Water-based inkjet inks

Since the introduction of HP s Thinkjet printer in 1984, to the end of 2007, over 500 million inkjet printers have been sold for home and business use by numerous manufacturers. Nearly all of these printers utilize water-based inks. In this chapter, a general overview of the composition and properties of water-based inkjet inks will be given. Particular emphasis is placed on the relationships between ink properties and print performance attributes. The unmistakable theme arises, that ink properties must be finely balanced to meet demanding performance specifications. 

In conclusion, there are many performance attributes to consider when formulating water-based inkjet inks, and multitudes of ink additives that can be employed. To achieve effective formulations, it is useful to first consider the relationship between ink physical properties and desired performance targets. Taking such an enlightened approach helps narrow the list of ink additives to be tried, expedites ink development, and ultimately increases a product s chances for commercial success. 

Kabalnov described water-based inkjet ink compositions that are miniemulsions, i.e., an aqueous vehicle having emulsified oil particles with dissolved dye molecules, where the oil droplets have a diameter of less than 1 m. In his patent, Kabalnov mentioned the advantages of miniemulsions in comparison to microemulsions, namely the surfactant nature and concentration which allow better penetration control to the printed papers, and the dye load in miniemulsions can also be increased compared to microemulsions at acceptable viscosity limits. According to this invention, the aqueous inkjet ink composition is comprised of an oil-soluble dye, a solvent, and an aqueous vehicle wherein particles of the oil-soluble dye are dissolved in low-polarity oil particles having a particle size of less than 1 m, the particles forming miniemulsions in water. 

G. Nakhmanovich, I. Hidana, and M. Frenkel, Water-based inkjet inks containing an ultraviolet curable humectant, US Patent 6 846 851, January 25, 2005. 

In another microemulsion system, ° the colorant is incorporated into the ink as an aqueous pigment dispersion-based inkjet ink composition by formulating the ink to comprise at least one aqueous pigment dispersion and a microemulsion with at least one water-insoluble organic compound, one hydrotropic amphiphile, and water. This ink system was reported to improve waterfastness and bleed control, "" providing a fast drying ink. 

A water based ink was developed for writing, drawing and marking using foxmtain and ball pens. An organic solvent based ink was developed for inkjet systems. The ink contains 40 to 98% solvent. Typical solvents include ethanol, isopropanol, acetone and methyl ethyl ketone. In still another development, a water based inkjet composition was developed. 

There are currently four main types of inkjet inks phase-change, solvent-based, water-based, and UV curable. Other types exist, but are less prevalent, such as oil-based and hquid toner (for electrostatic inkjet technology). Hybrid versions of the four main types also exist (e.g., water-based inks containing some amount of solvent). The various inkjet ink types will be discussed briefly in this chapter, and will be followed by detailed description in separate chapters (solvent-based, water-based, and UV cmable inks). 

Conventional water-based and non-aqueous inkjet inks are mixtures of several components, including volatile solvents, dissolved materials, and dispersed solids (for pigment inks). When the ink reaches the nozzles prior to jetting, the volatile components may evaporate from the nozzle. Therefore, the liquid in the vicinity of the nozzle can have a composition which differs from that of the bulk ink which is further back in the print head supply channels. This disparity causes differences in the physicochemical properties of the ink (e.g., an increase in viscosity or decrease in surface tension)... 

We have developed an oil-in-water and bicontinuous microemulsion inkjet ink composition comprising a solubilized hydrophobic dye which forms nanoparticles ("pigment-like") upon application on a substrate surface. The concept was demonstrated for direct patterning of water-insoluble organic molecules in the form of nanoparticles. The method is based on formation of thermodynamically stable oil-in-water microemulsions, in which volatile "oil" contains the dissolved organic molecules. As schematically illustrated in Fig. 3, the microemulsion droplets are converted into organic nanoparticles upon impact with the substrate surface due to evaporation of the volatile solvent. 

Magdassi S, Ben-Moshe M. (2003) Inkjet ink compositions based on oil-in-water microemulsion forming nanoparticles upon application on a surface, US7115161. 

A more recent application for silicas is in the specialty papers used for inkjet printing. Silica gels and precipitated silicas offer superior absorption of water-based inks, which allows for high resolution printing. Silica may be also found in high-quality direct thermal papers because of its superior insulation and absorption properties. 

The most common inkjet inks are water based, containing either dyes (low cost but prone to fading in the images) or dispersed pigments (more expensive but more permanent images). Some commercial/industrial inkjet inks use solvent-based inks containing dispersed pigments. 

Caputo P. (1998) Stable oil-in-water ink emulsion based upon water-reducible nigrosine dyes for inkjet printers and felt-tip and roller-ball pens, US5746815. 

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