Since ancient times, humans have used pearls as one of the symbols of beauty, because of its unique and beautiful color, which brings people elegant color enjoyment. In trying to imitate this luster - we call it the pearl effect. After years of research, people have a necessary understanding of the causes and found that this is mainly determined by the physical structure of the pearl itself.
Pearls are formed by alternating wrapping and covering of calcium carbonate layer and protein layer, both of which have different optical refractive indexes, so multiple reflections occur at different levels of pearls. In the same direction, there are multiple beams of light that experience different light paths inside the pearls that are reflected in parallel, and the optical interference that occurs between these rays is the main reason for the formation of the so-called "pearlescent effect."
Since the 17th century, Europeans have begun to use pearl scale extracts to make pearlescent pigments, primarily to meet the needs of the cosmetics industry. To date, there are still some expensive pearlescent pigments produced in this way. The main disadvantages are the high cost and poor stability. Subsequent counterfeit products include lead carbonate crystals of gallium oxychloride crystals, but the former has poor optical stability and cannot be durable; the latter is highly toxic.
In the 1950s and 1960s, pearlescent pigments that had practical significance were developed. This is the "metal oxide/mica" pigment. The German company Merck is not only the pioneer in the development of such products, it still holds more than 400 patents in this area, representing a high quality and continuous creation work spirit.
Although customarily referred to as “pearlescent pigmentsâ€, the range of optical effects exhibited by these products has expanded even further. It has long been not merely a pearl shade, such as the S- and L-grade pigments produced by Merck & Co., Ltd. The sparkling sheen that can be seen clearly can be observed; in another example, the Irodin®/Afflair® 300 and 500 series products are distinguished from the light pearl concept by their color. So for the "metal oxide/mica" class of pigments, people began to call them "special effect pigments."
In order not to confuse the concept, the term “pearlescent pigment†is still used in the following text. The pearlescent pigment cross-section has a physical structure similar to that of a pearl: the core is a mica with a low optical refractive index, and the outer layer is surrounded by a high refractive index metal oxide such as titanium dioxide or iron oxide.
In an ideal application, the pearlescent pigments are uniformly dispersed in the coating and form a multilayer distribution parallel to the surface of the material. As in pearls, the incident light will exhibit pearlescent effects through multiple reflections and interference.
Compared with traditional optical absorption organic and inorganic pigments and optical reflective metal pigments, the coloring principle of pearlescent pigments is completely different, so its effect is also unique. Pearlescent pigments are the main representatives of optical interference pigments.
Pearlescent pigments, with their different particle sizes, exhibit different effects in use. In general, the larger the particles, the higher the gloss and the weaker the hiding power of the background color; conversely, the smaller the particles, the stronger the hiding power of the background and the lower the gloss. Changing the thickness of the metal oxide coated on the mica core, or the type of metal oxide, brings about color changes.
Classified by material composition and light color characteristics, there are mainly several types of pearlescent pigments in the market (take example of IriodinR/AfflairR pigment from Merck in Germany):
Silver white (Iriodin®/Afflair®100s):
The most commonly used varieties consist of anatase or rutile titanium dioxide coated mica flakes. A variety of silvery white luster is displayed from delicate soft to crystal sparkle.
Iriodin®/Afflair® 200s:
The composition of matter is the same as above, except that the titanium dioxide layer is thick and uniform, resulting in selective interference of reflected light. At a particular viewing angle, certain specific colors of light are highlighted, and their complementary colors disappear. Therefore, this series of products have the characteristics of "color change". There are different sizes of products available. Note that different interference color products cannot be mixed, otherwise only a dim gray can be obtained.
Iriodin®/Afflair® 300s:
Titanium oxide and titanium dioxide composite mica composition, different products have a variety of hue golden luster. Compared with lead powder, it has good transparency, soft color and strong three-dimensional effect. There are different sizes of products available.
Iriodin®/Afflair® 500s:
It is composed of iron oxide directly coated with mica and has a warm metallic luster. Products with different particle sizes are available.
In general, pearlescent pigments are used to express gloss more than the proportion of color less.
Another advantage of pearlescent pigments lies in its good physicochemical properties, which are determined by its material composition:
â– Inorganic: stable, good resistance to temperature, strong light and acid-base environment;
â– Non-metallic: No heavy metals, chemically inert, no harm to the environment and human body.
Pearlescent pigments differ greatly from conventional pigments in terms of chemical composition and structure, as follows:
(a) The particle size is relatively large: for offset printing, for example, the grain size of ordinary coloring materials is generally 0.02 to 0.08 μm, carbon black is 0.2 to 0.7 μm, and the size of pearlescent pigments used for printing is 5 μm to 25 μm. Micron is much higher than the former. Larger grain sizes give certain difficulties in printing transfer.
(b) Lamellar structure: This structure is determined by the shape of the mica core and is the basis for the expression of the pearlescent effect. However, it caused inconvenience to the transfer of printing. In the preparation of the ink, it is impossible to apply high speed, large shear force or excessive rolling operation, otherwise the pigment will be destroyed.
(c) Surface morphology: The microscopic surface of the pearlescent pigment is composed of many grooves, giving it a rather high surface energy.
In order to avoid the above-mentioned characteristics causing trouble in the actual printing, major pearlescent pigment suppliers (such as Merck) summed up some practical and effective experiences based on years of research for printing inks and printing companies to adopt:
Pre-wetting of pigments: The pigment should be wetted before it is mixed into the ink. The solvent used for wetting should be compatible with the ink system. Good wetting allows the pigment to be evenly dispersed into the ink, which is the basis for obtaining high-quality pearlescent printing effects. Wetting also overcomes the "dusting" of dry powders during dispersion.
Dispersion of pigments in ink: Pearlescent pigments have good dispersion ability, generally low-speed stirring can be used in low-viscosity inks, try to avoid the use of three-roller machine, high-speed mixer or ball / bead mill and other equipment, resulting in pigment breakage To lose luster, it is recommended that pigments be mixed in the final stage of ink production. When using a disperser or a high-speed mixer, the stirring time for each batch should be kept constant and shortest.
Choose a good transparency of the ink media: whether it is ink color or link material, the level of transparency is an important factor affecting the pearl luster of the ink.
The distribution of the pigment determines the effect: The more pearlescent pigments are distributed in the print coating, the better the uniformity is, the better the pearlescent effect will be. The other point is also important: Only when the pigment wafer is aligned parallel to the surface of the substrate Get the ideal pearl effect.
Iriodin® Pearlescent Pigments Used in the Printing Industry
Since 1956, Merck Co., Ltd. has started to work on the research and development of mica titanium pearlescent pigments. So far, it has three production bases and scientific research institutions in Germany, the United States, and Japan, and its technology has reached the highest level in the world. Currently Merck has more than 400 patents for pearlescent pigments and has been a pioneer in this field.
Merck's Iriodin® pearlescent pigments range from bright, silvery, neon illusions to gold luster similar to metal pigments, and rich light color changes such as bronze and copper. According to different printing methods and customers' unique requirements, Iriodin® pigments with different particle sizes can also be used.
Like other products produced by Merck, Iriodin® also means reliable quality, and its entire range of products has passed the ISO9001 quality system certification. Iriodin® exhibits excellent resistance to harsh light, high temperature and corrosive chemical environments. On the other hand, stable chemistry enables Iriodin® to comply with FDA's strict regulations in food packaging products.
As a special glossy spot color pigment, Iriodin® is easy to combine with commonly used solvent-based or water-based media to make various printing inks with excellent performance and stable performance. And it is easy to operate and will not cause environmental pollution. Iriodin® can be transferred to various substrates such as paper, plastic film, and textile by flexo printing, gravure printing, screen printing, offset printing, etc., so it can be widely used in packaging printing (cosmetics, food, alcohol, tobacco, and pharmaceuticals). Etc.), label printing (beer, soft drinks) and printing (apparel, home textiles, ceramic printing), and even illustrations of books, advertisements, calendars, etc. Iriodin® enables business operators to have more personalized ways to improve the quality and grade of their products, and to effectively highlight their products in a highly competitive market.
Worldwide Merck
The Merck Group is an internationally renowned chemical and pharmaceutical company. The General Office has a history of more than 300 years in Darmstadt, Germany. Currently, there are branch offices in 21 major countries around the world, including 65 production bases in 28 countries.
Merck is known for its strict requirements on product quality. In 1992, Merck's headquarters received the ISO9001 quality management system.
Merck is not only the world's first company to synthesize vitamins C, B, E and K, but is also a world leader in the manufacture of liquid crystals, Iriodin pearlescent pigments, laboratory products and ultra-pure chemical products for the semiconductor industry.
Merck in China
☆1900 Export high-purity reagents to China through ports such as Shanghai, Guangzhou and Tianjin.
☆1927-1931 Pharmaceutical products enter the Chinese market through agents.
☆About 1935 Established E.Merck Co., Ltd. in Shanghai.
☆1960- Marketing laboratory products, pearlescent pigments and other industrial products through agents in China.
☆ 1994-1995 Merck once again dispatched commissioners directly to China, and began to provide product technical consulting for the Chinese market.
☆ 1996-1997 Merck established representatives in Shanghai, Guangzhou and Beijing