The term “discoloration†is used in a wide range of applications. Any change in color that occurs when the ink is chemically treated or changes its physical conditions, such as changes in temperature or humidity, is called discoloration. Color-changing inks have many uses, among which can be used for industrial production, such as for sterilization, temperature control, security measures, but also for the production of various novelties, such as for children's toys and games, T-shirts, postcards. There are hundreds of chemicals that change color because of chemical reactions with other substances or because of physical influence. Some of these chemical species are simple inorganic compounds, while others are quite complex organic molecules, but they can be formulated. There is not much to go into various ink media.
A review of the available chemicals below will discuss some uses and limitations. Disinfection ink disinfection is defined as the process of killing or removing various bacteria and microorganisms. Disinfection is mainly used in the pharmaceutical industry to sterilize surgical and medical devices. Sterilization methods include dry heat, damp heat (high pressure steam sterilization), and gas sterilization or radiation sterilization. Assuming that the packaging material can keep the contents of the package in a sterile state, one of the problems that the user of the device has to clarify in the case of dispensing surgical instruments like in an operating room is that the surgical package has been sterilized.
One widely used method is to use a printing ink that can have an irreversible color change in sterilization as an indicator. High-pressure steam sterilization is a popular technique. It disposes the packaged goods under high pressure and superheated steam at temperatures above 100°C. This method of disinfection is more effective than dry heat sterilization because it requires a lower temperature, the shorter the dwell time of the packaged goods in the sterilizer, and the weaker resistance of the bacteria to damp heat. For a variety of reasons, ink manufacturers are greatly limited in the types of chemicals they can use and the types of chemical compounds they use. Due to the low amount of ink, the color change must be quite noticeable so that a noticeable effect can be easily seen on the substrate. The reaction can only occur under high pressure steam sterilization conditions and cannot occur during dry heat nor in wet ink. The reactants must also be able to disperse in the relevant ink solution to form a stable ink. The choice of raw materials: the choice of raw materials The types of inks that can be used for high-pressure steam sterilization are significantly limited, so the various systems that are commercially available are often the use of certain colorless aluminum compounds that convert to aluminum sulfide. The color changes from white to black.
Although various systems differing in the time of discoloration can be obtained, the more reactive the varieties are, the worse their stability is, and they are more easily discolored under dry heat conditions. Certain metal carbonates also exhibit satisfactory color changes, and now high pressure steam sterilization inks containing iron cyanide are available and put into industrial applications. Since such inks cannot be formulated for use in lithography, and the amount of ink under dry offset is so small that color changes are difficult to perceive, gravure printing and flexographic printing are preferred printing techniques for such inks. Screen printing or many can solve the ink problem, but for the long-lived work, this printing method appears too slow.
Another type of printing technology, ink jet printing, is used in high speed packaging lines due to the use of a specialized ink that contains a material that can be bleed through under high pressure steam sterilization conditions. The gas sterilization method is also subject to many similar restrictions. The advantage of the gas sterilization method is that the operation can be performed at a low temperature, and thus the sterilization method can be used to sterilize products with poor thermal stability. The commonly used gas is ethylene oxide, but care must be taken when using it because ethylene oxide can form an explosive mixture with air. The color change indicator used must have a production effect on the reaction of ethylene oxide. A substance that can be added to the ink solvent is hydrated magnesium chloride. During the reaction, the resulting magnesium hydroxide makes the acid-base indicator (e.g., Bromophenol blue or methyl red) causes color changes. Another suggested method is to use a mixture that produces a color change when irradiated. This mixture consists of a bleeding pigment and a non-bleeding pigment. Securities Printing In the field of securities printing, the application of color-shifting inks is not uncommon. However, for obvious reasons, various technical details cannot be discussed.
The purpose of using color-shifting inks in the field of securities printing is all to make it more difficult for securities to be forged or to prevent tampering with securities. The illustrations of cheques, airline tickets and passports printed with various fading inks are examples. These inks are manufactured from a slowly printing diol-like embossed ink medium that contains soluble dyes that bleed or discolor when treated with various organic or inorganic solutions or solvents: the ink is displayed in a well-chosen object. It is difficult to be perceived on the surface, but it is visible under some special conditions. This principle may be used more in children's books, but it has proven to be a useful tool for the rapid detection of counterfeits. The color development of hidden ink can be achieved by underwater methods.
Such as: slight heating, water or other reagents slightly moistened, exposed to a specific steam, with a soft pencil on the surface writing or placed under a special light source for observation, the specific method depends on the ink formulation. A variety of novel inks As mentioned earlier, the hidden ink can be used in children's books. It relies on the reaction between two chemicals. One of the chemicals is dispersed in the proper dry offset ink solution and printed. The pattern, another chemical used to color the pattern, can be conveniently added to the felt-tip pen. The phantom book also uses a color change reaction, that is, an edible dye is formulated into a osmotic drying type. Embossed in black ink, the black is then printed into a relief pattern of the mesh. When water is used to paint on the book page, the dye color will penetrate the area around the dot; the pattern seen by the eye changes color. Another interesting technique is to print with a hidden ink containing soft and moderate abrasives. The ink can only develop color when rubbed with a coin. Recently, liquid crystals have also been used to produce some interesting effects.
The phrase "liquid crystal" appears to be somewhat contradictory in its literal meaning because liquid molecules are usually in an irregular configuration, whereas the crystal structure means that the molecules are arranged in an orderly manner. Collective structure usually means that the crystal is a solid and its molecules cannot move. The liquid crystals exhibit the same ordered assembly shape, but because they are fluids, the liquid crystal molecules themselves can be distorted and move between each other. This distortion and movement can be produced by gradually heating the liquid crystal. At this point, due to the destruction of the ordered arrangement of the liquid crystal molecules, the wavelength of the reflected light is changed, so that the liquid crystal changes color, and once cooled down, the liquid crystal can be changed back to the original color. This is a very simple explanation of liquid crystal chemistry, but the reason why liquid crystal is applied in many industrial fields and novelty production fields that require permanent reversible color change is based on this interpretation.
Some uses of liquid crystals include digital thermometers, health diagnostics, and quality control of electrical components. The interest of ink manufacturers is more in terms of novelty. Although the liquid crystals are not easy and costly to allocate to ink media, they still find many uses for LCDs, for example, people can buy them. Heated on the back of the hand can show postcards with hidden patterns and T-shirt shirts that can change color with body temperature, and some even use LCD to advertise in advertisements.
For most ink manufacturers, color inks have not attracted enough interest, but through careful research and the application of simple or complex physical and chemical theories, there have been many interesting products, these products are currently To meet the needs of a small part of the market, however, there is no doubt that the market will continue to propose new requirements that challenge the ink manufacturer's skills. Disinfection ink disinfection is defined as the process of killing or removing various bacteria and microorganisms. Disinfection is mainly used in the pharmaceutical industry to sterilize surgical and medical devices.
Sterilization methods include dry heat, damp heat (high pressure steam sterilization), and gas sterilization or radiation sterilization. Assuming that the packaging material can keep the contents of the package in a sterile state, one of the problems that the user of the device has to clarify in the case of dispensing surgical instruments like in an operating room is that the surgical package has been sterilized. One widely used method is to use a printing ink that can have an irreversible color change in sterilization as an indicator. High-pressure steam sterilization is a popular technique. It disposes the packaged goods under high pressure and superheated steam at temperatures above 100°C. This method of disinfection is more effective than dry heat sterilization because it requires a lower temperature, the shorter the dwell time of the packaged goods in the sterilizer, and the weaker resistance of the bacteria to damp heat. For a variety of reasons, ink manufacturers are greatly limited in the types of chemicals they can use and the types of chemical compounds they use.
Due to the low amount of ink, the color change must be quite noticeable so that a noticeable effect can be easily seen on the substrate. The reaction can only occur under high pressure steam sterilization conditions and cannot occur during dry heat nor in wet ink. The reactants must also be able to disperse in the relevant ink solution to form a stable ink. The choice of raw materials: the choice of raw materials The types of inks that can be used for high-pressure steam sterilization are significantly limited, so the various systems that are commercially available are often the use of certain colorless aluminum compounds that convert to aluminum sulfide. The color changes from white to black. Although various systems differing in the time of discoloration can be obtained, the more reactive the varieties are, the worse their stability is, and they are more easily discolored under dry heat conditions. Certain metal carbonates also exhibit satisfactory color changes, and now high pressure steam sterilization inks containing iron cyanide are available and put into industrial applications. Since such inks cannot be formulated for use in lithography, and the amount of ink under dry offset is so small that color changes are difficult to perceive, gravure printing and flexographic printing are preferred printing techniques for such inks. Screen printing or many can solve the ink problem, but for the long-lived work, this printing method appears too slow.
Another type of printing technology, ink jet printing, is used in high speed packaging lines due to the use of a specialized ink that contains a material that can be bleed through under high pressure steam sterilization conditions.
The gas sterilization method is also subject to many similar restrictions. The advantage of the gas sterilization method is that the operation can be performed at a low temperature, and thus the sterilization method can be used to sterilize products with poor thermal stability. The commonly used gas is ethylene oxide, but care must be taken when using it because ethylene oxide can form an explosive mixture with air.
The color change indicator used must have a production effect on the reaction of ethylene oxide. A substance that can be added to the ink solvent is hydrated magnesium chloride. During the reaction, the resulting magnesium hydroxide makes the acid-base indicator (e.g., Bromophenol blue or methyl red) causes color changes. Another suggested method is to use a mixture that produces a color change when irradiated. This mixture consists of a bleeding pigment and a non-bleeding pigment.
Source: 21st Century Fine Chemicals Network