The Ultimate Comparison: Flexo vs Offset Printing

Flexo Printing

Flexo printing is not a new technology, but it has grown up through all kinds of innovation, this development makes flexo printing becomes the most popular printing technology.

In the past, people used printing plates made of rubbers, but now, everybody uses flexible photopolymer printing plates, because it has flexible enough to wrap around the printing cylinder.

Flexo printing is unique, it not only can adapt all kinds of printing materials, such as thin paper, cardboard, paper, corrugated, soft packaging, and more, but it also can use extensive oil-based inks, including water-based inks and UV inks.

Durable and adaptable is the biggest features of flexo printing because they can print in all kinds of base materials, such as plastics, metals, and various papers.

Offset Printing

Offset printing also called litho-offset, is widely used in business printing, it uses a rubber roller to print on various materials, such as timber, clothing, metal, and various paper materials.

In offset printing, the material to be printed is neither above the surface of the plate (as in letterpress printing) nor sinks below it (as in gravure or gravure printing). Instead, it is flush with the surface of the plate; this offset printing is classified as a lithographic method.

Offset printing is based on the principle that water and grease do not mix so that a greasy ink can be deposited on grease-treated printing areas of the plate, while nonprinting areas, which hold water, reject the ink.

v Different 1: plates

As said before, 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.

v Different 2 Ink

offset printing is made of four "primary colors"- cyan, magenta, yellow, and key (which is black), that's what we often say CMYK color, 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.

(※ Tips: Flexo printing is expensive than offset printing)

v 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, printing 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, label stock, and so on.

The main difference between both processes is that offset printing is only done on flat surfaces 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.