Ink vehicles

Absorption. Some inks (eg, oil-based newspaper inks) dry by penetration or absorption into the pores of the printed stock, which has a blotter or sponge effect. This is accompHshed by the gross penetration of the ink vehicle into the pores of the substrate, the partial separation of the vehicle from the pigment, and the diffusion of the vehicle throughout the paper. The abiHty of an ink to penetrate into paper depends on the number and size of the air spaces present in the paper, the affinity or receptivity of the stock for the ink, and the mobiHty of the ink. 

Preformed Two-Piece Metal Containers. Ink vehicles for letterset printing of two-piece aluminum or steel containers are mainly based on special polyester vehicles used in conjunction with melamine cross-linkers. Short cycle ovens which dry inks in 1—5 seconds are now used and operate at temperatures as high as 350 °C. The rheology of these inks must be adjusted to the unique geometry of the press. Desired rheological properties are achieved by the use of additives as weU as extender pigments. 

Solvents. Common terminologies used interchangeably are solvents, diluents, reducers, and thinners (Table 2). Technically, solvents are materials that completely dissolve resins in the ink vehicle. Diluents are Hquids that may not completely dissolve the resin by itself. Solvents can also be thinners, but most often thinners are blends of solvents and diluents. Reducer is another name for thinner, referring to the solvent blends used to reduce the viscosity of a virgin ink on the press to miming viscosity. 

The alcohols, proprietary denatured ethyl alcohol and isopropyl alcohol, are commonly used for E-type inks. Many E-type inks benefit from the addition of small amounts of ethyl acetate, MEK, or normal propyl acetate to the solvent blends. Aromatic hydrocarbon solvents are used for M-type inks. Polystyrene resins are used to reduce the cost of top lacquers. T-type inks are also reduced with aromatic hydrocarbons. Acryflc resins are used to achieve specific properties for V-type inks. Vehicles containing vinyl chloride and vinyl acetate copolymer resins make up the vinyl ink category. Ketones are commonly used solvents for these inks. 

Humectants and low vapor pressure cosolvents are added to inhibit drying of ink in the no22les. Surfactants or cosolvents that lower surface tension are added to promote absorption of ink vehicle by the paper and to prevent bleed. For improvements in durabiUty, additional materials such as film-forming polymers have been added. Ink developments are providing ink-jet prints with improved lightfastness, waterfastness, and durabiUty. As a result, such prints are beginning to rival the quaUty of electrophotographic prints. 

Vehicles. The soHd pigments are dispersed iato the ink vehicle, which consists of a combination of resia, oil, and solvent. The solvent is absorbed by the paper, leaving a partially dry ink film of resia and oil that biads the pigment to the paper. This film then hardens by oxidation. Oxidation of the vehicle is aided by varnish driers, ie, metallic salts. Cobalt driers are considered the most effective (see Driers and metallic soaps). 

Paper absorbency is important for proper ink drying. A paper s surface should allow the ink vehicle to penetrate at the proper rate to achieve proper setting of the ink. If the surface is too absorbent, it causes low ink holdout and loss of gloss. If it is not absorbent enough, it causes ink to transfer to other sheets in a stack, or sheets to stick together. 

For ink vehicles based on hydroxyl group containing binders such as nitrocellulose and cellulose acetate, the tetraalkyl titanates cross-link the binder prematurely, limiting the storage stabiUty of the printing ink. Chelated organic titanates such as TYZOR AA and TYZOR TE are preferred for use in these cases because they only initiate cross-linking when the ink is heated to temperatures above 80°C (503). 

The major drawback of this technology is that it requires the application of an extra layer on top of the substrate. This makes the printing process more comphcated and will require either an extra coating step (when done off the inkjet printer) or a proper application tool in-line with the printer itself. Using bi-component ink, no matter which of the approaches is taken, it will stiU require drying of the ink vehicle — the water and solvent — before the ink is dry. Full drying is not required when using the absorptive layers. 

One of them is its poor lightfastness, which is especially noticeable when the pigment is dispersed to particle sizes below 100 nm. Another one is the shght solubility of this pigment in some components of ink vehicles, which makes formulation work more difficult and sometimes compromises the long-term colloidal stability of the inks. 

Another approach which was presented by Moffatt et al described aqueous inkjet inks comprised of water-soluble amphiphilic dye having a chromophore and a hydrophobic tail attached. This amphiphilic dye is present at a concentration greater than the critical micelle concentration (cmc) for the dye such that micelles are formed that incorporate the dye residue. These inks are described as having a pKa value greater than the pKa of the surfactant, otherwise the amphiphilic dye loses its waterfastness. If the pH is too low, the amphiphilic dye is insoluble in the ink vehicle. 

Inkjet formulations may also include an adhesive binder. The binder is usually a resin or resin system that is soluble or dispersed in the ink vehicle. Upon drying, the resin is heat- or UV-cured. The binder provides adhesion of the printed pattern to the substrate, imparts solvent resistance, and may protect against abrasion. Careful adjustment of the type and amomit of binder is required in order to achieve proper adhesion and substrate matching. As the binder systems are mostly non-conductive, an optimmn ratio between the metal and the binder system must be fomid. Generally, there is no one generic binder suitable for aU substrates or aU conditions. 

We will describe typical members of the Uvimer series In terms of their composition and physical properties. UvlmerTM 530, the first member of the series. Is a relatively hard, brittle and fast-curing resin which is suitable for use as an ink vehicle and as a coating on rigid substrates. The table below gives basic formulation and cured film properties of this UvlmerTM ... 

Use Synthesis of other amyl compounds, solvent, rotogravure ink vehicles, soil fumigation. 

Post-printing nip capillary sorption of ink and ink vehicles is discussed using Lucas-Washburn theory and the influence of the rate of capillary sorption on ink holdout, show through and set off are discussed. Finally, the long-term migration of oil vehicles over fibre surfaces by spreading with the attendant loss of paper opacity is described. 

DeGrSce and Mangin— have treated the case of ink transfer to nonporous model substrates such an mylar. The surface of mylar contains pits of about 1 pm depth. Very little void volume exists for ink immobilization, thus allowing ink film splitting to be examined in isolation. The transfer of two ink vehicle... 

The chemistries of commercial oil vehicles vary with respect to the ratio of aromatic, paraffinic and cycloparaffinic carbon (generally about 20, 40, and 40 percent, respectively), degree of oxidation, and amount and character of impurities. The surface energies of the high and low viscosity ink vehicles shown in Figure 8 were 31.3, and 26.0 mN/rn, respectively (as measured by the Du NoUy ring method). 

Three mechanisms can be considered for the migration of an ink vehicle such as oil capillary imbibition, spreading, and bulk diffusion. It takes about 100 ms for a fresh print to travel from one nip of the printing press to the next in a commercial multicolor printing press. In this time the oil vehicle is sufficiently drained from the ink that set off does not occur in the second colour unit. The driving force for capillary imbibition is surface tension ... 

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