Gravure and Offset Quality (I)

Because gravure printing and offset printing are different, if you look at the printed matter, it will be very different. The representative differences are as follows:

Field text outline

The field part in the offset printing does not need to have a dot, so the outline of the printed text is as smooth as the bottom plate; however, the gravure printing mode requires an ink groove regardless of the occasion, so the outline of the text is also due to this groove (grooves form independent holes). The existence of a sawtooth. In order to make this serration as small as possible, it is necessary to consider a suitable plate making method.

Field ink movement

This phenomenon is unique when using gravure ink with low viscosity. When the deep ink in the depth of the groove is transferred to a substrate such as paper, a uniform density is not obtained and slight unevenness occurs. As a countermeasure, the viscosity of the ink, the angle of the ink tank (screen angle), the change in the depth and shape of the groove, and the like can be adjusted.

Hue changes

The printing ink is the same, but the hue will be different due to the different thickness of the ink film. In offset printing, the dot size is different. In principle, the thickness of the ink film is constant (strictly speaking, there are differences). However, in the gravure printing method, particularly when the depth of the groove is used to express the layer, the thickness of the ink film also changes due to the depth change, so that the hue change that does not need to be considered in the offset printing occurs with the level change. However, with a constant depth, this phenomenon is difficult to occur. This phenomenon, no matter what kind of method is used for color proofing, the same chromatic aberration problem as the production machine's printing will appear.

The impact of static electricity

Gravure inks require special attention to fire protection due to the use of highly volatile, flammable solvents. Static electricity also has a great influence on the transfer of ink. Due to the electrostatic effect, the ink overflows the image area and hinders the transfer of the ink. However, the use of an electrostatic inking device is very effective for the transfer of ink.

Plate making and proofing

Compared with before, in the production of film masters, there is no need to continuously adjust the bottom version, and the production method is also different from offset printing. In particular, the production of dot bases, proofing can be as easy as offset proofing, and the process is shortened.

In the previous method, a drum for proofing was produced by the same method as that used in the printing on the production machine, and it was printed with a special gravure proofer. However, because of the difference in the printing environment between the proofer and the production machine, the printing quality is also different. Now, in order to get good quality printed products and satisfactory results, there are also proofing on the production machine. If the print quality is satisfactory, use it as an official printing plate.

Recently, platemaking has been digitized, and digital color proofing printers have been mostly used in order to be able to develop to filmless. Publication of gravure platemaking and color proofing The gravure platemaking method was published. From the preparation of the master plate to the imposition process, the plate making process and the quality management of the offset printing were exactly the same. Therefore, the work of gravure printing can be turned into offset printing if it is urgently needed.

Its plate making method, like offset printing, is divided into the method of making the film bottom plate and the method of making it completely using digital plate making data. With color proofing made with film masters, starting from the bottom plate, proofing plates were made with PS plates, and proof printing was done like offset printing. With regard to proofing inks, it is also considered to use the same color inks as gravure inks. However, as described above, if the printing method is different, ink characteristics are different, and it is difficult to achieve the same color reproduction.

In the proofing method using a digital color proofing printer, it is more difficult to maintain the consistency of the color reproduction of the gravure ink. Because printers currently used in the market are almost always aimed at offset printing, the color reproduction range of the used color materials is made to conform to the color reproduction range of the offset printing ink as much as possible even if a color matching technology is used, but it is difficult to achieve a sense of transparency. And the sense of concentration of gravure ink color reproduction. There are also better dye-based ink-jet printers, but in general different from the printing method, and the printed body is based on the printer and uses special paper. Therefore, when selecting a printer, it is necessary to decide based on satisfactory results.

Packaging gravure plates and color proofing

The method of packaging a plate and publishing a plate is basically the same. However, if a plastic film is added to a printed object different from the publication, a spot color ink is often used. Generally, six colors and seven colors are used for printing. Therefore, the plate making method that meets these conditions must be considered in the plate making, which is different from publishing printing.

Packaging prints are usually printed in multiple impositions on the same screen, but a single plate is made in the platemaking, and color proofing is also performed in a single frame. The problem of proofing can be said to be the same as that of publishing, but there are many problems with spot colors. In the printing proofing, the spot color ink can be used to correspond, but a color printer is used, and only the basic ink is used together with the method of expression. In such cases, too high quality cannot be expected. (to be continued)