Lith Printing

The History and principles of Flyer Printing

The development of lithographic printing in the later half of this century has been the result of extensive research into the preparation and use of the litho plate. The process of lithography was originally confined to stone slabs which were prepared for printing with the use of greasy drawing inks and crayons to form an image on the flat surface of the stone, and various chemicals applied to ensure that when inked, the non-image areas of the stone remained free from ink. Zinc plates were introduced by about 1820 to replace the cumbersome stone and by.

Flyer printing is helped by new photographic techniques

1860 a photographic process was being used to form an image on the plate instead of hand drawing. The use of zinc plate permitted the development of rotary presses and at the turn of the twentieth century an American developed a paper printing press with a rubber covered cylinder between the plate and impression cylinders of the conventional direct press. Thus offset lithography became the predominant method of printing from litho plates. Plate development was gradual. Aluminium plate was introduced in 1900 but its use limited because of serious oxidation problems.


Lithoprinting or Litho-printing

Lithoprinting remained a problem until the 1950's when anodising was applied to the surface of the aluminium plate and a new generation of litho plates was born. This development, coupled with the use of new light sensitive coatings, has led to the present popularity of lithography.

The principles of lithographic flyer printing

IThe principle of lithography exploits the phenomenon that grease repels water. An ink-attracting, water repelling image is formed on the modern aluminium plate by photgraphic means. The non-image areas of the plate are rendered w ater- attracting by coating the plate. When processed, the plate is fitted to the cylinder of the offset press where it is first damped by cloth rollers and then inked by rubber rollers.

The inked plate image is then transferred by contact pressure to a rubber covered cylinder (blanket cylinder) which in turn impresses the image onto paper which is pressed into close contact with the blanket by an impression cylinder. The image is thus offset from the plate to the paper. The use of this soft rubber covering on the offset cylinder allows a variety of coarse surfaced papers to be printed by lithography with success.

Most of the aluminium plates used today carry a tough coating of aluminium oxide (anodised) on the surface which gives the plate good water carrying properties together with corrosion resistance. The photographic plate image is formed by exposure of a photosensitive diazo or photopolymer resin which has oleophilic qualities and is capable of producing 200 000 press copies or more.

The non-image areas of the plate are treated with Gum Arabic to make them water-receptive. On the press, moisture is applied to the plate to allow for differential inking of the image. Water may be quite suitable for plate damping but it is more common for the water to be doctored with a mild acid to bring its pH to about 5.6 and substances such as Gum Arabic or alcohol are added to reduce the surface tension of the water. Fountain solution additives of this nature are supplied commercially and are recommended by plate manufacturers for the efficient working of their plates.