News (rotary), typography and copperplate printing are typical letterpress printing, and their common feature is that they all use metal as letterpress plates (now some of them use plastic plates). Although the printing speed of the former is faster and the printing speed of the latter is slower, their basic printing principles are similar. The printing material of the former is mainly general news (newspaper) paper. Printing is mainly letterpress paper. Copperplate printing mostly uses good coated paper. The inks used in these three kinds of printing are quite different: news ink is non-drying (mainly depends on the penetration and drying of paper absorption), very thin fluid, and copperplate ink is a paste-like fluid that dries faster; The properties of lithographic inks can be somewhere in between.
(1) Feimo
1. Phenomenon : The so-called flying ink (also known as ink flying color) refers to the phenomenon that very small ink particles "fly" out from the running printing machine. These particles are electrically charged. When the climate is dry, they fly A little closer. The ink particles that fly out are drifting.
2. Reason : If the ink is placed on a high-speed rotating roller, it will never throw (throw) the ink out due to centrifugal force, but when the lepton comes into contact with another roller, the flying ink will will happen immediately. This is due to the fact that the filaments are drawn between the two wheels when the ink is transferred, and when the filaments are disconnected, a multi-head (phase) fracture is formed. Except for a part of the shrinkage (pumping) back to the wheel, the rest is due to surface tension. Relationships form droplets that are driven out by the running printing press.
Flying ink droplets can be positively or negatively charged. Due to the breakdown of the electrical double layer that occurs in the oiler, the small particles formed can be individually charged. At this time, the relative charge dissipates in the air to increase the white power. The retracted (drawn) portion of the disconnected ink filament (that is, the portion retracted onto the roller and onto the paper) is also charged. At this point, the dotted ink drop will repel the similarly charged inked roller and move away from the roller.
Microscopic studies of charged ink droplets have shown that carbon black is migratory. One is to migrate to the periphery of the ink drop, and the other is to migrate to the center of the ink drop. Since the carbon black particles are always charged, if the ink has an excessive surface charge, the carbon black will undergo electrophoresis. The ejected ink droplets are very likely to repel each other and scatter.
There are cavities, air bubbles, etc. between the two rollers, which can promote the generation of flying ink.
The printing speed is fast, too much ink is supplied, the relative humidity of the workshop is too low, the temperature is too high, the dielectric constant of the ink is too low, and the influence of air flow can also cause flying ink.
3. Solution : add a cover as much as possible outside the ink set and ink transfer roller of the printing press. A so-called Diefenbach copper wire collection network is used. Increase the humidity in the printing room. Reduce the speed of the printing press (not very desirable, but effective). Reduce the amount of ink to make the ink on the wheel as little as possible. Of course, ink with high concentration should be used. Or use paper with smooth surface and poor absorbency (Japanese ones also reduce ink supply). Reduce the temperature of the printing chamber or install a cooling device on the printing press. Eliminate all possibility of air movement. Water-emulsified oil is used, because it is more conductive, which can also increase the dielectric constant of the ink; generally speaking, when the oil contains 5% water, its electrical conductivity is still very low. Shorten the ink with an anti-offset additive. Add a viscous linking material to the ink. For news ink, it can be made of carbon black with good wettability and relatively viscous mineral oil, and long-chain amines can be used as ink flow agents. Use 0.5% glyceryl monostearate or glyceryl monoricinoleate in the ink or add a small amount of defoaming agent. Install a mechanical device on the stick of the machine: for example, the particles that fly out are blown back by low-pressure air, etc.
(2) Sticky and dirty on the back
1. Phenomenon : The ink on the printed surface of a printed matter stains the back of the above paper. This phenomenon mostly occurs in the solid (or low-key) parts of the printed matter with a large amount of ink. It is generally caused by contact between moments (friction rubbing) and later dryness (slow drying).
Sticking pages, pasting, and blocking (as the saying goes, sticking together --- Blocking) is the most serious phenomenon of sticking back. This is a case of fingerprinted stacks of prints sticking together.
Second Impression Offset (Second Impression Offset) means that the first side is printed immediately after the first side is printed, resulting in stickiness in news printing. This is because part of the wet ink from the first impression is transferred to the second impression cylinder, causing smearing on the second plate. In this type of printing, due to the slow drying of the ink, there is also frequent smudging caused by the guide rollers.
2. Reason : ink drying is too slow. Ink is too soft, too thin and gives too much ink. Sometimes when printing paper with a rough surface, more (thick) oil layers are required to print properly. This phenomenon cannot be ignored: when printing double-sided smooth paper and some special substrates (such as cellophane, plastic film, etc.), they are very easy to approach each other in stacking. In the field and at the denser outlets, due to the relatively large amount of supply. When printed with oxidative and dry inks on non-absorbent paper, it is very easy to smudge. When the amount of desiccant in the ink is too much, it is easy to oxidize and generate heat in the paper pile, resulting in stickiness and sticking of the paper together. Ink chalking causes smearing. Static electricity in the stack causes the sheets to stick to each other, promoting smearing. The ink cuts when it is not dry enough, which can result in many small blotches of ink being pulled up. Improper movement (taking) of paper from corners.
3. Solution : Under the condition of meeting the printing requirements, the less ink supply on the plate, the better. The underlayment should be suitable, this will make the solid parts slightly higher and dry the high-profile parts, and the roller will also allow better transfer of ink to the plate. The backing should enable dots to be solidified with a small amount of ink. For rough paper, relatively high pressure should be used so that more ink can be printed on it, but not too much, so as not to cause sticking due to bumps rubbing against the back of another paper. Ink should be used with a little coupling, but not too thick, so as not to cause paper plucking. Use faster-than-type inks. If you use a new ink, you can print less and study its stickiness before making a corresponding decision. Check whether the ink fountain is adjusted properly? If the sticky phenomenon looks like one by one, it may be caused by uneven adjustment (flatness) of the ink fountain. A plug gauge or thin steel sheet can be used to measure whether the ink fountain is placed consistently. If it is chromatic printing, the latter ink should have more desiccant than the previous ink to shorten the drying time. Check whether the mixing is correct. If the adjustment is not good, streaks (wipe) may be formed , resulting in a very shallow line of sticky dirt. Use powder spraying and anti-sticking agent. Use a bottomless box (a square frame smaller than printed matter paper) to allow the paper to float down slowly under a cushion of air. Pad paper. Keep the printed paper free from dirt from other parts of the machine. Use a static eliminator. Use quick-drying inks instead of general inks, such as wet-setting inks. Use a high concentration of ink to use less ink, especially on slippery, poorly absorbent paper. Add some wax or other anti-sticking dirt to the ink.
(3) crystallization, vitrification, mirror surface
1. Phenomenon : The ink printed later is not printed flat, or cannot be printed at all. Overlay (stack) printing. The oil on the top is latent in the color of the bottom, showing a bead-like or a piece of very high-colored product. Moisturizing inks hold together poorly, and some can even be rubbed off.
2. Reason : The ink on the bottom is too hard (thousand through), and the surface free energy is reduced. The storage time is too long after the previous color is printed. Too many desiccants, especially cobalt desiccants. Or use other fast and vigorous drying methods-such as drying and so on.
3. Solution : Overprint with quick-drying ink that contains more solvents. The solvent used should be able to submerge and soften the ink film of the underlying layer, but sometimes it does not help. Master the overprinting time, and print the second color as soon as possible after the previous color is printed. Add some additives to delay drying in the previous ink, such as vaseline, lanolin, wax additives and so on. Different base colors that are easy to overprint can be used in the pattern design. The cobalt desiccant should be used less in the ink formulation, and the fast-drying resin-type binder can be used to reduce the amount of desiccant in the ink.
(4) Pulverization
1. Phenomenon : The ink on the printed matter can be wiped off like dry powder after drying.
2. Reason : The linking material in the ink penetrates into the paper in a large amount, so that the ink loses its adhesion (connection) effect. The binder used in the ink is too thin or too much non-volatile, non-miscible solvent is used. Paper is too absorbent, allowing the vehicle to penetrate too deeply. The drying of the ink is too slow, which promotes the penetration of the link material. The quality of the linking material used as the binder is too low, or the formed film is easily broken.
3. Solution : Incorporate the structure and consistency of the linking material. Use non-reactive resin and linseed oil, cooking oil or medium-viscosity varnish as a binder. Add a small amount of varnish or varnish to the ink . If possible, try to improve the properties of the ink, and use inks that have good adhesion to pigments and paper. When designing ink formulations, it is better to replace pigments with large specific gravity and low oil absorption with pigments with small specific gravity and large oil absorption, such as Hansa yellow and benzidine yellow instead of chrome yellow.
(5) Don't Drop Ink and Ink Off Series
1. Phenomenon : The ink does not rotate with the ink fountain wheel. Prints are lighter in tone and different shades.
2. Reason : The pigment content in the ink is too high. The ink is too thick and the yield value is too high. The ink is too short and creamy.
3. Solution : Add thin or medium-viscosity linking material to make the oil tank longer. Add a small amount of wetting agent, such as zinc naphthalate, calcium naphthalate, etc. Put a stirrer in the fountain.
(6) pull paper (hair)
1. Phenomenon : Generally speaking, the separation in the paper-ink-printing plate system occurs in the ink film close to the printing plate. Therefore, if the separation occurs on the paper, the surface of the paper will be broken due to the pulling (pulling) force. See Figure 28-1.
2. Reason : Because the ink is too viscous, the adhesion between the paper and the ink is greater than the adhesion between the paper surface coating and the fiber.
Generally, it is easier to happen when printing on the ground with coated paper. The paper is full of holes after being pulled off by the ink, leaving many small spots on the plate. These dots do not stick to the ink and form a ring around the dot after imprinting. If these rings are higher than the plane of the paper, they can also cause smearing. Another reason is that the speed of the machine is too fast.
3. Solution : increase the temperature of the printing room, or let the printing machine idle for a certain period of time to preheat the series. Reduce the viscosity of the ink and lighten it properly, but not too much, so as not to lose the concentration and hiding power. Reduce the printing speed, because the degree of reducing fuzz is directly proportional to reducing the separation ratio of the ink film. Use good coated paper. The paper should not become "green" in quality. Ink should be clean, skin-free and grain-free. Check ink viscosity, dryness and flow. When printing with chrome yellow ink, it should be used to print the first color first.
(7) Paste version
1. Phenomenon : The characters in Indian dramas such as "口", "品", and "晶" are filled with ink into solid shapes. Or the dots are connected into one piece.
2. Reason : The viscosity of the ink is too high, causing small coating spots on the paper or paper scraps and paper wool to concentrate on the plate or dots. The ink in the ink fountain has skins or dry particles. Ink dries too quickly. The ink is too thin and the ink is squeezed out under pressure. The paper absorbs too much binder, resulting in too much pigment in the ink. Wheels are defective or improperly adjusted. The layout is uneven and too tall. Use an ink that is too thick on the gummed paper soil.
3. Solution : Use ink with reasonable dryness and relatively long time. If the ink is too thick, you can add some thinner varnish to increase the distribution performance of the ink. Reduces pressure if pasting in high profile. The appropriate ink should be selected according to the paper. The fineness of the ink is better, generally 20-25 microns.
