Affected by various factors, various failures are unavoidable in the printing process, affecting the quality of the printed matter. This requires that the printing operator must have the ability to discriminate the failure of the printed product and adjust the corresponding printing parameters according to the failure.
1. Damage analysis and resolution of printed products
The damage of printed products mainly refers to the damage of the paper garnishes. The causes of damage and adjustment methods are as follows.
(1) Inaccurate delivery teeth and drum teeth. Adjustment method: Correctly adjust the feeder, or adjust the height of the front gauge.
(2) Improper adjustment of each tooth in the part of the press of the offset press. Correcting method: Re-adjust the tooth pads of the collection tooth row to make it straight, high and low, and then carefully adjust the balance of the teeth.
2. Print product folds failure analysis and solution
(1) There is a phenomenon such as "foliage" or "tight edge" on the paper, so that the paper cannot be printed in a flat state. Adjustment method: humidity treatment in the printing workshop to keep the temperature and humidity of the workshop constant, the general requirements of temperature 23 °C ± 3 °C, humidity 50% ± 5%; establish a paper library with the same temperature or humidity of the printing environment or the same, keep the paper Water content is stable.
(2) Inconsistent drum pressure. When the grippers hold the paper into the cylinder, the airflow will be generated on the surface of the paper. If the roll cannot evenly press the air and press the paper evenly, it will cause wrinkles. Adjustment method: Calibrate the roller pressure. According to the standard lining and pressure of the equipment, it is adjusted and the measurement and calculation are carried out several times to make the pressure of the roller uniform; the blanket is replaced in time to prevent the printing product from wrinkling due to its aging and loss of elasticity. Beijing Kelei Sunshine Printing Technology Co., Ltd.
(3) The gripper force is different or the gripper transfer time is inconsistent, resulting in inconsistent overall displacement or deformation of the paper. Adjustment method: Check the grippers. The focus is on checking the flatness of the gripper, the uniformity of the denture, the evenness of the force, the gap between the braces, the elasticity of the gripper spring, etc., and check whether the related screws and pins are loose or broken. Ensure smooth paper transfer.
(4) Drum deposits on the surface of the drum to make the surface of the drum uneven, and the paper is not evenly compressed, resulting in wrinkles. Adjustment method: Clean the surface of the drum and the dirt on the roller timely, and keep it clean.
3. Print spot failure analysis and solution
(1) The surface of the paper is irregular, that is, the smoothness of the paper is low, resulting in spots on the surface of the paper that are uneven by the ink. Adjustment method: Replace the paper, increase the printing pressure and so on.
(2) Ink emulsification is severe. For a good transparency ink, the ink emulsification is too fast, will make the viscosity of the ink lower, when the larger printing pressure is applied, the ink on the protruding surface of the paper can be easily squeezed out, and the ink falls on the real part of the printing plate and the like. It will produce spots. Adjustment method: reduce the amount of fountain solution, select the higher viscosity ink, and appropriately adjust the printing pressure.
4. Analysis and solution of the back fault of printed products
(1) The pH of the fountain solution is too high. The pH of the dampening solution, which is advantageous for printing, should be between 4.3 and 5.5. When the pH is higher than 5.5, the drying speed of the ink will be reduced and the back surface will be soiled. Adjustment method: A certain amount of acid can be added to the fountain solution to lower the pH of the fountain solution.
(2) The viscosity of the ink is too low, resulting in excessive fluidity. When printing, the ink on the plate will cause the plate to be dirty, and it will also affect the drying speed of the ink, resulting in dirt on the back. Adjustment method: adjust the amount of ink or ink with high viscosity.
(3) The ink layer of the printing product is too thick, or the amount of the auxiliary agent is not appropriate when the ink is transferred, which slows the drying of the ink and causes back rubbing. Adjustment method: Add proper desiccant and anti-adhesive to the ink to speed up drying.
(4) The ink is not dry or the ink is too large. Adjustment method: Add proper amount of desiccant and anti-adhesive to the ink, or reduce the amount of ink properly without affecting the ink color of the printed product.
5. Print product through the print and back through the failure analysis and resolution
Possible reason and adjustment method: The ink contains too much non-drying oil, and the ink drying speed should be accelerated. If the viscosity of the ink used is low, ink with high viscosity can be mixed and mixed, but be sure to mix the ink before use. Uniform. With high printing pressure and slow printing speed, the printing pressure and printing speed should be properly adjusted. The reason for back penetration and adjustment method: If the ink layer is too thick, the ink with thin ink and high color concentration can be used instead. If the paper is thin and transparent, reduce the pressure and use thick, low-transparency paper.
6. Print product failure analysis and solution
(1) Causes of low density in the field and adjustment methods
1 printing plate outlets are not true. This may be due to the fact that the dots on the film have not reached a sufficient standard, or that there are problems with the exposure and the plate-making process, such as excessive exposure time or inappropriate proportioning of the liquid medicine. Adjustment method: Check whether the density of the film on-site is up to the standard, and then consider whether the operation of printing, exposure, and edging is correct.
2 paper problems. The paper itself is not smooth enough to allow the impression cylinder to make good contact with the paper; or because the paper has poor ink absorption, it cannot absorb enough ink during the printing process. Adjustment method: Replace paper with high smoothness and good ink absorption; or increase printing pressure appropriately to ensure good contact between paper and roller.
3 The printing speed is too high and the printing pressure is insufficient. If only the printing speed is increased during printing without corresponding increase in printing pressure, the density of the printed field will be insufficient due to the reduced contact time between the printing plate and the blanket, the blanket and the printed sheet, and insufficient pressure. Adjustment method: reasonably adjust the correspondence between printing speed and printing pressure.
4 The embossing cylinder is worn badly, making the contact between the paper and the embossing cylinder unfavorable, resulting in false printing sites and unreal ground. Adjustment method: Replace the impression cylinder.
(2) Inconsistencies in circumferential and axial solid density and adjustment methods
1 Abrasion of ink keys results in inaccurate ink discharge. Adjustment method: According to the change of density, find out the abnormal area under the ink, check the working condition of the corresponding ink key, and adjust it to the normal working state.
2 Axial or circumferential pressure is not uniform. Adjustment method: According to the press mechanism of the printing press, adjust the pressure between the printing plate cylinder and the blanket cylinder, the blanket cylinder and the impression cylinder to balance; or replace the blanket to prevent the pressure from being uneven due to aging.
7. Printing ink unevenness analysis and resolution
(1) The viscosity of the ink is too high, resulting in low fluidity, inhomogeneous ink in the roller, and uneven ink in the print. Adjustment method: Add ink or retreat agent to the ink to increase ink fluidity.
(2) The ink drying speed is too fast to cause the phenomenon of early conjunctiva formation in the ink layer, which causes uneven printing ink, which is caused by the excessive amount of dry oil added in the ink and excessive air drying. Adjustment method: Add an appropriate amount of dry oil in the ink to suppress the ink drying speed.
(3) The water supply is too large and the ink emulsification is serious. Adjustment method: Adjust the water supply according to the structural characteristics of the water supply system. When the ink emulsification is serious, use the water scour method to wash the ink roller, replace the ink in the ink tank, and strictly control the amount of water when printing ink.
(4) The parts of the water supply and ink supply device are aged or the pressure between the rollers is uneven.
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