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The main aim of the inkjet ink composition described in Table 5 is to provide some examples for a jettable composition by adjusting the parameters that have influence on the ejection of the fluid from different types of print heads. There are complex inter-relationships between these components in stabilizing the ink fluid and for a better understanding of the role of each component is briefly described here.

Solvent

In most cases to apply functionality on printed textiles the solvent or vehicle used in the inkjet ink formulation should preferably be de-ionized, de-mineralized water which provides the ink a highly significant chemical basis for the interaction of the active agents or the colorants with the textile after printing. Sometimes post treatment is required on inkjet printed textiles for a number of reasons including the enhancement of technical performances. In this type of cases sometimes alternative inkjet ink compositions using non-water based solvents such as ethanol or lactates may also be used which fulfill the desired characteristics. There is a wide range of solvents which can be used in different types of inkjet ink formulations which can meet particular requirements which are expected from the inks.

Co-Solvent

A co-solvent can be used along with a main solvent in an ink formulation to address certain desires aspect from the formulated ink. For instance, in a drying ink formulation a co- solvent is often required to provide solubility for the conductivity agent in which case a small amount of ethanol is used to dissolve a conductivity agent that is not soluble in MEK alone. Additionally, a co-solvent may also be used to improve the solubility of the active component(s) and their compatibility with the conductivity agent (where the incompatibility between these materials is a common formulation issue). More particularly, in continuous inkjet printing systems the non-printing fluid is often mixed with air during the recirculation process which has a tendency to lead to air entrapment related to foaming issues. In these cases, co-solvents are usually used to control foaming in these systems.

Humectant

Usually a humectant is a low volatility, high boiling point liquid which is used in the inkjet ink formulation to prevent crusting of the nozzle when the jet(s) are not active. During different types of inkjet inks formulations humectants are generally selected from the group consisting of polyhydric alcohols, glycols, especially polyethylene glycol (PEG), glycerol, n- methyl pyrrolidone (NMP). There is no hard and fast rule for this selection, for example, during certain formulations it may appear that more than 5% humectant is being used, however, it is in fact the case that the same material may also be present as a viscosity modifier.

Viscosity Control Agent

Viscosity control agent is the most important component of ink. Because it has a significant control on the inkjet printing reliability and the quality of droplet formation and break up process. Additionally, sometimes it acts as an active component and provides some of the end user properties particularly in the cases of functional inkjet inks. During the selection of viscosity controlling agent high molecular weight polymers should be avoided, because of their higher elastic nature sometimes they cause difficulty in jets breaking up of inkjet inks. Some of the widely used viscosity control agents are, polyvinyl pyrrolidone, polyethylene oxide, polyethylene glycol, polypropylene glycol, acrylics, styrene acrylics, polyethyleneimine, polyacrylic acid.

Conductivity Agent

Particularly in the cases of inkjet ink formulations for continuous inkjet systems conductivity imparting agents (such as, electrolytes) are used to produce charged ink droplets which can be deflected during actual printing. An electrolyte is usually used when there is insufficient conductivity in the ink. It is important to note that conductivity agents should be compatible with the other components of the ink formulation and they should not promote corrosion. Some commonly used conductivity agents are lithium nitrate, potassium thiocyanate, dimethylamine hydrochloride, thiophene-based materials. These materials show different level of conductivity, for example, it was observed that the use of a small amount of potassium thiocyanate was sufficient to provide required level of conductivity to produce uniformly jettable continuous inkjet inks.

Surfactant

In typical inkjet ink formulations, surfactants are usually used either to reduce foaming of the formulation and release dissolved gases or to lower the surface tension of the droplet and to improve wetting. Some usually used surfactants are – Surfynol DF75, Surfynol 104E, Dynol 604 (Air Products, USA) and Zonyl FSA (Du Pont, USA). Additionally, BYK 022 (BYK-Chemie) and Respumit S (Bayer, Germany) are both silicone based antifoam agents that have proved very effective for smooth and uniform jetting purposes.

Biocide

Sometimes a small amount of biocide is usually used in an aqueous based inkjet ink formulation to prevent bacterial growth in the inks when stored for a long time. However, in the solvent based inkjet ink formulation biocides are not usually required, for example, when solvent like isopropyl alcohol is present in the composition in sufficient amount it can prevent bacterial growth.

pH Modifier

Different types of buffer solutions or pH modifiers are sometimes used in the inkjet ink formulation to maintain a pH at which the components of the ink formulation are soluble or make a stable dispersion. In typical formulation the pH is usually neutral (pH 7.0) or slightly alkaline. Additionally, the pH modifier may also be used to modify the chemical interaction between the different suitable components of the ink and the printed substrates (such as, textile). Some usually used pH modifers are, ammonia, morpholine, diethanolamine, triethanolamine and acetic acid. However, it is desirable from an inkjet perspective to use relatively neutral solutions to reduce corrosion in the print heads.

Corrosion Inhibitor

A corrosion inhibitor is mostly used in an inkjet ink formulation to prevent unwanted ions present in the ink fluid (as impurities coming from the active components) that may cause corrosion to the printer.

Wetting Agent

Wetting agents are usually in ink formulations to improve the surface wetting of the fluid on the internal capillaries of the digital nozzles. Some of the usually used wetting agents are based on acetylinicdiols. In addition, sometimes, surfactants and co-solvents may also act as wetting agents.

Active Ingredients

The active ingredients (such as in this case photochromic dyes) are the materials which are usually used in the inkjet ink formulation to impart desired properties on the printed substrates. For example, when the photochromic dye based inkjet inks were disposed onto the textile substrates, all the printed substrates showed photochromic colour change under UV or sunlight exposure, so in this particular case photochromic dyes played as active ingredients.

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Recent studies indicates that there is very significantly increasing growing demand for environmentally friendly high performance and technically robust inkjet ink system which can be used for wide format inkjet printing on different substrates including textile printing. So, a very precise discussion within the very limit of this chapter will focus on selective important aspects of UV inks, inkjet technologies that use UV inks for wide format inkjet printing systems is included here in the following subsequent sections.