As a special type of ink, fluorescent ink is mainly used in the field of anti-counterfeiting and packaging printing (such as anti-counterfeiting and packaging printing for banknotes, bank checks, stamps, cards, and high-grade cigarettes, oils, medicines, cosmetics, etc.), Gravure, offset, flexo and other printing methods. However, in recent years, with the wider and deeper research and development of fluorescent inks, fluorescent inks that can be used for fine screen printing have been continuously developed, thus making fluorescent inks more widely used in screen printing, such as for printing window displays. , decals, bumper guards, industrial insurance equipment, body and outdoor advertising, posters, magazine covers, invitations, cloth labels, etc. Especially in the screen printing of outdoor and indoor advertisements, fluorescent ink printing has the advantage that ordinary ink printing cannot match, and it is gradually popularized and applied in the screen printing of these advertisements. Since fluorescent ink is a kind of special ink, there are some differences between its use technology and general ink. Therefore, it is necessary to be familiar with its characteristics and various printability in order to print beautiful prints. First, the main features and application of fluorescent ink Fluorescent inks, also commonly known as leuco inks, are specialty inks that emit visible light (400-800 nm) under irradiation with a light source such as ultraviolet light (200-400 nm). The main component of the fluorescent ink is a fluorescent pigment. It is a functional luminescent pigment. The difference from ordinary pigments is that when external light (including ultraviolet light) is irradiated, it absorbs certain forms of energy and does not convert into heat energy. The photons are excited, and the absorbed energy is released in the form of visible light, resulting in fluorescence phenomena of different hue. Different shades of light combine to form an unusually bright color, and when the light ceases to shine, the glow phenomenon disappears. This ink, which is sometimes invisible to the naked eye, emits light under ultraviolet light or infrared light, and its use has become more and more popular due to its switchable and hidden characteristics and its inability to accurately reproduce on a color copying machine. Fluorescent ink is a fluorescent pigment added to a certain proportion of polymer resin binders, fillers, stabilizers, and desiccants, and is ground or processed with an ink-making three-roll mill. Fluorescent pigments are the main raw material for the manufacture of fluorescent inks, which can be excited by ultraviolet light to show color. According to their different molecular structures, they can be divided into inorganic fluorescent pigments and organic fluorescent pigments. Inorganic fluorescent pigments are also called ultraviolet fluorescent pigments. They are metal (zinc, chromium, etc.) sulfides or rare earth oxides and trace active agents. Calcined, five-color or light-colored, showing different colors under ultraviolet light irradiation. Its stability is good, but it is difficult to disperse in oily media, poor water resistance, there is a certain amount of wear and corrosion on the plate material. Organic fluorescent pigments, also known as daylight fluorescent pigments, are mainly synthetic resin solid solutions containing fluorescent dyes. They are made of fluorescent dyes (phosphors) that are well dispersed in transparent, brittle resin carriers. When sunlight is irradiated, emission is different from ordinary. The color of the high-brightness visible light, by appropriate blending or with a suitable amount of non-fluorescent pigments, different shades of fluorescent pigments can be obtained. Organic fluorescent pigments are characterized by easy synthesis, good dispersion in oily media, but mostly sunlight excitation, and most of the current stability is not good. In addition, there are organic rare earth fluorescent complexes, which have the advantages of simple preparation, easy refinement, dispersion in oily media, good solubility, colorlessness under visible light, strong fluorescence effect under ultraviolet light excitation, and The advantages of high stability, but the cost is high, and because the organic rare earth fluorescent complex fluorescent ink viscosity is small, can easily cause emulsification in the printing and produce dirty or ink roller deinking phenomenon, especially colorless and transparent ink, often required Check to prevent ink leakage due to deinking, so this kind of fluorescent ink is generally not suitable for lithography. Inks or pigments display color by reflected light, but the ordinary ink color and fluorescent ink color have different reflection characteristics. Fluorescent inks convert short-wavelength light to long-wavelength light and superimpose them to produce fluorescence. By converting and superimposing, a fluorescent color with special brightness and visibility is formed. If fluorescent red has partially reflected red, and other colors (green, blue, and purple) are converted to red wavelengths to emit as red light, as if radiating from the interior of the object, printed matter using fluorescent ink can be obtained four times as much General ink brightness and visibility. Fluorescent inks appear bright in dim light, such as at dusk and dawn. The manufacture of fluorescent inks requires special manufacturing processes and printing processes. We know that fluorescent particles produce a range of bright and particularly clean colors such as yellow, orange, red, crystal red, green, and blue. In a dark environment, fluorescent ink emits this light. The key to this effect lies in the fact that this ink contains a special color pigment that absorbs energy in the ultraviolet region and converts this energy into longer wavelengths of visible light. The application of fluorescent ink in anti-counterfeit printing is very extensive, and has the characteristics of simple implementation, low cost, good concealment, colorful, easy inspection, strong reproducibility, diverse color change, and adaptability to large-scale production lines or packaging printing needs. It is commonly used in banknotes, stamps, financial vouchers (such as cheques, bonds, stocks, commercial papers, bank acceptance tickets, etc.), name cigarettes, famous wines, and some high-end products such as packaging security printing. If used in combination with other anti-counterfeiting technologies, it can produce a better anti-counterfeiting effect. In the printing of banknotes, fluorescent anti-counterfeit inks have been used in many countries today, such as China's fifth set of RMB 100 yuan, 20 yuan using colorless UV fluorescent ink printing five-color fluorescent pattern: is under the name of the underlined offset printing At the printing, the denominations "100" and "20" can be seen under a specific wavelength of ultraviolet light, and the pattern is available for machine reading. In the printing of stamps, there are many countries that have issued fluorescent stamps. For example, the “White Crane†sheetlet issued by China in 1936 has fluorescent substances added to both yellow and red inks. Under ultraviolet light, the small white cranes The eyes are yellow-fluorescent, while the mouth and feet are red and the patterns are exquisite; the "Zhaojun out of the plug" sheetlet not only emits the same color as yellow, orange, and yellow in the pattern, but also the postage stamp with the white ticket edge and the small sheet edged pattern. Ultraviolet light can also emit light blue and blue light, respectively. Stamps with such complex fluorescent characteristics are difficult to forge. In order to achieve the purpose of authenticating the stamps, the commemorative stamps and special stamps issued by our country are almost all fluorescent stamps. In addition, the use of fluorescent digital strips on full-page stamps has also been widely used. Generally, the number of fluorescent security inks is printed in the upper right corner of full-page stamps. Its characteristic is that it is colorless under normal light conditions, and exhibits different colors of fluorescence when exposed to ultraviolet light. Fluorescent stamps have greatly improved the anti-counterfeiting function of our stamps, and also made our stamps very beautiful under ultraviolet light. In the printing of various documents and value-added tax invoices, anti-counterfeiting technologies such as explicit and recessive fluorescent inks are commonly used today. In the packaging and printing of many products such as cigarettes and wine, the use of fluorescent ink is also very widespread. It not only provides a good anti-counterfeiting effect for goods, but also plays an important role in the improvement of the creativity of packaging and decorating. In anti-counterfeiting and packaging printing, the constituent particles of the fluorescent ink are generally softer than other oil-based or rubber-based ink particles, but this does not affect its performance. When using fluorescent inks to print paper products, it is best not to use light or colored paper because the colored paper will reduce or even minimize the brightness of the ink. White or bright paper will enhance the fluorescence effect. Non-coated papers with higher brightness and better ink absorbability are preferably fluorescent inks. Coated white paper can also have a more beautiful effect. However, since only a small amount of ink can be used for printing with coated paper, it is necessary to perform two printings for the best printing effect. In addition, since the fluorescent ink is transparent, it is often imprinted at one time and does not transfer enough ink. In general, a desired density is obtained and multiple printings are required to achieve it. The early fluorescent inks have poor fluorescence effects, low fluorescence intensity, and poor light stability. This is the most common problem in the printing of fluorescent security inks. Nowadays, a new anti-counterfeiting fluorescent agent has been researched and developed, which overcomes the disadvantages of poor stability of general organic fluorescent materials, such as stable fluorescence, high intensity, and novel, clear and long-lasting visible light upon excitation. The new anti-counterfeit fluorescent agent has visual color of colorless or almost five colors, and it is colored by ultraviolet light; in solid, its fluorescence intensity is high, and even if it is exposed to ultraviolet light for a long time, it rarely fades, and there is strong light stability. Anti-sweat, anti sebum; good acid and alkali resistance; easy to disperse, good abrasion resistance; insoluble in water. In order to improve the printing effect of fluorescent inks, fluorescent inks are best printed on papers with high whiteness and substrates such as vinyl films, which can be printed by various methods such as plain printing, gravure printing, flexo printing, screen printing, etc. Fluorescent ink prints are brightly colored and glittering, and the concentration of fluorescent ink pigments can be appropriately increased. However, it is more important to ensure that the printed ink film is as thick as possible. This will make the fluorescent effect better and make up for the fluorescent ink. Poor resistance. On the other hand, screen printing has the feature of thick ink film, which is very suitable for fluorescent ink printing. With the development of screen printing technology and equipment, the use effect of fluorescent ink can be fully utilized in the field of screen printing. Therefore, screen printing has become an ideal printing method for fluorescent ink in recent years. The screen printed fluorescent ink prints can form a uniform ink film layer, which is required for good gloss, stability and weatherability. Since the particle size of the photoluminescent pigment in the fluorescent ink is coarser than that of the conventional pigment, the fluorescent ink generally uses a lower mesh (usually 80 to 150 mesh) screen in screen printing, and is only used for comparison. Rough printing. However, with the continuous emergence of new fluorescent ink products, the particle size of their pigments has become finer and finer screen printing products have now been fully printed. The rheological characteristics of most fluorescent inks are pseudo-plastic flow, and the viscosity is small. This characteristic determines that the printing process is very different from the printing process of ordinary inks. In screen printing, the tension of the screen is high, and an appropriate squeegee is selected to increase the thickness of the ink layer, thereby improving the luminescent effect of the ink. Since the inorganic fluorescent substance emits light from the crystal, if the pressure is too high, the crystal will be broken and the luminous brightness will be reduced. Therefore, in addition to stickiness, connection material, and drying property, the screen printing should pay attention to printing.
The surface of the print can emit a strong, saturated color that attracts attention. Fluorescent inks can be classified into two types of fluorescent printing inks: short-wavelength ultraviolet (excitation wavelength: 254nm) and long-wavelength ultraviolet (excitation wavelength: 365nm), depending on the wavelength of the excitation light source. The color of the fluorescent ink can be divided into colorless fluorescent ink, colored ink. Fluorescent inks and color-changing fluorescent inks. Under normal light sources, colorless fluorescent inks are five-color transparent or nearly white, printed on paper and other substrates are invisible colors, but in the ultraviolet light will show red, yellow, green, blue, white, orange, purple and other colors The colored fluorescent ink can make the original pattern appear more vivid; the color changing fluorescent ink can make the printed product become another color under the irradiation of ultraviolet light. Today, the production technology of electronic ink has been applied to the production of fluorescent inks, and its quality and function have been greatly improved. There are fluorescent fluorescent inks, secondary fluorescent inks and fluorescent penetrating inks in fluorescent inks. The primary fluorescent ink is an ordinary fluorescent ink, which emits a strong fluorescence under the irradiation of 365 nm ultraviolet rays. The types thereof include colorless fluorescent ink, color fluorescent ink, and special short ultraviolet ink. The secondary fluorescent ink is the original printed ink without any fluorescent display under the irradiation of 365 nm ultraviolet light, however, when the printed document encounters water or aqueous ink remover, visible fluorescence can be seen under the irradiation of 365 nm ultraviolet light. This secondary (or hidden) fluorescence effect is mainly applied to the need for two fluorescent materials in the same file (eg, British checks) and anti-counterfeiting facilities that need to be more hidden than primary fluorescence (eg, no fluorescence at the initial exposure to ultraviolet light). Printing) is a more effective security facility than primary fluorescence. The fluorescent penetrating ink penetrates into the matrix of the material after printing for a period of time and discolors. The printed number is reflected on the back of the paper (having the characteristics of black on the front and red on the back), and has excellent anti-printing properties. Sex.
Second, the screen printing of fluorescent ink