur.
The main raw material of red dry oil is brownish cobalt, which is a translucent liquid and is a good drier for printing inks. Due to the reaction of brownish cobalt, it has a certain discoloration effect on light-colored inks, and it is more suitable for inks with poorer dryness such as black ink, green lotus, and blue light. Its dry form is also an oxidized conjunctiva that gradually dries from the surface to the bottom. Due to its vulnerability to air oxidation, the surface of the ink film is very dry, so it should not be put more. If the same amount of white dry oil is used at the same time, good effects can be obtained with less dosage, faster drying and fewer side effects. Under normal circumstances, the amount of red dry oil is half of white dry oil, that is, the amount of red dry oil can be about 2.5-5%.
Third, with reference to many factors, flexible addition and desiccant
In order to accurately grasp the drying speed of offset printing inks, it is necessary to refer to a variety of factors to flexibly add and release desiccants.
1. Refer to the dryness of the ink itself
Quick-drying light offset ink is composed of resin binder and pigment. When it is printed on the surface of paper, selective penetration phenomenon mainly occurs. Under normal circumstances, it takes only 10 to 30 seconds for initial fixation. Printing on coated paper with high smoothness, the effect is ideal, just put a small amount of desiccant to quickly dry.
Quick fix ink, its characteristics is not simply rely on the addition of desiccant to increase the drying speed of the ink, it depends mainly on the penetration of the liquid. When the ink is transferred to the surface of the paper, the solvent in the ink quickly penetrates into the gaps in the fiber of the paper, and the pigment, etc., is instantly increased and fixed on the surface of the paper to form a pseudo dry phenomenon, which can greatly shorten the printing cycle.
Yellow ink is made from inorganic pigments such as lead chromate, which contains less binders, only 25-30%, while containing more pigments, up to 70-75%; red ink is almost the opposite, it contains about 55- 70%, but only 30-45% with pigments. Due to their different composition, yellow ink containing less ink dries faster, and red ink containing more ink dries slowly. In addition, the pigments also have a great influence, such as chrome yellow and iron blue, which have a priming effect, so the yellow and blue inks are easy to dry, while the black and red inks have no stimulative effect, so yellow and blue ink should be put less Desiccant, black, red ink should put some more desiccant.
2. Refers to the strength of ink absorption capacity and pH
The surface of the paper is porous, and the higher the porosity, the stronger the ability to absorb the binder and part of the pigment particles in the ink. The newsprint void rate is 58-65%, the relief paper void ratio is 50%, and the coated paper void ratio is only 38-40%. The paper with the stronger ink absorption ability dries faster and the paper with weaker ink absorption ability dries more slowly. Therefore, newsprint paper and letterpress paper should be provided with less desiccant, and coating paper should be provided with more desiccant.
In addition, the acidity and alkalinity of the paper also have a great influence on the drying speed of the ink. For paper with strong acidity, the drying speed of the ink is slow, and more desiccants can be put in. The paper with weak alkalinity is advantageous for the drying of the ink, and can be appropriately less Some desiccants.
3. Reference temperature and humidity level
As the temperature rises, the drying and polymerization of the ink increases, and vice versa. Therefore, when the temperature rises, some desiccants should be put in place. When the temperature drops, the amount of desiccant added increases. At the same time, relative humidity is also an important factor affecting the ink drying. When the humidity increases, the drying speed of the ink will slow down, and more desiccants should be placed. When the relative humidity drops, the climate is relatively dry, and less desiccant should be placed.
4. Reference to the number of prints and overprint
Some prints have fewer prints and shorter overprint cycles. They require the ink film to be dried faster. The amount of desiccant must be added more. On the contrary, products with more prints are not in a hurry to overprint, and desiccants can be used less. . Some products are more stacked color, not easy to dry, you can put some more dry, but not excessive, so as not to crystallize the ink film, there is the phenomenon of the next ink not printed.
First, the dry form of offset printing ink
The dry form of offset printing inks is penetration, oxidative conjunctiva drying. The ink is made of dried vegetable oil that has been refined and used as a binder. After the ink is printed on the paper, it penetrates through the paper on the one hand. On the other hand, under the catalysis of the desiccant, it slowly absorbs oxygen in the air and gradually polymerizes it. Conjunctiva can take hours or dozens of hours to fully dry. Ink is usually dried at room temperature.
Second, the catalytic properties of various desiccants
In order to accurately grasp the amount of desiccant, the catalytic properties of various desiccants must be understood. There are two kinds of desiccants: white and red dry oil. The main raw material of white dry oil is metal lead and manganese, which is in the form of a creamy white paste. It does not affect the discoloration of light-colored inks. Its dry form is mainly oxidized conjunctiva. The ink surface and the bottom layer are simultaneously dried, and in general, the temperature At 14-18°C, it is sufficient to add 5-10% white dry oil for drying. Excessive stickiness may occur.
The main raw material of red dry oil is brownish cobalt, which is a translucent liquid and is a good drier for printing inks. Due to the reaction of brownish cobalt, it has a certain discoloration effect on light-colored inks, and it is more suitable for inks with poorer dryness such as black ink, green lotus, and blue light. Its dry form is also an oxidized conjunctiva that gradually dries from the surface to the bottom. Due to its vulnerability to air oxidation, the surface of the ink film is very dry, so it should not be put more. If the same amount of white dry oil is used at the same time, good effects can be obtained with less dosage, faster drying and fewer side effects. Under normal circumstances, the amount of red dry oil is half of white dry oil, that is, the amount of red dry oil can be about 2.5-5%.
Third, with reference to many factors, flexible addition and desiccant
In order to accurately grasp the drying speed of offset printing inks, it is necessary to refer to a variety of factors to flexibly add and release desiccants.
1. Refer to the dryness of the ink itself
Quick-drying light offset ink is composed of resin binder and pigment. When it is printed on the surface of paper, selective penetration phenomenon mainly occurs. Under normal circumstances, it takes only 10 to 30 seconds for initial fixation. Printing on coated paper with high smoothness, the effect is ideal, just put a small amount of desiccant to quickly dry.
Quick fix ink, its characteristics is not simply rely on the addition of desiccant to increase the drying speed of the ink, it depends mainly on the penetration of the liquid. When the ink is transferred to the surface of the paper, the solvent in the ink quickly penetrates into the gaps in the fiber of the paper, and the pigment, etc., is instantly increased and fixed on the surface of the paper to form a pseudo dry phenomenon, which can greatly shorten the printing cycle.
Yellow ink is made from inorganic pigments such as lead chromate, which contains less binders, only 25-30%, while containing more pigments, up to 70-75%; red ink is almost the opposite, it contains about 55- 70%, but only 30-45% with pigments. Due to their different composition, yellow ink containing less ink dries faster, and red ink containing more ink dries slowly. In addition, the pigments also have a great influence, such as chrome yellow and iron blue, which have a priming effect, so the yellow and blue inks are easy to dry, while the black and red inks have no stimulative effect, so yellow and blue ink should be put less Desiccant, black, red ink should put some more desiccant.
2. Refers to the strength of ink absorption capacity and pH
The surface of the paper is porous, and the higher the porosity, the stronger the ability to absorb the binder and part of the pigment particles in the ink. The newsprint void rate is 58-65%, the relief paper void ratio is 50%, and the coated paper void ratio is only 38-40%. The paper with the stronger ink absorption ability dries faster and the paper with weaker ink absorption ability dries more slowly. Therefore, newsprint paper and letterpress paper should be provided with less desiccant, and coating paper should be provided with more desiccant.
In addition, the acidity and alkalinity of the paper also have a great influence on the drying speed of the ink. For paper with strong acidity, the drying speed of the ink is slow, and more desiccants can be put in. The paper with weak alkalinity is advantageous for the drying of the ink, and can be appropriately less Some desiccants.
3. Reference temperature and humidity level
As the temperature rises, the drying and polymerization of the ink increases, and vice versa. Therefore, when the temperature rises, some desiccants should be put in place. When the temperature drops, the amount of desiccant added increases. At the same time, relative humidity is also an important factor affecting the ink drying. When the humidity increases, the drying speed of the ink will slow down, and more desiccants should be placed. When the relative humidity drops, the climate is relatively dry, and less desiccant should be placed.
4. Reference to the number of prints and overprint
Some prints have fewer prints and shorter overprint cycles. They require the ink film to be dried faster. The amount of desiccant must be added more. On the contrary, products with more prints are not in a hurry to overprint, and desiccants can be used less. . Some products are more stacked color, not easy to dry, you can put some more dry, but not excessive, so as not to crystallize the ink film, there is the phenomenon of the next ink not printed.
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