Quality control of the hottest proofing 0

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Quality control of proofing

proofing is a very important process in the process of prepress plate making. Proofing can check the production quality of the previous processes. At the same time, proofing is also the standard for color tracking of a large number of subsequent printing. Therefore, proofing plays a connecting role and is an important link in the quality management and control of plate making companies

there are many factors that affect the quality of proofing, such as making up, printing, developing, inking, wiping, field density, dot increase, maintenance of proofing machine, temperature and humidity of environment, etc. No matter which of these factors has a problem, it will have a great impact on the final proofing results. Therefore, only standardized and data-based management and operation can make the point copy and restore meet the requirements in the proofing process, and provide qualified proofs for mass printing. Next, I will discuss with readers how to effectively control the main factors and relevant data in the proofing process

I. making up, printing and developing

the making up of proofs is very different from the making up of large printing plates. The large version of the printing must be assembled according to the folding order according to the binding method, and the cross lines and corner lines of some films must be cut off. Therefore, the compositor can only align and register according to the edges of the image on the film or the lines and color blocks that are easy to distinguish. For proofing, there is no need to consider the problem of folding hands (Xie Xingxing, ye Xintong), and the cross lines and corner lines on the film will also be saved. As long as the crosshairs and corner lines of each color film are aligned when making up. Generally speaking, the color order of proofing determines the color order of making up. Because it can improve work efficiency. When putting together the first color, the film should be placed horizontally, not tilted, and the four corners should be glued with transparent tape. The other three color plates are aligned with each other on this basis. The standard for registration is that the eye cannot see the offset of the crosshairs and corners of the upper and lower films

the control of plate printing and development is realized through the UGRA control strip. The UGRA control strip has five functional segments, each with its own different functions. As shown in the figure:

paragraph I: it is used to control the development of the printing plate and also to evaluate the exposure of the printing plate. If it is qualified, the classification starts from the third level, and the classification cannot be distinguished from the Ninth level

stage II: the micron coil is used to control the exposure time. Qualified at 12 μ The micron coil is clearly distinguished at M

section III: there are 10 blocks in total from 10% point to 100% field, which are used to check the exposure and development, and also used as the standard for measuring the printing characteristic curve. If it is qualified, 2% points appear and 3% points are clear

segment IV: along the fine lines at different angles, you can check whether there is point deformation and ghosting

Section V: the fine point section is divided into positive chart 0.5% to 5% and negative chart 95% to 99.5%, which is used to check whether the midpoint is reduced during the proofing process

although exposure and development can be controlled accurately through UGRA control strip, operators need to make appropriate adjustments according to experience in some subtle places to achieve the best point replication and restoration. For example, adjust the air extraction time for plates of different thickness, adjust the temperature and speed of the developer to match, and clean and maintain the glass of the plate printer

II. Proofing

proofing machines are very different from printing machines. The printing machine adopts the printing method of "round DSM serves for food and health products, personal care, feed, medical equipment, automobile, coating and paint, electronics and electrical, life protection" while the proofing machine adopts the printing method of "round flattening". In addition, the printing machine inking, registration of a very high degree of automation. The proofing machine is mostly adjusted by the operator according to his personal experience, and the registration of various color versions is also carried out manually. During the proofing process, the operator must also rely on the densimeter to continuously measure the field density and the point density and point increase at 80% to adjust the ink feeding amount and ink balance. However, in the inking process, the ink must be shoveled onto the roller of the proofing machine with an ink shovel. Therefore, the quality of proofing is closely related to the level of operators

field density value is the most important technical parameter for control point replication and restoration. Different companies have their own different technical indicators and error ranges. This technical index is determined by each company according to its own specific situation. Generally, the field density of each color plate is y:1.30, m:1.45, c:1.50, k:1.80. As for the error range, the European standard is ± 0.07. It is said that the error range of a domestic company is controlled within ± 0.05

like printing, proofing is also very important to control the ink balance. In essence, the principle of printing is the principle of oil-water incompatibility: the exposed points on the PS plate are lipophilic but not hydrophilic, and the unexposed blank parts are hydrophilic but not lipophilic. Therefore, it is very important to maintain a good balance between ink and water. Too little water will lead to a dry version, which is reflected in the level and level of dark tone on the sample; Too much water will cause point deformation, and "hollow points" will appear on the printing sheet. So, how to control the amount of wiping water? Generally speaking, the less water you wipe, the better. Master the scale is when the water roller after the version of the platform can not see the existence of water

the real-time rotation and forwarding experimental results of fountain solution can only be judged. The retrieval of experimental results, data analysis and statistical technical parameters are often neglected factors in the quality control of proofing. The technical parameters of fountain solution mainly include conductivity and pH value. Their standards are: the conductivity is 800 ~ 1200, and the pH value is 4.8 ~ 5.2

the quality control of proofing also involves the adjustment of proofing machine. The adjustment contents mainly include the following:

① the pressure of the rubber drum is ± 0.03 mm (measured once every 120 ° rotation, and the average value is taken), that is, the rubber blanket thickness + pad thickness = (2.286 ± 0.03) mm

② the platen pressure (including the thickness of PS platen) is +0.12 mm ~ +0.15 mm, that is, the height of PS platen surface above the guide rail

③ the paper table pressure (including the thickness of the paper) is +0.15 mm ~ +0.18 mm, that is, the height of the paper surface above the guide rail

④ there are two rollers under both sides of the movable rack. When the frame moves to the side of the inking system and the machine is not pressurized, the pressure on the roller and the lower guide rail surface should be just able to rotate with manual force. Both too tight and too loose shall be adjusted

⑤ ink leveling system: the width of the ink bar on the plate table of the inking roller shall be consistent with the width of the embossing ink bar on the paper table

III. maintenance of the proofing machine

in the process of proofing, the operation of the proofing machine is the most important. Of course, the working state of the proofing machine is also very important. Only when the proofing machine is in the best working state, can we ensure that the points maintain good quality in the transmission process, and finally get qualified samples. As the maintenance of the proofing machine is a continuous process, a set of practical maintenance procedures must be established and standardized

① ink roller maintenance

the point change of the proofing sheet will deteriorate with the hardening of the ink roller of the proofing machine. The hardening of the ink roller means that the surface of the roller will become smooth and hard until a "crystalline layer" is formed. When the surface of the roller crystallizes seriously, its ink transfer performance will be affected, and the ink balance in the proofing process will be difficult to maintain. In particular, magenta ink, due to the decline in water absorption, will cause point hollow phenomenon. In this way, the spot area on the sample sheet will be smaller than the spot area on the film, and the color will become lighter. That is, the saturation decreases. In some cases, when the points of one color change, the tone of the sample will deviate from the expected effect, and the tone change of multi-color overprint will be greater. This shows how important it is to maintain the ink roller. In addition to the regular daily and weekly cleaning procedures, there should also be specific maintenance measures. That is, take down the ink roller of the proofing machine every two weeks to "rest" and replace it with a spare ink roller. In this way, the ink roller can maintain a good working condition, so as to obtain a satisfactory point reduction quality

② maintenance of blanket

blanket is the medium that transfers the point from the printing plate to the paper. Its performance directly affects the transmission quality of points. After the rubber blanket is used for a long time, chemical residues will adhere to its surface, making the elasticity of the rubber blanket smaller. This will make the edges of the points transferred to the paper not sharp enough. Therefore, Dow, who has been working on the blanket for a period of time in the future, should also let it "rest" in order to avoid over fatigue

③ daily maintenance of the proofing machine

generally speaking, the proofing machine is composed of mechanical part and electrical part. For the mechanical part, it is necessary to regularly add lubricating oil to the transmission part (such as chain) of each fixed oil hole and surface to avoid excessive wear; For the electrical part, it is mainly to check and ensure the smoothness of the air path, and keep the surface of the panel clean. In the proofing process, when changing the ink, clean the oil black on the ink roller and blanket, and then add other colors of ink. Do not change the ink at will. Otherwise, the residual ink will mix with the added ink and affect the proofing quality. In addition, dust and paper powder near the plate table and rules should also be wiped off on time, because excessive accumulation will affect the registration accuracy

IV. environmental factors

temperature and relative humidity are the main environmental factors that affect the proofing quality. If the temperature is too high or too low, the water on the PS plate will evaporate too fast or too slowly, thus damaging the ink balance. Too large or too small environmental relative humidity will also destroy the ink balance, and even produce ink emulsification, resulting in the production of hollow spots. In addition, more serious is that the instability of temperature and humidity will deform the paper, resulting in the decline of registration accuracy. Therefore, it is very important to keep constant temperature and humidity in the proofing workshop. Generally speaking, the ambient temperature should be 22 ℃ ~ 23 ℃, and the relative humidity should be about 50%

v. conclusion

there are many factors that need to be controlled to improve the proofing quality. The above is a brief analysis and introduction of some main control means and empirical data, and there are many subtle factors that have not been listed one by one. In the proofing process, a small error may lead to the generation of waste products. Therefore, a complete and feasible management system and operating procedures should be formulated according to the specific conditions of the company or the Department, so as to make the proofing move towards the track of standardization and digitalization. Only in this way can the quality of proofing be stabilized on the basis of a high level

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