Green ink printing technology

At present, China's printing industry is facing a great deal of environmental pressure. Since most of the inks used in printing contain organic solvents, and organic solvents are discharged into the atmosphere almost without any treatment, the annual organic emissions to the atmosphere are volatilized. The substance (VOC) is as high as hundreds of thousands of tons. In addition, the ink contains harmful heavy metal elements such as lead, chromium, cadmium, mercury, arsenic and antimony, which are extremely harmful to the human body and the environment. These substances have caused major pollution to the environment we produce and live in. After seeing all the above, people can't help asking where the green ink is, why not develop and use green ink?

First, define the green ink

At present, China has not established the criteria for the determination of green inks or environmentally friendly inks, but the general understanding of green inks should be viewed in a narrow sense and in a broad sense. In a narrow sense, green ink refers to the use of raw materials that are almost harmless to the human body for the manufacture of inks. There is almost no pollution during the production and printing of inks, and it poses almost no harm to human production and living environments. Ink varieties. In a broad sense, green ink is a relatively environmentally friendly product and it contains the following three layers of meaning.
(1) To significantly reduce the harmful components of ink, mainly include reducing the content of aromatic hydrocarbons and ketones, reducing the content of heavy metals, and reducing other harmful components to the human body.
(2) To significantly reduce the hazards to the operators and the environment during the production and use of the ink, and to improve the first-line production environment. At the same time, the energy consumed by the ink during its manufacture and use is not significantly increased.
(3) It must be conducive to the recovery and disposal of packaging waste, and there should be no "secondary pollution".

Although at present, the research and development of China's environment-friendly ink is still constrained by many factors, but for the Chinese ink industry, the ultimate realization of the broad-based green ink is its ultimate goal, and the manufacture and promotion of narrow-defined green ink is the current development goal. And the ultimate pursuit. With the development of technology, people began to consider factors such as ease of use, cost of use, and environmental performance. What are the green inks currently on the market? Here are some of them.

Second, energy curing ink

Energy-curable inks use UV light or accelerated high-energy electron beams (EB) to polymerize the monomers in the ink into a polymer. Currently, energy-curable inks mainly include UV inks and EB inks.

Compared with common inks, the main advantages of energy-curable inks are: they do not contain harmful VOCs to the human body and the environment, do not pollute the environment, have fast drying and curing speeds, consume less energy, and have a large cross-link curing density, and a degree of cure of 100%. %, can be printed on a variety of substrates, with excellent mechanical properties and physicochemical properties. Therefore, once energy-curable inks are available, they are sought after by the market.

The UV ink is mainly composed of a prepolymer resin, a diluent monomer, a photoinitiator, a photosensitizer, a photosensitizer, a polymerization inhibitor, and a pigment. UV inks mainly include offset UV inks, letterpress UV inks, gravure UV inks, screen printing UV inks, UV inkjet inks, and UV printed circuit board inks. The environmental protection of UV inks is only relative to the ordinary printing process, and there are also many problems.
(1) Some components of UV inks come in contact with the skin and may cause some irritating effects and may even cause skin irritation.
(2) UV light has some damage to the human body.
(3) The cured ink layer is very hard to degrade due to the high density of cross-linking, and the ink residue is also difficult to handle.

For this reason, people are actively researching and developing water-based UV inks and expect to solve the problems existing in UV inks.

EB ink is a kind of ink with great development potential. It can be used for web offset and flexo printing. Compared to UV inks, they do not use photoinitiators, have no odor, do not release ozone, do not require cold curing of the heat source, and are not affected by the color of the ink during curing. The curing is more thorough and the quality is more stable. However, the high cost of EB ink curing equipment is the biggest obstacle in the promotion and application. At the same time, EB inks also have degradation problems after they are discarded.

At present, most of the inks used for gravure printing contain benzene solvents. Due to volatilization, the exhaust gas emitted by gravure printing is a major source of pollution in the packaging and printing industry. Although water-based gravure inks have been received as a substitute for solvent-based gravure inks and have received high expectations, the water-based process of gravure inks is still slow.

The following are some of the factors that prevent the gravure ink from becoming water-based.

(1) Poor print quality: At present, water-based inks have poor adhesion and rub resistance to plastics, poor printability, and poorer printability than solvent inks.
(2) Dryness is not good: The water-based ink has poor drying properties, resulting in low printing speed during printing, which increases energy consumption and costs. It is necessary to reconstruct the original drying equipment or use a special printing press suitable for water-based gravure ink.
(3) The printing plate must be reconstructed: In order to improve the drying property of the water-based gravure ink and to strengthen the printing effect, the printing plate must be reconstructed to achieve a shallow plate.

At present, water-based gravure printing inks are still under research and development. Although there have been reports of successful research and development, they have only stayed at the laboratory level and a process is still needed to achieve industrialization. However, water-based gravure inks have already begun trials on some special substrates. If the above problem is solved, the water-based gravure ink can achieve a wide range of applications.

Third, alcohol soluble ink

Solvent-based gravure inks want to achieve environmental protection while ensuring printing performance and quality. Alcohol-soluble inks are the most likely varieties, and they are also the focus of current major ink manufacturers.

In addition, in the field of plastic flexible packaging printing, benzene-free ink is also very popular, the current progress is mainly polyurethane inks, many companies have developed benzene-free or even ketone-free ink varieties, suitable for plastic film printing and printing requirements There are also alcohol-soluble inks made mainly of special polyamide resins and polyvinyl butyral resins.

Fourth, environmental protection offset printing ink

Offset printing inks account for almost 50% of the market share in China. There are several types of environmentally friendly offset printing inks.

(1) Vegetable oil-based offset printing ink

The use of lithographic printing inks has a long history. Due to the limitation of VOC emissions and the impact of its environment, vegetable oil-based offset printing inks have become popular. The U.S. Soybean Oil Association has developed a special certification standard for the popularization of soybean oil inks. U.S. soybean oil inks are gradually replacing ordinary offset inks and are widely used in commercial printing applications.

Soybean oil offset inks are the main varieties of vegetable oil based offset inks. At present, many ink companies and research institutions in China are engaged in the research and manufacture of such inks. Vegetable oil-based offset printing inks have made progress, but there is currently no obvious advantage in the adaptability, product quality, and sales price of high-speed printing.

(2) Non-aromatic offset printing ink

In Japan, almost all ink manufacturers have begun to use AF solvents that remove aromatics (less than 1%) in ink solvents to improve the environmental pollution of inks during production and printing. It should be said that the use of AF solvent offset printing ink is also an environmentally friendly ink, but in our country there is currently no AF solvent available, which also restricts the development of China's non-aromatic offset printing ink.

(3) waterless offset ink

Waterless offset printing uses an ink-repellent silicone resin-coated printing plate, which removes the coating in the graphic part to absorb the ink and achieve graphic transfer. This eliminates the use of fountain solution and can be said to have contributed significantly to environmental protection. However, in the actual printing process, the waterless offset printing ink is greatly influenced by the ambient temperature, and is easy to get dirty. The ink transferability and the ink ink properties are not as good as those of ordinary offset printing inks, and a special waterless offset printing apparatus is also needed. Application and promotion are affected. Certain restrictions. However, under the pressure of environmental protection, the United States and Japan have already actively tried waterless offset printing, which is worthy of attention.

Although the core technologies of inks are still being mastered by developed countries such as the United States, Japan, and Germany, China has begun to pay attention to the development and development of generalized green inks. By increasing research and development efforts and capital investment, we are improving the environment for our survival and development. Unremitting efforts, especially some green ink varieties are close to the world's advanced technology level, this is our hope for China's ink!


[Source: PCB Information Network]