Overview of the most popular safety inks

Overview of safety ink (Part 2)

3. Pearlescent and metal ink

(a) mother titanium pearlescent ink

the chemical composition of pearlescent pigment used in pearlescent ink is: wrap a layer of titanium dioxide with high refractive index on the outer layer of mica. Titanium dioxide with high refractive index and mica with low refractive index can produce rainbow colors, which vary according to the thickness of the coated titanium dioxide. 40-60nm is silver, 60-80nm is yellow, 80-100nm is red, 100-120 is blue, 120-160 is green. Because pearlescent pigments only have rainbow color and do not change color, they are low-end products compared with the above mica titanium OVL. However, its low price and good durability can prevent the replication of scanners, extension machines and color copiers, so it has been widely valued. There are many processes used in banknote printing, such as silk printing and coating on paper in the papermaking process. More than 20 countries have adopted pearlescent ink in banknotes. The representative ones are Deutsche mark, Singapore dollar and Austrian shilling. The phosphorescent material is added to the pearlescent ink of Swiss franc, forming the composite safety feature of pearlescent phosphorescence. Pearlescent ink is also used on the yen 2000 denomination

the top manufacturer of pearlescent pigments in the world is German Merck. The pearlescent pigments used on the above banknotes are mostly from the company. In addition, many companies in Finland and the United States also produce pearlescent pigments. There are many varieties of pearlescent pigments produced in China, but the quality is poor

(b) metal ink

at present, the only metal ink used is gravure gold metal ink developed by de La Rue company in the UK. This variety overcomes the shortcomings of spring tension compression testing machine, spring change testing machine and spring fatigue testing machine with poor durability of general metal ink. The printing effect is like pure gold, which is quite noble. Metal ink can prevent scanning and color copying. Gravure metal ink is used on the front of Singapore ten thousand dollar bills

4. Luminous inks

luminous inks are a larger class of safety inks, which are mainly characterized by visible or invisible light excitation in the wavelength range of 200 ~ 2000Nm, emitting visible or invisible light. There are the following types of luminous inks:

(a) UV fluorescent (phosphorescent) inks

UV fluorescent inks refer to inks that emit visible light and invisible light (infrared light) by exciting the ink with 200-400nm ultraviolet light

the properties of UV fluorescent inks depend on the properties of fluorescent pigments used. There are many kinds of fluorescent pigments, which can be divided into three categories chemically; Organic multi light pigments, inorganic fluorescent pigments, rare earth organic complexes. However, only a few varieties of the first two categories are used for banknote printing, and rare earth organic complexes can only be used for general securities due to their poor stability

inorganic fluorescent pigments are used for banknote printing, such as rare earth oxysulfide, zinc sulfide, copper, etc. the luminescence mechanism of inorganic compounds is different from that of organic compounds, which rely on the crystal structure of compounds (organic compounds rely on molecular vibration); Therefore, the particle size of pigment has a great influence on luminescence. The luminescence chromatograms of inorganic fluorescent pigments are relatively complete, including blue, green, yellow, red and infrared. This is a stool light that will react to ultraviolet rays and produce color changes. Some do not emit visible light at 365nm in the long wave, but emit visible light at 254nm in the short wave. The ink made by mixing the two pigments is a dual band ink, which can emit visible light of different colors at two wavelengths (such as French francs)

the ink that emits infrared invisible light excited by ultraviolet light is a relatively new variety. Because it emits invisible light, human eyes cannot recognize it, so it can only be detected with special probes and instruments

inorganic fluorescent pigments have poor printability due to their large particle size. Few of them can be used for offset printing inks. They are generally used for embossing inks, gravure inks, silk screen inks, etc. This kind of ink has good acid resistance

rare earth organic complex fluorescent pigments are rarely used in banknote printing inks (can be used in fluorescent fibers), and are only used in general securities. Due to its poor chemical structure stability, its fluorescence stability and physicochemical resistance are also poor. The color of this kind of pigment is very bright (mainly green and red fluorescence), and there are both long and short wave varieties. A very prominent variety is that there is no fluorescence reaction when it is excited by ultraviolet light at room temperature, but it emits fluorescence at minus 5 ~ 20 ℃ (reactive fluorescent ink, some substances are added to the ink to be printed on the print, and the other part is made into a pen. During identification, the part marked with strokes reacts to produce fluorescence). This kind of ink has good printability

in inorganic fluorescent pigments, most pigments have a certain afterglow, with a time of less than 50 milliseconds as a short afterglow, 50 ~ 100 milliseconds as a medium afterglow, and more than 100 milliseconds as a long afterglow. The ink made of this pigment is called phosphorescent ink. Special instruments can detect the luminous intensity within the afterglow time (such as 5 milliseconds, 10 milliseconds, 20 milliseconds), so as to achieve the purpose of machine reading

(b) visible light fluorescent ink

visible light fluorescent ink refers to an ink that excites visible light or infrared light from 400 ~ 700nm visible light (including monochromatic light and polychromatic light such as sunlight). Generally, fluorescent ink is common, that is, it emits strong fluorescence under sunlight

(c) X-ray fluorescent ink

this kind of ink has been less used at present. The excitation light is X-ray, which was used for machine-readable anti-counterfeiting purposes in some countries in the 1970s. With the development of science and technology, most countries have applied more advanced machine-readable anti-counterfeiting technology

this ink contains compounds that respond to X-rays to achieve machine-readable anti-counterfeiting. The ink cost is low. Generally only gravure printing ink

(d) electroluminescent ink

this kind of ink emits visible or invisible light (infrared light) in the electric field, and this kind of ink has just begun to receive attention

in fact, many materials have luminescence phenomenon in the middle of the electric field (such as UV fluorescent ink, Ovi, etc.), but its luminous intensity is difficult to read by high-speed machine. 45 and 40Cr steel are the most commonly used detector probes. Therefore, efficient electroluminescent materials are selected

electroluminescent materials include organic and inorganic luminescent materials, and inorganic luminescent materials are used in juqian

electroluminescent ink is gravure ink, and its detector can be portable and can also be added to the sorter

in a word, this ink is an effective machine-readable anti-counterfeiting ink

in addition to the above luminous inks, there are some new luminous inks, such as conversion inks

5. Infrared ink

infrared ink is an ink that is transparent or opaque in the near infrared (700-1000nm). Using its characteristics, half of the printed matter can be seen on the instrument, while the other half cannot be seen

6. Magnetic ink

magnetic ink is divided into hard magnetic ink and soft magnetic ink; The difference between the two inks is that hard magnetic inks have residual magnetism while soft magnetic inks basically do not (there is magnetism when there is a magnetic field). (the hysteresis loop is basically a straight line) the magnetic pigments used in hard magnetic inks are generally iron oxide black and iron oxide brown. Hard magnetic pigments are generally used in embossing inks and gravure inks. This kind of ink has poor printability but good durability due to its high content of magnetic pigments

the main production company of hard magnetic pigments is BASF in Germany. The cost of this pigment is low, and the cost of the ink made is also low

soft magnetic ink is a machine-readable anti-counterfeiting ink developed in recent years

7. Forensic ink

the so-called forensic ink contains some substances in the ink, which are difficult to identify on ordinary optical, electrical and magnetic instruments, and can only be identified on large instruments. This kind of ink is rarely known when it is used, and it is only identified when necessary (as evidence in court)

at present, the materials used in this kind of ink are: superconducting materials, polymer liquid crystal materials, inorganic compounds. The physical properties, chemical structure, elemental composition of these materials can be detected only on large instruments, and some of them must be determined by more than two instruments, such as sicpasecu

8. Anti erasure ink

anti erasure ink is used in checks, drafts and other securities to prevent losses caused by the erasure of numbers and signatures

generally, there are two kinds of erasure, one is chemical erasure, and the other is mechanical erasure (erasure with a knife). Therefore, when the anti erasure ink encounters chemical erasure, the printing pattern should change color or fade, and when it encounters mechanical erasure, it should also see the change. (generally observe the changes under the fluorescent lamp)

the anti erasure ink is generally water-based ink, and the formula includes chromogenic agent (diphenylguanidine, etc.), dye, fluorescent material, etc., which can prevent chemical erasure (oxidant, reductant, etc.). The British government and Masdar company announced to continue to invest £ 60million to establish the graphene Engineering Innovation Center at the University of Manchester for mechanical erasure, and the printing method is generally embossing

IV. anti counterfeiting characteristics of safety inks

every safety ink is not omnipotent in anti-counterfeiting. They can only play an anti-counterfeiting role in a certain crowd, a certain machine, and a certain environment

(1) gravure printing ink

it is characterized by its unique convex feel and special optical performance (invisible pattern), which is a public anti-counterfeiting feature. Most counterfeit banknotes are offset printed (there are also counterfeit banknotes with protruding feeling), and why can't some members of the public recognize them? I think there are the following reasons: first, the publicity is not enough, and the public does not understand the characteristics of gravure printing; Secondly, the gravure printing effect of the printed product itself is not good; Secondly, everyone feels different; Finally, because banknotes will wear out in circulation, their hand feel will become worse, and their optical properties will disappear

(2) ovi

ovi has good public anti-counterfeiting characteristics. At present, there are two kinds of Ovi counterfeiting 100 yuan, one is ordinary green ink, and the other is pearlescent ink. Why can Ovi, which is not very similar, deceive some people? I think: OVL must have a better light to have color change effect, and it is difficult for people to distinguish Ovi in the evening or in places with poor light. Secondly, according to statistics, more than 10% of the population cannot recognize Ovi, such as color blindness, color weakness, myopia, astigmatism and the decline of eye discrimination ability of the elderly

(3) pearlescent ink and metal ink

these two kinds of ink only have the characteristics of anti color copier. Because pearlescent ink and metal ink are easy to obtain, it is easy to forge

(4) luminous ink

fluorescent ink (phosphorescent ink)

fluorescent ink is easy to be forged. Now it is used as a common ink. Due to the low price of fluorescent lamp and high ownership rate, fluorescent ink has been regarded as an important anti-counterfeiting ink

(5) magnetic ink

hard magnetic ink is likely to be forged, because magnetic particles are easy to obtain, and the toner of black-and-white copier has strong magnetism. Soft magnetic is not. It is not easy to forge a system with very good cooperation between magnetic and detector

(8) it is difficult to forge forensic ink and to detect it. But sometimes I have to use it

v. new progress of safety inks

the development of safety inks in the future has the following trends: in gravure inks, the goal is to improve production efficiency, reduce costs, strengthen environmental protection and improve gravure hand feel. The goal of Ovi is to improve the effect of light change and reduce the cost. At present, companies are making efforts to develop polymer liquid crystals. In terms of luminous ink, we aim to develop the system, that is, when developing ink, we also develop detectors and related technologies to improve its machine-readable anti-counterfeiting performance. In terms of infrared ink, it focuses on the development of unique infrared transparent and infrared absorbing materials, and in terms of magnetic ink and forensic ink, it focuses on the development of new materials

VI. conclusion

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