Flexographic Ink

Flexographic printing is printing process that uses a flexible relief plate. The basic principles of this method can be foimd elsewhere (18,19). The first patent for a flexographic type printing press dates from 1909, even when such machines were fabricated earlier (20). 

flexographic presses and letterpress presses, for newspaper printing, use t q)es made of photo-sensitive polymeric materials that can be formed directly from a light image. The polymeric cylinder when properly developed presents raised areas that reproduce the image to be printed. 

This plate is mounted on a cylindrical roll that rotates against an ink cylinder so as to become coated in its raised areas. These areas rotate against a substrate (generally paper) which is backed by a hardened rubber roller (21). 

Letterpress and flexographic systems can be used with either solvent based or aqueous based ink systems. In either case, current practice consists of mixing a solvent or water in the presence of a binder resin such as, for example, nitrocellulose, maleic anhydride, an acrylic copolymer, or various starch derivatives. The pigment is applied over the paper by the printing roller and the binder serves to hold the pigment particles in place. 

In some instances, the pigment is carbon black directly suspended in a high boiling point aliphatic hydrocarbon solution. This ink has no binder but instead is fixed to the paper by diffusion of the oil into the paper thus leaving a highly blackened layer of carbon black and oil upon the surface of the paper. 

---

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. 

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...

Flexographic Printing Flexographic Ink Derivatives, Alcohols, Glycol... 

Flexipac 1-4, characteristics, 8 774t Flexitray valve, 8 763 Flexographic inks, 14 320, 322-324 FlexS, 6 11 Flexsorb SE, 1 72... 

P.Y.12 types are used in packaging gravure and flexographic inks for their reasonable price, but they can also be utilized in aqueous printing inks, provided they are sufficiently fast to light. They cannot be applied as decorative printing inks to laminated paper. 

P.O.62 is frequently used in the printing inks field to produce lightfast offset and aqueous flexographic inks. Its lightfastness in these media equals step 5 to step 6 on the Blue Scale, depending on the standard depth of shade. The prints are not completely fast to alkali and do not tolerate clear lacquer coatings and sterilization. 

Other fastness properties in application largely equal those of P.B.15 1. In printing inks, P.B.15 2 is employed mostly in special gravure and flexographic inks. This is an area in which lack of fastness to overcoating is frequently of no consequence. P.B.15 2, like other a-Copper Phthalocyanine Blue types, is too reddish to be used as a standard cyan for three or four color printing. 

Examples of such effects are the SubChem cases for the substitution of DEHP as a plasticiser in PVC by other phthalates (instead of switching over to underbody hard shells), optimisation of formulations in water-soluble cooling lubricants (instead of switching over to minimum quantity lubrication) or the use of water-based flexographic inks (instead of switching over to UV-drying printing inks). 

Flexographic inks -cellulose nitrate m [CELLULOSE ESTERS - INORGANIC ESTERS] (Vol 5) -dispersed pigment [PIGMENT DISPERSIONS] (Vol 18) -fluorescent pigments m [LUMINESCENT MATERIALS - FLUORESCENT PIGMENTS (DAYLIGHT)] (Vol 15) -from triarylmethane dyes [T RIPHENYLMETHANE AND RELATED DYES] (Vol 24)... 

Water-Based Inks. Approximately 50% of all flexographic inks use water as their primary solvent and diluent. They contain vehicles based on either acrylic emulsions, or hydrosols or an alkali-soluble rosin ester having a high acid number such as partially esterified fiimurated rosin and shellac. Carboxylated acrylic polymers, usually containing some styrene, have largely replaced natural resins because they provide better abrasion and water resistance. Ammonia or other volatile amines are used to solubilize these carboxylated resins and form resin salts. The volatile alkali evaporates from the ink film, rendering the printed matter water resistant. 

With the exception of the blue copper phthalocyanine derivatives, these products are azo dyes that are soluble in polar solvents such as alcohols, glycols, esters, glycol ethers, and ketones. Dyes soluble in alcohols and esters are used in protective lacquers for the transparent coating of metal (aluminum) foils and other materials, such as wood (greening lacquers) in flexographic inks for the printing of metal foils, cellophane, and paper as well as for the coloration of cellulose esters, celluloid, and poly(vinyl acetates), and, in the office supplies sector, for... 

The choice of polymers and resins from which flexographic inks can be formulated is restricted by the need to dissolve them in combinations of alcohols,... 

---