Gravure Preprint Digital Development

At present, the digitization of prepress processing and plate making is the mainstream and trend of technology. The progress of “Computer To Plate” in the field of offset printing is remarkable. In fact, gravure has also made considerable progress in digital direct plate making.

First, the characteristics of gravure

1. Use different depth, different opening area of ​​the network to accommodate the ink, the performance of different shades of graphic color. The continuity of image changes in depth and depth is good, and the quality of image reproduction is high.

2. The net points must have a net wall protection and no real area. The edge of Shanghai's printed text was slightly roughened by the wall and its quality was lower than that of offset printing.

3. Due to trace spillage when the gravure ink is transferred to the printed material, at the same time, the brightening of the depth of some network points is shallow, which is beneficial to reduce the interference of the white line of the network wall and improve the image reproduction quality.

4. The gravure plate making cost is high, it is suitable for printing products with large print and high quality requirements. For example: exquisite packaging and decorating products, high printing (more than 500,000) journals and product samples.

II. Gravure Prepress and Platemaking Digitization Process (CTC)

The gravure digital direct platemaking is called "CTC (Computer To Cylinder)", that is, the computer directly makes a gravure cylinder. This is the most commonly used plate making method in the industry. The key equipment for gravure plate making is the electronic engraving machine.

As early as the 1980s, under the environment of electronic full-page imposition systems, digital electronic engraving and gravure technology has been put into use. This is a pioneer in the use of computer graphic information to drive electronic engraving machines for plate making.

Gravure prepress processing and offset printing process is roughly the same, both in the computer system for text input and processing, image scanning and color separation processing, graphics rendering and processing, graphics and text combination. Afterwards, it is necessary to make a large version according to the requirements of gravure plate making, to form digital information that can be electronically engraved, and to make digital color proofing. Only after the customer approves does the electronic carving begin and a gravure cylinder is produced. After electroplating, the finished gravure roll is sent to the printing department.

In the above process, it is necessary to consider the characteristics of gravure in terms of color separation, tone adjustment, resolution and color management settings, and digital color proofing.

Different from the offset prepress, when the offset color separation/dividing version is recorded, it needs RIP interpretation to generate a 1-bit “pure black and white” 0/1 digital signal, and the digital signal required for gravure engraving is not “pure black and white”. The 0/1 digital signal is a multi-bit "grayscale" digital signal. This is because each point (cell) in the gravure engraving has a different depth, and the different values ​​of the gray signal control the depth and the opening area of ​​the engraving hole. In publishing-oriented gravure plates, RIP interpretation is also required and electronic engraving information is generated. However, in addition to interpreting the PS language, the gravure RIP task also generates multi-bit grayscale signals.

III. Overview of Digital Intaglio Carving Technology

Gravure engraving was created in the 1960s. The famous Hell invented the electromagnetic electronic engraving machine, which promoted the remarkable improvement in the quality and efficiency of gravure plate making. In the following decades, electronic engraving has always been an indispensable technology for gravure plate making and has made many advancements.

The type of gravure engraving technique.

In terms of application, electromagnetic engraving has the highest proportion, followed by laser engraving, and piezoelectric crystal driven engraving and electron beam engraving are less applied.

The electromagnetic engraving and laser engraving techniques are roughly as follows.

Electromagnetic engraving

Electromagnetic engraving. The copper-plated roller rotates and the engraving knife on its side vibrates in a reciprocating manner. The power of Shanghai's printing vibration comes from the electromagnet. The strength of the electromagnet magnetic field is related to the size of the engraving signal. The amplitude of the sculpting knife changes with the depth of the text, so that the depth of the sculpted cut is different. Engraving vibration frequency 4000 ~ 8000 times / second.

2. Laser direct engraving

Laser direct engraving. The galvanized roller rotates. The engraving tool is not a carving knife but a high-energy laser beam. When a laser ablates metallic zinc, its energy level varies with the teletext signal: the depth corresponding to the image color is high, and the ablation depth is large, whereas the depth is small. The area of ​​the cell opening can be changed by changing the laser spot size or multi-point combination. The engraving frequency is 35000 to 70000 times/sec.

3. Laser Ablation and Corrosion Plate Making

Laser ablation. A layer of black base paint is applied on the outer surface of the copper plating drum, and text and image dot portions are ablated with a laser. After the ablation is completed, the drum is etched in a solution of ferric chloride to obtain net holes with different areas and the same depth. This technology belongs to offset printing like "net dot gravure." Shanghai prints its ablation record with a resolution of up to 2540 dpi. Its outstanding advantages are: the quality of text and lines is high.

As mentioned earlier, with the promotion of digital technology and the enhancement of the level of social consumption, gravure prepress, plate making and printing technologies have been steadily developed, and they have made due contributions to improving people’s quality of life and disseminating information.