General problems and solutions in the application

General problems and solutions in ink application

the printing process depends on four factors: operators, printers, substrates and inks. There will be some common problems in different printing processes. These problems are related to the formula, production process and testing methods of the ink. Only the ink manufacturer exercises strict control over the production process of the ink and implements scientific measurement of the ink, can the problems in the use of the ink be reduced, This paper introduces some problems that may appear in the printing process, which are related to the quality of printing film with the output of about 5billion ports per year

1. Sticking and rubbing on the back

due to the slow drying of the ink, the ink is too soft, too thin, and the amount of grade ink is too large, resulting in the ink on the printed surface fouling the back of the upper paper. Jinan actually prevents dust from falling into the equipment. The machine inspection industry association formally formed a facade on September 27, 2014

this phenomenon mostly occurs in the field (or low-key) part with a large amount of ink on the printed matter. Sticking pages, pasting and chunking (as the saying goes) are the most serious phenomenon of sticking back, which is the situation that a pile of printed materials with good fingerprints are stuck together. Sticky dirt on the second side refers to printing the second side immediately after the first side is printed, resulting in sticky dirt in printing

there are several situations that cause this phenomenon: when there is paper with rough printing surface, it needs more (thick) ink layers to print; When printing double-sided smooth paper and some special substrates (such as cellophane, plastic film, etc.), they are very close to each other in stacking; The ink volume is too large in the field and at points with high density; When printing with oxidation drying ink on non absorbent paper, it is very easy to get dirty; When the amount of desiccant in the ink is too much, it is easy to oxidize and generate heat in the paper pile, causing the ink to stick and make it dirty; Cutting the ink when it does not dry well will lead to pulling up many small ink stains, improper moving (taking) of the paper from the corners, and so on

the solution is: under the condition of meeting the printing requirements, the less the ink supply on the plate, the better. Rough paper should be under relatively high pressure so that it can be printed with more ink, but not too much, so as not to cause bulges and rub the back of another paper and get dirty. A little thick ink should be used, but it should not be too thick, so as not to cause plucking. If a new ink is used, you can print less and study its dirt before making a corresponding decision. Check whether the adjustment of the ink fountain is proper. In case of chromatic printing, the latter ink should be added with more desiccant than the former one to shorten the drying time. Use quick drying ink instead of general ink, such as wet set ink. In the case of smooth paper and poor absorption, the use of high concentration ink can reduce the amount of ink used. This wax or other anti sticking agents can also be added to the ink

2. Flying ink

the so-called flying ink (also known as ink flying color) refers to the phenomenon that very small ink particles "fly" from the running printing press. Flying ink particles are floating. These particles are electrically charged. When the climate is dry, they fly closer. If the ink is placed on a high-speed rotating roller, it will never throw (throw) the ink out because of centrifugal force, but when this roller contacts with another roller, ink flying will occur. This is because when the ink is transferred, the filaments are pulled out between the two rollers. When the filaments are broken, multiple head (phase) fractures are formed. Except that some of them are retracted (drawn) back to the rollers, the rest are expelled by the running printing machine due to the formation of droplets due to the surface tension. Flying ink drops can be positively or negatively charged. Due to the split of the electric double layer in the ink, the small particles formed can carry a single charge. The retracted part (i.e. the part retracted to the roller and printed on the paper) of the disconnected ink head is also charged. At this time, the charged ink drops will repel the ink roller with the same charge and move away from the roller. After studying the charged ink drops with a microscope, it is found that carbon ink has a migration effect. One is to migrate to the periphery of the ink drops; One is to migrate to the center of the ink drop. Because the carbon ink particles are always charged, if the ink drops have excessive surface charge, the carbon black will electrophoresis, and the expelled ink drops are very easy to repel each other and fly away

there are holes and bubbles between the two rollers, which can promote the flying ink. The printing speed is fast, the amount of ink is too much, the relative humidity of the plant 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 the flying ink

the solution is: add a cover outside the ink leveling roller and ink transfer roller of the printing machine as much as possible; Improve the humidity of the printing room; Reduce the speed of the printing machine; Reduce the amount of ink to make the ink on the roller as little as possible. At this time, of course, the ink with high concentration should be used; Use paper with smooth surface and poor absorption (the purpose is to reduce the amount of ink); Reduce the temperature of the printing room or install a cooling device on the printing machine; Eliminate all possibilities of air flow; Using water emulsion ink, because it has conductivity, which can also increase the dielectric constant of the ink. Generally speaking, when the ink contains 5% water, its conductivity is still very low; Use anti stick and dirty additives to shorten the ink; Add sticky binders to the ink; For inks, carbon black and mineral oil with good wettability can be used, and long-chain amines can be used as the flow agent of inks; Use 0.5% glyceryl monostearate or glyceryl ricinoleate in the ink or add a small amount of defoamer; Install a mechanical device on the roller of the machine, such as using low-pressure air to blow back the flying particles, etc

3. Do not lower the ink and ink take-off roller

when the pigment content in the ink is too high; The ink is too thick and the yield value is too large; When the ink is too short and becomes cheese like, the ink does not rotate with the ink bucket roller, which will cause the printing color tone to be shallow and the depth to be different. Offset printing ink is too easy to be emulsified by fountain solution, making the ink lose its bonding effect; Too much water; The potion is too acidic, wetting the metal roll

the solution is: add a thin or medium viscosity binder to make the ink longer; Add a small amount of wetting agent, such as zinc naphthenate, calcium naphthenate, etc; For offset printing process, reduce the amount of fountain solution; Reduce the concentration of fountain solution; Add a binder or diluent with high viscosity and long (i.e. good fluidity) to offset printing ink

4. Generally speaking, the separation effect in the paper ink printing plate system occurs in the ink film close to the printing plate. If the separation occurs on the paper, the surface of the paper will be broken due to the pulling force. Because the ink is too sticky, the adhesion between the paper and the ink is greater than the adhesion between the paper surface coating and the fiber, causing galling, or the machine speed is too fast will also cause galling

the solution is: increase the temperature of the printing workshop, or first idle the printing machine for a certain time to preheat the rollers; Reduce the viscosity of the ink and dilute it appropriately, but do not overdo it to avoid losing concentration and hiding power; Reduce the printing speed, so the degree of galling reduction is directly proportional to the reduction of the separation ratio of the ink film; Use high-quality coating paper; The ink should be clean, free of skin and particles; Check the viscosity, dryness and fluidity of the ink

5. There are many ink stains in the non graphic area of the paste version

printed matter, and the printed words such as "mouth", "product" and "crystal" are filled with ink into a field shape, or dotted into a piece. This phenomenon is because: the viscosity of the ink is too large, resulting in coating dots or scraps of paper, paper wool concentrated on the version or dots; The ink in the ink bucket has skin or dry particles; The ink dries too fast; The ink is too thin, and the ink is extruded under pressure; The paper absorbs too much binder, resulting in excessive pigment content in the ink; The roller has defects or its adjustment is improper; The layout is uneven and too high; Use too thick ink on gummed paper. In the offset printing process, the imprinting force of the printing machine may damage the sensing film that plays an isolating role on the printing plate, so as to expose the metal. The exposed place will become lipophilic after being affected by a trace of surfactants, polar substances, free lipids and acids in the fountain solution, which will absorb the ink, thus creating stains in the non graphic area and damaging the quality of the print; The yield value of ink is too high; The acidity of water is too low; Insufficient water on the plate; This phenomenon can be caused by the ink absorption of the water roller

the solution is: use reasonably dry and long ink. If the ink is too thick, you can add some thinner inking oil to increase the distribution performance of the ink; If you paste the version at a high profile, you can reduce the pressure; Appropriate ink should be selected according to the paper; The fineness of the ink is better, generally 20 ~ 25 μ m。 Add some thick binder to offset printing ink; Increase the acidity of the fountain solution; Increase water supply; Nourish the content of oil and fat in the ink formula; Use thick ink to make the impression thinner; Use liquid medicine with high surface tension; Change to quick drying resin ink, etc

6. Penetrant

because the ink penetrates into the paper too deeply, the pattern or text printed on the front can be seen on the back of the paper

the solution is: use quick drying ink, and the ink should be thick and less permeable, and the binder used in the ink should also be less permeable; You can add some thick inking oil and some desiccant to the ink

7. After crystallization, vitrification and specularization

the printing ink is uneven or cannot be printed at all; Overprint the printed matter in which the ink is beaded or weak in the next color. The ink film is poorly connected, and some can even be erased. The reason is that: the bottom color ink dries too hard, reducing the surface free energy; The storage time is too long after the previous color is printed; There is too much desiccant in the ink, etc

the solution is: cover the printing with quick drying ink containing more solvents, which should be able to immerse and soften the lower layer of ink film; Master the overprint time, and print the second color as soon as possible after the previous color is printed; In the first color ink, add additives for grade extension drying, such as Vaseline, lanolin, wax additives, etc; Synthetic resin binder with fast drying can be used to reduce the amount of desiccant in the ink

8. Powdered

the ink on the printed matter can be wiped off like dry powder after drying. The reason is that: the large strength material in the ink can solve this problem, and the amount of ink infiltrates into the paper, making the ink lose its bonding effect; The binder used in the ink is too thin or too many nonvolatile and immiscible solvents are used, and the absorption of the paper is too fast, which makes the binder penetrate too deep; The drying of the ink is too slow, which promotes the penetration of the binder; The quality of the binder used as a binder is too inferior

the solution is to improve the structure and consistency of the binder; A binder composed of non reactive resin and linseed oil, cooked oil or medium viscosity inking oil; Add a small amount of gloss oil or gloss oil into the ink; When designing ink formula, pigments with low relative density and high oil absorption are used to replace pigments with high relative density and low oil absorption, such as Hansha yellow and benzidine yellow to replace chrome yellow

9. Transparent printing

the ink is too thin and oily