Paper and printing electrical failure analysis
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First, paper caused printing failure
(1) Quality factors
1. Paper coating, uneven sizing
The paper consists of fibers, and the paper surface cannot be completely uniform. Therefore, it is necessary to apply a layer of inorganic mineral pigment and an adhesive coating on the surface of the paper to improve the surface quality of the paper. The finer the pigment, the smoother and finer the coated paper surface; on the contrary, the rougher the paper surface.
In addition, in order to reduce the phenomenon of powder removal and hair loss of paper, a surface sizing process is adopted in papermaking, that is, a layer of adhesive is applied on the surface of the paper to improve the surface strength and gloss of the paper. Due to the fast printing speed of the modern printing press, the ink and the paper surface are instantaneously disengaged, and the ink has a large pulling force on the paper surface, and the coating and sizing of the paper surface is required to be uniform.
2. Poor paper flatness
The flatness of the paper is not good, the specific performance is:
1 Bubbling The surface of the paper is bubbling because the water escapes from the surface of the paper when the paper passes through the thermal dryer. The velocity of the paper is lower than the velocity generated by the internal vapor of the paper. The internal vapor is generated by the pressure inside the paper.
2There are holes and blocks in the paper.
This is formed in the process of screening and purifying paper. The occurrence of holes is the formation of impurities from the paper surface after the paper is formed. Large holes can cause downtime or waste during printing; large, hard blocks can damage the plates and erasers during printing, affecting the printing process.
In order to avoid the above phenomena, the main measures taken are:
The 1 paper dryer has good ventilation so that the water vapor evaporated from the paper can be quickly discharged outside the house.
2 Perform secondary drying to accelerate water removal.
3 operation carefully screened to purify the pulp.
(2) Water content factor of paper
1, the cause analysis
1. In the process from paper mill to printing house to printing, the temperature and humidity of the surrounding environment in the transportation, storage and use are combined, and the molecular structure of the paper fiber contains hydroxyl groups to form hydrogen bonds. When wet, it is hydrophilic. Expansion occurs; syneresis occurs during drying. The paper absorbs water around and the dehydration speed is faster than the center of the paper. Thus, the water content in the center and the periphery of the paper is uneven, which causes the paper to be pressed and the edge of the paper. If used for printing, the printing is inaccurate; The finished product has wrinkles and causes waste. The specific performance is:
1 Tight edge phenomenon When the paper is in a dry environment, dehumidification occurs, that is, the center of the dehumidification speed paper is smaller than the paper circumference, so that the paper is tightly stretched to form a tight edge phenomenon.
2 The lotus leaf enters the phenomenon that the paper is in a humid air environment, and moisture absorption occurs, that is, the peripheral moisture absorption elongation speed is faster than the center of the paper, and the paper forms a lotus edge.
2, the elimination method
1 When the paper is tight, sprinkle water around the pile or around the machine to re-absorb the water around the paper, balance the water content of the paper, and restore the paper to a smooth level.
Dry the paper in an environment where the relative humidity is 6 to 8% higher than the printing shop.
2 When the paper has a ruffled edge, the paper can be knocked out by hand, and the paper can be knocked out with a crease of about 1 cm in width and about 10 cm in length, thereby increasing the stiffness of the paper to facilitate paper feeding;
In serious cases, the paper should be re-hanged.
(3) Electrostatic factors of paper
1. Causes and hazards
During the printing process, the paper on the stack is separated and transported forward under the friction of the paper feed belt and the platen. Between paper and paper, paper and machine are always in friction. Friction generates a charge. When the charge is collected, the paper carries a charge. When the paper has the same kind of polar charge, the papers are mutually exclusive, which causes the overprinting to be out of alignment with the delivery when printing; when the paper has a different kind of charge, it causes empty, double, and multiple sheets when feeding. The overprinting is not allowed to be faulty; the surface of the paper with static electricity is also easy to absorb some paper wool and dust, which causes the image of the printed product to be smeared or spotted, so it is important to eliminate the static electricity of the paper during printing.
2. Exclusion method
1 Eliminate with a static eliminator
The static eliminator used on the printing machine has an inductive static eliminator, a high frequency high voltage static eliminator, a power frequency high voltage static eliminator, etc., and should be placed near the drum during installation.
2 Improve the relative humidity of the printing workshop
The generation of static electricity is related to the relative humidity of the operating environment. When the relative humidity of the workshop is lower than 40%, static electricity is prone to occur. Therefore, when printing, sprinkle some water around the paper pile and the machine, or use an air humidifier to adjust the printing workshop. Relative humidity to avoid static electricity.
3 paper conditioning
When the water content of the paper is low, the paper is easily electrostatically charged. When the paper is heavily static, it is necessary to hang the paper or place the paper in a relatively humid environment for a period of time, but care should be taken to prevent the paper from flanging.
4 reduce the speed of the printing press
When the static electricity is severe, the friction between the paper and the paper, the paper and the machine is reduced by reducing the speed of the printing machine, thereby reducing the generation of static charges.
Second, the paper machine failure caused by improper adjustment of the printing machine
During printing, the paper passes through the feeder, the paper feeding table, and then passes through the pre-regulation and the specified position. Finally, the printing is completed by the rolling of the blanket cylinder and the impression cylinder. In these links, improper adjustment of a certain part of the machine will affect the operation of the paper and print failure, so adjust the following machine parts.
1. nozzle, mouthpiece, platen
Due to the uneven size of the blown mouth of the paper, or the improper suction position of the nozzle, the paper can not be separated, forming double sheets and multiple sheets; the suction of the nozzle is too large, causing double or multiple sheets of paper, forming too small Zhang.
Remedy: Adjust the amount of air blowing and inhalation through two air valves on the air pump until they are suitable; adjust the position of the nozzle to the right.
2. crepe paper and pressure roller
When the tension of the paper feeding belt is inconsistent, the rotation speed of each paper feeding belt is inconsistent, which makes the paper skew; when the paper pressing wheel is placed improperly or the rotation is not flexible, the paper feeding is skewed, or the paper cannot be naturally stretched on the paper feeding table. To make the paper arched unevenly, after rolling, the printed product has wrinkles.
Remedy: By adjusting the axle of the paper feeding belt under the paper feeding table, the paper feeding belts on the paperboard are tightly aligned; check the wheel axle for wear, so that the pressure is uniform and regular, and the lubricating oil is regularly added.
3. Side gauge pull
The paper is pulled to the side gauge baffle to complete the positioning according to the pre-regulation and routine. When the side gauge tension is too large, the paper is arched under the resistance of the side gauge baffle, and after printing, the printed product forms an inverted circular arc wrinkle.
Remedy: Adjust the side gauge to normal.
4. Imprint cylinder
When printing, when the impression cylinder is inconsistent, the paper will form a dome at the mouth. After imprinting, the printed product forms a circular pleat at the bite; or the paper corner is just half of the nip of the embossing cylinder, causing the edge of the paper to be overstressed, and a wrinkle is formed at the edge of the paper after printing.
Remedy: Check the teeth and the pads for wear. If there is wear, replace them in time; adjust the biting force to make it uniform; check if the bite position is appropriate.
Printing quality has a great relationship with paper. As a printing job, we must fully understand this point, accumulate experience and take corresponding countermeasures to improve the quality of printed materials and reduce the scrap rate caused by paper factors.