A commonly used printing technique is offset printing or offset lithography, which produces precise and high-quality prints. The method has been in use since the 20th century and has a wide range of uses in commercial printing.
In addition to producing many high-quality prints, it can label boxes and cartons. The process may be old, but it may be more suitable in certain instances than other printing methods.
In contrast, offset printing is more cost-effective than digital printing in terms of producing a large number of prints with good quality. Below you will find how does it work? What is the purpose of offset printing? The type of ink used for offset printing, as well as a step-by-step guide.
What is Offset Printing?
Essentially, offset lithography refers to a method of printing by transferring ink from the plate to the rubber sheet and then to the printing surface. Printing this way is offset printing since the image does not adhere directly to the paper, unlike other methods.
Before the ink goes to paper, it goes into a rubber cylinder. Using the three-step process, you can prevent the printing plate from wearing out, helping it last longer.
What is 4-color offset printing?
There are four colors of ink used in four-color offset printers as well as digital printers. This set has four colors: (CMYK) Cyan, Magenta, Yellow, and Black. As a result, multiple colors are possible by combining them.
Printing in CMYK is also known as four-color printing, Process Printing, 4CP, or full-color printing. Commercial printers commonly use the 4CP method for projects with multiple colors in their artwork or design.
There are a wide variety of printed items in full color, including books, magazines, postcards, and manuals. Separate layers of the four inks mix to create a full-color photograph.
The designer can reproduce thousands of colors by overlapping these four colors in distinct amounts. Four sets of rollers for each color are on an offset press used for 4-color printing.
A monitor or digital image also uses RGB color coding (red, green, and blue). Almost all photo editing programs have an RGB setting by default, giving you the best display of your digital photos.
Types of Offset Printing
Two types of offset printing machines are on the market today. There are two types of offset printing: sheet-fed and web-fed. Let’s take a look at both details.
Sheet Fed Offset Printing:
- Paper sheets are fed into the offset machine one by one in sheet-fed offset printing. Before feeding the paper to the machine, you can resize the pages to the print size. And to see what kind of paper you might need, you can check out our paper guide.
- In smaller quantities that do not require a strict deadline, sheet-fed offset printing machines are a good choice. While it does not print as fast as a web offset method, this method is still more accurate than most other types of printers.
- It is possible to print 12,000 to 24,000 sheets per hour on most sheet-fed offset printing machines of today. Hopefully, sheet-fed offset printing machines will achieve faster printing speeds with advances in technology.
Web Fed Offset Printing:
- Most industries use web-fed offset printing for jobs requiring a fast turnaround to get the job done on time. Newspapers and custom packaging often come with web offset printing machines.
- Offset printing using web-fed rolls involves continuous feeding of paper into the press. Paper is cut into identical sheets after printing is complete. A machine does this on its own. In fact, you can produce over 5000 different kinds of print materials using web-fed offset machines.
- Fast completion of projects is possible with web-fed offset printing machines. It is possible to print 80,000 sheets in an hour with a web-fed offset printer that can print 3,000 sheets a minute. The result is that whether you’re using a web-fed offset printer for a small job or a large job, you’ll be able to produce larger quantities more quickly.
How does it work?
Three cylinders/rollers make up the offset printer: the impression cylinder, the plate cylinder, and the blanket cylinder. A printing press using offset uses rollers to transfer the ink to the paper.
A plate cylinder does each printing task with aluminum or plastic printing plates. A plate is a sheet of paper on which images appear. A water solution repels ink from non-image areas and attracts ink from image areas.
Water solution sprays onto the plate as the plate roller spins, soaking the plate with ink. As a result, image areas receive ink, while non-image areas lose ink by the water solution.
A rubber blanket covers the blanket cylinder and rotates the opposite way. A rubber blanket helps to transfer the ink to the plate cylinder as it rolls against the blanket cylinder.
In this process, the ink design that will go on print reverses in order to create a reversed image. Clean steel serves as the material for the impression cylinder that spins the opposite way to the blanket cylinder.
As a result, the rubber blanket compresses the paper and transfers ink to it. Due to this, a printed image represents what a plate would look like. As a result, offset printing is also called this method of printing.
There is no direct transfer of the image to the paper. Rather than applying it directly to the paper, it is offset to a middle roller. This method of printing has a variety of uses, for example printing long runs of magazines, newspapers, manuals, brochures, books, and letterhead.
A Step-by-Step Guide to Offset Printing
There are a number of steps in the offset printing process from beginning to end, and all of them follow the same process.
A great artwork design is the first step to a great printing job. The next step is where can pick out the coatings, colors, fonts, type of layout, and paper. Get an estimate once you know the specifications for the print media.
The pre-press stage
It’s time to review the evidence after making the digital art file into proof. A PDF version of the warranty often goes to the client, also known as soft proof. If you need to make any changes, you may do so
The platemaking process
In the computer-to-plate system, images and digital files are engraved onto aluminum plates using digitally controlled laser engraving systems. As a result, the printing is accurate and of high quality. One roller is used for each color to fix the plates.
First, wet rollers pass over the plates so that the ink can adhere to them. Wetting the entire plate is easy since the water and additive solution continuously flow, soaking all of it. In areas where color needs to print, the treated plates resist water.
With the help of special vibrating rollers, the ink spreads to the plate in an even distribution using oil-based ink. The ink sticks to the untreated parts of the plate once the roller comes into contact with the wet plate.
Rubber rollers lift ink from plates, transforming the image on their surface into its reverse. Due to its flexibility, the roller is suitable for use on a variety of papers, including glossy, rough, and textured papers.
This final process involves folding, trimming, perforating, collating, binding, etc., the printed materials to meet the needs. Paper may also come with Matt lamination or gloss.
The finishing stage
Great artwork design is the key to an excellent printing job. It is here that we can select the coating, the color, the font, and the type of paper. After that, get an estimate once you have the print material specs.
What does offset printing used for?
The primary purpose of offset printing is to produce continuous quantities, for example, newspapers, magazines, brochures, and office stationery. In the printing industry, this technique is well known as a source of accurate results and output of high quality.
In addition, promotional items such as branded coasters and product ads are printed using offset printing. If you want pictures that are colorful and detailed, this is the best option for you.
Also, when it comes to printing tent cards, menus, and door hangers for hotels, it is also an effective method. Generally, it’s an excellent choice for low-budget projects requiring high-quality work.
In a simple process, pipes and metal bars have a continuous, repeating message. Also, offset printing is a common method for printing business cards with a clear brand message. In addition to stationery and reading materials, this method is also used by schools.
What type of ink is used in offset printing?
Offset printing machines use oil-based inks as offset printing inks. There has to be a way for this ink to withstand water emulsion on the press as well as other chemicals.
If an engraved plate contains water-emulsified ink on non-printing areas, the ink should not mix with the fountain solution. As a result of these mixing issues, the ink may appear colored or dry incorrectly, creating tints on the printed pages as well as non-printed areas.
Three main ingredients make up oil-based ink: pigment, vehicle, and modifier. A pigment colors the ink, while a vehicle carries pigment to the paper by holding it in place.
In contrast, modifiers control the drying, smell, resistance, and scuffing of the ink as well as other properties of the ink. Nowadays, oil-based inks primarily use soy-based ink instead of petroleum-based ink, which is a more eco-friendly and reliable alternative.
In addition, it enhances the color of paper and allows easy de-ink recycling. However, it is not recyclable because it contains iron oxide, acrylate, and styrene, which do not degrade. Moreover, it dries more slowly than other inks, such as water-based inks.