Proofing is a very important process in the prepress platemaking process. Proofing can check the production quality of the previous processes. At the same time, proofing proofs are also the standard for color tracking for a large number of subsequent printings. Therefore, proofing plays an important role, which is an important part of the quality management and control of each plate-making company.
There are many factors that affect the quality of proofing, such as: imposition, printing, developing, inking, wiping, solid density, dot increase, maintenance and maintenance of the proofing machine, environmental temperature and humidity, etc. No matter which of these factors has a problem, it will have a great impact on the final proofing results. Therefore, only the standardized and data-based management and operation can make the copy and restoration of the dots meet the requirements during the proofing process, and provide qualified sample proofs for mass printing. Below I will discuss with readers how to effectively control the main factors and related data during the proofing process.
1. Imposition, printing and developing
Proofing imposition is very different from printed imposition. The printed imposition must be assembled in the folding order according to the binding method, and the crosshairs and corners of part of the film should be cut off. Therefore, the imposition personnel can only easily find the edges or lines and color blocks of the image on the film. Align and register the discriminating place. The imposition of proofing does not need to consider the problem of folding hands, and the cross and corner lines on the film will also be saved. As long as the cross lines and corner lines of the films of various colors are aligned during imposition. Generally speaking, the color sequence of the proofing determines the color sequence of the imposition. Because this can improve work efficiency. When fighting the first color, the film should be placed horizontally, not tilted, and the four corners should be glued together with transparent tape. The other three color versions are aligned with them on this basis. The standard of registration is that the cross line and corner line of the upper and lower films are not visible to the eyes.
The control of printing and developing is realized through the UGRA control strip. The UGRA control bar has five functional sections, each with its own different role.
Section I: Used to control the development of the printing plate, and also to evaluate the exposure of the printing plate. The pass is graded from the third level, and the grade is unclear from the ninth level.
Section II: The micron coil is used to control the exposure time. The pass is to start to clearly distinguish the micrometer coil at 12μm.
Section III: The dot section is divided into 10 blocks from 10% dots to 100% field. It is used to check the exposure and development, and is also used as the standard for measuring the printing characteristics. 2% of the outlets appear qualified, and 3% of the outlets are clear.
Section IV: Fine mesh lines along different angles can be inspected for dot deformation and ghosting.
Section â…¤: Fine dots are divided into positive images 0.5% to 5% and negative images 95% to 99.5%, used to check whether the dots are reduced during the proofing process. [next]
Although the UGRA control strip can be used to control the exposure and development more accurately, in some subtle places, the operator needs to make appropriate adjustments based on experience to optimize the reproduction and restoration of the dots. For example, adjust the suction time for plates of different thicknesses, adjust the temperature and speed of the developing machine, and clean and maintain the glass of the printing machine.
Second, proofing
Proofing machines are very different from printing machines. The printing machine adopts the printing method of 'round pressing round', while the proofing machine adopts the printing method of 'round pressing flat'. In addition, the degree of automation of the printing machine inking and registration is very high. Proofers are mostly adjusted by the operator according to personal experience, and the registration of each color version is also carried out by hand. Although during the proofing process, the operator must also rely on the density meter to continuously measure the field density and the dot density and dot increase at 80% to adjust the amount of ink supply and the balance of water and ink, but the ink process must still use an ink shovel Shovel the ink onto the proofer roller. Therefore, the quality of the proofing is closely related to the level of the operator.
The field density value is the most important technical parameter for controlling the copying and restoration of network points. 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 solid density of each color version is Y: 1.30, M: 1.45, C: 1.50, K: 1.80. As for the margin of error, the European standard is ± 0.07. It is said that the error range of a domestic company is controlled within ± 0.05.
As with printing, proofing control of water-ink balance is also very important. The principle of printing is essentially the principle of oil-water incompatibility: the dots on the PS plate exposed to form an image are oleophilic and not hydrophilic, and the unexposed blank parts are hydrophilic and oleophilic. Therefore, maintaining a good water-ink balance is essential. Too little water wiping will result in a dry plate, which is reflected in the proofs as dark levels and grading; too much water wiping will cause the dots to deform, and the dots on the printed sheets will appear as "hollow dots." So, how to control the amount of water? In general, the less water you wipe, the better. The mastered scale is that there is no water on the plate after the water roller passes.
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