Anti-set-off spray powder
Encyclopedia
In printing
, 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
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
) 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 (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
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), wheat, semolina
, potato, tapioca
and rice
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 (anti-static) and hydrophobic properties.
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 manufactures have introduced highly clarified powders 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. A s each sheet is individually dried there is no need for spray powder. However, as these machines require specialist 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 today (2007) still use anti-set-off spray powder.
Spray powder is not used on rotary presses
including rotary letterpress, web offset (often used for printing magazines), flexo (often used for printing flexible packaging) or gravure (often used for printing long-run catalogues). Similarly, spray powder is not generally used in sheet-fed (silk) screen-printing
, ink-jet or toner based digital printing.
In addition to its use in the printing and packaging industry, spray powder is also used in the manufacture of float glass
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.
Printing
Printing is a process for reproducing text and image, typically with ink on paper using a printing press. It is often carried out as a large-scale industrial process, and is an essential part of publishing and transaction printing....
, 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
Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store...
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
Talc is a mineral composed of hydrated magnesium silicate with the chemical formula H2Mg34 or Mg3Si4O102. In loose form, it is the widely-used substance known as talcum powder. It occurs as foliated to fibrous masses, its crystals being so rare as to be almost unknown...
) used in offset
Offset printing
Offset printing is a commonly used printing technique in which the inked image is transferred from a plate to a rubber blanket, then to the printing surface...
litho
Lithography
Lithography is a method for printing using a stone or a metal plate with a completely smooth surface...
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 (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
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
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
Cornstarch
Corn starch, cornstarch, cornflour or maize starch is the starch of the corn grain obtained from the endosperm of the corn kernel.-History:...
(maize), wheat, semolina
Semolina
Semolina is the coarse, purified wheat middlings of durum wheat used in making pasta, and also used for breakfast cereals and puddings. Semolina is also used to designate coarse middlings from other varieties of wheat, and from other grains such as rice and corn.-Name:The term semolina derives from...
, potato, tapioca
Tapioca
Tapioca is a starch extracted Manihot esculenta. This species, native to the Amazon, Brazil, Colombia, Venezuela, Cuba, Puerto Rico, Haiti, the Dominican Republic, Honduras, and most of the West Indies, is now cultivated worldwide and has many names, including cassava, manioc, aipim,...
and rice
Rice
Rice is the seed of the monocot plants Oryza sativa or Oryza glaberrima . As a cereal grain, it is the most important staple food for a large part of the world's human population, especially in East Asia, Southeast Asia, South Asia, the Middle East, and the West Indies...
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 (anti-static) and hydrophobic properties.
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 manufactures have introduced highly clarified powders 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
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
lamps. A s each sheet is individually dried there is no need for spray powder. However, as these machines require specialist 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 today (2007) still use anti-set-off spray powder.
Spray powder is not used on rotary presses
Rotary printing press
A rotary printing press is a printing press in which the images to be printed are curved around a cylinder. Printing can be done on large number of substrates, including paper, cardboard, and plastic. Substrates can be sheet feed or unwound on a continuous roll through the press to be printed and...
including rotary letterpress, web offset (often used for printing magazines), flexo (often used for printing flexible packaging) or gravure (often used for printing long-run catalogues). Similarly, spray powder is not generally used in sheet-fed (silk) screen-printing
Screen-printing
Screen printing is a printing technique that uses a woven mesh to support an ink-blocking stencil. The attached stencil forms open areas of mesh that transfer ink or other printable materials which can be pressed through the mesh as a sharp-edged image onto a substrate...
, ink-jet or toner based digital printing.
In addition to its use in the printing and packaging industry, spray powder is also used in the manufacture of float glass
Float glass
Float glass is a sheet of glass made by floating molten glass on a bed of molten metal, typically tin, although lead and various low melting point alloys were used in the past. This method gives the sheet uniform thickness and very flat surfaces. Modern windows are made from float glass...
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.
External links
- Learn about printing — International Paper
- Glossary of printing terms — International Paper