Talking about the Cause of Flying Ink

When the art printing factory of Shanxi Province used the Heidelberg Speedmaster CD102 offset printing machine to print ordinary high school geography textbooks, the blue ink ink phenomenon appeared, which polluted the environment and damaged the health of the operators. The following author analyzes this issue.

1 Causes of flying ink

When the ink is transferred, a filamentous fibrous material is drawn at the outlet of the two ink rollers rotating in contact with each other, and when the fibrous material is cut or pulled at two or more places at the same time, the resulting fibrous product is broken. Because the surface tension becomes spherical, at the same time, the electric double layer existing at the interface between the fibrous material and the broken piece is destroyed and divided into positive and negative charges. Some of it remains in the ink, and the other part of the opposite charge escapes to the atmosphere. When the fibrous material is shortened, the residual charge in the ink is gradually accumulated on the ink roller and the surface of the paper. Due to the charge with the same symbol as the ink, the fragment is repelled and floats in the air to form a flying ink when it is close to the ink roller or paper.

The generation of flying ink does not originate from centrifugal force. There must be more than two ink rollers, and the ink will be generated when the ink is split between the nips. When the high-speed machine uses a highly viscous ink, and is a low-quality linking material, it is easy for the ink to not normally break during the rotation of the ink roller, and pull the filaments to cause a serious ink flying phenomenon, so different types of printing presses are based on actual Need to select the appropriate ink to match. Under normal circumstances, high-speed ink stickiness is 3.0 to 4.0, medium-speed ink stickiness is 4.5 to 5.5, and low-speed ink stickiness is 6.0 to 7.0.

2 Factors Affecting Flying Ink

1) Ink viscosity

Ink viscosity is an important indicator, too high and low will affect the printability of the ink. If the viscosity is too high, the ink is pulled into filaments at the ink roller outlet, which may cause ink flying phenomenon. At the same time, it will cause uneven ink transfer, make the paper fluffed off, remove the paper from the blanket, and break the middle layer of the ink layer. Insufficient ink protection layer of the layout and graphics, under the influence of dampening fluid and pressure friction force, easy to print version, off version, etc.: the viscosity is too small, the ink layer is not well split, easy to produce flying ink, and easy to make the ink emulsification , from the dirty, paste version, network expansion, thus affecting the quality of printed products.

2) The thicker the ink layer on the ink roller, the greater the ink flying

When printing offset paper, it is necessary to increase the amount of ink in order to match the printed product with the print color pattern. Proofing on the coated paper to achieve the field density requirements, the ink layer thickness of 1.2μm, the ink on the plate as long as the 2.8g/m2 on the line. However, when using offset paper for printing, to achieve the requirement of proofing the field density, the ink on the plate should reach at least 4g/m2, and even exceed this value. In this way, the operator will increase the amount of ink and encounter the performance of the paper against the ink. Adhesion is not good, it is easy to cause ink roller heap phenomenon. This creates flying ink.

Offset printing is indirect printing, in which the ink is transferred from the printing plate to the blanket and transferred from the blanket to the paper. Therefore, the printability of the blanket is good and plays an important role in the good transfer of the ink. Multi-color offset presses have high machine speeds and high yields. The surface of the blanket is eroded by potions, inks, paper powder, and car wash water. With the use of a hard lining, the surface is extremely susceptible to smooth aging, and some even produce "aurora. "(Mirror-like), the original structure of the villous structure no longer exists, affecting the ink-bearing rate of the blanket, but also reduce the transfer performance of the blanket. If operators at this time blindly increase the amount of ink, causing the ink roller to pile up ink, easy to produce ink flying phenomenon.

3) When the surface of the ink roller is uneven and the surface is cracked, some of the ink layers are thickened, and the amount of ink mist is increased, and flying ink is also easily generated.

4) The printing speed increases and the flying ink increases.

5) The relative humidity of the air is small, which will promote the generation of flying ink. When the humidity increases, the charge decreases and the amount of flying ink decreases.

6) Effect of wetting liquid on ink transfer.

The scientific use of dampening solution is an important auxiliary means in the lithographic process to assist the ink and the aqueous phase to resist miscibility, maintain the best hydrophilicity of the plate, stabilize and improve the product quality. In the actual production must be scientific, accurate and reasonable.

Ink and water are not absolutely insoluble. In the actual printing process, the ink and water are pressed together and they fuse together, which determines that the emulsification is more or less always present in the production process. Only when the water content in the ink reaches 21% (ie, 100g ink contains 26g water), the print quality is best. If there is too much fountain solution in the ink and a severe W/() emulsion ink is formed, the viscosity will drastically decrease and the ink will become shorter, causing serious ink flying. At the same time, the fountain solution immersed in the ink will also corrode the metal ink roller, forming a hydrophilic layer on the surface of the ink roller and repelling the ink, resulting in deinking of the metal ink roller. The intermediate roller is an ink roller that connects the water circuit and the ink path on alcohol moistening devices (such as Heidelberg 102v, cp2000). The main role of the intermediate roller is to transfer the fountain solution to the ink circuit system, so that the ink is emulsified as necessary so that the ink balance is quickly reached before printing. The width of the contact area between the intermediate roller and the first inking roller is 3 mm, and the contact width with the water roller is 3 mm. Therefore, whether the adjustment of the middle roller is correct or not is the key to the degree of ink and water emulsification.

7) The binder of high molecular weight inks tends to draw filaments when the ink is split, resulting in ink flying. In order to improve the drying properties of the ink vehicle, for example, replacing the low-molecular-weight binder with a high-molecular-weight binder increases the drying speed of the ink. However, because the molecular weight is high, the filaments can be drawn and become flying ink.

3 How to eliminate flying ink

1) The ink factory is required to provide high-quality, alcohol-resistant inks to suit high-speed printing presses.

2) Remove the rubber roller periodically and clean it thoroughly to make the ink layer of the ink roll uniform and enhance the ink transfer performance.

3) Alcohol concentration should be controlled between 10% and 15%, too low or too high are not suitable for printing.

4) Dosage should not be too large, otherwise it will cause the ink to become short, which is not conducive to printing.

5) When the electrolyte is added to the ink, the flying ink phenomenon will be reduced. As the electrolyte is added, the electrical conductivity increases, and the flying ink phenomenon will be reduced or even completely disappeared. This is because the addition of the conductive material makes it difficult for the charge to accumulate to prevent scattering of the ink. Water-based inks or vapor-treated inks generally do not produce ink mist. Adding 5% water to an oil-based ink as a W/O type ink or adding an electrolyte such as ammonium chloride can also reduce or eliminate flying ink.

Although the polar material can reduce the flying ink and even eliminate the flying ink after the ink is added, it is easy to make the ink filament shorten or be creamy, and it is not suitable to print at a high speed. Some people propose adding aromatic amines to inks to make W/O inks with good flowability, but they have excellent aromatic solubility, bad odor, and high toxicity. Generally, the content of aromatics in the solvent used in the ink is 10% to 20%, and the environment-friendly ink uses an aromatic-free solvent, ie, the aromatic content in the solvent is less than 1%, and the aromatic hydrocarbon is harmful to the environment and the health of the body.

Increasing the rigidity of the ink and reducing the chance of the ink breaking at two or more places can prevent the occurrence of ink mist. For example, in the black ink of the mineral system that easily produces ink mist, add silicone resin, sodium stearate, etc. The elasticity of the ink is increased, the elongation time of the fibrous material is shortened, and the ink mist is reduced, but the ink is poorly transferred on the ink roller.

With the increasing awareness of environmental protection in China, environmental protection inks are increasingly favored by printing houses. Many printers, on the premise of paying attention to the quality of ink, require ink manufacturers to provide MSDS data, heavy metal content data and proof of compliance with environmental ink standards. This has also promoted the rapid development of offset printing inks in China.

In short, the flying ink phenomenon may occur at any time during the printing process due to the contact rotation of the two rollers. This requires the operator to not only have a high-skilled operation level, but also requires the operator to be fully aware of the data and specifications involved in printing. Minimizing the occurrence of flying ink is beneficial to the environment.

Source: Western Packaging Network