The hottest special gloss printing technology I

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All aspects of special gloss printing technology (I)

Special gloss printing is a new printing technology with relatively popular behavior in the packaging printing industry in recent years. At present, special gloss printing processes mainly include: metal gloss printing, pearlescent printing, pearl gloss printing, refractive printing, photochromic printing (fluorescence, variable gloss), laser holographic logo printing, metal like etching printing, crystalline gloss printing, etc. Among them, metal gloss printing uses aluminum foil metal composite paper and printing ink with high transparency to form a special metal gloss effect on the printed matter. Laser holographic marking printing and photochromic printing have been introduced in other chapters, and will not be discussed in detail here. This section will focus on pearl printing anti-counterfeiting technology and mirror gloss ink anti-counterfeiting technology, which have relatively weak anti-counterfeiting performance

(I) pearlescent ink anti-counterfeiting printing technology

pearlescent printing is to first lay silver paste on the surface of the printed matter, and then print high transparency ink. The silver paste refracts a pearlescent effect through the transparent ink layer. Pearl gloss printing is printing with ink mixed with mica particles, which makes the printed matter produce a gloss effect similar to pearls and shellfish. Pearlescent printing can be carried out by offset printing, flexographic printing, gravure printing or silk printing. Pearlescent pigments are basically similar to gold and silver powders, which are easy to master and operate

1 pearlescent pigment

pearlescent pigment has developed from the earliest natural angular scale to the pearlescent pigment synthesized from basic aluminum carbonate and aluminum hydrogen arsenate. It is a translucent flaky pigment that can produce pearlescent effect. Because the former has limited sources and is expensive, while the latter is toxic, which limits their use. At present, mica pearlescent pigments (mica pearlescent pigments for short) are widely used in titanium dioxide coating with mica as carrier and multi-layer metal oxide coating. Pearlescent pigments are inorganic pigments. This pearlescent pigment is different from other general pigments. It becomes powder through the reflection and refraction of light, and each powder is about 3 ~ 150 μ M is different in size. Its color can be achieved by controlling the type of metal oxide on the mica sheet and the thickness of the metal oxide envelope layer. For example, white titanium dioxide is used to envelop mica, and the thickness of the enveloping layer is 60 μ M, the interference color of the pigment is silver white, and the transmission color is colorless; Thickness is 90 μ M, the interference color is gold, and the transmission color is purple; Thickness 115 μ M, the interference color is red, the transmission color is green, etc. If a non-ferrous metal oxide is used for enveloping, a flashing pigment with the color of the metal oxide can also be obtained

at present, the pigment specifications of pearl ink used in packaging and printing include 325 mesh, 400 mesh and 800 mesh. In terms of varieties, there are inorganic pigments, such as gold, brick red, common blue, light yellow, etc; It is colored with organic pigments, such as orange, blue, green, yellow and so on. No matter what kind of pearlescent ink pigments, they should have the characteristics of sheet shape and high reflectivity

(1) natural pearlescent pigments are guanine crystals (guanine) extracted from the scales of marine fish, that is, 2-amino-6-hydroxyurine c5h5n50

(2) synthetic pearlescent pigments. The standard for their selection through chemistry has always been the basic lead carbonate, bismuth oxychloride (bi0cl), lead hydrogen arsenate or lead hydrogen phosphite metal oxides synthesized by uncertain methods

2pbc03 · Pb (0h) 2, 3 [Pb (ch2c00) 2 · 2PB (0h) 2]+4h2c03 - 2 [2pbc03 · Pb (0h) 2]+ 3PB (ch3c00) 2 + 8h20 + 3PB (ch3c00) 2 + 2h2c03 + 2h20 - 2pbc03 · Pb (0h) 2 + 6ch3c00h

(3) composite pearlescent pigments are formed by the co melting crystallization of fatty acid glycol ester and fatty acid dialkylamide

(4) compound coated pearlescent pigment is a common kind at present. Using the adsorption of metal compounds on the surface of non-metallic mica and the refraction and diffraction of light, the carrier forms pearlescent color. Generally, the gas-phase coating method and liquid-phase coating method are used. The liquid phase hydrolysis process has the advantages of simple operation, mild reaction conditions and less equipment investment. Mica titanium and iron are formed by depositing coating films such as Ti02 or Fe (0h) 3 on the surface of mica sheet, which are dried and burned. According to the thickness of the coating layer on the surface of mica or different materials, they show various colors, such as rainbow type, silver white type, golden type and mica iron type

1), silver white type: coating thin Ti02 on the surface of mica substrate

2), iridescent interference type: COATING TiO2 in the middle layer on the surface of mica substrate

3), micaceous iron coloring type: coating multiple layers of different kinds of oxides or organics on the surface of mica based trees:

4), golden type: coating oxides on the surface of substrates

2 the deployment of pearlescent ink

(1) the selection of pearlescent pigments

pearlescent pigments are characterized by the flashing effect of pearl luster. In order to give full play to this feature, three relationships should be mastered when selecting pearlescent pigments for ink blending

first, master the relationship between the diameter of pearlescent pigments and the flash effect. Generally, if the diameter of the pigment flake is large, the distance between the flash sources (that is, the distance between the pearlescent pigment flakes) is large, and the flash effect is dispersed; On the contrary, if the film diameter is small and the distance between flash sources is small, the flash effect will be concentrated

second, master the relationship between the diameter of pearlescent pigment and the flash intensity. The larger the flake diameter of pearlescent pigment, the more opportunities for its surface to be subject to multiple reflection and refraction of light, and the stronger the intensity of flash; On the contrary, the intensity of flash is weak

third, master the relationship between the diameter of pearlescent pigment and its cohesion and suspension sedimentation in binder. In general, the smaller the flake diameter of pearlescent pigment is, the easier it is to condense, and the smaller the aspect ratio of particles is, so it is easy to settle in the binder. The larger the flake diameter of pearlescent pigment is, the easier it is to disperse, the larger the aspect ratio of particles is, and the easier it is to be suspended in the binder

in order to obtain a satisfactory ink evenly dispersed in the binder, in addition to mastering the above three relationships, it is also necessary to select the appropriate pearlescent pigment with sheet diameter and aspect ratio according to the density of the binder. In the mixing process of ink, thickener can be added to prevent the settlement of pearlescent pigment, or the pearlescent pigment can be wetted in advance and then dispersed in the binder, so as to avoid the problem of particle condensation and sedimentation

if you need color pearlescent effect, you can add 0.5 ~ 1% ordinary color ink to the adjusted pearlescent powder to achieve color pearlescent effect

(2) formulation of pearlescent ink

the formulation of pearlescent ink is by adding 10 ~ 20g pearlescent pigment to transparent ink; Or mix the pearlescent pigment directly with the binder (such as nitrocellulose) in the ratio of 1:1, so that the fluidity of the pearlescent ink prepared by mixing meets the printing requirements

the mixing method is: first put the pre weighed pearlescent pigment into a measuring tool, then add the same amount of transparent ink or binder, carefully stir it evenly with a wooden stick to make it completely wet and become non agglomerating powder particles, and then pour the remaining transparent ink or binder into it, and stir it evenly with a wooden stick or spiral mixer. Do not use a mixer with large shear force during mixing, such as sanding, ball milling, etc. Do not mix for too long. Because both of them will destroy or peel off the film coated by pearlescent pigment on mica sheet, pearlescent pigment will lose its original acid resistance and be vulnerable to the erosion of acid and alkali substances in the binder, thus reducing or destroying the luster of pearlescent pigment

some trace organic pigments can be added when preparing pearlescent ink. In order to reduce costs, white pearlescent pigments are generally used, together with the blending methods of other pigments. For example, if carbon black is added to white pearlescent pigment, the effect of ancient silver can be obtained. Pearlescent color deployment is mainly light color, because when deploying dark colors, a large amount of dark pigments will cover part of the pearlescent luster, especially dark inorganic pigments, thus reducing the pearlescent effect, so it is generally not suitable to use. Secondly, we cannot mix pearlescent ink series products. Unlike ordinary inks, they can get a third color by mixing two inks. If color matching pearlescent inks are mixed, although ceramics and graphene are brittle between two or more kinds of pearlescent inks, there will be complementary color phenomenon, which will reduce the pearlescent effect. (to be continued)

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