Pigments for Inkjet Applications

These improved properties often come at a cost. Replacing a colorant solution by a colorant dispersion raises several issues. 

In the case of thermal IJ print heads, where the surface of the firing resistor is briefly heated to a very high temperature, no deposition on the resistor should take place. Such a deposit is thermally insulating and usually damages the resistor irreversibly. Preventing this phenomenon adds additional requirements to the ink purity and composition. 

Depositing pigment particles on the paper surface creates many problems related to the penetration, adhesion and cohesion of these particles, and sometimes results in poor highligter smear resistance, gloss inconsistency of photo prints and the like. 

Inks with high solids contents are required for some lightfast pigments that have low color strength compared to dyes. This problem, however, seems to be limited mainly to quinacridones. 

Carbon black is produced by the partial combustion or thermal decomposition of hydrocarbons. Several methods are used, including the furnace black, thermal black, lamp black and acetylene black processes. The furnace black process is the most common. In this process, natural gas (or another fuel) is burned to form a hot gas stream that is directed into a timnel. An aromatic oil is sprayed in and the black forms as the gas moves down the tunnel. The reaction is quenched with the addition of water, and the product is collected as a low density powder (fluffy black) or is further processed into millimeter sized peUets. 

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As we will discuss next, the purple of Cassius is the best red ink used in the latest technology of ceramic pigments for inkjet applications [5]. 

The number of academic entries in the Google-Academic search tool is around 1200 (as of March 2014) (Figure 37.1), and the academic publications is about 98% of total publications. We can consider three main steps in the development of ceramic pigments for glazed ceramics (i) before the discovery of European porcelain (1710), after this discovery up to 1900 with the introduction of the green of Sevres as the main relevant novelty in 1802, (ii) the twentieth century with the discovery of the zircon stain family, and (iii) the twenty-first century with the development of submicrometer size pigments for inkjet applications. 

Yellow Antimony-nickel-codoped rutile was the first yellow pigment used in 2000 in the glaze doped with anatase. Ni(N03)2-9H20 and SbCls dissolved and complexed with citrates at adequate pH for inkjet applications react with the anatase in the glaze during firing to produce the antimony-nickel-codoped rutile yellow pigment. 

For inks which contain pigments, the most common problem is aggregation of the pigment particles due to the inherent instability of most dispersion systems. Since most modern inkjet inks for graphic applications contain dispersed pigments, the stabilization mechanisms of dispersions will be briefly discussed below. 

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. 

The special properties of nanomaterials, such as those currently used as the conductive "pigment" in conductive inkjet inks, will be exploited more and more in advanced second-generation products. New inks will be developed to print additional electronic functionalities such as resistors, capacitors, and semiconductors, thereby enabling inkjet printing of complete electronic components and devices. Inkjet s capability to layer materials and build 3D structures will be further developed for microelectronics applications. These efforts have already been initiated in universities, research institutes, and commercial entities — in the large established ink companies as well as smaller startups financed by joint VC and government funding. 

Both soluble dyes and dispersible pigments are employed as colorants in inkjet inks. The choice of colorant type depends somewhat on the application and media to be used. For example, on plain copier paper, light that is reflected off the surface of the ink film... 

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