Since organic pigments have bright shades and high color strength, especially in recent years, the output of high-end organic pigments with high performance such as light resistance, heat resistance and migration resistance has increased year by year, and their application scope has also continued to expand.
Today, let ’s talk about the application of organic pigments in inks. In a certain sense, the basic composition and characteristics of printing inks are similar to paints. They are composed of different resins as binders, colorants and auxiliary agents. They are dispersed and rolled. Become a uniform product with good printing performance, bright colors and drying and transfer performance.
1. Composition and type of printing ink
(1) Link material
As a fluid part, the binder can evenly disperse the colorant in it, and has specific adhesion on the printing object, the necessary gloss and drying characteristics, and has appropriate viscosity. There are many types of link materials:
Oil-type linking material: It can be obtained by heating and polymerizing dry vegetable oils (such as tung oil, linseed oil, etc.). The commonly used polymer oils form dimers, trimers or polymers based on the intermolecular double bond. Has different viscosities.
Resin type linking material: it is made from different types of synthetic resin and high boiling mineral oil, etc., and can be divided into high temperature resin oil: 250 ^ to disperse and dissolve the resin in the vegetable oil / mineral oil system, the printing ink has good gloss, High stability; low temperature resin oil: Disperse and dissolve the resin in the oil at 200 degrees, the gloss is slightly worse, but the fixation is fast.
Solvent type binder: It is composed of resin and organic solvent, does not contain vegetable oil, and belongs to volatile drying type.
Water-based binder: Water is used as the dispersion medium to disperse and dissolve the hydrophilic polymer in it uniformly. It has the characteristics of safety, non-toxicity, and reduced environmental pollution.
The application of organic pigments and inorganic pigments (a few) as printing ink colorants can make the substrate exhibit different colors and good printing characteristics (such as gloss, viscosity, etc.). Different types of inks have their specific pigments for coloring.
(3) Filling materials and additives
Mainly used to adjust the viscosity, fluidity, and hiding power of ink, improve the body and constitution of ink, and reduce costs. The fillers are mostly inorganic compounds, such as ultra-fine calcium carbonate or colloidal calcium carbonate, which have excellent transparency and brightness, and others such as aluminum hydroxide and sulfuric acid. The additives in the printing ink can improve the application performance, such as: wetting agent, viscosity reducer, drier, etc.
The type of printing ink can be divided into: letterpress ink, planographic ink, gravure ink, mesh ink, etc. according to the type of printing; according to its use can be divided into: printing iron ink, plastic ink, glass ink, copper plate ink, etc .; can be divided according to product characteristics For: resin ink, bright ink, ultraviolet light solid (UV) ink, solvent ink, water-based ink, etc.
In recent years, various inks with different characteristics have developed rapidly, and application performance has been continuously improved. Especially for packaging paper and plastic printing ink, the output of varieties has increased significantly. Taking gravure plastic printing ink as an example, it is widely used in a variety of plastic films. According to its printing performance comparison, PVC, PET, ethylene-vinyl acetate copolymer is better; and there are a variety of printing methods, such as PE and PP films. Printed with a single layer surface, using the composite film printing method of the corresponding composite ink.
Water-based printing ink is to select specific water-soluble resins, such as water-based acrylic resin, water-based maleic acid rosin resin, polyvinyl alcohol, latex, and methyl cellulose, etc., using water as a dispersion medium, adding a co-solvent (such as ethanol , Propanol, isopropanol, ethylene glycol, etc.) and colorants.
2. The requirements of printing ink on colorants
Ink is the main application area of organic pigments. In developed countries, organic pigments used in printing inks account for about 50% -60% of its total output. With the development of printing technology equipment and the increase in the consumption of cultural goods, organic pigments The quality raises higher requirements. Organic pigments as printing ink colorants should have the following main application characteristics:
① The spectral characteristics of the three complementary colors (yellow, magenta, and cyan, that is, Y. M. C.) that meet the printing requirements have little harmful absorption of the spectrum.
②The color is bright and the color saturation is high; high coloring strength and high gloss.
③ In four-color printing, the yellow pigment should have excellent transparency to meet the quality requirements of color reproduction.
④Good ink printing suitability, such as the fluidity of colored ink, ink transfer characteristics, plastic viscosity, thixotropy, etc.
⑤Compatibility with linking materials, soft pigment particles, good dispersibility (ED), to ensure high production efficiency of rolling ink.
⑥ As a solvent printing ink coloring pigments should have good solvent resistance, no color change, and do not increase the viscosity of the ink.
⑦ Preparation of iron printing ink should be subjected to 170Y heat treatment without color change.
3. Varieties of organic pigments for inks
The organic pigment varieties used in conventional offset printing inks have undergone long-term practical screening and the structural varieties have not changed much. The key is to continuously improve their intrinsic quality and prepare special dosage products with different application properties through surface modification treatment. The commonly used chromatographic varieties can be listed as follows:
Yellow and orange spectrum: C. I. Pigment Yellow 12, C. 1. Pigment Yellow 13, C. I. Pigment Yellow 14, C. I. Pigment Yellow 74, C. I. Pigment Yellow 81, C. I. Pigment Yellow 83; C. I. Pigment Orange 5, C. I. Pigment Orange 13, etc.
Blue spectrum: C. I. Pigment Blue 15: 1, C. I, Pigment Blue 15: 3, C. I. Pigment Blue 15: 4, C. I. Pigment Blue 61, etc.
Among them, the mass-produced and used varieties include: CI Pigment Yellow 12, CI Pigment Red 57: 1, CI Pigment Blue 15: 3, etc. It has bright colors, low prices, high color strength, and high light fastness. It is widely used in In lithography, gravure, and screen printing inks; Pigment Yellow 12 and Pigment Blue 15: 3 are also important pigments for solvent inks and water-based inks.