Printing material. Printing ink

a) Printing processes involve the application of a thin film of functional material to a substrate, such as paper, fabric, film, foil or sheet stock. Paper is thin material mainly used for writing upon, printing upon or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets. Paper is a versatile material with many uses. Fabric refers to any material made through weaving, knitting, crocheting or bonding. It is a flexible material consisting of a network of natural or artificial fibers often referred to as thread or yarn. Yarn is produced by spinning raw wool fibers, linen, cotton, or other material on a spinning wheel to produce long strands. Foil is a thin sheet of metal. Foil stamping is a printmaking technique, typically a commercial print process, the application of pigment or metallic foil, often gold or silver. It can also be what is known as pastel foil which is a flat opaque color or white special film-backed material, to paper where a heated die is stamped onto the foil, making it adhere to the surface leaving the design of the die on the paper. Foil stamping can be combined with embossing to create a more striking 3D image. Sheet stock is a paper stock that is thicker and more durable than normal writing or printing paper, but thinner and more flexible than other forms of paperboard. Sheet stock is often used for postcards, playing cards, catalog covers, scrap booking, and other uses which require higher durability than regular paper. The texture is usually smooth, but can be textured, metallic, or glossy.

b) Ink is a liquid containing various pigments and dyes used for coloring a surface to produce an image, text, or design. Inks in paste form are used extensively in letterpress and lithographic printing. Ink is a complex medium composed of solvents, pigments, dyes, resins, lubricants, surfactants, particulate matter, fluoresces, and other materials. The components of ink serve many purposes: the ink’s carrier, colorants, and other additives are used to control flow and thickness of the ink and its appearance when dry. There are many types of paste inks available for employment in offset lithographic printing and each have their own advantages and disadvantages. These include heat-set, cold-set, and energy-curable (or EC), such as ultraviolet- (or UV-) curable, and electron beam- (or EB-) curable. Heat-set inks are the most common variety and are "set" by applying heat and then rapid cooling to catalyze the curing process. They are used in magazines, catalogs, and inserts. Cold-set inks are set simply by absorption into non-coated stocks and are generally used for newspapers and books but are also found in insert printing and are the most cost-conscious option. Energy-curable inks are the highest-quality offset litho inks and are set by application of light energy. They require specialized equipment are usually the most expensive type of offset litho ink.

c) Fountain solution is the water-based (or "aqueous") component in the lithographic process that cleans the background area of the plate in order to keep ink from depositing (and thus printing) in the non-image (or "white") areas of the paper. Historically, fountain solutions were acid-based and comprised of gum arabic, chromates and/or phosphates, and magnesium nitrate. While the acid fountain solution has come a long way in the last several decades, neutral and alkaline fountain solutions have also been developed. Both of these chemistries rely heavily on surfactants/emulsifiers and phosphates and silicates to provide adequate cleaning and desensitizing, respectively. Since about 2000, alkaline-based fountain solutions have started becoming less common due to the inherent health hazards of high pH and the objectionable odor of the necessary microbiological additives. Acid-based fountain solutions are still the most common variety and yield the best quality results by means of superior protection of the printing plate, lower dot gains, and longer plate life. Acids are also the most versatile, capable of running with all types of offset litho inks. However, because these products require more active ingredients to run well than do neutrals and alkaline, they are also the most expensive to produce.