1. Correctly understand the relationship between printing pressure and ink layer thickness
Appropriate printing pressure is an important condition for achieving uniform transfer of the ink layer on the plate surface. Insufficient or uneven printing pressure on the plate surface will affect the uniform transfer of the ink layer. When the pressure on the layout is insufficient or uneven during printing, the ink color of the printed product will be blurred, and the thickness of the ink color on the entire layout will also be inconsistent. Increasing the amount of ink can indeed make up for the defects caused by the poor contact between the ink layer of the layout and the substrate caused by insufficient printing pressure, but it is also easy to cause smearing of the printed product. Therefore, you should adjust the printing pressure first, and then adjust the ink delivery on the layout, so that you can get a good printing effect.
2. Handle the relationship between the printability of the paper and the thickness of the ink layer
Paper with poor surface smoothness has fast ink absorption and large ink absorption. When printing this kind of paper, if the printing pressure is insufficient or uneven, it will be easy to show up after printing. If the ink volume is increased, the ink layer will be thicker, and if the printing speed is slow, smearing will easily occur. For paper with poor surface smoothness, the printing pressure should be increased accordingly; for paper with good surface smoothness, such as coated paper and glass cardboard, the ink layer should be as thin as possible to avoid smearing. From the perspective of anti-adhesion, printing large-area plates should adopt "dark ink thin printing", that is, the hue of the ink should be adjusted to a darker, and the ink layer should be thinner, so that it can not only meet the requirements of printing hue, but also Avoid dirt.
3. Grasp the relationship between the characteristics of the plate and the thickness of the printing ink layer
The quality of the plate, the thickness of the printing ink layer and the printing pressure have a certain relationship. If the smoothness of the plate surface is poor, the ink layer and pressure required for printing are large; on the contrary, it is small. If the zinc plate is used for printing, due to its poor ink affinity and poor surface gloss, only increasing the printing pressure and the thickness of the ink layer can achieve the effect of full printing ink layer, but this can easily lead to smearing, so it is not suitable to use zinc plate Color printing products with more than octave format. Because the photosensitive resin plate has good surface gloss, soft texture, good flatness and ink affinity, its printing ink layer is correspondingly thinned, and it can still achieve better printing results, and it is not easy to smudge. Therefore, photosensitive resin plates should be used when printing large-area images.
4. Avoid dirt on the back caused by improper printing ink layer thickness
To determine whether the printing ink layer is moderate, the main basis is that the printing plate is evenly pressed, the plate is evenly pressed to achieve no bottoming, no false printing, and the hue of the printed product is consistent with the sample manuscript. If the printing pressure is uneven or insufficient, the gloss of the printed paper is poor, the hue of the printed manuscript is dark, and the ink hue is lightly adjusted, it will easily lead to inaccurate judgment of the printing ink layer thickness. At this time, if you blindly increase the ink volume, If the ink layer is too thick, the back of the printed product will be smeared.
5. Avoid dirty printing caused by improper operation
(1) Improper adjustment of the ink roller, excessive or uneven ink volume
When there is a large gap or eccentricity between the ink roller head and shaft hole due to wear; when the elasticity of the ink roller gel becomes poor, the ink roller will not evenly contact the plate surface during the rolling and ink brushing process, which is easy to cause local ink brushing on the plate surface. Uneven, thin ink layer appears. In addition, if the ink roller is adjusted too high or one head is too high, it is easy to cause insufficient or uneven coating of the ink layer on the plate surface. At this time, if the ink volume is increased blindly, the ink layer on the partial plate surface will be thicker and cause smearing. Therefore, when printing large-area plate products, the ink roller is required to have high precision, good roundness, appropriate softness and hardness of the rubber roller, uniform contact between the ink roller and the inking roller, and the height adjustment should be accurate to reduce the occurrence of smearing on the printed product. chance.
(2) Improper receipt of papers
When printing and receiving paper, you should accurately adjust the angle and height of the falling paper according to the size of the printed product and the hardness of the paper. Otherwise, the edge of the printed sheet will easily touch the mark of the previous printed sheet, which will damage the ink on the surface of the printed product. In addition, the printed sheets should be handled gently to prevent the upper and lower printed sheets from moving and friction causing stickiness. The quantity of air-drying paper should be grasped according to the ink-receiving condition of the printing plate, so as to prevent heavy pressure and stickiness.
(3) The bottom support of the printing plate is not solid and the pressure is uneven
The plywood material is not solid enough, and the compression deformation coefficient is large. If this material is used as the bottom support of the printing plate, the printing pressure and the thickness of the ink layer must be increased, so it is easy to make the printed product sticky. Therefore, it is best not to use the plywood bottom support when printing on the ground. A magnetic plate table or other metal bottom support should be used to make the printed ink layer thin and not expensive, which is beneficial to prevent sticking and staining.
(4) The paper is too acidic, the climate is humid, and the printed products are not easy to dry.
When printing with offset paper or some domestic copperplate paper, because the printing ink layer is thick and the paper is acidic, the ink layer is not easy to dry, and it is also prone to smearing. At this time, dry oil should be appropriately added to the ink to prevent the printed product from sticking.
(5) Knock the crease of the paper to cause friction on the printed product
When printing coated paper, since the surface of the paper is relatively smooth, if the paper crease is prominent, it is easy to rub against the print and cause stickiness. Therefore, knocking the paper should be mastered according to the layout structure and paper characteristics. For thicker coated paper, try not to knock, and only use the method of kneading up or down, and knead the paper straight and firm.