GB439078A - An improved method of and means for preventing offset of ink in printing operations - Google Patents

Abstract

<PICT:0439078/IV/1> Offset is prevented by applying to a newly printed sheet or web particles of a material of such composition as will be acted on, e.g. dissolved or suspended by, the printing inks in a subsequent printing operation so as to permit reprinting of the sheet without further treatment thereof, for example, by applying a mist-like spray of a material containing a solid and a volatile liquid, leaving on the sheet separate particles of the solid material to constitute a spacing medium. The applied material may be a substantially colourless varnish or lacquer with or without added alcohol or other highly volatile solvent; gum arabic dissolved in a non-inflammable mixture of wood alcohol and carbon tetrachloride; or a colloidal suspension of gum arabic, glucose, alcohol, and water. The sheets or webs 11 are passed on a carrier 10 through a chamber 13 under an air spray 15. Compressed air is led to the spray from a tank 19 through oil and water separators 21, a conduit 24, and pressure regulators 27<a>, and also passes through a conduit 25 and regulators 27<a> to force the spraying composition from a tank 27, equipped with a bleeder valve 28. The solvent volatilizes as the spray falls and is drawn off by a duct and fan 14. A light source 33, photoelectric cell 31, relay 38, and valve 40 cut off the spray when a sheet is not in position. A second spray 15<a> may be positioned so as to treat the lower side of the sheet through apertures in the chamber 13 and supporting table 10<a>.ALSO:<PICT:0439078/III/1> Offset is prevented by applying to a newly printed sheet or web particles of a material of such composition as will be acted on, e.g. dissolved or suspended by, the printing ink in a subsequent printing operation so as to permit reprinting of the sheet without further treatment thereof, for example, by applying a mist-like spray of a material containing a solid and a volatile liquid, leaving on the sheet separate particles of the solid material to constitute a spacing medium. The applied material may be a substantially colourless varnish or lacquer with or without added alcohol or other highly volatile solvent; gum arabic dissolved in a non-inflammable mixture of wood alcohol and carbon tetrachloride; or a colloidal suspension of gum arabic, glucose, alcohol, and water. The sheets or webs 11 are passed on a carrier 10 through a chamber 13 under an air spray 15. Compressed air is led to the spray from a tank 19 through oil and water separators 21, a conduit 24, and pressure regulators 27<a>, and also passes through a conduit 25 and regulators 27<a> to force the spraying composition from a tank 27, equipped with a bleeder valve 28. The solvent volatilizes as the spray falls and is drawn off by a duct and fan 14. A light source 33, photoelectric cell 31, relay 38, and valve 40 cut off the spray when a sheet is not in position. A second spray 15<a> may be positioned so as to treat the lower side of the sheet through apertures in the chamber 13 and supporting table 10<a>.