Special glossy printing is a new type of printing technology that has become more popular in the packaging printing industry in recent years. Special glossy printing processes currently include: metallic glossy printing, pearlescent printing, pearlescent printing, refractive printing, photochromic printing (fluorescent, variable gloss). ), laser holographic logo printing, imitation metal etching printing, crystal luster printing and so on. Among them, metal-gloss printing uses aluminum-foil metal composite paper, which is printed with high-transparency ink and forms a special metallic luster effect on prints. Laser holographic logo printing and photochromic printing have already been introduced in other chapters. We will not elaborate here. This section will focus on pearl printing anti-counterfeiting technology and mirror glossy ink anti-counterfeiting technology with relatively weak anti-counterfeiting performance.
(I) Pearlescent ink anti-counterfeiting printing technology
Pearlescent printing is the first printing of silver paste on the surface of the printed material, and then printed with a high transparency ink. The silver paste reflects a pearlescent effect through the transparent ink layer. Pearlescent printing is printed using inks that incorporate mica particles, giving the prints a glossy effect similar to that of pearls and shellfish. Pearlescent printing can be carried out by means of offset printing, flexo printing, gravure printing or screen printing. The use of pearlescent pigments is similar to the use of gold and silver powders and is easier to master and operate.
1 Pearlescent pigment
Pearlescent pigments developed from the earliest natural angular scales to synthetic pearlescent pigments made from basic aluminum carbonate and aluminum hydrogen arsenate. It is a semi-transparent, micro-flaky pigment that produces a pearlescent effect. Because the former have limited sources and are expensive, the latter are toxic, limiting their use. Currently, titanium dioxide-coated mica pearlescent pigments (hereinafter referred to as mica pearlescent pigments) coated with mica as a carrier and multilayered metal oxides are widely used. Pearlescent pigments are inorganic pigments. This pearlescent pigment is different from other general pigment pigments in that it is made into a powder by reflection and refraction of light, each powder having a size of about 3 to 150 μm. Its color can be achieved by controlling the type of metal oxide on the mica sheet and the thickness of the metal oxide Envelope. For example, with white titanium dioxide enveloping mica, when the thickness of the enveloping layer is 60 μm, the interference color of the pigment is silver-white, and the transmission color is colorless; when the thickness is 90 μm, the interference color is gold, and the transmission color is purple; the thickness is At 115 μm, the interference color is red and the transmission color is green. If enveloping with a non-ferrous metal oxide, it is also possible to obtain a shiny pigment in the color of the metal oxide.
At present, there are 325 mesh, 400 mesh and 800 mesh pigments for pearlescent inks used in packaging and printing. In the variety of inorganic pigments, such as gold, brick red, blue, light yellow, etc.; useful organic pigments, orange, blue, green, yellow and other kinds. No matter what kind of pearlescent ink pigments, they should have the characteristics of sheet form and high reflectivity.
(1) Natural pearlescent pigments are guanine crystals (Guanine) that are 2-amino-6-hydroxyuridine ring C5H5N50 extracted from the scales of living marine fish.
(2) Synthetic pearlescent pigments Basic lead carbonate, bismuth oxychloride (BiOCl), lead hydrogen arsenate, or lead hydrogen phosphite metal oxide synthesized by chemical 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) The complex pearlescent pigments are formed by the co-melting of fatty acid glycol esters and fatty acid dialkyl alcohol amides.
(4) A common type of compound-coated pearlescent pigment. The use of metal compounds on the surface of non-metal mica adsorption, the use of light refraction and diffraction of the carrier to form a pearl color, the general use of gas phase coating and liquid phase coating method. The liquid-phase hydrolysis process is simple in operation, mild in reaction conditions, and less in equipment investment. Mica titanium and iron are formed on the mica sheet by deposition of TiO2 or Fe(OH)3 coating on the surface of the mica sheet, and are formed by baking and baking. According to the thickness of mica or the material of the coating layer, various color shades appear. Iridescent, silver, gold and mica iron.
1), silver type: coated thin TiO2 on the surface of mica substrate;
2), iridescent interference type: in the mica substrate surface coating TiO2;
3), Mica iron coloring: Mica-based tree surface coated with different types of oxides or organic substances:
4) Gold type: coated oxide on the surface of substrate
2 Pearl ink preparation
(1) Selection of pearlescent pigments
Pearlescent pigments are characterized by a pearlescent glitter effect. In order to give full play to this feature, when deploying pearlescent pigments, there are three relationships that should be mastered.
First, master the relationship between the size of the pearlescent pigment and the flash effect. Generally, the diameter of the pigment flakes (short diameter) is large, the distance between the flash sources (ie, the distance between the pearlescent pigment flakes and the flakes) is large, and the flash effect is dispersed; conversely, the diameter of the flakes is small and the distance between the flashlight sources is small, and the flash effect is small. Focus on.
Second, to grasp the relationship between the size of pearlescent pigments and the flash intensity. The larger the diameter of the pearlescent pigment, the more chance that the surface receives multiple reflections and refractions of light, and the stronger the intensity of the flash, and vice versa, the intensity of the flash is weak.
Third, the relationship between the size of the pearlescent pigments and the cohesiveness and the suspension settling property in the binders are well understood. Generally, pearlescent pigments have a smaller particle size and are more likely to agglomerate, and the aspect ratio of the particles is also smaller, so that sedimentation is more likely to occur in the binder. The larger the diameter of the pearlescent pigment, the easier it is to disperse, and the larger the aspect ratio of the particles is. The more easily it is suspended in the link material.
In order to obtain a satisfactorily and evenly dispersed ink in the binder, in addition to grasping the above three relationships, it is also necessary to select an appropriate pearl size pigment having a diameter and an aspect ratio depending on the density of the binder. In the preparation process of the ink, a thickening agent may be added to prevent the sedimentation of the pearlescent pigment, or the pearlescent pigment may be wetted before being dispersed in the binder, so as to avoid the problem of sedimentation caused by aggregation of the particles.
If you need color pearl effect, you can add 0.5 ~ 1% of ordinary color ink in the adjusted pearl powder, you can achieve color pearl effect.
(2) Preparation of pearlescent ink
The pearlescent ink is prepared by adding 10-20g pearlescent pigment to the transparent ink, or blending the pearlescent pigment and the linking material (such as nitrocellulose) in a 1:1 ratio to make the pearlescent ink prepared by blending. Fluidity meets printing requirements.
The preparation method is: first place the pre-weighed pearlescent pigment in a measuring device, and then add the same amount of transparent ink or linking material, and carefully stir with a wooden stick to make it completely wet and become no ball or block The powder is then poured into the remaining amount of clear ink or binder and stirred until homogeneous with a wooden stick or auger. Mixers with large shear forces such as sanding, ball milling, etc. cannot be used when stirring. Do not stir for too long. Because both of these will destroy or exfoliate the pearlescent pigment coating on the mica sheet, the pearlescent pigment loses its original acid resistance and is easily attacked by the acid-base substances in the binder, thereby reducing or destroying the pearl luster.
When blending pearlescent inks, some trace organic pigments can be added. In order to reduce costs, white pearlescent pigments are generally used in combination with other pigment preparation methods. For example, adding white carbon black pigment, you can get ancient silver effect. Pearl color deployment is mainly based on light color, because the dark color when adding dark colors will cover some pearl luster for a long time, especially dark inorganic pigments, thus reducing the pearlescent effect, so generally should not be used. Second, we cannot mix pearlescent ink products. Unlike conventional inks, they can be used to obtain a third color by mixing two inks. If colored pearlescent inks are used for color mixing, complementary colors will appear between two or more pearlescent inks, which in turn will reduce the pearlescent effect. (to be continued)