Aqueous ink

For aqueous inks, the resins are water- or alkali-soluble or dispersible and the solvent is mosdy water containing sufficient alcohol (as much as 25%) to help solubilize the resin. To keep the alkah-soluble resin in solution, pH must be maintained at the correct level. Advances include the development of uv inks. These are high viscosity inks that require no drying but are photocurable by uv radiation. In these formulations, the solvent is replaced by monomers and photoinitiators that can be cross-linked by exposure to uv radiation. The advantage of this system is the complete elimination of volatile organic compounds (VOC) as components of the system and better halftone print quaUty. Aqueous and uv inks are becoming more popular as environmental pressure to reduce VOC increases. 

Title Aqueous Inks Containing Colored Polymers... 

Similar to ink-jet dyes, dyes used for writing, drawing and marking materials fall into two categories water soluble dyes for aqueous inks and dyes for solvent inks [1,5]. Dyes are listed according to application in Tables 5.9-5.13. Many of these dyes can also be used for ink jet applications. However, ink jet dyes have to satisfy more stringent criteria with regard to purify and salt content. 

Water-based or aqueous inks are prevalent on the desktop and enjoy the advantage of being relatively inexpensive and environmentally friendly, but penetration in industrial applications has been slow for a variety of reasons. Water-based inks tend to require porous or specially treated substrates or even lamination to impart durability and the ink tends not to adhere to non-porous substrates. Additionally, many piezoelectric industrial print heads are incompatible with water-based ink formulations, although this is changing in some part due to market demand for systems that can jet water-based biological or food contact fluids. 

This definition precludes aqueous inks, but further distinctions remain. There are solvent inks where the vehicle is a fluid with very low vapor pressure at room temperature. These inks are based either on glycols, or on oils and are used on absorbent substrates such as paper. The inks most commonly referred to as solvent inks are those in which the carrier is a solvent that evaporates or is driven off subsequent to printing. 

The significance of the latter parameters can be realised if one considers the initial drop impact. In a fibrous structure such as paper a liquid is unable to discern differences in pore depth until entering the bulk structure. Prior to penetration, following dissipation of mechanical forces, drop wetting and spreading of an aqueous ink jet drop will be primarily determined by the combined effects of chemical heterogenity and physical roughness. The combination of these effects can be approximated (24) in terms of Cassie and Baxter (25) and Shuttleworth and Bailey s (26) equations ... 

A wide variation in the rate of absorption drying and image quality of an aqueous ink jet ink was apparent among the commer-... 

Nearly all of the commercial inks available for thermal iniqet systems are water-based, so they contain more than 50% water. Such aqueous inks have one or more drawbacks such as long ink dry times or poor adhesion to semiporous or nonporous substrates. 

M. Sugiyama, A. Ogawa, and S. Imai, Aqueous ink composition, US Patent 4 388115, assigned to Fuji Photo Film Co., Ltd. (Kanagawa, JP), June 14,1983. 

The pH of aqueous ink compositions may be adjusted by the addition of organic or inorganic acids or bases. Useful inks may have a preferred pH of from about 2 to 10, depending upon the type... 

However, from the viewpoint of global environment protection and safety, aqueous ink compositions containing water as solvent are more desirable. 

But such a composition has an inferior storage stability at low temperatures. Therefore, a moisturizing component such as glycerol is added to prevent the aqueous ink composition with a yellow pigment from freezing. 

The aqueous ink composition was continuously ejected onto plain paper for 10 min without heating the plain paper, and it was confirmed that aU the nozzles normally ejected the ink composition. Then, a continuous printing was performed for a predetermined time to form a pattern with an average duty of 10% including characters and pictures on a plain paper heated to 45°C, thus producing a recorded material. The weight of ink ejected for each dot was set... 

It was confirmed that the images formed with the aqueous ink composition on a plastic medium have superior characteristics against bleeding (15). In contrast, when glycerol is added, the resulting image is inferior in rub fastness. 

An aqueous ink composition is ejected as droplets onto a plastic medium to form an image on the plastic medium. A method for ejecting the droplets may utilize the vibration of a piezoelectric element, which enables excellent image recording. The plastic medium is then heated to 40-60°C with a print heater of the inlqet recording apparatus and a dryer to dry the deposited aqueous ink composition. 

This step rapidly evaporates the water in the deposited aqueous ink composition and resin particles form a film. This method produces high-quality images even on a plastic medium in a short period of time with reduced occurrence of inconsistencies in density and bleeding or blurring. The formation of the film formed by the resin particles allows the dried ink to adhere to the plastic medium. 

K. Aoki and H. Mukai, Aqueous ink composition, ink jet recording method and recorded material, US Patent 8 614 264, assigned to Seiko Epson Corporation (Tokyo, JP), December 24, 2013. 

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