The problem of attention should be paid to the four-color printing
2024-01-24 07:07:35
At present, many small and medium-sized printing companies use monochrome offset printing machines to overprint color printing, simple printing and overprinting of two colors. Generally speaking, overprinting of single-color and four-colors is the most common, but there are also printing factories overprinting the front and back of a total of eight colors. This requires high-quality, high-precision printing presses, but also requires the printing operator to have a more sophisticated technology, and in the process of overprinting should pay attention to the following content.
First, paper paper is one of the six major elements in the printing process. The quality of paper directly affects the speed of printing and the quality of printed matter. First, the paper needs to be flat, the cutting size must be the same, and the straightness and straightness errors are relatively small. For printed sheets, the error of the web size (width x length) shall not exceed ±1 mm. For printed covers and finer albums, the error of the web size (width × length) shall not exceed ±0.5 mm, and the positioning edge shall be marked. , which is the rule edge; paper smoothness refers to the level of the paper surface is smooth, smoothness determines the degree of contact between the paper and the blanket, under the same printing pressure, printed on the paper with a low degree of smooth print The clarity of the text is poor. For example, under the same printing conditions, the use of coated paper is better than the use of coated paper; the moisture content of the paper is required to be between 6% and 8%, and the water content is too high then the surface of the paper. Tension and surface strength decrease, plasticity increases, and the imprinted ink film cures slowly. If the water content is too low, the paper is prone to static electricity and tends to be brittle, which is not conducive to printing. Uneven moisture content will form tight edges and flounces. Uneven deformation of curl or unevenness, pleats and other defects will appear after printing. This requires the printing shop to have suitable temperature and humidity, generally require temperature control at 18 °C ~ 25 °C, relative humidity maintained at 50% ~ 60%, which is conducive to the preservation of the paper and printing smoothly. In addition, the paper's own fiber type and pH will also have a greater impact on printing.
Second, ink ink viscosity and fluidity have an important role for print quality. The viscosity of the ink increases the viscosity of the ink while decreasing its flowability. On the contrary, the fluidity is increased. The thick ink does not have the same viscosity as the thick ink. The ink with the high viscosity does not have to be thick. Only the ink with the same viscosity has the greater consistency, the lower the fluidity. If the fluidity is too small, the ink transfer during the printing process is not smooth and uneven, resulting in a shallow front and back depth on the same printing surface and other ink supply failures. The fluidity is too large, the imprinting cannot be accurately transferred, and the graphic level is not clear. Ink is not full, the color is not bright, at the same time, the ink flow is too large can also lead to the production of dirty plates and ink bars. During the printing process, the viscosity and fluidity of the ink can be adjusted by using a varnish, but it is not advisable to add corn flour to the ink in order to allow the print to dry. It can also be achieved by using fast-drying inks. Therefore, in the printing process, the ink viscosity and fluidity should be adjusted.
The preservation of ink has always been a headache for printing companies. Because the ink rotates in the air for a little longer, it is easily oxidized by the air and forms a thick layer of ink. When the ink is taken for the next printing, it must be Scratching the ink, this will inevitably waste some of the ink. The printing factory generally adopts a measure to add a certain amount of water to the ink cartridge to prevent the ink from contacting the air. However, actually the oxygen contained in water also oxidizes the ink, and the contact time between the water and the ink is long; the ink is easily emulsified, and the phenomenon of non-inking occurs when printing on the machine. Although the amount of ink is large, Evenly distributed rollers (mainly hard rollers) are still not inked. It is advisable to use wax paper to isolate the ink from the air when it is stored, or to seal it with plastic paper. That is, wax paper or plastic paper is attached to the surface of the ink layer, and the wax paper or plastic paper can be peeled off before the next printing.
Third, the fountain solution dampening solution is the role of wetting the blank part of the printing plate, and the formation of metal oxide or hydrophilic salt layer, the use of the principle of ink repulsion between the blank part and the ink to establish a barrier between the ink is not Stained printing blanks. General requirements dampening fluid must be a weak acid medium, adjust the dampening solution PH value between 5.0 ~ 6.0 is appropriate. The pH is too low, ie the fountain solution is acidic. Too strong will cause serious corrosion of the substrate, and the ink will dry slowly. If it is too high, the diazo compound in the graphic part of the photo-decomposition PS will be dissolved, resulting in the incompleteness of the plate image. Cause ink emulsification, so that the quality of the print product is seriously reduced. At present, the wetting device used in the small offset press, the Daglen wetted mechanism and the Kunpak direct water supply unit for the small offset printing press must control the amount of water according to different dampening modes in the printing process, regardless of the type of water supply. In the method, when the amount of water is too large, water spray occurs on the printed matter, the small outlets are easily washed away by water, and the printed paper absorbs water and expands and deforms, which causes troubles for overprinting. If the amount of water is too small, it will obviously be dirty, but care should be taken to avoid water and large ink. The amount of water can be based on the area and distribution of the layout text and the type of paper used. The machine speed and the surrounding environment are determined in several ways. The ink-jet offset of offset printing has only dynamic relative balance, and there is no ideal absolute balance. Mastering ink-water balance is also an important aspect. In the printing process, operators must constantly observe the effects of printing to ensure the printing quality.
Fourth, the test machine is good, overprinting must be accurate printing before printing can accurately check whether the printing can be printed first 10 to 20 prints, respectively, testing the world, around the rules line. If the rule line is not on the paper (the paper is slightly farther away from the rule line), a rule line may be manually drawn on the plate corresponding to the edge of the paper, and an ink is printed on the rule line and then printed for inspection. Overprinting; prints can be printed once more, checking whether they can be accurately overlaid together after printing.
In the printing process, we must first ensure that the paper is stable, the paper can reach the front gauge in an equal and flat manner, and the distance between the paper and the baffle plate is required to be 3mm to 5mm, to ensure that the pull gauge can pull the paper to the required position, and not As far as pulling the paper is too long, pull the paper too far. Furthermore, the pressure of the pull gauge pressure spring should be moderate, and a thick compression spring should be used when printing thick paper. When printing thin paper, a thin compression spring should be used, and the spring force of the spring should be moderated by the spiral adjustment on the spring. The excessive pressure of the pressure spring leads to a long time for pulling the paper, it is easy to pull the paper to deform, and it affects the action of the pull gauge and other mechanisms. If the pressure is too low, the paper is not easily pulled to the side shutter. Obviously, overprinting will not occur. Only properly set the distance between the paper and the side cover of the pull gauge, and the spring pressure is appropriate, to ensure that the paper pull force is proper and overprinting is accurate. The use of small offset printing rules should pay attention to the distance between the paper and the regulatory panel baffle, and push the paper on the other side of the reed has a certain amount of compression.
Fifth, the paper position printing process, generally speaking about the small offset press on the left and right position requirements of the paper, that is, pull the left and right position requirements are not very strict, but under certain circumstances, print overprint is accurate with the position of the paper is very large Relationship. Since small offset presses have their own particularities, different from large offset presses, the continuous feed used by large-scale presses with four or more web formats is usually direct or indirect. In contrast, small offset presses generally use transcendent paper feed. In the paper, the continuity of the paper is given to the impression cylinder by the friction between the two upper and lower transfer rollers, the paper is positioned once at the front gauge, and the secondary positioning is performed at the impression cylinder. There are two cases where overprinting does not occur because the position of the paper is not good. One is that after the paper reaches the front gauge, the front end of the paper is not pulled to the front side of the front gauge when the pull paper is pulled. , resulting in inaccurate overprinting. In another case, the front side of the paper does not touch the face of the front face, but in the secondary positioning, the edge of the paper just touches the face of the small stop on the impression cylinder, and in this case also There may be inaccurate overprinting caused by poor paper position. Therefore, in the offset printing machine overprinting should also pay attention to the left and right position of the paper on the overprint caused by the impact.
Sixth, the rational arrangement of the printing color sequence The general four-color machine printing color sequence reasonable arrangement is: black, blue, red, yellow, but also according to the color sequence of yellow, red, blue, black printing. When the four-color printer prints, the printing interval between color and color is short, and the ink does not have drying time, which is a wet and superimposed overprinting mode, and the printing interval between color and color is longer in the monochrome machine printing, and printing is second. When the color, the first color has been dry, so it is a wet stack of superimposed printing, it is precisely because of the different overprinting methods, the color sequence arrangement is also not the same. There are many color sequential arrangements in a monochrome machine, but the specific choice of color sequence can be considered from various aspects as follows: 1. According to the brightness of the three primary colors to arrange the color sequence must first print dark, bright color after printing, that is, blue, black and India, red, yellow and India. 2. According to the three primary colors ink transparency and hiding power arrangement color sequence, poor transparency of the blue, black print, good transparency, yellow and red ink after printing. 3. According to the size of the text area to arrange the color sequence is to print a small picture, after printing full version or large format graphics. 4. According to the characteristics of the manuscripts, color pictures based on warm colors must be printed in red or yellow first. 5. Considering overprinting, the overprinting of difficult colors is first done. In general, landscapes are printed in blue and yellow, while portraits are printed in red and yellow. The printing color sequence recommended when using a monochrome machine to print four colors is: blue, red, yellow, and black, so that as long as the previous two colors are overprinted accurately. The color tone is good, and the two-color overprint behind it will not be too obvious even if it is a bit inaccurate. The operator should pay attention when changing the ink. In order to maintain the purity of the ink, the next color ink that is to be printed in the color ink is cleaned and washed again. Especially when dark ink is used for light color inks, it is better to clean the machine twice.
VII. Others In the process of overprinting, if it is not a full-print version of the printed matter in the field or in color, it is best not to use a dusting device. Although the powder can make the ink dry quickly and prevent the back of the printed material from getting dirty, the powder is mastered. Bad, directly affect the print quality and brightness, generally use the powder in the last color printing. In the process of four-color overprinting, it is better to print at the same speed and not to change the printing speed. Because the speed change will more or less affect the overprint accuracy of the print. In addition, if the accuracy of color printing is very demanding, conditional printers can also run the water once before the official printing, that is, install the printing plate, fold down the printing roller, or make the ink supply system not supply ink, and only supply water. The "printing" is not performed for the ink, so that the overprinting due to paper deformation can be reduced.
In summary, the monochrome offset press overprints color prints, both for the machine and the operator. Only by mastering the overprinting technology, can we print fine and high-quality printed matter under the conditions of sophisticated equipment and printing consumables. (Li Han) ("China Packaging News")
First, paper paper is one of the six major elements in the printing process. The quality of paper directly affects the speed of printing and the quality of printed matter. First, the paper needs to be flat, the cutting size must be the same, and the straightness and straightness errors are relatively small. For printed sheets, the error of the web size (width x length) shall not exceed ±1 mm. For printed covers and finer albums, the error of the web size (width × length) shall not exceed ±0.5 mm, and the positioning edge shall be marked. , which is the rule edge; paper smoothness refers to the level of the paper surface is smooth, smoothness determines the degree of contact between the paper and the blanket, under the same printing pressure, printed on the paper with a low degree of smooth print The clarity of the text is poor. For example, under the same printing conditions, the use of coated paper is better than the use of coated paper; the moisture content of the paper is required to be between 6% and 8%, and the water content is too high then the surface of the paper. Tension and surface strength decrease, plasticity increases, and the imprinted ink film cures slowly. If the water content is too low, the paper is prone to static electricity and tends to be brittle, which is not conducive to printing. Uneven moisture content will form tight edges and flounces. Uneven deformation of curl or unevenness, pleats and other defects will appear after printing. This requires the printing shop to have suitable temperature and humidity, generally require temperature control at 18 °C ~ 25 °C, relative humidity maintained at 50% ~ 60%, which is conducive to the preservation of the paper and printing smoothly. In addition, the paper's own fiber type and pH will also have a greater impact on printing.
Second, ink ink viscosity and fluidity have an important role for print quality. The viscosity of the ink increases the viscosity of the ink while decreasing its flowability. On the contrary, the fluidity is increased. The thick ink does not have the same viscosity as the thick ink. The ink with the high viscosity does not have to be thick. Only the ink with the same viscosity has the greater consistency, the lower the fluidity. If the fluidity is too small, the ink transfer during the printing process is not smooth and uneven, resulting in a shallow front and back depth on the same printing surface and other ink supply failures. The fluidity is too large, the imprinting cannot be accurately transferred, and the graphic level is not clear. Ink is not full, the color is not bright, at the same time, the ink flow is too large can also lead to the production of dirty plates and ink bars. During the printing process, the viscosity and fluidity of the ink can be adjusted by using a varnish, but it is not advisable to add corn flour to the ink in order to allow the print to dry. It can also be achieved by using fast-drying inks. Therefore, in the printing process, the ink viscosity and fluidity should be adjusted.
The preservation of ink has always been a headache for printing companies. Because the ink rotates in the air for a little longer, it is easily oxidized by the air and forms a thick layer of ink. When the ink is taken for the next printing, it must be Scratching the ink, this will inevitably waste some of the ink. The printing factory generally adopts a measure to add a certain amount of water to the ink cartridge to prevent the ink from contacting the air. However, actually the oxygen contained in water also oxidizes the ink, and the contact time between the water and the ink is long; the ink is easily emulsified, and the phenomenon of non-inking occurs when printing on the machine. Although the amount of ink is large, Evenly distributed rollers (mainly hard rollers) are still not inked. It is advisable to use wax paper to isolate the ink from the air when it is stored, or to seal it with plastic paper. That is, wax paper or plastic paper is attached to the surface of the ink layer, and the wax paper or plastic paper can be peeled off before the next printing.
Third, the fountain solution dampening solution is the role of wetting the blank part of the printing plate, and the formation of metal oxide or hydrophilic salt layer, the use of the principle of ink repulsion between the blank part and the ink to establish a barrier between the ink is not Stained printing blanks. General requirements dampening fluid must be a weak acid medium, adjust the dampening solution PH value between 5.0 ~ 6.0 is appropriate. The pH is too low, ie the fountain solution is acidic. Too strong will cause serious corrosion of the substrate, and the ink will dry slowly. If it is too high, the diazo compound in the graphic part of the photo-decomposition PS will be dissolved, resulting in the incompleteness of the plate image. Cause ink emulsification, so that the quality of the print product is seriously reduced. At present, the wetting device used in the small offset press, the Daglen wetted mechanism and the Kunpak direct water supply unit for the small offset printing press must control the amount of water according to different dampening modes in the printing process, regardless of the type of water supply. In the method, when the amount of water is too large, water spray occurs on the printed matter, the small outlets are easily washed away by water, and the printed paper absorbs water and expands and deforms, which causes troubles for overprinting. If the amount of water is too small, it will obviously be dirty, but care should be taken to avoid water and large ink. The amount of water can be based on the area and distribution of the layout text and the type of paper used. The machine speed and the surrounding environment are determined in several ways. The ink-jet offset of offset printing has only dynamic relative balance, and there is no ideal absolute balance. Mastering ink-water balance is also an important aspect. In the printing process, operators must constantly observe the effects of printing to ensure the printing quality.
Fourth, the test machine is good, overprinting must be accurate printing before printing can accurately check whether the printing can be printed first 10 to 20 prints, respectively, testing the world, around the rules line. If the rule line is not on the paper (the paper is slightly farther away from the rule line), a rule line may be manually drawn on the plate corresponding to the edge of the paper, and an ink is printed on the rule line and then printed for inspection. Overprinting; prints can be printed once more, checking whether they can be accurately overlaid together after printing.
In the printing process, we must first ensure that the paper is stable, the paper can reach the front gauge in an equal and flat manner, and the distance between the paper and the baffle plate is required to be 3mm to 5mm, to ensure that the pull gauge can pull the paper to the required position, and not As far as pulling the paper is too long, pull the paper too far. Furthermore, the pressure of the pull gauge pressure spring should be moderate, and a thick compression spring should be used when printing thick paper. When printing thin paper, a thin compression spring should be used, and the spring force of the spring should be moderated by the spiral adjustment on the spring. The excessive pressure of the pressure spring leads to a long time for pulling the paper, it is easy to pull the paper to deform, and it affects the action of the pull gauge and other mechanisms. If the pressure is too low, the paper is not easily pulled to the side shutter. Obviously, overprinting will not occur. Only properly set the distance between the paper and the side cover of the pull gauge, and the spring pressure is appropriate, to ensure that the paper pull force is proper and overprinting is accurate. The use of small offset printing rules should pay attention to the distance between the paper and the regulatory panel baffle, and push the paper on the other side of the reed has a certain amount of compression.
Fifth, the paper position printing process, generally speaking about the small offset press on the left and right position requirements of the paper, that is, pull the left and right position requirements are not very strict, but under certain circumstances, print overprint is accurate with the position of the paper is very large Relationship. Since small offset presses have their own particularities, different from large offset presses, the continuous feed used by large-scale presses with four or more web formats is usually direct or indirect. In contrast, small offset presses generally use transcendent paper feed. In the paper, the continuity of the paper is given to the impression cylinder by the friction between the two upper and lower transfer rollers, the paper is positioned once at the front gauge, and the secondary positioning is performed at the impression cylinder. There are two cases where overprinting does not occur because the position of the paper is not good. One is that after the paper reaches the front gauge, the front end of the paper is not pulled to the front side of the front gauge when the pull paper is pulled. , resulting in inaccurate overprinting. In another case, the front side of the paper does not touch the face of the front face, but in the secondary positioning, the edge of the paper just touches the face of the small stop on the impression cylinder, and in this case also There may be inaccurate overprinting caused by poor paper position. Therefore, in the offset printing machine overprinting should also pay attention to the left and right position of the paper on the overprint caused by the impact.
Sixth, the rational arrangement of the printing color sequence The general four-color machine printing color sequence reasonable arrangement is: black, blue, red, yellow, but also according to the color sequence of yellow, red, blue, black printing. When the four-color printer prints, the printing interval between color and color is short, and the ink does not have drying time, which is a wet and superimposed overprinting mode, and the printing interval between color and color is longer in the monochrome machine printing, and printing is second. When the color, the first color has been dry, so it is a wet stack of superimposed printing, it is precisely because of the different overprinting methods, the color sequence arrangement is also not the same. There are many color sequential arrangements in a monochrome machine, but the specific choice of color sequence can be considered from various aspects as follows: 1. According to the brightness of the three primary colors to arrange the color sequence must first print dark, bright color after printing, that is, blue, black and India, red, yellow and India. 2. According to the three primary colors ink transparency and hiding power arrangement color sequence, poor transparency of the blue, black print, good transparency, yellow and red ink after printing. 3. According to the size of the text area to arrange the color sequence is to print a small picture, after printing full version or large format graphics. 4. According to the characteristics of the manuscripts, color pictures based on warm colors must be printed in red or yellow first. 5. Considering overprinting, the overprinting of difficult colors is first done. In general, landscapes are printed in blue and yellow, while portraits are printed in red and yellow. The printing color sequence recommended when using a monochrome machine to print four colors is: blue, red, yellow, and black, so that as long as the previous two colors are overprinted accurately. The color tone is good, and the two-color overprint behind it will not be too obvious even if it is a bit inaccurate. The operator should pay attention when changing the ink. In order to maintain the purity of the ink, the next color ink that is to be printed in the color ink is cleaned and washed again. Especially when dark ink is used for light color inks, it is better to clean the machine twice.
VII. Others In the process of overprinting, if it is not a full-print version of the printed matter in the field or in color, it is best not to use a dusting device. Although the powder can make the ink dry quickly and prevent the back of the printed material from getting dirty, the powder is mastered. Bad, directly affect the print quality and brightness, generally use the powder in the last color printing. In the process of four-color overprinting, it is better to print at the same speed and not to change the printing speed. Because the speed change will more or less affect the overprint accuracy of the print. In addition, if the accuracy of color printing is very demanding, conditional printers can also run the water once before the official printing, that is, install the printing plate, fold down the printing roller, or make the ink supply system not supply ink, and only supply water. The "printing" is not performed for the ink, so that the overprinting due to paper deformation can be reduced.
In summary, the monochrome offset press overprints color prints, both for the machine and the operator. Only by mastering the overprinting technology, can we print fine and high-quality printed matter under the conditions of sophisticated equipment and printing consumables. (Li Han) ("China Packaging News")
NINGBO HOZ TRADING CO.,LTD , https://www.howzkitchenware.com