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 technique employs a flat (planographic) image carrier on which the image to be printed obtains ink from ink rollers, while the non-printing area attracts a water-based film (called “fountain solution”), keeping the non-printing areas ink-free.

Development of the offset press came in two versions: In 1875 by Robert Barclay of England for printing on tin, and in 1903 by Ira Washington Rubel of the United States for printing on paper.

Offset Printing Today

Offset lithography is one of the most common ways of creating printed matter. A few of its common applications include newspapers, magazines, brochures, stationery, and books. Compared to other printing methods, offset printing is best suited for economically producing large volumes of high-quality prints in a manner that requires little maintenance.[6] Many modern offset presses use a computer to plate systems as opposed to the older computer to film workflows, which further increases their quality.

Advantages of offset printing compared to other printing methods include:

• Consistent high image quality. Offset printing produces sharp and clean images and types more easily than, for example, letterpress printing; this is because the rubber blanket conforms to the texture of the printing surface.
• Quick and easy production of printing plates.
• Longer printing plate life than on direct litho presses because there is no direct contact between the plate and the printing surface. Properly developed plates used with optimized inks and fountain solution may achieve run lengths of more than a million impressions.
• Offset printing is the cheapest method for producing high-quality prints in commercial printing quantities.

A further advantage of offset printing is the possibility of adjusting the amount of ink on the fountain roller with screw keys. Most commonly, a metal blade controls the amount of ink transferred from the ink trough to the fountain roller. By adjusting the screws, the gap between the blade and the fountain roller is altered, leading to the amount of ink applied to the roller to be increased or decreased in certain areas. Consequently, the density of the color in the respective area of the image is modified. On older machines, the screws are adjusted manually, but on modern machines the screw keys are operated electronically by the printer controlling the machine, enabling a much more precise result.[7]

Disadvantages of offset printing compared to other printing methods include:

• Slightly inferior image quality compared to rotogravure or photogravure printing.
• The propensity for anodized aluminum printing plates to become sensitive (due to chemical oxidation) and print in non-image/background areas when developed plates are not cared for properly.
• Time and cost associated with producing plates and printing press setup. As a result, very small quantity printing jobs may now use digital offset machines.

Digital vs. Offset Printing:

Advantages of each and how to decide which is right for your project.

The growth of digital printing technology has brought technical advancements, more options, and exciting new features to today’s commercial printing. It’s also brought some confusion. An understanding of the advantages and disadvantages of digital printing and how those compare to traditional offset lithography is critical in making the right choice.

Most Common

Offset lithography is the most common high volume commercial printing technology. In offset printing, the desired print image is burned onto a plate and is then transferred (or offset) from the plate to a rubber blanket, and then to the printing surface. The lithographic process is based on the repulsion of oil and water. The image to be printed gets ink from ink rollers, while the nonprinting area attracts a film of water, keeping the nonprinting areas ink-free.

Mechanical Steps Eliminated in Digital Printing

Digital printing eliminates many of the mechanical steps required for conventional printing, including making films and color proofs, manually stripping the pieces together and making plates.

Advantages of Digital

• Shorter turnaround.
• Every print is the same. More accurate counts, less waste and fewer variations, due to not having to balance ink and water during the press run.
• Cheaper low volume printing. While the unit cost of each piece may be higher than with offset printing when setup costs are included digital printing provides lower per-unit costs for very small print runs.
• Variable Data Printing is a form of customizable digital printing. Using information from a database or external file, text and graphics can be changed on each piece without stopping or slowing down the press. For example, personalized letters can be printed with a different name and address on each letter. Variable data printing is used primarily for direct marketing, customer relationship development and advertising.

Advantages of Offset

• High image quality.
• Works on a wide range of printing surfaces including paper, wood, cloth, metal, leather, rough paper and plastic.
• The unit cost goes down as the quantity goes up.
• Quality and cost-effectiveness in high volume jobs. While today’s digital presses are close to the cost/benefit ratio of offset for high-quality work, they are not yet able to compete with the volume an offset press can produce.
• Many modern offset presses use computer-to-plate systems as opposed to the older computer-to-film workflows, further increasing quality.

Still Not Sure Which is Right?

Use this checklist to help decide:

• Quantity. Offset printing has a front-end cost load. Short runs may have a high unit cost. But as quantities increase, the unit cost goes down with offset printing. Very short runs can be much more cost-effective with digital printing; while larger quantities are likely to have a lower unit cost with offset printing.
• Printing medium. Do you need or want a special paper, finish or unusual printing surface, or unique size? The options are increasing continually for digital, but offset printing still offers the most flexibility.
• Color. Digital presses use four-color process printing. If you need only black ink or one or two ink colors, offset printing may offer a more cost-effective solution. If you need four-color printing, digital may offer advantages in lower up-front costs.
• More on color. If you’re planning to print using the Pantone® Matching System, offset printing will give you the best match, since it uses actual Pantone® ink. Digital printing simulates the color using a four-color matching process, so some digital printers may offer less accurate color matching on projects.
• Turnaround. If you need it fast, digital usually offers quicker delivery.
• Proofing. Digital offers accurate proofs since you see an actual sample of the printed piece. Accurate color proofing for offset printing can be expensive.
• Customization. Without question, digital printing offers the most affordable way to customize marketing materials, direct mail pieces, letters, etc.

FLEXO VS. OFFSET PRINTING (THE 3 MAIN DIFFERENCES EXPLAINED)

Although both methods use wet ink and printing plates, these two printing processes are quite different. Technically, offset printing can refer to any printing technique that uses a printing plate to transfer an image to an intermediate carrier and then onto the printed substrate. Whereas flexo transfers ink from the plate directly to the substrate.

Flexo and offset are both popular, but they perform their tasks differently. It is important to understand what roles they perform and have a clear understanding of both types of printing processes. The type of press to use depends on the final product and quality required, as well as volumes and substrates.

DIFFERENCE 1: PLATES

As the name suggests, flexo printing utilizes flexible plates for a rotary printing process. The plates are made from a photopolymer compound and are flexible enough to be wrapped around a printing cylinder. The relief image on the plate is fixed via a laser image-setter and the polymer in the ‘non-print’ areas is washed away in a processing unit, where it is dissolved into a solvent or water solution. Ink is transferred from the ink well via a rotating ‘anilox’ roller onto the flexo plate. A separate printing station & flexo plate is required for each color to be printed. The image is then printed directly onto the substrate. The printing plates are quite durable and if stored correctly, can be re-used several times, before they eventually need to be replaced.

For offset printing, again as the name suggests, ink is transferred (offset) via a series of rollers onto the printing plate. This can be either a flat-bed or rotary process – depending on the type of offset press. The plate is usually made of aluminum. The complete wet image (either single color or multicolor) is then transferred onto a ‘blanket’ and in turn onto the substrate, before drying.

DIFFERENCE 2: INK

Offset printing usually consists of four ‘process’ colors; cyan, magenta, yellow, and key (which is black). Each color has a dedicated printing station. Any spot colors are made from a combination of the process colors. Ink can be water-based or UV curable.

Although process colors are also used in the flexo process, additional print stations tend to be used for spot colors.  Spot colors can be supplied pre-mixed or can be mixed in-house, as required. Flexo inks can also be water-based or UV curable. Solvent-based inks can also be used. UV inks enable higher running speeds and can be left in the press at the end of the day, without the need to empty & clean each print station.  Water-based inks need to be removed from the press when it is not in use – to prevent ink from drying on the rollers & in the ink trays.

DIFFERENCE 3: TYPES OF MATERIALS TO PRINT ON

Offset printing machines can print on materials such as; paper, metal, cardboard, cellophane and vinyl. The printing surface must be flat and smooth. It is excellent for printing newspapers, books, magazines, stationery, posters, brochures and so on. Generally, to print onto both sides of the substrate will require a second pass. Similarly, any die-cutting, slitting, folding, creasing, laminating, etc is done as a secondary, off-line process.

Flexography is used on both absorbent and non-absorbent materials, for example, cellophane, foil, cardboard, fabric, plastic, metal, etc. It is mostly used for packaging; envelopes, retail bags, wallpaper, paper, newspapers, sweet wrappers, labelstock and so on. The main difference between both processes is that offset printing is only done on a flat surface while Flexographic printing can be used on almost any substrate with a flexible surface. Flexo printing can achieve high-speed production and many presses have multiple converting options integrated into the press, enabling a single pass operation.

MAKING THE RIGHT CHOICE

Both Flexographic and offset machines have their advantages. Flexography is excellent for high-speed production and overall quality. It is great inefficiency in many ways and is generally appropriate for most large-scale printing tasks. In the label printing sector,  most businesses prefer flexographic printing because of its adaptability and economy of scale. When looking for a printing solution, look for one with the future in mind, and invest in the printing technology of the future. One current trend for flexo is for it to be combined with digital printing technology to produce a powerful hybrid solution that outperforms most traditional offset presses.

Flexography beats offset printing in many circumstances because of its flexibility & productivity benefits. A flexographic press is a sound, long term investment and is adaptable enough to accommodate and integrate a wide range of in-line processes, including new digital technology.

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