Influence of the hottest viscosity on gravure inks

2022-09-23
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The influence of viscosity on gravure ink

Abstract: This paper briefly explores the problems caused by the viscosity of gravure ink in actual printing, and briefly explains how to adjust the reasons

key words: viscosity, version fog, flying ink, printing speed, gloss, surface tension value

the ink used in gravure printing is a highly volatile solvent ink, which uses high-quality ink absorbing gravure paper and solvent volatilization to dry it. Because gravure printing ink requires good fluidity and low viscosity for its own viscosity, and the dryness requires real-time adjustment suitable for the speed of the printing machine, the length of the travel route, the quality of the printing materials, the corrosion of the layout, and the indoor temperature and humidity, once the operator is negligent or improperly controlled, it is very easy to have various problems

viscosity plays a very important restrictive role in this. This paper briefly explores the problems caused by the viscosity of gravure ink in actual printing, and briefly explains how to adjust the reasons

I. version fog problem

in plastic intaglio printing, the non printing surface of the printing plate roller is often adhered with a layer of hazy ink. After being transferred to the printing substrate, it often presents a sheet or line like dirty version, which is dirty version, also known as fog version. This cannot be avoided in gravure printing. The reason for the dirty version is that the ink is transferred by the doctor blade. Specifically, the ink in the non graphic part is not scraped clean in the scraping process. The blank part can be updated according to the instructions or the oil pipe joint can be checked for looseness. The main reason for the unclean ink scraping is the problem of machinery and ink composition

mechanical factors: the first reason is that the doctor blade is severely worn. During the normal use of the doctor blade, it will eventually be worn. To solve this problem, you can check the direction of the doctor blade along the gravure cylinder to ensure that the doctor blade is evenly pressed on the gravure cylinder. At the same time, make sure that the doctor blade itself has no wear points and dirty spots, which will affect the ink scraping effect of the doctor blade. If these problems cannot be solved, it is best to replace the doctor blade; The second reason is that if the surface of the copper coating and chromium coating of the gravure cylinder is rough, it will also lead to the unclean scraping of the doctor blade. Sometimes changing the angle of the doctor blade can solve this problem. If the roughness on the gravure roller cannot be overcome by adjusting the doctor blade, it is necessary to polish the gravure roller

ink component factor: if the doctor blade needs to be replaced frequently in the production process, it is likely that the pigment in the ink has strong abrasiveness, so we should consider whether to replace another kind of ink. In addition, improper or excessive use of solvent in the ink will cause the pigment in the ink to flocculate, which will leave the pigment under the doctor blade, resulting in dirty version or wear of the doctor blade. In addition, the lubrication performance of ink is also a reason for the dirty version. The lubricity of the ink is related to the resin in the ink component. Some gravure ink manufacturers will add a small amount of Dark asphalt to the ink component to improve the ink scraping performance

in a word, the main reason for the problem of plate fog is that a large number of resins precipitate and coalesce, or the selected resin has affinity to the plate cylinder. Under the pressure of the scraper, the resin will stick tightly to the cylinder

the cause of the dirty plate problem is not only related to the ink formula itself, the pressure and contact angle of the doctor blade and the quality of the printing plate, but also related to the printing viscosity of the ink. If the printing viscosity of ink is too high, the viscosity of ink will become larger. Under the high-speed movement of the printing plate, the ink will produce a great impact on the doctor blade, so it is difficult for the doctor blade to scrape off the ink of the non graphic part smoothly, and thus the version pollution will occur. If the pigment in the ink is unevenly distributed in the ink system, or the resin in the ink fails to wrap the pigment particles well, the pigment particles will regroup. Form pigment groups, which is often called coarsening phenomenon. These larger particles are easy to form linear or strip knife lines in printing. Generally speaking, the lower the printing viscosity of the ink, the less likely it is to cause the problem of dirty plates. Therefore, in the actual printing process, we should pay special attention to the change of the printing ink viscosity, adjust the printing viscosity in time, and improve the quality of prints

second, the problem of flying ink in high-speed printing

when the gravure printing speed exceeds 20m/min, if the gravure printing ink adopts domestic chlorinated polypropylene resin with wide molecular weight distribution, resulting in the low viscosity of the printing ink, it may lead to the problem of "flying ink"

the reason is that the viscosity of printing ink is too low. The cohesion of the ink decreases significantly. When the ink is transferred to the printing film, the low molecular weight resin is easy to be separated, and a small "ink dot" can be seen in the blank part of the print. To solve the problem of "flying ink", we can generally start from the following two aspects: - chlorinated polypropylene resin with narrow molecular weight distribution; Second, according to the printing situation, appropriately improve the printing viscosity of the ink

third, the influence of viscosity on color, transfer rate and color saturation

gravure ink depends on the ink of the concave point of gravure to transfer to the printing substrate. Relatively speaking, the volume of the printing point is basically fixed. With the increase of the printing viscosity of the ink, the viscosity of the ink also increases, and the more ink is transferred from the point, so the color concentration and saturation of the print are higher, but there is a certain limit

when the viscosity of the ink continues to rise to a certain degree, the transfer rate of the ink also achieves a synchronous increase. If the viscosity of the ink continues to rise, the viscosity of the ink becomes stronger and stronger, and the ink begins to be difficult to enter a small point, the ink in the point becomes less and less, the transfer rate of the ink begins to gradually decline, and the color concentration of the printed matter also begins to decline. Ink manufacturers suggest that the printing viscosity of gravure ink is generally 13 ~ 22 seconds (3# chaen cup), which is only an empirical value. In the actual printing process, in order to achieve good printing transfer effect, it is necessary to carefully adjust the printing viscosity

IV. The Influence of viscosity on the printing speed

the printing speed of the existing gravure printing machine ranges from 30m/min to 300m/min, and the printing speed of the general printing machine ranges from 80 to 200m/min. In actual printing, viscosity should be selected according to the printing speed of the printing machine. When the printing speed increases, the printing viscosity value will decrease

1. Even at the same printing speed, due to the difference of ink formula design. Its printing viscosity will also be different. Therefore, in the actual printing process, it must be adjusted according to the printing effect

2. Affected by seasonal temperature. The viscosity of the same printing ink is different in summer and winter. Many ink manufacturers have been working hard to reduce the impact of temperature on ink viscosity

3. Select the most appropriate ink printing viscosity according to the actual conditions of the printing plate roller

v. influence of viscosity on printing gloss

after adding more solvents to the original ink, the viscosity of gravure ink will be lower, and the content of resin and pigment in printing ink will be reduced. After the ink is transferred to the printing substrate and dried, it is not easy to form a smooth ink layer, resulting in white flowers, which directly leads to the lack of gloss of the printed matter. Therefore, in order to obtain excellent gloss, we must ensure that the printing ink has the appropriate resin and pigment content. Therefore, many ink manufacturers have repeatedly asked the printing workers not to blindly wash the solvent in the ink, but to choose the matching ink blending oil or diluent, which is also to ensure that there is enough binder resin and pigment ratio in the machine ink

VI. ink viscosity and electrostatic problems

generally, OPP internal printing ink has limited antistatic ability, which is easier to generate static electricity than polyamide surface printing ink and polyurethane system ink. For OPP internal printing ink, the higher the viscosity of the printing ink, the more likely it is to produce electrostatic problems. Under normal temperature conditions, the viscosity of the printing ink is more than 16 seconds (3 chaen cup). Electrostatic generally does not occur; If the printing viscosity is lower than 16 seconds/3 × cup, there will be beard like, striped, edge rejection and other faults, which are easy to occur

if the viscosity of the printing ink has been within 15 seconds/3 cup, it is generally recommended not to use the method of increasing the viscosity of the printing ink, because increasing the viscosity of the printing ink will not only increase the printing cost, but also bring difficulties in printing transfer, which is prone to printing failures such as dirty plates

take other methods to eliminate static electricity according to the specific situation of static electricity. For example, it can be adjusted by changing the proportion of solvent in the diluent. Some insiders pointed out that the oil would leak through the gap. Adding 5% isopropyl alcohol (a polar solvent with good conductivity) or adding a small amount of antistatic agent as appropriate can achieve the purpose of eliminating static electricity, "Spencer said

VII. Ink viscosity and gelation problems

it is generally believed that the phenomenon of viscosity increase of solvent based liquid ink is due to insufficient adsorption of resin on the surface of pigment particles. If the polymer resin is not completely adsorbed on the surface of the pigment particles, the surfaces of the pigment particles without adsorption resin will aggregate with each other to form flocculation

from a technical point of view, the pigment surface is not completely surrounded by resin, and adsorption does not exist in isolation, but will make the solvent adsorb on the surface of pigment particles. Although the solvent can sometimes wet the pigment, the dispersion of the solvent to the pigment cannot be in a stable position. Therefore, a solvent rather than a polymer resin surrounds and adsorbs on the surface of the pigment particles. With the passage of time, the surface of pigment particles. With the passage of time, the pigment particles flocculate slowly, and the final result is that the fluidity of the ink changes

theoretically, the solution to the problem of solvent adsorption of pigment particles is to use a resin with high affinity with pigment particles, so that the affinity between the solvent and the surface of pigment particles is lower than that between the resin and pigment particles. Similarly, if the polymer resin has good solubility in the solvent mixing system, the flocculation probability of pigment particles can be reduced to the minimum, because the solvent/resin has better binding than the pigment/solvent

VIII. Surface tension value of ink

if we need to measure the surface tension of ink in work, we can use a tensiometer to measure it. However, this measurement method can only measure the static surface tension of the ink (the surface tension of the ink at rest). However, the ink will definitely receive dynamic force on the printing machine. Therefore, the really effective surface tension should be the surface tension measured when the dynamic force exists. Sometimes the dynamic surface tension is not easy to measure

when printing with water-based ink, surface tension is an important problem. This is because the surface tension of the water-based ink is higher than the surface energy of the substrate. In these water-based inks, some additives are often added to reduce the surface tension of the ink, so that the water-based ink can be well wetted on the surface of the substrate

for any specific water-based ink formula, the main role of surface tension is to affect the leveling of ink on the substrate surface. The surface tension of solvent based inks is generally low,

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