A vividly coloured, structured, print with a strong sense of texture and space can make one feel happy and fall in love. The imprints left on the printed matter are formed by ink. During the actual printing process, the same paper, the same ink, and the same conditions are often encountered. The color of the printed materials is very different and the quality of the products is not satisfactory. The author believes that this is caused by errors in the operation of the printing process, mainly in the following aspects.
1 Printing pressure
The printing pressure directly affects the degree of ink transfer, and whether the thickness of the imprinted ink layer meets the standard, affects the gloss of the printed matter. If the pressure is too high, the ink will not be deformed when the ink is transferred to the paper. The gloss of the print will be poor. If the pressure is too light, the ink will barely be transferred to the paper, but the ink layer will float on the surface of the paper, resulting in rough printing. Uneven ink layer, affect the gloss effect, after the two-color or multicolor overprinting, especially when the field version and the on-site version of the overprint, if the former color fixation is not good or improper additives added, it may affect the print gloss.
The ideal printing pressure is to make the print on the print clear, thick ink layer, tone and color reappear well with minimal printing pressure. The offset press must control the proper ideal pressure, accurately measure and calculate the thickness of the liner, properly monitor the unevenness between the printing plate and the blanket, and effectively fill the unevenness to make the roller surface contact evenly and achieve an ideal realm. The difference in paper smoothness allows for flexible control of printing pressure. The dot enlargement rate is well controlled at about 15%. The printed ink has a thick, deep layered print and good gloss.
2 fountain solution pH
Offset printing is based on the principle of immiscible oil and water. The graphic part of the offset printing plate has the characteristics of oleophilic and water repellent, while the blank part has hydrophilic and oil repellent properties. During the printing process, the printing plate is wetted with water. The blank part of the film will form a water film. When the ink is transferred to the plate, only the graphic part will be covered with ink to print the graphic.
The pH of the formulated fountain solution is generally between 4.5 and 5.5, the pH of the fountain solution is too high, the hydrophilicity of the plate is poor, and the blank part of the printing plate is easy to get dirty, if the ink based on the dry vegetable oil binder is used When the pH of the fountain solution is greater than a certain value, the interfacial tension between the ink and the dampening water will drop, causing serious emulsification of the ink and directly affecting the gloss of the printed matter; the pH of the fountain solution is too low and the surface of the printing plate will be seriously affected. Corrosion, or even destroy the blank part of the printing plate does not feel the fat layer, so that the blank part of the plate appears trachoma. Therefore, a strong hydrophilic layer cannot be formed. The dampening water with a low pH also affects the ink transfer and the drying of the print. In the worst case, the combination of the graphic part and the metal base is destroyed when the corrosion further expands. , causing damage to outlets and reducing the gloss of prints.
3 Ink emulsion
Ink emulsification includes two forms of oil-in-water and water-in-oil. The oil-in-water type rarely occurs during the offset printing process, and the water-in-oil type is inevitable.
During the printing process, the ink will emulsify when the moisture is too large, and the ink layer is very thick on the imprint, but the ink molecules become oil-in-oil, resulting in dullness and reduced gloss after the imprint is dried. Blurring of the contours, large variations in color, errors in the color of the printed product and the signature, but also a series of other failures, slow drying of the imprinting, making the back of the printed product sticky, the viscosity of the ink decreasing, the printing plate floating, the pigment particles agglutinating, Causes flower and paste.
In the printing process, adhere to the small ink thick water method, as much as possible to make the ink thick, small water, this is because the thick ink viscosity, which is the cohesion of the ink increases, and accordingly enhance the adhesion of the ink molecules Force, thereby improving the ink's water resistance, reducing the ratio of water droplets dispersed in the ink, reducing the emulsification value of the ink, thus ensuring that the printed product is pure hue, high saturation, colorful, ink layer Thick dot gains are small, clear and full. In the offset printing process, in addition to the nature of the paper, the composition of the liquid in the fountain, the temperature and humidity of the workshop, the properties of the components of the ink, and the auxiliary materials for the ink, etc., the amount of water in the printing plate surface is controlled, and the minimum amount of water is ensured so that the printing plate is not The best dynamic and balanced state of sticky and dirty, in order to achieve the reduction of the color of the graphic printing, gray balance, good glossiness, various color density and tone value meet the requirements of the printed matter.
4 Effect of Ink Aids
In the printing process, limitations of the printing process and technical conditions, the physical properties, chemical properties, or printability of the ink cannot be matched with the printing job, and ink adjuvants are needed to make appropriate adjustments to facilitate smooth printing. Most of the adjuvants such as anti-sticking agents, detackifiers, varnish, and desiccants in the adjuvant adversely affect the gloss of printed products, such as our common No. 6 varnish, in inks. Plays a dilution effect and also plays a role in reducing the viscosity of the ink. After adding ink to the ink, the fluidity of the ink is increased, and at the same time, the dryness of the ink is also reduced, but the gloss of the print is unfavorable. For another example, the main ingredient of the anti-adhesive agent is corn flour. After the ink is added to the ink, the surface of the imprinted film layer becomes rough due to the refraction of the corn powder, and the gloss of the finished product is deteriorated.
Offset printing inks have adequate drying performance under normal temperature conditions, but the temperature in winter decreases, or in the case that anti-adhesive agents, dirt removing agents, ink adjustments, etc. have been added to the ink, desiccants should be added to the process operations. In the correct use of desiccants is beneficial to the formation of gloss prints, because the paper absorption of the connection material takes a certain amount of time, in the process as soon as possible to agglutinate the connection material, until the conjunctiva drying is the key to a good finish gloss, ink preparation process should be strict Addition and release of control aids, if considering the gloss effect, should be less or no adjuvant.
5 Effect of Ink Layer Thickness
The correct and reasonable use of ink is an important link to ensure the color of the printed matter. The ink is too thick and too thin, which is not conducive to uniform ink and cloth. The ink is too thick, the printed film layer is too thick, and the ink flowability is poor, resulting in poor transmission. The dark tone of the screen darkens the area, the color darkens, and the layers are boring. The ink is too thin, the ink layer of the printing is too thin, the ink of the printed material appears pale, and the printing of the printing sheet is similar to the sun exposure of the sun for many years. It is old and unpalatable. The ink is not easy to be too thick and too thin. When printing, the ink is only moderate and the color is close. The raw materials are structured and the bright areas reflect bright levels.
The thickness of the ink layer printed on the paper is generally measured by photometric method. That is, the density value of the ink film printed on the paper is measured by a reflection density meter. The larger the density value is, the thicker the ink layer is. Experience has shown that black ink 1.8 ~ 2.0, cyan ink 1.45 ~ 1.70, magenta ink 1.25 ~ 1.50, yellow ink 0.9 ~ 1.05, the printing effect is more ideal, in the absence of reflective densitometers, many printed control signatures printed The proofs of the proofs are based on the actual ink color in the region and the ink color in the dot areas. The ink proofs are basically the same as the proof drafts, and the printing ink thickness is slightly thicker than the proof drafts. If offset paper is used for printing, the ink layer should be printed thicker.
Source: "Printing World" Author: Wang Yu
1 Printing pressure
The printing pressure directly affects the degree of ink transfer, and whether the thickness of the imprinted ink layer meets the standard, affects the gloss of the printed matter. If the pressure is too high, the ink will not be deformed when the ink is transferred to the paper. The gloss of the print will be poor. If the pressure is too light, the ink will barely be transferred to the paper, but the ink layer will float on the surface of the paper, resulting in rough printing. Uneven ink layer, affect the gloss effect, after the two-color or multicolor overprinting, especially when the field version and the on-site version of the overprint, if the former color fixation is not good or improper additives added, it may affect the print gloss.
The ideal printing pressure is to make the print on the print clear, thick ink layer, tone and color reappear well with minimal printing pressure. The offset press must control the proper ideal pressure, accurately measure and calculate the thickness of the liner, properly monitor the unevenness between the printing plate and the blanket, and effectively fill the unevenness to make the roller surface contact evenly and achieve an ideal realm. The difference in paper smoothness allows for flexible control of printing pressure. The dot enlargement rate is well controlled at about 15%. The printed ink has a thick, deep layered print and good gloss.
2 fountain solution pH
Offset printing is based on the principle of immiscible oil and water. The graphic part of the offset printing plate has the characteristics of oleophilic and water repellent, while the blank part has hydrophilic and oil repellent properties. During the printing process, the printing plate is wetted with water. The blank part of the film will form a water film. When the ink is transferred to the plate, only the graphic part will be covered with ink to print the graphic.
The pH of the formulated fountain solution is generally between 4.5 and 5.5, the pH of the fountain solution is too high, the hydrophilicity of the plate is poor, and the blank part of the printing plate is easy to get dirty, if the ink based on the dry vegetable oil binder is used When the pH of the fountain solution is greater than a certain value, the interfacial tension between the ink and the dampening water will drop, causing serious emulsification of the ink and directly affecting the gloss of the printed matter; the pH of the fountain solution is too low and the surface of the printing plate will be seriously affected. Corrosion, or even destroy the blank part of the printing plate does not feel the fat layer, so that the blank part of the plate appears trachoma. Therefore, a strong hydrophilic layer cannot be formed. The dampening water with a low pH also affects the ink transfer and the drying of the print. In the worst case, the combination of the graphic part and the metal base is destroyed when the corrosion further expands. , causing damage to outlets and reducing the gloss of prints.
3 Ink emulsion
Ink emulsification includes two forms of oil-in-water and water-in-oil. The oil-in-water type rarely occurs during the offset printing process, and the water-in-oil type is inevitable.
During the printing process, the ink will emulsify when the moisture is too large, and the ink layer is very thick on the imprint, but the ink molecules become oil-in-oil, resulting in dullness and reduced gloss after the imprint is dried. Blurring of the contours, large variations in color, errors in the color of the printed product and the signature, but also a series of other failures, slow drying of the imprinting, making the back of the printed product sticky, the viscosity of the ink decreasing, the printing plate floating, the pigment particles agglutinating, Causes flower and paste.
In the printing process, adhere to the small ink thick water method, as much as possible to make the ink thick, small water, this is because the thick ink viscosity, which is the cohesion of the ink increases, and accordingly enhance the adhesion of the ink molecules Force, thereby improving the ink's water resistance, reducing the ratio of water droplets dispersed in the ink, reducing the emulsification value of the ink, thus ensuring that the printed product is pure hue, high saturation, colorful, ink layer Thick dot gains are small, clear and full. In the offset printing process, in addition to the nature of the paper, the composition of the liquid in the fountain, the temperature and humidity of the workshop, the properties of the components of the ink, and the auxiliary materials for the ink, etc., the amount of water in the printing plate surface is controlled, and the minimum amount of water is ensured so that the printing plate is not The best dynamic and balanced state of sticky and dirty, in order to achieve the reduction of the color of the graphic printing, gray balance, good glossiness, various color density and tone value meet the requirements of the printed matter.
4 Effect of Ink Aids
In the printing process, limitations of the printing process and technical conditions, the physical properties, chemical properties, or printability of the ink cannot be matched with the printing job, and ink adjuvants are needed to make appropriate adjustments to facilitate smooth printing. Most of the adjuvants such as anti-sticking agents, detackifiers, varnish, and desiccants in the adjuvant adversely affect the gloss of printed products, such as our common No. 6 varnish, in inks. Plays a dilution effect and also plays a role in reducing the viscosity of the ink. After adding ink to the ink, the fluidity of the ink is increased, and at the same time, the dryness of the ink is also reduced, but the gloss of the print is unfavorable. For another example, the main ingredient of the anti-adhesive agent is corn flour. After the ink is added to the ink, the surface of the imprinted film layer becomes rough due to the refraction of the corn powder, and the gloss of the finished product is deteriorated.
Offset printing inks have adequate drying performance under normal temperature conditions, but the temperature in winter decreases, or in the case that anti-adhesive agents, dirt removing agents, ink adjustments, etc. have been added to the ink, desiccants should be added to the process operations. In the correct use of desiccants is beneficial to the formation of gloss prints, because the paper absorption of the connection material takes a certain amount of time, in the process as soon as possible to agglutinate the connection material, until the conjunctiva drying is the key to a good finish gloss, ink preparation process should be strict Addition and release of control aids, if considering the gloss effect, should be less or no adjuvant.
5 Effect of Ink Layer Thickness
The correct and reasonable use of ink is an important link to ensure the color of the printed matter. The ink is too thick and too thin, which is not conducive to uniform ink and cloth. The ink is too thick, the printed film layer is too thick, and the ink flowability is poor, resulting in poor transmission. The dark tone of the screen darkens the area, the color darkens, and the layers are boring. The ink is too thin, the ink layer of the printing is too thin, the ink of the printed material appears pale, and the printing of the printing sheet is similar to the sun exposure of the sun for many years. It is old and unpalatable. The ink is not easy to be too thick and too thin. When printing, the ink is only moderate and the color is close. The raw materials are structured and the bright areas reflect bright levels.
The thickness of the ink layer printed on the paper is generally measured by photometric method. That is, the density value of the ink film printed on the paper is measured by a reflection density meter. The larger the density value is, the thicker the ink layer is. Experience has shown that black ink 1.8 ~ 2.0, cyan ink 1.45 ~ 1.70, magenta ink 1.25 ~ 1.50, yellow ink 0.9 ~ 1.05, the printing effect is more ideal, in the absence of reflective densitometers, many printed control signatures printed The proofs of the proofs are based on the actual ink color in the region and the ink color in the dot areas. The ink proofs are basically the same as the proof drafts, and the printing ink thickness is slightly thicker than the proof drafts. If offset paper is used for printing, the ink layer should be printed thicker.
Source: "Printing World" Author: Wang Yu
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