Lithographic Printing

How Offset Printing Works

A Brief History of Printing

• The early " revolution"  of moveable printing failed to ignite the world.

• The process of producing printed versions of Chinese texts was more time consuming than traditional hand-inscribing.

• Storing the thousands of characters in the Chinese alphabet was a problem.

• Pen and oil-based ink was more efficient.

Johannes Gutenberg 1436• Johannes Gutenberg,

1436 was a profit-minded goldsmith from Southern Germany.

• His motivation was personal profit: he hoped to get rich by mass-producing the Church's ever-popular "indulgences".

The Printing Press

• The amount of information in one Sunday New York Times is greater than the amount of information an 18th century person in England would be exposed to in his lifetime.

The Passage of Time

• As the New World ( America ) grew in importance so did the media of printed communication.

• Gutenberg's technology did not change for 400 years.

• The next revolution was the invention of continuous rolls of paper.

• Print availability to the public jumped astronomically.

The Creative Process

Every print piece starts with the creative process.

Writers, editors, graphic designers and artists are the

initial step in the creation of magazines, newspapers,

brochures, flyers, catalogues and other print pieces.

When each article is written, edited and approved with

final art, the pieces are sent electronically to the

director of graphic design for page layout.

From a simple sketch

To a final colour drawing

When each article is written, edited and

approved with final art, the pieces are sent

electronically to the director of graphic

design for page layout. The director

determines what page a story will appear on,

where art will be in relation to words and, in

some publications, where advertising will

appear.

Lithography

• Lithography is a chemical process .

• Lithography depends on the principle that oil and water do not mix

Images (words and art) are put on

plates which are dampened first by

water, then ink. The ink sticks to the

image area, the water to the non-

image area. Then the image is

transferred to a rubber blanket, and

from the rubber blanket to paper.

Pre-Press Production

Before the job can be printed, the document must be

converted to film and "plates." Images from the negatives are

transferred to printing plates in much the same way as

photographs are developed. A measured amount of light is

allowed to pass through the film negatives to expose the

printing plate. When the plates are exposed to light, a

chemical reaction occurs that allows an ink-receptive coating

to be activated.

                                                                   

                                                                                                                                                                      

       

Formatting the page by cutting negatives and placing them in place before the plate is made.

                                                            

                                                                                                                                                                      

            A blueprint of the negative and plate layout, used to check image positions before printing.

There are different materials for plates, including paper (which produces a lower-quality product). The best plate material is aluminium, which is more costly. Each of the primary colours -- black, cyan (blue), magenta (red), and yellow -- has a separate plate. Even though you see many, many colours in the finished product, only these four colours are used

The Press Run

The printing process used to print our newspapers is called web offset lithography. The paper is fed through the press as one continuous stream pulled from rolls of paper. Each roll can weigh as much as 2,000 pounds (1 ton). The paper is cut to size after printing. Offset lithography can also be done with pre-cut paper in sheet fed presses.

Web presses print at very high speeds and use very large sheets of paper. Press speeds can reach up to 50,000 impressions per hour. An impression is equal to one full press sheet (38 inches x 22 and three quarters), which is 8 pages of the Express & Star.

                                                                

                                                                                                                                                                      

          

                                                             

                                                                                                                                                                      

             

The press has to maintain a constant

balance between the force required to

move the paper forward and the amount

of backpressure (resistance) that allows

the paper to remain tight and flat while

travelling through the equipment..

The Inking Process

Ink and water do not mix -- this is the underlying

principle of offset lithography. The ink is distributed

to the plates through a series of rollers. On the

press, the plates are dampened, first by water

rollers, then ink rollers. The rollers distribute the ink

from the ink fountain onto the plates.

The image area of the plate picks up ink from the

ink rollers. The water rollers keep the ink off of the

non-image areas of the plate. Each plate then

transfers its image to a rubber blanket that in turn

transfers the image to the paper. The plate itself

does not actually touch the paper -- thus the term

"offset" lithography. All of this occurs at an

extremely high speed.

Colour control is a process that

involves the way in which the ink blends

together, and is tied closely to the plate

registration. The amount of ink that is

released into the units depends on how

much ink is needed to achieve a desired

look. The ink is adjusted via the control

panel that is part of the overall control

console.

Bindery

The bindery is where the printed product is

completed. The huge rolls of now-printed

paper are cut and put together so that the

pages fall in the correct order. Pages are

also bound together, by staples or glue, in

this step of the process.

The "stitcher" gathers, assembles and staples the magazines (called books) before they are sent for final trimming.