Analysis on the Quality Control Points of Fine Newspaper Printing
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
Today, with the rapid development of network and mobile internet technologies, computers, tablets, and smartphones have penetrated thousands of households, gradually changing people's lifestyles and reading habits. The traditional paper media represented by newspapers and books has been very obviously squeezed in the market, living space and development. Facing this situation, newspapers with news dissemination, fast consumption and low price as the main directions and characteristics are based on the original basis. Upgrading product grades and creating quality print quality is an important way to enhance the competitiveness of paper media products and maximize readers' competition against other media markets. This article will mainly combine the quality standards of newspaper printing and some common quality problems, talk about how to systematically control related links, solve corresponding problems, and print out fine-quality newspapers.
As the saying goes, the equipment determines the quality. Advanced printing equipment is an important guarantee for quality products, but only advanced equipment is not enough. In recent years, from the printing presses of the central and provincial newspapers to the print shops of various local newspapers, the printing equipment has been upgraded. The printing quality of newspapers in all regions has been generally improved, but the quality of printing has to be improved. The level of quality, in addition to advanced equipment, high-quality printed materials require careful technical research and system control from pre-press to post-press. Only the combination of soft and hard can achieve the improvement of newspaper printing quality. Below I will combine my own experience to briefly talk about how to achieve the quality of newspaper fine print.
First, the main evaluation index and control focus of newspaper printing quality
At present, the main standard basis for the quality evaluation of newspaper printing is the national standard of newspaper printing G B / T 1 7 9 3 4 - 3 , and the evaluation method is "Printing Quality Requirements and Testing Methods for Newspaper Printing Committee of China Press Association". The quality inspection of newspapers is mainly divided into four major items: picture, inscription, ink color and appearance. Among the four major items, the best quality control level is also the most able to open the gap in the quality score of the newspaper is the ink color, especially the uniformity of black ink color and the precise control level of ink volume. Of course, the other three major items, such as pictures, inscriptions, and appearances, are also essential to the details of newspaper quality. In addition to the visual judgment, density measurement, gray balance and ink balance control of the above-mentioned items, prepress design control, plate quality control and printing equipment adjustment are also critical.
Second, the common problems in the quality of newspaper printing
Newspaper printing features high printing speed, short ink path, cold coagulation ink, dry drying by osmosis drying, and blanket cylinders as impression cylinders. The entire process of transferring ink from the plate cylinder to the substrate involves the printing materials of ink, dampening solution, printing plate, blanket and paper, as well as the inking unit, water delivery device and printing cylinder of the printing press. Due to the high printing speed and short ink contact time, the printing suitability and matching of the respective materials not only directly affect the printing quality of the newspaper, but also make the ink transfer become very complicated. The poor control matching directly causes the printing to occur. Here are some questions:
1. The layout of the ink is dirty, dirty, dirty
Dirty dirty tissue is the most common and most intuitive quality problem in newspapers. The main reason is that the ink on the surface of the printed product is not dried. The ink is transferred to the paper roller or belt after contact with the printing machine, folding machine or conveying mechanism. To a certain extent, it will in turn contaminate the printed products. In addition, after the newspaper is printed, the graphic on the newspaper layout is still moist, and then through the folding machine, the keel part is subjected to the external force mechanical action of the paper pulling roller, the discharging roller, the brush, the splint, the belt, etc. The front and back layouts of the newspaper and the one-fold and two-fold positions became easy to dirty and dirty, and these factors directly affected the aesthetics of the printed layout.
The main causes of the above problems are: The ink itself is poor in drying, the ink layer is too thick, the water is large, the ink is emulsified, and the water content in the ink layer is large. In order to reduce the occurrence of these problems, in addition to controlling the printing process of ink and water balance, improving ink performance, adjusting the pressure of post-press equipment, etc., the pre-press process, especially the process control of the image processing process is also essential.
2. The paper is shed, the powder is dropped, and the ink is too sticky to draw the paper and the blanket.
When the surface strength of the paper is low and the viscosity of the ink is large, the ink will stick to the fine particles on the surface of the paper, causing the paper to fall off the powder and even tear the paper surface in severe cases. After the paper particles are peeled off, white spots are caused by the ink being not stained. Paper scraps falling off the paper stick to the blanket and the plate, which will accelerate the wear of the plate and contaminate the blanket. The paper scraps are filled on the graphic of the printing plate, which will make the printed matter paste. When it is transferred to the ink fountain or the water bucket, it will pollute the ink and fountain solution.
Since the paper dust has good hydrophilicity, it absorbs water when it comes into contact with the water roller. When the water-impregnated particles are in contact with the new ink, it is not easy to get the ink, so that the image is partially white, if it is a fine paper. The powder will gradually pull on the edges of the image, causing the blanket to pile up, which will degrade the print quality. At the same time, it will cause grinding, increase the number of cleaning of blankets and ink rollers, and even interrupt printing when it is serious.
The main cause of this quality problem is the surface properties of the paper and the viscosity of the ink. Therefore, it is necessary to monitor the printing performance of the two materials in time, and find that the problem is replaced in time. In the production, it is necessary to stop the cleaning of the blanket, the printing plate and the water and the ink roller in time. Failure to do so may result in rapid wear and tear on the plates and will not be printed.
In the newsprint rotary printing, the folding and folding of the finished product by the folding machine also generates a large amount of paper powder, so the ink in the ink tank of the printing tower near the folding machine is relatively easily contaminated by dust, thereby affecting the purity of the ink. This is also an important factor contributing to the decline in ink transfer performance. In addition, the accumulation of impurities in the ink at the ink ports under the ink affects the transfer performance of the ink and also adversely affects quality control. Therefore, the protection and cleaning of the ink tank should pay special attention to daily production work.
3. Inadequate control of ink and water balance results in poor image text reproduction. Both dirty and paste are blank. The ink balance is not properly controlled. The hydrophilicity of the ink after emulsification is enhanced. The hydrophilicity of the blank part of the PS plate is reduced due to the change of ink transfer performance. Quality issues. In addition, the improper control of the ink balance will directly affect the ink color of the text picture, causing quality problems such as graying of the text and strokes of the stroke, which affects the overall effect of the layout.
Third, several key nodes of newspaper printing quality control
The core idea of creating a print quality of newspapers is to control the transfer of ink. The key control nodes mainly have the following aspects:
(1) Prepress processing and layout design
Most of the prepress group and image processing links of the newspaper are integrated in the editorial editing department of the newspaper. The printing factory is only responsible for the plate printing of the formed printing plate. As the leader of printing quality control, the prepress processing and layout design are difficult to directly control. , has been in a relatively passive position. Because the technicians responsible for the layout design and the prepress processing technicians pay more attention to the visual effect of the art when performing the group work, due to the lack of printing related knowledge and the insensitivity to the parameter setting, the effect seen on the computer is printed. It is often difficult to express it, and it can even bring negative effects, which also hinders the improvement of the quality of newspaper printing. Therefore, for most newspaper printing houses, under the premise of conditions, it is necessary to actively contact the editorial department, organize the beauty editing, layout design and photo processing personnel to carry out printing knowledge training, and enhance technical communication is an indirect control of prepress processing services. Necessary measures in the printing process. So, prepress processing should focus on those issues? There are mainly the following aspects:
1. Picture tone and ink total control
When color image processing, please pay attention to open the contrast of the picture. Try to make the tone of each level evenly distributed to avoid the picture being too bright, too dark or too flat. The total ink volume of the color overprinting ink should be controlled below 2 600. When the picture or color block is black, you should pay attention to the use of monochrome black. Try not to make four-color synthetic black. When the image can achieve the same effect, the neutral gray in the color is replaced by black as much as possible, so as to reduce the amount and total amount of the overprinted ink as much as possible, and reduce the dryness caused by the excessive use of the ink, resulting in smudging and dragging. Dirty and other phenomena.
2 . The placement of the image in the layout
① Avoid large amounts of ink or people's face pictures at the folding position.
At present, there are two main types of folding of newspaper rotary printing presses: one is impact type folding, and the other is plywood type folding. Both methods have advantages and disadvantages. When the impact speed of the machine changes, the position of the crease on the newspaper product changes. When the amount of printing water and the amount of ink are large, the newspaper is easily embossed by the folding nip. The splint folding method has a high stability, but since a set of cavities is required to complete the folding of the finished product, the gripper must have sufficient pressure to hold the folded product at high speed. If there is a picture at the folding position, and the amount of ink in the picture is relatively large, it is inevitable that there will be obvious smearing in the position of the line of the adjacent newspaper. Therefore, in the layout design, it is best to avoid placing large ink pictures or facial pictures in the fold and fold positions of the newspaper.
If the layout design needs to use the continuous version, the false version or the middle seam, the pressure of the folding machine's paper feed roller should be lightened as much as possible to reduce the dirty position in the middle seam position. Since the light-weighting paper-feeding roller is prone to paper running, which affects the printing speed and the printing tension control, the layout is designed to avoid the arrangement of the middle seam position.
② Avoid arranging two pictures with strong contrast in color tone at the same position above and below the same ink-adjusting area.
The amount of ink in the upper and lower positions of the paper travel direction is controlled by the same set of ink keys. If two pictures with strong contrast between cold and warm colors are arranged under the same set of ink paths, it will bring inconvenience to the printing work. Two sets of different style pictures Color reproduction is difficult to take care of at the same time, so pay special attention to the selection and use of pictures.
③ . Use of pictures black and cyan
A problem often encountered in color picture printing is that when the proportion of black and cyan plates is too large, the printing effect is much more boring than the computer screen. If you intentionally lighten the ink color during printing, it will cause other pictures to be color cast or text color. To the density requirement. This situation is mainly caused by the dark characteristics of black and blue inks and the expansion of dots. If the black and blue colors are too dark, the proportion of the dark areas of the picture will increase, and the picture level will be unclear and paste. When such a picture is used by large reduction or small magnification, if the picture is not reprocessed, the image layer is automatically compressed or enlarged by the computer. If the original pixel of the picture is not enough, the printed picture is very likely to have an overall effect. Darker black. Therefore, special attention should be paid to the black and cyan plates for individual adjustments during prepress processing.
④. Use of text size and color registration
The color newspaper printing quality industry standard for overprinting requirements is any two color error less than 0.15 m m. Due to the characteristics of newsprint, slight variations in paper tension during printing may cause overprinting deviations. Therefore, in the use of color texts, we recommend that the US editors should reduce the number of color registrations of the colors used on the basis of satisfactory color. The fewer the number of color registrations, the less likely it is to mix and paste on newsprint. The principle of color for color text is that the smaller the number of color registrations, the better. You can use three colors to resolutely use three colors; the small characters should be monochromatic as much as possible, and the large font color should not exceed 3 colors. In addition, try not to use small white characters on multi-color overprinted images to avoid minor overprinting and blurring of fonts. In the design of advertising pictures, try not to use multi-color overprinting or multi-color hollowing out in small fonts. Monochrome text or monochrome hollowing is the best choice.
⑤. The effect of solid color blocks on printing quality
It is common knowledge to think that the headline pressed by the field or the color strip and the color block with larger area are more saturated. However, in actual printing, we found that the headline or the larger color strips and color blocks that are pressed out in the field are easy to be stacked and embossed, which is not easy to be printed, and is easy to cause grinding. The larger the title and patch area, the more obvious this phenomenon is. Using a deep network of 85 % - 9.5 % instead of the field will get better results. For newspapers with high aging requirements and large print volumes, grinding will seriously affect quality, and sometimes even if it can be changed, it will affect the efficiency of production and the stability of quality.
⑥. Contrast control of picture shading pattern
In newspaper printing, sometimes the shading pattern of the picture does not appear or the effect is not obvious. This situation mainly occurs in the shading pattern on some dark backgrounds. As shown in Figure 1: The shading of the gear is basically not displayed after the newspaper is printed. The reason is that the dark background is generally superimposed by two colors or three colors of red, black and blue nets. , make the shading pattern dot no effect. Therefore, it is recommended that the shading pattern should be contrasted with the background color to make the contrast between the light and the dark.
(2) Plate quality control
As the price of CTP plates continues to fall, the cost of the entire CTP platemaking process is gradually accepted by most newspaper printing companies. CTP direct plate making technology has been more widely used, and the improvement of plate making quality has also made the printing quality obvious. help. Although C T P plate making has obvious advantages such as high speed, high precision, dot deformation and stable quality, it should pay attention to the inspection and control of plate quality in the process of application. There are many factors affecting the quality of C T P plate making, so we should pay attention to the following points:
1. C T P laser path cleaning and maintenance and laser waveform calibration
Due to the adhesion of dust or other suspended particles in the environment, after the CTP is used for a period of time, the external optical path and internal optical path of the laser will be contaminated, resulting in a certain loss of the laser during the operation of the optical path, and the laser energy reaching the surface of the plate. There is a certain attenuation, so that the dot on the surface of the CTP plate is deformed or the thin strokes of the finer characters are jagged, resulting in the loss or deformation of the dots in the highlight portion of the picture during printing, and the text is broken. In addition, as the use time is extended, the laser itself will attenuate, and the waveform of the laser emitted by the laser will also change, so that the laser energy is not optimal. Therefore, regular cleaning of the C T P laser path and calibration of the laser waveform based on laser energy attenuation is a key part of plate quality control.
2. Adjust the laser energy and R I P dot gain curve according to the plate brand model
Different brands and models of plates have different requirements for the laser energy required for exposure due to the manufacturing process and the photosensitive materials used. In order to ensure a high printing durability of the newspaper C T P plate, each manufacturer has adopted some new technologies, and the adoption of these new technologies also puts higher requirements on the performance of the C T P device. In addition, the dot gain ratio of different plates under the corresponding laser energy is also different. The same CTP device must use the laser energy value and calibration curve of different meshes before using different types of CTP plates. Test to see if the parameter settings meet the basic requirements for plate making quality. Otherwise, it will affect the print quality control of the printing process.
3. Temperature and concentration control of developer and coating of protective glue
Whether the P S version is fully developed and the uniform coating of the protective glue is also a key factor affecting the printing quality. Insufficient development, residual oleophilic coating on the blank part of the printing plate; uneven coating of protective glue, oxidation of the blank part of the printing plate, change of hydrophilicity, insufficient hydrophilicity of the surface of the printing plate during printing, unable to meet the demand of ink balance, affecting the ink Transfer performance, resulting in dirty version.
(3) Quality control of printing links
The factors affecting the printing quality are very complicated. From the perspective of ink transfer performance, the nodes that control the environmental temperature and humidity, the use of dampening solution, the ink balance, the printing pressure and the adjustment of the ink roller can effectively improve the nodes. Printing quality.
1. Environmental temperature and humidity and control of temperature, acidity and alkalinity and conductivity of dampening solution
Stable temperature and humidity control is the basic guarantee for the quality control of printed products. Humidity is very important for the stability of paper printing. It is the key to determining the accuracy of printing and overprinting. Temperature mainly affects the rheology of ink, which in turn affects the ink balance and ink of printing. Transfer effect. The temperature, acidity and alkalinity of the fountain solution directly affect the ink balance control of the printing. Controlling these links is a basic requirement for smooth printing and stable quality.
2. Ink balance control
Maintaining a stable relationship between the fountain solution and the ink is the key to ensuring the printing operation and obtaining high-quality prints with rich prints, vivid colors and clear images. In addition to careful observation of the printed product, the ink balance control should pay special attention to the setting and use of the ink-jet balance tracking curve of the printing machine.
Since the rotary printing process often has a transition from low speed to high speed or high speed to low speed, for example, before and after the web is connected, it must compensate the water amount or the amount of ink according to the speed change, that is, the ink tracking curve is completed. . Although the general printing machine sets the basic ink tracking curve after leaving the factory, the ink, dampening solution, paper brand, model and printed layout are not the same. When the speed changes greatly, the operator should explore the ink and water balance law when adapting to the speed change of the machine according to the long-term exploration and actual situation. If the machine is well-printed from a low speed, optimistic about the color of the ink, and then accelerated to high-speed printing, then its ink-and-water balance must have a certain change. It is necessary to adjust the percentage of ink-and-water balance to reduce fluctuations in the color of the ink. Layout, at different printing speeds, the law of ink color changes is different, so the numerical setting of the ink-and-water balance tracking curve is also different. Only by mastering these rules well, can we control the dynamic ink-and-wash balance with ease.
3. Lining, blanket selection and printing pressure control
When the ink on the printing plate is transferred from the blanket to the printed matter, the pressure between the blanket and the substrate should be uniform, and the rebound elasticity of the blanket can be good to print a high-quality newspaper. Therefore, the blanket installation and use status is critical to print quality control.
The factors affecting the pressure of the blanket are mainly the lining, the installation process of the blanket, the performance of the blanket and the processing technology of the fixture. The material of the lining has a significant influence on the change of printing pressure. In the newsprint rotary printing, due to the high printing speed, the ink transfer contact time is short, the soft package lining recovery time is prone to performance fatigue, and the pressure decay is obvious for a long time. The stability of the quality of the product has a certain impact. In addition, the paper lining is close to the edge portion of the drum and easily absorbs moisture on the printing plate to cause expansion, causing moisture deformation at the bottom of the blanket to increase the printing pressure of the edge portion. The lining installation is not good. The offset during the printing process will also cause uneven printing pressure. Therefore, the use of a rigid liner in high-speed rotary printing is more advantageous for the stability of printing pressure.
The T-bar type blanket installation should pay attention to the balance of the locking force of the locking screws at both ends. It is best to use a tool with torque torque measurement. Otherwise, the uneven installation of the blanket is easy to produce distortion and the pressure at both ends is unstable. The uniformity of installing the blanket by the worm method is better, but it is necessary to pay attention to whether the processing technology of fixing the metal handle at both ends of the blanket is passed. Otherwise, the blanket is easily loosened or peeled off during the printing, and the blanket is loosened, causing printing pressure. Changes affect the ink transfer effect and print quality.
4. Adjustment and inspection of ink roller
Whether the adjustment of the ink roller is the key factor affecting the printing quality, the adjustment of the ink roller should pay attention to the moderate force. Too large or too small is not conducive to water transfer. In addition, it is more important to level the two ends. If the ink glue is not leveled, it will definitely appear that the water is large or the water is small, resulting in serious emulsification, resulting in a dirty plate that does not reach the optimum state of ink balance. Therefore, it is indispensable to check the pressure of the ink roller water roller regularly after the production shift, and to establish a replacement file to monitor the use state of the ink roller. The ink roller should be replaced in time for the use of the replacement cycle or wear to a certain extent. In the production process, the temperature of the rubber roller can be measured by using a thermometer, and the ink transfer problem caused by the dynamic imbalance of the wear of the ink roller bearing is found in time.
5. Mechanical adjustment of newspaper conveying and stacking
If you print the best newspaper, if you don't pay attention to the belt pressure of the conveying keel and the packing and packing, the mechanical performance adjustment, all the efforts of the front end quality control will be abandoned. Therefore, the belt pressure and the transfer mechanism of the conveying and stacking equipment will be carefully adjusted. Reducing the occurrence of smudging is also an indispensable part of building quality.
Fourth, the conclusion
The quality control of newspaper printing is a systematic problem. Many quality problems are caused by many reasons. In the production, new problems are encountered. It is necessary to combine the specific analysis of the equipment, materials and processes of the enterprise to analyze the situation from multiple angles. It is even necessary to do some experimentation to eliminate the root cause and solution of the problem. This also requires the technicians of the printing enterprise to seriously study and improve the technical strength in order to conform to the trend of the times and to develop new equipment. The advantages of new technologies enable high levels of print quality control and improved print quality.