Bio-ink in green printing

American scientists have long been working on a protein molecule called bacteriorhodopsin. Natural materials can often exhibit complications that cannot be easily obtained from fabricated materials such as semiconductors. Bacteriorhodopsin originates from an intense purple cell membrane that is grown in the body of a salt marsh known as the "halophilic halophilic salt." Illuminating its protein can trigger a photochemical reaction circle. The principle is that the photochemical reaction circle transports protons along the channels surrounding the cell membrane. The purple color of this cell membrane originates from the bacteriorhodopsin component known as the "retina." Acetamic acid in the cell membrane channel strongly binds to the "retina." The dissolved "retina" does not bind with amino acid and is pale yellow. Two sets of lasers of different wavelengths are alternately irradiated onto the protein molecules, and the protein molecules can be switched back and forth between the purple structure and the yellow structure. It is this habit that motivates people to study and use it. It can be used as a photosensitive element in an analog retina, as a memory element in a germanium-based processing device or as a memory element in an optical computer, and its thin film can also change color in accordance with the conversion of an external electric field. In conventional bacteriorhodopsin, under the influence of different electric fields, a low contrast color change from purple to blue is formed. However, the bacteriorhodopsin structure produced by certain mutants changes from blue to light yellow under the action of a strong electric field. By sandwiching the protein film in a transparent plate combined with a large number of electrodes, a display plate can be made. Applying appropriate voltages to different parts of the film can "write" a page of text or "place" an image. Just like ink, images on the bacteriorhodopsin display can also be seen under normal light. Moreover, the color transition time can be accelerated to 200μm. At present, the main difficulty faced by the entire development work is the need to consume hundreds of volts of electric field to stimulate its color transformation. Researchers are working hard to conduct research in this area and expect breakthroughs.

With the rising demand for environmental protection, as the main component of green printing, the environmental protection requirements for ink are also increasing. It can be said that environmental protection inks are the first issues that must be considered in ink development in the future.

Injury to the environment

Ink is the largest source of pollution in the printing industry. The annual output of ink in the world has reached 3 million tons. Annual global emissions of organic volatile compounds (VOC) caused by ink have reached hundreds of thousands of tons. These organic volatiles can form a more serious greenhouse effect than carbon dioxide, and they can form oxides and photochemical smog under the irradiation of the sun, seriously polluting the atmosphere and affecting people's health. In addition, foods, toys and other packaging and printing ordinary ink heavy metals and other harmful components of the human body will also directly harm the health of consumers.

(1) Impact on human health

Printing inks consist of pigments, binders, solvents, and adjuvants. Among them, organic solvents and heavy metal elements cause serious damage to the human body. There are two kinds of pigments in the ink - inorganic and organic, both are insoluble in water and other media, and has a distinctive color and stability. Some inorganic pigments contain lead, chromium, copper, mercury and other heavy metal elements, which have certain toxicity and can not be used for printing food packaging and children's toys. Some organic pigments contain biphenyl rubber and have carcinogenic components and should be strictly prohibited. Organic solvents can dissolve many natural resins and synthetic resins. They are important components of various inks, but some of them can damage human and subcutaneous fats. Long-term exposure can make skin dry and rough. If it penetrates skin or blood vessels, it can endanger people with blood. Hematocrit and hematopoietic function; being sucked into the airway, bronchus, lungs, or through blood vessels, lymphatic vessels to other organs, and may even cause chronic body poisoning. Some inks have the toxicity problem of heavy metal ions. Pigments and dyes contain carcinogenic ingredients, which are harmful to human health. In the printing of composite packaging materials, a large amount of ink, organic solvents and adhesives are used. Although these accessories do not have direct contact with the food, some toxic substances will migrate into the food during the process of food packaging and storage and endanger people's health. Ethanol, isopropyl alcohol, butanol, propanol, butanone, ethyl acetate, butyl acetate, toluene, xylene and other organic solvents are often used in printing inks. Although most of these solvents can be removed by drying, residual solvents can migrate into foods and harm the human body. Solvents used in gravure inks typically include butanone, xylene, toluene, butanol, and the like. Especially butanone, the residual odor is very strong. Because the pigment particles in the ink are very small and have strong adsorption power, they are heated and dried during printing, but due to short time and high speed, they often do not dry completely, especially the printed matter with large inked area and thick ink layer. Its residual solvent is more. These residual solvents are brought into the compounding process. After compounding, it is more difficult to run away and the permeation will slowly migrate. Therefore, the solvent residue must be controlled to a minimum.

(2) Impact on environmental quality

The problem of air pollution caused by the volatilization of solvents in the ink is the most serious with gravure ink, because it uses more VOC as a solvent. Long-term exposure to high concentrations of VOCs will cause significant damage to the human body, especially the nervous system. VOCs will also react photochemically with nitrogen oxides in the air to produce ozone and fumes, causing atmospheric pollution. To reduce VOCs, there are two solutions for recovering and burning the discharged solvent, but many gravure machines are not equipped with such devices. In addition, the discharge of water-based cleaning ink and offset fountain solution can contaminate the water quality. The disposal of industrial waste such as printed materials and ink containers is also very tricky.