Offset ‘Flat’ Printing

Offset Printing is also known as flat printing. Offset printing is a ‘flat’ printing process based on the antagonism between water and ink. An aluminum-based plate, typically 0.3 mm thick is covered with a thin photopolymer layer of 1 to 2 µm is used and the latter is the ‘image’ area.

The plate is first dampened by an acidic dampening solution. It spreads easily on the aluminum surface due to the high surface energy of the aluminum oxide, around 70 mJ/m². The dampening solution weakly wets the image areas, which are non-polar and have low surface energy or around 35 mJ/m². The images are formed quickly, as the ink does not spread on the wet areas, but spreads on the image areas not affected by the dampening solution.

The image is first transferred onto an intermediate elastomeric plate called the ‘blanket’ and then onto a substrate. The blanket allows a reduction in the amount of water brought to the substrate. Moreover, its elastomeric properties improve the transfer, in case of rough substrates. The name ‘offset’ comes from this double transfer. Offset inks are very viscous and their surface tension is around 35 mN/m, with low polarity levels. Thus, offset printing is less expensive than engraving and thermography.

Plates are easy to make and rather economical too. The resolution is excellent, especially when they are obtained through direct exposure to a laser beam.
Offset printing offers high-quality printing at an affordable price. The offset printing process is only applicable for ventures requiring multiple colors, high quality and a specific quantity. These requirements are met easily by the modern printing presses that offer the latest in quality and productivity enhancement.

Uses Of Offset ‘Flat’ Printing

Flat or offset printing on letterheads differs from other printing techniques because it does not have the raised ink texture. Flat printed letterheads have a sharp page image text that is clear and concise. In most cases flat printed stationery costs slightly more than raised ink printed stationary. Flat Ink is mostly used in communication mediums like envelopes, letter heads and business cards.

Over a 1000 different colors of Flat ink are available, though most printers use a standard set of ink colors that are employed all the time. Metallic flat inks such as gold, copper and silver are also available. These inks contain real metal in them, which is harder to clean during the printing process. Thus, metallic ink prints cost more.

Advantages of Offset Printing

In the gravure procedure, ink is transferred from the recesses or wells. In offset or flat printing, the ink to be transferred and the undisplaced surface are placed at the same level. The non-printable and printable areas work along the theory that ‘oil repels water’.

In offset printing, the inks are water-soluble, while in gravure the inks are toluene soluble. The inks used in gravure are transparent and hence they can be applied on top of each other. Offset inks are opaque and this is not possible. They have to be applied separately.

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