Quality control and maintenance of the hottest pro

Quality control and maintenance of proofing machine

proofing is a very important process in the process of prepress plate making. Proofing can check the production quality of the previous processes, and 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 part of 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 goes wrong, it will have a great impact on the final proofing result. 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 proofing is very different from the making up of printing. The large version of the printing must be assembled according to the folding order according to the binding method, and the crosshairs and corners 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 other places that are easy to distinguish, such as lines and color patches. The problem of folding hands does not need to be considered in proofing, and the crosshairs and corners on the film will also be saved. As long as the crosshairs and corner lines of various colors of films are aligned during the making up. Generally speaking, the color order of proofing determines the color order of making up. Because this 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 of registration is that the eye cannot see the offset of the crosshairs and corners of the upper and lower films

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

paragraph I: it is used to control the development of the printing plate, and it can also 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. It is acceptable to start to clearly distinguish the micron coil at 12 M

section III: a total of 10 blocks from 10% point to 100% field are used to check exposure and development, and also used as the standard for the measurement of printing characteristic curve. If 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 dot 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 in the proofing process is reduced

although exposure and development can be controlled more accurately through UGRA control strip, operators still 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 with 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 pressing, while the proofing machine adopts the printing method of round pressing. 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 by hand. Although in the process of proofing, the operator must also rely on the densimeter to constantly measure the field density and the point density and point increase at 80% to adjust the size of the ink supply and the ink balance, the ink must be shoveled onto the roller of the proofing machine with an ink shovel in the process of inking. 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 version 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 points exposed to form images 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. If you wipe too little water, it will lead to a dry version, which is reflected in the sample sheet, and there is a level of dark tone; Wiping 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. The standard to master is that when the water roller is behind the plate, there is no water on the table

the technical parameters of fountain solution are often neglected in the quality control of the more stable operation of the measurement and control system of the sample company. The technical parameters of fountain solution are mainly conductivity and pH value. Their standards are: conductivity 800 ~ 1200, pH 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 0.03mm (measured every 120 revolutions, take the average value), that is, the thickness of the rubber blanket + the thickness of the liner = (2.286 0.03) mm

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

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

④ there are two rollers under both sides of the movable frame. 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 need to be adjusted

⑤ inking system: the width of the ink bar of the inking roller on the plate table should be uniform and 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, at the proofing machine, we will combine the specific conditions of the frequent use of friction testing and surface texture measurement to determine the working state. 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 maintenance of ink roller

the point change of proofing sheet will deteriorate with the hardening of ink roller of proofing machine. The hardening of the ink roller refers to 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 it is difficult to maintain the water ink balance in the proofing process. In particular, magenta ink, due to the decline in water absorption, will cause points to appear hollow. In this way, the spot area on the sample will be smaller than that on the film, and the color will become lighter. That is, the saturation decreases. In some cases, when the dots 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 daily and weekly fixed cleaning procedures, there should also be specific maintenance measures. That is, take down the ink roller of the proofing machine every two weeks to have a 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 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, after working for a period of time, the blanket should also be let down to have a rest, so as not to make it too tired

③ daily maintenance of the proofing machine itself

generally speaking, the proofing machine is composed of mechanical parts and electrical parts. 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, etc. In the proofing process, when changing the ink, you should clean the oil black on the ink roller and blanket, and then add other colors of ink. You can't do it 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 quality of proofing. If the temperature is too high or too low, Binzhou will build five hundred billion level industrial clusters, and the water wiped on the PS version will evaporate too fast or too slowly, thus destroying the balance of ink and water. Too high or too low environmental relative humidity will also destroy the balance of ink and water, and even produce ink emulsification, resulting in the production of hollow spots. In addition, what is 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 maintain 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 simple 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, often a small error may lead to waste products. Therefore, a complete and feasible management system and operating procedures should be formulated according to the specific situation of the company or department, so as to further support the development of graphene industry; In order to support the development of graphene industry, proofing in Ningbo is on the track of standardization and digitalization. Only in this way can the quality of proofing be stabilized on the basis of a high level