How to solve the uneven delivery of the offset printing press

Solve the problem of uneven delivery of the offset press in the offset printing process. During the offset printing process, due to the offset mechanism of the offset press, the paper flapper, paper delivery teeth, paper brakes are improperly adjusted, and the plate layout moisture is large. Large areas, and thin paper, flatness, poor formation and other reasons, easily lead to the uneven delivery of the offset press delivery table, and even make the paper appear folded, fold the print creases, affect product quality, and give the printed sheet The number of bindings, sorting, and statistics, etc., caused trouble.

The quality requirements for the delivery press of the offset printing press are loose, balanced, flat, with no corners, crushing loss, and oil debris, especially for semi-finished products, requiring the tipping and biting, and the positive and negative sides. Can not be reversed, try to avoid the receipt of paper is not neat, messy phenomenon. The reasons for the uneven offset of offset printing are various, and the specific offset printing operations should be comprehensively inspected and comprehensively analyzed to solve problems in a targeted manner.

1. In the offset printing, the curling of the paper is uneven, mainly due to improper control of the layout moisture. In general, the moisture content of the paper should be in a flat state under normal conditions, and the paper fiber absorption ability is strong. However, when the water in the printing plate is too large, and the moisture content of the paper exceeds the normal limit, the fibers will absorb water and swell, causing the paper to be warped and curled. This causes the paperboard of the delivery part to be incapable of controlling the soft and weak curled paper, resulting in uneven delivery. failure. Offset should strictly control the layout of the water, in the premise of not dirty version, the use of the least amount of water; according to the location of the layout of the plate layout, to adjust the amount of water supply, in order to reduce the paper's bending deformation, to avoid uneven delivery.

2. The large area of ​​the printed product's graphics and texts caused the delivery to be uneven. When printing large-scale prints on the ground, paper curling often occurs, especially when the mechanical strength of the paper is poor and ink viscosity is large. Offset printing ink belongs to the oxidized conjunctiva type drying. Under the pressure of the printing plate and the rubber two rollers, the freshly printed ink sheet is not dry, affecting the flatness of the paper and causing the paper to be delivered unevenly.

When the full-print version is printed in the field, the printing speed can be appropriately reduced to reduce the viscosity of the ink. For products with large printed image area, attention should be paid to adjusting the printing color sequence. Rubber bands and gauze strips can be added to the receiving paper board. Such methods can also be effective on the downward curled paper, and achieve the purpose of receiving paper in order.

3. The distance between the left and right or front and back paper baffles is large, and it is not suitable for the size of the printing paper web, resulting in uneven delivery. In this case, adjust the left and right or front and rear wipers to adjust their position and height so that they are the same size or slightly larger than the print size.

In addition, if the timing of the swinging of the paper damper in the front and rear of the delivery table is not correct, the printing paper will be hindered from falling into the falling process, and it will not be able to fall into the delivery table smoothly. The position of the control flapper control cam should be adjusted so that its swing time coincides with the time it takes for the delivery to catch the paper to ensure that the paper is received neatly.

4. The printed paper flicked upwards when it entered the delivery table, causing the paper to arrive unevenly. This is due to the poor stress of the printed paper itself, and on the other hand due to the failure of the suction wheel of the print brake or the suction of the suction wheel being too small. After the suction wheel loses its function, it can pick out things stuck in the holes in the suction wheel wall and clean the paper dust and dirt on the suction wheel. If the suction wheel is too small, adjust it Suction.

5. The delivery of the teeth in the chain-type paper feeder is too early or too late to allow the printed paper to accurately enter the delivery table, and the problem of uneven delivery is also likely to occur. At this time, it is necessary to adjust the time for the teeth to reach the receiving end so that the paper can enter the delivery table at a proper time.

6. When printing, if the paper is too thin, it is often prone to paper misfeeds. Since the offset printing paper is usually larger in web size (above four sheets of paper), it needs to moisten the printing plate with water, and the paper is too thin. (35g/m228g/m2), after passing between the impression cylinder and the blanket cylinder, the moisture will be transmitted to the paper via the blanket, the paper will be soft and weak, it will be difficult to close the delivery, so it is better to protect the offset printing paper. Above 52g/m2, to ensure that the delivery table is neat and tidy.

7. Due to paper quality reasons such as: flatness, poor uniformity, often cause the paper to enter the paper delivery table when the next roll, upturned, bow, wrinkle, lotus leaf and other phenomena, resulting in uneven delivery. Before the printing, the above-mentioned poor-quality papers should be carefully handled by hanging and drying. After the hanging, they should be put in the warehouse or stacked and stored in the offset printing shop for a period of time. The paper baskets should be put on paper plywood and the heavy objects (large stones) should be pressed. Iron plate, etc.) to make it flat, the paper on the machine in addition to coated paper to knock processing, in order to increase the paper's stress.

8. The relative humidity of the offset printing shop is too low, especially when the climate in winter is dry. The water content of the paper is too small, and static electricity is easily generated. As a result, the paper sucks each other and the paper is not evenly distributed. In this case, you can use static eliminators to eliminate static electricity or increase the relative humidity in your workshop, especially in the dry weather in winter. If possible, humidifiers can be used to humidify the workshop. In addition, the offset printing shop should minimize windows, glass windows should be sealed, and some water can be sprinkled on the floor of the workshop to regulate humidity.