Third, the printing material factors Offset materials, mainly paper, ink, printing plates, blankets and pad lining four categories. Various materials must meet the printability requirements of offset printing properties, otherwise there will be various printing failures.
1. Paper-based paper physicochemical properties and technical indicators, including physical performance indicators, optical performance indicators, printing performance indicators, chemical performance indicators. Among them, tightness, tensile strength, stretchability, whiteness, absorbency, smoothness, glossiness, pH, etc. are closely related to offset printing suitability.
The tightness and tensile strength of the paper, and the pressure and separation during the printing process, the viscosity of the ink and the sticky force generated by the surface of the blanket can cause hair loss and powder fall, resulting in burr-like spots on the printed material or in the field. Loss of money.
The retractility of the paper is related to the direction in which the fibers are arranged. The stretch rate in the direction of the filaments is smaller than the retractility in the direction of the fibers at both sides, so the offset printing is usually done with the paper in the direction of the filaments parallel to the axis of the cylinder to minimize the size. The overprint of the paper due to wet stretch is not allowed.
The whiteness and smoothness of the paper are related to the vividness and saturation of the printed image. After the paper with high whiteness is printed with colored ink, the light projected on the paper is absorbed less by the paper and reflects more. The original appearance of ink color is better presented. The paper with poor whiteness has confetti, absorbs much of the projected light, has less reflected light, and the printed image is dark. Papers with poor smoothness have a rough surface, strong oil absorption, dullness after imprinting, more projection light, and a diffuse reflection of reflected light, poor visual quality of printed matter, and dullness of colors.
The oil-absorbing paper absorbs a large amount of the binder in the imprinted ink before the blot has dried and the conjunctiva, so that the surface of the imprinted film is rough, and the product does not stain. In severe cases, imprinting failures may also occur.
General paper pH value, above 5.5, was slightly acidic, when the pH dropped below 5.5, the acidity of the paper increased, this paper can damage the drying of the ink, resulting in imprinting failure.
2. Ink is used to represent the image image and color of the ink, is a plastic fluidity, through the ink roller transmission, coated on the plate on the graphic, with a blanket, and finally transferred to the paper After drying the conjunctiva, it becomes solid. Offset printing requirements The main indicators of printing ink suitability are: fixing, drying, coloring rate, fineness, viscosity, fluidity, and resistance to acids, alkalis, water, and light.
With the increase in the speed of offset presses and the emergence of multicolor machines, the fixation of inks is becoming more and more important. Most multi-color machines have a printing speed of 8,000 sheets/hour or more, and each sheet is printed with about 0.5 seconds (s) to be transferred to the second color. If the fixing speed of the ink is slow, the pre-color blots will stay on the back-color blanket more and reverse the transfer step by step, resulting in color misuse of the post-color. The drying of the ink blots generally takes more than four hours. The early drying inks are crusted on the rollers and cause troubles for normal printing and cleaning work. If the blots printed on the paper are dried too far, crystallization (vitrification) occurs, which makes the post-color printing impossible. On the contrary, if the imprints do not dry, the back color cannot be printed, which reduces the production efficiency.
The higher the ink coloring rate is, the better, the requirement is up to 100%. However, some ink coloring rates can only reach 80 to 90%. In order to achieve color saturation, the offset printing operator must take measures to increase the thickness of the ink layer to remedy the problem. , but the ink layer is printed too thick, it is easy to cause the back of the product dirty and dark tone of the network area blur.
Generally, the diameter of the ink particles is about 7.5μm. If the 200-line one-lit dot area is 1613μm2, it can accommodate 68 pigment particles. According to the printability requirements of 15 or more, it has been more than enough. However, in actual printing, domestic inks have poor anti-polymerization performance. Since the ink rollers rub against each other during the operation of the machine, the viscosity of the ink increases. In addition, the powder and the paper are mixed on the paper, which can make the particles coarser and coarser. The clarity and level of expressiveness.
3. Printing plate offset printing plate is currently in the PS plate stage, but there are still a large number of factories using protein plates, PVA plates, and multi-layered metal plates. In recent years, zinc oxide papers have been developed for special printing. Basic version. The platemaking process of these plates is different. As the printing process, the drying of the PS plate is the simplest, and the PVA plate and the multilayer metal plate process are relatively complicated.
PVA version of the development, corrosion, base paint operation rely entirely on manual control, therefore, the printing plate is difficult to control the paint, resulting in print color reproduction often fails to meet the original requirements. And the thickness of the zinc skin matte is entirely controlled by experience. Quality is not guaranteed. Sometimes the zinc plate has been plated more often, and the plate material has been reduced from the original 0.55mm to 0.45mm. The operator of the machine also pads the plate with experience, often padding too much or too little, which is equivalent to changing the plate cylinder. The radius also changes the size of the inner image so that the inner image is overprinted.
Multi-layered metal plates have an imprint rate of several million sheets and are suitable for printing with invoices, tax forms, thin books, books, etc. that have a uniform and large print volume. However, in the printing process, in the event of paper particles falling off from the sand, the plated chromium layer is often crushed and exposed to copper, resulting in dereliction of the upper part of the sense of fat. It is very troublesome to eliminate the chrome plated layer and crush the upper parts. It is necessary to use potassium yellow beforehand. Dirty and then electroplated with special equipment, it takes more time.
Zinc Oxide Paper Base Plate has a low cost. Although the production process is simple, it has high requirements on environmental temperature and humidity, the current and voltage of the electrostatic plate making machine, the moisture content of the paper plate body, the ink sensitivity, and the electrostatic conductivity of the toner. Often there is a slight deviation in some links, and the resulting version of the text is dirty or full version, with a lot of bad versions.
Fourth, the operating environment factors China currently has a lot of new offset presses and new offset printing plants, but due to lack of understanding of the offset printing process, managers can not strictly control the temperature and humidity of the operating environment. Problems such as paper bow wrinkling, overprinting caused by stretching, and paper electrostatic influence printing have long been difficult to completely solve and cannot be properly produced and exert their due benefits. The operating environment here refers to the area, height, level, and drying. Paper covers land, doors and windows and floor, workshop orientation and lighting, process arrangement, logistics direction, as well as wind pumps and pools, and safety, dust prevention, shockproof, fire prevention, heating, ventilation, and lighting. The operating environment has an important influence on the quality of printed matter. A good operating environment can reduce the occurrence of failures.
Fifth, maintenance factors Practice has proved that many mechanical failures in addition to the design of the machine itself, manufacturing factors, maintenance is not enough, improper operation is also an important cause of failure. If the same equipment is properly maintained, in the absence of accidents, it can be used for about ten years without major repairs, and vice versa, it may be as small as three years, and as many as five years, fine products cannot be printed. Although there are delays in maintenance and affect some of the output, it is worth considering in the long run. It is actually irresponsible to take that kind of task when it is busy with little maintenance or maintenance or to maintain it when it is not busy; some even take the practice of driving express trains and equipment, and it is even more wrong.
Maintenance is nothing more than according to the requirements of the user's manual, according to the site is divided into daily maintenance, weekly maintenance, monthly maintenance, seasonal maintenance and half a year maintenance. The contents include periodic fueling, oil change, cleaning of parts, cleaning of various parts of the filter; maintenance of various motors and electrical appliances, adjustment and replacement of carbon brushes; periodic inspection, verification and inspection of various data of water (ink) rollers and cylinders. Whether the parts have looseness and wear; and do a good job of cleaning and sanitation of the machine, so that their equipment is in a good state of operation. In order to extend the service life of the machine and reduce various failures caused by poor maintenance.
Section 2 Methods for checking and eliminating offset faults The biggest dilemma for offset press operators lies in the failure of the printing process and the failure to find the cause. Often for overprinting errors, bars, ghosts, paper baskets, inverted hairs and other faults, we had to stop the school bus. It is common to use two or three hours each time. Sometimes it takes a few days to resolve a fault. Serious loss of working hours. It is estimated that the time taken for offset printing to eliminate malfunctions in daily production accounts for about 5-10% of the total man-hours, which is more than double that of lead printing. This is unfavorable for improving product quality, shortening the publishing cycle, and increasing economic efficiency. For this reason, every operator of an offset press can work hard to improve its technical level in solving problems, and can make greater contributions to factories and countries.
The offset press has a complex structure and high printing process requirements. In addition, the variable factors of paper and ink are large, so the operating technology must be improved. Generally speaking, new workers learn to operate easily. It is more difficult to find out the cause and eliminate the trouble in time whenever there is a defect or malfunction.
There are many factors that produce offset printing faults, and sometimes there are dozens of possible causes for a failure. For example, to identify the source of the record, to avoid taking unnecessary detours and to avoid wasting unnecessary and effective man-hours, the following can be used: Ways.
1. Paper-based paper physicochemical properties and technical indicators, including physical performance indicators, optical performance indicators, printing performance indicators, chemical performance indicators. Among them, tightness, tensile strength, stretchability, whiteness, absorbency, smoothness, glossiness, pH, etc. are closely related to offset printing suitability.
The tightness and tensile strength of the paper, and the pressure and separation during the printing process, the viscosity of the ink and the sticky force generated by the surface of the blanket can cause hair loss and powder fall, resulting in burr-like spots on the printed material or in the field. Loss of money.
The retractility of the paper is related to the direction in which the fibers are arranged. The stretch rate in the direction of the filaments is smaller than the retractility in the direction of the fibers at both sides, so the offset printing is usually done with the paper in the direction of the filaments parallel to the axis of the cylinder to minimize the size. The overprint of the paper due to wet stretch is not allowed.
The whiteness and smoothness of the paper are related to the vividness and saturation of the printed image. After the paper with high whiteness is printed with colored ink, the light projected on the paper is absorbed less by the paper and reflects more. The original appearance of ink color is better presented. The paper with poor whiteness has confetti, absorbs much of the projected light, has less reflected light, and the printed image is dark. Papers with poor smoothness have a rough surface, strong oil absorption, dullness after imprinting, more projection light, and a diffuse reflection of reflected light, poor visual quality of printed matter, and dullness of colors.
The oil-absorbing paper absorbs a large amount of the binder in the imprinted ink before the blot has dried and the conjunctiva, so that the surface of the imprinted film is rough, and the product does not stain. In severe cases, imprinting failures may also occur.
General paper pH value, above 5.5, was slightly acidic, when the pH dropped below 5.5, the acidity of the paper increased, this paper can damage the drying of the ink, resulting in imprinting failure.
2. Ink is used to represent the image image and color of the ink, is a plastic fluidity, through the ink roller transmission, coated on the plate on the graphic, with a blanket, and finally transferred to the paper After drying the conjunctiva, it becomes solid. Offset printing requirements The main indicators of printing ink suitability are: fixing, drying, coloring rate, fineness, viscosity, fluidity, and resistance to acids, alkalis, water, and light.
With the increase in the speed of offset presses and the emergence of multicolor machines, the fixation of inks is becoming more and more important. Most multi-color machines have a printing speed of 8,000 sheets/hour or more, and each sheet is printed with about 0.5 seconds (s) to be transferred to the second color. If the fixing speed of the ink is slow, the pre-color blots will stay on the back-color blanket more and reverse the transfer step by step, resulting in color misuse of the post-color. The drying of the ink blots generally takes more than four hours. The early drying inks are crusted on the rollers and cause troubles for normal printing and cleaning work. If the blots printed on the paper are dried too far, crystallization (vitrification) occurs, which makes the post-color printing impossible. On the contrary, if the imprints do not dry, the back color cannot be printed, which reduces the production efficiency.
The higher the ink coloring rate is, the better, the requirement is up to 100%. However, some ink coloring rates can only reach 80 to 90%. In order to achieve color saturation, the offset printing operator must take measures to increase the thickness of the ink layer to remedy the problem. , but the ink layer is printed too thick, it is easy to cause the back of the product dirty and dark tone of the network area blur.
Generally, the diameter of the ink particles is about 7.5μm. If the 200-line one-lit dot area is 1613μm2, it can accommodate 68 pigment particles. According to the printability requirements of 15 or more, it has been more than enough. However, in actual printing, domestic inks have poor anti-polymerization performance. Since the ink rollers rub against each other during the operation of the machine, the viscosity of the ink increases. In addition, the powder and the paper are mixed on the paper, which can make the particles coarser and coarser. The clarity and level of expressiveness.
3. Printing plate offset printing plate is currently in the PS plate stage, but there are still a large number of factories using protein plates, PVA plates, and multi-layered metal plates. In recent years, zinc oxide papers have been developed for special printing. Basic version. The platemaking process of these plates is different. As the printing process, the drying of the PS plate is the simplest, and the PVA plate and the multilayer metal plate process are relatively complicated.
PVA version of the development, corrosion, base paint operation rely entirely on manual control, therefore, the printing plate is difficult to control the paint, resulting in print color reproduction often fails to meet the original requirements. And the thickness of the zinc skin matte is entirely controlled by experience. Quality is not guaranteed. Sometimes the zinc plate has been plated more often, and the plate material has been reduced from the original 0.55mm to 0.45mm. The operator of the machine also pads the plate with experience, often padding too much or too little, which is equivalent to changing the plate cylinder. The radius also changes the size of the inner image so that the inner image is overprinted.
Multi-layered metal plates have an imprint rate of several million sheets and are suitable for printing with invoices, tax forms, thin books, books, etc. that have a uniform and large print volume. However, in the printing process, in the event of paper particles falling off from the sand, the plated chromium layer is often crushed and exposed to copper, resulting in dereliction of the upper part of the sense of fat. It is very troublesome to eliminate the chrome plated layer and crush the upper parts. It is necessary to use potassium yellow beforehand. Dirty and then electroplated with special equipment, it takes more time.
Zinc Oxide Paper Base Plate has a low cost. Although the production process is simple, it has high requirements on environmental temperature and humidity, the current and voltage of the electrostatic plate making machine, the moisture content of the paper plate body, the ink sensitivity, and the electrostatic conductivity of the toner. Often there is a slight deviation in some links, and the resulting version of the text is dirty or full version, with a lot of bad versions.
Fourth, the operating environment factors China currently has a lot of new offset presses and new offset printing plants, but due to lack of understanding of the offset printing process, managers can not strictly control the temperature and humidity of the operating environment. Problems such as paper bow wrinkling, overprinting caused by stretching, and paper electrostatic influence printing have long been difficult to completely solve and cannot be properly produced and exert their due benefits. The operating environment here refers to the area, height, level, and drying. Paper covers land, doors and windows and floor, workshop orientation and lighting, process arrangement, logistics direction, as well as wind pumps and pools, and safety, dust prevention, shockproof, fire prevention, heating, ventilation, and lighting. The operating environment has an important influence on the quality of printed matter. A good operating environment can reduce the occurrence of failures.
Fifth, maintenance factors Practice has proved that many mechanical failures in addition to the design of the machine itself, manufacturing factors, maintenance is not enough, improper operation is also an important cause of failure. If the same equipment is properly maintained, in the absence of accidents, it can be used for about ten years without major repairs, and vice versa, it may be as small as three years, and as many as five years, fine products cannot be printed. Although there are delays in maintenance and affect some of the output, it is worth considering in the long run. It is actually irresponsible to take that kind of task when it is busy with little maintenance or maintenance or to maintain it when it is not busy; some even take the practice of driving express trains and equipment, and it is even more wrong.
Maintenance is nothing more than according to the requirements of the user's manual, according to the site is divided into daily maintenance, weekly maintenance, monthly maintenance, seasonal maintenance and half a year maintenance. The contents include periodic fueling, oil change, cleaning of parts, cleaning of various parts of the filter; maintenance of various motors and electrical appliances, adjustment and replacement of carbon brushes; periodic inspection, verification and inspection of various data of water (ink) rollers and cylinders. Whether the parts have looseness and wear; and do a good job of cleaning and sanitation of the machine, so that their equipment is in a good state of operation. In order to extend the service life of the machine and reduce various failures caused by poor maintenance.
Section 2 Methods for checking and eliminating offset faults The biggest dilemma for offset press operators lies in the failure of the printing process and the failure to find the cause. Often for overprinting errors, bars, ghosts, paper baskets, inverted hairs and other faults, we had to stop the school bus. It is common to use two or three hours each time. Sometimes it takes a few days to resolve a fault. Serious loss of working hours. It is estimated that the time taken for offset printing to eliminate malfunctions in daily production accounts for about 5-10% of the total man-hours, which is more than double that of lead printing. This is unfavorable for improving product quality, shortening the publishing cycle, and increasing economic efficiency. For this reason, every operator of an offset press can work hard to improve its technical level in solving problems, and can make greater contributions to factories and countries.
The offset press has a complex structure and high printing process requirements. In addition, the variable factors of paper and ink are large, so the operating technology must be improved. Generally speaking, new workers learn to operate easily. It is more difficult to find out the cause and eliminate the trouble in time whenever there is a defect or malfunction.
There are many factors that produce offset printing faults, and sometimes there are dozens of possible causes for a failure. For example, to identify the source of the record, to avoid taking unnecessary detours and to avoid wasting unnecessary and effective man-hours, the following can be used: Ways.
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