How the Printing Press Works
The printing press allowed books to be produced more quickly and made them more accessible. This increased the amount of new and old knowledge that people could read.
Before Gutenberg’s invention, scribes labored for years to hand-copy Latin texts on vellum and other processed materials. This process was time consuming and expensive.
The printing plates are flat pieces of aluminum with a polymer layer on them. The polymer is wetted by the oil-based printing ink and repels water.
Today’s most common lithographic plate uses a hybrid coating of conventional photopolymer on the bottom and silver halide on top. As the plate is exposed to ultraviolet light, the photopolymer dissolves and the image areas are lowered and ready for printing. The non-image areas remain protected by the silver halide.
The computer file for a job is split into four colors, CMYK – Cyan, Magenta, Yellow and Black. Each color requires its own plate. The plates are delivered to the printer from a plate making machine as rolls of aluminum that need several processes before they can be used on the press.
Blankets are used to distribute the pressure of the rollers. They should be in good condition and sized appropriately for your paper stock. They should be abrasion resistant and be able to resist the penetration of chemicals (plate wash, fountain solutions or inks) that can cause them to swell.
A well-designed blanket will have desirable levels of resilience, in particular smash recovery (the ability to return to original dimensions following an instance of increased printing pressure) and durability. The compressible layer of the blanket, which sits between the fabric layers and surface layer, should be free of pits and depressions (although a small amount of grit is sometimes beneficial to draining water from the plate).
The surface of the blanket that touches the plate is called the face. This should be constructed with a smooth surface to allow for maximum image transfer.
The inked plate presses against the second main cylinder, a soft rubbery blanket that is called the blanket cylinder. The blanket holds the ink until it is transferred to the paper by a series of rollers.
Depending upon the printing process, inks are generally low to high viscosity and may contain natural or synthetic resins, with volatile solvents. Litho and gravure inks are typically of a high viscosity, while rotary letterpress and screen printing inks are of an intermediate viscosity.
Ink manufacturers tend to specialize in one of these processes, with only the largest groups producing a broader range. Skin contact with pigments and solvents occurs during mixing, weighing, and pot washing (in which workers climb into drums to scrub them with toluene-soaked rags). Inhalation exposures are usually greatest in the liquid ink department.
A gripper is a space along the edge of a sheet that is where the machine physically grabs and holds it. It is why some printers can leave a white stripe along the edge of a page, where the paper was held during printing.
Gripping can be external or internal and can be powered by a variety of methods including electric actuation. Electric actuation is the most common and usually uses a combination of motors and servos to precisely control the Gripper.
With the conjugate cam system adopted in the gripper opening/closing mechanism provided on the sheet transfer cylinder, torsion that would normally occur in the gripper shaft during opening/closing can be prevented and the opening/closing of the grippers can be made consistent. In addition, the roller and lever assemblies are forcibly constrained to prevent them from jumping during high speed rotation.
Modern printing presses use a process called offset lithography. The computer digitally etches a plate for the design or text, one plate for each color of ink (cyan, magenta, yellow, and black). The inked plates are mounted on a cylinder along with a soft rubber blanket that prints onto the paper.
The resulting printed product allows information to be distributed much more widely than in the past. It allowed new ideas in the worlds of science and philosophy to spread, encouraging people to question custom and tradition and prize personal freedom.
It also allowed newspapers to be produced much more quickly and easily, enabling literacy to spread. Today, most newspapers are produced using an offset print press. One of these can print over 70,000 sheets per hour, about 280 times as fast as Gutenberg’s original press.