Gravure common faults and solutions
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In the process of gravure printing, printing failures caused by factors such as machinery, process, raw and auxiliary materials, and working environment often occur, which affects product quality and production progress. Below, the author will share the experience accumulated in the work of gravure printing for everyone's reference.
Cut line
The knife line is a relatively common fault, which occurs mostly in the non-image part. It is caused by the scraper not scraping the ink off the blank surface of the printing plate. The cut lines are generally divided into regular fixed cut lines and irregular intermittent cut lines.
The fixed knife line appears in the same position of the printed product, mainly because the surface finish of the printing plate is not good, and the edge of the cell hole is burred during the electric carving process. The burr is not cleaned during polishing, resulting in a burr on the printing surface. The ink is not easily scratched, resulting in a fixed cut line. Gently polish the plate with a 1200 mesh fine sandpaper solvent to make the surface of the plate smooth and burr-free.
The position of the intermittent knife line on the printed product is not fixed, sometimes there is no, sometimes it is less, and there is no regularity as the squeegee of the squeegee moves back and forth along the lateral direction of the layout. The main reason for the occurrence is that the ink is mixed with impurities, the ink pigment is not fully ground, the particles are coarse and insoluble in the connecting material and the solvent, and the ink sticks in the squeegee when printing, which affects the squeegee effect of the squeegee and causes the squeegee. Not clean, forming a knife line. In addition, if the squeegee is damaged, the excess ink cannot be scraped clean and the knives will be caused. The solution is to replace the damaged squeegee, filter the ink with a 2000-3000 mesh filter, filter out the impurities in the ink, and add a filter to the ink circuit. Double filtration ensures that the ink is clean and free of debris.
Ghosting
Ghosting refers to the appearance of shallow lines next to printed lines or side shadows near printed dots. The silhouette is lighter than the main line or main mesh point. The ghost emphasizes the word "heavy", that is, two shadows of one deep, one light, or the same color are repeated on one dot or image. The ghosting will reduce the sharpness of the edge of the printed product, affecting the color reproduction of the printed image, and the color of the entire printed product is blurred, the layer is distorted, and the sharpness is significantly reduced. The ghosting is mainly caused by the excessive pressure of the embossing roller, the pressure of the squeegee and the unadjusted angle. If there is a ghost in the circumferential direction and the axial direction of the printed product, it means that the pressure of the pressure roller is too large to cause the ink to be extruded. At this time, we should reduce the pressure of the pressure roller appropriately until the ghost image disappears. If there is only a ghosting in the circumferential direction, it means that the pressure of the doctor blade is too small, the contact with the printing plate is poor, or the angle of the doctor blade is too small. At this time, the pressure of the doctor blade should be increased and the ink is appropriately adjusted. Knife angle. When the ghosting is not serious, it can be solved by appropriately increasing the printing speed.
Sticky
Sticky dirt is classified into three types: adhesion, smear, and back tack after printing. Adhesion is the printing of the back side of the printed product to the front side of the previous print during the winding process, so that the upper and lower prints are adhered together, causing damage to the printed product. Dirty is the ink portion of the surface of the previous printed ink film transferred to the back of the next print, so that the back of the next print has ink, and the front of the previous print is in the form of a piebald. Back-tack is a phenomenon in which the printed product has a sticky back on the back during the placement process.
The above problems arise from the fact that the ink is dried too slowly after printing, or the ink is not completely dried to cause false drying, the solvent evaporation rate is low, and the residual solvent in the printed product is excessive. In the production process, the ink printing thickness can be appropriately reduced, the drying temperature can be increased, the printing speed can be lowered, the ink drying performance can be improved, and the solvent with high evaporation rate can be used instead.
Imprinting is not allowed
Overprinting is not allowed to mean that the various colors and images are not transferred to the fixed geometric position of the substrate. The overprinting accuracy of each color graphic does not meet the requirements of the industry standard, resulting in a large deviation between the printed product and the original. The factors that affect the overprinting are mainly paper, printing workshop temperature and humidity, and printing machine drying temperature.
Paper
The paper itself contains a certain amount of water, and the production is generally controlled at about 6%. However, when the temperature and humidity of the printing workshop are inconsistent with the temperature and humidity during the production of the paper, the moisture in the paper changes to deform the paper, resulting in inaccurate printing overprint. In this regard, the paper can be placed in the printing workshop a few days in advance when printing, so that the paper can fully adapt to the temperature and humidity of the printing workshop, so that the paper deformation will be smaller during printing, and the printing overprinting is guaranteed.
2. Printing workshop temperature and humidity
The printing workshop should be relatively closed, maintaining a relatively stable temperature and humidity to ensure that the paper is not deformed.
3. Printing machine drying temperature
Reduce the drying temperature of the printing press while ensuring that the printing ink can be completely dried out, so that the paper is deformed in a small range.
Paper wrinkles
Wrinkling of the paper means that the paper is wrinkled and wrinkled due to pressure and the like during the printing process, so that the printed product has wrinkles and affects the quality of the product. The main reason for the occurrence is that the pressure at both ends of the pressure roller is unbalanced, or the pressure roller is damaged. When the circumferential surface of the pressure roller contacts the paper during the rotation, the force at both ends causes the paper to wrinkle. The pressure at both ends of the pressure roller should be adjusted during printing. The specific operation: there is a pressure gauge on the printing machine, and the pressure is adjusted according to the pressure gauge; use the dial gauge to check whether the pressure roller is damaged, and if it is damaged, replace it in time; check all The stressed paper feed roller ensures that all the paper feed rollers are in the same horizontal position.
Blocking
Blocking means that the ink in the printing grid at the time of printing will be partially dried by the influence of certain factors, the ink transfer rate will be reduced, and the cells will be blocked more and more shallow until the blocking condition occurs. After the blockage, the printed graphics are illegible, and the colors of the printed products are inconsistent and cannot reproduce the originals well. It can solve the problem of blocking in printing by reducing the drying speed of the ink or increasing the speed of the printing machine to match the drying speed of the ink.