What is offset printing?
Offset printing is a method where images are first put on a plate which is usually made out of aluminum. After this, the plates are moistened with water, which sticks to the image surface, and then with ink, which sticks to the non-image surface. Then, the image is put onto a rubber blanket and from there it is transferred on paper. Because the image does not go directly onto paper this method is called ”offset”.
It all started with lithography, which was used to make cheap artwork, and was limited to use on a flat and absorbent surface. In 1875, Robert Barclay invented the first turning offset lithographic printing press, which used a metal cylinder. This cylinder was coated with cardboard, which took the image from a stone and put it onto metal. Few years after, the cylinder was changed from metal to rubber and this is still in use today.
How does it work?
There are few steps of how offset printing works. First is the pre-press production stage where images are transferred onto plates, similar to how photographs are developed. A certain amount of light is then put through the film negatives and when plates are exposed to light, the coating which is responsive to ink is activated. As a result of this the image is transferred onto the plate. Second stage is the press run stage where paper goes continuously through a press and this is done at high speeds and with large sheets of paper. Ink is dispersed onto the plate with the help of rollers and plates are first dampened with water and then ink.
Next is the offset process, where water sticks to the image area and ink sticks to the non-image area. Plates then transfer the image onto a rubber blanket, which transfers the image onto paper. Since the paper is wet and there is a chance of smudging the paper is put through an oven to avoid this. After this the paper goes through chill rollers which cools down the paper. Last step is called bindery where the rolls of paper are cut to the correct size and then put together in the right order. After this pages are bound together, whether it be by using a staple or glue.
Digital printing differences
Digital printing is different from offset printing in several aspects. Firstly, it does not use plates, but instead it uses toners or liquid ink. Secondly, this method is more appropriate when you need only few items printed and not large quantities. Lastly, digital printing offers you the option of printing codes, addresses or names on the product whereas that is not possible with offset printing.
Methods of offset printing
There are several methods of offset printing. Firstly, there is a method where paper goes through two blanket cylinders and not rubber and this way the paper is printed on both sides, which means printing takes less time. Second method is the one where the plate and cylinder pressure are very precise and those are one-color presses. Thirdly, the process uses cassettes, inserts or printing units, which are removable, in order to print on one side and it uses the first method to print on both sides. Last method removes residual ink and uses new and fresh ink for each revolution.
Digital printing advantages
There are few advantages of digital printing. It is best to use when there is a need for printing smaller quantities and you can print whatever you want when you want it. It offers cheap black and white printing and it has an option to use addresses, codes or names. Lastly, every print is the same since there is no need to balance water and ink during printing, which also means there is less waste.
Which products are printed better with offset printing and which ones with digital printing?
You should choose offset printing when you want the finished product to look clean and professional and when you need larger quantities printed, for example newspapers. With offset printing there is also a variety of different papers you can choose from. On the other hand, digital printing is better when printing smaller quantities, for example postcards and business cards. This method is also cheaper than offset printing, therefore, it is better for people with a smaller budget.
It is hard to say whether offset printing is better than digital printing and vice versa. It all comes down to the needs and desires of the customer and what works for them and no matter which method you choose the final product will still look great.