Types and Composition of Digital Printing Inks (I)

      Liquid digital printing inks are often used for ink jet printing. The type of ink is related to the structure of ink heads of ink jet printers. The ink heads can be divided into two types: thermal compression type and piezoelectric type. Piezoelectric type is divided into high precision and low precision, such as EPSON. The inkjet head is a high-precision product, while Xaar and Spectra's inkjet heads are less accurate, with the former mostly using water-based inks and the latter mostly using solvent-based inks.

1. Composition and performance of water-based ink

Water-based inks are mainly composed of solvents, colorants, surfactants, pH regulators, driers, and other additives. For hot-press inkjet printing systems, only aqueous inks can be used; on-demand ink-jet printing inks are also commonly used. Water-based ink.

(1) Colorant

Dyes are mainly used as the colorant for water-based inks, because for aqueous inks, the dyes can be completely dissolved in a solvent and fuse well with the solvent in the form of macromolecules to exhibit good colorability. Such as azo dyes, metal complex dyes, naphthol dyes, anthraquinone dyes, indigo dyes, quinoneimine dyes, cyanine dyes, quinoline dyes, nitro dyes, nitroso dyes, benzoquinone dyes, naphthoquinone dyes A phthalocyanine dye or a metal phthalocyanine dye, with an oil-soluble dye being particularly preferred.

For pigmented water-based inks, because the pigment is insoluble in the solvent, it is necessary to ensure its dispersion stability in the solvent and the color effect also requires other components and higher technical requirements. Pigments are divided into inorganic pigments and organic pigments, including carbon black, chrome red, molybdenum red, chrome yellow, titanium yellow, chromium oxide, Viridian pigments, titanium cobalt green, ultramarine blue, cobalt blue, diketopyrrolopyrrole Indole, quinone, benzimidazolone, indenopyrimidine, and azo, phthalocyanine, strychnine, perylene ketones, sulfhydryls, quinophthalones, metal complex pigments, and the like.

The pigment or dye may be used alone, or two or more kinds of pigments or dyes may be used in combination. The average diameter of the pigment particles is preferably 50 to 500 nm, and the content thereof is appropriately selected depending on the use of the ink or the printing property, and is the total weight of the ink. 1.0% to 10.0%.
(2) Solvent

Water-based ink solvent is generally deionized water as the main solvent, and then add an appropriate amount of organic solvent, the organic solvent content is 0.1% to 1.0% of the total weight of the ink, mainly using the following categories.

Polyhydric alcohols: ethylene glycol, propylene glycol, butanediol, diethylene glycol, triethylene glycol, 1,2-pentanediol, 1,2,6-hexanetriol, thiodiglycol, polyethylen Diols and polypropylene glycols.

Glycol esters: Glycerol, polyalkylene glycols, lower alkyl esters of polyhydric alcohols.

Alcohol amines: diethanolamine, triethanolamine.

Amides: dimethylformamide, dimethylacetamide, dimethyl sulfoxide and sulfolane.

Ketones or ketoalcohols: acetone, cyclobutanone, N-methyl-2-pyrrolidone, N-(2-hydroxyethyl)-2-pyrrolidone, 2-pyrrolidone.

Ethers: tetrahydrofuran, dioxane, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monoethyl ether Triethylene glycol monoethyl ether, triethylene glycol diethyl ether, triethylene glycol dibutyl ether, tetraethylene glycol dimethyl ether, and tetraethylene glycol diethyl ether.

(3) Surfactants

Surfactants commonly used are benzene sulfonates, alkylamine oxides and amine salts, acetylenic diols, and fluorosurfactants, typically 0.1% to 1.0% by weight of the ink, preferably 0.5%.

(4) Dispersing agent

For pigment-based inks, it is necessary to add a dispersant to the ink in order to ensure its dispersion stability in water. Usually water-soluble pigment dispersion resins are used, including styrene-maleic acid copolymers, styrene-maleic acid- Acrylic naphthalene-maleic acid copolymer, styrene-maleic acid half ester copolymer, vinyl naphthalene-acrylic acid copolymer, ethylene naphthalene-maleic acid copolymer, and the like. The concentration of the dispersion resin is preferably 0.05% to 2.0% with respect to the total weight of the ink.

(5) pH regulators and other regulators

pH regulators, also called buffers, can use inorganic acids or inorganic bases. Common inorganic acids include hydrochloric acid, phosphoric acid or sulfuric acid; organic acids include methanesulfonic acid, acetic acid and lactic acid; inorganic bases include alkali metal hydroxides and carbonates; common organic bases include ammonia, triethanol and tetramethylethylenediamine.

Other additives can be added according to the specific application requirements of the ink, such as UV absorbers, metal chelating agents, defoaming silicone oil, and the like. The content of these additives is generally 0.1% to 1.0%, preferably 0.5% by weight of the ink.

Example of composition of liquid water-based ink:

Dyes 4.0% Sodium benzenesulfonate 0.5%

Chelating agent 0.5% Sodium borate 0.5%

Ethylene glycol 20.0% deionized water balance

2. Composition and properties of solvent ink

(1) Colorant

The colorant in the solvent type ink may use a pigment or a dye, and its type and name are the same as the water-based ink.

(2) Solvent

Solvent-based inks generally use organic solvent as the main solvent, and add the appropriate amount of water. Commonly used organic solvents are diethylene glycol compounds and dipropylene glycol compounds that are liquid at normal temperature and pressure, and diethylene glycol compounds may be diethylene glycol ethers (especially alkyl ethers) such as diethylene glycol monomethyl ether; Diethylene glycol esters such as diethylene glycol monoethyl ether acetate; may also contain polyethylene glycol monoether compounds and other polar organic solvents such as alcohols (methanol, ethanol, propanol, etc.), ketones Classes (acetone, methyl ethyl ketone, cyclohexanone, etc.) and carboxylic esters.

The mixing ratio (weight ratio) of the diethylene glycol compound and the dipropylene glycol compound is from 20:80 to 80:20, and the content is preferably from 85% to 95% with respect to the total weight of the ink.

(3) Dispersing agent

When a pigment is used as a colorant, a polyester polymer compound is added as a dispersant to the ink mixture. It is preferably used in an amount of 30% to 120% by weight of the colorant (especially pigment).

(4) Other additives

Other additives include stabilizers (such as antioxidants or UV absorbers), surfactants, binder resins, and wetting agents. Antioxidants can use BHA (2,3-butyl-4-oxyanisole) or BHT (2,6-di-tert-butyl-p-cresol); UV absorbers can use benzophenones or benzotriazole Azo compounds; Surfactants can be any of anionic, cationic, amphoteric or nonionic surfactants; adhesive resins are acrylic resin, styrene acrylic resin, rosin modified resin, polyester resin, polyamide Resin, epoxy resin, polyethylene vinyl acetate copolymer, cellulose resin, etc. In addition, the use of a wetting agent helps prevent the ink from drying or crusting within the spray head. Commonly used wetting agents include polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, tetraethylene glycol, poly Ethylene glycol, glycerol and the like are used in an amount of 5.0% to 6.0% of the total weight of the ink mixture.


The composition of the liquid solvent type ink is as follows:

Formula 1:

Pigments 4.0%

Polyester polymer compound (dispersant) 2.4%

Polycyclic ethylene derivatives 0.5%

Mixed organic solvents 93.1%

Formula 2:

Oil dye 1.0% oil 30.0%

Propyl alcohol 29.0% Formamide 40.0%

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