Flexographic

There are four principal classes of printing ink, which vary considerably in physical appearance, composition, method of appHcation, and drying mechanism. These also fall into two general types of consistency or viscosity, paste and Hquid. The classes are letter press and Hthographic (Utho) inks, which are called paste inks, and flexographic (flexo) and rotogravure (gravure) inks, which are called Hquid inks (1). 

For example, Day-Glo HM Series toners come ia a range of colors suitable for flexographic and gravure inks of the solvent-base type. The Radiant GF Series and Lawter HVT Series are also suitable for this type of apphcation (see Table 2). Generally, these toners are of the formaldehyde—sulfonamide type and requite oxygenated solvents, primarily alcohol—ester blends, for proper solution. For appHcations such as flexographic printing on film, these materials are modified with other resias such as nitrocellulose or polyamides ia the finished ink. 

Flexographic Inks. Fluorescent toners such as the Radiant GF, Lawter HVT, and Day-Glo HM and HMS Series toners are used in flexographic ink formulations. These products are soluble in blends of alcohol (80%) and ester solvents (20%) and are compatible with modifying materials such as nitroceUulose resins and acryHc solution polymers. Flexographic inks of this type are used most commonly to print products such as ceUophane and polyethylene film for packaging, and also to print paper products such as gift wrap and price labels. 

Other Applications. PEO has also been used as an antistat additive (178,179), water-soluble packaging material of seeds and fertilizers (180), and rheology modifier in aqueous flexographic printing inks (qv) (181). 

In gravure, all elements within the image are screened. This is in contrast to flexographic and Hthographic plates, which can contain tme soflds as well as halftones. 

Fig. 15. Flexographic printing station, where the fountain pan suppHes ink to the mbber fountain roU, which in turn suppHes ink to the anilox roU. The doctor blade removes excess ink from the surface of the anilox roU so that it transfers a uniform layer of ink to the printing plate. The printing plate then...

Fig. 16. Schematics of flexographic presses, where the arrow designates the direction of the web flow and I-1 represents an interstation dryer, (a) Stack...

Flexographic Printing Plates. There are three primary types of flexographic printing plates molded mbber, soHd-sheet photopolymer, and hquid photopolymer. 

Inorganic chemicals may also be used. Beatonite may be used as a flocculant ia combination with polymer treatmeat. Alum, oace a common coagulant, is less used because its concentration can build up ia recycle water. Alum oftea biads ink to fibers and iacreases the difficulty of deinking. Removal of the very small flexographic ink particles ia process water is difficult. Ultrafiltratioa (qv) has beea proposed for removing these very small dispersed ink particles (53). 

Table 14. Flexographic Ink Formulation Containing Alcohol-Soluble Cellulose Acetate Propionate...

---