The development and manufacturing of optically variable pigments have expanded beyond traditional optically variable pigments to include a range of new optical color-changing pigment products such as high chroma optically variable pigments, same color different spectra optically variable pigments, eco-friendly optically variable pigments, and all medium (transparent) optically variable pigments. Here is a brief introduction to the principles of three new types of optically variable pigments: High Chroma Optically Variable Pigments High chroma optically variable pigments are a new type of optically variable pigment with a large color gamut, bright colors, and strong coverage. Its principle is to compress the spectral reflection peak to the maximum extent by constructing a multilayer metal medium thin film, which gives it excellent color saturation and a special metal shimmer. High Transparency Optically Variable Pigments This type of optically variable pigment achieves its unique effect by combining multiple layers of all medium (transparent) nano-thin film materials with different refractive indices. The materials used in the manufacturing process do not contain heavy metals, and the substrates used are transparent materials, making it widely applicable to different colored substrates. High transparency optically variable pigments are widely used in the cosmetics industry. 3D Dynamic Optically Variable Pigments The color-changing effect of traditional optically variable pigments is often singular, and there is no obvious difference in display effect with changes in the viewing angle. 3D dynamic optically variable pigments use a new type of magnetic material as the substrate and incorporate it into the structure of the optically variable pigment using nanotechnology, resulting in a significant 3D color-changing effect. It is one of the optically variable pigments with the highest technical content currently available.
UV fluorescent ink has strict requirements for printing technology due to its unique characteristics in the ink system. The following points need to be paid special attention to during use: (1) Slow volatility: Advantages: good reproduction of printing images; Disadvantages: unable to completely evaporate, the fluorescent ink layer is easy to stick together, the anti-counterfeiting image is blurred, and the layout is dirty, affecting anti-counterfeiting and appearance. (2) Fast volatility: Phenomena such as ink turning white, roller sticking, and ink layer sticking can cause the back of the packaging material to become dirty and may also affect coating and composite processes. Due to differences in printing equipment and operating environment among different manufacturers, such as printing machine speed, drying structure, substrate material characteristics, indoor temperature and humidity, the use of solvents in the printing process needs to be considered comprehensively. It is recommended to compare the dissolution parameters of the binder resin and use 2-3 solvents with different boiling points to print a complete anti-counterfeiting effect pattern. (1) The price of fluorescent ink is more than ten times higher than that of ordinary ink; (2) Fluorescent ink cannot be reused and is easy to get dirty; (3) Long-term solvent flushing of the ink system can dilute the fluorescent pigment and fail to meet anti-counterfeiting requirements.
The luminescence principle of fluorescent ink is to store the light energy under illumination and convert it into internal energy, and then convert it into light energy through photochemical reaction and emit it. Generally speaking, the emitted light after absorbing light energy can be divided into phosphorescence and fluorescence. Although both have similar luminescent effects in the environment, they have significant differences. Phosphorescent materials need to be in the dark environment to emit light after absorbing light energy, while the fluorescence emitted by fluorescent ink requires the presence of light to emit light. In terms of ink display, the color of ordinary ink is presented by the color of reflected light, and the color of absorbed light determines the color of reflected light. However, the color presentation effect of fluorescent ink is significantly different from that of ordinary ink. It can not only output light of different wavelengths but also light of different intensities. For example, the color of fluorescent ink itself is blue, which can absorb the energy of red, blue, purple and other light in the light and convert them into blue wavelength light to emit. This effect makes the object printed with fluorescent ink not only reflect light but also emit light like a radiation source. From a physical point of view, fluorescent ink integrates light of different wavelengths, converts them, and then overlays and emits them, creating a fluorescent color different from reflected light.
As we all know, there are many different types of optically variable ink depending on the manufacturing process. Here, we will take a few common examples of optically variable ink and introduce their operation and application. This is a widely used optically variable ink in fiber products due to its safety and convenience, and is a water-based ink. When printing, a mesh count of 80 to 120 is required for screen printing. After using water-based screen printing optically variable ink, it needs to be heated to 100 degrees and dried for one minute. If time allows, it can be left for 12 hours to dry completely. Then, it needs to be heated at 130 degrees for three minutes in an environmental reaction bridge to obtain a product with excellent fiber adhesion. This is an optically variable ink mainly used for printing on plastic films, metal plates, and other surfaces, and is an oil-based ink. When printing, a mesh count of 100 to 200 is required for screen printing. It should be noted that when using this type of optically variable ink, solvents such as esters, ketones, or adhesives such as resins and minerals need to be added. This optically variable ink is made by adding DOP plasticizer to ultrafine particles of vinyl acetate copolymer, which expands the particles. Compared with other optically variable inks, it has the characteristic of being not easy to dry. After using screen printing to print, the plate does not need to be cleaned, and the residual ink on it can be used without being affected.
When using fluorescent ink for printing, patterns with large color differences may have a defect called white spots. In this case, it is necessary to perform defect handling. For example, when printing large areas, yellow fluorescent ink is used for patterns containing black text, and defect handling is required for the colored parts other than the black text. The specific range of the white spot correction is determined by the thickness of the strokes of the text to be processed and the area of ink deposition of the fluorescent ink in the pattern, which is generally between 0.015-0.025mm. For patterns with wider lines and more ink deposition, a larger value of white spot correction can be applied, which does not affect the overall color effect. However, for more delicate patterns and lighter strokes of text, it is necessary to control the correction to below 0.020mm to prevent distortion of the overall pattern. Due to the wide application of fluorescent ink and the advancement of technology, multi-color fluorescent ink printing is becoming more and more common. In order to achieve better color effects for printed products, it is necessary to arrange the ink colors accurately during printing. Colored fluorescent inks should not be mixed with other inks, and should be strictly separated during printing. If a five-color printing machine is used, colored fluorescent ink and the other four inks can be printed together at once, but it should be noted that the colored fluorescent ink should be printed last to avoid being covered by other inks and losing its characteristics. If a four-color printing machine is used, the four basic colors should be printed first and allowed to dry before printing the colored fluorescent ink.
When using fluorescent ink for printing, there may be a defect called "white gap" in the color effect of patterns with large color difference. In this case, hazard printing should be carried out. For example, when using yellow fluorescent ink for printing patterns containing black text on a large area, hazard printing should be carried out on the remaining colored parts except for the black text. The specific scope of the white gap to be filled is determined by the thickness of the strokes of the text to be processed and the area of the fluorescent ink printing of the pattern, generally between 0.015mm and 0.025mm. For patterns with wide lines and more ink, a larger value of white gap can be filled, which will not affect the overall color effect. However, for fine patterns and delicate strokes of text, it is necessary to control it below 0.020mm to prevent overall distortion. With the wide application and technological advancement of fluorescent ink, the printing application of multi-color fluorescent ink is becoming more and more popular. In order to make the color effect of the product after printing better, it is necessary to accurately sort the ink colors during printing. Colored fluorescent ink should not be mixed with other inks, and should be strictly separated during printing. If a five-color printing machine is used, colored fluorescent ink and other four-color inks can be printed together at one time, but it should be noted that colored fluorescent ink should be printed last, otherwise it will be covered by other inks and cannot well present the characteristics of colored fluorescent ink. If a four-color printing machine is used, the ordinary four colors should be printed first and allowed to dry before printing the colored fluorescent ink.
Fluorescent ink is a special pigment with unique luminescent properties. Here, we introduce its performance characteristics and printing techniques. Special color pigments in fluorescent ink can absorb energy from ultraviolet light and convert it into visible light of longer wavelengths. Thus, in a dark environment, products printed with fluorescent ink can produce a vibrant colored light. Compared to other oil-based or rubber-based ink particles, fluorescent ink particles are finer and softer, which gives it a unique transfer method during the printing process. When selecting printing plates for fluorescent ink, metal plates should be used. Additionally, in order to ensure the luminous effect of fluorescent ink, paper with light or colored shades should be avoided, and instead, brighter and whiter paper should be chosen. This will make the luminescent properties more noticeable. When using coating printing, a small amount of ink should be used for the first printing and a second printing should be done. If printing on black or colored objects, an opaque ink should be used as a base layer before applying fluorescent ink.
UV fluorescent ink is a special type of ink that emits visible light between 400nm to 800nm when exposed to ultraviolet radiation between 200nm to 400nm. This ink is easy to print, cost-effective, has good concealment, bright colors, and convenient inspection, making it highly favored by consumers. Since fluorescent ink uses additive color mixing, the brightness of the mixed color increases with the increasing mixing amount, which is significantly different from subtractive color mixing. Different color hues can also be obtained using different mixing ratios. The luminous performance of fluorescent ink printed by screen printing depends on the content of fluorescent powder. The higher the content of fluorescent powder, the higher the luminous brightness. However, if water-based fluorescent ink is used, the highest luminous intensity is achieved only when the fluorescent powder content is 6%, excessive or insufficient content will reduce the luminous intensity of the ink. Regarding the color rendering of fluorescent ink, the red, green, and blue colors have different color tone reproduction abilities. The blue ink will cause a loss of the bright tone layer due to its bright component. The performance of the printing substrate also affects the color rendering of fluorescent ink. It is best to use paper without fluorescent agents and good water absorption.
Optical variable ink is a typical anti-counterfeiting ink in the field of packaging printing. In recent years, it has become a common practice to apply anti-counterfeiting technology to packaging in order to protect consumers' rights and ensure the reputation of enterprises. Here we will introduce the application of optical variable ink in packaging printing. Due to its complex manufacturing process, difficult formulation technology, and high difficulty of imitation, optical variable ink occupies an important position in the field of anti-counterfeiting. Its manufacturing process first selects materials with different refractive indices to make optical variable thin film fragments, and then uses a series of physical and chemical methods to make different optical variable inks suitable for offset printing, letterpress printing, gravure printing, and screen printing. After being printed on the item packaging, the fragments in the optical variable ink can still maintain their original dynamic color-changing effect, pearl luster, metallic luster effect, and other characteristics. It is precisely because of this special point that it has anti-counterfeiting characteristics that other inks do not have. At the same time, optical variable ink is non-toxic and harmless after printing, and does not pollute the environment, so it is widely used in packaging fields such as cigarettes, alcohol, and cosmetics.
