How to achieve high-quality printing

High-quality newspapers should have bright pictures, full ink color of Chinese characters, and clear stroke outlines, and the overall appearance should be pleasing to the eye. To achieve this goal, it is difficult to rely on the printing department alone, and the whole process control must be strengthened to print newspapers that meet the quality requirements. The specific control points are as follows.

Design typesetting link

Newspaper typesetting is usually done by the editorial typesetting department, and the printing unit receives mostly non-editable files that have been converted to PS format or PDF format. Because typesetting editors are proficient in typesetting specifications, they may not necessarily understand the principles of printing, so the documents produced may not meet the requirements of printing. The editorial department believes that the design and arrangement of very exquisite special effects, but the effect after printing is deviated from expectations, and this kind of problem is often not caused by the operation of the printing unit, but the problem in the typesetting design link.

For example, in terms of color, editing department personnel often use RGB mode when processing images on computers, which has a wide color gamut and vivid colors. However, the printing process adopts the globally common CMYK mode, and the color gamut is not as wide as the RGB mode. RGB format images need to be converted to CMYK mode before printing, and color gamut compression will cause the color of the printed product to be less vivid than that of electronic files, which is a normal phenomenon and not a print quality problem. Based on the characteristics of the printing process, the editorial department needs to focus on the following issues:

(1) Pay attention to changing color modes. When typesetting, all pictures must be converted to CMYK mode to avoid information loss caused by the forced conversion of color mode by the printing unit personnel.

(2) Control the gradation of the picture and the total amount of ink. When processing the picture, it is necessary to open the contrast of the picture, so that the gradation of each level is evenly distributed, and avoid the picture being too bright or too dark. The color picture should ensure that the total ink content of the overprint ink is less than 260%. Pictures with black as the main color should be converted to gray tones, and avoid using four-color synthetic black, so as to avoid slowing down the drying speed of ink during the printing process due to ink accumulation, resulting in rubbing and dragging.

(3) Reasonable processing of pictures. In the process of printing pictures, if the proportion of blue and black plates is large, the printing effect will be much worse than that displayed on the computer screen. This situation is mainly due to the dark nature of blue and black inks and the expansion of dots. The color of the blue and black versions is too dark, which will cause the proportion of dark areas of the picture to increase, and the image level is unclear, making it easy to paste the version. Therefore, when processing pictures, if the amount of blue and black plates is too large, it should be appropriately reduced (it is recommended to reduce it by about 15%).

(4) Pay attention to the placement of the picture. When typography, do not arrange pictures with large contrasting tones and styles in the same ink mixing area at the same time. During the printing process, the amount of ink in the same position is controlled by the same set of ink keys. If two pictures with strong color contrasts are in the same set of ink paths, it is difficult to take into account the color reproduction of different styles of pictures at the same time.

(5) Reasonably arrange the field color blocks. Field headings or large area color bars are commonly used in editing and typesetting to enhance visual appeal, but such designs are prone to stacking, flowering and grinding during printing. Therefore, it is recommended to use more than 90% deep web to replace the field design, and improve the printing effect by setting the color density reasonably.

(6) Optimize the shading design of the picture. If the shading pattern of the picture is too close to the background color, the shading may not be obvious or unrecognizable after printing, because the background color is too dark, making it difficult to present the shading dots.

(7) Avoid overprinting problems in text. According to industry standards, the overprinting error of any two colors of color newspapers should be less than 0.15mm. This is due to the fact that there is a certain tension in newsprint, and slight changes in tension during printing may cause overprinting deviations, so the use of four-color text should be minimized, and it is best to use monochrome text to avoid overprinting problems that cause unclear text.

(8) Choose the font type reasonably. The body of the newspaper is best to use the Bao Song font, and some editors choose other fonts for the pursuit of personality, which are beautiful when displayed on the screen, but during the printing process, they are affected by the expansion of the dots and the accumulation of ink, and are prone to problems such as "broken scratches" and "pasted plates". This is due to the strong ink absorption and high surface roughness of newsprint, which will cause the font strokes to become thicker or even pasted together, while the structure of the Baosong font strokes is simple, horizontal and thin and vertical, which can adapt to the material characteristics of newsprint, effectively resist the uneven absorption of ink by paper fibers, reduce printing defects, and remain clearly distinguishable even in small font sizes.

Plate making

At present, computer direct plate making (CTP) technology has been widely used in newspaper plate making, and the traditional film output and plate drying process has been eliminated. CTP plate making has the advantages of fast output speed, high accuracy, small network deformation, stable quality, and manpower saving, but it has high requirements for operators, and it is necessary to have an in-depth grasp of the imposition process and hardware maintenance knowledge, the specific requirements are as follows:

(1) Do a good job in process docking. The plate making link is a window directly connected to the editorial department, and if there is a problem, the printing work will not be carried out. Therefore, the plate maker should know in advance the software used by the editorial department for typesetting, the type of font library and the file format generated. If there is a process incompatibility, priority should be given to coordination, replace the production software or font library, reduce cost loss, and avoid major losses caused by the plate making process replacement.

(2) Do a good job in CTP equipment maintenance. Due to the presence of dust or other suspended particles and other pollutants in the environment, after the equipment is used for a period of time, the external optical path and the internal optical path of the laser may be stuck with dust, resulting in loss of the laser during the operation of the optical path, causing the output dots to deform or shrink, which in turn causes small font sizes and fine strokes to appear jagged or even broken, and some dots of the image highlights are lost or deformed. Therefore, the laser light path needs to be cleaned regularly and the laser waveform calibrated.

(3) Do a good job in the linearization curve of the plate. In the process of CTP plate making, due to the change of the brand, production batch and external conditions of plate making, plate makers should regularly linearize the entire production process to ensure that the output graphic information is faithful to the original and avoid information loss or distortion.

(4) Control the conditions of developing and printing processes. At present, the no-rinse version has been widely used, but the process of potion development and plate printing still exists. For the latter, the plate maker needs to reasonably control the temperature and concentration of the developer solution, and arrange the coating of protective adhesive to ensure the quality of the printing plate. If the CTP plate is not fully developed, the blank part of the printing plate will remain with an oleophilic coating, and the newspaper will be dirty when printing on the machine; If the protective adhesive coating is uneven, the blank plate will be partially oxidized, the hydrophilicity will be weakened, and the ink will be stained when printing on the machine, causing dirty plates, so it needs to be prevented.

Printing link

The newspaper printing equipment is mainly based on rotary machines, with fast printing speed and short ink paths, using cold-solidifying ink, using penetration drying mode, and printing through rubber rollers to achieve mutual embossing. The process of transferring ink from the plate roller to the substrate involves printing plates, inks, wetting fluids, blankets, paper and other printing materials, as well as the ink conveying device, water conveying device and printing roller of the printing machine. Due to the fast printing speed and short ink contact time, the printing suitability and mutual matching of these materials directly affect the printing quality, and the following five types of problems are prone to occur:

(1) The layout is dirty. This is the most common quality problem in newspaper printing, mainly because the ink on the surface of the printed product is not dry, and after contact with the printing machine, folding machine or conveyor belt, part of the ink is transferred to the equipment parts, resulting in the printing product rubbing dirt; In addition, the graphic area of the printed newspaper is still in a wet state, and when passing through the folding machine or keel, it may also be dirty due to the mechanical action of external forces such as paper pulling rollers, newspaper rollers, brushes, cleats and belts, and the front page, tail plate and folding parts are particularly prominent. The causes of such problems include poor ink dryness, excessive ink layer, excessive ink volume, or excessive ink moisture content, which need to be solved by controlling ink balance, improving ink performance, and adjusting the pressure of post-press equipment.

(2) Paper-ink matching problem. If the surface strength of the paper is low and the ink is sticky, the ink will adhere to the small particles on the surface of the paper, causing the paper to lose lint and powder, and in severe cases, it will even tear off the paper surface, resulting in paper breakage and shutdown; The detachment of paper particles will form white spots, resulting in graphic defects; If the detached paper scraps adhere to the blanket and printing plate, it will stain the rubber blanket or accelerate the wear of the printing plate. If the paper scraps are filled with the graphics and text of the printing plate, it will make the printed product mushy; If it enters the ink hopper or water bucket, it will also contaminate the ink and dampening liquid. Such problems stem from the mismatch between the surface properties of the paper and the viscosity of the ink, and the printing performance of the two materials needs to be tested in time and replaced immediately if the problem is found.

(3) The problem of ink balance. During the printing process, the staining and pasting plates are caused by improper control of the ink balance in the blank part of the printing plate, resulting in the enhancement of the hydrophilicity of the ink after emulsification and the decrease of the hydrophilic ability of the blank part of the printing plate, which in turn causes problems such as staining and pasting. In addition, it will also affect the ink color of the pictures and texts in the newspaper, causing problems such as graying of the layout and broken strokes, and affecting the overall effect of the newspaper layout.

(4) Rubber blanket problem. During the printing process, when the ink on the printing plate is transferred from the blanket to the paper, the pressure between the blanket and the paper should be uniform, and the rebound performance of the blanket should be good in order to print high-quality newspaper. Therefore, the condition of the blanket has a great impact on the quality of the newspaper. The key factor affecting the condition of the blanket is the lining. In newspaper printing, due to the fast printing speed, short ink transfer contact time, and long recovery time of soft lining deformation, long-term use will attenuate the elasticity, which has a certain impact on the stability of newspaper quality. Therefore, the choice of hard overlay in high-speed rotary printing is more beneficial to the stability of printing pressure. In addition, the lining installation is also very important, if the installation is not good, the offset during the printing process will also cause the printing pressure to be uneven, resulting in poor printing results.

(5) Ink glue roller problem. The adjustment of the ink adhesive roller is an important factor affecting the printing quality. If the adjustment force of the ink rubber roller is too large or too small, it is not conducive to water transfer, and more importantly, the two ends must be leveled. Therefore, the pressure of the ink roller should be checked regularly during production, and the ink rubber roller that has reached the replacement cycle or worn to a certain extent should be replaced in time.

A high-quality newspaper requires the full cooperation of all processes to be printed. Although the newspaper is finally produced by the printing machine, the front-end typesetting design, plate making and other processes have basically determined the printing quality, and the printing machine only faithfully realizes the design intention of the previous process under the premise of ensuring the normal state. Therefore, in the control of newspaper printing quality, it is necessary to strengthen the control of the whole process.