Dirty offset printing is one of the common faults in printing. In the production process, we must carry out specific analysis according to the signs and parts of the layout. Find out the cause of the malfunction and take effective measures to prevent and solve it. In general, offset printing is dirty and can be classified as floating. Dirty oil, paste version. Dark stripe and so on.
Dirty floatation refers to a phenomenon in which a non-graphical part with a relatively large range and a relatively low density is dirty. Unlike the oily dirty, the dirty part is not covered with a lipid-based basis and is not caused by the printing plate. It is caused by ink emulsification. There are two types of ink emulsification, water-in-oil (W/O) type and oil-in-water (O/W) type. Among them, the water-in-oil type ink emulsification is the situation where the ink emulsification is too severe, the viscosity of the ink is reduced, and the ink droplets splash on the surface of the plate to form a buoyancy due to centrifugal force: the oil-in-water type ink emulsification is the phenomenon of “water†of the ink, Make the blank part of the plate lighter ink marks.
In the actual operation, we can judge by the following signs. (1) Contaminated parts can be easily wiped off; (2) Since the hydrophilic salt layer is not destroyed, the dirty parts will often change; (3) The floating dirt or ink residue will fall into the fountain solution, and the flocculent ink particles (water-in-oil) will appear. Ink emulsification caused); 4 fountain solution in the precipitation of pigment or flocculation, printing full version of a color shadow (oil-in-water emulsion caused by), that is, the ink "water" phenomenon. Causes: 1 The pH value of the fountain solution and the paper is not suitable. When embossing the printing ink, the ambassador ink is emulsified. At this time, the water-in-oil type ink is mostly emulsified. 2 The layout volume is too large and the quality of the ink binder is poor. , resulting in oil-in-water type emulsification, ink is too soft; 3 pigment water resistance. Poor acid resistance, poor affinity with the link material; 4 Ink pigments dissolved in the fountain solution, the ink was flocculent dispersed in the fountain solution, causing a large area of ​​dirty, may also be due to inappropriate printing pressure, water roller and Improper assembly of the ink roller and insufficient hardness of the plate roller.
Dirty oil Dirty oil refers to the blank part of the printing plate that is not fat-sensitive, so that the ink adheres to it and forms a dirty plate. The main reasons for causing blank parts of the printing plate: insufficient amount of water in the blank or weak acidity of the fountain solution; the hydrophilic salt layer in the blank part of the printing plate is unstable or even worn due to machine operation, paper, etc., resulting in decreased water retention. The fatty acids in the ink are dissolved in the fountain solution, leaving the blank part of the printing plate feeling fat.
In the actual operation, we can judge by the following signs. 1Dirty parts are not easily wiped; 2Dirty parts are relatively fixed; 3Water can be used. The method of rubbing the potion and the resin was eliminated, but the dirty oil with badly worn blisters could not be eradicated. The reasons are as follows: 1 The pressure of the printing plate and the blanket cylinder is too large or the liner is too thick, resulting in increased friction or sliding friction, which accelerates the wear of the printing plate. Through careful observation, we found that the mouth of the printing plate is most likely to lose its ability to hold water because of the sanding hole; 2 the blanket is aging and hard due to long use time, loses its elasticity, and reduces compression deformation. Small, causing insufficient printing pressure. If it is not replaced in time, adding only some paper to the liner can increase the pressure, but the friction will increase accordingly. Therefore, during the transfer process, the water layer on the surface of the printing plate will be used for a long time. And was destroyed, causing a large area of ​​the printing plate oil; 3 for the aging of the blanket. Hardening phenomenon, we usually first wipe the aging and damaged parts, and then use polypropylene tape for bonding, because polypropylene tape is cheap, this method is very popular; 4 loading plate is also critical if the loading If it is not tightened, it will cause the printing plate and the roller to not be affixed. The unconformed part will rub against the rubber roller, and the contact with the water roller will be too tight. This will not only produce excessive friction, but also will squeeze out moisture. Therefore, the layout is often dirty due to insufficient water supply. The reason for the 5 ink roller: If the ink roller is too heavy, it will produce a jump when the plate cylinder is turned to the mouth part, and dirty oil will appear at the mouth of the printing plate. Relying on the plate is too heavy to wear the printing plate and the oil is dirty; 6 The ink's lipophilicity and additives are used improperly, resulting in too strong oiliness; 7 When the glue is wiped, the moisture content of the wet cloth is too large, resulting in the phenomenon of "dew bottom" after wiping. Dirty oil; 8 The pH value of the paper is too high, which greatly reduces the acidity of the fountain solution. The water roller is dirty and the water roller assembly is not suitable, resulting in insufficient water supply and dirty oil.
Paste paste refers to the printing of text and parts of the lines and lines. Between the network and the outlets, as well as in the highlights, there should not be dirty spots in the ink, but it is sometimes classified as dirty, and sometimes it is in the category of floating.
In the actual operation, we can judge by the following signs. 1 The level of the imprinting is unclear, and parts with denser lines (above 50:6) are frequently found; 2 If it is dirty, the position with dirty spots is dark, and early detection can be ruled out; 3 If it is dirty , with dirty position will change, ink is light, easy to remove. Reasons for the production: 1) Excessive or excessive amount of dry oil will change the ink's adaptability; when printing, the ink layer of the graphic part will spread; 2 the ink layer is too thick. Too little water or ink is too thin and fluidity; 3 Ink emulsification serious; 4 Pressure is too large, the graphic part of the ink layer spread or lining is not suitable; 5 Part of the deformation of the roller, water roller and the layout of the poor contact caused by water supply Insufficient or uneven; 6 ink roller surface aging, especially after the two ink roller adsorption performance is poor, can not be the layout of the floating ink, dirty ink away; 7 off the plate when the dry oxidation even paper from the hair, leaving in the ink roller Produce heaps of ink and paste.
There are many signs and reasons for offset faults on offset printing plates. In the actual operation, they should be carefully distinguished and classified, and the phenomena that occur should be analyzed and resolved in a timely manner.
In order to solve the problem of circumferential overprinting, it is not possible to print a four-color offset press for many years. There are often problems with the overprinting of printing products. The crosshairs are very accurate, and the size of the crosshairs at the tips is not the same. Under normal circumstances, it is generally believed that the stripping tension after the imprinting of the paper through the four color groups is large and the blanket is not the same. During an inspection of the machine, an audible noise was heard from the second color group. According to experience, it was judged that the sound was made when the blanket was not tight. Therefore, the machine stopped immediately, stretched the blanket, and reprinted. Imprinting is more accurate than the original.
According to the characteristics of the air-cushion blanket, the blanket can always be deformed during the printing process. When the blanket is printed under slack, it will make the print on the paper more prolonged than the actual one. Conversely, if it is shorter, changing the tightness of the blanket can change the circumference of the print, so that the overlay can be accurately printed. purpose. This method is easy to operate, and can receive satisfactory results, but it needs special emphasis, this can only be fine-tuned in the case of unable to solve the pull plate method, especially when relaxing the blanket should pay attention to safety and to prevent Ghosting and other failures must not be abused.
Dirty floatation refers to a phenomenon in which a non-graphical part with a relatively large range and a relatively low density is dirty. Unlike the oily dirty, the dirty part is not covered with a lipid-based basis and is not caused by the printing plate. It is caused by ink emulsification. There are two types of ink emulsification, water-in-oil (W/O) type and oil-in-water (O/W) type. Among them, the water-in-oil type ink emulsification is the situation where the ink emulsification is too severe, the viscosity of the ink is reduced, and the ink droplets splash on the surface of the plate to form a buoyancy due to centrifugal force: the oil-in-water type ink emulsification is the phenomenon of “water†of the ink, Make the blank part of the plate lighter ink marks.
In the actual operation, we can judge by the following signs. (1) Contaminated parts can be easily wiped off; (2) Since the hydrophilic salt layer is not destroyed, the dirty parts will often change; (3) The floating dirt or ink residue will fall into the fountain solution, and the flocculent ink particles (water-in-oil) will appear. Ink emulsification caused); 4 fountain solution in the precipitation of pigment or flocculation, printing full version of a color shadow (oil-in-water emulsion caused by), that is, the ink "water" phenomenon. Causes: 1 The pH value of the fountain solution and the paper is not suitable. When embossing the printing ink, the ambassador ink is emulsified. At this time, the water-in-oil type ink is mostly emulsified. 2 The layout volume is too large and the quality of the ink binder is poor. , resulting in oil-in-water type emulsification, ink is too soft; 3 pigment water resistance. Poor acid resistance, poor affinity with the link material; 4 Ink pigments dissolved in the fountain solution, the ink was flocculent dispersed in the fountain solution, causing a large area of ​​dirty, may also be due to inappropriate printing pressure, water roller and Improper assembly of the ink roller and insufficient hardness of the plate roller.
Dirty oil Dirty oil refers to the blank part of the printing plate that is not fat-sensitive, so that the ink adheres to it and forms a dirty plate. The main reasons for causing blank parts of the printing plate: insufficient amount of water in the blank or weak acidity of the fountain solution; the hydrophilic salt layer in the blank part of the printing plate is unstable or even worn due to machine operation, paper, etc., resulting in decreased water retention. The fatty acids in the ink are dissolved in the fountain solution, leaving the blank part of the printing plate feeling fat.
In the actual operation, we can judge by the following signs. 1Dirty parts are not easily wiped; 2Dirty parts are relatively fixed; 3Water can be used. The method of rubbing the potion and the resin was eliminated, but the dirty oil with badly worn blisters could not be eradicated. The reasons are as follows: 1 The pressure of the printing plate and the blanket cylinder is too large or the liner is too thick, resulting in increased friction or sliding friction, which accelerates the wear of the printing plate. Through careful observation, we found that the mouth of the printing plate is most likely to lose its ability to hold water because of the sanding hole; 2 the blanket is aging and hard due to long use time, loses its elasticity, and reduces compression deformation. Small, causing insufficient printing pressure. If it is not replaced in time, adding only some paper to the liner can increase the pressure, but the friction will increase accordingly. Therefore, during the transfer process, the water layer on the surface of the printing plate will be used for a long time. And was destroyed, causing a large area of ​​the printing plate oil; 3 for the aging of the blanket. Hardening phenomenon, we usually first wipe the aging and damaged parts, and then use polypropylene tape for bonding, because polypropylene tape is cheap, this method is very popular; 4 loading plate is also critical if the loading If it is not tightened, it will cause the printing plate and the roller to not be affixed. The unconformed part will rub against the rubber roller, and the contact with the water roller will be too tight. This will not only produce excessive friction, but also will squeeze out moisture. Therefore, the layout is often dirty due to insufficient water supply. The reason for the 5 ink roller: If the ink roller is too heavy, it will produce a jump when the plate cylinder is turned to the mouth part, and dirty oil will appear at the mouth of the printing plate. Relying on the plate is too heavy to wear the printing plate and the oil is dirty; 6 The ink's lipophilicity and additives are used improperly, resulting in too strong oiliness; 7 When the glue is wiped, the moisture content of the wet cloth is too large, resulting in the phenomenon of "dew bottom" after wiping. Dirty oil; 8 The pH value of the paper is too high, which greatly reduces the acidity of the fountain solution. The water roller is dirty and the water roller assembly is not suitable, resulting in insufficient water supply and dirty oil.
Paste paste refers to the printing of text and parts of the lines and lines. Between the network and the outlets, as well as in the highlights, there should not be dirty spots in the ink, but it is sometimes classified as dirty, and sometimes it is in the category of floating.
In the actual operation, we can judge by the following signs. 1 The level of the imprinting is unclear, and parts with denser lines (above 50:6) are frequently found; 2 If it is dirty, the position with dirty spots is dark, and early detection can be ruled out; 3 If it is dirty , with dirty position will change, ink is light, easy to remove. Reasons for the production: 1) Excessive or excessive amount of dry oil will change the ink's adaptability; when printing, the ink layer of the graphic part will spread; 2 the ink layer is too thick. Too little water or ink is too thin and fluidity; 3 Ink emulsification serious; 4 Pressure is too large, the graphic part of the ink layer spread or lining is not suitable; 5 Part of the deformation of the roller, water roller and the layout of the poor contact caused by water supply Insufficient or uneven; 6 ink roller surface aging, especially after the two ink roller adsorption performance is poor, can not be the layout of the floating ink, dirty ink away; 7 off the plate when the dry oxidation even paper from the hair, leaving in the ink roller Produce heaps of ink and paste.
There are many signs and reasons for offset faults on offset printing plates. In the actual operation, they should be carefully distinguished and classified, and the phenomena that occur should be analyzed and resolved in a timely manner.
In order to solve the problem of circumferential overprinting, it is not possible to print a four-color offset press for many years. There are often problems with the overprinting of printing products. The crosshairs are very accurate, and the size of the crosshairs at the tips is not the same. Under normal circumstances, it is generally believed that the stripping tension after the imprinting of the paper through the four color groups is large and the blanket is not the same. During an inspection of the machine, an audible noise was heard from the second color group. According to experience, it was judged that the sound was made when the blanket was not tight. Therefore, the machine stopped immediately, stretched the blanket, and reprinted. Imprinting is more accurate than the original.
According to the characteristics of the air-cushion blanket, the blanket can always be deformed during the printing process. When the blanket is printed under slack, it will make the print on the paper more prolonged than the actual one. Conversely, if it is shorter, changing the tightness of the blanket can change the circumference of the print, so that the overlay can be accurately printed. purpose. This method is easy to operate, and can receive satisfactory results, but it needs special emphasis, this can only be fine-tuned in the case of unable to solve the pull plate method, especially when relaxing the blanket should pay attention to safety and to prevent Ghosting and other failures must not be abused.
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