The development trend of several green inks
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The development of the printing industry is closely related to the development of printing ink, so the environmental protection of ink is an important development trend. In the past, the printing industry generally used traditional solvent-based inks, but its environmental pollution is obvious to all. To this end, all countries in the world attach great importance to the development and research of environmentally friendly inks, and China is no exception. New printing ink printing materials and accessories without pollution and less pollution are being developed and applied more and more, and green inks are increasingly becoming the consensus and joint action of the printing ink industry.
To study environmentally friendly inks, we must first understand the harm of traditional solvent-based inks to us:
The printing ink consists of a pigment, a binder, a solvent and an adjuvant. Among them, the organic solvent in the binder is particularly harmful to the human body. Organic solvents can dissolve many natural resins and synthetic resins. They are important components of various inks, but some of them can damage the human body and subcutaneous fat. Long-term contact can cause dry and rough skin. If it penetrates into skin or blood vessels, it will endanger people with blood. Blood cells and hematopoietic function. Although these solvents can be removed by drying, the residual solvent migrates into the food and harms the human body. If solvent-based inks are used to print packaging and printing products with strict hygiene conditions such as tobacco, wine, food, medicines, beverages, children's toys, etc., some toxic and harmful substances in solvent-based inks will remain in the printed matter, which is environmental and Human health is very harmful.
In the gravure and flexo solvent type inks, the content of the organic solvent is as high as 40% to 60%, and the dried form is volatilized and dried, so the content of VOC (Volatile Organic Compound) in the solvent is large. The volatilization of a large amount of organic solvents causes air pollution and other problems, and is absorbed into the air intake tube, bronchus, lungs or blood vessels, lymphatic vessels to other organs, and may even cause chronic poisoning in the human body. At present, both domestic and foreign companies are strictly controlling the VOC content of a series of products such as paints and inks to reduce the damage to the human body and the environment.
In view of the harm of traditional solvent-based inks to humans, researchers are working hard to fundamentally improve the environmental impact of inks. This requires changing the composition of inks and using environmentally-friendly materials to formulate new environmentally-friendly inks. Reducing the emission of VOCs and improving the efficiency of energy use, researchers in various countries are stepping up development in this area. At present, there are three main types of environmentally-friendly inks that are most widely used in China, namely water-based inks, ultraviolet-curable inks, and alcohol-soluble inks.
1, water-based ink
The water-based ink is a kind of liquid printing ink which is prepared by using an aqueous resin as a binder, a high-grade pigment or dye as a coloring agent, water as a main solvent, a small amount of ethanol as a co-solvent, and a plurality of additives to be finely ground.
The biggest difference between it and traditional solvent-based inks is that the solvent used in water-based inks is water and ethanol, and the VOC content is extremely low, which is less polluting to the environment. At present, 95% of flexographic prints, 80% of gravure prints, and 40% of plastic film prints in the United States are printed with water-based inks. In other developed countries, more and more water-based inks are used in packaging printing. In recent years, China has made some regulations on the packaging of food. The status of “green” printing is constantly improving in China, and water-based inks have also developed rapidly in China. At present, the water-based inks for flexible packaging in China are ranked first among other printing inks at 35%. With the development of scientific research personnel, the variety of water-based inks has also been increasing, such as plastic ink, fluorescent ink, transparent ink, heat-resistant ink, bright ink, water-based gold and silver ink and water-based varnish ink have been applied. .
The most important application areas of environmentally friendly water-based inks in China are flexographic printing, gravure printing and screen printing. Due to the low VOC content in the solvent, not only the pollution to the atmospheric environment is small, but also the toxicity of the residual surface of the printed matter is reduced. Therefore, most of the products using the aqueous ink are packaging products, among which food packaging, tobacco and alcohol packaging, children Toy packaging and the like account for a considerable proportion.
Although water-based inks have been widely used in the printing of coated paper, white paperboard, corrugated paper and plastic film, many packaging manufacturers are reluctant to adopt it because of its cost; and there are still some problems in the printing of ink, such as ink It is easy to dry on the anilox roller, which affects the uniformity of ink transfer; the ink is easy to foam and affect the color density; the water resistance, solvent resistance and abrasion resistance of the ink are relatively poor. This requires researchers to further develop research to make water-based inks develop more rapidly.
2, UV curing ink
Ultraviolet light-solid ink is a kind of energy-saving environmentally-friendly printing ink that has been rapidly developed in recent years, also called UV ink. This ink is irradiated with ultraviolet rays to cause polymerization of the ink binder to be dried. It is free of volatile organic solvents and is solvent free. In order to eliminate the emission of solvent-based ink VOC and meet the strict requirements of air quality standards, the printing industry gradually adopts UV ink technology to print products, so UV inks can quickly occupy a place in the market.
UV inks are also composed of colorants, binders, and auxiliary materials. However, the composition of the binder is different from the conventional solvent-based ink.
From the comparison of the composition of the UV ink and the solvent type ink, the UV ink which is instantaneously cured by the ultraviolet irradiation to generate a group reaction, and the conventional solvent type ink and the solvent which are dried by the oxidative polymerization reaction which is infiltrated into the paper by the solvent for several hours. Compared with the water-based ink which is dried by the evaporation of water and the penetration of paper, the other components are different except for the pigment. The main components of the binder are photoinitiators, prepolymers and reactive monomers. The curing mechanism of the UV ink is that the photoinitiator in the ink is directly affected by the ultraviolet light, and the initiator molecules are chemically rearranged to form a radical, which in turn initiates chain polymerization of the functional groups in the prepolymer and the reactive monomer. The reaction forms a linear polymer, causing the photochemical reaction product to undergo a photocrosslinking reaction between the polymer chains, converting the liquid component into a three-dimensional network solid polymer, and finally forming a hard ink film, which is a a way to dry instantly.
At present, UV ink has become a more mature ink technology, and its pollutant emission is almost zero. In addition to solvent-free, UV inks have the advantages of fast drying speed, poor paste, clear dots, bright and bright ink, excellent chemical resistance and low dosage. According to statistics, the annual output of UV ink is about 16,000 tons in Japan, about 18,000 tons in Europe, and about 19,000 tons in North America. It is also widely used in offset, flexo, gravure, screen printing and inkjet printing in China.
Waterborne UV inks are the new direction in the field of UV inks. Prepolymers in conventional UV inks are generally very viscous and need to be diluted with reactive diluents. While the currently used diluent acrylate compounds have varying degrees of skin irritation and toxicity, while developing low viscosity prepolymers and low toxicity reactive diluents, another development direction is to study aqueous UV inks, ie, water. And ethanol as a diluent, so that lower toxicity can be achieved with low VOC emissions. Waterborne UV inks have been successfully developed and are used in some printing industries.
In addition, cationic UV-curable inks are also a promising prospect for the development of UV inks. Compared with the free radical photocuring system, the cationic photocuring system is not affected by oxygen inhibition, has good surface curability, is less irritating to human skin, has small internal stress in the ink layer, has small volume shrinkage, and has good flexibility and adhesion. It has become a hot topic in ink research and development. [next]
3. Alcohol soluble ink
The non-phenyl alcohol-soluble ink, which mainly plays a role in gravure printing, is also a kind of ink with little pollution, and is mainly used in food, medicine, beverage, tobacco and alcohol, and packaging and printing of daily necessities in contact with human body.
For a long time, the surface ink printing of packaging bags in China's composite packaging is mainly based on benzene-soluble gravure composite plastic film ink. Due to the release or residual of a large amount of toluene, it will cause certain potential harm to the environment and production, as well as to human health.
The solvent used in the gravure ink is generally butanone, xylene, toluene, butanol or the like. Especially butanone, the residual smell is very strong. Since the pigment particles in the ink are small and have strong adsorption force, although they are heated and dried during printing, they are often incompletely dried due to short time and high speed, especially for printed matter having a large inking area and a thick ink layer. There are many residual solvents. These residual solvents are brought to the compounding process, which is more difficult to run off after compounding, and will gradually migrate and penetrate, so solvent residue must be kept to a minimum.
The alcohol ester composite ink has the characteristics of low odor, no benzene, ketone, etc., and the ink industry has been working hard to develop such an alcohol-soluble ink which is less polluting to the environment. Alcohol-soluble inks can help us solve the problem of the quality of packaged foods caused by benzene and benzene residues in toluene inks. The production of such environmentally friendly inks has greatly enhanced the competitiveness of gravure printing in the field of plastic flexible packaging printing. In Japan, South Korea and Southeast Asia, toluene inks have been eliminated and replaced by alcohol-soluble gravure inks. In Europe, it is strongly advocated that flexographic printing and gravure printing can only use alcohol-soluble inks (benzene-soluble inks are forbidden); in China, the alcohol-soluble ink gravure printing industry has also been gradually applied. It is foreseeable that in the near future, the development trend of inks for flexible packaging in China is that benzene-soluble inks will be replaced by alcohol-soluble inks.
A new generation of non-benzene alcohol-soluble environmentally friendly inks has developed a new world for alcohol-soluble inks. The ink is made of alcohol-soluble nitrocellulose and other high-grade resin mixed with non-toxic pigment and anhydrous ethanol. It can be used for high-speed printing on gravure machine. Its biggest advantage is that it does not contain benzene, and its cost is low and it is suitable for printing. The wide range, printing effect and composite strength are ideal for environmentally friendly inks in line with international food packaging standards. [next]
At the same time, Toyo Ink Co., Ltd. is also promoting the development of benzene-free butanone-free high-performance inks in various ink varieties to meet the safety needs of food packages. This ink can be used for soft-pack printing for various purposes. After printing, the soft bag can be boiled and cooked without the addition of a hardener; it is suitable for almost any type of plastic film when used in composite packaging materials. The ink adheres firmly and high, does not affect the composite; the printing effect is good, especially the high-light part is good in ink; the single-component use can be used, and the operation is stable; the residual solvent after printing is small, the package is guaranteed to meet the national standard requirements; Toluene and methyl ethyl ketone, the working environment is safe and hygienic. Obviously, the development of alcohol-soluble inks in China is unstoppable.
In addition to water-based inks, UV-curable inks and alcohol-soluble inks, researchers are constantly developing new types of environmentally-friendly inks, of which vegetable oil-based inks can be said to be typical environmental representatives.
The vegetable oil type ink refers to an environmentally friendly ink which uses vegetable oil instead of some petroleum series solvents in ordinary inks and other components such as resins and pigments. At present, the most commonly used one is soy oil type ink, and the raw material used is edible oil such as salad oil. The printed matter printed with soybean ink does not produce toxic and harmful substances that pollute the environment during use and regeneration, so it is called environmentally friendly printed matter. Nowadays, some prints using soy inks in Europe and the United States must be marked with the eye-catching mark "SoySeal" to expand the social influence of environmentally friendly products.
Soybean ink has more excellent characteristics than traditional petroleum-based inks, so it has gradually become the new darling of the ink market. It has the following advantages:
A. Excellent environmental protection;
B. Excellent rub resistance;
C. Good light and heat resistance;
D. Deinking of waste paper is easy;
E. The overall printing cost is low;
F. In line with industrial policies.
At present, soy oil type inks for various forms of printing have appeared on the market, including newspaper inks, sheet-fed inks, thermosetting inks, cold-setting inks, commercial form printing inks, and letterpress inks. Due to the increasing demand for the quality of the living environment and the high environmental awareness in recent years, the use of new environmentally friendly soybean inks to replace petroleum-based inks to ensure a clean and beautiful living environment will be another best option. Easy to be environmentally friendly.
Although soybean oil type inks have the above advantages, they still have some shortcomings:
A. Slow drying speed
As far as the current technology is concerned, it is not possible to replace all of the petroleum distillate in the ink formulation with vegetable oil due to the drying performance of the vegetable oil type ink. Therefore, the primary purpose of research and development in this field is to ensure the maximum content of vegetable oil in printing inks that meet high quality and performance.
B. Narrow application range
Not all types of printing inks are well suited for vegetable oil type inks. For example, gravure ink. Because such inks are volatile drying inks, the binders are required to be volatile, while vegetable oil inks have low vapor pressure and high boiling point and are non-volatile solvents. Therefore, how to expand the application range of vegetable oil type ink is also an urgent problem to be solved.
In summary, whether it is water-based ink, UV-curable ink, alcohol-soluble ink, or soybean oil-based ink, it is based on the composition of the ink, replacing the toxic components in the traditional solvent-based ink with environmentally friendly materials, and it is environmentally friendly. The effectiveness is obvious. And now the United States and some European countries have banned the use of solvent-based inks containing benzene, replaced by green inks. Therefore, the development of environmentally friendly inks has a very important impact on the printing industry. It is foreseeable that environmentally friendly inks will be the market force in the future ink field.