Gravure Platemaking and Gravure Printing (2)

(B) Gravure Printing PLATES and Proofing

Compared with the past, the original version no longer requires the production of continuous adjustment of the original version, the production method is almost no different from offset printing. In particular, the production of color screening films, color proofing by offset proofing machine to complete, the process is very simple and time-saving. The previous method was to make a proofing roller the same as the upper Plate roller for proofing. However, the environmental conditions for proofing and printing are not the same, and there are differences in the printing quality. Nowadays, for customers with high requirements or quality requirements, on-site proofing is often done on the press. If the quality is approved, the proofing drum is used as the upper drum.

In recent years, due to continuous progress in the digitization and non-filming of plate making, the use of digital color proofing has increased.

1. Publication of Gravure Printing and Color Proofing

The gravure printing method of publishing gravure is carried out from the production of black paper to imposition. It is carried out entirely in accordance with the offset printing method, the same process, and the same quality management. Therefore, when the customer is in a hurry to make a gravure printing product, Even if it is replaced with offset printing, there is no problem.

The gravure platemaking method is divided into two types. One is to make an original (separation film) that is the same as offset printing, and the other is to use a digital file to make a plate. The color proofing of the former method is the same as offset printing. As for the proofing ink, an ink close to the gravure ink is often used, but as described above, it is difficult to completely reproduce the colors due to the different characteristics of the heart ink in the printing method. As for digital color proofing, it is even more difficult to achieve consistency with color reproduction of gravure inks. The reason is that currently on the market printers, all use offset printing as their design and production target. Whether it is the color reproduction range of the used color material or the color matching technology used, the reproduced color is at best the same as that of offset printing, and the reproduction is to be transparent. The color of gravure ink with a sense of sensibility and expressiveness is very difficult. Although there is an ideal dye-based inkjet printer in the printer, no matter what kind of printer is different from printing. When using a printer for proofing, it must be agreed upon with the customer. In addition, due to the lack of spot color, it is easy to achieve proofing effect by using a printer.

2. Gravure plate making and color proofing

Both gravure printing and gravure printing basically use the same plate making method. However, in general, unlike gravure printing, the gravure-printed substrates must be combined with plastic film. The heart often uses spot colors, usually 6-7 colors, and the platemaking method takes these conditions into consideration. This is different from publishing gravure.

Packaging products are often printed using plates that are joined together on the same screen. Platemaking is single-sided plate making, and color proofing is also single-sided proofing. The problem of color proofing can be said to be the same as the publication of gravure, but the topic of spot colors is more. Printing proofing can be consistent with spot color inks, and color printing cannot express spot colors with a combination of three primary colors. Do not expect to achieve high print quality on this occasion.

Summarizing the above points, the special software for packaging gravure plates has: 1 connection function software; 2 splicing function software for creating seamless images; 3 spot color printing software; 4 trapping software (to compensate for printing registration Deviation, a small amount of overlap of the color version of the image outline, mainly for plastic film gravure).

(III) Production of Gravure Rollers

No matter how good the original is made or how accurate the digital plate data is, if a high-precision plate cylinder cannot be produced, the quality of the printed matter cannot be guaranteed. In this respect, gravure can be said to be the most demanding of all kinds of printing plates. The production process is as follows.

1. Production of roller base

The material of the roller base is generally steel pipe because of the low price and firmness of the steel pipe. Weights range from 10 kg (pack gravure) to several hundred kg (published, gravure building materials), and some can weigh up to 1 ton depending on the print product requirements. In recent years, aluminum rollers have been used for packaging gravure printing, and in particular, plastic rollers have recently been used.

The wall thickness of the steel pipe is from 20mm to 30mm, and the large size roller is thicker. Roller is divided into non-axis (mainly package gravure) and shaft.

2. Roller plated copper

Regardless of the type of roller base material (as long as it meets the requirements), the surface of its newly machined roller should be plated with copper. This bottom copper layer is not a copper layer for engraving or etching, but is used to achieve the precision requirements of the drum. For example, the tolerance of the drum diameter is within 10 μm and the parallelism is not more than 10 μm. The thickness of the copper layer is about 600 μm. Next, a layer of copper, which is necessary for etching and engraving, is also plated on the copper layer. The thickness varies depending on the plate cylinders of various specifications, and is generally about 80 μm. In the case of electric engraving, hard copper must be plated.

3. Making of plate image

After the drum has been completely plated with copper, an image is created on the drum by: 1 using a resist film. Transfer or apply a resist film on the copper layer, or use carbon paper or a photosensitive resin to print the image; use a high-sensitivity resin or black primer to form an image with a laser, then pass the resist film, use ferric chloride for chemistry corrosion. 2 carving method. Unetched directly on the copper layer. Although there have been methods of forming an image by laser with an alloy layer and a resin layer instead of copper plating, most of them are still under development.

The depth of the mesh formed on the drum is generally from several μm to 60 μm. The mesh usually uses a density in the range of 2500-10000 meshes/cm2, and the use of lasers can further increase the mesh density.

4. Chrome plating

After forming a mesh hole in the copper layer, the roller production is completed. However, when the ink is dropped on the non-mesh portion of the surface of the copper layer during the printing process, the copper surface is easily scratched by a doctor blade. Therefore, a layer of chromium of about 10 μm is plated on the surface of the copper layer. At this point, a gravure plate cylinder was made.

The gravure platemaking technology has achieved highly efficient and tangible progress in the prepress digital environment. The technical trend in recent years is the full automation of plate cylinder production. The use of lasers in chemical etching processes can provide better reproduction of details and, if possible, future elimination of chemical corrosion.

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