The surface of the triple impression cylinder is worn, worn, or has foreign objects stuck The surface of the impression cylinder is made of rubber or polyurethane material. Due to the large embossing force during printing, and long-term erosion by the solvent, it is extremely prone to aging or wear, and cracks or tiny pits appear on the surface. When printing, the part of the pattern that is in contact with the defect location will not be inked, resulting in the lack of graphics. This phenomenon is more noticeable when printing low-quantity papers such as coated paper, and it is less likely to occur when printing high-quantity papers such as whiteboard. Four ink viscosity is bad Viscosity is the most important control index of ink. It directly affects the transfer performance of ink and the quality of printed products. In actual production, ink viscosity is determined according to the process requirements of the product. Low viscosity may easily cause ink spreading, poor hiding power, and insufficient hue. The ink will not be saturated when printed, and the ink will not be saturated. If the viscosity is too high, the transfer performance of the ink will be poor. Ink on the spot will be uneven. Spots, dots, and text are incomplete, but they also increase the amount of ink used. Five other factors 1. The role and influence of static electricity Conference Chair,Conference Chair Stackable,Conference Chair Wheels,Conference Chair Office Taihe Fangyuan Muye Co.,Ltd , https://www.fyofficefurniture.com
Imprinting caused by aging or wear on the surface of the impression cylinder is generally irregular or irregular. (The large-area solid color block is easier to observe.) Its transverse position is basically unchanged, and its longitudinal position is indefinite. The impression cylinder needs to be replaced. If there is no spare part, it can be used interchangeably with the other impression cylinders of the color group to avoid the contact of the defect position with the graphic part, or through the repair and grinding method to solve the urgent need.
The width of the paper is too small, the squeegee cannot clean the ink on the plate, or the ink is improperly applied, so that the ink is stuck on both sides of the platen, so that no insulation is formed, and the discharge current generated by the electrostatic electrode is turned on and off. , Which affects the ink's adsorptive force, so that the printing product's inking effect is weakened, especially for the screen printing products is more obvious. When this happens, the solvent must be used to wipe off the ink on both sides of the impression cylinder, properly adjust the squeegee, or lengthen the length of the squeegee (the length of the squeegee is slightly longer than the length of the plate 5-6cm), Make it clean the ink on the surface of the plate. At the same time, according to the long-term actual printing width, the diameter of the excess part of the two sides of the impression cylinder can be appropriately reduced by 2 to 4 mm.
When the surface of the impression cylinder is affixed with ink, paper wool, paper powder, or other substances, it will also affect the even distribution of the imprinting force, and the ink transfer in the partial area of ​​the printing plate will be insufficient, resulting in false imprinting of the printed matter. Can stop the foreign matter on the impression cylinder clean and then open the printing.
In the printing process, the ink must maintain a certain viscosity value; to ensure the effective circulation of ink, so that the ink maintains good fluidity; to measure the viscosity of the ink (usually 20 to 30 minutes once), add the solvent in time to maintain the viscosity consistency.
When gravure printing is used to print products with halftone dots, the reproducibility of the print layer is poor, and fine floc-like spots usually appear. This is mainly due to the shallow depth of the dots in the halftone dots, poor ink transfer performance, and easy ink. It is difficult to truly reflect the tone (level) of the pattern in the network. This can be solved by adding or opening the electrostatic printing auxiliary ink suction system. As shown in FIG. 1 , since the impression cylinder uses a rubber or polyurethane semiconductor material to form a conductive surface layer, the discharge current generated by the electrostatic electrode can be transferred to the surface of the impression cylinder through the electrostatic brush so that the ink molecules and the impression cylinder are Between the generation of potential difference, the formation of an electric field, so that the ink polarization, moving toward the direction of the printed material, which is conducive to the full transfer of ink, effectively improve the printing effect.
The presence of static electricity on the surface of the paper is not conducive to printing, it directly affects the quality of printed products, so that the phenomenon of spots appear on printed products. At the same time, it also has a certain negative impact on electrostatically assisted printing, because it affects the even distribution of electrostatic charge on the surface of the impression cylinder, and thus affects the adsorption of ink on the surface of the paper. Especially in the dry season, paper is prone to static electricity. Static electricity can be eliminated by installing a static elimination device and adjusting the humidity in the printing shop.
2. Effect of squeegee
The squeegee's squeegee angle and pressure also have a certain influence on the impression of the ink. For example, excessive pressure on the squeegee can easily result in incomplete printing of dots and lines, and wear of the printing plate; the pressure of the squeegee is too small, and the ink on the printing plate is not clean. The squeegee angle affects the depth of the ink layer, thereby affecting the ink hiding power. If the squeegee angle is small, the ink squeegee effect is weak, the ink layer of the print product is thick, the hiding power is strong, and the gloss is good, but the squeegee is not easily cleaned and the graphic is vague, and the pressure of the squeegee may be appropriately increased. When printing, the pressure of the squeegee and the angle of the squeegee should be determined according to the depth of the printing plate graphic and the ink situation of the printing product.
3. Effect of the surface quality of the printing plate
The surface wear of the printing plate will usually cause the solid color ink to become lighter, the ink is not uniform, the graphic is not clear enough, and the phenomenon of imprinting is too weak and the bottom is exposed; the surface of the printing plate is stained with oil and has not been cleaned, which may cause the printing product to be badly inked. Stop using the decontamination powder to clean the plate and print it again.
The above lists some common factors in which inks are not accurately printed. In actual production, we may also encounter other situations. As long as we carefully observe and seriously analyze the problems we have encountered, we can find out the root causes and solve them one by one.
Source "Printing Technology"