The experience of printing offset paper using commercial rotary machines

Commercial rotary machines are mostly used for printing high-end products, such as printing papers, coated papers, magazines and various commercial advertisements with light-coated paper and coated paper, but are not suitable for printing offset paper. However, due to the increasing number of color illustrations in student textbooks, the use of traditional rotary printing machines without drying devices is often prone to quality problems such as smudging and ink instability. Although reducing the amount of ink can be solved, the printed products are often dark in color and have poor level performance. For this reason, commercial rotary printing machines with drying devices can be used instead, which can eliminate the quality problems such as scratching, and the ink color is bright and the screen level is rich. However, when printing offset paper with a commercial web press, the following issues should be noted.

1. Reduce the tension of the tape

The tape tension plays a decisive role in the overprinting of the web. The principle of setting is: The smaller the tape tension is, the better the accuracy of overprinting is guaranteed. Compared with coated paper, offset paper has poor toughness, is brittle and easily breaks. In view of this situation, under the premise of ensuring accurate overprinting, try to gradually reduce the tension after starting the machine. Our experience is that the same amount of light coated paper and offset paper, in general, the tension of the former is more than 2 times the tension of the latter. Adjusting the tension by this ratio can basically guarantee the continuous paper in printing, and the overprint is accurate and stable.

2. Reduce the printing speed

The faster the press, the higher the paper's tensile force requirements. For light coated paper, no breaks occur when the press speed reaches 40,000 prints/hour; for offset paper, the print speed is typically 32,000 prints/hour, and sometimes only 28,000 print/hour. In production, when the offset paper is printed, it usually occurs when the paper roll is small, especially when the paper is stored. The paper speed displayed on the paper tray display screen is not consistent with the speed of the host computer. For example, the speed before paper storage is 25,000 prints/ Hours, and the speed at which paper is stored at the time of paper storage is 30,000 prints/hour, which means that when the paper is stored, the machine speed equivalent to the host computer is increased by 20%, and the paper tape is easily broken. Therefore, when paper rolls are stored, the speed should be reduced by 1/5 in advance to prevent paper breaks.

3. Automatic cleaning of the blanket when shutting down

When printing light-coated paper, automatic cleaning of the blanket without stopping the machine can increase work efficiency, but this cannot be done when printing offset paper. Because the offset paper is more brittle, paper and paper powder are more, and it is difficult to clean the paper piled on the blanket, and the paper is easy to break when the machine is not stopped. Therefore, the automatic cleaning of the blanket is often used to stop the machine. Not only can the continuous paper be guaranteed, but also each time. The blanket can be thoroughly cleaned.

4. The oven temperature is properly reduced

The oven can heat the print for quick drying, and the higher the temperature, the better the drying effect. Offset paper has good ink absorption performance. When setting the oven temperature, it can be reduced to some extent, but it depends on whether the print product can dry out, whether it is dirty or dirty. Generally, the oven temperature is lower than when using light coated paper. ~20. C can be.

5. Silicon oil concentration ratio is appropriately lower

The role of silicone oil coating is to prevent dirt, dirt, static electricity. Due to the rough surface of the offset paper, the ink absorption performance is much greater than that of the light-coated paper, so the proportion of the silicone oil should be appropriately lower, which is generally half of the printing concentration ratio of the light-coated paper.

6. Concentration ratio of fountain solution is slightly higher

Offset paper has more paper powder and is continuously transferred to the fountain solution during the printing process. Since the paper powder is alkaline, the acidity of the fountain solution is reduced, and the printed product is easily dirty. Therefore, the fountain solution should have a slightly higher concentration, and the water supply should be slightly larger.

7. Clean the water tank and water bucket regularly

The offset paper has more paper powder, and the paper powder is continuously transmitted to the water bucket and the water tank through the water roller, and the printing plate is constantly worn, which reduces the printing plate's resistance to printing force and blocks the filter in the water tank and the water bucket. Therefore, the water tank and the water bucket should be cleaned once a week, and the paper dust and other dirt should be cleaned to prevent the paper powder from harm.

8. Car wash should be done once

There are many paper powders in the ink roller and the water roller when printing offset paper, which not only wears the ink roller and the water roller, but also affects the ink transmission, and it also wears the printing plate to accelerate the aging of the ink roller and the water roller. Therefore, the ink roller and water roller should be cleaned every class to clean the paper powder. Use car wash water before cleaning, then rinse with water.

9. Two-sided application of paper

When printing, it is inevitable that you will encounter a large area of ​​graphic and text, and the other side of the picture is very few cases. When there is a large area of ​​graphic matter on one side where hair loss is extremely serious, we have used methods such as reducing the amount of ink, water, adding additives, replacing inks, changing the printing sequence, and so on, all of which have not been resolved. Finally, we try to change the paper roll to one surface. Printing a large area of ​​graphics with a relatively smooth surface works well.

10. Secondary use of printing plates

Sometimes, because of the printing cycle requirements, the product cannot be printed at once, but it is a pity that the plates that can be used are discarded. We use the manual unloading method so that the printing plate can be used twice. However, be sure to bend the deformed plate in the plate, so that it can be used normally.

Source: Printing Technology