Editing Rotogravure (section)

== Process and components ==
In direct gravure printing, the ink is applied directly to the cylinder and from the cylinder it is transferred to the substrate. One printing unit consists of the following components:

* an engraved cylinder (also known as "gravure cylinder") whose circumference can differ according to the layout of the product being made.
* an ink fountain
* a [[doctor blade]] assembly
* an impression roller
* a dryer

For indirect gravure processes, the engraved cylinder transfers ink in the desired areas to a transfer roller, and the transfer roller transfers it to the substrate.

=== Engraved cylinder ===
The first step of Gravure is to create the cylinder with the engraved images that need to be printed: the engraving process will create on the cylinder surface the cells that will contain the ink in order to transfer it to the paper. Since the amount of ink contained in the cells corresponds to different colour intensities on the paper, the dimensions of the cells must be carefully set: deeper or larger cells will produce more intense colours whereas smaller cells will produce less intense ones.  There are three methods of photoengraving that have been used for engraving of gravure cylinders, where the cell open size or the depth of cells can be uniform or variable:

{| class="wikitable" style="margin:1em auto;"
! Method
! cell size
! cell depth
|-
| Conventional
| uniform
| variable
|-
| "Two positive" or "Lateral hard dot"
| variable
| variable
|-
| Direct transfer
| variable
| uniform
|}

Gravure cylinders are usually made of steel and plated with copper, though other materials, e.g. ceramics can also be used. The desired pattern is achieved by engraving with a laser or a diamond tool, or by chemical etching.  If the cylinder is chemically etched, a resist (in the form of a negative image) is transferred to the cylinder before etching. The resist protects the non-image areas of the cylinder from the etchant. After etching, the resist is stripped off. The operation is analogous to the manufacture of printed circuit boards. Following engraving, the cylinder is proofed and tested, reworked if necessary, and then chrome plated.

=== Process ===
While the press is in operation, the engraved cylinder is partially immersed in the ink tray, filling the recessed cells. As the cylinder rotates, it draws excess ink onto its surface and into the cells. Acting as a [[squeegee]], the doctor blade scrapes the cylinder before it makes contact with the paper, removing the excess ink from the non-printing (non-recessed) areas and leaving in the cells the right amount of ink required. The position of the blade relative to the nip is normally variable.

Next, the substrate gets sandwiched between the impression roller and the gravure cylinder: this is where the ink gets transferred from the recessed cells to the web. The purpose of the impression roller is to apply force, ensuring that the entire substrate is brought into contact with the gravure cylinder, which in turn ensures even and maximum coverage of the ink. Once in contact with the substrate, the ink's surface tension pulls (part of) the ink out of the cell and transfers it to the substrate.

Then the inked substrate goes through a dryer because it must be completely dry before going through the next color unit and accepting another coat of ink. A rotogravure printing press has one printing unit for each [[color]], typically [[CMYK]] or cyan, magenta, yellow and key (printing terminology for black), but the number of units varies depending on what colors are required to produce the final image.<ref>{{cite web |title=Rotogravure printing process |url=https://www.bobst.com/usen/products/rotogravure-printing/process/ |website=BOBST |access-date=11 November 2020}}</ref>