Gravure Printing

Gravure is an ‘intglio’ rotary high quality printing process, which means that the image is engraved or etched into an image carrier, which in the printing process is a copper cylinder, then placed onto a revolving print press, the same as the previous rotary systems of litho and flexo.

The print produced by the gravure process is accomplished transferring ink from ‘cells’ of various sizes and depths that are etched into a copper covered steel cylinder. The cylinder may contain as many as 22,500 cells per square inch. The various sizes and depths of the depressions create the different solid areas of the image. A larger or deeper depression, transfers more ink to the printing surface creating a larger and/or darker area. The areas of the cylinder that are not etched become the non-image areas.

The cells that are engraved in the cylinders are different in area and depth or they can be the same depth but different in area. This allows for greater flexibility in producing high quality work for different types of print applications. Cells that vary in area but are of equal depth are often used on gravure cylinders for printing packaging. The gravure cylinders with cells that vary in area and depth are reserved for the highest quality printing such as photography in books or high-end glamour magazines.

Printing Process

Because of the cylinders being made of copper, this printing process is expensive, and so as a result gravure is largely performed as a rotary web process (rotogravure) to offset the costs. It is most often used for very long runs of up to a million+ to be cost effective. For print runs of a million or more, the cylinders are plated with chromium to provide extra durability.

During the printing process, the gravure cylinder revolves in an ink fountain where it is coated with fluid ink. A stainless steel blade (doctor blade) clears the ink from the unwanted areas, leaving the ink in the depressions of the cylinder. The printing material passes between the gravure cylinder and an impression cylinder covered in rubber and the ink from the cells is deposited onto the material.

Other than being very thin and fluid, the ink colours used with process colour (CMYK) printing differ in hue than the inks used with other processes. Instead of the usual cyan, magenta, yellow, and black used with offset lithography, blue, red, yellow, and black are used.

Gravure is a direct printing method so there is no need to use a fountain solution to keep the non-image areas clean. Removing this process allows for better print quality control and jobs can be run at higher speeds. Some print jobs can be run as high as 3,000 feet per minute. The microscopic depressions on the gravure cylinder create an almost continuous tone image on the printed surface, which is why it is often used for high quality image reproduction.

Gravure Plating Methods

*Image depicts the copper gravure printing plates having the artwork etched onto the plates.

Diffusion-etch: Diffusion-etch is a method that uses a carbon tissue ‘rotofilm’ onto which positive images are exposed. Rotofilm is a special four layer film. A special screen is used with the rotofilm during the exposure to form a square dot pattern of the image. After processing, the rotofilm is applied to the cylinder and the image is etched chemically into the cylinder. The screen used during the exposure helps to create the walls of the depressions made during the etching process. The diffusion-etch process produces an image that is of high quality but the copper plate/cylinder may only last for 50,000 impressions.

Photopolymer: A photopolymer plate is also used with the gravure process. The photopolymer method is less expensive than the diffused- etched gravure plate , so it can be competitive with offset printing and flexography for runs under 100,000. The plates are made of stainless steel and are mounted on magnetic cylinders. The exposed plates are then chemically etched to produce the image on the plate. The main difference between the photopolymer plate and a relief plate is that the image on the gravure plate is below the plate surface rather than being above the surface as with a relief plates.

The Gravure printing process is most commonly used for many packaging applications, magazines, and pressure sensitive labels. Gravure is the preferred method of producing magazines and catalogs in high volumes.

Rotogravure is used for printing specialty items such as gift wrap, wallpaper, plastic laminates, printed upholstery, imitation wood grain finishes, and vinyl flooring. Many of the specialty items are printed on very wide presses. Some of them, such as those that print patterns on floor coverings.

A gravure sheet-fed process is used for smaller runs for such items as limited edition prints and other artwork, photographic books, stock certificates, and some advertising pieces.

Advantages of Gravure printing

Gravures advantages include lower printing costs when printing jobs are of high volume, around 50,000 + , otherwise lower printing volumes costs are offset with the price of running the machines and the printing plates.

The printing cylinders last for millions of prints and so for longer print jobs are much more economical and cost effective.

The gravure inks are relatively low cost compared to those of other printing processes, so it is common for coatings to be added to designs to add a nicer finish quality to the products. Metallic effects are most commonly added with gravure printing as it is the best method for adding such a finish, and the cheapest on long volume runs, proving a major alternative to mass hot foil blocking.

Another advantage is the overall printing quality of gravure printing over the other printing processes, the depth of colour and tone is much richer with gravure printing due to the use of controllable cells to create different tones within the printed images.