Influencing factors of different shades of printed ink
In offset printing, the phenomenon that the ink color of the printed product is dark before and then dark or light before dark sometimes appears (in terms of pressure, it is shown as heavy before light or light before heavy), which affects the quality of the print. The reasons for such phenomena can be analyzed from the aspects of the roller, ink roller and water roller.
(1) The center of gravity of the roller is biased towards the middle of the mouth, and the front is deep and then shallow, which is front to back and light; the side to the trailing side is shallow and front to back, which is front and back. This is caused by the inconsistent pressure between the mouth and the tip of the roller when the roller is rolling. The dots on the side with heavy pressure increase and the ink color is dark; the dots on the side with light pressure shrink and the ink color is light.
(2) The change in the radius of the printing surface of the cylinder can also cause malfunctions. For example, the pad of the cylinder produces pleats, or the quality of the pad is poor, and the thickness is inconsistent. As a result, the pressure is inconsistent, resulting in different ink shades.
(3) The pressure between the inking roller and the inking roller is too light, resulting in uneven ink transfer, large and small. In particular, the pressure between the inking roller and the inking roller and the printing plate must be adjusted evenly, not light and heavy. It should be noted that the pressure of the inking roller and the printing plate is greater than the pressure of the inking roller and the inking roller to facilitate the separation and transfer of ink.
(4) The diameter of the inking roller should not be too small, otherwise the amount of ink transfer cannot reach the demand for printed graphics.
(5) The surface of the inking roller is aging, and the capillary hole is changed to a smooth surface, which causes uneven ink transfer and is prone to failures in inconsistent ink colors. This type of ink roller can be grinded under the condition that the diameter allows, to roughen its surface and increase the absorption and transfer performance of ink. Especially after printing the varnish, the ink roller should be carefully washed (the varnish remains on the ink roller to crystallize the surface of the ink roller and fill the pores on the ink roller. In severe cases, the rubber on the ink roller will be pulled out, causing Ink roller scrapped).
(6) The pressure adjustment of the water roller and the printing plate and the pressure adjustment of the water roller and the water roller are inconsistent, which causes the water to rise and fall, affecting the adsorption of the ink on the plate.
(7) Uneven water supply caused by the bending of the water roller should be replaced in time.
(8) When installing the water velvet cover, there are foreign objects loaded, which causes the water roller radius to change and affect the uneven water supply.
Author: Tai in Shandong Daily printing plant Li Chao
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