Flexo Printing Water Ink Composition and Function

With its environmental advantages, flexo printing has been incisively developed in Europe, America and especially the United States. Flexo printing has a wide range of applications. Printed materials include newspapers, corrugated cardboard, plastic films, and aluminum coated paper. The ink used for flexo printing in the production process is compatible with the printed material and is basically the same in terms of main components, including colorants, resins, solvents and additives.

Pigment

The colorant can impart a certain color to the ink, and it can selectively absorb and then emit light waves of a certain wavelength to present a specific color. In addition, the colorants also provide the necessary resistance to flexo printing inks, such as light resistance, high temperature resistance and weather resistance. The third role of the colorant is to some extent affect the viscosity of the ink.

The colorants used in flexographic printing water-based inks mainly include dyes that can be dissolved in solvents, triphenylmethane dyes, light-resistant alcohol solvent dyes, and acid dyes. Dyestuffs have bright colors and strong coloring power, which can meet the requirements of printing for decoration.

Resin

The function of the resin is to disperse the adhesion of the colorant and the printed material to form a firm imprint and form a certain gloss after the ink is dried and formed into a film. The resin also affects the dryness, rheology, and other printability of the flexographic ink. There are many kinds of resins that are suitable for flexo printing water-based inks, and are mainly selected according to the nature of the printed material. The flexo-printing water-based resin generally includes nitrocellulose, acrylic resin, polyketone-based resin, epoxy resin, alkyd resin, shellac, casein, and the like. These resins generally contain soluble groups such as carboxy <-COOH>, hydroxyl <-OH> or amino groups.

Solvent

The main role of the solvent in the flexo-based water-based ink is to dissolve the resin, adjust the viscosity, adjust the drying speed, and promote the wetting of the flexographic surface. Therefore, the solvent must first be able to dissolve the resin in order to formulate the ink. Secondly, the purity, color, and flammability of the solvent in the ink should be considered. More importantly, it is necessary to consider whether the solvent in the ink will cause corrosion to the flexible resin printing plate to ensure the printing plate's resistance to printing force.

The flexo-printing water-based ink uses water as the dominant solvent and also adds a certain amount of alcohol. In general, the amount of water solvent is twice as much as the alcohol solvent. Commonly used alcohol solvents are ethanol, isopropyl alcohol, etc., which help to improve the stability of the ink, speed up the ink drying speed, reduce the surface tension, isopropyl alcohol can also play a role in preventing water-based ink foaming.

additive

The physicochemical properties of flexographic inks are largely determined by the additives in the aqueous ink. The addition of additives to the ink to obtain certain specific physicochemical properties is a common practice in the flexographic printing industry. In water-based inks, pigments, resins, and solvents make up about 95% of the ink components, and the remaining 5% are various additives:

(1) Lubricants

Ink formulations generally contain lubricants. The role of lubricants is to provide abrasion resistance to prints, to prevent smudging inks during printing, and to reduce the vitrification of ink film layers. The amount of lubricant in the ink composition is related to the end use of the printing industry and prints. Do not use a lubricant in the adhesive ink, otherwise it will affect the adhesion of the fit.

The most used lubricants in the ink are polyethylene <PE> wax, polypropylene <PP> wax, silicone resin wax, fluorocarbon resin wax (for example, PTFE wax), and the like. These lubricants vary widely in terms of lubrication performance, transfer rate, and high temperature resistance. PTFE (polytetrafluoroethylene wax) gives the ink a high resistance to high temperatures and abrasion resistance, but the price of this lubricant is relatively high. The most experienced ink factory will use these lubricants in combination to obtain the best ink lubricity.

(2) Surfactants

The surfactant in the additive can be used to improve the printability of the ink. It can reduce the surface tension of the ink, increase the ability of the ink to lubricate a variety of printed materials, and improve the printability of the ink on a printing press. The amount of surfactant is very small, about 0.1% of the ink composition. Use extreme caution when using surfactants because some surfactants can cause microbubbles in the ink.

(3) Crosslinking agent

The cross-linking agent acts on the binder by a chemical reaction, thereby improving the chemical resistance of the binder, and can also be used to improve the resistance of the ink to corrosion and heat resistance.

(4) Adhesion promoter

Adhesion promoters are used to increase the adhesion of inks. They are very reactive materials or low molecular weight solvents. Adhesion promoters give the ink a strong ability to adhere, but its use must be strictly controlled to avoid negative effects such as heavy ink odors or ink fading.

(5) Defoamers

Defoamers are an integral part of the ink, accounting for approximately 0.1% of the total composition.

(6) Fungicides

Most aqueous inks need to be sterilized to prevent the growth of bacteria in the ink. If you want to store water-based inks for a long time, fungicides are indispensable additives.

(7) Minerals

The minerals in the water-based ink can dissolve the resin binder to maintain the stable PH value of the water-based ink while ensuring the printability of the water-based ink. Since the chemical properties of ammonium hydroxide are very unstable, the minerals commonly used in aqueous inks are amine compounds because of their better stability.

(8) Additives

In aqueous inks, the resin binder tends to give the ink a certain degree of fluidity. If the printing industry requires a larger viscosity of the ink, experienced ink masters add additives to the aqueous ink.

(9) Oxidizers

Some binders in aqueous inks can polymerize under the action of oxidants. Such water-based inks are used in applications where strong alkali resistance is required for applications such as soap boxes.

(10) Plasticizers

Plasticizers are used to increase the ink film's elasticity. Common plasticizers are high boiling ester compounds that remain in the ink film even after the ink has dried. When plasticizers are used in water-based inks, the concentration of the plasticizers should be controlled within the smallest possible range. Because the concentration of the plasticizers is too large, some negative effects may be caused, such as a decrease in the abrasion resistance of the ink.

In addition to the above-mentioned additives, other auxiliaries such as deodorants, release agents, and the like are also used in the flexo ink.

Source: China Printing City