Analysis of the Causes of Mistakes in Paper Supply by Offset Printing Machines

1. The paper curls when the offset is offset

Mainly due to improper layout of water control. 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. Inaccurate delivery due to large print area

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. There is a large distance between the left and right or front and back paper baffles, which is not suitable for the size of the printing paper format, 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. Printed paper flicks up when it enters the delivery table, resulting in uneven delivery

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 easy to appear uneven

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. Paper quality problems

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.