Gravure and offset quality (2)

As mentioned above, the platemaking software unique to packaging plates includes:

(1) Multi-format imposition function;

(2) The function of the jointless ring image connection;

(3) Spot color separation function;

(4) Trapping function (corresponding to misplacement during printing, outline of the pattern is slightly overlapped, especially when the film is printed).

Plate making and upper printing plate

No matter how good the film master and digital plate data are, if the accuracy of the printing roller cannot be guaranteed, the quality of the printed matter cannot be guaranteed. This is considered to be the most stringent in gravure printing in various printing plate formats. The following are the contents of the process and processing from the preparation of the roller to the final production of the printing press.

roller

The substrate of the drum is generally an iron pipe, which is due to its low cost and robustness. Weights range from tens of kilograms (related to packaging) to hundreds of kilograms (related to publishing, building materials), and depending on the application, some are nearly one ton. Recently, aluminum has been used. More recently, plastics have also been used for the manufacture of packaging rolls.

The wall thickness of the iron pipe is from 20mm to 300mm, and the large-diameter drum wall is thicker. No shaft in the drum (for packaging purposes) or with shaft.

Roller copper plating

Regardless of the substrate, copper plating is applied to the surface of the newly manufactured roll. This copper layer is not an engraving and etching layer, but uses this copper plating layer to make the precision of the drum. For example, for cylinders with diameter accuracy within 10 μ and parallelism within 10 μ, the copper plating thickness is 600 μm. In this copper plating layer, the copper layer required for etching and engraving is usually plated, and the thickness is about 80 μm depending on the pattern of the plate. When using the engraving method, hard copper plating is required.

Image formation

After copper plating on the drum, image formation processing was performed on the copper surface. Treatment methods are:

(1) When a resist film (carbon paper, photosensitive resin, black paint) is used, the resist is transferred or coated onto the copper plated surface

Image copying is performed on carbon paper or photosensitive resin, an image is formed by laser on a high-sensitivity resin and black paint, and then chemical etching is performed using ferric chloride or the like through a resist film;

(2) Engraving method

Engraved directly on the copper surface. Alloys and resin layers have been used instead of copper plating to form images using lasers, but most of them are under development.

The depth of the formed ink groove is generally from several μ to 60μ. The density of the grooves is from 2500/cm2 to 10000/cm2. Laser can be used to make higher density.

Chrome plating

After the ink tank is formed on the copper plating surface, it can be used as a printing roller. However, the ink falling on the outside of the groove during the printing easily scratches the copper surface by the scraper. Therefore, chromium is plated on the copper surface (about 10 μm). After this series of processes, the intaglio printing cylinder was made.

postscript

Gravure printing technology has indeed evolved to high efficiency and high productivity in the prepress digital environment. In recent years, full automation of roller production has become a research topic. At this point, depending on how the ink tank is formed, the development is not the same. The introduction of a chemically etched laser provides excellent detail reproduction, but chemical etching may no longer be used in the future.

In this regard, the engraving method does not have a corrosion process, but it is inferior to the laser method in reproduction and productivity of details. As various ways are still under development, this is also the hope for the future. (Finish)