printing Printing is a process for mass reproducing text and images using a master form or template. The earliest non-paper products involving printing include cylinder seals and objects such as the Cyrus Cylinder and the Cylinders of Nabonidus. The ...

, anti-set-off spray powder is used to make an air gap between printed sheets of paper. This enables the ink to dry naturally and therefore avoid the unwanted transfer of ink from one printed sheet to another. The problem can occur with most types of printing. Anti-set-off spray powder is generally made from natural

starch Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diet ...

es from plants and vegetables. There remains a demand for soluble powders (sometimes known as vanished powders) based on natural sugars which are often used when the final printed sheet is to be varnished. In addition there is still a relatively small amount of powder made from minerals (e.g. Calcium Carbonate, rather than

Talc Talc, or talcum, is a clay mineral composed of hydrated magnesium silicate, with the chemical formula . Talc in powdered form, often combined with corn starch, is used as baby powder. This mineral is used as a thickening agent and lubricant ...

) used in offset litho printing; however these mineral powders are not so popular because of the potential health implications and abrasive properties. Spray powder is used to separate printed sheets to enable air to naturally dry the printing ink. The diameter of the powder used is relative to the

density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...

(g/m²) of the stock (paper or board) being printed. For 150 g/m² paper the ideal anti-set-off spray powder would be 15

μm The micrometre (Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a unit of length in the International System ...

in diameter, for 200 g/m² 20 μm, through to 70 μm for heavy board (700 g/m²). Most manufactures of spray powder offer both coated and uncoated powders. Uncoated powders are generally less expensive and are based on natural food-grade starches typically derived from

corn Maize (; ''Zea mays''), also known as corn in North American English, is a tall stout Poaceae, grass that produces cereal grain. It was domesticated by indigenous peoples of Mexico, indigenous peoples in southern Mexico about 9,000 years ago ...

(maize), wheat,

semolina Semolina is the name given to roughly milled durum wheat mainly used in making pasta and sweet puddings. The term ''semolina'' is also used to designate coarse millings of other varieties of wheat, and sometimes other grains (such as rice or ma ...

, potato,

tapioca Tapioca (; ) is a starch extracted from the tubers of the cassava plant (''Manihot esculenta,'' also known as manioc), a species native to the North Region, Brazil, North and Northeast Region, Brazil, Northeast regions of Brazil, but which has ...

and

rice Rice is a cereal grain and in its Domestication, domesticated form is the staple food of over half of the world's population, particularly in Asia and Africa. Rice is the seed of the grass species ''Oryza sativa'' (Asian rice)—or, much l ...

depending on the diameter required. Coated powders use the same range of raw materials but are encapsulated with a minuscule amount of natural coatings which enable the powders to flow freely though the spray guns on sheet-fed offset-litho printing presses. Enhanced versions of these coatings are used to give specific

electrostatic Electrostatics is a branch of physics that studies slow-moving or stationary electric charges. Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word (), mean ...

(anti-static) and

hydrophobic In chemistry, hydrophobicity is the chemical property of a molecule (called a hydrophobe) that is seemingly repelled from a mass of water. In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, thu ...

properties. Spray powder is not used on rotary presses including rotary letterpress, web offset (often used for printing magazines), flexographic (often used for printing flexible packaging and labels) or gravure (often used for printing long-run catalogues). Similarly, spray powder is not generally used in sheet-fed (silk)

screen-printing Screen printing is a printing technique where a mesh is used to transfer ink (or dye) onto a Substrate (printing), substrate, except in areas made impermeable to the ink by a blocking stencil. A blade or squeegee is moved across the screen i ...

, ink-jet or toner based digital printing. In the UK, many

Carrom Carrom is a tabletop game of Indian origin in which players flick discs, attempting to knock them to the corners of the board. In South Asia, many clubs and cafés hold regular tournaments. Carrom is commonly played by families, including c ...

players use a version of anti-set-off spray powder from the printing industry which has specific electrostatic properties with particles of 50 micrometres in diameter.

Modern developments

As health and safety has become more important to the environment and to the work forces, a small number of anti-set-off spray powder manufacturers had introduced highly clarified powders by 2007, in advance of EU legislation. This new generation of powders have typically less than 3% of particles of less than 10 μm and almost no particles below 5 μm which are generally regarded in the industry as dust. To put this in context typical human hair is 20 – 40 μm. The printing industry regards anti-set-off spray powder as a necessary evil. Ideally printers would prefer not to use it, but it remains the only practical way to ensure a stack of printed paper at the end of a printing press does not set-off. In recent years there has been an emergence of printing presses which use inks that are cured (dried) with powerful UV lamps. As each sheet is individually dried there is no need for spray powder. However, as these machines require specialty inks which are much more expensive than conventional inks, and the UV lamps use a significant amount of energy, the vast majority of new sheet-fed presses sold in 2007 still used anti-set-off spray powder.

Other uses

In addition to its use in the printing and packaging industry, spray powder is also used in the manufacture of

float glass Float glass is a sheet of glass made by floating molten glass on a bed of molten metal of a low melting point, typically tin, although lead was used for the process in the past. This method gives the sheet uniform thickness and a very flat surfa ...

to enable the large sheets to slide easily over each other. It is also used in the manufacture of plastic food wrap and similar products to help prevent pieces of plastic from sticking together because of static electricity. In the UK, many carrom players use a version of anti-set-off spray powder from the printing industry which has specific electrostatic properties with particles of 50 micrometres in diameter.

External links

* — International Paper * — International Paper

References

{{reflist Printing materials Powders

Modern developments

Other uses

See also

External links

References