Добавил:
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз: Предмет: Файл:
Скачиваний:
13
Добавлен:
07.10.2014
Размер:
26.62 Кб
Скачать

Offset lithography.

Offset printing is an indirect lithographic printing technology. Offset press was invented in 1870s. Offset printing has spread markedly since approximately 1970 and has, to a great extent, ousted the letterpress printing technology which prevailed until that time.

The printing areas of the printing plate are oleophilic — ink-accepting and water-repellent, that is, hydrophobic. The non-printing areas of the printing plate are hydrophilic, consequently oleophobic in behavior.

Printing unit consists of inking and dampening units, the plate cylinder with the printing plate, the blanket cylinder with the blanket fixed to it, and the impression cylinder.

On most offset presses, as the plate cylinder rotates, the plate comes in contact with the dampening rollers first, and then the inking rollers,

The dampeners wet the plate so the non-printing areas repel ink.

The inked image is then transferred to the rubber blanket, and paper or other substrate is printed as it passes, between the blanket and impression cylinders.

Offset printing technology can be sheet-fed offset printing and web-fed offset printing. Fundamental attributes of sheet-fed offset are flexible production options and the relatively economical production of printed products of a very high quality for a wide range of print volumes. Sheet-fed can be work and turn or work and tumble.

Web-fed offset presses are production flow lines where product is also a means of transportation. Web offset presses are usually categorized into either press types operating on the heatset principle for the production of commercial print jobs, magazines, and publications or newspaper offset presses operating on the coldset principle.

The simplest version of a printing unit is the vertical blanket-to-blanket one which uses a horizontal web-lead to print one color on the front and reverse side of the web.

Advantages of offset printing are:

-materials with different sheet size and grammages can be processed;

-nearly all finishing operations are possible;

-the quality is rather high.

Disadvantages are:

-complicated method-causes misprints;

-sheet size just as big as machine size;

-expensive printing machines.

Productions of sheet-fed lithography: books, catalogs, greeting cards, posters, etc.

Production of web-fed: newspaper, inserts, encyclopedias, magazines, etc.

Соседние файлы в папке Топик По Английскому Языку (Петренко Ю. М.)