A Complete Guide to Offset Printing

A Complete Guide to Offset Printing

What is offset printing?

In our current article series, we will be discussing various types of printing procedures including screen, offset and digital printing etc. We will explain every bit of the printing process in detail. Today, we will be studying the foundations of offset printing. Another name of offset printing is offset lithography. Offset printing is the main method for printing longer runs of posters, books, direct-mail pieces, magazines, manuals, letterhead, brochures, paper-based labels and packaging, and much more.

Offset printing involves the fixed costs of setting up each job. Each copy’s price in a 10,000-copy job is lower than the value of each piece in a 250-copy job. The big order offers you affordable rates as compared to small orders. That’s why offset printing technology is highly recommended for custom product boxes.

How It Works

How Offset Printing Works

Let’s discuss the working procedure of Offset lithography. It involves several steps. Kindly have a look at them below:

  • Etched Metal Plates
  • Water
  • Impression Cylinders
  • Water Repellent Inks (oil-based)
  • Blanket Cylinders

The etched metal plates are created with the purpose that these oily inks stick to the parts of the plates containing the text and images. A thin film of water is placed on the blank areas of the metal plate that strict the oil-based inks. Firstly, the ink which is present on metal plates is shifted to a rubber-wrapped blanket cylinder. The ink will reach towards the paper once we roll the inked blanked cylinder above the paper.

The impression cylinder is useful for applying pressure to the paper, so the ink sticks to the paper surface smoothly and quickly. It is also beneficial for moving the sheets through the presses. The separate plates and blanket rollers are required for each color of ink that we will use in our offset printing procedure. There are several plates, inks, and presses used for diverse substrate requirements and run lengths.

Let us consider an example. Some presses companies may be printing millions of pieces of a magazine, and other companies may be printing 300 large sheets that can be folded for making multi-page brochures or designs. There are many types of Offset printing. We will go in detail below.

Web Press

Web press printers are useful and a time saver. As it automatically feeds a bulk amount of papers starting with one ink station then onto the next until the reasonable amount of ink is applied to each page. Web press is ideal for printing 10K or more copies of multi-paper documents like catalogs, books, and magazines.

Coldset and Heatset Web Press

Coldset Web Offset

The ink is applied and fixed into the paper with the absorption process’s help.

Heatset Web Offset

The heat-set web offset involves two steps. One is fixing ink into the paper by the absorption process and then evaporation at high temperatures. It is a more robust and quicker method. It is four to five times faster as compared to sheetfed presses. Heatset Web Offset also includes the inline folding equipment.

Sheetfed Press

The sheetfed press uses the flat pre-cut sheets for printing through the press. In this type of offset printing equipment, the printing speed has a range of 5K to 20k copies per hour. The benefit of the sheetfed press is that it can accommodate various thicknesses and substrate types compared to web presses. Sheetfed presses are both large and small. The small sheetfed presses can hold papers of 4 x 6 inches, but larger presses can handle sheets as large as 40 x 26 inches.

Sheetfed Press Process

We call sheets with larger sizes as parents. It is due to the fact that one sheet can hold multiple pages of a manual or book. The page formats on each parent sheet (“marks”) may have 4, 8, or 12 book pages on each side. The pages must be spread out in a legitimate pattern so the pages will show up in the best possible succession when the pages are tended to, collapsed, and bound.

Perfecting Press

In this type of printing process, print is automatically printed on both sides of the paper. All web presses are built on perfecting press phenomenon, but sheetfed presses cannot automatically print both sides of the page.

Prepress

Before print employment can go to an offset press, the page plans made on a PC must be isolated by the sorts of inks that will be utilized to make up each page. For quite a long time, a photograph etching measure uncovered shading isolated movies onto photosensitive plates. Today, PC to-plate frameworks utilize carefully controlled laser etching frameworks to carve the imaging information from advanced documents onto aluminum plates. 

CTP frameworks have diminished the time and cost engaged with setting up offset printing occupations and making minutes ago updates to the plates. The prepress cycle for offset printing frequently incorporates more detailed sealing techniques, such as burden confirmations that empower purchasers to watch that the entirety of the pages of a distributed magazine will show up in the ideal grouping. 

Offset Inks 

An enormous assortment of inks is accessible only for use with various sorts of offset presses.

What is Offset Printing - Offset Inks

Colors: The press operators primarily use four process colors: cyan, yellow, black, and magenta. But they can also use inks according to the requirements of the client. It increases the demand for printing as well.

Formulations: The offset inks use various oils derived from plants to transfer the pigment. The most commonly used plant-derived oils include linseed oil and soya oil. Other inks also use water-repellant fluids that are prepared from synthetic chemical mixtures.

Special Properties

The offset inks are composed to alter the production of the ink on the sheets. Consider an example, and prints can be prepared with the help of metallic inks, UV-curing inks, thermochromic (color-changing) inks, and magnetic inks. The polymer-based inks are very popular among the sheetfed presses owners because it quickly dries the prints when exposed to UV-LED. It saves their time and cost of using heat or spray-on powders for accelerating the drying process during the press procedure. The sheetfed offset presses can print on non-porous synthetic sheets, plastic sheets, paperboards for packaging, foil-laminated sheets, and a more comprehensive range of label stocks and cards. It can only be done efficiently if the UV-LED inks and curing units are correctly formulated.

Substrates

We are thankful for the advancements in substrates and offset inks. Due to these innovations, offset printing can print on a more excellent range of textured and smooth paper, tear-resistant synthetic papers, paperboards, and several plastics utilized in bags, envelopes, gift cards, and packaging. Some unique materials present for offset printing, including carbonless papers for business forms, metal-laminated papers with silver and gold foils, and security papers.

While printing, the cost is always kept in consideration. The web offset presses use the economic coated and uncoated papers for printing the high volumes of manuals, catalogs, books, and magazines. It is also done to reduce printing costs. These inexpensive papers should be solid enough to cater to the roll-to-roll fast speed printing. This specialized material is primarily prepared for use on sheetfed presses.

Finishing Processes

What is Offset Printing Finishing Processes

The kind of finishing equipment you want to use will depend on the volumes and types of publications, packaging, manuals, direct mail pieces, or stationery being created. Various finishing equipment includes tools for cutting or trimming the paper, varnishing, binding, laminating, folding, or die-cutting printed sheets. Some of the printed sheets are perforated, glued, foil stamped, or pushed into mailing envelopes. Few finishing types of equipment allow us to utilize transparent UV-curable inks for decorative effects or added stability.

Trends

With the advancement in digital printing technologies, the efficiency of offset printing has also increased above expectations. The offset printing equipment manufacturers have produced software, prepress processes, and consumables that let offset press companies create shorter-run and fast-turnaround print jobs.

The press manufacturers like Heidelberg have set a goal of developing systems that permit more steps in the finishing process and offset printing. It will help to handle the process automatically without the interference of a human press operator. We are expecting to see a lot of innovations for offset printing in the upcoming drupe global print show, which is scheduled in Dusseldorf, Germany.

Final Words

In our post, we tried our best to thoroughly and clearly explain to you the offset printing. We hope that you have learned every bit of information by reading our article. If you have any queries about offset print, you may ask in the comment section. We will happily reply to you with the required information.Also, don’t miss a great comparison between digital vs offset printing.

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