Relationship between Quality Control and Printing of Proofing (I)

Proofing is a very important process in the prepress plate making process. Proofing can be used to check the quality of the previous steps. Proofing proofs at the same time is also a standard for color tracking of large numbers of prints. Therefore, proofing has played an important role in the quality control and control of various platemaking companies.

There are many factors that affect the quality of proofing, such as: imposition, printing, development, ink, wipe water, field density, dot gain, maintenance and maintenance of proofer, temperature and humidity of the environment and so on. Whichever of these factors occurs, it will have a great impact on the final proofing results. Therefore, only the standardized and data-oriented management and operation can make the copy and restore of the outlets meet the requirements in the proofing process, and provide qualified follow-up proofs for large-volume printing. Now I will discuss with readers how to effectively control the main factors and related data in the proofing process.

First, make, print and develop

Proofing imposition and printing imposition are very different. The printed layout must be folded in the order of folding according to the binding method, and the crosshairs and corners of some films should be cut off. Therefore, the imposition staff can only easily follow the edge of the image on the film or the lines and color blocks. Debate places and aligns. Proofing the imposition does not need to worry about the problem of hand-folding. Crosses and corners on the film will also be preserved. When imposition, cross lines and corner lines of colored films can be aligned. In general, the color sequence of proofing determines the color sequence of the imposition. Because it can improve work efficiency. In the fight for the first color, the film should be placed horizontally, and it should not be tilted. The four corners should be glued with transparent tape. The other three color plates are aligned on this basis. The standard of registration is that the cross and corner lines of the upper and lower films cannot be seen by the eyes.

The control of the printing and development is achieved through the UGRA control bar. The UGRA control strip has five functional segments, each with its own distinct role. as the picture shows:

Paragraph I: Used to control the development of the printing plate, it is also possible to evaluate the exposure of the printing plate. Eligible for the grade to begin with the third grade, ninth grade began to distinguish the grade.

Section II: Microcoils are used to control the exposure time. Passed to start clearly recognizing microcoils at 12 μm.

Section III: The network segment is divided into 10 blocks from 10% to 100% on the ground. It is used to check the exposure and development, and is also used as the standard for printing characteristic curve measurement. Qualified for 2% outlets, 3% outlets are clear.

Section IV: Fine mesh lines along different angles can be checked for dot distortion and ghosting.

Paragraph V: Fine dot plots are 0.5% to 5% for positive pictures and 95% to 99.5% for negative pictures, used to check whether or not the dots are reduced during the proofing process.

Although the UGRA control bar can be used to control the exposure and development more precisely, it is still necessary to make adjustments based on experience in some subtle areas to optimize the reproduction and restoration of dots. For example, the adjustment of the pumping time for different thicknesses of the plate, the adjustment of the temperature and speed of the developing machine, and the cleaning and maintenance of the printing plate glass, and the like.

Second, proofing

Proofers and presses are very different. The printing press uses a "circular press" printing method, while the proofer uses a "circular press" printing method. In addition, the degree of automation of ink and register printing presses is very high. Most of the proofing machines are adjusted by the operator according to personal experience, and the color version of the registration is also performed manually. Although during the proofing process, the operator must rely on the density meter to continuously measure the density of the spot and the dot density and dot gain at 80% to adjust the ink volume and the ink balance, but the process of inking must still use ink scoops. Scoop the ink onto the proofer roller.

Therefore, the quality of proofing is closely related to the level of the operator.
The field density value is the most important technical parameter for control network copy and restoration. Different companies have their own different technical indicators and error ranges. This technical indicator is based on the company's specific circumstances. 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, the control of ink and water balance is also very important. The principle of printing is essentially the principle of oil and water incompatibility: the dots on the PS plate that are exposed to form images are not hydrophilic, and the unexposed blanks are not hydrophilic. Therefore, it is important to maintain a good ink balance. If the water is rubbed too little, it will result in a dry version, and reflecting on the proofs will be the level and level of the dark tone; if the water is rubbed too much, the dots will be deformed and the dots on the printed sheets will appear as “hollow dots”. So, how much should we wipe the water? In general, the less water you rub, the better. The mastery is that when water rolls over, there is no visible water on the platform.