First, the concept of security ink
The so-called security ink refers to the ink used in various kinds of securities (such as banknotes, cheques, stamps, passports, etc.), there is a certain copying equipment (such as commercial offset printing presses, screen printing machines, color copiers, desktop printing System) Forged features. At present, security ink has been widely used in the anti-counterfeiting of commodities.
Second, the type of security ink
There are many types of security inks that can be roughly classified into the following categories;
1) Engraving gravure ink 2) OVI (light variable ink)
3) Pearlescent and metallic inks 4) Luminous inks 5) Infrared inks 6) Magnetic inks 7) Forensic inks 8) Anti-printing inks
Third, security ink technology, economic analysis
l, engraving gravure ink
Engraving and gravure printing is a very old way of printing. The unique touch and optical characteristics of printed products have produced excellent public anti-counterfeiting effects. Therefore, it has been used for the printing of advanced security products such as banknotes and stamps. The development of engraving and gravure printing machines has gone through such stages as hand gravure printing, electric rotary gravure printing, and Orlov gravure printing. Gravure inks also continue to improve with the development of gravure printing machines.
The development of modern gravure ink has undergone the following three stages;
A) Wipe the large cloth, roll the long cloth into a roll and press the excess ink under pressure in direct contact with the printing plate.
B) Gravure inks suitable for trichloroethylene wipes with backing paper. Our country still used this kind of ink before the seventies. Although the trichloroethylene wiper works well for this type of ink, and the hand feel of the print is also very prominent, but trichloroethylene is a toxic organic chemical solvent, which is harmful to the human body. For the sake of environmental protection, India has to develop new inks.
C) Cover liner gravure ink. In order to solve the problem that trichloroethylene is harmful to the human body, companies that produce gravure inks in the world have successively developed gravure inks for gravure backing papers. The predecessors of printing inks developed water-striped backing gravure inks in the mid-seventies.
D) Water does not smear dirty gravure ink. In the early 1980s, this kind of ink began to appear. Its application was a revolution in banknote printing technology. With the elimination of liners, it improved production efficiency, reduced the labor intensity of workers, and was more environmentally friendly.
2, OVI (light variable ink)
OVI is an excellent public security feature. At present, there are three types of OVIs in the world. They are OVI optical film pigments from SICPA, OVI liquid crystal from G&D, and Mica titanium OVI from MERK. But the most widely used is SICPA's OVI.
(1) SICPA's OVI features a 60-degree change in viewing angle. There will be two apparently different colors. The first color can be observed under total reflection, in other words at a viewing angle of 90 degrees. When the observation angle is rotated from 60 degrees to about 30 degrees, the first color disappears and the second color appears to be strengthened.
The OVI uses pigments specially prepared for multi-layer films produced by FLEX, USA.
The role of the ink matrix (the binder) is to transmit the optically variable material and to permanently and firmly fix the optically variable material on the printed substrate in a directional manner.
The difference in color at different angles is the result of reflection, refraction, and interference of light at the multilayer interface of the film. The degree of reflection and refraction depends on the wavelength of the light and the material at the interface. For a given multilayer structure, the reflected light interferes with the refracted light such that the reflected light on the second surface has a longer wavelength and some wavelengths of light cancel. As the viewing angle changes, the interference condition that produces a given color disappears, and then the interference condition that produces the second color appears.
The choice of materials, number of layers, and thickness determine the color pair. It can be theoretically any combination including the infrared portion of light. For the observation of the human eye, strong contrasts such as gold/green, magenta/green, green/blue, and green/magenta are preferred.
OVP manufacturing suitable for adding printing inks is a complex process that involves multilayer high precision vacuum deposition of dielectric layer materials and metals. Finely selected particle size distributions, special organic treatments of pigments (OVPs), and reasonable components of the binder produce OVI products that are validated by industrial production, thereby introducing light variability into the banknote design section. Therefore, ink has a relatively high cost due to its complicated structure and difficult manufacturing process. Therefore, ink consumption and printing surface are very important. In the smallest 100mm2 printing area, the ink coverage between 60 and 80% can be easily identified by the public.
In order not to affect the OVI's light-variable effects, the tint and background offset should be carefully selected.
The general color around the OVI can be the same as the light variable print hue under the 90 degree viewing angle. In this way, the contrast between two colors at a small angle can be improved.
OVI's printing methods include gravure gravure printing and screen printing. Both types of printing have their own characteristics. Gravure printing combines the gravure gravure with the light-transforming effect.
Screen printing is a very suitable printing method, and it is possible to obtain excellent prints with light-transforming effects. When printing large webs, such as solid bottom or large ink coverage, the light-changing effect and the contrast of the two colors can be further improved.
(2) G&D's liquid crystal OVI also has the property of changing the viewing angle, that is, the color change. The study of liquid crystals by humans dates back to 1888, but industrial applications of liquid crystals started late. Until the 1960s, Americans measured the surface temperature through the color change of cholesteric liquid crystals, which opened up the precedent of liquid crystal applications. After decades of development, liquid crystals have been used in many fields, such as liquid crystal displays (computers, televisions), liquid crystal filters for optical fibers, and so on. Liquid crystals have both the fluidity of the liquid and the birefringence of the crystal, and thus belong to the branch of condensed matter physics. Through intensive research on the symmetry of liquid crystals, diffraction physics of cyclic structures, and structural analysis, people have accumulated knowledge of many unique properties of liquid crystals, making liquid crystals a new material with broad application prospects.
Liquid crystal OVI is an optical property that utilizes the selective reflection of cholesteric liquid crystals. Since the cholesteric liquid crystal has a helical structure, its intrinsic pitch is generally several thousand A degrees, which is equivalent to the wavelength of visible light, and thus Bragg reflection (ie, light variable effect) of visible light occurs. In order to improve the resistance of the liquid crystal OVI, the liquid crystal is generally polymerized, that is, a polymer liquid crystal material.
The liquid crystal OVI may be a gravure ink and a screen ink, but it must be printed on a dark-colored background when applied, and it has not yet been applied to currency notes.
Liquid crystal OVI is lower in price than OV1 of SIGPA.
Polymer liquid crystal is used in OVlg [, can also be used for forensic ink.
(3) The new mica titanium OVI launched by MERK in November last year is the latest type. The pigment used in the ink is a four-layer structure. The center is mica, the second layer is coated with titanium dioxide by electroless plating, and the third layer is silicon dioxide. The fourth layer is titanium dioxide. Titanium dioxide is divided into two types: one is rutile, the specific gravity is 4.62, and the refractive index is 2.72: one is anatase, the specific gravity is 3.84, and the refractive index is 2.55. The pigment uses perovskite titanium dioxide. Since the refractive index is significantly different from that of mica and silica, color change is likely to occur after refraction, reflection, and interference. (where titanium dioxide and silicon dioxide are transparent)
This OVI only has good results for screen printing.
The so-called security ink refers to the ink used in various kinds of securities (such as banknotes, cheques, stamps, passports, etc.), there is a certain copying equipment (such as commercial offset printing presses, screen printing machines, color copiers, desktop printing System) Forged features. At present, security ink has been widely used in the anti-counterfeiting of commodities.
Second, the type of security ink
There are many types of security inks that can be roughly classified into the following categories;
1) Engraving gravure ink 2) OVI (light variable ink)
3) Pearlescent and metallic inks 4) Luminous inks 5) Infrared inks 6) Magnetic inks 7) Forensic inks 8) Anti-printing inks
Third, security ink technology, economic analysis
l, engraving gravure ink
Engraving and gravure printing is a very old way of printing. The unique touch and optical characteristics of printed products have produced excellent public anti-counterfeiting effects. Therefore, it has been used for the printing of advanced security products such as banknotes and stamps. The development of engraving and gravure printing machines has gone through such stages as hand gravure printing, electric rotary gravure printing, and Orlov gravure printing. Gravure inks also continue to improve with the development of gravure printing machines.
The development of modern gravure ink has undergone the following three stages;
A) Wipe the large cloth, roll the long cloth into a roll and press the excess ink under pressure in direct contact with the printing plate.
B) Gravure inks suitable for trichloroethylene wipes with backing paper. Our country still used this kind of ink before the seventies. Although the trichloroethylene wiper works well for this type of ink, and the hand feel of the print is also very prominent, but trichloroethylene is a toxic organic chemical solvent, which is harmful to the human body. For the sake of environmental protection, India has to develop new inks.
C) Cover liner gravure ink. In order to solve the problem that trichloroethylene is harmful to the human body, companies that produce gravure inks in the world have successively developed gravure inks for gravure backing papers. The predecessors of printing inks developed water-striped backing gravure inks in the mid-seventies.
D) Water does not smear dirty gravure ink. In the early 1980s, this kind of ink began to appear. Its application was a revolution in banknote printing technology. With the elimination of liners, it improved production efficiency, reduced the labor intensity of workers, and was more environmentally friendly.
2, OVI (light variable ink)
OVI is an excellent public security feature. At present, there are three types of OVIs in the world. They are OVI optical film pigments from SICPA, OVI liquid crystal from G&D, and Mica titanium OVI from MERK. But the most widely used is SICPA's OVI.
(1) SICPA's OVI features a 60-degree change in viewing angle. There will be two apparently different colors. The first color can be observed under total reflection, in other words at a viewing angle of 90 degrees. When the observation angle is rotated from 60 degrees to about 30 degrees, the first color disappears and the second color appears to be strengthened.
The OVI uses pigments specially prepared for multi-layer films produced by FLEX, USA.
The role of the ink matrix (the binder) is to transmit the optically variable material and to permanently and firmly fix the optically variable material on the printed substrate in a directional manner.
The difference in color at different angles is the result of reflection, refraction, and interference of light at the multilayer interface of the film. The degree of reflection and refraction depends on the wavelength of the light and the material at the interface. For a given multilayer structure, the reflected light interferes with the refracted light such that the reflected light on the second surface has a longer wavelength and some wavelengths of light cancel. As the viewing angle changes, the interference condition that produces a given color disappears, and then the interference condition that produces the second color appears.
The choice of materials, number of layers, and thickness determine the color pair. It can be theoretically any combination including the infrared portion of light. For the observation of the human eye, strong contrasts such as gold/green, magenta/green, green/blue, and green/magenta are preferred.
OVP manufacturing suitable for adding printing inks is a complex process that involves multilayer high precision vacuum deposition of dielectric layer materials and metals. Finely selected particle size distributions, special organic treatments of pigments (OVPs), and reasonable components of the binder produce OVI products that are validated by industrial production, thereby introducing light variability into the banknote design section. Therefore, ink has a relatively high cost due to its complicated structure and difficult manufacturing process. Therefore, ink consumption and printing surface are very important. In the smallest 100mm2 printing area, the ink coverage between 60 and 80% can be easily identified by the public.
In order not to affect the OVI's light-variable effects, the tint and background offset should be carefully selected.
The general color around the OVI can be the same as the light variable print hue under the 90 degree viewing angle. In this way, the contrast between two colors at a small angle can be improved.
OVI's printing methods include gravure gravure printing and screen printing. Both types of printing have their own characteristics. Gravure printing combines the gravure gravure with the light-transforming effect.
Screen printing is a very suitable printing method, and it is possible to obtain excellent prints with light-transforming effects. When printing large webs, such as solid bottom or large ink coverage, the light-changing effect and the contrast of the two colors can be further improved.
(2) G&D's liquid crystal OVI also has the property of changing the viewing angle, that is, the color change. The study of liquid crystals by humans dates back to 1888, but industrial applications of liquid crystals started late. Until the 1960s, Americans measured the surface temperature through the color change of cholesteric liquid crystals, which opened up the precedent of liquid crystal applications. After decades of development, liquid crystals have been used in many fields, such as liquid crystal displays (computers, televisions), liquid crystal filters for optical fibers, and so on. Liquid crystals have both the fluidity of the liquid and the birefringence of the crystal, and thus belong to the branch of condensed matter physics. Through intensive research on the symmetry of liquid crystals, diffraction physics of cyclic structures, and structural analysis, people have accumulated knowledge of many unique properties of liquid crystals, making liquid crystals a new material with broad application prospects.
Liquid crystal OVI is an optical property that utilizes the selective reflection of cholesteric liquid crystals. Since the cholesteric liquid crystal has a helical structure, its intrinsic pitch is generally several thousand A degrees, which is equivalent to the wavelength of visible light, and thus Bragg reflection (ie, light variable effect) of visible light occurs. In order to improve the resistance of the liquid crystal OVI, the liquid crystal is generally polymerized, that is, a polymer liquid crystal material.
The liquid crystal OVI may be a gravure ink and a screen ink, but it must be printed on a dark-colored background when applied, and it has not yet been applied to currency notes.
Liquid crystal OVI is lower in price than OV1 of SIGPA.
Polymer liquid crystal is used in OVlg [, can also be used for forensic ink.
(3) The new mica titanium OVI launched by MERK in November last year is the latest type. The pigment used in the ink is a four-layer structure. The center is mica, the second layer is coated with titanium dioxide by electroless plating, and the third layer is silicon dioxide. The fourth layer is titanium dioxide. Titanium dioxide is divided into two types: one is rutile, the specific gravity is 4.62, and the refractive index is 2.72: one is anatase, the specific gravity is 3.84, and the refractive index is 2.55. The pigment uses perovskite titanium dioxide. Since the refractive index is significantly different from that of mica and silica, color change is likely to occur after refraction, reflection, and interference. (where titanium dioxide and silicon dioxide are transparent)
This OVI only has good results for screen printing.
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