Application and drying mechanism of soybean oil ink (2)

Application characteristics of soybean oil ink

At present, soybean oil offset printing inks have different viscosity type products for customers to choose from, but have higher prices compared with petroleum-based inks.

The content of soybean oil in the ink varies depending on the use of the ink, generally between 5% and 55:6. The advantage of the soybean oil ink is high transparency, which is very favorable for the color printing of newspapers. Soybean oil inks are less likely to lose ink and have a higher color rendering than petroleum-based inks. The same amount of soyoil ink can print 10% to 15% more print than traditional inks.

1. Good rub resistance

Soybean oil ink is resistant to rubbing, readers will not touch their hands black when reading newspapers or magazines, at the same time there is no bad stimulus odor, and traditional petroleum-based inks due to poor friction, printed books, especially newspapers can easily contaminate the reader's hand , And smell bad.

2. Waste paper is easy to deink

Soybean ink has good deinking performance in paper recycling process, recycled paper has good paper quality, less waste, and low recycling costs.

3. Less printing ink

Soybean inks have bright colors and high saturation, and can be used to obtain brightly colored prints with less ink, thereby reducing ink usage, saving printing costs, and more economical for color printing.

4. Good ink

Compared with cured inks or waterless offset inks, soy oil inks dry more slowly. However, from the perspective of practical results, the transferability of the ink is good, and the ink repellency in the field is good, and the highlights of the dots are evenly distributed. After ordinary offset ink reaches the paper, the solvent penetrates quickly. In the part near the paper surface, the ink film will break off, while the soybean oil ink will penetrate slowly, and the peeling surface of the ink is closer to the side of the blanket. The thicker ink film is transferred to the paper surface, so the ink transfer amount increases.

Drying mechanism of soybean oil ink

Although many printability of soybean oil ink is better than that of petroleum-based inks, its drying performance is poor. After many improvements, the current soybean oil ink is similar to the conventional ink cabinet in terms of dryness, ie, it is well-dried on coated paper. The time to reach 2-4 hours, non-coated paper for 4 to 6 hours. However, its anti-dryness on the machine is excellent, up to 30 hours.

The drying mechanism of soybean oil offset inks is the drying of the oxidized conjunctiva to control the ink oxidation process and it is necessary to control the various components of the ink.

1. The composition of the soybean oil ink is therefore mainly composed of a resin, a binder, a filler, and an auxiliary material. The link material consists of oil, solvent, resin and other substances. Among them, soybean oil is a linking material that provides ink flowability. Soybean oil inks are composed of refined soybean oil, clear tung oil, and petroleum synthetic resins.

2. Soybean oil ink drying process

Ink drying is generally divided into two stages, namely, osmotic drying and oxidative conjunctiva drying. First, the ink that has just been transferred to the substrate is brought into contact with oxygen to initiate curing; the solvent in the ink begins to penetrate into the gaps in the fibers or coatings of the substrate. The pigment remains in the soybean oil component and fixes the pigment on the print surface by oxidizing the conjunctiva. At this time, the ink is not completely dried. Due to the loss of the solvent, the viscosity of the ink film increases, reacts with oxygen in the air, and the viscosity of the resin in the binder increases. At this stage, the ink on the surface has been fixed, but the ink in the middle of the ink film still maintains a certain degree of fluidity. Depending on the composition of the ink, the thickness of the printing ink film, the nature of the paper, and the environmental conditions, it takes about 1.5 hours for the ink to completely settle.

3. Soybean oil ink drying speed control

In order to accelerate the drying speed of the soybean oil ink, oxidation can be accelerated by adding a desiccant. There are three types of desiccants used, namely cobalt (which can accelerate surface drying and fixation), manganese (which accelerates the internal drying process), and lead.

When printing with soybean oil inks, the use of desiccants accelerates the drying of the surface and interior of the ink and allows it to dry completely. In the drying of soybean oil ink, the following points should be noted.

(1) When printing on fine and smooth paper surface, soy oil ink should be avoided as much as possible. Because soybean oil is a semi-dry oil, the drying speed is slower.
(2) The pH of the fountain solution during printing should be controlled within the range of 5.0 to 6.0. Since the acidity is too high (low pH), the drying process of the ink will be prolonged.
(3) When printing a large area on the field, the use of a desiccant-containing varnish can speed up drying, but too much desiccant will plasticize the ink, resulting in slow drying.
(4) Some desiccants can be added to the dampening solution to increase the drying speed of the ink, or to spray powder with large particles, so that more air enters the paper gap to accelerate the drying speed of the ink.
(5) The use of an infrared drying device to accelerate ink drying is also a better method.

Author: Zheng Li Han Xuanwu sunny Changsha University

Source: Print Technology 2005, 10 (Publishing and Commercial Printing)

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