What Is Offset Printing How It’s Work

Offset printing is one of the most commonly used methods of industrial printing technique. It is used to print a wide range of products including leaflets, cards, books, magazines, stationery, brochures etc. It can also be used to print custom packaging like cartons or custom boxes. Offset printing makes the best choice especially when a print is to be made in large quantity. It provides a perfect colour reproduction, cleanliness, crisp and a professional look to the product. Various custom printed boxes can be made by using it which serves as an excellent packaging solution.

Why Called Offset Printing:

The offset printing technique uses plates which are normally made up of aluminum. These plates are used to transfer the image to a rubber blanket also known as a roller which is then rolled to transfer the image to a sheet of paper. Instead of paper, some other material can also be used like paperboard or even cardboard to make custom boxes. The technique is called offset as the ink is not directly transferred to the paper.

In other words, we can say that offset printing transfer the ink from the printing plate to the paper but this process is not carried directly. Another step is involved. First, the inked plates are press onto rubber roller transferring the image onto it, and then the roller is pressed against the printing surface. Offset printing prevents the plate to wear out even after repeated impressions on a sheet of paper, consistently producing high-quality printing results.

A Brief History Of Offset Printing

Offset printing technique was accidentally invented by a paper mill owner, named Ira Rubel, at the beginning of 20th century. He used to print bank deposit slips by using a lithographic stone press (lithography means stone-writing). One day his press operators accidentally missed a sheet, which causes the press to print the image on a soft rubber surface. As a result, when the next page was fed to the press, it gets the image printed on both sides.

On one side the image got printed from lithographic stone and on the other side due to the ink on impression roller. He noticed that the image formed by the rubber blanket was much clearer and sharper than the one formed from the stone plate.

He then joined the setup with another printer to build a press which always transfers it a rubber roller which is then offset to a sheet of the paper. Thus he named the technique as offset printing. The first official offset printing press was soon opened and now it has become one of the most widely used techniques.

The modern offset printing technique is the updated version of the same basic idea. The difference is that the stone is replaced by a metallic printing plate. The image is first transferred to the plate. The parts of the plate onto which image is to be printed, are covered with lacquer (varnish) to attract ink. The remaining plate is coated with glue so that it attracts water. The metallic plates are curved around printing rollers/cylinders.

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How Offset Printing Works

Step 1: Pre-Press

Pre-press is the step prior to the printing process. Before the required image can be printed, it is converted to plates. There is a separate plate for each primary color like black, magenta, yellow and cyan. Paper plates were also common a few years back. Although they are cheap but do not produce good results. The high-quality aluminum plate is used which give the best printing effects.

Black and three subtractive colors like cyan, yellow and magenta are the main colors which are printed in the process. Other links which are added to the main colors are highly saturated spot colors. They are used for giving striking artistic effect. The offset printing unit has a separate tower for each color of ink.

Step 2: Press-Run

In the second phase, the pre-cut paper is put into the press. The image area of the plates picks up the ink from the inked rollers/cylinders. The dampening water rollers (colored as blue in the image) keep the ink off from non-image parts of the plate. Each plate transfers the image to the rubber blanket which in turn transfers the image to paper.

In this process, the plate not actually touches the paper thus called offset printing. All this occurs at a very high speed. Some printing units are so fast that they can undergo 15,000 impressions per hour. The following video clip illustrates the process:

Step 3: The Inking Process

The main principle of offset lithography is that water and ink do not mix. The ink gets distributed to the plates by a series of rollers or cylinders named as impression cylinder, plate cylinder and the blanket cylinder. The blanket cylinder is present in between the other two cylinders. Three of them rotate in a way with same surface velocity.

This makes them contact each other without sliding. The plates are first dampened by water rollers and then the ink rollers. As shown in the figure below, the image is first transferred to plate cylinder, then to the blanket cylinder. The sheet of paper is present between the last two cylinders, which makes the image to get imprinted from the blanket cylinder (rubber roller) onto the paper.

Advantages of Offset Printing

Offset printing is extensively used worldwide with a wide range of features that make them acceptable. It proves beneficial and cost effective especially when a large quantity is to be printed. The more copies you print, the rice of each piece gets reduced. It can use different types of paper with a custom finish.

Custom packaging solutions including all type of cardboard boxes and custom boxes can also be printed using the offset technique. Specialized ink with metallic and Pantone colors is used to produce high-quality printing results with minute details.

So, next time whenever you read your favorite magazine or come across any custom packaging like custom printed boxes, stop and think for a while that how this publication began and what might be its printing process, how these custom printed boxes undergo offset printing technique. This article gives a clear understanding to readers about what is offset printing and how it works. Following video provides more understanding in this regard:

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