What is Offset printing? How does offset lithography work?

What is Offset Printing? How Does Offset Lithography Work?

Offset printing technology is one of the most prevalent and demanded printing techniques used in various industries. The reason behind this is the fact that it has the ability to produce a large volume of prints in a short period. This printing technology can be applied to various substrates, including paper, metal, plastic, glass, and even textile. The lithography offset printing also features versatility as it has no limitations on the size or shape of the substrate.

Understand Offset Printing

Offset printing is a commonly used printing technique in which the inked image is transferred (or “offset”) from a plate to a rubber blanket, then to the printing surface.

When used in combination with the lithographic process, which is based on the repulsion of oil and water, the offset lithography printing technique employs a flat (planographic) image carrier. Your color will be spot on with offset printing technology, and your print will be flawless. The offset printing method can be used for printing on paper, cardboard, and plastic.

The lithography offset printing process involves creating an image on paper using three chemicals: cyan, magenta, and yellow. These three colors can be combined in various proportions to create any color needed. The black ink commonly used in printing is also produced using these three colors.

How does the offset printing technique work?

The term offset comes from the fact that when a print job is carried out, the rubber blanket is first stamped with the image on the plate. Then it is transferred (offset) onto a sheet of paper. Basically, four colors are used in the offset printing method – cyan, magenta, yellow, and black (commonly known as K). These four colors are combined to produce any shade or color required for an image. This is considered one of the most versatile printing techniques available because offset printers can produce any kind of quantity for a cost-effective price.

The offset printing technique relies on the principle of hydrophobicity (repulsion of water) and hydrophilicity (attraction to water). On a basic level, ink (hydrophobic) is repelled by water, while the image area accepts ink and repels water. This makes it possible to have fine details and a high-quality resolution.

Types of Offset Printers

Offset printing is a high-volume printing method that transfers images from metal plates to rubber pads and then finally onto paper. It can be used for printing on paper, cardboard, plastic, or other materials, but these have to have a flat surface.

Modern offset printers generally employ a four-color process: cyan (a shade of blue), magenta, yellow and black (CMYK). These links are usually mixed to produce thousands of other colors. However, some high-end printers use spot colors which are specially mixed inks applied directly to the press in specific areas. There are several types of offset printers:

Sheetfed offset printer

Sheetfed Offset Printer

A Sheetfed offset printer (sheet format up to 100×140 cm) is used to print on cardboard with a weight of about 250 g/m2. There is no limit to the number of colors used, but usually, there are only 4 or 5 colors printed.

Web-fed offset printer

Web-fed Offset Printer

 Web-fed offset printer (web width up to 260 cm) is used for printing on paper with a basis weight from 30 to 180 g/m2. Up to 12 colors may be printed in one pass on such printers.

Narrow web offset printers

Narrow web Offset printers

Narrow web offset printers (web width up to 55 cm) are used for printing labels and self-adhesive films with a basis weight of 40 to 80 g/m2. This type of printer allows you to print up to 8 colors in one pass.

Understand different kinds of offset printing methods

Offset printing is done by employing automatic machines that include multitasking units for simultaneously performing various operations. A sheetfed offset press feeds single sheets of paper, whereas a web offset press feeds a continuous roll of paper.

The quality and efficiency of such presses depend on their design and processing capabilities and on their components, such as dampening systems, plate cylinders, ink fountains, and impression cylinders.

Sheetfed offset printing

Sheetfed offset presses do exactly what their name implies: They are fed sheets of paper, one by one. The press prints on both sides by taking each sheet through two separate mechanisms that apply ink, wetting agents, and drying solutions (for special inks). After the front side is printed, it goes through the second cylinder, and the backside is printed. This means that with each pass through the press, only one side gets printed on. This allows for printing on different types of stocks and sizes.

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Sheetfed presses also have better quality for smaller runs because each sheet can be monitored individually throughout the printing process. A stacker keeps track of how many copies are needed for each job and arranges them accordingly after they are printed.

Offset lithographic printing

The offset lithographic printing process is based on the principle that oil and water do not mix. The image areas of an offset printing plate are treated so that they attract ink while the non-image areas repel ink.

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When a printing plate is mounted on a press cylinder (offset cylinder) and moistened with water, the non-image areas become hydrophilic or water-attracting because of the chemical treatment that the plate has undergone. When ink is applied to the printing plate, it will adhere only to the image areas since these are oleophilic or ink-attracting. The image areas do not accept moisture from the dampening system. Each color requires its own separate lithographic printing plate.

Web-offset printing

Web offset printing is a printing technique that uses the power of the internet to produce high-quality printed materials from virtually any source, such as a digital file. Web offset printing, also known as digital printing, utilizes computer programs to place images on a flatbed printer. As the name suggests, it is similar to printing on a web page — you send your image to the printer and get back a printed image exactly like you sent it. This can be sent via email or fax, so there’s no need for any physical delivery.

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This is different from traditional offset printing. With offset printing, you send your paper-based artwork through a machine that lays down ink on the page and then transfers that image to the paper (with some variations).

It offers a variety of advantages over traditional offset printing methods. The process can be completed in the customer’s own office, saving travel costs and time. It also eliminates the need for large print runs. It allows customers to apply their brand, logo, and message to a broad range of products, including books, magazines, folders, brochures, direct mail pieces, presentation packages, and more.

Benefits of offset printing

Offset printing technology is a type of printing in which a colored, textured, or patterned layer is transferred to the surface of a printed piece. In offset printing, the colored or patterned layer is applied directly to the substrate (the material being printed).

This type of lithography offset printing allows for consistent quality and longevity of your printed images, which are especially important for promotional and commercial items. The lithography offset printing process is generally used for high-volume products, such as magazines, catalogs, brochures, packaging, and other printed materials.

One of the main advantages is that offset printing allows for multi-color printing, ideal for packaging products with multiple colors (for example primary and secondary colors). Some of the other benefits include the following:

High quality

Offset lithography printing technology has been refined over a long period, and it has become one of the most sophisticated methods of printing. It produces images with high resolution and clarity. The result is an image that can be used as fine art or more easily reproduced as a poster or print than other methods of image reproduction.

Speed

The key advantage of offset printing, besides its lower cost, is that it’s fast. Because this process involves two steps instead of one, offset lithography printing generally takes much less time than other forms of printing, such as screen and inkjet.

Printing on different materials

Another advantage of lithography offset printing is its ability to print on various types of materials. Offset printers can print on different types of paper, such as glossy and matte paper, card stock, and plastic films. The best part is that you can use multiple other materials in one single package; you can even offer customers a choice between different materials.

Portability

 This method is especially useful when you need to make large quantities of prints because it can produce multiple copies at once. A batch of photos can be printed in as little as 15 minutes, compared to 30 minutes to 1 hour for digital printers that use computer imaging to create a product image.

Affordability

When compared to digital printers or letterpress machines, offset printing machines are more affordable. As mentioned above, it is the preferred method for high-volume projects because it has a lower cost per sheet than digital printing machines.

While digital printers produce copies on a per-page basis, offset, printing produces copies in sheets that can be cut into small pieces after the printing process has been completed. In addition, offset machines are capable of producing thousands of copies within a short period.

Use of quality paper and ink

The paper and ink used by offset printing are superior to regular paper and ink. They are made specifically for offset printing, making them resistant to water, humidity, and air pollution damage.

What is the offset printing process?

Offset printing requires more steps than digital printing, but each step in the process allows for more control over color, shade, and image quality.

Plate

The first step in the offset printing process is the plate. The plate is an aluminum plate containing the image to be printed. The plate is placed on a cylinder so that it can rotate as it prints. The offset printer creates a printing plate using a laser that exposes a photosensitive coating on the metal plate, burning an image into the plate. The exposed metal on the plate is treated with ink, while the non-image area is treated with water. The water causes the ink to repel this area.

Cylinder

The plate cylinder is situated near a roller called an impression cylinder. The ink on the plate transfers (offsets) to a rubber cylinder or impression cylinder. When it comes into contact with it, it transfers the image onto paper or any other material used for printing. The impression cylinder creates pressure between itself and the plate cylinder to imprint the image onto paper properly.

Ink

The ink is applied to the cylinder, which transfers it to whatever surface needs to be printed on. To make sure the image is clear and legible, only a small amount of ink should be applied at one time. A roller called a fountain roll controls the amount of water that rolls along with your paper as it goes through your press and determines how much ink will be transferred onto your paper.

Water and dampening system

The water and dampening system keeps the ink from smearing or running off of its intended target when applied to different surfaces. However, if too much water is used, the ink will not stick properly and will run off of whatever surface you are trying to print on.

Bottom line

So, offset printing is one of the best methods to produce high-quality and great-looking printings. Lithography offset printing has eliminated the intermediate stages of printing wherein they used to take place. The printing job is directly transferred from the plate to the web via offset printing.

Offset printing uses a high-quality plate that transfers an image onto a rubber blanket which is then transferred onto the paper. Due to this, it saves time and money, which were earlier wasted when dealing with other types of printing machines like treadle or platen. It has proven over the years to be one of the most cost-effective and efficient ways of producing print media for various applications.