The method to solve the uneven paper collection of the offset printing machine during the offset printing process. During the offset printing process, due to the straightening mechanism of the offset printing machine, the front and back, left and right paper sorting baffles, the paper collection teeth, the improper adjustment of the paper brake, the plate plate moisture, the printed product graphics The large area, and the thin paper, flatness, unevenness and other reasons, it is easy to cause the uneven paper collection of the offset press receiving table, and even make the paper corners, fold the printed matter out of the crease, affect the quality of the product, and give the printed sheet The binding, sorting, and statistical quantity of the software caused trouble.
The quality requirements of the paper collection table of the offset printing machine are loose, well-collected, piled flat, without angles, crushing losses and oily debris, especially printing semi-finished products, requiring trailing and biting, front and back positions Don't turn it upside down, try to avoid the untidy paper collection and disorder. There are many reasons for the uneven collection of offset printing. The specific offset printing operation should be comprehensively inspected and analyzed to solve the problem in a targeted manner.
1. During curling, the paper curls unevenly, mainly due to improper moisture control of the plate. Generally speaking, the paper moisture content should be in a smooth state under normal circumstances, and the paper fiber absorption capacity is strong. However, when the water content of the printing plate is too large, and the paper moisture content exceeds the normal limit, its fibers will absorb water and swell, causing the paper to deform and curl. In this way, the paperboard of the paper collection component cannot control the soft and curled paper, resulting in uneven paper collection. failure. Offset printing should strictly control the moisture content of the plate, and use the least amount of water under the premise that the plate is not dirty; adjust the water supply according to the position of the graphic distribution of the plate to reduce the bending deformation of the paper and avoid uneven paper collection.
2. Uneven paper collection caused by large graphic area of ​​printed products. When printing printed materials with a large solid area, the paper often curls downwards, especially when the paper has poor mechanical strength and the ink viscosity is high. Offset printing ink is oxidized and conjunctive type drying. Under the pressure of the printing plate and rubber roller, the printed ink is not dry, which affects the flatness of the paper and causes uneven paper collection.
When printing the full version of the field, you can take the appropriate method to reduce the printing speed and reduce the viscosity of the ink; for products with large graphics and text area, pay attention to adjusting the printing color sequence, and add rubber bands and gauze strips on the cardboard of the receiving table Other methods can also be effective on paper that curls downwards, so as to achieve the purpose of neatly collecting paper.
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3. The distance between the left and right or front and rear paper sorting baffles is large, which is not suitable for the size of the printed paper, resulting in uneven paper collection. At this time, adjust the extension and position of the left and right or front and rear paper sorting flaps to be the same size as the printing paper or a little larger.
In addition, if the swing time of the paper sorting flaps on the front, back, left, and right sides of the paper collection table is incorrect, the printing paper is hindered during the falling process and cannot fall into the paper collection table smoothly, which may also cause uneven paper collection. The position of the control cam of the paper trimming baffle should be adjusted so that its swing time is coordinated with the time when the paper is collected and the teeth are placed to ensure that the paper is collected neatly.
4. The printed paper moves up when entering the delivery table, resulting in uneven delivery. This is due to the poor stress of the printed paper itself, on the other hand, it is caused by the failure of the suction wheel of the printing sheet brake or the suction wheel suction is too small. After the suction wheel loses function, you can take out the things that are blocked by the small holes on the wall of the suction wheel, clean the paper dust and dirt on the suction wheel and use it. If the wind of the suction wheel is too small, it can be adjusted up. Suction.
5. The paper collection teeth in the chain paper conveyor are too early or too late to allow the printed paper to enter the paper collection table accurately, and the problem of uneven paper collection is also prone to occur. At this time, it is necessary to adjust the timing of the teeth of the paper collection teeth to facilitate the paper to enter the paper collection table in a timely manner.
6. When printing, if the paper is too thin, it is often prone to uneven delivery. Because the size of offset printing paper is usually large (more than four sheets of paper), we need to wet the printing plate with water, if the paper is too thin. (35g /? 28g /?), After passing between the impression cylinder and the rubber cylinder, the water will be transferred to the paper through the blanket, the paper will be soft and weak, and it is difficult to collect the paper, so the offset paper is best protected Above 52g / ?, to ensure that the paper collection table is tidy.
7. Due to paper quality reasons such as poor flatness and uniformity, the paper tends to roll down, curl up, bow, wrinkle, and ruffle when the paper enters the paper collection table, causing uneven paper collection. Before printing, the above-mentioned poor-quality paper should be carefully hung and humidified. After hanging, it should be stored in a warehouse or an offset printing workshop for a period of time. The paper stack is put on a paper plywood board, and heavy objects (large stones, Iron plate, etc.) to make it flat, the paper on the machine except the coated paper should be knocked to increase the stress of the paper.
8. The relative humidity in the offset printing workshop is too low, especially in winter when the climate is dry, the paper has too little water content, and it is easy to generate static electricity, which causes the paper to suck each other and appear to be uneven. In this case, you can use a static eliminator to eliminate static electricity or increase the relative humidity of the workshop, especially in dry weather in winter. If conditions permit, you can use a humidifier to adjust the humidity of the workshop. In addition, the offset printing workshop should open windows as little as possible, and the glass windows should be sealed, and some water can be sprinkled on the floor of the workshop to adjust the humidity.
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