Proof quality control and printing relationship

Proof quality control and printing relationship

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Proofing is a very important process in the prepress process. Proofing can check the quality of the previous processes, and the proofs are also the standard for color tracking of a large number of subsequent prints. Therefore, proofing plays a role in linking up and down, and 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, development, inking, wiping water, density in the field, dot gain, maintenance and maintenance of the proofer, temperature and humidity of the environment, and so on. No matter which of these factors is a problem, it will have a great impact on the final proofing result. Therefore, only the standardization and data management and operation can make the copying and restoration of the outlets meet the requirements in the proofing process, and provide qualified proofs for large-volume printing. Below I will discuss how to effectively control the main factors in the proofing process and related data.

First, imposition, printing and development

The proofing of the proofing is very different from the printed version. The printed layout must be spelled in the order of folding according to the binding method, and the cross lines and corners of some films should be cut off. Therefore, the imposition personnel can only be based on the edges of the image on the film or the lines and color blocks. Identify where to align and register. The proofing of the proof does not need to consider the problem of folding hands, the crosshairs and corners on the film will also be saved. As long as the imposition of the film is aligned with the crosshairs and corners of the film. In general, the color sequence of the proof determines the color sequence of the imposition. Because this can improve work efficiency. When the first color is spelled, the film should be horizontal, not tilted, and the corners should be glued with transparent tape. The other three color plates are aligned with each other based on this. The standard for registration is that the cross lines and corners of the upper and lower film are not visible to the eye.

Control of the printing and development is achieved by the UGRA control strip. The UGRA control strip has five functional sections, each with its own different role. as the picture shows:

Section I: Used to control the development of the plate, and also to evaluate the exposure of the plate. The qualification is that the classification starts from the third level, and the ninth level begins to distinguish the classification.

Paragraph II: The micron coil is used to control the exposure time. It was qualified to start clear discrimination of the micro-coil at 12 μm.

Paragraph III: The dot segment is divided into 10% from 10% to 100% in the field, used to check exposure and development, and is also used as a standard for measurement of printed characteristic curves. Passed 2% outlets and 3% outlets are clear.

Paragraph IV: Fine mesh along different angles, you can check for dot distortion and ghosting.

Section V: The fine dot segment is divided into 0.5% to 5% of the positive image and 95% to 99.5% of the negative image, which is used to check whether the dot is reduced during the proofing process.

Although the UGRA control strip allows for precise control of exposure and development, in some subtle areas it is necessary for the operator to make appropriate adjustments based on experience to optimize the reproduction and reproduction of the dots. For example, the adjustment of the pumping time for the plates of different thicknesses, the adjustment of the temperature and speed of the developing machine, and the cleaning and maintenance of the glass of the printer are carried out.

Second, proofing

The proofer is very different from the press. The printing machine adopts the "round and round" printing method, while the proofing machine adopts the "circular flattening" printing method. In addition, the automation of printing and registration of the printing press is very high. Most of the proofing machines are adjusted by the operator according to personal experience, and the registration of each color version is also carried out by hand. Although in the proofing process, the operator must rely on the density meter to continuously measure the density of the ground and the dot density and dot gain at 80% to adjust the amount of ink and the ink balance, but the process of inking must still use the inkjet Shovel the ink onto the rollers of the proofer. Therefore, the quality of the proof is closely related to the level of the operator.

The field density value is the most important technical parameter for controlling the replication and restoration of the network. Different companies have different technical indicators and margins of error. This technical indicator is determined by each company according to its own specific circumstances. Generally, the solid 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.

As with printing, proofing is also very important for the control of ink balance. The principle of printing is essentially the principle of oil-water incompatibility: the part of the spot on which the image is formed by exposure on the PS plate is not hydrophilic, and the unexposed blank is hydrophilic and not lipophilic. Therefore, it is important to maintain a good ink balance. If the water is wiped too little, it will lead to a dry plate, which is reflected in the level of the dark tone. The water is rubbed too much, which will cause the dot to be deformed, and the dots on the printed sheet will have a "hollow point". So how much should the amount of water wipe be controlled? In general, the less the water is rubbed, the better. The mastery of the scale is that there is no water present on the platen after the water roll.

The technical parameters of the fountain solution are often neglected in the quality control of proofing. The technical parameters of the fountain solution are mainly conductivity and pH. Their standards are: conductivity is 800 ~ 1 200, pH value is 4.8 ~ 5.2.

Proof quality control also involves adjustments to the proofer. The main contents of the adjustment are as follows:

1The pressure of the blanket cylinder is ±0.03 mm (measured once every 120° rotation, average), ie blanket thickness + pad thickness = (2.286±0.03) Mm.

2 The pressure of the 2 plate (including the thickness of the PS plate) is +0.12 mm to +0.15 mm, that is, the surface of the PS plate is higher than the height of the guide rail.

3 The pressure of the paper table (including the thickness of the paper) is +0.15 mm to +0.18 mm, that is, the height of the paper surface is higher than the height of the guide rail.

4 There are two rollers on each side of the movable rack. When the frame is moved to the side of the ink-distributing system, and the machine is not pressurized, the pressure of the roller and the lower rail surface can be rotated just by hand. Too tight and too loose need to be adjusted.

5 Tonerization system: The width of the ink bar on the platen should be uniform with the width of the impression ink on the paper table.

Third, the maintenance and 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 condition can the outlets be kept in good quality during the transfer process, and finally the qualified samples will be obtained. Since the maintenance and maintenance of the proofer is an ongoing process, a set of practical maintenance procedures must be established and standardized and standardized.

1 ink roller maintenance

The change in the dot of the proof sheet will deteriorate with the hardening of the proofer roller. Hardening of the ink roller means that the roller has been used for a long time, and its surface becomes light and hard until a "crystalline layer" is formed. When the surface of the roller is crystallized seriously, its ink transfer performance is affected, and the ink balance during the proofing process is difficult to maintain. In particular, magenta inks cause a hollow phenomenon at the dots due to a decrease in water absorption. The area of the sample dot will be smaller than the dot area on the film, and the color will become lighter. That is, the saturation drops. In some instances, when the dot of one color changes, the hue of the proof will deviate from the expected effect, and the hue of the multicolor overprint will change more. This shows how important it is to maintain the ink roller. In addition to daily fixed cleaning procedures, there are specific maintenance measures. That is, the ink roller of the proofing machine is taken off every two weeks to "rest" and replaced with a spare ink roller. In this way, the ink roller can be kept in a good working state, thereby obtaining a satisfactory quality of dot reduction.

2 blanket maintenance

A blanket is a medium that transfers dots from a plate to paper. Its performance directly affects the quality of the delivery of the outlets. After the blanket is used for a long time, chemical residues adhere to the surface, making the elasticity of the blanket smaller. This will make the edges of the dots that are transferred to the paper less sharp. Therefore, after working for a period of time on the blanket, let it "rest" to avoid excessive fatigue.

3 daily maintenance and maintenance of the proofer itself

The proofing machine is generally composed of a mechanical part and an electrical part. For the mechanical part, it is necessary to regularly add lubricating oil to the fixed oil holes and the transmission parts of the surface (such as the chain) to avoid excessive wear; and for the electrical part, it is mainly to check and ensure the smoothness of the gas path, and to maintain The surface of the panel is cleaned and so on. In the process of proofing, when the ink is changed, the oil black on the ink roller and the blanket should be cleaned and then other colors of ink should be added. Otherwise, the residual ink will be mixed with the added ink to affect the proofing quality. In addition, dust and paper powder near the plate and the rules should be wiped off on time, because excessive accumulation will affect the registration accuracy.

Fourth, environmental factors

The main factors affecting the quality of proofing in environmental factors are temperature and relative humidity. If the temperature is too high or too low, the water rubbed onto the PS plate will evaporate too quickly or too slowly, thus destroying the ink balance. If the relative humidity of the environment is too large or too small, the balance of ink and ink will be destroyed, and even the phenomenon of ink emulsification will result in the generation of hollow dots. In addition, it is more serious that the instability of temperature and humidity will deform the paper, resulting in a decrease in registration accuracy. Therefore, it is very important to maintain constant temperature and humidity in the proofing workshop. Generally, the ambient temperature should be 22 ° C ~ 23 ° C, and the relative humidity is about 50%.

V. Conclusion

There are many factors that need to be controlled to improve the quality of proofing. The above is just a simple analysis and introduction of some major control methods and empirical data, and there are many subtle factors not listed. In the proofing process, often a small mistake can lead to the production of waste. Therefore, a complete and practical management system and operational procedures should be developed for the specific situation of the company or the department to make the proofing move to the track of standardization and data. Only in this way can the quality of the proof be stabilized on a high level.