The basic principle of corrugated board flexo printing

Flexographic printing is the use of a flexographic printing plate to print by means of an ink transfer roller, which is a type of relief printing process. The printing plates used by them are all raised in graphic parts. During printing, the anilox roller applies a certain thickness of ink layer evenly to the graphic portion of the printing plate, and then under the pressure of the impression cylinder, the ink layer of the graphic portion is transferred to the surface of the substrate to form a clear graphic. . The inking mechanism of a flexographic corrugated paper press is usually a two-roller ink transfer mechanism.

(1) Two Roll Ink System
The plate cylinder rotates on the side of the impression cylinder and coincides with the linear speed of the impression cylinder. When stopped briefly, the ink fountain roller and the anilox roller are moved up and out of the plate cylinder, and the ink fountain roller and the anilox roller continue to rotate to facilitate even ink and keep the ink on the anilox roller from drying. The ink fountain roller rotates on one side of the anilox roller, and its tangential speed is lower than the tangential speed of the anilox roller in order to control the ink volume and prevent the ink from splashing. Most printing presses for printing corrugated paper are modular flexographic printing presses. The units of this flexographic printing press are independent and horizontally aligned.

(2) Flexo plate

The flexographic plate is divided into a rubber plate and a photosensitive resin plate: the plate of the rubber plate is selected from natural rubber or synthetic rubber; the types of the photosensitive resin plate are various and can be classified into liquid photosensitive resin plates and Solid photosensitive resin plate. The seamless printing plate is made of a plate-shaped solid photosensitive resin plate.

The photosensitive resin flexographic plate is composed of a protective layer, a release layer, a photosensitive layer, an adhesive layer, and a base layer.

The function of the protective layer and the release layer is to protect the photosensitive layer; the role of the subbing layer is to support the photosensitive layer; the function of the adhesive layer is to tightly bond the photosensitive layer and the subbing layer together. The photosensitive layer is the main body of the printing plate. After exposure and development, it is a flexible printing plate. The photosensitive layer is mainly composed of a highly elastic unsaturated rubber polymer, a photoinitiator, a cross-linking agent, a sensitizer, a thermal polymerization inhibitor, and the like.

It should be noted that due to the rough surface of corrugated paper, a thick flexible plate must be used; if high-grade products are to be printed, a flexographic plate with high resolution and small retractility must be used.

(3) Anilox roller

Anilox roller is the core of the flexographic printing press. It has many types, such as chrome-plated anilox roller, ceramic anilox roller, etc. No matter which one, its structure, function and principle are the same.

1) The structure of the anilox roller. The surface of the anilox transfer roller is provided with a recessed mesh groove line for controlling the ink transfer amount during printing. The surface of the anilox roller is regularly arranged on the surface of the grooved roller, forming a recessed cell. The ink transfer performance of the anilox ink transfer roller is related to the number of lines of the mesh slot line, the shape of the cell site, and the arrangement of the cell site.

1 Number of reticulate lines: The number of network sites per cm in the shortest direction of the network spacing is the number of reticulate lines, which indicates the distribution density of the network sites.

The number of reticulate lines of the anilox roller influences the amount of ink transferred: the greater the number of reticulate lines, the greater the density of the cell sites, the smaller the volume of the cell sites, and the smaller the amount of ink transferred. Corrugated printing generally uses a low number of anilox rollers (typically 65 lines/inch or less).

2 net shape: generally refers to the three-dimensional shape of the net. There are many types of cell sites, which are basically divided into nuclear cones and pyramidal tables.

2) The characteristics of anilox roller

1 The mesh size on the anilox roller is uniform and evenly distributed, which can effectively transfer and control the ink volume, making the ink film uniform in thickness and uniform in ink volume. In addition, there is less occurrence of a phenomenon in which ink is not easily applied due to the difference in the viscosity of the ink.

2 The high precision of the anilox roller ensures that the ink can be transferred under a small pressure and the ink-moistening phenomenon of the graphic edge is reduced. The ink is evenly distributed, and edges are not easily hardened.

3 The use of anilox roller to transmit ink, there are few ghosts or bars and other ink transmission failures, high-speed printing less ink phenomenon.

4 The use of anilox roller ink device ink is easy to adjust, the thickness of the ink layer is thin and very uniform, making dot color printing possible, and ink film density from the minimum dot to the ground are consistent.

5 The anilox roller has high durability and corrosion resistance, especially the application of laser-engraved ceramic anilox roller greatly improves the service life of the anilox roller and the stability of the ink transfer.