Reference Book
series of single printing units connected in tandem to form one press. The
paper can be fed in either sheets or rolls.
Perfecting Presses:- Presses that print on both sides of paper at the same time
are known as perfecting presses or perfectors. Both sheet-fed and web-fed
presses can be perfecting.
Waterless offset Presses:- Waterless offset presses do not use dampening
solution to keep the plate’s non-image area free of ink. These presses function
because the plate’s non-image area consists of a layer of silicon that repels ink.
Direct imaging (digital) offset presses are waterless, with no dampening system.
Digital Offset Presses:- Conventional offset presses are not linked directly to
the prepress function. Plates are imaged away from the press and then carried
to it. But digital offset presses use direct imaging (digital) in which blank
plates are mounted on to the press and then imaged by digital-driven lasers.Working principle of an offset press
Offset printing is a planographic printing process in which the image area and
the non image area are on a same plane in the image carrier. This process
works under the principle oil and water repels each other. It was invented by a
German named Alois Senefelder in 1798. In 1903 Ira Washington Rubel from
New Jersey developed an offset press design. On Rubel’s new press design,
the inked plate transferred the image to a rubber covered cylinder, called the
blanket cylinder, which then trasferred the image to the paper.Operating Units of an Offset machine
All presses are composed of four basic units - feeder unit, registration unit,
printing unit and delivery unit.Feeder Unit
The feeding system is the mechanism that sends the substrate into the press.
The feeder unit of a sheet-fed offset must separate the top sheet of paper from
the infeed pile, pick it up and deliver it to the registration unit. Only one sheet
can be fed at a time and each must reach the registration unit at a precise
movement to be registered and sent to the printing unit.
Types of feeding systems
There are two types of feeding systems: successive or single sheet feeding
system and continuous or stream feeding system.