Printing FAQ
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First, get dirty
Generally, it means that the non-image area is dirty. It also includes the phenomenon of imprinting, paste, and dot-linking. However, the dirty can be divided into two cases of floating dirt and oil dirty. It is now described as follows:
1, floating dirty
Phenomenon: It produces light stains in the non-image area. Because it is not dyed from the printing plate, it is easy to wipe off.
Reasons: (1) Mainly the ink is relatively soft. After being affected by the dampening solution, some of the ink enters the dampening solution due to emulsification to form an oily emulsion in water. (2) Chemicals and wetting agents in the paper promote ink emulsification. (3) The fountain solution contains soap or detergent to cause ink emulsification.
Treatment method: (1) Replace the viscous ink with high viscosity and thickness, or add high viscosity varnish to the original ink. (2) Replace the paper. (3) Adjust the dampening solution component and pH value.
2, oil dirty
Phenomenon: The non-image area of the 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) Free fatty acids, resin acids, and surfactants are present in the ink. (4) Effect of the treatment agent in the pigment. (5) The pressure of the inking roller dampening roller and the blanket is too large, which damages the surface structure of the printing plate. (6) Dissolving the lipid material from the paper coating.
Treatment method: (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 sticky and elastic. (2) Adjust the amount of ink supplied. (3) Adjust the appropriate amount of dampening solution. (4) Use a dampening solution with a high surface tension. (5) Adjust the pressure. When (6) replace the paper.
Second, poor overprinting
Phenomenon: The ink printed on the back of the wet-on-wet overprint cannot be smoothly attached to the first printed ink.
Reasons: (1) The ink density of the post-printed ink is too high compared to the ink that is printed first. (2) The ink that is printed first is slow to fix and the amount of ink is large. (3) The color intensity balance of the four-color ink is not appropriate.
Treatment method: (1) Printing with high viscosity ink, printing with low viscosity ink, the ideal viscosity requirement should be reduced in the order of overprint color. (2) It adopts a fast-fixing ink mark, and the density is printed to be thinner, and the pattern area is small and printed first, so as to facilitate overprinting. (3) Any set of wet multi-color overprinting inks whose color intensity is balanced, can be used to apply the same amount of ink when overprinting. If it is not printed with the same set of inks, it should be handled properly.
Third, crystallization
Phenomenon, when overprinting on a dried base ink, it is possible to overprint the ink of the post-printing, and even if it is barely printed, the pool can be easily wiped off.
Reason: This is because the ink printed first contains too much desiccant, the ink dries too fast, the interval between prints is too long, and the surface of the ink film is formed by a smooth hard film, which makes it difficult to ink the next color ink.
Treatment method: (1) Reasonably master the interval of overprinting, and print the next color ink before the ink of the first printing is completely 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 a resin binder or 05-90 gloss paste.
Fourth, sticky
Phenomenon: When the printed printed matter is stacked, the ink on the front side is sticky and the back of the printed matter on the back of the printed matter is sticky.
Reasons: (1) The fixing 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 the absorption is poor. The ink does not penetrate and fix quickly on the paper.
Treatment method: (2) switch to fast fixing type ink. (2) Switch to high-concentration ink for thin-layer printing. (3) Adopt the method of surface dusting. (4) Add 59 anti-sticking agent or six-grain powder to the ink.
Five, stacking ink
Phenomenon: It means that the ink is accumulated on the blanket, the printing plate and the ink roller, and the transferability of the ink is poor, which makes the ink color of the printing object.
Reasons: (1) The ink is too short and lacks fluidity. (2) High pigment content, coarse particles, large specific gravity, insufficient grinding, and insufficient wetting. (3) The viscosity of the ink and the binder is low, and milking occurs with the fountain solution. (4) The paper powder is peeled off and mixed into the ink to shorten the ink.
Treatment method: (1) A resin binder which is excellent in water resistance which can lengthen the ink is added. (2) Replace the pigment with high concentration, and reduce the amount of pigment and solid content to re-roll the ink. (3) Try to reduce the amount of dampening solution, such as countless inks that can be exchanged for good water resistance. (4) Appropriately add some 05-92 debonding agent to reduce viscosity. Replace the paper if it is invalid.
Six, flying ink
Phenomenon: When the printing machine is running, the ink splits between the printing machine's ink rollers, and the long ink forms long filaments. These filaments break into fine droplets and are scattered in the mist and distributed in the air of the printing workshop.
Reason: (1) Printing speed is too fast. (2) Too much ink is supplied, and the ink layer on the ink roller is too thick. (3) The ink is too long and too sticky. (4) The ink roller is not properly installed or damaged.
Treatment method: (1) Reduce the printing speed. (2) Switch to a high color ink to reduce the amount of ink. (3) Add wax additives to make the ink shorter and lower the viscosity. (4) Check the ink roller and open the ink fountain to adjust the ratchet to make the rotation faster.
Seven, the ink does not fall
Phenomenon: The ink in the printing lacks fluidity and cannot be transferred from the ink fountain to the ink roller.
Reasons: (1) The yield value of the ink is too large, and the ink ink has a short fluidity. (2) The ink thixotropy is large.
Treatment method: (1) Add #3 varnish which can lengthen the ink or a high-viscosity resin oil which improves the fluidity of the ink. (2) Frequently agitate the ink or install a stirrer in the fountain. (3) Switch to a good fluidity ink.
Eight, paper lint or powder
Phenomenon: When printing, the fibers or filler particles are dropped from the surface of the paper and piled on the graphic of the blanket to reduce the quality of the printed product.
Reason: (1) The paper quality is poor. (2) The viscosity of the ink is large, or the viscosity is increased due to evaporation of the solvent in the ink. (3) Printing speed is too fast. The printing pressure is too high, causing excessive friction between the paper and the blanket.
Treatment method: (1) Replace paper. (2) Add #6 varnish or 05-92 detackifier to reduce the initial viscosity of the ink. (3) Adjust the printing pressure and reduce the printing speed.
Nine, emulsified
Phenomenon: In the lithographic printing, the ink and the fountain solution are subjected to high-speed extrusion contact, and the ink and the fountain solution are emulsified to form an oil-type water emulsion. The fluidity and viscosity of the ink are changed, the printability is deteriorated, and the drying becomes slow, resulting in printing failure. In addition, when the oil-based emulsion is formed by emulsification, the ink particles are dispersed in the fountain solution to cause floating.
Reasons: (1) Polar substances and surfactants are present in the ink. (2) A low viscosity oil is used. (3) The amount of wet plate solution is large. (4) The graphic area is small, the ink consumption is small, and the ink on the printing machine is emulsified by contact with water for a long time.
Treatment method: In lithography, the ink and dampening solution should form a moderate oil-in-water emulsion to make the printing go smoothly. If the emulsification becomes a printing failure, it is necessary to solve various situations and take various countermeasures.
Ten, ring white spots
Phenomenon: Ring-shaped white spots appear in printed graphics.
Reason: (1) The ink drying film is mixed into the ink and attached to the printing plate blanket. (2) Paper powder, dust and other foreign matter are mixed into the ink.
Treatment method: (1) Do not mix the ink dry film into the ink when removing the ink in the tank. (2) Replace the paper. (3) Carefully clean the ink fountain, ink roller, blanket and plate. (4) It is necessary to replace the ink when there is ink in the ink.