Pigment for Paper Ink - Use of Pigment for Paint in Paper Solutions

Paper inks are mainly affected by pigment properties, such as the color, coloring power, density, fineness, activity, solubility, oil absorption, covering power, dispersion, apparent specific volume, surface properties, adhesion, etc.

Main components:

Colorants

Colorants include pigments (organic and inorganic) and dyes. Among them, organic pigments featuring bright color, high coloring powder and fast drying are widely applied in inks, such as azo and phthalocyanine pigments. Inorganic pigments have high light fastness, heat fastness, solvent fastness and covering powder, such as titanium white, cadmium red, chromium green and ultramarine. Pigments are in the particle form instead of dissolution, as the most common colorants for inks. Dyes are in the solution form for coloring at the molecular level, so their effects are inferior to those of pigments. Colorants can change the ink color, concentration, consistency and dryness.

Binders

As a major component of inks, binders are able to disperse colorants and auxiliary materials. They are prepared by dissolving a small amount of natural resin, synthetic resin, cellulose and rubber derivatives in drying oil or solvent. Inks containing binders are in the fluid form, which can be applied into an even and thin layer and change to a dry film of certain strength to protect pigments from peeling.

Binders have significant impact on the printability (e.g. transfer, brightness and adhesion rate) and effectiveness of inks. It is critical to use appropriate binders in printing. Adjust the composition and mix ratio of binder from time to time based on packaging materials, printing requirements, etc.

Paper pigments are mostly inorganic, such as iron oxide and carbon black. But organic dyes are widely applied for more colors.

By colors, major paper pigments include the following.

Color-changing pigments

They mainly consist of pearlescent pigments, thermochromic pigments and photochromic pigments. They are applied in various fields due to color changes on paper under different conditions.

Black pigments

Black pigments rank only second to white pigments. An important black pigment is carbon black, with the blackness and hue as its main quality indicators.

Red pigments

Among inorganic pigments, iron oxide red is a major red pigment, varying from yellow to red/brown and then black. As the most common type, it has high covering power, coloring power, chemical resistance, color retention, dispersion, and low price.

Yellow pigments

Mainly include iron oxide yellow (hydrated iron oxide), etc. Despite dark color, iron oxide yellow has high durability, dispersibility, covering power, heat fastness, chemical resistance, alkali resistance and low price. They are widely applied in building materials.

Green pigments

Major green pigments include chromium oxide green and lead chromium green. The former has high light fastness, heat fastness and chemical resistance, but dark color and low coloring and covering power. The latter has lower durability and heat fastness than chromium oxide green, but brighter color and higher dispersibility. They can be easily processed. Due to toxic heavy metals, organic pigments such as phthalocyanine green have been used less than before.

Blue pigments

Major blue pigments include iron blue, cobalt blue, ultramarine, etc. Among them, ultramarine with large output has alkali resistance, bright color and heat fastness, but no acid resistance. Iron blue has higher acid resistance, covering power and coloring power than ultramarine, but lower alkali resistance and durability. As phthalocyanine blue has better properties, with the coloring power twice higher than that of iron blue, iron blue is used less year by year. Cobalt blue has high heat fastness and light fastness, but low coloring and covering power and high price leading to restrictions in applications.

There are a variety of paper inks, which are classified as follows by printing methods, printing stocks, drying methods, ink characteristics, ink composition, etc.

By printing methods, paper inks are classified into relief printing inks, planographic printing inks, intaglio printing inks, gravure printing inks, screen printing inks, etc. For instance, relief printing inks are mainly for journals, magazines and newspapers, while gravure printing inks for high-quality albums and bills.

By printing stocks, paper inks are divided into paper, metal, plastic and fabric inks.

By drying methods, paper inks are divided into penetration drying inks, oxidative polymerization inks, volatile drying inks, photo-hardening inks, thermosetting inks, cold setting inks, etc. They can be dried by means of natural drying, hot air drying, infrared drying, ultraviolet drying, drying by cooling, etc.

By ink characteristics, paper inks are divided into color inks (e.g. yellow, red, blue, white, black, gold and silver), functional inks (e.g. magnetic inks, anti-counterfeiting inks, food-grade inks, foaming inks, aromatic inks and recording ink) and resistant inks (e.g. light resistance, heat resistance, solvent resistance, abrasion resistance, alcohol resistance and drug resistance).

By ink ingredients, paper inks are divided into dry oil-based inks, resin oil-based inks, organic solvent-based inks, water-based inks, paraffin-based inks, glycol-based inks, etc. They can also be classified into gel, liquid and powder categories.

In short, inks are used according to specific printing needs and conditions, such as printing methods, printing stocks, drying methods and ink characteristics.