Causes and treatment methods of common offset printing ink failures
Poor registration
Phenomenon: During wet-to-wet overprinting, the ink printed later cannot be smoothly attached to the ink printed earlier.
reason:
(1) Compared with the ink printed first, the viscosity of the ink printed later is too high.
(2) The ink printed first is slow to fix and has a large amount of ink.
(3) The color intensity balance of the four-color ink is not appropriate.
Approach:
(1) Print with high-viscosity ink first, and then print with low-viscosity ink. The more satisfactory viscosity requirement is that it should be gradually reduced in the order of overprinting colors.
(2) Use fast-fixing ink to print, and the density is high to print thinner, and the pattern area is small to print first, so as to facilitate subsequent overprinting.
(3) The color strength of any set of wet multi-color overprint inks is balanced, and the same amount of ink can be used for overprinting. If the same set of inks is not used for printing together, it must be handled properly when used.
crystallization
Phenomenon : When overprinting on the dried base ink, it is possible that the post-printed ink cannot be overprinted, and even if it is barely printed, it can be easily wiped off.
Reason : This is because the first printed ink contains too much desiccant, the ink dries too quickly, the interval after printing is too long, and the surface of the ink film forms a smooth hard film, which makes it difficult for the next color ink to ink.
Approach:
(1) Reasonably grasp the interval time of overprinting, and print the next color of ink before the first printed ink is effectively dried.
(2) Reduce the amount of desiccant in the ink and slow down the drying speed of the ink.
(3) If crystallization has occurred, it can be remedied by printing resin binder or 05-90 gloss paste once.
Dirty
Phenomenon: When the printed matter just printed is stacked, the ink on the front is dirty and the back of the printed matter on it is called dirty.
reason:
(1) The fixation and drying of the ink is slow.
(2) The amount of ink is too large.
(3) The surface of the paper is relatively tight and smooth, and its absorption is poor. Ink cannot penetrate and fix quickly on paper.
Approach:
(1) Change to fast-fixing type ink.
(2) Switch to high-concentration ink and use thin-layer printing.
(3) Take the method of surface powder spraying.
(4) Add 59 anti-sticking agent or six grain powder to the ink.
pile of ink
Phenomenon: refers to the accumulation of ink on the blanket, printing plate and ink roller, poor ink transfer and transfer, making the printed ink blurred.
reason:
(1) The ink is too short and lacks fluidity.
(2) High pigment content, coarse particles, high specific gravity, insufficient grinding, and insufficient wetting.
(3) The viscosity of the ink and the binder is low, and the emulsification occurs with the fountain solution.
(4) The paper powder is peeled off and mixed into the ink to shorten the ink.
Approach:
(1) Add a resin binder with good water resistance that can make the ink longer.
(2) Change to high-concentration pigments, properly reduce the amount of pigments and solids, and re-roll the ink.
(3) Minimize the amount of dampening solution as much as possible and replace it with ink with good water resistance.
(4) Appropriately add some 05-92 detackifier to reduce viscosity. If invalid replace the paper. The ink should be replaced when peeling.
Dirty
Generally, it refers to the dirt in the non-graphic area. It also includes imprinting auxiliary, paste, dot paralleling and other phenomena. However, dirt can be divided into floating dirt and oil dirt. Now it is described as follows:
1. Floating dirt
Phenomenon: There is light color stain in the non-graphic area, which is easy to wipe off because it is not stained from the printing plate.
Reasons: (1) The main reason is that the ink is relatively soft, and after being affected by the fountain solution, some ink enters into the fountain solution due to emulsification, forming an oil-in-water emulsion.
(2) Chemicals and wetting agents in the paper promote ink emulsification. (3) Soap or detergent contained in the fountain solution causes ink emulsification.
Approach:
(1) Change to high-viscosity, thicker and difficult-to-emulsify ink, or add high-viscosity varnish to the original ink.
(2) Replace the paper.
(3) Adjust fountain solution components and PH value.
2. Oil dirty
Phenomenon: The non-graphic area of the printing plate becomes fat-sensitive, and the ink adheres to it, staining the printed matter.
reason:
(1) The ink is too soft and thin.
(2) The amount of ink supplied is too large.
(3) There are free fatty acids, resin acids and surfactants in the ink.
(4) The influence of the processing agent in the pigment.
(5) The pressure of the ink form roller, dampening roller and blanket is too high, which damages the surface structure of the printing plate.
(6) Dissolving fat-sensitive substances from paper coatings.
Approach:
(1) Replace the ink or add high-viscosity resin oil (or No. 0 oil) and colloidal oil to the original ink to make the ink viscous and elastic.
(2) Adjust the amount of ink supply.
(3) Adjust the proper amount of dampening solution.
(4) Use fountain solution with high surface tension.
(5) Adjust the pressure properly.
(6) Replace the paper.
