Liquid digital printing ink is often used in inkjet printing. The type of ink is related to the ink head structure of the inkjet printer. The ink head can be divided into two types: hot press type and piezoelectric type, and the piezoelectric type is divided into high precision and low precision, such as EPSON. The inkjet head is a high-precision product, while the inkjet heads of Xaar and Spectra have lower accuracy. The former mostly uses water-based inks, and the latter mostly uses 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 water-based inks can be used; on-demand inkjet printing inks are usually also used Water-based ink.
(1) Colorant
The colorants of water-based inks mainly use dyes, because for water-based inks, the dyes can be completely dissolved in the solvent, and are well fused with the solvent in the form of large molecules to show good colorability. Such as azo dye, metal complex dye, naphthol dye, anthraquinone dye, indigo dye, quinone imine dye, cyanine dye, quinoline dye, nitro dye, nitroso dye, benzoquinone dye, naphthoquinone dye , Phthalocyanine dyes or metal phthalocyanine dyes, particularly preferably oil-soluble dyes.
For water-based inks that use pigments as colorants, since pigments are insoluble in solvents, other components and higher technical requirements are needed to ensure their dispersion stability and color development in solvents. 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 , Anthraquinone, benzimidazolone, anthrapyrimidine, and azo, phthalocyanine, Shilin, perillone, thioindigo, quinophthalone or metal complex pigments, etc.
The pigment or dye can be used alone, or two or more pigments or dyes can be used in combination. The average diameter of the pigment particles is preferably 50 to 500 nm, and the content is appropriately selected according to the ink application or printing characteristics, and is the total weight of the ink 1.0% ～ 10.0%.
(2) Solvent
The solvent of water-based ink is generally deionized water as the main solvent, and then an appropriate amount of organic solvent is added. The content of the organic solvent is 0.1% to 1.0% of the total weight of the ink.
Polyhydric alcohols: ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, triethylene glycol, 1, 2-pentanediol, 1, 2, 6-hexanetriol, thiodiglycol, polyethylene glycol Glycol and polypropylene glycol.
Glycol esters: glycerin, multi-alkane diols, lower alkyl esters of polyhydric alcohols.
Alcoholamines: diethanolamine, triethanolamine.
Amides: dimethylformamide, dimethylacetamide, dimethylsulfoxide, and sulfolane.
Ketones or ketone alcohols: 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, tetraethylene glycol diethyl ether.
(3) Surfactant
The commonly used surfactants are mainly benzenesulfonate, alkylamine oxides and amine salts, acetylene glycol and fluorosurfactants, generally 0.1% to 1.0% by weight of the ink, preferably 0.5%.
(4) Dispersant
For pigment-based ink, in order to ensure its dispersion stability in water, it is necessary to add a dispersant to the ink, usually using water-soluble pigment dispersion resin, including styrene-maleic acid copolymer, styrene-maleic acid- Acrylic acid naphthalene-maleic acid copolymer, styrene-maleic acid half ester copolymer, vinyl naphthalene-acrylic acid copolymer, ethylene naphthalene-maleic acid copolymer, etc. The concentration of the dispersion resin is preferably 0.05% to 2.0% relative to the total weight of the ink.
(5) pH regulator and other regulators
The pH adjusting agent is also called a buffer, and inorganic acids or inorganic bases can be used. Commonly used 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; commonly used organic bases include ammonia, triethanol and tetramethylethylenediamine.
Other additives can be added according to the specific use requirements of the ink, such as ultraviolet absorbers, metal chelating agents, defoaming silicone oil, etc. The content of these additives is generally 0.1% to 1.0% by weight of the ink, preferably 0.5%.
Examples of composition formula of liquid water-based ink:
Dyestuff 4.0% Sodium benzenesulfonate 0.5%
Chelating agent 0.5% Sodium borate 0.5%
Glycol 20.0% Deionized Water Balance [next]
2. Composition and performance of solvent-based ink
(1) Colorant
The colorant in the solvent-based ink can use pigments or dyes, and its type and product name are the same as those of the water-based ink.
(2) Solvent
Solvent-based inks generally use organic solvents as the main solvent, and add an appropriate amount of water. Commonly used organic solvents are diethylene glycol compounds and dipropylene glycol compounds that are liquid at normal temperature and pressure. The diethylene glycol compounds may be diethylene glycol ethers (especially alkyl ethers), such as diethylene glycol monomethyl ether; Or diethylene glycol esters, such as diethylene glycol monoethyl ether acetate; can also contain polyethylene glycol monoether compounds and other polar organic solvents, such as alcohols (methanol, ethanol, propanol, etc.), ketones (Acetone, methyl ethyl ketone, cyclohexanone, etc.) and carboxylic acid esters.
The mixing ratio (weight ratio) of the diethylene glycol compound and the dipropylene glycol compound is between 20:80 and 80:20, and the content is preferably 85% to 95% relative to the total weight of the ink.
(3) Dispersant
When using pigments as colorants, polyester polymer compounds should be added to the ink mixture as dispersants. The preferred amount is 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. Antioxidant can use BHA (2,3-butyl-4-oxyanisole) or BHT (2,6-di-tert-butyl-p-cresol); UV absorber can use benzophenone compounds or benzotris Azole compounds; any one of anionic, cationic, amphoteric or nonionic surfactants can be used as the surfactant; the binder resin includes acrylic resin, styrene acrylic resin, rosin modified resin, polyester resin, polyamide Resins, epoxy resins, polyethylene vinyl acetate copolymers, cellulose resins, etc. In addition, the use of a wetting agent helps prevent the ink from drying or skinning in the nozzle. Commonly used wetting agents are polyols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, tetraethylene glycol, poly The amount of ethylene glycol, glycerin, etc. is 5.0% to 6.0% of the total weight of the ink mixture.
Examples of composition formula of liquid solvent ink:
Pigment 4.0%
Polyester polymer compound (dispersant) 2.4%
Polycycloethylene derivative 0.5%
Mixed organic solvent 93.1%
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