Influence of Printing Process on Print Quality (Part 2)

The filming, also called output, includes several processes such as RIP dispensing, photo-exposure film exposure and rinsing, and inspection. Controlling this process with data and standardization is an important means of ensuring print quality. The main impact of this process on print quality is:

1 Due to the poor linearization of the output film, the text is thick and fat, the printing effect is too dark, the color of the picture is deviated and the level reproduction is poor, and the color of the color block is deviated.

2 The film bottom ash is too large and the density is insufficient due to improper film exposure and processing conditions. Reflected on the layout is the layout from the dirty, real hair virtual, low-key network level lost, absolutely network, paste network.

3 Due to the excessively high or low mesh number, the picture paste network, absolute network, and picture level performance are poor.
4 Due to improper screen angle, moire and poor color performance.

5 Overprint errors and rule lines due to the low positioning accuracy of the film have caused the imposition error.

6 Inconsistent appearance of the layout parameters varies from layout to layout.

7 Due to improper operation such as flushing and inspection, it can cause scribes, horseshoe prints, dirty tracks, etc., which are directly reflected on the layout, such as scratches, imaginary dots, and layout stains.

Therefore, the following points should be noted during the output of the film:

1 Data control is the basis for a good film output process control and quality assurance. There are two aspects of the data control of the output of the film, one is to ensure the accuracy of the output network, the network error should be controlled within 2%; the second is the bottom of the film after the output of the film, the maximum density value meets the requirements, bottom ash should be less than 0.04 The maximum density Dmax ≥ 3.0. This requires a series of tests on the exposure and washing process of the film to find an accurate set of system parameters and make corresponding adjustments for different batches of raw materials at different times. For the different films, through the test and multiple linear adjustments, so that the film meets the above requirements.

2 meticulous operation, careful adjustment. Normalized operation is an important step to ensure the quality of output. The output must ensure that all layout parameters are consistent, the number of screen lines meets the printing requirements, the screen angle does not produce moiré accurately, and the four-color version repeat positioning accuracy is within 25 μm, and the registration cross position, size, and thickness are uniform.

After the completion of the filming task, it will be proofed. There are two types of proofing: digital proofing and mock proofing. The quality of the film directly depends on the effect of the sample. Therefore, how well the film is handled will have a great influence on the proofing and the backside printing. Shaiban should pay attention to the choice of light intensity and exposure time. The solution configuration in the plate processor is also required to be done. Generally, the test can be done first, and then the relevant values ​​can be determined.

Fourth, printing

Printing is also a very important process. Of course, there are many technical points.
First of all, mastering and controlling the balance between water and ink is the key to stably improving the quality of printing. The ink-and-wash balance is the basis of printing. Only ink and water control is just right, so that printed newspapers can be clearly illustrated and shaded with ink—so that overprinting can be accurate. The key to good ink-and-wash balance is water. On the premise of ensuring that it is not dirty, the water is controlled within a minimum range, and the amount of water and ink are in a relatively stable state. The water is too little, not only dirty, but the plate writing is dull, pale gray, imprinting is false, sometimes there are snow spots; water is too large, there will be imprinted, graphic lightening, writing is empty, no Levels and so on. The absolute balance of ink and wash is no, only relatively balanced. In order to stabilize the ink balance, it is required to do the following in practical work:

1 Note the proportion of fountain solution equipped. The proportion of the equipment is generally 2% to 2.5%. The water temperature is controlled at about 16°C, the pH is about 5.5 to 6.5, the conductivity value is about 1600, and the salinity is about 0.50.

2 According to the different quality of paper, adjust the ink supply in time. Due to the different paper origins, the smoothness of the paper is also different. Different seasons, the paper's moisture content is also different. Therefore, when printing different papers, the ink balance should be adjusted in time. Generally, newsprint paper with less smoothness and less paper particles has a slightly smaller amount of water, and rough and contaminated newsprints have a slightly larger amount of water; when the machine is running at a high speed, the speed of water is relatively small, and it may be slightly larger at low speeds. . This mainly depends on the general performance of the equipment, paper, ink, and the different conditions inside and outside the room to take advantage of the ink supply.

3 Control the environment and temperature and humidity of the workshop, which will help improve the printing quality. Because the layout water is distributed in a direct and indirect manner, the layout water is mostly distributed to the space when the printing ink meets the ink and ink balance requirements during printing. In general, the higher the ambient temperature, the faster the emission.

4 When purchasing auxiliary materials, we try to meet the needs of ink-water balance. Ink, plate, air-cushion blankets, paper, etc. have a lot to do with ink. The ratio of paper is significant, and the poor quality of printing is considered in terms of economic aspects. However, the choice of materials must be kept in relation to plates, inks, etc. Good materials should be used as much as possible. Under normal circumstances, do not change the brand frequently. Let the shop use a regular pattern. In principle, what should be used to buy what, not what to buy.

5 Strengthening the maintenance and inspection of printing equipment is a means to improve the printing quality. Whether the printing equipment is advanced or not, and whether maintenance and maintenance keep pace with it is crucial to improving the quality of printing. Therefore, in actual work, if we want to improve the quality of printed products, we must strengthen the maintenance and maintenance of printing equipment. Clean the ink roller, ink tank, water tank, water roller, and sink frequently. This cleaning includes daily cleaning after the end of printing, cleaning before each color change and regular thorough cleaning, does not allow ink to remain in the pores on the surface of the blanket, otherwise it will oxidize the conjunctiva for a long time, reduce the ink adsorption capacity, and make the ink Transferred lower. The residual ink in the ink tank and the impurities around the ink keys are often removed so that the ink keys can be released freely. In particular, the current remote ink-control device should ensure the cleanliness of its ink keys. Always clean the water tank, the water tank and the water roller to ensure the circulation of the water circuit. When changing the water, pay attention to the proportion of the dampening water, so that the pH of the water is in the normal state.

6 Check the pressure of the drive part regularly. As the season changes, the machine will continue to operate for a long time, and the pressure of each part will change slightly. These changes have a direct impact on the printing quality. Because of the pressure between the print cylinders, the pressure between the water rollers between the ink rollers is critical to the print quality. In particular, the pressure between the rollers is more severe with the seasons. Under normal circumstances, in March and November of each year, during the two months when climate change is particularly noticeable, a large adjustment of the pressure of the rubber roller must be carried out. Normally, the machine and maintenance personnel must check the pressure of the rubber roller and the roller pressure every half a month - and find that the problem is adjusted and resolved at any time.

(author/Yang Xiaoyue)

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