Offset printing is a process that combines the art of printing with science. It is a popular method for high-quality print runs. It involves transferring images (text and art) from one material to another using plates and a rubber blanket. It’s an ideal solution for large or commercial-scale print runs and is ideal for Pantone colors.
The Process
Offset printing is a popular way to print a wide range of materials. It can be used on paper, cardboard, wood, leather, and many other materials. It can also print special finishes and other design requests. It’s also the best option when you want to print a larger run of your product packaging or if you need to use a specific Pantone color.
Offset printing uses a large press with a series of plates that transfer ink onto the paper. This process can be a little more expensive up front, but the benefits are worth it when you need to print in larger quantities.
Plates
Plates in offset printing are the basic image-carrying surfaces that transfer ink to paper. They are manufactured with different metals, plastic or rubber materials and then go through certain chemical processes before they are mounted on the printing cylinder.
Monometal plates are based on zinc or aluminum, which have hydrophilic (water-receptive) properties. They are coated with a photosensitive substance and then covered with a negative of the text and photographic illustrations to be printed on them, and exposed to light.
They are then processed to remove the unexposed non-image areas, lowering them and leaving the image areas in relief. After drying and curing, the plate is ready for printing.
Blanket Cylinders
Blanket cylinders are a common type of roller used in offset printing. They have a rubber blanket around them and are used to transfer the image from the plate onto paper or another material.
They are used in both sheet-fed and roll-fed machines. The latter are designed as series of printing units with the sheets being transferred from one unit to another on drums of large diameter with a system of articulated grippers.
In sheet-fed offset printing machinery, the impression cylinders are usually designed in such a way that their movement is synchronized to prevent damage to the blanket cylinders. The machine must be able to operate at high speeds and with a high amount of pressure, and the blanket compressibility is extremely important.
Inks
Offset printing requires inks that are formulated to work with the press and paper and to produce the desired results. Color, body, temperature stability, tack, adhesion and drying are all important aspects of the ink.
Opacity refers to how opaque or transparent an ink is, and it also relates to how much the background on which the ink has been printed can be seen. The opacity of an ink also depends on the colorants and the vehicle system it uses.
There are two main kinds of ink vehicles used in offset printing, oil-based and synthetic. Both can contain a mixture of chemicals that make phenolic resins, but plant-derived oils such as soya oil or linseed oil are often the vehicles of choice for offset inks.
Paper
Offset printing paper is the substrate that is used to receive the inked image from the metal plates. It is usually manufactured in a variety of weights, colors and textures.
A paper's surface properties impact the quality and durability of a printed product. Some papers are very glossy, while others have a matte or smooth finish. This difference in the texture and finish of a paper can cause problems when printing. If the paper's surface is too rough, it may not be able to accept the ink properly or it can blister.
Choosing the right paper for your specific application is important. It should be thick enough to support the press's weight but thin enough to print well without creating wrinkles or folds. It should also have the proper caliper (thickness to thickness) to accommodate the press's equipment.
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