Reasons and Treatments of Paper Loss and Powder Removal in Offset Printing Process

Paper is composed of raw materials such as fibers, lignin, resins, fillers, compounds, and colorants.

Paper lint and powder removal are caused by the fact that the fibers on the surface are not sufficiently strong and dense. In the printing process, when the paper and the rubber are peeled off, a certain pulling force is formed between them due to mutual adhesion. If the paper fiber structure is firm and dense, no hair loss phenomenon occurs. On the contrary, it is easy to pull down the fibers on the surface of the paper to cause depilation.

In the printing process, the offset printing press is generally operated at a speed of 6,000 sheets per hour, 10,000 sheets, and at a high speed, and the transfer of the graphics on the printing plate is completed within a short instant. In this brief moment there is an extremely complex mechanical interaction between the ink on the plate and the paper. The speed of the offset press is very fast. Accordingly, the influence of the inertial force is relatively increased. To make the ink transfer to the paper ideally, the paper must have a certain surface strength.

Paper lint can cause dirty prints, directly destroying the sharpness of the print on the print sheet, and reducing the print quality.

The reason why the paper produces powder and hair loss is not due to the low surface strength of the paper, but the improper selection of fillers and rubber materials. In addition, it is also produced in the case of high-speed printing.

The occurrence of lint and powder failure on the paper is generally caused by the poor quality of the paper. In addition to recommending that papermakers improve the quality of their products and require the return of their products as soon as possible, operators of printing companies may also take appropriate remedial measures based on the specific conditions of the printed paper:

1) Due to raw materials and manufacturing processes, the paper may be de-powdered and lost in the printing process and accumulated on the surface of the blanket, thus affecting the correct transmission of the dots. In severe cases, the blanket must be wiped every 1,000 sheets or so. Otherwise, the blanket is covered with powder off, and the gloss of the printed product is significantly reduced. Under conditions, if white ink and clear water are overprinted on the surface of the paper, the blanket should generally be scrubbed.

2) Properly adjust the viscosity of the used ink, add an appropriate amount of scuffing agent and diluent to the ink, reduce the viscosity of the ink, in order to improve the adhesion of the ink on the paper. Because the ink viscosity is too large, it is easy to make the paper lose powder.

3) Adjust the printing pressure so that the embossing force between the blanket cylinder and the impression cylinder is appropriately reduced. Or choose the right printing speed, and properly reduce the speed. In this way, after the imprint, the peeling force between the blanket and the sheet can be reduced.

4) When the blanket is used for a long time, a vulcanization reaction occurs, or when it is affected by light, heat, and wear, especially in summer, the old blanket is liable to become sticky and cause hair loss and powder removal. At this point, you can apply a layer of sulfur powder on the blanket. If it is not enough, you have to replace the new blanket.

5) For papers that are susceptible to lint removal and deinking, such as offset paper, relief paper, writing paper, etc., paper must be processed before printing to disperse paper dust, paper dust, paper dust, and dust on the surface of the paper. Paper and other clean.

Offset printing differs from other printing methods in that it uses "water" for offset printing, and the emulsification of ink, the stretching and deformation of paper, etc. often occur in "water", and the deinking and lint removal of paper is similar to offset printing. Direct relationship.

The paper used in offset printing generally must be filled and treated. In order to increase the retention rate of the added filler in the paper, the surface strength of the paper and the glossiness of the paper should be improved, and the paper should have a certain degree of sizing, otherwise the paper is After contact with water, it will cause softness and weakness, resulting in undesirable phenomena such as shedding of fillers.

Author: Wang Town

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